Chain extension reactions of unsaturated polyesters with bis(2‐oxazoline)s

Two different bisoxazolines, 2,2′-(1,3-phenylene) bis(2-oxazoline) (1,3-PBO) and 2,2′-bis(2-oxazoline) (BO) were investigated as chain extenders for short chain unsaturated polyesters (UPEs). These extenders reacted readily with carboxyl ends of unsaturated polyesters, leading to rapid molecular weight increase through coupling of oligomeric chains. Commercially available unsaturated polyesters commonly have molecular weights around 1500, usually reached after a 20-h polyesterification reaction. When bisoxazolines were reacted with short UPE chains obtained at the 6th hour of a commercial polyesterification reaction, the molecular weight of UPE reached 1500 within 5–30 min, which provides economies and prevents the glycol loss and yellowing which are associated with extended reaction times. Styrene solubility, gel time, and thermal and mechanical properties of the chain extended polyesters remained comparable to the commercial UPE, with 8–10 min of gel time and a storage modulus about 3000 MPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012