Investigate the Glass Transition Temperature of Hyperbranched Copolymers with Segmented Monomer Sequence

Abstract

Hyperbranched copolymers with segmented structures were synthesized using a chain-growth copper-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization via sequential monomer addition in one pot. Three AB₂-type monomers that contained one alkynyl group (A), two azido groups (B), and one dangling group, either benzyl or oligo­(ethylene oxide) (EO_<i>x</i>, <i>x</i> = 3 and 7.5), were used in these CuAAC reactions. Varying the addition sequences and feed ratios of the monomers produced a variety of hyperbranched copolymers with tunable compositions, molecular weights, segmented structures, and consequently glass transition temperature (<i>T</i>_g). It was found that the <i>T</i>_g of hyperbranched copolymers was little affected by the polymer molecular weights when <i>M</i>_n ≥ 5000. However, the values of <i>T</i>_g were significantly determined by the compositions of the terminal groups and the outermost segment of the hyperbranched copolymers. The last added AB₂ monomer in the polymerization formed an outermost “shell” and shielded the contribution of inner segments to the glass transition of the copolymers, reflecting a chain sequence effect of hyperbranched polymers on the thermal properties