Synthesis and ‘Schizophrenic' Micellization of Double Hydrophilic AB₄Miktoarm Star and AB Diblock Copolymers:  Structure and Kinetics of Micellization

Abstract

Poly(N-isopropylacrylamide) (PNIPAM)-based tetrafunctional atom transfer radical polymerization (ATRP) macroinitiator (1b) was synthesized via addition reaction of mono-amino-terminated PNIPAM (1a) with glycidol, followed by esterification with excess 2-bromoisobutyryl bromide. Well-defined double hydrophilic miktoarm AB4 star copolymer, PNIPAM-b-(PDEA)4, was then synthesized by polymerizing 2-(diethylamino)ethyl methacrylate (DEA) via ATRP in 2-propanol at 45 degrees C using 1b, where PDEA was poly(2-(diethylamino)ethyl methacrylate). For comparison, PNIPAM-b-PDEA linear diblock copolymer with comparable molecular weight and composition to that of PNIPAM-b-(PDEA)4 was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. The pH- and thermoresponsive "schizophrenic" micellization behavior of the obtained PNIPAM65-b-(PDEA63)4 miktoarm star and PNIPAM70-b-PDEA260 linear diblock copolymers were investigated by 1H NMR and laser light scattering (LLS). In acidic solution and elevated temperatures, PNIPAM-core micelles were formed; whereas at slightly alkaline conditions and room temperature, structurally inverted PDEA-core micelles were formed. The size of the PDEA-core micelles of PNIPAM65-b-(PDEA63)4 is much smaller than that of PNIPAM70-b-PDEA260. Furthermore, the pH-induced micellization kinetics of the AB4 miktoarm star and AB block copolymers were investigated by the stopped-flow light scattering technique upon a pH jump from 4 to 10. Typical kinetic traces for the micellization of both types of copolymers can be well fitted with double-exponential functions, yielding a fast (tau1) and a slow (tau2) relaxation processes. tau1 for both copolymers decreased with increasing polymer concentration. tau2 was independent of polymer concentration for PNIPAM65-b-(PDEA63)4, whereas it decreased with increasing polymer concentration for PNIPAM70-b-PDEA260. The chain architectural effects on the micellization properties and the underlying mechanisms were discussed in detail.

Synthesis of amphiphilic and thermoresponsive ABC miktoarm star terpolymer via a combination of consecutive click reactions and atom transfer radical polymerization

“…Our research interests involve the controlled synthesis of responsive block copolymers and their supramolecular self-assembly in aqueous solution. [31][32][33][34] In this work, we synthesized a novel ABC miktoarm star terpolymer consisting of hydrophilic PEG, hydrophobic poly(tert-butyl methacrylate) (PtBMA), and thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) arms via a combination of consecutive click reactions and ATRP, starting from bis(2-azidoethyl)amine, (N 3 ) 2 ANH, which contains two azide groups and one secondary amine moiety (Schemes 1 and 2). We then investigated the supramolecular self-assembly behavior of PEG(-b-PtBMA)-b-PNIPAM miktoarm star terpolymer in aqueous solution.…”

“…[51][52][53] The phase transition of PNIPAM coronas or cores in micelles selfassembled from amphiphilic or double hydrophilic block or star copolymers have also been investigated. 33,[54][55][56][57][58][59][60][61] To the best of our knowledge, the phase transition of micelles containing mixed coronas of thermoresponsive PNIPAM and hydrophilic chain sequences has not been reported yet. The close neighboring between PNIPAM and PEG chains will surely affect the phase transition behavior.…”

Efficient metal‐free coupling of polystyrene chains using silane radical atom abstraction

“…[1][2][3][4][5][6][7][8][9][10][11][12][13] Regardless of the specific CRP method being utilized, the essential phenomenon is the reversible trapping of active polymer radicals, temporarily transforming them into dormant species and thus minimizing bimolecular radical reactions that polymer radicals are susceptible to, such as radical-radical coupling, chain transfer, or disproportionation.…”

Water-Soluble Stimuli Responsive Star-Shaped Segmented Macromolecules

“…A well-defined double hydrophilic AB 4 miktoarm star copolymer, PNIPAM(PDEAEMA) 4 was synthesized by ATRP and its self-assembly and responsive behavior was investigated in aqueous solutions via 1 H NMR and laser light scattering (LLS) [23]. Due to the thermo-sensitivity of poly(N-isopropylacrylamide) (PNIPAM) and pH-sensitivity of PDEAEMA arms, this star exhibits a dual responsiveness.…”