End capped polyalkylene carbonates having improved thermal stability

A process for improving the thermal stability of a normally solid polycarbonate having substantially alternating epoxide and carbon dioxide units and having a plurality of free hydroxyl groups represented by the formula:

• ##STR3## wherein:
• R.sub.1 is hydrogen, a halomethyl group, or a hydrocarbyl group having from 1 to 6 carbon atoms;
• R.sub.3 is hydrogen, a halomethyl group, or a hydrocarbyl group having from 1 to 6 carbon atoms;
• R.sub.2 and R.sub.4 are hydrogen or a hydrocarbyl group having from 1 to 6 carbon atoms;
• R.sub.1, r.sub.2, r.sub.3 and R.sub.4 are combined together constituting a carboxylic ring of from 4 to 7 carbon atoms;
• and
• n is a number from about 250-6,500;
• which comprises end-capping at least a portion of the free hydroxyl groups of said polycarbonate by reacting said hydroxyl groups with a hydroxyl reactive organic compound having the ability to replace the active hydrogen atom on said hydroxyl group for forming an oxygen-carbon bond, said reaction being carried out under conditions sufficient for effecting said reaction.