Role of cyclization in the synthesis of hyperbranched aliphatic polyesters

Abstract

The intramolecular cyclization in hyperbranching polycondensation reactions of the type AB2/Bf was investigated both theoretically and experimentally. Hyperbranched aliphatic polyesters prepared from 2,2-bis(hydroxymethyl)propionic acid (BisMPA) and 1,1,1-tris(hydroxymethyl)propane (TMP) as B3 core molecule as well as commercially available samples with ethoxylated pentaerythrol as B4 core (Perstorp, Boltorn®) have been investigated with a combination of methods (NMR, vapor pressure osmometry (VPO), size exclusion chromatography (SEC), MALDI-TOF-MS) with respect to the formation of intramolecular cycles during polymerization. Absolute molecular weights were determined for the first time and found to be in the range of 632 (G2) to 1046 g/mol (G5) and 827 (PG2) to 1974 g/mol (PG5) for the commercial samples, respectively, i. e. considerably lower than reported previously. Theoretical considerations as well as experimental data clearly demonstrate cyclization to be an important reaction regardless of the presence of a core. The fraction if cyclized molecules was found to increase with molecular weights from 32% to 48%, limiting molecular weights drastically. In summary, previously reported results could not be confirmed. Incremental addition of the BisMPA monomer to the TMP-core did not permit to control molecular weights and the term “pseudogeneration” is inappropriate for the low molecular weight materials formed.