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Alkaline condensation reactions of 2,4,6-trimethyl-1,3,5-triazine ( 1 ) and substituted benzaldehydes ( 2a – n ) yield 2,4,6-tristyryl-1,3,5-triazines ( 3a – n ). A sufficient number and length of the alkoxy chains at the benzene rings provide liquid crystalline phases Col hd . A special structure was found for compound 3i with 9 hexyloxy chains; it exists in the solid state in a helical columnar arrangement, which is transformed by heating to a hexagonal columnar mesophase. Irradiation of the mesophases of 3i – 3m leads to partial cyclodimerization reactions, which cause different textures and lower the clearing points. The border line between the irradiated and the unirradiated zones is preserved in the solid and the liquid crystalline temperature range but also over a surprisingly long period in the molten state. A detailed study of this imaging technique was performed for the LC phase of 3i .

Melts of linear brush polymers with PEO side chains attached at each repeat unit of the backbones have been doped with CF3SO3−Li+. Mechanical properties and ionic conductivity of such systems have been analyzed using mechanical and dielectric spectroscopies. Mechanical spectra indicated a presence of super soft states for samples with long backbones or for systems which have been slightly cross-linked (G′

Various non-linear highly branched polymers such as multiarm stars, block copolymer micelles and bottlebrush-like polymers have been studied in order to analyze their intramolecular structure and effects of spatial ordering resulting from their specific macromolecular architecture. These polymers constitute a class of compact macromolecules which, due to the high intramolecular density, interact strongly, excluding each other in space. Investigations of the structure and dynamics in such systems, using various experimental methods as well as computer simulations, have been performed. Small angle X-ray scattering is used to characterize the structure and mechanical spectroscopy is used for the detection of the dynamic behavior of the systems. Simulations have been performed using the cooperative motion algorithm with lattice polymers equivalent to the considered macromolecules. Results of both experiments and the simulation seem to support the concept of slow structural cooperative rearrangements controlling the flow in such systems. The effects are analogous to those related to flow in low molecular liquids but take place on another size scale. The new slow relaxation processes creates new super soft-states which are characterized by shear modulus plateau lower than 10 4 Pa.

Calcium containing poly(urethane-ether)s (PUEs) were synthesized by the reaction of hexamethylene diisocyanate or toluylene 2,4-diisocyanate (HMDI or TDI) with a mixture of calcium salt of mono(hydroxybutyl)phthalate $[Ca(HBP)_2]$ and polyethylene glycol ($PEG_2_0_0$ or $PEG_4_0_0$). A series of calcium containing PUEs having different composition were synthesized by taking the mole ratio of $Ca(HBP)_2$:$PEG_2_0_0$ or $PEG_4_0_0$:diisocyanate (HMDI or TDI) as 3:1:4, 2:2:4 and 1:3:4 to study the effect of calcium content on the properties of the copolymer. The structure of the polymers were confirmed by IR, $^1H-NMR,$ $^13C-NMR,$ and solid state $^13C-CP-MAS$ NMR. The polymers were soluble in dimethyl sulfoxide and dimethyl formamide. The initial decomposition temperature of the polymers decreases with increase in calcium content. The $T_g$ value of PUEs increases with increase in calcium content and decreases with increase in soft segment content and length. A single $T_g$ value is observed for the calcium containing PUEs based on $PEG_2_0_0$ shows the presence of homogeneous phase. However, two $T_g$ values for the PUEs based on $PEG_4_0_0$ for various composition of $Ca(HBP)_2$, $PEG_4_0_0$ and diisocyanate (HMDI or TDI) shows the presence of heterogeneous phase. The viscosity of the calcium containing PUEs increases with increase in the soft segment content as well as its length and decreases with increase in calcium content. X-ray diffraction patterns of the polymers show that the HMDI based polymers are partially crystalline and TDI based polymers are amorphous in nature. The dynamic mechanical analysis of the calcium containing PUEs based on HMDI shows that at any given temperature modulus $(g^' and g^")$ increases with increase in the ionic content in the polymers.

We have studied the temperature dependence of anisotropy in the optical absorption and charge transport properties of an aligned film of hexakis-dodecyl-hexa-peri-hexabenzocoronene (HBC-C12) formed by zone-casting on a quartz substrate. At room temperature the film displays a large anisotropy in (photo)conductivity, as determined using the flash photolysis time-resolved microwave conductivity technique, with charge transport in the casting direction favoured by a factor of at least 10. The anisotropy in the optical absorption is however negligible. At the temperature corresponding to the transition from the crystalline solid to the liquid crystalline mesophase (c. 110°C), the optical anisotropy increases abruptly, with absorption of light polarized in the direction perpendicular to the alignment direction favoured by a factor of c. 3. On cooling, the dichroism reverts to its initial very low value with a hysteresis of c. 30°C. The results are explained in terms of a reversible change in the orientation of...

The morphology and thermomechanical properties of well-defined polyethylene-graft-poly(n-butyl acrylate) (PE-g-PBA) copolymers prepared via atom transfer radical polymerization were investigated. Differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), dynamic mechanical measurement and large deformation tensile tests were performed on the graft copolymers and the results were compared with the behavior of the polyethylene macroinitiator. The existence of both crystalline polyethylene segments and amorphous poly(n-butyl acrylate) segments in the copolymers leads to microphase separation and unique thermomechanical behavior. Strong microphase separation was observed by DSC and X-ray diffraction studies. Correlation of morphology and thermomechanical properties was also studied using dynamic mechanical measurement and large deformation tensile tests.

First through fourth generation (G1-G4) dendronized macromonomers, 3, 5, 7, and 9, with a methyleneoxycarbonyl spacer between the polymerizable group and dendritic side chain (dendron) were synthesized, and their polymerization behavior to the corresponding dendronized polymers PG1s, PG2s, PG3s, and PG4s, respectively, was investigated by heating the monomers to 55 degrees C without intentional addition of initiator. This self-induced polymerization is referred to as thermally induced radical polymerization (TRP). The molar masses of PG1s-PG4s were determined by gel permeation chromatography in DMF calibrated to a recently developed G1 dendronized polymer standard (PG1). A comparison of this homologous series' polymerization results with those of an already existing one, which differed only by the lack of this spacer (referred to as PG1-PG4), was made to contribute to the issue of whether short spacers have an effect on polymerization. Several representatives of both series were also used in the first systematic and generation-dependent investigation of these unusual comb polymers' bulk properties. Both structure and dynamics were investigated by DSC, X-ray diffraction, and dynamic mechanical measurements.

Cylindrical brushes with a macromolecular backbone and well-defined side chains of different length (4≤ P n sc ≤38) were synthesized by polymerization of macromonomers. The effect of side chain length on the intermolecular order has been investigated by means of X-ray scattering on the melt-extruded samples. The increase of the side chain molar mass results in an increase of the intermolecular distance d according to d ∼( M n sc ) 0.476 . The contour length of the cylindrical brush polymers per main chain monomer unit, l m , was determined to slightly vary with side chain molar mass M n sc according to l m ∼( M n sc ) 0.059 . The resulting values are much less than the maximum extension, l m =0.25 nm , which is found to be almost independent of side chain molar mass. Also, supermolecular structure formation of a random copolymer brush prepared by radical copolymerization of methacryloyl end functionalized polyvinylpyridine and polymethylmethacrylate macromonomers has been observed and is interpreted as a consequence of intramolecular phase separation.

Methods of analysing the dielectric α relaxation and equation-of-state data for supercooled glass-forming materials, to determine the relative contribution of volume and temperature, are illustrated using measurements on poly[(o-cresyl glycidyl ether)–co-formaldehyde] (PCGE). The ratio E V /E P = 0.66 of apparent activation energies and the ratio |α τ |/α P = 1.7, of the thermal expansivities, evaluated at τ = 1 s and P = 0.1 MPa respectively, reveal that for PCGE the volume and temperature both exert a substantial influence on the relaxation times. In this regard, PCGE is similar to other polymers and non-associated molecular liquids for which such analyses have been carried out. This means that the underlying bases of both free-volume and thermal activation models are not correct. The exceptional behaviour is that of hydrogen-bonded liquids, such as polyalcohols, for which competing effects minimize the sensitivity to pressure, whereby temperature becomes the dominant control variable.

Side-chain dendronized polymers consisting of regularly segmented alternating rigid−flexible main-chain units and side dendritic wedges are synthesized and analyzed in their bulk state using variou...

We report the synthesis and characterization of covalent dyads and multiads of electron acceptors (A) and donors (D), with the purpose of exploiting their nanophase separation behavior toward (a) two-dimensional (2D) surface patterning with well-defined integrated arrays of dissimilar molecular electronic features and (b) bulk self-assembly to noncovalent columnar versions of the so-called "double cable" systems, the likes of which could eventually provide side-by-side percolation pathways for electrons and holes in solar cells. Soluble, alkylated hexa-peri-hexabenzocoronenes (HBCs) bearing tethered anthraquinones (AQs) are shown by scanning tunneling microscopy (STM) to self-assemble at the solution-graphite interface into either defect-rich polycrystalline monolayers or extended 2D crystalline domains, depending on the number of tethered AQs. In the bulk, the thermal stability of the room-temperature HBC columnar phase is increased, which is attributed to the desired nanotriphase separation of HBC columns, insulating alkyl sheaths, and AQ units. Homeotropic alignment (columns normal to surfaces), predicted to be ideal for potential exploitation of such "double cables" in photovoltaic devices, is demonstrated.

The configurational properties of strongly charged polyelectrolytes accompanied by neutralizing counterions in dilute solutions are simulated using the cooperative motion algorithm on the face-centered-cubic lattice. The full Coulomb potential and the excluded volume condition between different ions/beads are taken into account and the reduced temperature T* is considered the main, variable parameter. The calculations that have been carried out for solutions of both single and several chains indicate a few regions of their behavior: (1) for T*--infinity, it corresponds to that of neutral, self-avoiding polymers under good solvent conditions; (2) for T* approximately 1, due to the electrostatic interactions being effectively stronger, the chains are more outstretched compared to their size at other temperatures; (3) for T* well below one, the counterion condensation becomes more and more dominant, which gradually leads to strongly collapsed chains; and (4) at the lowest temperatures the chains and counterions assume low-energy configurations in the form of neutral, compact aggregates.

This paper reports the phase belavior of photochemically crosslinked poly(butyl acrylate) networkds in nematic liquid crystal (LC) solvents. The swelling properties are studied studied as a function of temperature for two low molecular weight LCs, 4-cyano-4'-Pentylbiphenyl (5CB) and the eutectic mixtyure of cyanoparaphenylenes (E7). Chemically crosslinked plymer networkds were formed bye the UV radiation of initial solutions of the reactive monomer, butyl acrylate, a crosslinker (hexanediol diacrylate), and a photoinitiator. To obtain different network densities, the ratio of butyl acrylate to hexanediol diacrylate was varied prior to polymeriztion/crosslinking reactions. Immersion in an excess of the LC solvent allowed fort ther measurement of size increase bye polarized optical microscophy in terms of temperature. Length, width, and diagonal ratios were calculated considering swollen to dry network states of the samples. In general, swelling leads to an increase in the network size by increasing the temperature with a significant dependence on the degree of crosslinking. A large shift in the swelling ratio was found in the vicinity of the nematic to isotropic transition temperatures of the LCs.

Experimental static Small Angle Light Scattering(SALS)data obtained from a selected monomer–liquid crystal system are presented. A blend involving the eutectic nematic mixture of low molecular weight liquid crystals(E7)and a difunctional monomer(tripropyleneglycoldiacrylate or TPGDA)was choosen to highlight the variations of the light scattering intensity in terms of scattering and azimuthal angles. Measurements of SALS were made in the VH mode under cross-polarized optical alignments.The experimental results were compared to a theory developed originally for bulk semi-crystalline polymers showing an anisotropic behavior and adapted to liquid crystalline systems. Depolarized light scattering intensities were calculated for isolated spherical droplets of liquid crystal molecules exhibiting a radial configuration. In particular, the characteristic anisotropic features of radial droplets in the VH mode were obtained both experimentally and theoretically. A good agreement between theoretical results and exper...

Some salient features of physical properties of Tripropyleneglycol diacrylate (TPGDA) and the low molecular weight nematic liquid crystal E7 are discussed. A variety of experimental techniques giving complementary information of monomer and Electron Beam (EB) cured systems are employed to illustrate the effect of curing. A detailed thermophysical analysis is made first to assess the conditions of miscibility, determine the order-disorder transition and the glass transition temperature. DSC spectra yield the energy change at the transitions from which important parameters are readily extracted such as solubility limits and amount of liquid crystal dissolved in the polymer. Polarized Optical Microscopy enables us to follow phase transitions and morphology changes in different regions of the phase diagram. Consistent data are obtained from mechanical measurements in particular with regards to the variation of the glass transition temperature with liquid crystal concentration and the related plasticizing effect.

This paper reports a study of static and dynamic mechanical properties of electron beam (EB) cured polymer dispersed liquid crystals. These systems consist of micron-sized droplets dispersed in a solid polymer matrix. They are prepared according to the polymerization induced phase separation process initiated by exposure to electron radiation. A difunctional monomer Tripropylene Glycol Diacrylate in short TPGDA is used with the eutectic liquid crystal mixture E7 having a nematic to isotropic transition temperature at 60°C. Strong effects are found on Young modulus and rubbery state modulus in terms of the EB dose and the liquid crystal concentration. As the concentration of small molecules increases, these mechanical parameters drop significantly together with the glass transition temperature Tg of the polymer showing a plasticizing effect. The results for Tg are confirmed by DSC thermograms in terms of liquid crystal concentration and EB dose.

Polymerization and cross-linking induced phase separation initiated by electron beam radiation is used to elaborate Polymer Dispersed Liquid Crystal (PDLC) films made of polydimethylsiloxane and 5CB. Electro-optical properties of the obtained films are investigated in terms of the composition of the initial mixture and amplitude of the applied AC voltage. A particular attention is given to transmission levels and operating voltages.

In this paper, we present recent electro-optical data of Polymer Dispersed Liquid Crystal (PDLC) films operating under reverse mode conditions. We consider systems prepared by Polymerization Induced Phase Separation (PIPS) using Electron Beam (EB) curing of acrylate monomers mixed with a low molecular weight liquid crystal (LC). In the present investigation, a low molecular weight LC exhibiting a negative dielectric anisotropy is used yielding electro-optical curves characterized by a transparent initial off-state and an opaque on-state film under the influence of an external field. The results enable us to characterize the sensitivity of electro-optical responses to the functionality of monomers in the precursor mixtures as well as the conditions of film preparation. Data showing the phase behavior of a monomer/LC system are also presented to rationalize the electro-optical results of these interesting but relatively less known materials.

A static light scattering study of monomeric (uncured) and Electron Beam (EB) cured Tripropyleneglycoldiacrylate (TPGDA) and E7 (a nematic Liquid Crystal) systems is reported. This study includes a detailed investigation of the structural properties in terms of temperature, composition and scattering angle. Knowledge of the phase diagrams helps us to achieve a better understanding of the scattering curves and rationalize data in terms of the LC configuration inside droplets. The depolarized component of the scattered intensity measured under cross polarizers exhibits patterns reminiscent of anisotropic objects. The results can be correlated to the electro-optical responses of the investigated systems relevant to applications in display technology and smart windows.

Phase diagrams of various polysiloxanes and the eutectic liquid cristalline mixture of cyanoparaphenylenes E7 are established. Thermophysical properties are investigated considering the case of Poly(dimethylsiloxane) and Poly(methylphenylsiloxane) with different molecular weights. Differential Scanning Calorimetry and Polarized Optical Microscopy are used to construct the phase diagrams and obtain thermophysical data that are rationalized using a combination of the Flory-Huggins theory of isotropic mixing and the Maier-Saupe theory of nematic order. The glass transition temperature versus composition of the blends investigated yields information of the plasticising effect of the small liquid crystal molecules.

Two novel tetra- and hexahydroxy functionalized perylene chromophores have been used as initiators for the Sn(oct)2 catalyzed ring-opening polymerization of different lactones. The arms of the resulting star polymers were comprised of either crystallizable poly(L-lactide) or poly(ε-caprolactone) arms or of amorphous poly[γ-(tert-amyl)-ε-caprolactone] chains. The star polymers were investigated by differential scanning calorimetry. X-ray scattering and dynamic mechanical and optical spectroscopy. Whereas the thermal properties of the poly(ε-caprolactone) stars were barely affected by the star topology, crystallization of the poly(L-lactide) stars was strongly hindered by the star-shaped architecture. Interestingly, for the amorphous poly[γ-(tertamyl)-ε-caprolactone] stars a decrease in Tg with increasing chain length was found, reflecting the declining influence of the rigid perylene core on segmental mobility with increasing arm length. While the solid state and solution optical properties of high molar mass polyester stars were identical, the excitation and fluorescence emission spectra of spin-coated films of the low molecular weight polymers revealed a red shift, pointing towards perylene - perylene interactions in these samples. The optical spectroscopy experiments suggested that arm length, rather than the-number of arms, is the most important parameter determining, encapsulation and preventing aggregation of the perylene core moieties in the solid state.

A lattice computer simulation of a symmetric A–B–A triblock copolymer melt is reported. This melt is quenched, in simulation, from an athermal state to 39 different temperatures using cooperative motion algorithm. Energy, specific heat, copolymer end-to-end distance, bridging fraction, lamellar spacing, concentration profiles, and microstructure visualizations are reported. The quenching simulation results are compared with those obtained by alternative thermal treatments, that is by slow heating and slow cooling. Quenches yield data consistent with theory and experiment, whereas slow cooling and slow heating results do not capture the expected behavior for the lamellar spacing and the bridging fraction. Finally, at very low temperatures, below the conventional order–disorder transition temperature, an additional ordering is recorded, from a conventional lamellar phase to a lamellar structure showing copolymer junction points condensed into a two-dimensional plane.

The structure and the associated dynamics have been investigated in a series of oligopeptides of gamma-benzyl-l-glutamate using DSC, WAXS, FTIR, NMR and dielectric spectroscopy, and rheology, respectively. The peptides with degrees of polymerization below 18 are mixtures of a lamellar assembly of beta sheets and of columnar hexagonal arrangement of alpha helices, whereas for longer chains, the intramolecular hydrogen bonds stabilize only the alpha-helical conformations. Multiple dielectrically active processes were found. Starting from low temperatures, the two Arrhenius processes (gamma and beta), with apparent activation energies of 20.6 and 50.2 kJ/mol, respectively, associate with the local relaxation of the side-chain methylene units (gamma process) and with more cooperative motions of the side chain dipoles sensitive to the 7/2 helical packing (beta process). The glass transition is manifested in the thermal properties with a step in the heat capacity and with an intense dielectric process bearing characteristics (molecular weight dependence, temperature dependence of relaxation times) known from amorphous polymers. Based on these findings, the alpha process is attributed to the relaxation of amorphous segments located between and at the end of helically ordered segments. Two slower processes were identified with opposite molecular weight dependence. The weak intermediate mode with an M2 molecular weight dependence of the characteristic relaxation times suggests amorphous-like chains, whereas the strong slower process originates from the loss of dipole orientational capacity caused by structural defects and reflects the migration of helical sequences along the chains. This identifies the helices as structures extending over rather short fragments of chains (i.e., of low persistence length). The viscoelastic response indicated that the structural defects arise from locally aggregated chains that inhibit the flow of oligopeptides.

A series of P[(HEMA-TMS)- co -PEOMA] graft copolymers with different amounts of incorporated macromonomer grafts were prepared by copolymerization of a PEO macromonomer (PEOMA, MW av =1100 g/mol, DP PEO =23) with 2-(trimethylsilyloxy)ethyl methacrylate (HEMA-TMS) using various initial ratios of the comonomers via atom transfer radical polymerization. After transformation of the HEMA-TMS units to 2-(2-bromopropionyloxy)ethyl methacrylate (BPEM), the resulting P(BPEM- co -PEOMA) copolymers were used as macroinitiators for the controlled polymerization of n BA in a ‘grafting from’ reaction. The resulting densely heterografted brush copolymers with a uniform length of PEO grafts (DP PEO =23) and a range of lengths for the P n BA side chains (DP P n BA =15–60) depending solely on the reaction time. Analysis of the bulk properties showed that the specific architecture of the copolymers suppresses crystallization of the PEO, and consequently leads to amorphous, homogeneous materials.

Photosensitive mesoionic polymers in which the polymerizable methacrylic group is attached to the malonic acid component of the mesoionic function were prepared and characterized. Dielectric measurements were performed, and the results were compared to those of liquid-crystalline mesoionic copolymers. The influence on the dielectric properties upon irradiation with UV light, which causes the photoconversion of the mesoionic groups to bis(β-lactame) structures, was determined. The glass-transition temperatures determined by dielectric spectroscopy were compared to those obtained by DSC. It could be observed by waveguide-mode spectroscopy that irradiating the mesoionic methacrylates results in remarkable effects on the film thickness and refractive index of spin-coated polymer films.

Two macromonomers containing ethylene oxide (EO) segments with different degrees of polymerization (DPPEO = 5 and 23), capped by a methoxy and a methacrylate group (PEOMA), were polymerized by atom transfer radical polymerization (ATRP) in organic solvents. In addition to the direct preparation of densely grafted brush copolymers by “grafting through” the macromonomers, the lower molecular weight PEOMA (MWav = 300 g/mol, DPPEO = 5) was also employed in a “grafting from” reaction using a well-defined multifunctional macroinitiator poly(2-(2-bromopropionyloxy)ethyl methacrylate) (PBPEM, Mn,app = 82 × 103 g/mol, Mw/Mn = 1.16, degree of polymerization of backbone DPb = 428). This procedure allowed the preparation of densely double-grafted brush copolymers with various degrees of polymerization of the side chains (DPsc = 12−43). Attempts to prepare double-grafted brushes with DPsc > 50 or to use a macromonomer with a longer PEO chain (MWav = 1100 g/mol, DPPEO = 23) in the “grafting from” reaction resulted in f...

The dynamic lattice liquid model was implemented as a simulation algorithm for simple liquids. This model works correctly for the density factor ρ=1 and becomes a base for a parallel algorithm. Such an algorithm takes into account coincidences of elementary molecular motion attempts resulting in local cooperative structural transformations. In this paper general conditions for simulating simple liquids on various lattices are presented. Interdiffusion coefficients were directly monitored as changes of composition profiles with time for both athermal and interacting binary (AB) mixtures. In the athermal case, the coefficients of self-diffusion and interdiffusion are equal. For interacting binary mixtures the interdiffusion exhibits a thermally activated character.

Atom transfer radical polymerization (ATRP), reversible addition−fragmentation chain transfer (RAFT) process, and the conventional radical polymerization (RP) were applied to the copolymerization of methyl methacrylate (MMA) and methacrylate-terminated poly(dimethylsiloxane) macromonomer (PDMS−MA). They resulted in PMMA-g-PDMS graft copolymers with various branching and molecular weight distributions. By applying appropriate conditions, ATRP led to homogeneously branched copolymer and RAFT to gradient branched copolymer. The RP process gave heterogeneously branched copolymer with large polydispersity. The structure and mechanical properties in these copolymers were analyzed.

New aromatic polyamides containing 1,3,4-oxadiazole or benzonitrile units in the main chain and 5-(4-acetoxybenzamido) groups in the side chain have been synthesized and their properties have been characterized and compared with those of related polyamides and polyoxadiazole-amides. These polymers show good thermal stability, with initial decomposition temperature being at about 300 °C and glass transition temperature in the range of 260–280 °C. They are easily soluble in certain solvents such as N-methylpyrrolidinone (NMP), N,N′-dimethylacetamide (DMA) and N,N′-dimethylformamide (DMF) and can be cast from solutions into thin flexible films. The polymer films had tensile strengths in the range of 77–97 MPa, tensile moduli in the range of 2.3–2.6 GPa and elongation at break values ranging from 6% to 24%. One of the polymers containing the 1,3,4-oxadiazole ring exhibited blue fluorescence.

Blends of functionalized polystyrenes (3NPS) having three dimethylamino groups {N(CH3)(2)} at one end, with sulfonic acid end-capped polyisoprenes (HO3SPI) were prepared in a ratio of N(CH3)(2)/ SO3H = 1. The morphology of these blends was studied by small-angle X-ray scattering and transmission electron microscopy and the associated dynamics by rheology. The results of the microdomain investigation, as well as of the associated dynamics, provide unambiguous evidence for controlled miktoarm star block copolymer formation via ionic interactions. Macromolecules

Linear flexible polymers both at low and high concentrations surrounding a single hard sphere are simulated using the cooperative motion algorithm on the face-centered cubic lattice. The excluded-volume condition between different monomers is taken into account and the size ratio q=R/Rg of the sphere radius and the mean radius of gyration of the chains is considered as a parameter. Structure of the system in the vicinity of the sphere is analyzed in comparison with the structure of the bulk solution for a wide range of q. The limiting case of the infinite sphere radius R→∞, i.e., the effect of the neutral wall on the chains, is also presented. The simulations indicate (1) a depletion layer in the neighborhood of the sphere, (2) an enhancement of the chain ends concentration at the particle surface, (3) an enhancement of the chain center-of-mass concentration at some distance from the surface for large q, (4) a penetration of the centers of mass into the sphere for small q, (5) an orientation ordering of t...

Phase diagrams of blends of poly(methylphenylsiloxane) in short PMPS and two low molecular weight liquid crystals (4-cyano-4′-n-pentyl-biphenyl and an eutectic mixture of paraphenylenes) are reported. Two polymers with very different weight-average molar masses are considered in an evaluation of the loss of miscibility resulting from a known increase in the weight-average molar mass. The experimental diagrams have been constructed via polarized optical microscopy and are rationalized in terms of the Flory–Huggins theory of isotropic mixtures and the Maier–Saupe theory of nematic order. The results show a good agreement between the theory and experiments and reveal a remarkable enhancement of miscibility with respect to similar systems involving poly(dimethylsiloxane). Variations of the interaction parameter with the temperature are compared for different systems of polysiloxanes. The effects of the nature of the liquid crystal and the polymer molar mass on the χ parameter are evaluated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 39–43, 2003

We report on the phase state of two new diblock copolymer systems, poly(butadiene-b-tert-butyl methacrylate) (BBMA) and poly(ethylene-b-tert-butyl methacrylate) (EBMA). The EBMA system was synthesized from the BBMA by hydrogenation of the polybutadiene block, thus creating two systems at practically the same volume fractions and identical degrees of polymerization, but with different segment interaction parameters and conformational asymmetries. Hydrogenation of the butadiene block resulted in an increased incompatibility and to an asymmetric phase diagram. In one of the EBMA copolymers with a PE volume fraction fPE = 0.42, crystallization of the PE blocks was confined by the cylindrical mesophase in a fluid matrix. Upon PE crystallization, the hexagonal order was found to improve significantly following a matrix-assisted reorganization.

This article reports on mechanical properties of electron beam cured tripropylene glycol diacrylate (TPGDA) and propoxylated glycerol triacrylate (GPTA) films. This study has been motivated by the need to have direct access to those properties for analyzing the thermo-mechanical behavior and electro-optical properties of polymer dispersed liquid crystal systems in general, and systems made either of TPGDA or GPTA and low molecular weight liquid crystals in particular. Representative examples of these systems are considered in this work. The effects of the degree of crosslinking on the mechanical strength of the polymer network are analyzed by considering different doses of the electron beam irradiation. As the radiation dose increases, the mechanical strength of the film is enhanced. Addition of a small amount of liquid crystals leads to remarkable plasticizing effects.

The solid-state structures of polystyrene–poly(Z- l -lysine) block copolymers were examined with respect to the polymer architecture and the secondary structure of the polypeptide using circular dichroism, quantitative small- and wide-angle X-ray scattering, and electron microscopy. Linear block copolymers exhibit a hexagonal-in-lamellar structure where folded and packed polypeptide α-helices form lamellae which extend over an exceptional broad range of the composition diagram. Star- or bottlebrush-shaped copolymers are able to stabilize a larger interface area than linear ones which promotes the formation of undulated lamellar mesophases. Depending on the secondary structure of polypeptide segments, plane lamellar, superundulated lamellar, or corrugated lamellar phases are formed. These results indicate the importance of a secondary structure and packing of polymer chains for the formation of new phases and ordering far from the ‘classical’ phase behavior.

The Dynamic Lattice Liquid (DLL) model has been implemented as a simulation algorithm for two-dimensional (2-D) polymeric systems. The model can work with density factor ρ=1 and became a basis for a parallel algorithm, which takes into account coincidences of elementary molecular motion attempts resulting in local cooperative structural transformations. Systematic studies of athermal polymer systems on the two-dimensional triangular lattice are presented for various concentrations of linear polymers with respect to an explicitly considered solvent. Both static and dynamic properties are characterized. The simulation results reflect molecular packing and other properties of monomolecular polymer layers, which can be relevant to these obtained in some thin film formation techniques.

The solid columnar discotic and liquid crystalline (LC) phases formed by alkyl-substituted hexabenzocoronene (HBC) mesogens have been investigated by a combination of X-ray scattering and a variety of advanced solid-state NMR methods. Correlations between chemical structure, molecular packing and dynamics are established. Maximum charge carrier mobility is observed for a crystal-like stacking of the disks in the column with optimized π−π interactions. For systems with lower intracolumnar order the charge carrier mobility is slightly lower and slow axial motion of the disks around the column axes occurs.

Poly(ether-ester) (PEE) Elitel 4450 - liquid crystalline polyester (LCP) Vectra RD 501 blends extruded (L/D = 20, D = 19mm) with a homogenizing head at 225°C, were studied by differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA), dielectric spectroscopy, and scanning electron microscopy (SEM). The blends exhibited a multiphase microstructure. Two mechanical relaxation temperatures were found to occur, and similarly two glass transition temperatures were recorded by DSC. There is a glass transition in the PTMO soft phase (ca. - 60°C) and in Vectra (+ 107°C). For the PBT hard phase (ca. +35°C), T g 2 is weakly pronounced because of the high crystallinity. The blend showed only one m.p., close to the m.p. of the PEE. Three dielectric relaxation processes were found to occur in PEE and three others in Vectra. In the blends, the dielectric spectra are seen to be superimposed. These blends are immiscible in terms of thermodynamics. Vectra modified the molecular mobility of the PEE rigid segments, as evident from nonisothermal crystallization of the PBT hard phase and degree of crystallinity as also from changes of the PTMO content in the soft phase. SEM disclosed either a spherical or a fibrous structure in the blends, depending on Vectra content.

Polyisobutene-graft-poly(methyl methacrylate) and polyisobutene-graft-polystyrene with controlled compositions and side chain architectures were prepared through atom transfer radical polymerization (ATRP). Poly[isobutene-co-(p-methylstyrene)-co-(p-bromomethylstyrene)] (PIB) was used as a macroinitiator in the presence of CuCl or CuBr as a catalyst and dNbpy as a ligand. The compositions were controlled by the conversion of the monomer with polymerization time. The molecular weight distributions of the side chains were controlled through ATRP in the presence/absence of a halogen exchange reaction. DSC and DMA measurements showed that graft copolymers have two glass transition temperatures suggesting microphase separated behavior, which was also confirmed by SAXS measurements. The phase and dynamic mechanical behaviors were strongly affected by the compositions and/or the side chain architectures. The properties of the graft copolymers were controlled in a wide range leading to toughened glassy polymers or elastomers.

New aromatic poly(ether-ketone)s containing hexafluoroisopropylidene groups have been prepared by aromatic nucleophylic displacement reaction of the potassium salts of aromatic dihydroxy compounds containing fluoren, 1,3,4-oxadiazole or phenylquinoxaline rings with 2,2-bis[4-(4-fluorobenzoylphenyl)hexafluoropropane. These polymers were readily soluble in various organic solvents such as N,N-dimethylformamide, pyridine, tetrahydrofuran and chloroform and gave flexible films by casting such solutions. Their glass transition temperatures (Tg) were in the range of 189–222°C and they were thermally stable up to 480°C. The polymer films displayed low dielectric constants, in the range of 2.8 – 3.2, and good mecanical properties, with tensile strength in the range of 46 – 61 MPa and elastic modulus of 1.4 – 1.6 GPa.

Structure and dynamics of complex macromolecules in computer simulated systems is analyzed. The algorithm based on cooperative molecular rearrangements is applied to various macromolecular structures represented in a simplified form on the lattice. Various macromolecular architectures such as linear chains, stars, dendrimers, bottle-brush polymers as well as cyclic chains and catenane are considered both as single molecules and as dense systems corresponding to polymer melts. A broad range of structural parameters characteristic for each system is taken into account. In some cases, the simulation results are compared with the behavior of real systems in which the structure and dynamics has been studied by X-ray scattering and mechanical spectroscopy, respectively.

A series of new heterocyclic polyethers, containing phenylquinoxaline and 1,3,4-oxadiazole rings, was synthesized by polycondensation of bis (4-fluorophenyl)-1,3,4-oxadiazole with a diphenol containing preformed phenylquinoxaline rings. These polymers showed good solubility in chloroform and gave transparent, flexible films, by casting their solutions onto glass plates. They exhibited glass transition temperatures in the range of 225–337°C and were stable when heated up to 420°C, the initial decomposition temperature being in the range of 425–465°C. Solutions of these polymers in chloroform exhibit violet fluorescence, having maximum emission wavelength in the range of 412–425 nm and fluorescence quantum yield in the range of 0.11–0.26. The polymer films displayed a low dielectric constant and tough mechanical properties.

Highly branched poly(methyl methacrylate) with an estimated degree of branching = 0.074 (i.e., 3.7 branchpoints per 100 monomer units) was prepared using self-condensing group transfer copolymerization (SCVCP) of methyl methacrylate (MMA) and 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (MTSHEMA) and fractionated by means of preparative SEC. The fractions were characterized in solution by SEC−viscosity coupling and in the melt by viscoelastic spectroscopy. In THF solution, a Mark−Houwink exponent of α = 0.40 was determined for the branched polymer, which is considerably lower than that of linear PMMA (α = 0.688). In the region between the relaxation times of the chain, τc, and of the segments, τs, of the viscoelastic spectrum of the branched polymer, both the storage and the loss moduli (log G‘ and log G‘ ‘) are nearly equal, and the complex viscosities show a practically linear dependence on log ω with a slope of −0.54. This is attributed to a broad distribution of relaxation times and t...

We describe the structure and dynamical behavior of a homogeneous mixture of hairy nanospheres, i.e., polyorganosiloxane microgels grafted with polystyrene chains, and linear polystyrene chains. Previously, it has been found that such mixtures are only homogeneous if the molecular weight of the polymer hairs is at least as large as that of the linear matrix chains. Otherwise, the depletion mechanism typical for most colloid−polymer mixtures leads to a phase separation. It indicates that the length of the polymer hairs with respect to the length of the matrix chains has an important effect on structure and dynamics of the colloid−polymer blends. Here we demonstrate that if the chains are much shorter than the hairs, the colloidal hair corona is strongly swollen by the matrix polymer, leading to a long-range soft interparticle repulsion (“wet brush”). If hairs and chains are comparable in length, the corona shows much less volume swelling, leading to a short-range repulsive potential similar to hard-sphere ...

Purpose To compare the rheological characteristics of a viscoadaptive viscoelastic formulation with those of 2 standard ophthalmic viscosurgical devices (OVDs). Setting Department of Ophthalmology, Johannes Gutenberg-University, and Max Planck-Institute for Polymer Research, Mainz, Germany. Methods An independent comparative study of 3 OVDs of sodium hyaluronate (Healon®, Healon GV®, and Healon®5) was performed using the Advanced Rheometric Expansion System to analyze rheologic behavior (eg, dynamic frequency dependence of the complex viscosity) as well as rheological parameters (eg, viscosity at zero shear rate, pseudoplasticity, relaxation time, elastic and viscous modulus). Results Mean viscosity at zero shear rate was 243 Pas ± 5 (SD) for Healon, 2451 ± 12 Pas for Healon GV, and 5525 ± 14 Pas for Healon5. Mean pseudoplasticity was 173 ± 7, 754 ± 10, and 591 ± 6, respectively. Mean relaxation time was 21 ± 3 sec, 83 ± 4 sec, and 88 ± 6 sec. At low shear rates, viscosity and elasticity (elastic and viscous modulus) increased from Healon through Healon5. Healon5 exhibited a dynamic behavior of the complex viscosity dependent on the duration of the shear rate exposure: At low shear rates, it slowly built up a high viscosity. At higher shear rates, it demonstrated a lower viscosity that decreased further during constant exposure to a specific shear rate. Conclusions Healon5 had the highest viscosity and elasticity when exposed to low and high shear rates. These characteristics maintain anterior chamber depth. Also, the high viscosity of Healon5 exhibited a dynamic frequency dependence. In the presence of turbulence and phaco power (continuous high shear rates), it became dispersive by fragmentation and formed a cavity with an outer retentive shell. The cohesive and dispersive properties of Healon5 make it the best of the 3 OVDs evaluated for use atall stages of phacoemulsification.

The dynamic Monte Carlo WO simulation using algorithms based on the cooperative motion algorithm (CMA) is presented in application to analysis of structure and dynamics of single complex macro-molecules. Linear chains, polymer rings and polymer stars are considered. Relations between details of molecular dynamics in such systems and quantities which can be considered as observable in the dielectric relaxation measurements are presented and discussed in comparison with the existing experimental evidence.

We describe the preparation of hairy nanospheres by grafting of polystyrene macromonomer chains onto polyorganosiloxane microgels. Our strategy was to obtain special surface-modified colloidal particles, which can be blended with linear polymer chains without depletion demixing found for standard colloid−polymer mixtures. For this purpose, the molecular weight of the polymer hairs and of the linear chains has been varied between 4000 and 19 000 g/mol. In all cases, the number of hairs per single particle with core radius about 10 nm exceeded 150. Studying the internal structure of mixtures of these hairy spheres with linear polymer chains by transmission electron microscopy and small-angle X-ray scattering, we identified homogeneous systems, i.e., suppression of depletion demixing, in case the molecular weight of the polymer hairs on the particle surface is at least as large as the molecular weight of the single polymer chains. This result is interpreted in terms of a new depletion model, taking into acco...

The Dynamic Lattice Liquid (DLL) model for molecular rearrangements in liquids is discussed in application to both simple supercooled liquids and polymer melts. It is shown, that the model is able to reproduce a broad class of various temperature dependencies of relaxation times, lying between the extremal cases represented by the Arrhenius relation on one and by the Vogel-Fulcher-Tamman (VFT) relation on the other hand. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements operating in a dense system under conditions of the excluded volume and continuity of the system. The model is implemented as a simulation algorithm, which is used to describe dynamic properties of liquids and polymer melts. Simulation results obtained for systems representing simple liquids as well as linear polymers, multiarm star polymers and microgels are presented. An analogy in the dynamic behavior between the low molecular liquids and melts of macromolecules with complex compact architectures is discussed.

In this paper, we demonstrate a computer simulation method allowing to study single model macromolecules with various complex topologies. The method is applied to branched macromolecules such as H-shaped polymers and polymer stars. Preliminary results describing both the structure and dynamics are presented.

The synthesis of di- and triblock copolymers using atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) and methyl methacrylate (MMA) is reported. In particular, synthetic procedures that allow for an easy and convenient synthesis of such block copolymers were developed by using CuBr and CuCl salts complexed with linear amines. Polymerizations were successfully conducted where the monomers were added to the reactor in a sequential manner. Poor cross-propagation between poly(n-butyl acrylate) (PBA) macroinitiators and MMA was minimized, and therefore control of molecular weights and distributions was realized, by using halogen exchange—a technique involving the addition of CuCl to the MMA during the chain extension of the PBA macroinitiator. High molecular weight (Mn ∼ 90,000) and low polydispersity (Mw /Mn < 1.35) ABA triblock copolymers were also prepared and their structure and properties in bulk have been preliminary characterized indicating the potential of ATRP for the production of all-acrylic thermoplastic elastomers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2023–2031, 2000