Synthesis and Study of Thermoresponsive Amphiphilic Copolymers via RAFT Polymerization.

Marija Kavaliauskaite,Vaidas Klimkevicius,Justina Kievisaite,Medeina Steponaviciute,Arturas Katelnikovas

doi:10.3390/polym14020229

Marija Kavaliauskaite, Vaidas Klimkevicius + Show 3 more

Open Access

https://doi.org/10.3390/polym14020229

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Journal: Polymers	Publication Date: Jan 6, 2022
Citations: 4	License type: CC BY 4.0

Affiliation: Vilnius University

Abstract

Synthesis and study of well-defined thermoresponsive amphiphilic copolymers with various compositions were reported. Kinetics of the reversible addition-fragmentation chain transfer (RAFT) (co)polymerization of styrene (St) and oligo(ethylene glycol) methyl ether methacrylate (PEO5MEMA) was studied by size exclusion chromatography (SEC) and 1H NMR spectroscopy, which allows calculating not only (co)polymerization parameters but also gives valuable information on RAFT (co)polymerization kinetics, process control, and chain propagation. Molecular weight Mn and dispersity Đ of the copolymers were determined by SEC with triple detection. The detailed investigation of styrene and PEO5MEMA (co)polymerization showed that both monomers prefer cross-polymerization due to their low reactivity ratios (r1 < 1, r2 < 1); therefore, the distribution of monomeric units across the copolymer chain of p(St-co-PEO5MEMA) with various compositions is almost ideally statistical or azeotropic. The thermoresponsive properties of p(St-co-PEO5MEMA) copolymers in aqueous solutions as a function of different hydrophilic/hydrophobic substituent ratios were evaluated by measuring the changes in hydrodynamic parameters under applied temperature using the dynamic light scattering method (DLS).

Highlights

Over the past few decades, multifunctional polymers have received significant interest and recognition
reversible addition-fragmentation chain transfer (RAFT) polymerization method is versatile for the synthesis of polymers with different functionality and shows better polymerization control in comparison with other reversible deactivation radical polymerization (RDRP) methods (ATRP, NPM, etc.,) [32,33]
In the case of styrene/PEO5MEMA, the determined reactivity ratio of styrene (r1) is higher if compared to the reactivity ratio of this monomer determined in styrene/methyl methacrylate (MMA) polymerization [40]. This is explained by the fact that PEO5MEMA is even more preferable for cross-polymerization than MMA. This assumption may be justified by recent studies of Boulding et al [41], where authors stated that the reactivity ratio of MMA is higher if compared to the used PEG-methacrylate during the free radical polymerization of such monomers

Summary

Introduction

Over the past few decades, multifunctional polymers have received significant interest and recognition. When stimuli-responsive polymers are designed, it is important to have the functional groups/substituents statistically distributed within copolymer chains. When the solution temperature rises above the LCST, the pNIPAM chains change from solvated (bound to water molecules) or extended random coil to globular conformation [19] These changes of polymer architecture can be controlled by changing polymer composition, i.e., by copolymerization with different hydrophilic or hydrophobic monomers, i.e., the LCST temperature can be increased or decreased. In this paper we clarify the monomers attachment to the polymer chain mechanism, which would allow the synthesis of thermosensitive polymers of the desired composition and architecture Another part of the work was designated to investigate these copolymers and evaluate the resulting polymers’ thermal sensitivity properties

Materials

RAFT Polymerization of Styrene

Study of Styrene Polymerization

Thermoresponsivity of Amphiphilic Copolymers

40 Physiological temperature