Dimethylammonium dimethyldithiocarbamate‐accelerated sulfur vulcanization. II. Vulcanization of rubbers and model compound 2,3‐dimethyl‐2‐butene

Rubber and model compound 2,3‐dimethyl‐2‐butene were vulcanized for various times with dimethylammonium dimethyldithiocarbamate [(dma)dmtc]‐accelerated sulfur formulations in the absence of ZnO. Model compound systems were analyzed by HPLC, and no reaction intermediates containing pendent groups were found. Crosslinked sulfides, characterized by ¹H‐NMR, were found to be essentially bis(alkenyl). Residual curatives were extracted from rubber compounds vulcanized for various times and analyzed by HPLC. Compounds, cured to various crosslink densities, were found to crystallize readily in a density column at subambient temperatures. This supports evidence from model compound systems that pendent groups are largely absent from vulcanizates. It is suggested that a reaction mechanism, similar to that applicable to zinc dimethyldithiocarbamate‐accelerated sulfur vulcanization, may be applicable with (dma)dmtc accelerated formulations. Very limited crosslinking occurred on heating compounds under vacuum, and this can be attributed largely to the rapid loss of (dma)dmtc from rubber at elevated temperatures. However, the slower rate of crystallization on cooling of the gels, compared to the rate in press‐cured vulcanizates of similar crosslink density, was interpreted as evidence that some pendent groups did form during heating with (dma)dmtc/sulfur. Crosslinking of such pendent groups may be inhibited by the loss of (dma)dmtc, that, like zinc dimethyldithiocarbamate, may catalyze their crosslinking, and/or to the loss under vacuum of dimethyldithiocarbamic acid that would form thiol pendent groups that would rapidly crosslink with thiuram pendent groups. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3074–3083, 2001     

Thermal stability of modified end‐capped poly(lactic acid)

The influence of functional end groups on the thermal stability of poly(lactic acid) (PLA) in nitrogen‐ and oxygen‐enriched atmospheres has been investigated in this article using differential scanning calorimetry, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Functional end groups of PLA were modified by succinic anhydride and l ‐cysteine by the addition–elimination reaction. PLA was synthesized by azeotropic condensation of l ‐lactic acid in xylene and characterized by nuclear magnetic resonance. The values of the activation energies determined by TGA in nitrogen and oxygen atmospheres revealed that the character of functional end groups has remarkable influence on the thermal stability of PLA. Moreover, DMA confirmed the strong influence of functional end groups of PLA on polymer chains motion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41105.     

Kinetics of sulfur vulcanization of 1,4‐cis‐polyisoprene by differential scanning calorimetry

The vulcanization of 1,4‐cis‐polyisoprene was studied by differential scanning calorimetry under isothermal and nonisothermal conditions. On the basis of thermal characteristics obtained, the kinetic parameters of crosslinking (the induction period, maximum rate, and effective energy of activation) were determined. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 754–757, 2007     

Effect of carboxylic acids on 2‐bisbenzothiazole‐2,2′‐disulfide‐ and tetramethylthiuram disulfide‐accelerated sulfur vulcanization. II. Vulcanization of polyisoprene in the absence of ZnO

Polyisoprene was vulcanized by 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur and tetramethylthiuram disulfide (TMTD)/sulfur in the absence and presence of benzoic and stearic acids. It was found that the crosslink density of MBTS vulcanizates is halved by the addition of carboxylic acids and this can be explained in terms of the attack of the acids on the accelerator polysulfides. TMTD polysulfides are more reactive toward polyisoprene than are MBTS polysulfides, and their addition to the polymer chain occurs before significant attack by the carboxylic acids can reduce the polysulfide concentration. Consequently, the acids have little effect on the crosslink density of TMTD vulcanizates. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1007–1012, 1999     

Thermal properties of low loss PTFE‐CeO2 dielectric ceramic composites for microwave substrate applications

Polytetrafluroethylene (PTFE) composites filled with CeO₂ were prepared by powder processing technique. The PTFE is used as the matrix and the loading fraction of CeO₂ in the composite varied up to 0.6 volume fraction. The thermal conductivity and coefficient of thermal expansion were studied in relation to filler concentration. The thermal conductivity increased and coefficient of thermal expansion decreased with increase in CeO₂ content. For 0.6 volume fraction loading of the ceramic, the composite has a thermal conductivity of 3.1 W/m°C and coefficient of thermal expansion 19.6 ppm/°C. Different theoretical approaches have been employed to predict the effective thermal conductivity and coefficient of thermal expansion of composite systems and the results were compared with the experimental data. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide on liquid oxygen compatibility of bisphenol a epoxy resin

In this study, bisphenol A epoxy resin (DGEBA) was chemically modified by 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), and the molecular structure of the modified epoxy resin was characterized by Fourier transform infrared spectra. The effects of DOPO on liquid oxygen compatibility of DGEBA were calculated using mechanical impact method. The results indicated that epoxy resin (EP‐P1)/4,4‐diaminobisphenol sulfone (DDS) was compatible with liquid oxygen. When compared with EP/DDS, differential scanning calorimetry and thermogravimetry analyses showed that EP‐P1/DDS and EP‐P2/DDS had much higher glass transition temperatures and char yield. X‐ray photoelectron spectroscopic analysis suggested that phosphorus atoms on the surface of EP‐P1/DDS and EP‐P2/DDS could act in the solid phase to restrain the incompatible reaction, which was in accordance with the flame‐retardant mechanism of phosphorus‐containing compounds. The compatibility mechanism of EP‐P1/DDS was further proposed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40848.     

A study of dynamic vulcanization for polyamide‐12 and chlorobutyl rubber

Polyamide‐12 and chlorobutyl rubber were blended by dynamic vulcanization in a high shear environment using curing systems based on sulfur, dithiocarbamate/ZnO, and 4,4‐methylenebiscyclohexylamine/MgO. As expected, all blends with curing agents show increased tensile strength and elongation at break in comparison to blends without curing agents. Maximum mechanical properties are obtained at relatively low levels of curing agent in all systems. Hexane extraction of the mixtures and measurement of percentage of insolubles along with the swelling index of the rubber phase confirm that a high level of cure is achieved at low levels of curing agent. Although the curatives are designed for the rubber phase, differential scanning calorimetry results indicate that both phases are affected during the dynamic vulcanization process, with polyamide‐12 showing a reduced melting temperature that is indicative of molecular weight reduction, structure changes, or reaction with the rubber phase. Scanning electron microscopy results indicate that phase size is reduced with increased blending time and level of curing agent. Rheological studies indicate that blends containing curing agents exhibit non‐Newtonian behavior to a greater extent than polyamide or nonvulcanized polyamide/chlorobutyl rubber blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 871–880, 2003     

Analysis of thermal properties of polymeric biomaterials. I. Ultrahigh-molecular-weight polyethylene

The effects of sample size and heating and cooling rates on thermal transitions of ultrahigh-molecular-weight polyethylene (UHMWPE) were investigated. The thermal parameters were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). While heating rates and sample size had strong effects on thermal properties, the influences of cooling rates were minor. For DSC, broad melting transitions were obtained at faster heating and/or slower cooling rates and larger sample sizes. Higher melting temperatures were obtained when heating rates and sample size were increased. Slower cooling rates also produced higher melting and crystallization temperatures. Faster cooling rates yielded lower heats of fusion during melting and also lower heats of crystallization. The dependence of peak melting and crystallization temperatures on the heating and cooling rates are illustrated by two empirical formulas. For TGA, it is found that faster heating rates and larger sample sizes produced higher decomposition temperatures. This detailed analysis may explain the large variations in the reported data on thermal properties and crystallinity of UHMWPE and provide solutions to the current clinical problems associated with polymeric biomaterials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1353–1361, 1998     

Thermal properties of proton-conducting radiation-grafted membranes

Proton-exchange membranes are required to exhibit chemical, mechanical, and thermal stability for fuel cell applications. The present investigation has been carried out to explore the thermal behavior of poly(ethylene-alt-tetrafluoroethylene) (ETFE)-based proton-conducting membranes, both uncrosslinked and crosslinked, prepared by radiation grafting and subsequent sulfonation. The influence of preparation steps (irradiation, grafting, sulfonation, crosslinking) on the thermal degradation, crystallinity, and melting behavior of membranes with varying degree of grafting was examined. ETFE base film and grafted films were studied as the reference materials. Furthermore, poly(tetrafluoroethylene-co-hexafluoropropylene)-based grafted films and membranes were investigated as well for comparison. Membrane preparation steps, degree of grafting, crosslinking, type of base polymer have considerable influence on the thermal properties of membranes. The crystallinity of the films decreases slightly by grafting, while a significant decrease was observed after sulfonation. For instance, crystallinity decreased from 37% (pristine ETFE) to 36% (uncrosslinked grafted film) and 23% (uncrosslinked ETFE-based membrane). On the other hand, the melting temperature of the base polymer was almost unaffected by irradiation and grafting. The crosslinked ETFE-based membranes exhibit a slightly higher melting temperature (262.5°C) than their corresponding grafted films (261.3°C) and the base film (260.6°C). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization of vulcanizates. I. Low‐temperature crystallization as a function of extent of cure for polyisoprene vulcanized with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide/sulfur

The crystallization of polyisoprene, vulcanized to various degrees of cure with tetramethylthiuram disulfide/sulfur and 2‐bisbenzothiazole‐2,2′‐disulfide (MBTS)/sulfur formulations, was studied in a density column at ?25°C. The densities of vulcanizates before crystallization decrease progressively with cure time, which is ascribed to an increase in free volume occasioned by the formation of accelerator‐terminated pendent groups on the polymer chain. The induction period before the onset of crystallization increases and both the rate of and the degree of crystallization decrease with extent of cure. This is attributed primarily to the presence of residual pendent groups on the polymer chain and secondly to crosslink formation. The changes are more marked with MBTS formulations where pendent groups are more bulky. MBTS compounds fail to crystallize once vulcanized to the point where a gel has formed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2565–2572, 2001     

Improvements in the thermal conductivity and mechanical properties of phase‐change microcapsules with oxygen‐plasma‐modified multiwalled carbon nanotubes

The thermal properties and mechanical properties are the key factors of phase‐change microcapsules (microPCMs) in energy‐storage applications. In this study, microPCMs based on an n‐octadecane (C18) core and a melamine–urea–formaldehyde (MUF) shell supplemented with O₂‐plasma‐modified multiwalled carbon nanotubes (CNTs) were synthesized through in situ polymerization. Meanwhile, two different addition methods, the addition of modified CNTs into the emulsion system or into the polymer system, were compared and examined. Scanning electron microscopy micrographs showed that the microPCMs were spherical and had a broadened size distribution. Fourier transform infrared testing demonstrated that the modified CNTs did not affect C18 coated by MUF resin. The results indicate that the thermal conductivity and mechanical properties of the microPCMs were remarkably improved by the addition of a moderate amount of modified CNTs, but the heat enthalpy and encapsulated efficiency decreased slightly. Moreover, the thermal conductivity and mechanical properties of microPCMs modified with CNTs directly added to the polymer system were superior to those with CNTs added to emulsion system. In particular, when 0.2 g of modified CNTs were added to the polymer system, the thermal conductivity of the microPCMs was improved by 225%, and the breakage rates of the microPCMs at 4000 rpm for 5, 10, and 20 min decreased by 74, 72, and 60%, respectively, compared with that of the microPCMs without modified CNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45269.     

Thermal properties of extruded/injection‐molded poly(lactic acid) and biobased composites

To determine the degree of compatibility between poly(lactic acid) and different biomaterials (fibers), poly(lactic acid) was compounded with sugar beet pulp and apple fibers. The fibers were added in 85 : 15 and 70 : 30 poly(lactic acid)/fiber ratios. The composites were blended by extrusion followed by injection molding. Differential scanning calorimetry and thermogravimetric analysis were used to analyze the extruded and extruded/injection‐molded composites. After melting in sealed differential scanning calorimetry pans, the composites were cooled through immersion in liquid nitrogen and aged (stored) at room temperature for 0, 7, 15, and 30 days. After storage, the samples were heated from 25 to 180°C at 10°C/min. The neat poly(lactic acid) showed a glass‐transition transition at 59°C with a change in heat capacity (ΔC_p) value of 0.464. The glass transition was followed by crystallization and melting transitions. The enthalpic relaxation of the poly(lactic acid) and composites steadily increased as a function of the storage time. Although the presence of fibers had little effect on the enthalpic relaxation, injection molding reduced the enthalpic relaxation. The crystallinity percentage of the unprocessed neat poly(lactic acid) dropped by 95% after extrusion and by 80% for the extruded/injection‐molded composites. The degradation was performed in air and nitrogen environments. The degradation activation energy of neat poly(lactic acid) exhibited a significant drop in the nitrogen environment, although it increased in air. This meant that the poly(lactic acid) was more resistant to degradation in the presence of oxygen. Overall, injection molding appeared to reduce the activation energy for all the composites. Sugar beet pulp significantly reduced the activation energy in a nitrogen environment. In an air environment, both sugar beet pulp and apple fibers increased the activation energy. The enzymatic degradation of the composites showed a higher degradation rate for the extruded samples versus the extruded/injection‐molded composites, whereas the apple composites exhibited higher weight loss. The thermogravimetric analysis data showed that the degradation of unprocessed and extruded neat poly(lactic acid) followed a one‐step mechanism, whereas extruded/injection‐molded composites showed two‐step degradation. A higher fiber content resulted in up to three‐step degradation mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

The thermal properties of a carbon nanotube‐enriched epoxy: Thermal conductivity,curing, and degradation kinetics

Multiwalled carbon nanotube‐enriched epoxy polymers were prepared by solvent evaporation based on a commercially available epoxy system and functionalized multiwalled carbon nanotubes (COOH–MWCNTs). Three weight ratio configurations (0.05, 0.5, and 1.0 wt %) of COOH–MWCNTs were considered and compared with neat epoxy and ethanol‐treated epoxy to investigate the effects of nano enrichment and processing. Here, the thermal properties of the epoxy polymers, including curing kinetics, thermal conductivity, and degradation kinetics were studied. Introducing the MWCNTs increased the curing activation energy as revealed by differential scanning calorimetry. The final thermal conductivity of the 0.5 and 1.0 wt % MWCNT‐enriched epoxy samples measured by laser flash technique increased by up to 15% compared with the neat material. The activation energy of the degradation process, investigated by thermogravimetric analysis, was found to increase with increasing CNT content, suggesting that the addition of MWCNTs improved the thermal stability of the epoxy polymers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2722–2733, 2013     

Synthesis,characterization, and performance evaluation of the AM/AMPS/DMDAAC/SSS quadripolymer as a fluid loss additive for water‐based drilling fluid

According to the molecular structure design requirements of the fluid loss additive resistant to high temperature, 2‐acrylamide‐2‐methyl propane sulfonic acid (AMPS), acrylamide (AM), dimethyl diallyl ammonium chloride (DMDAAC) and sodium styrene sulfonate (SSS) are selected as the structure monomers. Using ammonium persulfate as initiator, a new quadripolymer is synthesized through free radical aqueous solution polymerization. According to the minimum filtration loss of the fresh water‐based drilling fluid with 0.5 wt % quadripolymer, The synthesis conditions are optimized by orthogonal test: the mole ratio of AMPS/AM/DMDAAC/SSS is 5/7/2/1, the monomer concentration is 30 wt %, the initiator concentration is 0.8 wt %, the reaction temperature is 75°C and the pH is 10. The structure of the quadripolymer is characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance hydrogen spectroscopy. The results show that the quadripolymer contains all the designed functional groups. The thermal stability of the quadripolymer is tested by thermogravimetry, differential thermogravimetry, and differential scanning calorimetry. The results show that the thermal degradation of the quadripolymer is not obvious before 272.3°C. The rheological performance and filtration loss of the quadripolymer are evaluated. The results indicate that the filtration loss decreases with the increasing dosage of the quadripolymer before and after thermal aging test at 180°C for 16 h, and the filtration loss before the thermal aging test is smaller than that after the thermal aging test. The high temperature high pressure filtration loss (FL_(HTHP)) experiment results also show that the quadripolymer fluid loss additive has excellent temperature‐resistant performance. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41762.     

Studies on crosslinking and thermal behavior of phthalonitrile end‐capped imide monomer in presence of aromatic amines

This paper describes the synthesis and characterization of a bisphthalonitrile monomer having an imide linkage prepared by reacting 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride with 4‐(4‐aminophenoxy) phthalonitrile. The structure of the monomer was confirmed by Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The curing behavior of bisphthalonitrile monomer was investigated in the absence or presence of different diamines using differential scanning calorimetry. Diamines 4,4′‐diaminodiphenyl ether (DDE) and 4,4′‐diaminodiphenylsulfone (DDS) were used to investigate the effect of the structure of diamines on the curing behavior of bisphthalonitrile monomer. An exothermic transition due to curing was observed in the DSC scan, and the curing temperature was found to be dependent on the nucleophilicity of the amine. DDE was found to be more reactive than DDS. The thermal stability of the cured resins was evaluated using thermogravimetry in nitrogen atmosphere. All of the cured samples were stable up to 400 °C and leave behind 62% char residue at 800 °C, which was found to be dependent on the structure of the diamine used for curing as well as on the curing conditions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46151.     

Heterocyclic‐based epoxy‐terminated structural adhesive. II. Curing,adhesive strength,and thermal stability

We studied the curing behavior of heterocyclic‐based epoxy‐terminated resins using diaminodiphenyl ether, diaminodiphenyl sulfone, benzophenone tetracarboxylicdianhydride, and the commercial hardener of Ciba‐Geigy's two‐pack Araldite as curing agents. The adhesive strength of the adhesives was measured by various ASTM methods such as lap‐shear, peel, and cohesive tests on metal–metal, wood–wood, and wood–metal interfaces. All of these results were compared with those of an epoxy resin prepared from bisphenol‐A and epichlorohydrin resin with an epoxy equivalent value of 0.519. The thermal stability of both the virgin resin and its cured form was also studied by thermogravimetric analysis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3520–3526, 2002     

Preparation and characterization of low molecular weight silk fibroin by high‐temperature and high‐pressure method

A low molecular weight silk fibroin powder (LMSF) was prepared through high temperature (200°C) and high pressure (20 kgf/cm²), without any addition of chemicals. The carbonized adducts produced during this process were then removed by treatment with activated charcoal. The yield of LMSF by this preparation method was over 60% after the removal of carbonized adducts by using activated charcoal. Amino acid analysis showed an observable decrease in contents of serine and tyrosine in LMSF prepared by this method, as compared to those prepared by neutral salt. The molecular weight of this LMSF was also observably decreased with an increase in the reaction time. From the measurements of differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA), thermal properties of LMSF through high temperature and high pressure were also decreased as compared to those produced by neutral salts. In addition, wide‐angle X‐ray diffraction (WAXD) patterns showed that the crystallinity of LMSF differed from that of the original silk fibroin. It can be said that the preparation method of LMSF in this study is a simple, economical, and environmentally compatible process with many advantages. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2890–2895, 2002     

Phosphorus‐containing epoxy resins: Thermal characterization

Three novel aromatic phosphorylated diamines, i.e., bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl} pyromellitamic acid (AP), 4,4′‐oxo bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AB) and 4,4′‐hexafluoroisopropylidene‐bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AF) were synthesized and characterized. These amines were prepared by solution condensation reaction of bis(3‐aminophenyl)methyl phosphine oxide (BAP) with 1,2,4,5‐benzenetetracarboxylic acid anhydride (P)/3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride (B)/4,4′‐(hexafluoroisopropylidene)diphthalic acid anhydride (F), respectively. The structural characterization of amines was done by elemental analysis, DSC, TGA, ¹H‐NMR, ¹³C‐NMR and FTIR. Amine equivalent weight was determined by the acetylation method. Curing of DGEBA in the presence of phosphorylated amines was studied by DSC and curing exotherm was in the temperature range of 195–267°C, whereas with conventional amine 4,4′‐diamino diphenyl sulphone (D) a broad exotherm in temperature range of 180–310°C was observed. Curing of DGEBA with a mixture of phosphorylated amines and D, resulted in a decrease in characteristic curing temperatures. The effect of phosphorus content on the char residue and thermal stability of epoxy resin cured isothermally in the presence of these amines was evaluated in nitrogen atmosphere. Char residue increased significantly with an increase in the phosphorus content of epoxy network. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2235–2242, 2002     

Comparison and evaluation of the thermooxidative stability of medical natural rubber latex products prepared with a sulfur vulcanization system and a peroxide vulcanization system

This article deals with our study of the thermooxidative degradation of medical natural rubber latex tubes prepared with sulfur‐prevulcanized latex (sample I) and peroxide‐prevulcanized latex (sample II) in a dynamic air atmosphere by the use of the thermogravimetry/differential thermogravimetry method as well as the evaluation of the thermooxidative stability of these two samples. The test results showed that an oxygen‐absorption mass‐gain process occurred after a slight mass loss; the mass‐gain rate decreased with an increase in the temperature rising rate (β), and this was more prominent in sample II than in sample I. The maximum mass‐gain rate of sample II was 1.43% when β was 5°C/min, which was 5.02 times that of sample I; the thermooxidative stability of sample II was also lower than that of sample I. Because the oxygen absorption of sample II clearly caused serious oxidation, the balanced initial temperature, the temperature of the balanced degradation peak, and the balanced final temperature of sample II in the first reaction stage were obviously lower than those of sample I. The apparent activation energy (E_o = 143.6 kJ/mol) of sample I was significantly higher than that of sample II, and the stability of sample I was also higher than that of sample II. The temperature of the balanced degradation peak of sample II in the second reaction stage was higher than that of sample I, and E_o (154.0 kJ/mol) of sample II was significantly higher than that of sample I; the stability of sample II was also higher. Thermogravimetry curves of the two samples at various β values intercrossed each other, and the temperature at the crosspoint and the degradation rate increased linearly as β increased. On the temperature segment from the initial temperature to the crosspoint, the degradation rate of sample II was higher than that of sample I when the temperature of the two samples was the same, but on the segment from the crosspoint to the final temperature, the degradation rate of sample II was lower than that of sample I when the temperature of the two samples was the same. The degradation rate of the samples at 600°C was 99.2–99.5%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 591–597, 2005     

Study on co[poly(butylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester. II. Thermal behavior and crystalline morphology

The POB/PBT copolyesters, designated B28, B46, B64, and B82, were prepared from p‐acetoxybenzoic acid (PAB) and poly(butylene terephthalate) (PBT). The polymeric products obtained were then ground and subjected to solid‐state polymerization under vaccum for 4 h. The melting and crystallization behaviors of these copolyesters haven been studied by differential scanning calorimetry (DSC). In the DSC scan of the POB‐rich composition, the endothermic peak shows obscurely, and enthalpy of fussion becomes small due to the change in the crystalline morphology from isotropic to anisotropic. In general, the melting point of the copolyester is increased by the solid‐state polymerization reaction. Also, thermogravimetric analysis (TGA) were performed with these samples obtained. It was found that the decomposition temperature (T_d ) is increased as the POB content is increased. Effects of composition and solid‐state polymerization on the decomposition temperature of copolyesters are also discussed. The crystalline morphology of copolyester was investigated with a Zeiss polarized optical microscope. It was found that the POB/PBT copolyesters with 60 mol % POB was shown to be highly anisotropic. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2363–2368, 2000