| SYNTHESIS |
A preferred copolymer for use as the hydrophobic polyanhydride matrix were combinations of poly(terephthalic acid), (hereinafter "TA") and poly(sebacic acid), (hereinafter "SA") were used. TA and SA were individually mixed with excess acetic anhydride as described earlier to yield a pure recrystallized solid prepolymer. The resulting prepolymers comprising TA and SA respectively were combined in varying concentration ratios of 0:100, 30:70, 50:50, 80:20 and 100:20 TA to SA. Copolymers were then synthesized in each of these concentration ratios following an adaptation of the method of Yoda and Matsuda [Bull. Chem. Soc. Japan 32:1120-1129 (1959); Japanese Patent No. 10,944]. This technique of solution polymerization utilizes a dehydrative coupling reaction between an acyl chloride and a carboxyl group to obtain the polymer. This polymerization technique is preferable because the high melting point (372.degree. C.) of the TA polymer and its instability (charring) at this temperature makes the melt-polycondensation methodology previously described unsuitable. Preferably, the appropriate quantity of TA and SA, such as 0.02 mole is dissolved in 400 ml of chloroform in the presence of 0.04 mole of triethylamine. Tetraphthaloyl chloride in the desired quantity, such as 0.02 mole, previously dissolved in benzene is added to a dropping funnel over a 30 minute period under vigorous agitation. This liquid admixture is allowed to react for 3 hours at room temperature and is held under a nitrogen sweep at all times. The resulting copolymer is then purified by extraction with anhydrous ether in a Soxhlet Extractor for between 2-3 hours and was then stored in a dessicator over calcium chloride
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