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In the present work, nanoparticles of poly-(methyl methacrylate-co-butyl acrylate) (P-(MMA-co-BA)) and poly-(methyl methacrylate-co-vinyl acetate) (P-(MMA-co-VAc)) were synthesized by miniemulsion polymerization with the in situ encapsulation of praziquantel (PZQ) as a hydrophobic drug model. The reactions produced nanoparticles with diameters ranging from 67 ± 0.5 to 130 ± 1.1 nm, with an encapsulation efficiency of at least 99%. The glass transition temperatures (Tg's) of the produced copolymer nanoparticles were successfully reduced from 121.5 to −9.3 °C in the absence of PZQ and from 100.7 to −13.7 °C in the presence of encapsulated PZQ. In vitro release assays carried out at 37 and 50 °C showed that the rate of drug release increased with temperature, reaching maxima of 56 ± 3.7 and 38 ± 2.9% of release in 6 h for copolymers containing 40 wt % BA and 60 wt % VAc. Modeling of the available release data indicated the occurrence of an anomalous release mechanism as the driver for the drug release from the produced nanoparticles. Empirical mathematical modeling confirmed the influence of both the Tg and the test temperature on the rate of drug release. Finally, experimental results strongly suggested that PZQ exerts a plasticizer effect in the system, as confirmed by DSC analyses, suggesting the existence of specific interactions between the drug and the polymer matrix. Altogether, these results point out the occurrence of multifactorial effects on release of hydrophobic drugs from nondegradable polymer particles. [ABSTRACT FROM AUTHOR]

Due to the slow diffusion of photovoltaic molecules, in particular, small-molecule acceptors (SMAs), under light and heating, the morphology of the active layer in organic solar cells (OSCs) prefers to deviate from the favorably metastable status, leading to the challenge of stability during long-term operation. Employing materials with a high glass transition temperature ( T g ) as the third component to suppress molecular diffusion is an efficient method to achieve the balance of efficiency and stability of OSCs. Herein, a dimerized small-molecule acceptor denoted as F6D is synthesized by introducing a polyfluoride moiety as the linker to enhance the T g . Benefitting from a rational molecular design, F6D not only exhibits a higher T g , complementary absorption, and cascade energy levels with the host materials of the polymer donor PM6 and the SMA Y6 but also has excellent miscibility and multiple intermolecular interactions with Y6. As a result, a champion power conversion efficiency of 17.52% is achieved in the optimal PM6:Y6:F6D-based device. More importantly, the ternary device exhibits superior stability under continuous heating and lighting compared with the binary device.

Thermomechanical properties of ultrathin films are crucial for fabrication and use of reliable thin electronic devices. Due to the lack of precise measurement techniques, the thermal deformation behavior of ultrathin films has not yet been clarified. Here, we propose a film on heated liquid (FOHL) method to simultaneously measure the coefficient of thermal expansion (CTE) and glass transition temperature ( T g ) of multiple ultrathin polymer films. Free thermal expansion of thin films without substrate interaction can be guaranteed when the thin films are afloat on a liquid surface. To investigate the thermal behavior in a wide temperature range, glycerol is adopted as a thermally stable heating platform owing to its high boiling point of 290 °C. The thin films are transferred onto the glycerol surface from the water surface using the hygroscopic properties of glycerol. Highly accurate and high-throughput thermal strain measurement is achieved using three-dimensional digital image correlation (3D-DIC). The thermomechanical properties of ultrathin polystyrene thin films of various thicknesses (25-400 nm) are precisely characterized utilizing the FOHL and 3D-DIC method.

Sucrose and trehalose pharmaceutical excipients are employed to stabilize protein therapeutics in a dried state. The mechanism of therapeutic protein stabilization is dependent on the sugars being present in an amorphous solid-state. Colyophilization of sugars with high glass transition polymers, polyvinylpyrrolidone (PVP), and poly(vinylpyrrolidone vinyl acetate) (PVPVA), enhances amorphous sugar stability. This study investigates the stability of colyophilized sugar-polymer systems in the frozen solution state, dried state postlyophilization, and upon exposure to elevated humidity. Binary systems of sucrose or trehalose with PVP or PVPVA were lyophilized with sugar/polymer ratios ranging from 2:8 to 8:2. Frozen sugar-PVPVA solutions exhibited a higher glass transition temperature of the maximally freeze-concentrated amorphous phase ( T ') compared to sugar-PVP solutions, despite the glass transition temperature ( g ') compared to sugar-PVP solutions, despite the glass transition temperature ( T g ) of PVPVA being lower than PVP. T g values of all colyophilized systems were in a similar temperature range irrespective of polymer type. Greater hydrogen bonding between sugars and PVP and the lower hygroscopicity of PVPVA influenced polymer antiplasticization effects and the plasticization effects of residual water. Plasticization due to water sorption was investigated in a dynamic vapor sorption humidity ramping experiment. Lyophilized sucrose systems exhibited increased amorphous stability compared to trehalose upon exposure to the humidity. Recrystallization of trehalose was observed and stabilized by polymer addition. Lower concentrations of PVP inhibited trehalose recrystallization compared to PVPVA. These stabilizing effects were attributed to the increased hydrogen bonding between trehalose and PVP compared to trehalose and PVPVA. Overall, the study demonstrated how differences in polymer hygroscopicity and hydrogen bonding with sugars influence the stability of colyophilized amorphous dispersions. These insights into excipient solid-state stability are relevant to the development of stabilized biopharmaceutical solid-state formulations.

High temperature, high energy density, and low loss dielectric films are promising candidates for miniaturized capacitors in electric vehicles and high-speed trains. However, single-component polymers could not achieve these desired properties simultaneously. Polymer multilayer films (MLFs), which combine a high dielectric constant polymer [e.g., poly(vinylidene fluoride) (PVDF)] and a high breakdown/low loss polymer [e.g., polycarbonate (PC)] in a unique layered structure, have the potential achieve them at the same time. In this work, the effects of PC glass transition temperature ( T g ) on the dielectric insulation properties (breakdown strength and lifetime) were investigated at high temperatures of 100-150 °C. Three PC materials had T g values of 145 (PC1), 165 (PC2), and 185 °C (PC3), respectively. It is observed that MLF-PC3 with the highest T g of PC exhibited the highest Weibull direct/alternating current (DC/AC) breakdown strength and the longest DC/AC lifetime, whereas MLF-PC1 with the lowest T g showed the lowest Weibull DC/AC breakdown strength and the shortest DC/AC lifetime. A high-temperature high-volage leakage current study revealed that MLF-PC3 exhibited the lowest bulk conductivity at all temperatures under different electric fields. The knowledge obtained from this study will help us design better MLFs with high performance for next-generation miniaturized capacitors.

Co-amorphous systems are amorphous formulations stabilized by the miscible dispersion of small molecules. This study aimed to design a stable co-amorphous system for the co-delivery of two drugs to the lungs as an inhaled formulation. Theophylline (THE) and levofloxacin (LEV) were used as model drugs for treating lung infection with inflammation. Leucine (LEU) or tryptophan (TRP) was employed as the third component to improve the inhalation properties. The co-amorphous system containing THE and LEV in an equal molar ratio was successfully prepared via spray drying where reduction of the particle size and change to the spherical morphology were observed. The addition of LEU or TRP at a one-tenth molar ratio to THE-LEV did not affect the formation of the co-amorphous system, but only TRP acted as an antiplasticizer. The Fourier transform infrared spectroscopy spectra revealed intermolecular interactions between THE and LEV in the co-amorphous system that were retained after the addition of LEU or TRP. The co-amorphous THE-LEV system exhibited better in vitro aerodynamic performance than a physical mixture of these compounds and permitted the simultaneous delivery of both drugs in various stages. The co-amorphous THE-LEV system crystallized at 40 °C, and this crystallization was not prevented by LEU. However, THE-LEV-TRP maintained its amorphous state for 1 month. Thus, TRP can act as a third component to improve the physical stability of the co-amorphous THE-LEV system, while maintaining the enhanced aerodynamic properties.

Establishing the structure-property relationship by machine learning (ML) models is extremely valuable for accelerating the molecular design of polymers. However, existing ML models for the polymers are subject to scarcity issues of training data and fewer variations of graph structures of molecules. In addition, limited works have explored the interpretability of ML models to infer the latent knowledge in the field of polymer science that could inspire ML-assisted molecular design. In this contribution, we integrate graph convolutional neural networks (GCNs) with data augmentation strategy to predict the glass transition temperature T g of polymers. It is demonstrated that the data-augmented GCN model outperforms the conventional models and achieves a higher accuracy for the prediction of T g despite a small amount of training data. Furthermore, taking advantage of molecular graph representations, the data-augmented GCN model has the capability to infer the importance of atoms or substructures from the understanding of T g , which generally agrees with the experimental findings in the field of polymer science. The inferred knowledge of the GCN model is used to advise on the design of functional polymers with specific T g . The data-augmented GCN model possesses prominent superiorities in the establishment of structure-property relationship and also provides an efficient way for accelerating the rational design of polymer molecules.

Remote-controlled pulsatile or staged release has significant potential in a wide range of therapeutic treatments. However, most current approaches are hindered by the low resolution between the on- and off-states of drug release and the need for surgical implantation of larger controlled-release devices. Herein, we describe a method that addresses these limitations by combining injectable hydrogels, superparamagnetic iron oxide nanoparticles (SPIONs) that heat when exposed to an alternating magnetic field (AMF), and polymeric nanoparticles with a glass transition temperature ( T g ) just above physiological temperature. Miniemulsion polymerization was used to fabricate poly(methyl methacrylate- co -butyl methacrylate) (p(MMA- co -BMA)) nanoparticles loaded with a model hydrophobic drug and tuned to have a T g value just above physiological temperature (∼43 °C). Co-encapsulation of these drug-loaded nanoparticles with SPIONs inside a carbohydrate-based injectable hydrogel matrix (formed by rapid hydrazone cross-linking chemistry) enables injection and immobilization of the nanoparticles at the target site. Temperature cycling facilitated a 2.5:1 to 6:1 on/off rhodamine release ratio when the nanocomposites were switched between 37 and 45 °C; release was similarly enhanced by exposing the nanocomposite hydrogel to an AMF to drive heating, with enhanced release upon pulsing observed even 1 week after injection. Coupled with the apparent cytocompatibility of all of the nanocomposite components, these injectable nanocomposite hydrogels are promising as minimally invasive but remotely actuated release delivery vehicles capable of complex release kinetics with high on-off resolution.

Alkali aluminoborate glasses have recently been shown to exhibit a high threshold for indentation cracking compared to other bulk oxide glasses. However, to enable the use of these materials in engineering applications, there is a need to improve their hardness by tuning the chemical composition. In this study, we substitute alkaline earth for alkali network-modifying species at fixed aluminoborate base glass composition and correlate it with changes in the structure, mechanical properties, and densification behavior. We find that the increase in field strength (i.e., the charge-to-size ratio) achieved by substituting alkaline earth oxide from BaO to MgO manifests itself in a monotonic increase in several properties, such as atomic packing density, glass-transition temperature, densification ability, indentation hardness, and crack resistance. Although the use of alkaline earth oxides as modifier enables higher hardness values (increasing from 2.0 GPa for Cs to 5.8 GPa for Mg), their crack resistance is generally lower than that of the corresponding alkali aluminoborate glasses. We discuss the origin of this compromise between hardness and crack resistance in terms of the ability of the glass networks to undergo structural transformations and self-adapt under stress. We show that the extent of volume densification scales linearly with the number of pressure-induced coordination number changes of B and Al. [ABSTRACT FROM AUTHOR]

We show that key parameters of high refractive index (HRI) polymers may be accurately predicted based on the data of the HRI group and the polymer backbone comprising the spacer (S) and polymerizable group (PG). Five different HRI groups and the corresponding siloxane and methacrylate homopolymers were considered in this work. As a testbed we have chosen HRI polymers for ophthalmological implants, e.g., intraocular lenses, defining the figures-of-merit. In this case they need to be nonabsorbing throughout the visual wavelength range and should have a high refractive index nD and a high Abbe number νA as well. Finally, a low glass transition temperature Tg is required to receive flexible materials. All ten HRI polymers, among them five prepared first within this study, were synthesized and characterized. The received properties match the predicted within percentage range and show that the straightforward design principles introduced here are highly productive tools for polymer design. [ABSTRACT FROM AUTHOR]

A novel yet simple approach to fabricate and pattern wrinkled surfaces on polymers is presented. Only by irradiating an electron beam onto a polymer, wrinkles are created on the polymer surface. Electron irradiation produces a bilayer polymeric structure comprising a degrading upper layer and a pristine bottom layer. Electron irradiation also increases the polymer surface temperature to a point much higher than the glass-transition temperature of the upper layer, leading to drastic thermal expansion of the upper layer. As a result, significant compressive force is applied to form surface wrinkles. The mechanism behind the wrinkle formation and the effects of electron irradiation parameters on the wrinkle characteristics are discussed. In addition, by this electron irradiation approach, a patterned wrinkle structure is uniquely prepared. [ABSTRACT FROM AUTHOR]

In this study, vinyl-terminated polysiloxane (abbreviated VISR) and allyl-terminated polysiloxane (abbreviated ALSR) were synthesized and characterized. The curing behaviors and viscoelastic and thermal properties of VISR/PHSR and ALSR/PHSR were comparatively investigated. DSC and in situ FT-IR spectroscopy can be adopted to study the influence of molecular structures on reactivity. The results prove that ALSR/PHSR shows higher reactivity including a higher reaction rate constant and cure degree than VISR/PHSR. Moreover, it is found that the Šesták-Berggren equation can adequately depict the cure kinetic model of silicone resin in hydrosilylation comparing the calculated results with experimental data. Additionally, DMA exhibits that the glass transition temperature and cross-linking density of ALSR/PHSR are much lower than those of VISR/PHSR, TGA data reveal that they have similar thermal stability as well as high char yield, and the decomposition energy ranges from 100 to 270 kJ/mol with increment of degree of mass conversion (αd) (αd = 0.15-0.85). [ABSTRACT FROM AUTHOR]

Mechanical and viscoelastic properties of precision polyolefins, poly(4-phenylcyclopentene) (P4PCP) and its hydrogenated analog (H2-P4PCP) containing atactic phenyl branches at exactly every five carbons along the backbone are explored. Both materials are amorphous with a glass transition temperature of ~17 ± 3 °C. Rheological investigations determined that P4PCP has an entanglement molar mass (Me = 10.0 kg mol-1) much higher and closer to polystyrene than H2-P4PCP (Me = 3.6 kg mol-1). Both materials have elastomeric and shape memory properties at ambient temperatures, which were further explored through strain hysteresis measurements. H2-P4PCP has an elastic recovery of ~95% at max strain values up to 500% as determined by uniaxial tensile testing. Time--temperature superposition analysis, Williams--Landel--Ferry constants, and further mechanical analysis are discussed and compared to previously reported ethylene--styrene copolymers of similar phenyl-branch content within the microstructure. [ABSTRACT FROM AUTHOR]

Model thiol-click glassy networks with low shrinkage and sharp glass transition temperatures are studied down to cryogenic temperatures to relate viscoelastic damping to changes in microscopic hole volume. Networks synthesized by polymerization of divinyl sulfone with pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), trimethylolpropane tris(3-mercaptopropionate) (TMPTMP), and pentaerythritol tetrakis(2-mercaptoacetate) (PETT) were studied to ∼50 K using positron annihilation and thermal analysis methods. Across the glass transition temperature, overall volume expansivity is dominated by expansion of microscopic holes. Beneath Tg, holes contract upon cooling and then become static with negligible expansivity at temperatures well above 0 K. A trade-off between complete rigidity of static free volume and viscoelastic damping ability below Tg is discussed. All samples show moderate damping (tan δ > 0.05), and one sample exhibits a prominent β-transition in its viscoelastic loss spectra. These results indicate the potential for tuning the molecular design of low-temperature glassy networks to optimally incorporate damping with low shrinkage. [ABSTRACT FROM AUTHOR]

Glassy perfluoropolymers have become an exciting materials platform for membrane gas separation as they define the upper bounds for some gas separations, such as He/H2, He/CH4, and N2/CH4. However, due to the difficulty in synthesis, only a few glassy perfluoropolymers are commercially available, including Teflon AF and Hyflon AD derived from dioxoles and Cytop derived from dihydrofuran. In this study, two perfluoropolymers based on dioxolanes, poly(perfluoro-2-methylene-1,3-dioxolane) (poly(PFMD)) and poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane) (poly(PFMMD)), were synthesized by radical polymerization and characterized thoroughly for physical properties such as glass transition temperature (Tg), d-spacing between polymer chains, and fractional free volume (FFV). The gas permeability and solubility were determined at 35 °C for a series of pure gases in these perfluorodioxolanes and compared with the commercial perfluoropolymers. Poly(PFMD) and poly(PFMMD) exhibit separation properties of He/H2, He/CH4, H2/CH4, H2/CO2, and N2/CH4 near or above the upper bounds in Robeson's plots, and superior to the commercial perfluoropolymers, despite their similar Tg and FFV. The underlying reasons for the superior gas separation properties in these dioxolane-based perfluoropolymers are discussed. [ABSTRACT FROM AUTHOR]

Polyester block polymers containing polylactide have garnered significant attention as renewable, degradable alternatives to traditional elastomers. However, the low glass transition of the PLA blocks limits the upper-use temperatures of the resulting elastomers. To improve the thermal performance, we explore a series of multiblock polyesters composed of poly(ε-decalactone) (PDL) and poly(cyclohexene phthalate) (PCHPE). These materials are prepared using switchable polymerization catalysis followed by chain extension. The strategy involves (i) alternating ring-opening copolymerization (ROCOP) of cyclohexene oxide and phthalic anhydride, (ii) ε-decalactone ring-opening polymerization (ROP), and (iii) diisocyanate coupling of the telechelic triblocks to increase molar mass. The resulting multiblock polyesters are amorphous, and the blocks are phase separated; glass transition temperatures are ∼−45 and 100 °C. They show thermal resistance to mass loss with Td5% ∼ 285 °C and higher upper use temperatures compared to alternative aliphatic polyesters. The nanoscale phase behavior and correlated mechanical properties are highly sensitive to the block composition. The sample containing PCHPE = 26 wt % behaves as a thermoplastic elastomer with high elongation at break (εb > 2450%), moderate tensile strength (σb = 12 MPa), and low residual strain (εr ∼ 4%). It shows elastomeric behavior from −20 to 100 °C and has a processing temperature range of ∼170 °C. At higher PCHPE content (59 wt %), the material has shape memory character with high strain fixation (250%) and recovery (96%) over multiple (25) recovery cycles. The multiblock polyesters are straightforward to prepare, and the methods presented here can be extended to produce a wide range of new materials using a other epoxides, anhydrides, and lactones. This first report on the thermal and mechanical properties highlights the significant potential for this class of polyesters as elastomers, rigid plastics, and shape memory materials. [ABSTRACT FROM AUTHOR]

Adhesion of nanoparticles to polymer films plays a key role in various polymer technologies. Here we report experiments that reveal how silica nanoparticles adhere to a viscoelastic PMMA film above the glass transition temperature. The polymer was swollen with CO2, closely matching the conditions of nanoparticle-nucleated polymer foaming. It is found that the degree by which the particles sink into the viscoelastic substrate is strongly size dependent and can even lead to complete engulfment for particles of diameter below 12 nm. These findings are explained quantitatively by a thermodynamic analysis, combining elasticity, capillary adhesion, and line tension. We argue that line tension, here proposed for the first time in elastic media, is responsible for the nanoparticle engulfment. [ABSTRACT FROM AUTHOR]

Among all the emergent biobased polymers, poly(ethylene 2,5-furandicarboxylate) (2,5-PEF) seems to be particularly interesting for packaging applications. This work is focused on the investigation of the relaxation dynamics and the macromolecular mobility in totally amorphous 2,5-PEF as well as in the less studied poly(ethylene 2,4-furandicarboxylate) (2,4-PEF). Both biopolymers were investigated by differential scanning calorimetry and dielectric relaxation spectroscopy in a large range of temperatures and frequencies. The main parameters describing the relaxation dynamics and the molecular mobility in 2,5-PEF and 2,4-PEF, such as the glass transition temperature, the temperature dependence of the α and β relaxation times, the fragility index, and the apparent activation energy of the secondary relaxation, were determined and discussed. 2,5-PEF showed a higher value of the dielectric strength as compared to 2,4-PEF and other well-known polyesters, such as poly(ethylene terephthalate), which was confirmed by molecular dynamics simulations. According to the Angell's classification of glass-forming liquids, amorphous PEFs behave as stronger glass-formers in comparison with other polyesters, which may be correlated to the packing efficiency of the macromolecular chains and therefore to the free volume and the barrier properties. [ABSTRACT FROM AUTHOR]

A new nucleophilic monomer (2,2-bis(3-amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of ortho-acetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the TR process was evaluated by directly synthesizing PBOs, which were made from the reaction, and ulterior thermal cyclization, of 2,2-bis(4-chlorocarbonylphenyl)-hexafluoropropane with ADHAB/APAF. TR-PBO membranes made through a thermal treatment at 450 °C for 30 min showed excellent gas separation properties for the CO[sub 2]/CH[sub 4] gas pair with values close to the 2008 Robeson limit. [ABSTRACT FROM AUTHOR]

We have fabricated a series of supramolecular polymers with tailor-made structures and properties through supramolecular interfacial polymerization of miscible monomers. Compared with homogeneous solution polymerization, supramolecular interfacial polymerization is advantageous for fabricating supramolecular polymers with higher molecular weights. Their higher molecular weights are attributed to the higher effective concentration of monomers at the interface than in solutions and diffusion-limited characteristic of supramolecular interfacial polymerization. Moreover, the glass transition temperatures of supramolecular polymers are well tuned by tuning the monomer structures and supramolecular interfacial copolymerization. It is anticipated that this research will further enrich the methodology for fabricating supramolecular polymers with controlled structures and properties through supramolecular interfacial polymerization. [ABSTRACT FROM AUTHOR]

Spatial compositional heterogeneity strongly influences the dynamics of the A and B components of bulk miscible blends. Its effects are especially apparent in mixtures, such as poly(vinyl methyl ether) (PVME)/polystyrene (PS), where there exist significant disparities between the component glass transition temperatures (Tgs) and relaxation times. The relaxation processes characterized by distinct temperature dependencies and relaxation rates manifest different local compositional environments for temperatures above and below the glass transition temperature of the miscible blend. This same behavior is shown to exist in miscible PS/PVME films as thin as 100 nm. Moreover, in thin films, the characteristic segmental relaxation times τ of the PVME component of miscible PVME/PS blends confined between aluminum (Al) substrates decrease with increasing molecular weight M of the PS component. These relaxation rates are film thickness dependent, in films up to a few hundred nanometers in thickness. This is in remarkable contrast to homopolymer films, where thickness confinement effects are apparent only on length scales on the order of nanometers. These surprisingly large length scales and M dependence are associated with the preferential interfacial enrichment-wetting layer formation-of the PVME component at the external Al interfaces, which alters the local spatial blend composition within the interior of the film. The implications are that the dynamics of miscible thin film blends are dictated in part by component Tg differences, disparities in component relaxation rates, component-substrate interactions, and chain lengths (entropy of mixing). [ABSTRACT FROM AUTHOR]

A promising way to induce shape transformation in soft materials is via spatial variation in the orientation of the alignment of liquid crystalline elastomers (LCEs). Here, we improve the nascent thermomechanial shape transformation in main-chain LCEs prepared via aza-Michael addition reactions. Specifically, increasing the alkyl length in the n-alkylamine chain extender effectively reduces the actuation temperature by destabilizing the nematic phase as well as reduces the glass transition temperature (Tg) by increasing the free volume. In addition, incorporating a hydroxyl end-group in the amine chain extender (i.e., n-alkanolamine) increases the actuation strain and improves the film quality by preventing side-chain aggregates of n-alkylamine-functionalized LCEs. Interestingly, uniaxially aligned n-alkanolamine-functionalized LCEs exhibit an unprecedentedly large elongation and an enhanced toughness even along the loading direction likely due to hydrogen bonding between chains. Thus, our study highlights that the choice of amine chain extender during LCEs synthesis can be an efficient strategy to tailor the properties as well as to provide a new functionality in the LCEs which may expand their range of applications in shape morphing devices, smart coatings, and dynamic substrates. [ABSTRACT FROM AUTHOR]

Lignin nanospheres/poly(vinyl alcohol) (LNS/PVA) nanocomposite films were prepared through solvent casting approach. Compared with lignin/PVA blend film, LNS could be evenly dispersed in PVA matrix, and the nanocomposite films did not generate macroscopic phase separation. Maximum decomposition temperature (Tmax) and glass transition temperature (Tg) of pure PVA film were 264.7 and 104.2 °C, while the Tmax and Tg of the nanocomposite film containing 1 wt % LNS increased to 272.1 and 116.8 °C, respectively. Moreover, with increasing of LNS content in PVA matrix, the Tmax and Tg of the nanocomposite films gradually increased. Adding a certain amount of LNS in PVA could improve mechanical strength of the films under the condition of elongation at break in a small amount of loss. The nanocomposite films outperformed the lignin/PVA blend film in UV-absorbing and transparency, which are a promising candidate for medicine bottles and food packaging. [ABSTRACT FROM AUTHOR]

The gradient phenomenon is commonly seen in nature, and the gradual changes in structure could make materials with unique excellent performances compared with homogeneous materials. In this study, a novel approach to prepare damping structural integration epoxy thermosets has been developed. The damping mechanism was systematically discussed through TEM, SAXS, DSC, and DMA. It is shown that the damping property was obviously improved via the gradient plasticization at nanometer scale. Dynamic mechanical analysis showed that when the content of poly(ε-caprolactone)-b-polystyrene was 40 wt %, the glass transition temperature was decreased from 171.66 to 107.84 °C while the damping temperature range (tan δ > 0.2) of the composites was broadened from 28.02 to 52.95 °C. Meanwhile, the tensile properties of epoxy thermosets were also improved when the concentration of poly(ε-caprolactone)-b-polystyrene diblock copolymer was below 20 wt %. It is expected this method could provide a new idea to fabricate damping structural integration materials in the future. [ABSTRACT FROM AUTHOR]

We report an approach for programming electrical conductivity of a bio-based leathery skin devised with a layer of 60 nm metallic nanoparticles. Lignin-based renewable shape-memory materials were made, for the first time, to program and restore the materials' electrical conductivity after repeated deformation up to 100% strain amplitude, at a temperature 60-115 °C above the glass transition temperature (Tg) of the rubbery matrix. We cross-linked lignin macromolecules with an acrylonitrile-butadiene rubbery melt in high quantities ranging from 40 to 60 wt % and processed the resulting thermoplastics into thin films. Chemical and physical networks within the polymeric materials significantly enhanced key characteristics such as mechanical stiffness, strain fixity, and temperature-stimulated recovery of shape. The branched structures of the guaiacylpropane-dominant softwood lignin significantly improve the rubber's Tg and produced a film with stored and recoverable elastic work density that was an order of magnitude greater than those of the neat rubber and of samples made with syringylpropane-rich hardwood lignin. The devices could exhibit switching of conductivity before and after shape recovery [ABSTRACT FROM AUTHOR]

In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to study the intensity variations of the backscattered Ar clusters as a function of temperature for several amorphous polymer surfaces (polyolefins, polystyrene, and polymethyl methacrylate). For all these investigated polymers, our results show a transition of the ratio Ar /(Ar + Ar ) when the temperature is scanned from -120 °C to +125 °C (the exact limits depend on the studied polymer). This transition generally spans over a few tens of degrees and the temperature of the inflection point of each curve is always lower than the bulk glass transition temperature (T) reported for the considered polymer. Due to the surface sensitivity of the cluster backscattering process (several nanometers), the presented analysis could provide a new method to specifically evaluate a surface transition temperature of polymers, with the same lateral resolution as the gas cluster beam. [ABSTRACT FROM AUTHOR]

Prior bubble inflation studies have shown strong evidence of rubbery-like stiffening behaviors for several organic and inorganic thin films. The possible origin is still unclear, but recently Ngai et al. [ J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3), 214-224] and Li and McKenna [ Macromolecules 2015, 48 (17), 6329-6336] proposed that the separation of molecular motions and dynamic fragility are closely related to the observed rubber-like stiffening behavior. In the present work, we report observations from bubble inflation measurements on nanometric thin polyisobutylene (PIB) films that test the correlations suggested by the Ngai coupling model (stiffening is related to the shape parameter describing the α-relaxation) and Li and McKenna (the rubbery stiffening correlates with the dynamic fragility). Mechanical properties and surface tension of nanometric thin PIB films were investigated through strain-stress measurements for film thicknesses ranging from 13 to 126 nm. The tests were performed at room temperature far above the glass transition temperature of PIB. In addition to stiffness and surface tension, rupture strengths were also measured. We find that the stiffness increases with decreasing film thickness and that the surface tension remains constant, independent of the film thickness. The rupture stress is found to increase with decreasing film thickness, whereas the rupture strain decreases with decreasing film thickness. Similar to the prior bubble inflation measurements in polymeric thin films, the thickness dependence of the stiffening followed a power law behavior with film thickness. The observed stiffening behavior agrees with the suggestion from Ngai et al. that the rubbery stiffening should correlate with the separation of the α- and Rouse-mode relaxations. However, unlike prior results for ultrathin polymer films, the stiffening behavior of PIB did not follow the linear relationship with dynamic fragility that was proposed by Li and McKenna. [ABSTRACT FROM AUTHOR]

A series of high efficiency luminescent liquid crystalline polymers (LLCPs) based on aggregation-induced emission (AIE) and the "Jacketing" effect, namely, poly{2,5-bis{[2-(4-oxytetraphenylethylene)-n-alkyl]oxycarbonyl}styrene} (denoted as Pm, m = 2, 4, 6, 8, 10, 12), were successfully designed and synthesized via introducing tetraphenylethylene to the side group with different length spacers. Because of the AIE effect, the resultant LLCPs are completely free of aggregation caused quenching. The photophysical properties and phase behavior were studied via various techniques such as UV-vis absorption spectra, photoluminescence spectra (PL), polarized light microscopy (PLM), differential scanning calorimetry (DSC), and variable temperature one-dimensional wide-angle X-ray diffraction (1D WAXD). The results revealed that the resultant monomers showed typical AIE behavior and the polymers exhibited aggregation enhanced emission (AEE) behavior. Moreover, due to the "Jacketing" effect, the polymers showed high efficiency luminescence in the liquid crystalline state, which was significantly dependent on the spacer length (the solid-state quantum yields decreased from 52% to 18% with increasing spacer length). Meanwhile, the glass transition temperatures (Tg) decreased with increasing the length of spacers. With increasing the spacer length, the phase structure transformed from smectic A (SmA) (Pms, m = 2, 4, 6) to hexagonal columnar phase (ColH) (Pms, m = 8, 10, 12). All the polymers presented good film-forming property and processing performance, which made them be promising materials for the luminescent devices. [ABSTRACT FROM AUTHOR]

The low-strain mechanical properties of linear polyethylene (PE) can be substantially altered by the incorporation of a short block of a polymer with a high glass transition temperature (Tg) into a majority-PE block copolymer. In particular, the yield stress and the tensile modulus can be sharply increased with the addition of a relatively small fraction of glassy block, especially when combined with a thermal history that promotes high crystallinity and crystal thickness of the PE block. For example, the incorporation of 15 wt % of a hydrogenated poly(norbornyl norbornene) block (Tg = 115 °C) into a PE diblock copolymer, cooled from the melt at ~1 °C/min, doubles the yield stress (from ~30 to ~60 MPa) and tensile modulus (from ~1.5 to ~3.5 GPa) relative to the values for a PE homopolymer treated with the same thermal history. These property enhancements are closely associated with the composition of the amorphous layer between crystal lamellae and the spatial distribution of the glassy block within this layer. Finally, the ductility of these polymers at high strains is governed by the presence or absence of tie molecules, which can be correlated with the chain dimensions of the PE block in the melt and the distance between crystal lamellae. [ABSTRACT FROM AUTHOR]

Polymerized ionic liquids (PolyILs) are promising candidates for a wide range of technological applications due to their single ion conductivity and good mechanical properties. Tuning the glass transition temperature (Tg) in these materials constitutes a major strategy to improve room temperature conductivity while controlling their mechanical properties. In this work, we show experimental and simulation results demonstrating that in these materials Tg does not follow a universal scaling behavior with the volume of the structural units Vm (including monomer and counterion). Instead, Tg is significantly influenced by the chain flexibility and polymer dielectric constant. We propose a simplified empirical model that includes the electrostatic interactions and chain flexibility to describe Tg in PolyILs. Our model enables design of new functional PolyILs with the desired Tg. [ABSTRACT FROM AUTHOR]

In this work, we established a cascade cooling and two-step feeding technology for the energy-saving and fast synthesis of polyvinyl butyral (PVB) with a low molecular weight in a microreactor system. Because of the strong mixing capacity of the microreactor and the relatively higher initial reaction temperature of 60 °C compared to existing methods, the condensation reaction between the raw materials of poly(vinyl alcohol) (PVA) and n-butanal was highly intensified and the reaction rate was faster, along with less energy consumption for cooling. By reducing the aging temperature to 40-55 °C, which is far below the glass transition temperature of PVB, we could also lower energy consumption and improve the morphology of PVB. Benefiting from the new technology, the acetalization degree (AD) of PVB reached more than 78%. By applying the two-step n-butanal feeding method in the new technology, the utilization ratio of n-butanal was dramatically increased to more than 99.7%, which was the best result among current published reports. Moreover, a PVB product with a low molecular weight has been successfully prepared with the new technology. This work demonstrates a promising continuous microreaction process for greener and energy-saving synthesis of PVB. [ABSTRACT FROM AUTHOR]

Exposing a glassy polymer to a fluid phase (in gaseous or liquid state) containing a low molecular weight compound results in the sorption of the latter within the polymer, inducing, among other effects, the plasticization of the material which also promotes a change in the glass transition temperature. The amount of sorbed penetrant is often related in a complex fashion to the temperature and pressure of the fluid, thus determining that the locus of glass transition, when represented in pressure-temperature coordinates, may display as well rather complex patterns. This is an issue of particular importance in several applications of glassy polymers. In particular, we investigated the behavior of polystyrene in contact with toluene vapor by performing several modes of dynamic sorption experiments, in which the rate of change of the temperature of the system and/or of the pressure of the vapor phase are controlled with high accuracy, with the aim of creating a map of rubbery and glassy states of the polymer as a function of temperature and pressure of the toluene vapor. Isothermal tests were performed by changing the pressure at a controlled rate, isobaric tests were performed by changing the temperature at a controlled rate, and isoactivity tests were performed by concurrently changing, in a proper way, both temperature and pressure. A relevant feature resulting from these experiments is the presence of a discontinuity in the slope of the mass of toluene sorbed within polystyrene reported as a function of temperature and/or pressure. This discontinuity has been interpreted as the indication of the occurrence of a glass transition. The elaboration of the experimental results allowed identification of the pressure/temperature conditions at which rubbery or glassy states of the polymer mixture are established. Quite interestingly, the system displays the so- called "retrograde vitrification" phenomenon, which consists of the occurrence of a rubbery-to-glassy state transition as the temperature increases at a fixed pressure. The whole set of results has been successfully interpreted on the basis of thermodynamics of II order transitions accounting for the fact that experimental evidence of such transitions is significantly affected by the kinetics of polymer relaxation. [ABSTRACT FROM AUTHOR]

In this paper, we report two new phenanthroline-based compounds, 1,4-bis(2-phenyl-1,10-phenanthrolin-4-yl)benzene (p-bPPhenB) and 1,3-bis(2-phenyl-1,10-phenanthrolin-4-yl)benzene (m-bPPhenB), for the charge generation unit of tandem organic light-emitting diodes (OLEDs). These two compounds exhibited high electron mobility of (5.8-4.4) × 10-3 cm²/(V s), a very small injection barrier at the p-n junction interface, a high glass transition temperature of 123.9-182.1 °C, and exceptionally good operational stability. Because of such excellent characteristics, a single-stack red phosphorescent OLED (PhOLED) with p-bPPhenB showed a low driving voltage (2.7 V) and significantly improved maximum power efficiency (56.8 lm/W), external quantum efficiency (30.8%), and device lifetime (LT95, 130 h) compared to those of the control device using bathophenanthroline (Bphen) (3.7 V, 39 lm/W, 27.1%, and 13 h). Furthermore, a two-stack (tandem) red PhOLED using p-bPPhenB in the charge generation unit exhibited superior charge generation as well as electron transport properties and excellent device performances (5.0 V, 54.0 lm/W, 56.1%) compared to those of the tandem device using Bphen (6.2 V, 45.2 lm/W, 53.3%). [ABSTRACT FROM AUTHOR]

The glass transition temperature (Tg) is an important physical parameter and signifies the reversible transition process between the glassy state and the rubbery state in polymeric materials. Herein, a simple yet reliable method, denoted as ADEtect, utilizing aggregation-induced emission luminogens (AIEgens) for Tg measurement was developed. The fluorescent images of AIEgen-doped polymer films taken at different temperatures were monitored by a camera under the same settings. By using a MATLAB program, the grayscale of the selected area in each image was calculated. This value decreased steadily with increasing the temperature, and a significant change was observed at Tg. By plotting a graph of the second derivative of relative grayscale against temperature, the Tg of a polymer can be unambiguously determined from the lowest point. The present method shows performance comparable to that of conventional DSC measurement in terms of sensitivity and reliability. Besides, it can measure multiple samples in parallel, suggesting that ADEtect is a versatile technique with high commercial value and promising for high-throughput Tg measurement. [ABSTRACT FROM AUTHOR]

Multiblock copolymers (MBCPs) are an emerging class of materials that are becoming more accessible in recent years. However, to date there is still a lack of fundamental understanding of their physical properties. In particular, the glass transition temperature (Tg) which is known to be affected by the phase separation has not been well characterized experimentally. To this end, we report the first experimental study on the evolution of the Tgs and the corresponding phase separation of linear MBCPs with increasing number of blocks while keeping the overall degree of polymerization (DP) constant (DP = 200). Ethylene glycol methyl ether acrylate (EGMEA) and tert-butyl acrylate (tBA) were chosen as monomers for reversible addition-fragmentation chain transfer polymerization to synthesize MBCPs. We found the Tgs (as measured by differential scanning calorimetry) of EGMEA and tBA segments within the MCBPs to converge with increasing number of blocks and decreasing block length, correlating with the loss of the heterogeneity as observed from small-angle X-ray scattering (SAXS) analysis. The Tgs of the multiblock copolymers were also compared to the Tgs of the polymer blends of the corresponding homopolymers, and we found that Tgs of the polymer blends were similar to those of the respective homopolymers, as expected. SAXS experiments further demonstrated microphase separation of multiblock copolymers. This work demonstrates the enormous potential of multiblock architectures to tune the physical properties of synthetic polymers, by changing their glass transition temperature and their morphologies obtained from microphase separation, with domain sizes reaching under 10 nm. [ABSTRACT FROM AUTHOR]

Systematic variation of the size and number of inverse-tapered blocks in styrene-butadiene copolymers results in a wide range of accessible glass-transition temperatures (Tg), including Tg's approaching that predicted by the Fox equation. Composition-weighted average Tg's are expected for miscible blends or random copolymers, but such behavior has not previously been reported for block copolymers made from immiscible styrene and butadiene segments. In this work, 50:50 wt % multiblock copolymers with Mn = 120000 kg/mol were synthesized using an inverse-tapered block design for all blocks except the end blocks. The total composition and molecular weight were held constant, but the type and number of blocks were systematically varied in order to compare contributions from the inverse-tapered chain interfaces to the overall glass transition behavior. Discrete copolymers of similar block number and length were investigated as controls to help separate contributions from the inverse-tapered design and the molecular weight of individual blocks. Some copolymers were intentionally designed such that individual block molecular weights were between the entanglement molecular weight (Me) of polystyrene (PS) and polybutadiene (PB). A range of intermediate glass transitions was observed, but the inverse-tapered copolymers that satisfied this latter condition were the only copolymers that exhibited a Tg near a composition-weighted average. Solid state NMR reveals dynamic heterogeneity among monomeric components through chain-level identification of relatively large amounts of rigid PB segments and mobile PS chain segments versus that observed in discrete block analogues where essentially all PB segments are mobile and all PS segments are rigid. NMR revealed subtle differences in the temperature-dependent segmental chain dynamics of different inverse-tapered blocks, which were not obvious from the calorimetric studies but which presumably contribute to the longer length scale Tg behavior. [ABSTRACT FROM AUTHOR]

Conductivity in polymer electrolytes has been generally discussed with the assumption that the segmental motions control charge transport. However, much less attention has been paid to the mechanism of ion conductivity where the motions of ions are less dependent (decoupled) on segmental dynamics. This phenomenon is observed in ionic materials as they approach their glass transition temperature and becomes essential for design and development of highly conducting solid polymer electrolytes. In this paper, we study the effect of chain rigidity on the decoupling of ion transport from segmental motion in three polymerized ionic liquids (polyILs) containing the same cation-anion pair but differing in flexibility of the polymer backbones and side groups. Analysis of dielectric and rheology data reveals that decoupling is strong in vinyl-based rigid polymers while almost negligible in novel siloxane-based flexible polyILs. To explain this behavior, we investigated ion and chain dynamics at ambient and elevated pressure. Our results suggest that decoupling has a direct relationship to the frustration in chain packing and free volume. These conclusions are also supported by coarse-grained molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

The segmental relaxation times τA and τB of the A and B components, respectively, of an A/B polymer/polymer blend typically exhibit dissimilar temperature dependences and can differ by orders of magnitude, thereby manifesting the influence of spatial compositional heterogeneity. We show that for weakly miscible A/B blends the relaxations of the faster A component occur via separate and distinct mechanisms. In the melt state, τA increases in a nonlinear manner as temperature T decreases toward blend glass transition temperature Tg(blend) (or toward the local effective glass transition temperature of its component Tg(A)); this is the typical α relaxation process. For temperatures below the transition, 1/τA exhibits an Arrhenius temperature dependence; this is identified as the α' process. A third relaxation process, a so-called α0 process, also occurs in the melt state; it is slower than the α process and exhibits a significantly stronger dependence on temperature. Each relaxation process, characterized by a different dependence on temperature, occurs via a different mechanism and associated local composition. This behavior, the existence of the α0 and α' relaxations that accompany the α relaxations, would occur in miscible and weakly miscible blends whose component Tgs differ significantly. [ABSTRACT FROM AUTHOR]

Our aim here is to gain new insight into the nature of the crystalline phase formed in supercooled glycerol near the glass transition temperature and to establish the interrelationship between the kinetics of crystal growth and fundamental dynamic properties. The liquid's dynamics and the crystalline development in glycerol, a hydrogen-bonded liquid, is studied by means of dielectric spectroscopy. We monitored the kinetics of crystallization by isothermal treatment at temperatures between 220 and 240 K (T g = 185 K). Given the thermal protocol employed, we stimulated the growth of the crystalline phase from pre-existing nuclei, in such a way that the observed kinetics is dominated by the crystal growth step. Our experimental results are discussed in terms of the classical theory of crystallization which predicts a significant correlation between the liquid's diffusion and the crystal growth rate. The coupling between dynamic properties, such as dielectric α relaxation time, viscosity, and self-diffusion coefficient, and the characteristic crystal growth time is analyzed. We find that the crystal growth time scales with the glycerol's self-diffusion coefficient as τcryst ∝ D -0.85, confirming that the liquid's dynamics is the principal factor governing the crystal growth in glycerol above but close T g. [ABSTRACT FROM AUTHOR]

A new algorithm is developed to quantify the free-volume hole distribution and its evolution in coarse-grained molecular dynamics simulations of polymeric networks. This is achieved by analyzing the geometry of the network rather than a voxelized image of the structure to accurately and efficiently find and quantify free-volume hole distributions within large scale simulations of polymer networks. The free-volume holes are quantified by fitting the largest ellipsoids and spheres in the free-volumes between polymer chains. The free-volume hole distributions calculated from this algorithm are shown to be in excellent agreement with those measured from positron annihilation lifetime spectroscopy (PALS) experiments at different temperature and pressures. Based on the results predicted using this algorithm, an evolution model is proposed for the thermal behavior of an individual free-volume hole. This model is calibrated such that the average radius of free-volumes holes mimics the one predicted from the simulations. The model is then employed to predict the glass-transition temperature of epoxy polymers with different degrees of cross-linking and lengths of prepolymers. Comparison between the predicted glass-transition temperatures and those measured from simulations or experiments implies that this model is capable of successfully predicting the glass-transition temperature of the material using only a PDF of the initial free-volume holes radii of each microstructure. This provides an effective approach for the optimized design of polymeric systems on the basis of the glass-transition temperature, degree of cross-linking, and average length of prepolymers. [ABSTRACT FROM AUTHOR]

A novel self-curing epoxy resin was synthesized using bio-oil. Bio-oil was produced by hydrothermal liquefaction of loblolly pine and utilized as a biopolyol in the synthesis of bio-oil-based epoxy resin (BOBER) for the first time. Hydroxyl groups in bio-oil were analyzed by quantitative 31P NMR. It was found that not only does the total hydroxyl number of bio-oil influence the yield and epoxy equivalent weight of BOBER, but also the distribution of hydroxyl groups within bio-oil (aliphatic, phenolic, and acidic OH) played an important role in the determination of the optimum amount of catalyst in the synthesis of BOBER. Differential scanning calorimetry analysis proved the self-curing phenomena of BOBER, and Fourier transform infrared spectroscopy suggested that etherification reaction was the dominate reaction during the self-curing. Glass transition temperature, cross-linking density, and the storage modulus of self-cured BOBER were calculated using a dynamic mechanical analyzer. [ABSTRACT FROM AUTHOR]

In this work, 2-(bis(4-hydroxyphenyl)methyl)benzoic acid (BHPBA) was prepared by hydrolysis of phenolphthalein with addition of ferrous powder. Afterward, semiaromatic polyamides (SAPs) with varied carboxyl group content were prepared from BHPBA and the bisphenol 1,1-bis(4-hydroxyphenyl)-1-phenylethane (BHPPE) as well as 1,6-N,N'-bis(4-fluorobenzamide)hexane (BFBH). It was found that they all exhibited glass transition temperatures (Tg's) of 159.6-180.7 °C. The resultant copolymers could be hot compressed into films, which showed a failure strength of 60-70 MPa. Additionally, high storage moduli (1.0-1.6 GPa) were observed at 150 °C, indicating the good thermal mechanical performance for these resultant semiaromatic polyamides (SAPs). Interestingly, such copolymers can be used as the compatibilizer of composites of PA6T/carbon fiber (CF) in the case of the carboxyl group in the main chain, which was beneficial for the improvement of their interfacial adhesion force. [ABSTRACT FROM AUTHOR]

In this work, we discovered a very efficient method of crystallization of thermally evaporated rubrene, resulting in ultrathin, large-area, fully connected, and highly crystalline thin films of this organic semiconductor with a grain size of up to 500 μm and charge carrier mobility of up to 3.5 cm² V-1 s-1. We found that it is critical to use a 5 nm-thick organic underlayer on which a thin film of amorphous rubrene is evaporated and then annealed to dramatically influence the ability of rubrene to crystallize. The underlayer property that controls this influence is the glass transition temperature. By experimenting with different underlayers with glass transition temperatures varying over 120 °C, we identified the molecules leading to the best crystallinity of rubrene films and explained why values both above and below the optimum result in poor crystallinity. We discuss the formation of different crystalline morphologies of rubrene produced by this method and show that field-effect transistors made with films of a single-domain platelet morphology, achieved through the aid of the optimal underlayer, outperform their spherulite counterparts with a nearly four times higher charge carrier mobility. This large-area crystallization technique overcomes the fabrication bottleneck of high-mobility rubrene thin film transistors and other related devices and, given its scalability and patternability, may lead to practical technologies compatible with large-area flexible electronics. [ABSTRACT FROM AUTHOR]

A new organic electro-optic (EO) molecule was designed with two modifications aimed at increasing acentric order. The molecule is based on the well-known CLD donor-π bridge-acceptor template. The first structural modification introduces rigid aromatic fluorenyl and naphthyl site-isolation units (sterically bulky functional groups) to reduce aggregation. Site isolation units have been used in the past, but this is the first time that both the "front" and "back" of the CLD tetraene bridge have been modified with site-isolation units, and we had to introduce new synthetic methodology to do so. The second design element was the inclusion of cooperatively interacting aromatic dendron (HD) and fluoroaromatic dendron (FD) side groups to increase the acentric order. HD/FD units have previously been successfully used to increase EO performance, but we changed their location on the chromophore: they are attached to the donor and acceptor ends of the molecule to better match side chain ordering with the dipole moment of the molecule. Comparison chromophores were synthesized with alkyl (-MOM), hydroxyl (-OH), or HD units on the acceptor end of the molecule and either the traditional CLD bridge (T-bridge) or modified bridge (BB-bridge) for a family of eight chromophores. The HD/FD units increased glass transition temperature, Tg, by 4-21 °C, and the bulky bridge modification increased Tg by 27-44 °C, which is very beneficial as that results in extra thermal stability of the poling-induced acentric order. UV/vis absorbance spectroscopy shows that the site-isolation units reduce aggregation. Unfortunately, poor film formation of the neat materials precluded full chromophore evaluation in poling and r33 experiments. The EO performance obtained for HD-BB-FD and HD-BB-OH was lower than expected, with r33/Ep ≈ 1 nm2 V-2 at 1310 nm. We found that blending in 25 wt % YLD124 improved film-forming and poling efficiency. Due to the effect of blending and improved site isolation, r33/Ep improved to 2.1-2.3 nm2 V-2 for 3:1 HD-BB-FD:YLD124, HD-BB-OH:YLD124, and HD-BB-MOM:YLD124, and r33 as high as 351 pm V-1 was obtained with 3:1 HD-BB-MOM:YLD124. Chromophore blends were also evaluated in plasmonic organic hybrid (POH) phase modulators with slot lengths of 5-20 μm. In POH devices, r33 was as high as 325 pm V-1 at 1260 nm and 220 pm V-1 at 1520 nm. Overall, the increase in acentric order afforded by the HD/FD interactions was found to be small and resulted in no increase in r33 due to the reduced number density. Ultimately, the increase in r33/Ep afforded by the site isolation and blending resulted in a modest increase in r33/Ep relative to YLD124, but combined with the increased Tg, the chromophore system is a significant improvement and points to an important design strategy. [ABSTRACT FROM AUTHOR]

Utilizing glycerol as a plasticizer, an accelerated physical stability testing method of amorphous solid dispersions (ASDs) was developed. The influence of glycerol concentration on the glass transition temperature and α-relaxation time (a measure of molecular mobility) of amorphous ketoconazole, celecoxib, and the solid dispersions of each prepared with polyvinylpyrrolidone was investigated. By temperature scaling (Tg/T), the effects of glycerol concentration and temperature on the relaxation time were simultaneously evaluated. Glycerol, in a concentration dependent manner, accelerated crystallization in all of the systems without affecting the fragility. In celecoxib-PVP ASDs, the drug crystallization was well coupled to molecular mobility and was essentially unaltered at glycerol concentrations up to 2% w/w. The acceleration in crystallization brought about by glycerol expedited the determination of the coupling between molecular mobility and crystallization. As a result, we were able to predict the physical stability of the unplasticized ASD. This approach is especially useful for ASDs with high polymer content where drug crystallization is extremely slow at the relevant storage temperature. [ABSTRACT FROM AUTHOR]

The role of solvating plasticizer on lithium ion conduction is investigated for a poly(ethylene oxide)-based single-ion conductor, plasticized with 12 wt % 12-crown-4 (12C4). The addition of 12C4 not only increases the static dielectric constant (εs) but also accelerates the ion rearrangement (α2) and segmental motion (α) compared to the host ionomer. A physical model of electrode polarization is used to estimate number density of simultaneously conducting ions and their mobility. The complex of 12C4 with lithium cation lowers the activation energy of simultaneously conducting ions, increasing the simultaneously conducting ion content by >3×. This is consistent with an initial large increase in εs, which is higher than the prediction from the Landau and Lifshitz mixing rule, reflecting that ion aggregates observed in the host ionomer are solvated by 12 wt % 12C4. Furthermore, the dissolution of the aggregates promotes ion mobility owing to an increase in polymer chain flexibility, with a reduction in glass transition temperature. The plasticization directly boosts ionic conductivity of the plasticized ionomer by ~5× over the whole temperature range studied, revealing that ion motion is assisted by segmental dynamics. [ABSTRACT FROM AUTHOR]

Suppression of the glass transition temperature, T g, in polymer thin films is of great practical importance and theoretical significance. It is widely believed that such T g suppression results from enhanced segmental mobility at the free surface. To investigate these effects, we carry out united-atom molecular dynamics simulations on free-standing polystyrene thin films. Care has been taken to ensure consistent behavior between thin films and the bulk. The dilatometric T g inferred from the density versus temperature shows substantial reduction in thin films compared to the bulk even at high cooling rates. Furthermore, we find that dynamical T g shifts, obtained by collapsing temperature-dependent short-time dynamical properties onto a master curve, vary with film thickness just like the dilatometric T g. We apply the same data collapse procedure to dynamics of segments within a given distance from the free surface to obtain the local T g(z), which reveals a mobile surface layer of about 4 nm. [ABSTRACT FROM AUTHOR]

Poly(butyl acrylate) (PBA) side chain equipped isoindigo-bithiophene (II2T) conjugated polymers have been designed and synthesized for stretchable electronic applications. The PBA segment possesses low glass transition temperature and high softness, offering a great opportunity to improve the mechanical property of semiconducting polymer thin films that typically contain lots of rigid conjugated rings. Polymers with 0, 5, 10, 20 and 100% of PBA side chains, named PII2T, PII2T-PBA5, PII2T-PBA10, PII2T-PBA20, and PII2T-PBA100, were explored, and their polymer properties, surface morphology, electrical characteristics, and strain-dependent performance were investigated systematically. The series polymers showed a charge carrier mobility of 0.06-0.8 cm² V-1 s-1 with an on/off current ratio over 105 dependent on different amounts of PBA chains as probed using a top-contact transistor device. Moreover, we can still achieve a mobility higher than 0.2 cm² V-1 s-1 even if 10% of PBA side chains were added (i.e., PII2T-PBA10). Such PII2T-PBA polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus down to 0.12 GPa (PII2T-PBA20) due to the soft PBA side chain. The more PBA segment was incroporated, the lower modulus was reached. The mobility performance, at the same time, remained approximately 0.08 cm² V-1 s-1 based on PII2T-PBA10 films even under a 60% strain and could be simultaneously operated over 400 stretching/releasing cycles without significant electrical degradations. The above results suggest that the rational design of soft PBA side chains provides a great potential for next-generation soft and wearable electronic applications. [ABSTRACT FROM AUTHOR]

The effect of the chemical configuration of network segments on the physical properties, cure properties, mechanical performance, and chemical stability of polycyanurate networks was investigated via synthesis, network formation, and characterization of an isomeric series of n-propyl-bridged cyanate ester monomers. Configurations that provide cyanurate oxygen atoms with either nearby methyl groups or nearby bridge groups exhibited decreased moisture uptake by up to 50%, along with a roughly 20-40 °C reduction in the loss in glass transition temperatures due to hydrolysis, for networks immersed in 85 °C water for 96 h. In ortho,para-linked aryl cyanates, dry glass transition temperatures of cured networks were reduced compared to analogous para,para-linked networks by only about 10 °C, compared to a reduction of 30 °C in ortho-methylated cyanate ester networks, leading to higher "wet" glass transition temperatures in the ortho,para-linked networks. Neither methyl groups nor bridge groups in a position ortho to the reactive cyanate ester groups prevented the creation of networks with >99% conversion at cure temperatures of 230 °C. Networks with placement of methyl groups in a position ortho to the cyanate ester exhibited char yields in nitrogen at 600 °C of 46-47% compared to 43% for networks with methyl groups in the corresponding meta position, regardless of whether a sterically hindered environment was present around the cyanurate oxygen. These results illustrate the manner in which the chemical configuration around reactive groups can substantially modify the properties of networks even when the number density and type of reactive group present do not change. [ABSTRACT FROM AUTHOR]