New Polybutadiene-Based Thermoplastic Elastomers: Synthesis, Morphology and Mechanical Properties

Abstract

Abstract Well defined poly[styrene-b-butadiene-b-styrene] block copolymers (SBS) end-capped with poly(t-butyl methacrylate) (PtBMA) and poly (meth acrylic acid) (PMA) outer blocks, respectively, have been synthesized by the sequential anionic polymerization of butadiene, styrene and tBMA, followed by the selective hydrolysis of the PtBMA blocks into the corresponding PMA blocks. The structure-property relationships of these new thermoplastic elastomers have been investigated, with a special emphasis on the effect of the ester or acid outer blocks on the bulk properties. As a rule, tensile strength is improved by increasing the length of the ester or acid outer blocks from 0 to 140 methacrylic units. Dipole—dipole intermolecular interaction of the PtBMA blocks and hydrogen bonding of the PMA blocks may account for enhanced mechanical properties. However, too high a degree of strong intermolecular interactions can constitute a deterrent to good phase separation. This is supported by morphological observations and loss in tensile properties when the relative content of the ester or acid outer blocks exceeds some critical value. In the case of a high acid content, DSC analysis shows two thermal transitions at −70 °C and 230°C for PBD and PMA blocks, respectively.