Cyclization in reversible and irreversible step-growth polymerizations

Several aspects of cyclization reactions in step-growth polymerizations are considered. The Jacobson-Stockmayer ring-chain equilibrium theory provides the basis for understanding these systems, but there are circumstances whe re some modifications to the theory are needed. In particular, for ring exp ansion polymerizations, i.e. those for which there is never a significant f raction of open chains, the statistics are a bit different from those appro priate for ring-chain equilibrium. Also, if the reactions are irreversible the occurrence of rings is significantly different from the reversible case . Rings are more prevalent in irreversible reactions. The implications of t hese observations for the processing of polymers are briefly considered. (C ) 2000 Elsevier Science Ltd. All rights reserved.