Y. S. Yu

Difunctional initiator based on 1,3-diisopropenylbenzene. IV. Synthesis and modification of poly(alkyl methacrylate-b-styrene-b-butadiene-b-styrene-b-alkyl methacrylate (MSBSM) thermoplastic elastomers

MSBSM five-block copolymers where B stands for butadiene, S for styrene, and M for either methyl methacrylate (MMA) or tert-butyl methacrylate (tBMA) have been synthesized by sequential anionic polymerization in an apolar solvent by using a difunctional anionic initiator derived from 1,3-diisopropenylbenzene. These block copolymers show improved mechanical properties and an extended service temperature compared to traditional SBS thermoplastic elastomers. Upon hydrolysis and further neutralization of the PolytBMA end-blocks, the upper glass transition temperature (T g ) of the five-block copolymers has been raised up to about 150°C. A further increase in this service temperature (up to ca. 160°C) has resulted from the blending of sPMMA-SBS-sPMMA five-block copolymers with isotactic poly(methacrylate) (iPMMA), due to the formation of a stereocomplex. The tensile properties of these modified five-block copolymers have remained essentially unchanged.

Stereocomplexation of sPMMA-PBD-sPMMA triblock copolymers with isotactic PMMA: 1. Thermal and mechanical properties of stereocomplexes

Abstract A novel thermoplastic elastomer consisting of a triblock copolymer (MBM) with outer syndiotactic poly(methyl methacrylate) (sPMMA) blocks associated to an inner polybutadiene (PBD) block has been modified by stereocomplexation with isotactic PMMA (iPMMA). Solution cast films of stereocomplexes have been analysed by thermal analysis as a function of the iPMMA/sPMMA (i/s) mixing ratio and the solvent used for the film casting. Although self-aggregation of iPMMA is currently observed, this phenomenon does not occur in solvent cast films of iPMMA with the MBM copolymers. Extent of complexation depends on the i/s mixing ratio and the casting solvent. At a constant i/s ratio, molecular weight of iPMMA has no significant effect on the extent of stereocomplexation. Thermal stability of the stereocomplexes is only affected by the casting solvent, in contrast to tensile strength which is greatly influenced by the mixing ratio of the two PMMA stereoisomers. Tensile strength is increased when increasing amounts of iPMMA are blended with a triblock copolymer of low PMMA content (e.g. 12%). In case of triblocks of high PMMA content (ca. 30% or higher), a low i/s ratio ( 1 4 ) increases the tensile strength, whereas a high i/s mixing ratio ( 1 2 ) results in decreasing tensile strength. The same trend is observed for blends of sPMMA-polystyrene (PS) PBD-PS-sPMMA (MSBSM) pentablock copolymers with iPMMA.

Difunctional initiator based on 1,3-diisopropenylbenzene. 7. Mechanical and thermal properties of new butadiene-based thermoplastic elastomers

Abstract Mechanical and thermal properties of SBS thermoplastic elastomers, in which S stands for polystyrene and B for polybutadiene, can be remarkably improved through end-capping by syndiotactic poly(methyl methacrylate) sequences. Furthermore, the upper service temperature of these sPMMA teleblock copolymers can also be enhanced by blending with isotactic PMMA so that the rubbery PBD soft segments are connected to high-melting stereocomplexed hard segments. The factors which affect the mechanical and thermal properties of these novel thermoplastic elastomers have been extensively investigated.

New polybutadiene-based thermoplastic elastomers: synthesis, morphology and mechanical properties

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 observatio...