All Acrylic Based Thermoplastic Elastomers: Design and Synthesis for Improved Mechanical Performance

Thermoplastic elastomers (TPEs) have been widely studied because of their recyclability, good processability, low production cost and distinct performance. Compared to the widely-used styrenic TPEs, acrylate based TPEs have potential advantages including exceptional chemical, heat, oxygen and UV resistance, optical transparence, and oil resistance. However, their high entanglement molecular weight lead to “disappointing” mechanical performance as compared to styrenic TPEs. The work described in this dissertation is aimed at employing various approaches to develop the all acrylic based thermoplastic elastomers with improved mechanical performance.

The first part of this work focuses on the introduction of acrylic polymers with high glass transition temperatures. Poly(1-adamantyl acrylate) (PAdA) was studied including the anionic polymerization, molecular information, thermal properties, unperturbed chain dimensions and chain flexibility. The homopolymers exhibit a high glass transition temperature (133 °C) and decomposition temperature (376 °C). The polymer chain exhibits a comparable persistence length, diameter per bead, and characteristic ratio to those of poly(methylmethacrylate) and polystyrene. The outstanding properties of PAdA were utilized by the cooperation with poly(tetrahydrofurfuryl acrylate) (PTHFA) to make the PAdA-b-PTHF-b-PAdA (ATA) triblock copolymers. The resulting polymer showed distinct microphase separation behaviors and an upper service temperature at 123 °C, which is higher than that of both conventional styrenic TPEs and acrylic TPEs. The ATA triblock copolymers exhibited mechanical strength and elongation higher than those of commercial all acrylic TPEs.

The second part involves the synthesis of poly(butyl acrylate)-g-poly(methylmethacrylate) (PBA-g-PMMA) graft copolymers. Secondary-butyl lithium/N-isopropyl- 4-vinylbenzylamine (sec-BuLi/PVBA) initiation system was used to synthesize the PMMA macromonomer by anionic polymerization. By the combination of enhanced molecular weight and complex architecture, the resulting polymer showed exceptional microphase separation behavior, extraordinary mechanical strength and superelastomer characteristics with greatly improved elongation and exceptional recovery behavior.

In the final chapter, other approaches to improve the mechanical properties of all acrylic based TPEs are discussed and prospected, including the introduction of extra driving forces, and the possible combination routes of all the approaches attempted. In addition, the great potential of PVBA to build complex architectures is proposed, including triarm stars, multigraft copolymers with tetrafuntional branch points, four arm stars and H-shaped copolymers.