Polyesters 4,4’-dihydroxybiphenyl

The first LCP to be launched commercially was Dartco s Xydar, introduced in 1984 [11]. Xydar injectionmolding resins are aromatic polyesters based on terephthalic acid, p-hydroxybenzoic acid, and p,p -dihydroxybiphenyl. Xydar has a high melting point (close to 400°C), which necessitates certain modifications to processing equipment. It also has a high melt viscosity making it difficult to mold in... 

Photosetting cholesteric polyesters derived from DAS and 4-hydroxycinnamic acid [35], and from 2,5-bis(dode cyloxy)terephthalic acid and4,4 -dihydroxybiphenyl, were also described [36]. 

Kricheldorf H.R., Wulff D.F., Layer structures. 11. Cholesteric polyesters derived from isosorbide, 2,5-bis(dodecyloxy)tere phthalic acid and 4,4 -dihydroxybiphenyl, Polymer, 39, 1998,6145-6151. 

Kauth et al. (1988) have disclosed transesterification of aromatic polyesters and a polyphosphonate in a devolatiUzing extmder. For example, a polyester derived from bisphenol A and 1 1 iso/terephthalic acid dissolved in dichloromethane/chlorobenzene was devolatilized along with a similar solution of a polyphosphonate derived from methanephosphonic acid and 4,4 -dihydroxybiphenyl in a TSE at 340 °C. The isolated transparent product had a single Tg by DSC and improved impact strength compared to test parts of the individual homopolymers. Polycarbonate and polyestercarbonates were also successfully transesterified with polyphosphonate using this procedure. 

The next development in liquid crystal polyesters was the preparation by polycondensation based on terephthalic acid (TPA) and hydroquinone (HQ) or p-hydroxybenzoic acid (HBA). The polyesters are insoluble with very high melting temperatures of 600 °C for poly (TPA/HQ) and 610 °C for poly (HBA), which are by far too high to obtain stable liquid crystalline phases for melt processing. In 1972, Economy and coworkers patented several copolyester compositions, and one of these are the copolymerization of poly (4-hydroxybenzoic acid) (PHB) with 4,4 -dihydroxybiphenyl (BP) and terephthalic acid (TPA) due to the need for lower melting, melt-processable polymers. Considerable synthetic efforts have been attempted in order to decrease the melting temperatures of aromatic LC polyesters while retaining LC properties. The copolyester structure was tailored by partial substitution of TPA with isophthalic acid to produce a melt-spinnable material. 

Much wider interest has been aroused by the development of copolymers of p-hydroxybenzoic acid which are commonly known as liquid crystal polymers. Polyesters of this type were introduced commercially in 1985 and details of their nature have not been fully disclosed. Two commercial products are currently available one is based on p-hydroxybenzoic acid and a hydroxynaphthoic acid whilst the other is based on p-hydroxybenzoic acid, terephthalic acid and p,p -dihydroxybiphenyl. 

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