Synthesis of a doubly thermo-responsive schizophrenic diblock copolymer based on poly[N-(4-vinylbenzyl)-N,N-diethylamine] and its temperature-sensitive flip-flop micellization

Abstract

Synthesis of a doubly thermo-responsive schizophrenic diblock copolymer, poly(tert-butyl methacrylate)-block-poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PtBMA-b-PVEA), by reversible addition–fragmentation chain transfer (RAFT) polymerization and its temperature-sensitive flip-flop micellization are discussed. By employing 4-cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid as the RAFT agent, the schizophrenic PtBMA-b-PVEA diblock copolymers with different block lengths were prepared. The poly(tert-butyl methacrylate) (PtBMA) block exhibits insoluble-to-soluble phase transition at the upper critical solution temperature (UCST) and the poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PVEA) block exhibits soluble-to-insoluble phase transition at the lower critical solution temperature (LCST) in methanol, respectively. At temperatures below the UCST of the PtBMA block, PtBMA@PVEA micelles containing a PtBMA core and a PVEA corona are formed in methanol. At temperatures above the UCST of the PtBMA block while below the LCST of the PVEA block, PtBMA-b-PVEA is molecularly soluble in methanol. At temperatures above the LCST of the PVEA block, inverse PVEA@PtBMA micelles containing a PVEA core and a PtBMA corona are formed. The polymerization degree of the PtBMA block or the PVEA block affecting the UCST/LCST of the schizophrenic diblock copolymer and the size of the PtBMA@PVEA or PVEA@PtBMA micelles is investigated.