Construction and Properties of Hyperbranched Block Copolymer with Independently Adjustable Heterosubchains

Abstract

A trifunctional initiator with one alkyne, one hydroxyl, and one bromine group was used to construct Br-polystyrene-alkyne-poly(ε-caprolactone)-OH (Br–PS–≡–PCL–OH) diblock copolymer precursor with one terminal alkyne group located at the junction between the two blocks. Further bromination and azidation substitution of the precursor led to a seesaw-type macromonomer azide-polystyrene-alkyne-poly(ε-caprolactone)-azide (N3–PS–≡–PCL–N3). Subsequently, novel hyperbranched copolymers [HB-(PS-b-PCL)n] with independently adjustable PS and PCL branching subchains were prepared by “click” chemistry. All of the linear precursors and hyperbranched copolymers were characterized by FT-IR, 1H NMR, and GPC with triple detectors in detail. It was found that such hyperbranched copolymers are self-similar objects; namely, their intrinsic viscosities ([η]) are scaled to the weight-average molar masses (Mw) as [η] ∼ Mwν, where ν = 0.45 ± 0.01 and 0.48 ± 0.01 for the longer and shorter PS block, respectively. Moreover, the study on the crystallization behavior of unfractionated and fractionated HB-(PS-b-PCL)n copolymers indicated both the crystal size and the degree of crystallinity decrease with the PS subchain length and the overall degree of polymerization, and the remaining oligomer and macromonomer components could facilitate the crystallization of the unfractionated sample. Finally, it was found that the degree of crystallinity decreases dramatically when the weight fraction of fractionated hyperbranched copolymer in macromonomer/hyperbranched copolymer blend films exceeds ∼67%, indicating that the uncrystallizable hyperbranched chains may impose some extra restriction on the crystallization of the macromonomer chains.