Poly p-hydroxybenzoic acid

The old commercial synthesis starts with the dimethyl ester because of the insolubility and high melting point of terephthalic acid. Direct condensation with the acid presents difficulties because of the high temperatures necessary and the sublimation which then occurs. The dimethyl ester is transesterified in a first stage with excess glycol at 200°C, with acetates of alkaline earth metals as transesterifying catalysts, whereby the methanol is removed and an oligomeric polyester is formed  

Polyester is mainly melt-spun into fibers. A smaller quantity is used for very thin films for the electrical industry. Higher molecular weight poly(ethylene terephthalate) with added nucleating agents (salts of carboxylic acids) can also be used as thermoplastic synthetics. A definite disadvantage of polyester fiber is that it yellows in light. The mechanism for this process 

Poly(ethylene terephthalate) (PETP) produces a relatively hydrophobic fiber that is readily soiled by oil. The soiling tendency can be eliminated by grafting 0.5 % of acrylic acid onto the fiber with the aid of ionized gases or by partial hydrolysis of the surface (whereby free —COOH groups are produced). Incorporation of 5 % adipic acid into the polymer reduces the crystallinity and thereby improves the dyeability. Incorporation of small amounts of sulfonated terephthalic acid produces anionic sites for cationic dyestuffs. 

Tape recorder ribbons are produced from PETP (previously, these tapes or ribbons were produced from PVC, cellulose diacetate, or cellulose triacetate). The tapes are coated with magnetic oxides, which are embedded 

Construction components of poly(ethylene terephthalate) absorb practically no moisture. These components are hard and rigid, exhibit very little wear and tear, show very little creep, and tolerate high mechanical loads. These physical properties, together with the very small linear coefficient of expansion, make PETP ideal for high precision cog wheels and for moving components in, for example, sewing machines. 

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For example, the structure of poly p-hydroxybenzoic acid (PHBA) at high temperature was recently found to be in a disordered state with two molecules at each lattice point and with an occupancy of 0.5 [7/9]. At higher temperatures the... 

The AAP approach, with some variations, has recently been applied with varying degrees of success to the prediction of several other structures including, in order of increasing molecular complexity, high pressure solid phases of benzene [73], the three polymorphs of sulfanilamide [74], and the low and high temperature phases of poly(p-hydroxybenzoic acid) [75]. 

Among the commonly used monomer units are hydroxybenzoic acid,p-tereph-thalic acid, 2-6-naphthalene dicarboxylic acid, 2-hydroxy-6-naphthoic add, and 4,4 -biphenol. Thus, polymers can be prepared from simply one unit, as with poly(p-hydroxybenzoic acid) ... 

Figure 3. Monomers and polymer structures of the unsubstituted para-linked aromatic polyesters, poly-(p-phenylene terephthalate) [poly(TA/HQ)] and poly-(p-hydroxybenzoic acid) [poly(HBA)].

Monomers with phenyl substituents based on 4,4 -dihydroxybiphenyl, 4-hy-droxy-4 -carboxybiphenyl, and 2,6 functionalized naphthalene have been synthesized and incorporated in various LC copolyester systems. Bhowmik et al. used 3-phenyl-4,4 -dihydroxybiphenyl and 3,3 -dihydroxybiphenyl as comonomers to modify, for example, poly-(p-hydroxybenzoic acid) and poly-(6-hydroxy-2-naphthoic ac-... 

Figure 9.17 WAXS pattern at 25 C A = 154.18 pm (CuKa). Correlation of the WAXS peaks with the components in poly(p-hydroxybenzoic acid-co-ethylene terephthalate) (a) poly(p-hydroxybenzoic acid), a highly crystalline material (b) COP, 18h at 210-220 C and 4 MPa (c) PET, 60 min at 210-220 C and 4 MPa.

Injection molded bars of longitudinal PLC (poly(p-hydroxybenzoic acid-co-ethylene terephthalate) X7G ) showed a layered morphology [53]. Thinner specimens, of the order of 3 mm thick, showed three different layers symmetrically around the central plane of the specimen an oriented skin (s 0.5 Young s modulus at 23 C 15 GPa), an oriented layer beneath the skin (5 0.5-0.6 Young s modulus at... 

Unoriented poly (p-hydroxybenzoic acid-co-2,6-hydroxynaphthoic acid) exhibited smoothly wandering director fields in three dimensions. Alignment with a 1.1 T magnetic field for 30 min at 300 C transformed this structure to domains with an anisotropic shape within which the polymer was highly oriented, and the global order parameter amounted to 0.85 [110]. Boundaries were of the splay-bend type and involved a 180 director rotation. At lower field strengths, the domains were less... 

The relaxation behavior of nematic, longitudinal PLCs is greatly complicated by their multiphase character. The presence of both crystallites and a coexisting isotropic component has been reported [32]. Vectra A (poly(p-hydroxybenzoic acid-co-2,6-hydroxynaphthoic acid)), currently one of the more widely used and studied commercial polymers, exhibits, despite that fact that it is a statistical copolymer, a sizeable amount (10-60%) of crystallinity, either of the non-periodic layer type [121] or of a truly statistical type according to the model of Biswas and Blackwell [122]. It has become clear that the relaxation of oriented Vectra is to a substantial degree controlled by the thermal behavior of its tiny crystallites. 

PI A, polyimide amide PET, poly(ethylene terephthalate) PHB, poly(p-hydroxybenzoic acid) PI, polyimide PS, poly(styrene) LDPE, low-density poly(ethylene) GF, glass fiber. 

Semiflexible polymers—including regular AB type copolymers in which A is rigid while B flexible. Cellulose derivatives belong here, as well as poly(p-hydroxybenzoic acid) (PHB), and for instance poly(p-phenylene terephtha-lamide). They are of course stronger than flexible polymers, but their processing is more difficult. 

Econol Poly(p-hydroxybenzoic acid ester) Sumitomo Chem. 

Poly-p-hydroxybenzoic acid n. A homopolyester of repeating p-oxyenzoyl units with a high degree of crystallinity. It does not... 

Copolymerization can be employed in a similar fashion to modify the properties of the homopolymer of p-hydroxybenzoic acid (5-6). Poly(p-hydroxybenzoic acid) is an infusible polymer which can be shaped only by compression sintering. A melt processable variation of this high modulus, thermally stable material can be made, however, by copolymerizing an ester of 5-6 with equimolar quantities of terephthalic acid (5-7) and biphenol (5-8) to produce an aromatic polyester which can be fabricated at temperatures near 400°C but still retain many useful properties at 300°C. 

Poly-p-Hydroxybenzoic Acid n A homopolyester of repeating p-oxyenzoyl units with a high degree of crystallinity. It does not melt below its decomposition temperature, 550°C, but can be fabricated at 300-360°C by compression sintering and plasma-spray processes. Copolymers with aromatic dicarboxylic acids and aromatic bisphenols are processable by normal means. Applications include electrical connectors, valve seats, high-performance-aircraft parts, and automotive parts. 

Poly-p-Oxybenzoyl See Poly-p-Hydroxybenzoic Acid. Poly(p-phenylene)... 

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