Preparation Of High-heat Resistant Block Copolymer Via RAFT Emulsion Polymerization

In the past two decades, controlled/living radical polymerization (C/LRP) has received extensive attention from the academia and industry. However, the large-scale industrial application of C/LRP has not been realized yet. This thesis focused on the preparation of high-heat resistant block copolymer via reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization. Using poly(acrylic acid)n-b-poly(styrene)5-RAFT as both macroRAFT agent and emulsifier, systematic investigations were carried out on the emulsion copolymerization of y-methyl-a-methylene-y-butyrolactone (MeMBL) and styrene (St), and the synthesis and processing of poly (styrene-co-y-methyl-a-methylene-y-butyrolactone)-b-poly(n-butyl acrylate)-b-poly (styrene-co-y-methyl-a-methylene-y-butyrolactone)(S/M-nBA-S/M). The following was the main achievements:(1) Preparation of copolymer in a latex form with glass transition temperature (Tg) much higher than100℃Latexes with Tg of copolymer much higher than100℃were successfully prepared via RAFT emulsion copolymerization of MeMBL and St. The Tg of copolymer was much increased with the introduction of MeMBL. The Tgs of copolymers were as high as113℃,132℃,154℃and179℃when [MeMBL]:[St]=1:4,1:2,1:1, and2:1, respectively. The stable latexes of the copolymer of MeMBL and St were achieved with [MeMBL]:[St]≤2:1. The molecular weights were in good agreement with theoretical predictions and PDIs were about1.2when [MeMBL]:[St]≤≤1:2; in the case of [MeMBL]:[St]=1:1, the molecular weight became out of control with increasing PDI. The strong composition drifting, which was broadened with the increase of [MeMBL]:[St] and the solid contents, lead to the formation of linear gradient copolymer and the deviation between the Tgs of the copolymers and the Fox equation predictions. The strong composition drifting could be weakened by the semi-continuous feeding strategy.(2) Preparation of tough, transparent, rigid and high Tgstyrenic thermoplastics A series of styrenic thermoplastics with excellent properties was successfully prepared. It was found that only the triblock copolymers (30K-25K-30K, i.e.30000g/mol-25000g/mol-30000g/mol) with30%(mass fraction) of rubber (poly(nBA)) content achieved significant toughening effect. The rigidity and the vicat softening temperature were increased with the introduction of a monomer with higher polarity (MeMBL) into the plastic block. The sample of30K-25K-30K ([MeMBL]:[St]=1:2) showed the best comprehensive properties with the elastic modulus, yield strength, tensile strength, elongation at break, and fracture toughness up to1880MPa,35MPa,43MPa,60%, and22.35MJ/m3, respectively. The Tg of plastic block and the vicat softening temperature were as high as135℃and86.8℃, respectively. The visible light transmittance of the material was up to80%.(3) Preparation of high-heat resistant styrenic thermoplastic elastomer with Tg of plastic block much higher than100℃A series of S/M-nBA-S/M triblock copolymer with Tg of plastic block as high as132℃was successfully synthesized. The elastic modulus, yield strength, tensile strength, elongation at break of17K-30K-15K and16K-35K-15K at20℃were beyond200MPa,7～8MPa, about10MPa and350%, respectively. The elastic modulus of these samples decreased by more than half, and the yield strength, tensile strength and elongation at break of which were1.8～3.2MPa,3.7～4.7MPa and about400%at80℃, respectively. In addition, the sample of17K-45K-15K showed great elastomeric properties at80℃, the elastic modulus, yield strength, tensile strength and elongation at break of which were38MPa,1.1MPa,3.6MPa and540%, respectively.