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This study investigates melt spinnability of ethylene vinyl alcohol (EVOH) copolymers with various ethylene contents, which exhibits excellent biocompatibility but cannot easily undergo single-component fiber spinning. The chemical, thermal and rheological properties of EVOH were examined herein. Three EVOH copolymers, EV-32, 38 and 44, with different ratios of ethylene to vinyl alcohol (EV ratio), were used to evaluate the influence of the ratio on melt spinnability. The EV ratios of EV-32, EV-38 and EV-44 examined by nuclear magnetic resonance were 0.64, 0.82 and 1.0, respectively. The experimental results reveal that the melting temperature (Tm) and crystallinity (Xc) of EVOH decreased in the order EV-32 (178.9℃, 46.6 wt%) > EV-38 (171.9℃, 41.8 wt%) > EV-44 (166.0℃, 40.0 wt%). The thermal stability, however, increases in the order EV-32 < EV-38 < EV-44. The viscosity decreases in the order EV-32 > EV-38 > EV-44. EV-44 has much higher flow activation energy than EV-32 and EV-38, indicating that it has a temperature sensitivity higher than EV-32 and EV-38. The pellets of EV-32, EV-38 and EV-44 were melt spun. Three as-spun fibers, EV-32, EV-38 and EV-44 have cross-sectional diameters of 151.3, 150.9 and 154.1 µm and tensile stresses (strain (%) at breaking point) of 123.1 (205.2%), 121.4 (202.0%) and 131.1 MPa (180.2%), respectively. Most importantly, EV-44 can easily be spun at a relatively low temperature, 245℃, while the other two, EV-38 and EV-32, can hardly be made on condition that the spinning temperatures are higher than 255℃ and 265℃, respectively. Notably, once the spinning temperature of EVOH polymers was higher than 258℃, the degradation of vinyl alcohol segments would cause fuming and broken filaments to eventually terminate the entire spinning process. Ultimately, a brand new fiber, EVOH, with an EV ratio of 1.0, was successfully melt spun and mechanically characterized in this study. [ABSTRACT FROM AUTHOR]

In this study, we prepared a series of thermosensitive polymers with low polydispersity index (PDI) values by nitroxidemediated controlled radical polymerization (NMRP) with 2,2,6,6-tetramethyl-1-piperdinyloxy nitroxide (TEMPO) as a stable nitroxide-free radical. Poly(N-isopropyl acrylamide) (PNIPAAm)-block-poly(N-tert-butyl acrylamide) (PNTBA) was successfully synthesized, first, through polymerization with N-isopropyl acrylamide to obtain the reactive polymer PNIPAAm-TEMPO and, second, through polymerization by the addition of N-tert-butyl acrylamide (NTBA). The added molar fraction of NTBA during the second polymerization was adjusted accordingly to obtain the final polymerization product, a thermosensitive polymer (PNIPAAm-block- PNTBA), which had a targeted lower critical solution temperature (LCST). The result shows that the synthesis method used in this study effectively controlled the formation of the polymer to obtain a low PDI. The thermosensitive block copolymer, PNIPAAm-b- PNTBA (molar ratio = 9:1), with LCSTs in the range 27.7-39.8°C, was obtained through controlled living radical polymerization with PNIPAAm-TEMPO. Specifically, the 5 wt % aqueous solution of PNIPAAm-b-PNTBA (molar ratio = 9:1) had an LCST of 37.4°C; this was close to body temperature, 37°C. The 5 wt % aqueous solution of PNIPAAm-b-PNTBA (molar ratio59:1) showed potential for use in biomedical applications. [ABSTRACT FROM AUTHOR]

A series of aliphatic/aromatic copolyesters that contained different amounts of aliphatic segments, constructed from adipic acid (AA, 0∼0.117 mole ratios), were synthesized. The structure of each copolymer was confirmed by 1H nuclear magnetic resonance. The molecular weight was determined directly by gel permeation chromatography and indirectly by the intrinsic viscosity. The results of thermal tests revealed that both melting temperature (Tm) and crystallization temperature (Tc) decreased as the aliphatic segment content increased. The glass transition temperatures (Tg) that were determined by dynamic mechanical analysis followed the same trend as did Tm. Moreover, the thermal stability, determined from thermogravimetric analysis, declined as polyethylene glycol (PEG) and AA were incorporated into the poly(ethylene terephthalate) (PET) main chains. All of the polymers that were synthesized herein were spun into fibers and then physically characterized. The tenacity of the fibers decreased as the soft-segment content increased. The crystalline structures, revealed by wide-angle X-ray scattering, indicated that the crystallinity decreased with increasing AA content because of the reduction of regularity of the PET chains. Most importantly, the tests that were carried out on the knitted fabric demonstrated that the moisture regain and cool feeling (qmax) of the copolymer fabrics were better than those of fabrics that comprised neat PET chains, owing to the incorporation of soft PEG segments. Finally, the copolymer fabric exhibited better hydrolysis and enzymatic degradation than did neat PET fabric. [ABSTRACT FROM AUTHOR]

ABSTRACT Poly( N-isopropylacrylamide) (NIPAAm) is well known as a smart material with good thermal sensitivity and favorable biocompatibility. A series of new smart hydrogels, NIPAAm copolymerized with IAM (itaconamic acid; 4-amino-2-methylene-4-oxobutanoic acid), were synthesized through radical solution polymerization in this work. Poly(NIPAAm- co-IAM) can respond to the changes of temperature as well as pH value. Such a characteristic is due to the fact that IAM contains not only a hydrophilic acrylic acid moiety but also an acrylamide moiety to be thermal and pH sensitive. The experimental results show that the lower critical solution temperature (LCST) of the copolymer increases as the molar fraction of IAM increases. Moreover, based on the current experimental data, 3 wt % of Poly(NIPAAm- co-IAM) aqueous solution in this study exhibits a phase transition temperature (37.8°C) close to the human body temperature in the buffer solution of pH 7 possibly to be useful in drug delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42367. [ABSTRACT FROM AUTHOR]

Forming nano-scale interpenetrating networks in electron donor/acceptor blends via phase-separation tuning and maintaining their optimal morphology are of paramount importance for the favorable performance and operational lifetime of bulk heterojunction (BHJ) polymer solar cells. In this work, two fulleropyrrolidine derivatives that bear π-conjugated terthiophene (3T) and two hexyl (H) or ethylhexyl (EH) chains, abbreviated as 3T-H-C60 and 3T-EH-C60, are separately used as a compatibilizer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The effect of the loading of such an agent on the photovoltaic properties of solar devices and the morphological stability of the P3HT/PCBM blend was examined. The substitution of PCBM with a tiny amount of 3T-H-C60 or 3T-EH-C60 apparently enhances the short-circuit current density, reflecting the formation of small PCBM clusters within the P3HT matrix. More importantly, optical microscopy, transmission electron microscopy and photoluminescence measurements verify that the presence of 1 wt% 3T-H-C60 or 3 wt% 3T-EH-C60 effectively hinders the thermal motion of PCBM molecules to form micro-scale clusters, leading to an extremely stable morphology even under long-term exposure to elevated temperatures. Accordingly, the power conversion efficiencies of P3HT/PCBM:3T-H-C60 and P3HT/PCBM:3T-EH-C60 devices remain very steady during prolonged aging at 130 °C. This work provides valuable guidelines for the design of an effective compatibilizer for thermally stable polymer/fullerene BHJ solar cells. [ABSTRACT FROM AUTHOR]

A CNE (cresol-novolak epoxy) composite of CCL (copper-clad laminate), comprising glass fabrics and mCOC (metallocenebased cyclic olefin copolymer) fabrics with various laminated structures, was fabricated and its dielectricity at high frequency was examined. The dielectric constant, Dk, at 5 GHz of a conventional glass/CNE composite is 4.0, whereas that of a seven alternately layered mCOC/glass/CNE composite with an externally facing mCOC layer is 2.3. In the same manner, the former has a loss tangent, Df, of 0.035, whereas the latter has a loss tangent, Df, of 0.007. In addition, the decrease of Df with increasing mCOC content is not linear but logarithmical. The Tg (glass transition temperature) and scanning electron microscope results reveal the good compatibility of the mCOC and CNE at the interface between them. An optimal compression process, which involved a pressure of 20 kg/cm2 at 185℃ for 120 min, was followed by setting at 120℃ for 30 min, to relax the residual stress that built up inside the mCOC prepregs, with the purpose of fabricating a mCOC/glass/CNE CCL without any tilt angle. The worsening of the flame retardancy that is caused by replacing some of the nonflammable glass layers with organic mCOC layers can be overcome by blending more 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide dicyandiamide hardener into the CNE matrix. The highest flame-retardant standard, of grade UL 94 V0, can be achieved with a phosphorus content of the glass/CNE and glass/mCOC/CNE CCLs of 8000 and 12,500 ppm, respectively. Briefly, a flame-retardant mCOC/glass/CNE composite of CCL operated at high frequency is successfully produced. [ABSTRACT FROM PUBLISHER]

Tetraaniline-containing poly(urethane-urea) (TAPU), a new material, was synthesized in this study and blended with Ag nanowire (≤ 3 wt.%), denoted as TAPU/A, or graphene (≤ 3 wt.%), denoted as TAPU/G, to form a conductive elastomer. The conductivities can be improved from less than 10 S/cm, for pure PU, to 6 × 10 S/cm, for the TAPU/A 3 %. The tensile strength and modulus were increased twofold and 20- to 60-fold, respectively, for TAPU/A 3 % or TAPU/G 3 %. The viscoelastic creep was simulated effectively using a Burgers model. Additionally, TAPU/A and TAPU/G demonstrate a higher viscosity, a higher retardation time, and a lower compliance D than regular TAPU does. TAPU/Ag and TAPU/G exhibit less elasticity but more insignificant permanent deformation than TAPU does, because the additives function as a chain holder. The stretching tension induces the orientation of silver nanowire or graphene. Such orientation is believed to affect electrical conductivity positively. The solid form of the elastomer, TAPU/A or TAPU/G, can be heated and dissolved in a solvent to be reshaped, indicating that this compound is uniquely reworkable. [ABSTRACT FROM AUTHOR]

A star-shaped copolymer, poly( N-isopropylacrylamide-co-itaconamic acid (poly(NIPAAm-co-IAM)), being pH- and thermo-dual-responsive, was synthesized by atomic transfer radical polymerization (ATRP) and characterized in this work. The lower critical solution temperature (LCST) of the star copolymer increases with the molar fraction of IAM. The particle size decreases as the temperature increases but increases as the pH value increases. Transmission electron microscopy (TEM) reveals that the star-shaped copolymer has a near-spherical core-shell structure that favors drug delivery. The star copolymer can be used in drug encapsulation as well as drug release. The star copolymer has different drug release rates in environments of different pH, and thus it can carry drugs in an acidic (gastric) environment and release the drugs in a neutral or less acidic (intestinal) environment. [ABSTRACT FROM AUTHOR]

This study investigates liquid crystalline (LC) formation and lower critical solution temperature (LCST) of HPC solutions upon the addition of XG in various ratios. The LC region of HPC/HO/HPO tertiary system was significantly enlarged at low XG/HPC blending ratio of 1-10 wt%. The addition of well oriented 2-D XG molecules to HPC polymer induced easy orientation of linear HPC molecules to synergistically form a stable anisotropic phase. The LCST point of HPC solutions initially decreased with adding a little amount of XG and then increased with XG/HPC ratio of over 50/50. In HPC-rich medium, XG helices easily attracted HO molecules at high temperature owing to their hydroxyl groups. Consequently, the formation of intermolecular hydrogen bonds and the phase separation of HPC molecules proceeded at a lower temperature. In XG-rich medium, the upper critical solution temperature (UCST) behavior of XG obstructed the LCST behavior of HPC, the LCST point of HPC therefore increased and the boundary shrinkage of HPC binodal curve occurred. [ABSTRACT FROM AUTHOR]

This study investigates the difference in phase transition and rheological behavior between xanthan gum (XG)/HO/HPO (XWP) and XG/HO/HPO (XWP) tertiary systems using polarized optical microscopy, Fourier transform infrared spectroscopy, light transmission detection, and rheometry. The results show that the LC (liquid crystal) phase formation in the XWP system was more strongly suppressed than that in the XWP system because the former exhibited stronger interactions between acid and XG molecules. With respect to the transition from LC to I (isotropic) phase at high temperature, the transition time of the XWP system was found to be much shorter than that of the XWP system. The transition time, also called the relaxation time, was measured by observing the annealing time and fitted using the VFT expression. The activation energies E for this transition in XWP and XWP systems are 3.0 and 4.7 kJ/mole, respectively, indicating that the XWP system exhibits stronger intermolecular attraction and is more sensitive to variation in temperature. In the rheological tests, as the temperature of the XWP system increased from 25 to 95 °C, the viscosity in the transitional region declined consistently, while in the XWP system, the decline proceeded through three stages owing to the shifting tautomers of the HPO. In the LC region, the viscosity normally fell as the shear rate or temperature increased but increased with the heating rate or XG concentration. Most interestingly, all of the results herein demonstrated that the viscosity of the XG solution in the LC region followed a power law with an index of roughly 0.08, which was found to be independent of the type of acid, concentration of acid, and XG concentration. [ABSTRACT FROM AUTHOR]

Phase formation and transition in a xanthan gum (XG)/HO/HPO tertiary system were characterized by polarized optical microscopy, light transmission detection and rheological methods. Three distinct phases and a transition region-the completely separated (S) phase, the liquid crystalline (LC) miscible phase, the isotropically (I) miscible phase and the S plus LC region-were identified. The presence of HPO in the XG/HO system inhibited the evolution of both the S and LC phases. The S and LC phases contained less than 73 and 62 wt% of HPO, respectively. As the temperature increased over 65 °C, the LC phase in the HPO-rich and HO-poor region seriously shrunk owing to the breakup of hydrogen bonds among the XG helical structure. At the same XG loading, the viscosity of the XG solutions in LC phase was found to be much higher than that in I phase. It indicated the existence of numerous XG intermolecular interactions in the LC phase that suppress the movement of liquid. A study of the kinetics demonstrated that the shrinkage relaxation time ( τ) depended strongly on temperature and was fitted by the Volgel-Fulcher-Tammann (VFT) expression. The potential energy barrier of this liquid was quite low at approximately 3.0 kJ mol, falling in the range of hydrogen-bond disassociation. The light absorbance test in heating mode revealed a biphasic transitional region between the LC phase and I phase. The contour of this region depended on the heating rate, and this fact was explained again by the relaxation behavior of XG helices at temperatures higher than 65 °C. [ABSTRACT FROM AUTHOR]

In this study, sulfonated chitosan (SCS) with a water-soluble property was synthesized and rheologically characterized. The Maxwell Model can accurately describe a regular chitosan (CS) solution. The G′, G″ crossover shifted toward lower frequencies as the CS concentration increased, revealing an increase of relaxation time. A frequency-concentration superposition master curve of CS solution was therefore plotted and well fitted by the experiment result. However, a modified Maxwell Model, which captures the occurrence of the quasi-plateau region of G′ in the low-frequency range, representing the initially falsely connected structure between the sulfonic acid groups and the protonated ammonium groups, was proposed for the SCS solution. The crossover of G′ and G″ was found to be independent of the SCS concentration, indicating its lower molecular weight yields a high overlap concentration, Ce. The rheological properties of SCS solutions can be affected as the following factors are increased in the order of declining effect; pH level > temperature > salt concentration. [ABSTRACT FROM AUTHOR]

Abstract: The PAN/MA/DMI (poly(acrylonitrile/methyl acrylate/dimethyl itaconate)) copolymer was synthesized for being used as a carbon fiber precursor. Its high melt-spinnability at 175–210 °C has been demonstrated elsewhere but the cyclization kinetics was thoroughly investigated by DSC analysis herein. The isothermal analysis based on the Kamal equation demonstrates that at a given temperature, the cyclization rate constant k of PAN/MA/DMI system is five to seven times that of a regular PAN/MA system. The activation energy E a of the PAN/MA/DMI system, owing to the acid-catalysis by the DMI compound, is approximately 30 kJ/mol lower than that of a regular PAN/MA system. An isothermal Avrami analysis confirmed the above finding. Furthermore, based on the obtained nucleation index n, DMI may induce intermolecular cyclization which can rapidly stabilize the fiber shape of PAN/MA/DMI precursor. A nonisothermal analysis, obtained from the Ozawa's method, revealed the same tendency as did the isothermal results, but the difference between the average activation energies E a obtained with and without DMI was reduced from 30 to 25 kJ/mol. Finally, a cyclization mechanism that involves the formation of a cyclic anhydride was proposed. [Copyright &y& Elsevier]

Abstract: This work incorporated hexamethylene diamine and terephthalic acid, namely 6T, into typical polymerization processes of Nylon 6 and Nylon 66 to form Nylon 6/6T and Nylon 66/6T copolymers, respectively. The WAXD results showed that as the amount of 6T increased to 10mol%, all of the Nylon 6/6T copolymers transferred from α-form to γ-form. The DSC measurement revealed that the equilibrium melting point of Nylon 6/6T decreased as the amount of 6T increased. Moreover, the crystallization rate k decreased with the 6T content in Nylon 6/6T copolymers, and dropped greatly when the addition of 6T increased over 7mol%. In contrast, due to the similar molecular chain lengths of Nylon 66 and 6T, the WAXD results of Nylon 66/6T exhibited little crystal difference as the addition of 6T varied from 0 to 30mol%. The equilibrium melting point of Nylon 66/6T remained constant, proving that Nylon 66/6T is isomorphous. [Copyright &y& Elsevier]

In this study, a dendrimer with 19 sites was modified to form a waterborne oligomer with hydrophilic sites and polyurethane acrylate (PUA) sites. Two PU systems hexamethylene diisocyanate (HDI) and methylene-bis (4-cyclohexylisocyanate) (HMDI) were used; each of them had 5, 9, and 13 PUA sites, respectively. Experimental results revealed that the HDI system was more thermally stable than the HMDI system. The HMDI system, however, exhibited better hardness than the HDI system, even though the final curing conversion of HMDI was low. Additionally, more PUA sites of a dendrimer were associated with greater hardness of the cured resin. In a UV-curing study, simulations revealed that the autocatalysis model could describe the UV-curing mechanism of the PUA-dendrimer system. Both the reaction rate constant k and the final conversion α were highest at a concentration of the photoinitiator of approximately 3 wt% for both HDI and HMDI systems. The reaction rates of both systems were highest when the number of PUA sites was nine. The final conversion of both the systems, however, was optimal when the number of PUA sites was 13. The final conversion in the acrylic reaction increased with temperature up to 80 °C for both the systems, owing to an increase in the ratio of potentially active sites against nonactive sites, according to Arrhenius theory. The rate constant, k, however, was optimal at 60 °C because a higher temperature damaged the photoinitiator. Finally and most importantly, HMDI always had a lower rate constant k and final conversion α than HDI under similar conditions in studies that were conducted to examine the effects of photoinitiator concentration, number of PUA sites, and reaction temperature, revealing that the steric hindrance by the cyclohexane in HMDI negatively influenced its curing kinetics. [ABSTRACT FROM AUTHOR]

This study characterizes the rheological behavior of the HPC/HO/HPO tertiary system based on the 3-D phase diagram that was obtained in our earlier work. The effects of frequency, temperature, HPC concentration, liquid composition (HO/HPO ratio), and phase status on the rheological parameters were thoroughly investigated. The most useful parameter for distinguishing the isotropic (I) and liquid crystalline (LC) phases was tanδ. Agglomeration in the cloudy suspension (CS) phase at high temperature was too severe to allow a smooth flow, so the tanδ and η* represented significant damping, which is a good indicator of the presence of the CS phase. With an increase in temperature, the viscosity of the flow with a single homogeneous phase-either the I phase or the LC phase-or a combination of two homogeneous phases in sequence, obeyed the Arrhenius model. In contrast, once the temperature rose to that of the formation of heterogeneous CS phase, the Arrhenius model was no longer valid. The activation energy E of the I phase was greater, and more sensitive to the HPC concentration, than the LC phase. Finally, the concentration of the sol/gel transition (SGT) declined as temperature increased but increased as the HPO content increased. Furthermore, this tertiary system exhibited no clear order of the onsets of the formations of SGT phase, the LC phase, and the CS phase as HPC concentration was varied. [ABSTRACT FROM AUTHOR]

PCL-based biodegradable shape-memory polymers (SMPs) are limited in strength, which restricts their practical applications. In this study, a series of novel SMPs, composed of poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and poly(ε-caprolactone) (PCL), were synthesized and cross-linked using planar (benzene-1,3,5-tricarboxylic acid, BTC) or non-planar (glycerol, GC) cross-linkers via the one-pot method. The influence of different kinds of cross-linkers and hard segments of copolyesters on the thermal properties, crystallization behavior, mechanical properties, shape-memory performance, and degradability was investigated by FT-IR, 1H-NMR, DSC, DMA, TGA, XRD, tensile test, intrinsic viscosity measurement, and in vitro enzymatic degradation test. The results indicate that the tensile strength of the copolyester can be significantly improved from 27.8 to 53.2 MPa by partially replacing PET with PEN while maintaining its shape-memory characteristics. Moreover, a small amount of cross-linking modification leads to higher temperature sensitivity, improved shape recovery rate at third round (Rr(3) = 99.1%), and biodegradability in the cross-linked PET/PEN/PCL shape-memory polymers. By changing the crystallization morphology and cross-linking forms of the material, we have developed a shape-memory polymer with both high strength and a high shape recovery rate, which provides a new strategy for the development of shape-memory materials. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate/poly(ethylene glycol)/2, 6-naphthalene dicarboxylate (PET/PEG/NDC) copolymers were synthesized and characterized. The results demonstrated that T dramatically decreased-by approximately 20 °C-when 8 wt.% PEG was added to neat PET. However, T slightly increased-by around 6 °C-from the reduced value, when a third ingredient, NDC, was incorporated. The melting temperature T and fusion enthalpy △ H decreased when the 8 wt.% PEG was copolymerized. Further incorporation of NDC into the PET/8 % PEG copolymer, after a small initial increase in T and △ H for PET/8 % PEG/2.3 % NDC, caused substantially reduce in both properties for PET/8 % PEG/9.2 % NDC. A mechanical test revealed that PET/8 % PEG/NDC copolymers maintained high mechanical integrity until degradation, verifying that the inclusion of NDC enhances the weatherability of PET/PEG copolymer. The rheological Cole-Cole plots indicated the occurrence of phase separation in PET/PEG melt, but the incorporation of NDC suppressed this incompatibility. The biodegradation results indicated that the degradation comprised two stages-a period of rapid degradation, which was associated with the hydrolysis of PEG segments, and a period of slow degradation, which was caused by erosion of the short aliphatic segments by the microbes. [ABSTRACT FROM AUTHOR]

A 3-D phase diagram of the HPC/HO/HPO tertiary system against various temperatures was established. Four distinct phases-the completely separated phase (S), the cloudy suspension phase (CS), the liquid crystalline miscible phase (LC), and the isotropically miscible phase (I)-were identified. The S phase shrank as the temperature increased, revealing that the HPC solubility increased with temperature, regardless of the LCST (lower critical solution temperature) characteristic. The addition of HPO suppressed the formation of LC phase. However, as the temperature was raised sharply from 50 to 70 °C, the LC phase could only be maintained at high HPO concentration region; it was a triangular shape, and the top apex of the triangle was the temperature-invariant L* point (HPC/HO/HPO 38/9/53 wt%). The CS phase expanded considerably into the HO-rich but HPO-poor region when the temperature continued to increase over 48 °C. The LCST points of the CS phase that contained 0 and 15 wt% of HPO were 34 and 38 °C, respectively. These CS results demonstrate that HPO suppresses the occurrence of LCST behavior. Additionally, the binodal curve exhibits a weak or even zero dependence of binodal temperature on the HPC concentration at HPC concentrations of less than 30 wt% in a pure water system. A hypothesis concerning the sequential desorption of water molecules was proposed to explain such behavior. [ABSTRACT FROM AUTHOR]