EFFECTS OF CYCLIZATION AND ELECTROSTATIC INTERACTIONS ON THE TERMINATION RATE OF MACRORADICALS IN FREE-RADICAL CROSS-LINKING COPOLYMERIZATION

Effects of cyclization and ionic group contents on the termination rat e of macroradicals formed at zero monomer conversion were investigated . For this purpose, the pregel regime of free-radical methyl methacryl ate / ethylene glycol dimethacrylate (MMA/EGDM) and acrylamide / N,N'- methylenebisacrylamide (AAm/BAAm) copolymerization systems was studied by means of the dilatometric technique. To eliminate the chain-length dependent variation of the termination rates, different sets of exper iments were carried out each at a fixed monomer and initiator concentr ation. At low crosslinker contents, the termination rate of zero-conve rsion macroradicals was enhanced in crosslinking copolymerizations com pared to linear polymerization. This is due to the cyclization reactio ns which reduce the size of the macroradical coils and thus, enhance t he termination rates due to the lowering of the thermodynamic excluded volume effect. As the amount of the crosslinker increases, an enhance ment in the initial rate of polymerization is observed in all series o f experiments, indicating that steric effects on segmental diffusion d ominate at high crosslinker contents. The results also indicate a slow er rate of termination of ionic macroradicals compared to the non-ioni c radicals of the same molecular weight and points the significance of the thermodynamic excluded volume effect on rising the ionic group co ntent.