Morphology and rheology of poly(methyl methacrylate)-block-poly(isooctyl acrylate)-block-poly(methyl methacrylate) triblock copolymers, and potential as thermoplastic elastomers

The phase morphology and rheological properties of a series of poly(methyl methacrylate)-block-poly(isooctyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MIM) have been studied. These copolymers have well-defined molecular structures, with a molecular weight (MW) of poly(methyl methacrylate) (PMMA) in the range of 3 500-50 000 and MW of poly-(isoocryl acrylate) (PIOA) ranging from 100 000 to 140 000. Atomic force microscopy with phase detection imaging has shown a two-phase morphology for all the MIM copolymers. The typical spherical, cylindrical, and lamellar phase morphologies have been observed depending on the copolymer composition. MIM consisting of very short PMMA end blocks (MW 3 500-5 000) behave as thermoplastic elastomers (TPEs), with however an upper-service temperature higher than the traditional polystyrene-block-polyisoprene-block-polystyrene TPEs (Kraton D1107). A higher processing temperature is also noted, consistent with the higher viscosity of PMMA compared to PS.