4- -2-bromoterephthalate

Bromoterephthaloylchloride Pi mixture of 10 g bromoterephthalic acid, 20 g freshly distilled thionyl chloride, and 1 ml of DMF is refluxed under a stream of nitrogen for 3 h. Next, the excess thionyl chloride is removed by vacuum distillation (about 10 torr).The remaining bromoterephthalic dichloride is converted to bromoterephthalic acid dimethyl ester by adding the four-fold amount of anhydrous methanol.The excess of methanol is taken off on a rotary evaporator or by distillation and the pure bromoterephthalic acid dimethyl ester can be isolated by fractional distillation (p < 0.01 torr) over a... 

Random copolyesters based on bromoterephthalic acid, methyl hydroquinone, and hexane diol have been synthesized. Their mesophase properties were studied by differential scanning calorimetry, optical microscopy, realtime X-ray diffraction and melt rheology. At low molecular weight these copolymers exhibit triphasic behavior, where two mesomorphic phases coexist with an isotropic phase. Fractionation based on solubility in THF enables the identification of two components. Simple statistical arguments are employed to model the polymerization reaction and account for the observed phase behavior. 

Synthesis of Model Compounds. We have synthesized semi-rigid rod LC polyesters based on poly(methylphenylene bromoterephthalate-co-hexamethylene bromoterephthalate) (Fig. 1) by random copolymerization. The details of the synthesis of these polymers have been reported previously (fi), and are shown schematically in Fig. 1. All chemicals were purchased from Aldrich methyl hydroquinone, and 1,6-hexanediol were used as received. Bromoterephthalic arid (96%) was recrystallized with an 80/20 vol-% distilled water/ethanol solution. Pyridine (used a proton acceptor) was distilled and stored with desiccant. Solvents were used as received, and all glassware was oven dried. 

In a typical reaction, bromoterephthalic arid, (0.0132 mol), was first converted to its arid chloride by refluxing with thionyl chloride and 4-5 drops of DMF as catalyst. After two hours, the unreacted thionyl chloride was distilled off. Each polymerization step was carried out in the same reaction flask as the remaining diarid chloride. After distillation, in a typical polymerization, 0.82 g (6.59 x 10 3 mol) of methyl hydroquinone was dissolved in a graduated funnel with 20 ml methylene chloride and 25 ml pyridine. The solution was slowly dripped into the reaction flask and stirred over night under Nj atmosphere. 

In regioregularly substituted RR-BH the bromine substituents are located only on the terephthaloyl unit, whereas in RR-BB both the two structural units contain the substituents. If one polymerizes bromoterephthalic acid with hydroquinone or bromo-... 

Therefore, these polyesters, in the strict sense, should be taken to be random sequence copolyesters arising from the possible positional isomerism of the substituents. For a comparison purpose, the random positional polymers were synthesized in solution or in melt by reaction bromoterephthalic acid and hydroquinone or diacetate of bromohydroquinone. 

A number of dicarboxylic acids were employed including, a series of p-phe-nylene dicarboxyhc acids such as dimethylterephthalic, dimethylterphthalic acid, bromoterephthalic acid, nitroterephthahc acid, terephthalic acid, and dichloroter-ephthalic acid. The best yield of about 50% was achieved from terephthalic acid, consistent with steric concerns being important. A number of aliphatic diacids were employed including ferrocene-1,1 -dicarboxylic acid, fumaric acid, maleic acid, and oxalic acid. 

No product was recovered for the following reaction systems 2-bromoterephthalic, Et N and tetraammonium iodide, tetra-phenyl-phosphonium iodide and T5-Crown-5 for 10-360 secs 2-nitrotereph-thalic, Et-jN and tetraphenylphosphonium iodide (10 secs) and 15-Crown-5 (10 to 180 secs). 

The following chemicals were utilized as received (from Aldrich unless otherwise noted) phenylphosphoric dichloride (Alfa Inorganics), terephthalic acid, nitroterephthalic acid, methylterephthalic acid, 2,5-dimethylterephthalic acid, tetramethyl-terephthalic, bromoterephthalic acid, 2,5-dichloroterephthalic acid, tetrabromoethylammonium iodide, trlethylamine (Eastman Kodak Co.), tetrabutylphosphonium bromide, l8-Crown-6 and 15-Crown- 5. 

Reaction conditions Phenylphosphonic dichloride (4.00 mmoles) in 25 ml chloroform is added to rapidly stirred (18,500 rpm no load) solutions of dlacid salt (4.00 mmole) containing indicated PTA (0.20 mmole) contained in 25 ml water at 25 C. Molecular weights were determined in hexamethylphosphoramide at 25 C utilizing light scattering photometry. Unsuccessful - ditriethylamine bromoterephthalate, ditriethylamine nitroterephthalate. 

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