Yanqiu Wang

The group-transfer polymerization (GTP) of N,N-bis(2-methoxyethyl)acrylamide (MOEAm) initiated by Me₂EtSiH in the hydrosilylation-promoted method and by silylketene acetal (SKA) in the conventional method proceeded in a controlled/living manner to provide poly(N,N-bis(2-methoxyethyl)acrylamide) (PMOEAm) and PMOEAm with the SKA residue at the α-chain end (MCIP-PMOEAm), respectively. PMOEAm-b-poly(N,N-dimethylacrylamide) (PDMAm) and PMOEAm-s-PDMAm and PMOEAm-b-poly(N,N-bis(2-ethoxyethyl)acrylamide) (PEOEAm) and PMOEAm-s-PEOEAm were synthesized by the block and random group-transfer copolymerization of MOEAm and N,N-dimethylacrylamide or N,N-bis(2-ethoxyethyl)acrylamide. The homo- and copolymer structures affected the thermoresponsive properties; the cloud point temperature (T_cp) increasing by decreasing the degree of polymerization (x). The chain-end group in PMOEAm affected the T_cp with PMOEAm_x > MCIP-PMOEAm_x. The T_cp of statistical copolymers was higher than that of block copolymers, with PMOEAm_x-s-PDMAm_y > PMOEAm_x-b-PDMAm_y and PMOEAm_x-s-PEOEAm_y > PMOEAm_x-b-PEOEAm_y.

In this paper, we describe a comprehensive study of the thermoresponsive properties of statistic copolymers and multiblock copolymers synthesized by poly(glycidol)s (PG) and poly(ethyl glycidyl ether) (PEGE) with different copolymerization methods. These copolymers were first synthesized by ring-opening polymerization (ROP), which was initiated by tert-butylbenzyl alcohol (tBBA) and 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranylidenamino]-2Λ⁵,4Λ⁵-catenadi(phosphazene) (t-Bu-P₄) as the catalyst, and then the inherent protective groups were removed to obtain the copolymers without any specific chain end groups. The thermoresponsive property of the statistic copolymer PG_x-stat-PEGE_y was compared with the diblock copolymer PG_x-b-PEGE_y, and the triblock copolymers were compared with the pentablock copolymers. Among them, PG-stat-PEGE, PG-b-PEGE-b-PG-b-PEGE-b-PG, and PEGE-b-PG-b-PEGE-b-PG-b-PEGE, and even the specific ratio of PEGE-b-PG-b-PEGE, exhibited LCST-type phase transitions in water, which were characterized by cloud point (T_cp). Although the ratio of x to y affected the value of the T_cp of PG_x-stat-PEGE_y, we found that the disorder of the copolymer has a decisive effect on the phase-transition behavior. The phase-transition behaviors of PG-b-PEGE, part of PEGE-b-PG-b-PEGE, and PG-b-PEGE-b-PG copolymers in water present a two-stage phase transition, that is, firstly LCST-type and then the upper critical solution temperature (UCST)-like phase transition. In addition, we have extended the research on the thermoresponsive properties of EGE homopolymers without specific α-chain ends.