Block and Gradient Copolymers of 2-Hydroxyethyl Acrylate and 2-Methoxyethyl Acrylate via RAFT: Polymerization Kinetics, Thermoresponsive Properties, and Micellization

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• 作者：Wiktor Steinhauer ; Richard Hoogenboom ; Helmut Keul ; Martin Moeller
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：February 26, 2013
• 年：2013
• 卷：46
• 期：4
• 页码：1447-1460
• 全文大小：751K
• 年卷期：v.46,no.4(February 26, 2013)
• ISSN：1520-5835

文摘

Well-defined homopolymers of 2-hydroxyethyl acrylate (HEA) with different degrees of polymerization are synthesized via reversible addition鈥揻ragmentation chain transfer polymerization (RAFT), using dibenzyltrithiocarbonate (DBTTC) as chain transfer agent. Subsequently, well-defined triblock copolymers of HEA and 2-methoxyethyl acrylate (MEA) with the general microstructure P(HEA)-block-P(MEA)-block-P(HEA) and P(HEA)-block-P(HEA-grad-MEA)-block-P(HEA) are synthesized via RAFT, using previously prepared HEA-based homopolymers with degrees of polymerization of P_n 20鈥?0 as macro-chain transfer agents (MCTAs). Kinetic investigations on all of the performed (co)polymerizations are summarized, revealing that all polymerizations proceed in a controlled manner. The thermoresponsive properties of aqueous solutions of the synthesized copolymers with block or gradient microstructures are determined and discussed, revealing adjustable cloud point (CP) temperatures between 0 and 80 掳C for copolymers with the pure block microstructure and between 0 and 60 掳C for copolymers with gradient microstructures, showing differently pronounced hysteresis on heating and cooling. All of the obtained copolymers feature a temperature dependent amphiphilic character resulting in the formation of spherical aggregates above the CP temperature as proven by fluorescence spectroscopy, cryo-SEM, and DLS. Thus, new thermoresponsive materials were successfully prepared revealing insights into the differences between block and gradient microstructures.