Cyclizations in hyperbranched aliphatic polyesters and polyamides

Hyperbranched aliphatic polyesters of 2,2'-bis-(hydroxymethyl) propanoic acid and hyperbranched aliphatic polyamides obtained from new carboxy- and amino-functionalized caprolactams were studied by NMR spectroscopy and MALDI-TOF mass spectrometry. Ring-chain equilibria taking place through intramolecular hydroxy-ester, carboxy-amide or amine-amide interchanges and leading to the formation of cyclic branches or end-groups were found to exert a predominant influence on the molar mass of these hyperbranched polymers. A number of intra- or intermolecular side reactions, such as the formation of ethers in polyesters and the formation of anhydrides, imides, amidines and secondary amines in polyamides were also detected and resulted in polymer crosslinking on prolonged heating. The existence of such ring-chain equilibria and side-reactions make the control of hyperbranched polymer structure much more difficult than generally accepted.