Well-defined homopolymers of 2-hydroxyethyl acrylate (HEA) with different degrees of polymerization are synthesized via reversible addition–fragmentation 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 ∼ 20–70 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 °C for copolymers with the pure block microstructure and between 0 and 60 °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.

Kinetic studies of the (co)polymerization of 2-hydroxyethyl acrylate (HEA) and/or 2-methoxyethyl acrylate (MEA) via reversible addition-fragmentation chain transfer polymerization (RAFT), using dibenzyltrithiocarbonate (DBTTC) as chain-transfer agent, resulting in well-defined copolymers, are presented. Both monomers were found to have equal reactivity revealing the formation of ideal random (azeotropic) copolymers. The thermoresponsive properties of aqueous solutions of the copolymers at 5 mg/ mL, depending on the polymer composition, the chain length, and the end-groups, were investigated. The cloud point (CP) of the synthesized copolymers increases with the content of HEA and decreases with the decreasing chain length. Exchanging one of the hydrophobic benzylic end-groups of the copolymers by isobutyronitrile resulted in more hydrophilic copolymers with significantly higher CP-temperatures. Thus, new potential biomaterials with an adjustable cloud point between 0 and 60 °C, showing a small hysteresis between heating and cooling, were successfully prepared.

Poly(2-hydroxyethyl acrylate) (PHEA) is an interesting biomaterial with similar biocompatibility as the widespread used poly(2-hydroxyethyl methacrylate). Poly(2-hydroxypropyl acrylate) (PHPA) is a less frequently studied polymer that exhibits thermoresponsive behavior in water. Therefore, copolymers of HEA and HPA are interesting thermoresponsive polymers to evaluate as potential biomaterials. Here, we report the copolymerization kinetics of HEA and HPA by nitroxide-mediated polymerization, employing Blocbuilder® initiator and SG-1 free nitroxide, revealing an ideal random copolymerization. Furthermore, the thermoresponsive properties of the resulting copolymers are discussed, whereby the cloud points are related to both polymer composition as well as polymer concentration.

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