Structural and thermal properties of modified poly(ethylene terephthalate)

Abstract

High-molecular-weight copolyesters based on ethylene glycol, tetraphthalic and 4,4′-biphenyl dicarboxylic acids containing up to 10.3 mole % of a second component were synthesized in the presence of homo-and heterogeneous catalysts. It was found that synthesis of these copolymers with a heterogeneous catalyst yields polymers with a higher molecular weight. The thermochemical properties of the copolyesters obtained were investigated. The thermostabilizing effect on addition of up to 10.3 mole % ethylene-4,4′-biphenyl dicarboxylic acid units to the PET polymer substrate was demonstrated. It was hypothesized that this modifier is a mesogen with respect to poly(ethylene terephthalate).The major possibility of obtaining high-strength, high-modulus industrial fibres from thermotropic polyesters was established more than half a century ago [1]. However, intensive research in this area is continuing to this day, due to the importance of creating new, effective types of reinforcing materials.The basic problem whose solution will determine the possibility of practically implementing these technologies consists of developing methods of synthesizing fibre-forming copolyesters containing mesogenic units. Such polymers must pass into the viscous-flow state with formation of temperature and time stable melts and be characterized by lower (in comparison to the corresponding homopolyesters) mechanical glass transition temperatures (t mg ).p-Hydroxybenzoic, 2-hydroxy-6-naphthoic, and 2,6-naphthalene dicarboxylic acids were used as the mesogen for obtaining thermotropic homo-and copolyesters, and derivatives of hydroquinone, 2,6-dihydroxynaphthalene, and other products were used as diols [2]. High-temperature equilibrium polycondensation of aromatic dicarboxylic acids and diols, hydroxycarboxylic acids, etc., in inert medium at 300-350°C is the basic method of obtaining fibre-forming thermotropic polyesters [3].Incorporation of mesogenic units in the poly(ethylene terephthalate) (PET) macromolecule gives melts of fibre-forming polymers thermotropic properties and causes the appearance of a mesophase in the spun fibre, which makes it possible to attain high orientation draw ratios and consequently to increase the initial modulus, strength, and fatigue characteristics of the fibre. A similar processing effect can be attained in spinning fibres from melts of a mixture of PET/poly(ethylene-2,6-naphthalate)/poly(p-hydroxybenzoate) in the ratio of 22.5/67.5/10.0 [4].The information on the possibility of using dihydroxy-and dicarboxyl-containing biphenyls as mesogens is episodic in nature. Moreover, the use of these compounds as PET modifiers is of great interest for production of high-strength, highmodulus, industrial polyester fibres. As a result of the studies in [5, 6], a method of obtaining 4,4-biphenyl dicarboxylic acid (BPDA) from by-products of synthesis of terephthalic acid dimethyl ester (DMT) was proposed. We investigated the effect of catalysts of polycondensation based on antimony -Sb(III) -compounds on the physicochemical pr...

Characterization and thermal‐oxidative degradation behavior of poly(ethylene terephthalate‐co‐4,4′‐bibenzoate) prepared via direct esterification technique

“…As listed in Table 5, the values of apparent activation energies of PETBBs are higher than that of PET at each heating rate, and the apparent activation energies of PETBBs keep steady increasing with rising of BPDA unit, suggesting that the incorporation of BPDA unit to PET chain improved thermal‐oxidative stability and restrained thermal‐oxidative decomposition of PET chain. Similar result was also proved by Alekseeva et al, and they hypothesized that BPDA units in PETBB are present in a mesogen with respect to PET [20].…”