Synthesis of branched poly octamethylene-L- -tartrate

The tartaric acid, 1,8-octanediol and p-toluene sulfonic acid were placed in the flask and the latter flushed with N2. A positive pressure of N2 was then maintained throughout. The mixture was stirred as the temperature was raised to 140 °C to achieve a homogeneous solution the temperature was then allowed to fall to 125 °C and the reaction left to proceed for 3 days. 

Water and excess diol were removed by distillation under high vacuum to yield a solid mass. The latter was swollen in refluxing ethyl acetate (sufficient to make the mass mobile) and the resulting mixture poured into -hexane ( 3 fold volume excess). 

The solid was recovered by decanting off the solvents and the polymer dried under vacuum at 40 °C for 6 hours and at room temperature for 2 days to yield 16.6 g (95%) of poly(octamethylene tartrate) (3). 

Note 1 - small signals 8 = 5.41 and 4.62 correspond to methine H atoms on tartrate branch points the ratio of these intensities to the total intensity of all tartrate methine resonances allows estimation of the percentage branching. 

Note 2 - the percentage branching can vary with precise reaction conditions, up to 10% gives optimal results products insoluble in DMSO are crosslinked and should be discarded. 

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