Methacrylate Butadiene-Based Triblock Copolymers: Synthesis, Characterization, and Properties
Since Szwarc’s remarkable achievements in the 1950s (1), anionic polymerization has occupied a prominent position in polymer synthesis. Living anionic polyaddi tions allow synthetic polymers to be finely tailored (2). In addition to the precise control of molecular weight (MW), molecular architecture, and chain-end func tionality, spectacular advances have been reported in the tailoring of multiphase block copolymers. As a representative achievement, Shell Chemical Company and Phillips Petroleum Company have successfully commercialized thermoplastic elastomers (TPEs), which are well-defined triblock and radial-block copolymers of styrene and butadiene (SBS) or isoprene (SIS) prepared via anionic process. As result of the thermodynamic immiscibility of their constitutive components, TPEs combine the intrinsic properties of the parent homopolymers with the additional benefit of spontaneous and thermoreversible crosslinking in strong relation to the phase morphology (3). The tensile strength of TPEs depends mainly on the ability of the hard blocks to resist plastic deformation under stress. Thus, the strength de creases sharply as the glass transition is approached, which explains why the up per service temperature (UST) of SBS is limited to ca. 70°C (4). It is thus worth substituting a hard block of a higher service temperature (or TH) for polystyrene. Poly(a-methylstyrene) (5), poly(ethylene sulfide) (6), and poly(ter/-butyl methacrylate) (7) have been proposed as possible substitutes for polystyrene.