Effects of macromonomer chain length, solvent and concentration on the cyclization kinetics during AB-type step-growth polymerization

Abstract

For the first time, this work has explored the cyclization kinetics of multi-mers during step-growth polymerization by using alkyne-PS-azide (l-PS-N3) as model macromonomer, where PS represents polystyrene. First, three AB-type PS macromonomers with different chain lengths have been prepared by atom transfer radical polymerization (ATRP), namely, l-PS77-N3, l-PS240-N3 and l-PS380-N3. Second, the polymerization and cyclization kinetics has been monitored in dimethylformamide (DMF), tetrahydrofuran (THF) and cyclopentane (CyP). Third, by size exclusion chromatography (SEC) and liquid chromatography at the critical condition (LCCC) methods, we have quantified how the macromonomer chain length, solvent type and reaction concentration affect the intra-chain cyclization process. The analysis results have demonstrated that, for macromonomer l-PS77-N3 with shorter chain length, the reaction rate of macromonomer cyclization, multi-mer cyclization and inter-chain coupling, is significantly faster than that for l-PS240-N3 and l-PS380-N3 with longer chain lengths. The total percentage of final cyclic product (wtcyclic) slightly decreases with the increase of macromonomer chain length, namely, 33%, 25% and 23% for l-PS77-N3, l-PS240-N3 and l-PS380-N3, respectively. At the same time, we found that, solvent with lower solvent viscosity and relatively poor solvent quality is more conducive to the cyclization reaction of PS chains. In addition, we also found that the inter-chain and intra-chain reaction rate are both faster than that at other reaction concentrations when the reaction concentration is near the critical overlapping concentration.