CYCLIZATION IN HYPERBRANCHED POLYMER SYNTHESES - CHARACTERIZATION BY MALDI-TOF MASS-SPECTROMETRY

Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TO F) mass spectrometry allowed direct determination of the extent of mac rocycle formation that occurred during the polymerization and copolyme rization of A(2)B and A(4)B monomers. Cyclization in hyperbranched pen tafluorophenyl-terminated poly(benzyl ether)s was indicated by the pre sence of ions 20 Da less than the masses of acyclic species, owing to the loss of the HF chain ends during polymerization. This loss occurs by intramolecular nucleophilic aromatic substitution of the benzyl oxi de focal point functionality upon a pentafluorophenyl chain end. Homop olymerizations and copolymerization of A(2)B and A(4)B monomers gave c yclic products in all cases, and the extent of cyclization depended on counterion, reaction time, and reaction temperature. In the copolymer ization, product distributions revealed that larger proportions of A(2 )B repeat units in the product led to increased amounts of cyclic prod ucts.