Molecular weight development in the superacid-catalyzed polyhydroxyalkylation of 1-propylisatin and biphenyl at stoichiometric conditions

Abstract

An experimental study on the importance of cyclization on molecular weight development in superacid catalyzed polyhydroxyalkylation of 1-propylisatin (B2) and biphenyl (A2) at stoichiometric conditions, is presented. Evolution of molecular weight distributions measured by gel permeation chromatography (GPC) and matrix-assisted laser-desorption/ionization-time-of-flight (MALDI-TOF) show that although linear polymer formation dominates the polymerization, there is significant cyclization taking place, and that the polymerization is kinetically controlled. They also show that there are two polymer populations in the reaction system. The polymer population in the low molecular region is richer in cyclic polymer molecules. Diffusion coefficients were measured by GPC and 2D NMR DOSY. The values obtained confirm that cyclization is more important in low molecular weight polymer molecules. A polymerization at non-stoichiometric conditions (excess of A2) is compared with the stoichiometric case. Unlike other superacid catalyzed polyhydroxyalkylations studied in the past, lower molecular weights were obtained in the non-stoichiometric situation.