Macromolecules, Vol.50, No.16, 6218-6226, 2017
Triblock Copolymer Elastomers with Enhanced Mechanical Properties Synthesized by RAFT Polymerization and Subsequent Quaternization through Incorporation of a Comonomer with Imidazole Groups of about 2.0 Mass Percentage
ABA triblock copolymer elastomers (TBCPEs) were first synthesized-via reversible addition fragmentation chain transfer (RAFT) polymerization, for which poly(isobornyl acrylate) (PIBA) was chosen as the dispersed hard microdomains, whereas poly(n-butyl acrylate)-co-poly(1-vinylimidazole) (P(BA-co-VI)) was chosen as the rubbery matrix. Two much distinct glass transition temperatures were found, corresponding to the soft matrix and hard micro domains, respectively. Although the mass percentages of the incorporated third comonomer, 1-vinylimidazole, were just about 2.0%, the imidazole groups on the TBCPE chains could be ionically cross-linked by 1,6-dibromohexane to bring these TBCPEs into much strong ones, half-cross-linked TBCPEs-HC and full-cross-linked TBCPEs-FC. It is interesting to demonstrate that the ultimate tensile strength for TBCPEs-FC could be increased up to 10 times that for TBCPEs, and the elastic recovery could also be improved to above 90%, while the elongation at break just showed modest decreases. Transmission electron microscope (TEM) and small-angle X-ray scattering (SAXS) measurements disclosed that TBCPEs, TBCPEs-HC, and TBCPEs-FC all had typical microphase-separated morphology, with the interdomain distance tunable by the molecular mass of TBCPEs. In-situ SAXS measurements revealed that the hard microdomains in TBCPEs-HC could be orientated along the tensile direction during stretching and be recovered to the original state after stress release.