High molecular weight copolyesters were prepared by the acidolysis of poly(ethylene terephthalate) with p-acetoxybenzoic acid and polycondensation through the acetate and carboxyl groups. The mechanical properties of the injection-molded copolyesters containing 40–90 mole- % p-hydroxybenzoic acid (PHB) were highly anisotropic and dependent upon the PHB content, polyester molecular weight, injection-molding temperature, and specimen thickness. As the injection-molding temperature increased and the specimen thickness decreased, the tensile strength, stiffness, and Izod impact strength increased when measured along the direction of flow of the polymer melt, and the coefficient of thermal expansion was zero. In some compositions these properties were superior to those of commercial glass fiber reinforced polyesters. Maximum tensile strengths, flexural moduli, notched Izod impact strengths, and minimum melt viscosities were obtained with polyesters containing 60–70 mole-% PHB. Higher oxygen indicies (39-40) and heat deflection temperatures (150-220°C) were obtained with 80–90 mole-% PHB. 相似文献
Polyanhydrides composed of the following diacids–sebacic acid, bis(p-carboxyphenoxy)propane, bis(p-carboxyphenoxy)hexane, isophthalic acid, 1,4-phenylene dipropionic acid, and dodecanedioic acid–were synthesized by a melt polycondensation process. Polymers of molecular weight up to 137,010 (weight average) and intrinsic viscosity of 0.92 dL/g were achieved. These high molecular weight polymers were reached by using pure isolated mixed anhydrides of diacids and acetic acid, under optimized reaction conditions (temperature of 180°C for 90 min under vacuum of 10-4 mm Hg). Polymers of higher molecular weights were synthesized in shorter times by using heterogenic coordination catalysts: cadmium acetate, ZnEt2-H2O (1:1), barium oxide, calcium oxide, and calcium carbonate. By using these catalysts molecular weights of up to 245,000 were reached in 30 min of reaction. Films made of high molecular weight bis(p-carboxyphenoxy)propane–sebacic acid copolymers showed tensile strengths of 40–160 kg/cm2; the strength increased as a function of the bis(p-carboxyphenoxy)propane content and molecular weight. 相似文献
The flow behavior and the effect of the spinning conditions on the fiber properties and structure of poly(ethylene terephthalate) modified with 60 mol% p-hydroxybenzoic acid (PET/60PHB) were investigated. PET and its copolyesters with 28 and 80 mol% PHB were used as control samples. The melt of PET/60PHB at temperatures above 265°C exhibited extremely low viscosity and low flow activation energy. High birefringence, indicating the presence of a mesophase, was observed between 265 and 300°C on a hot-stage polarizing light microscope. The maximum tensile strength and initial modulus, 438 MPa and 37 GPa, respectively, were obtained at 275°C for a 0.69 IV polymer. The fiber strength and modulus were significantly lowered when extrusion was conducted at temperatures below 265°C. The fiber properties could also be improved when a high extrusion rate and/or a high draw down ratio was used. Scanning electron microscopy revealed that the fibers spun at temperatures above 265°C had a well-developed, highly oriented fibrillar structure. The fibers spun at lower temperatures, however, were poorly oriented and nonfibrillar in character. The high orientation and superior mechanical performance achieved at high temperatures were attributed to the presence of the nematic mesophase in the polymer melt. 相似文献
The crystal-nematic phase transition of a copolyester consisting of 20 mol% poly(ethylene terephthalate) and 80 mol% p-hydroxybenzoic acid (PHB) was characterized by depression of the crystal-nematic transition by the addition of a liquid crystal diluent. This copolyester contains blocks of crystalline PHB. Its transition behavior was compared with thatrandom copolyester with diluent of the same composition. From the extrapolated transition temperature depression data, the heat of transition per mole of p-oxybenzoate was calculated as about 1.3 kcal/mol, with an entropy of about 2 cal/deg mol. This assumes that only the p-oxybenzoate unit crystallized from the nematic state. The validity of the Flory-Huggins model for this transition point depression was confirmed graphically by comparison with two different thermotropic-liquid crystal polyesters. These results may represent the first reported crystal-nematic temperatures and heats generated by the dilution method for liquid crystal copolyesters of this type. 相似文献
Summary: Liquid‐nitrogen quenching was applied to study the enthalpy effect on the stress‐induced crystallization of microbial polyesters. Crystallization bands of poly(3‐hydroxybutyrate) exhibited the potential to reveal the stress distribution in the melt; while crystallization of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] gave shish‐kebab structures. Polarized‐light micrographs confirmed that the enhanced nucleation was attributed to the tensile stress. Furthermore, control of the quenching direction provides a method to direct the lamellar growth.
Polarized‐light micrographs of PHB film crystallized at 90 °C after quenching in liquid nitrogen from the melt. The normal of the bands, namely the lamellar growth direction, runs predominantly parallel to the stress direction. 相似文献
ABSTRACTIn this study, aromatic–aliphatic thermotropic copolyesters derived from p-hydroxybenzoic acid, p-hydroxycinnamic acid (HCA), terephthalic acid and polyethylene glycol (PEG) with different molecular weight (200, 400, 600) were directly synthesised via Vilsmeier adduct solution polymerisation method. The structure, thermal behaviour, liquid crystal property, hydrophylicity and photoactivity were investigated by Fourier transform infrared and nuclear magnetic resonance spectroscopy, differential scanning calorimeter, polarised optical microscopy, water contact angle measurement and ultraviolet (UV) spectrophotometer. The PEG incorporation ratio is 0.540–0.691 related to the HCA units, because of its low reactivity. And, the copolyesters have relatively low melting temperatures (96–107°C) and good hydrophylicity (water contact angle value 61.2–75.3°) as compared with wholly aromatic thermotropic copolyester. All of the copolyesters exhibited nematic liquid crystal behaviour and the stable mesophase temperature range was more than 60°C after being melted. The resulted copolyesters had enough thermal stability for melt processing without any degradation. The UV absorption intensities decreased with increased irradiation time, indicating that photocrosslinking occurred. 相似文献
Random copolyesters of different compositions were synthesized by melt polycondensation of poly(ethylene terephthalate) and 3-bromo - and 3,5-dibromo-p-hydroxybenzoic acids. The copolymer compositions were determined by proton nuclear magnetic resonance spectroscopy. The thermal behavior of these copolyesters was investigated by differential scanning calorimetry. The glass transition temperature, crystallization temperature, and decomposition temperature were found to increase with increase in the paraoxybenzoate content of the copolyesters. The limiting viscosity number and the weight-average molecular weight were determined. 相似文献
Abstract Network copolyesters were made from adipic acid and ethylene glycol with 10–40 mol% trimesic acid (Y). Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and postpolymerized at 260°C for various times to form a network. The degree of reaction (DR), estimated from the infrared absorbance of hydroxyl and methylene groups, increased with increasing postpolymerization time and leveled out at about 90% after 4–6 hours. Heat distortion temperatures (Th) measured by thermomechanical analysis increased greatly from ?83 to 48°C upon the incorporation of Y. Wide-angle x-ray diffraction patterns showed that the copolymer films are amorphous. Density, tensile strength, and Young's modulus decreased for the copolymers with 10–30 mol% Y, whereas they increased drastically for the copolymer with 40 mol% Y. The enzymatic degradation was estimated by the weight loss of the copolymer films in buffer solutions with a lipase at 37°C. The weight loss decreased remarkably with increasing Y and showed no weight loss for the copolymer with 40 mol% Y. On the other hand, the weight loss by alkali hydrolysis increased for the copolymers with 10 and 20 mol% Y, implying a difference in the degradation mechanism between enzymatic degradation and alkali hydrolysis. 相似文献
There is a need for high-performance applications for terephthalic acid (TPA) polyesters with high heat resistance, impact toughness, and optical clarity. Bisphenol A (BPA) based polycarbonates and polyarylates have such properties, but BPA is an endocrine disruptor. Therefore, new TPA polyesters that are less hazardous to health and the environment are becoming popular. Tetramethylcyclobutanediol (TMCD) is a difunctional monomer that can be polymerized with TPA and other diols to yield copolyesters with superior properties to conventional TPA polyesters. It has a cyclobutyl ring that makes it more rigid than cyclohexanedimethanol (CHDM) and EG. Thus, TMCD containing TPA copolyesters can have high heat resistance and impact strength. TPA can be made from abundantly available upcycled polyethylene terephthalate (PET). Therefore, this review discusses the synthesis of monomers and copolyesters, the impact of diol composition on material properties, molecular weight, effects of photodegradation, health safety, and substitution of cyclobutane diols for future polyesters. 相似文献