Jian Ming Yu

Triblock copolymer based thermoreversible gels. 1 : Self-association of sPMMA end-blocks in o-xylene and viscoelasticity of the gels

Abstract Syndiotactic poly(methyl methacrylate) (sPMMA) polybutadiene (PBD)-sPMMA triblock copolymers, or MBM, have been studied in the presence of o -xylene which is a selective solvent for the central PBD block. Syndiotactic PMMA is known to self associate in o -xylene. The central PBD sequence does not prevent the self-association of sPMMA from occurring. Actually, this phenomenon contributes to the stability of the gels formed at room temperature. An endotherm is observed at 35°C, which is responsible for a gel-sol transition. The original solutions have been heated up to 80°C and then rapidly cooled down below 35°C and maintained at 10, 20 and 25°C respectively. The self-association of the sPMMA outer blocks, and thus the liquid-solid transition, have been studied at each of these temperatures. Dependence of the gel viscosity on frequency and temperature effects on viscoelasticity has also been investigated.

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.

Poly[glycidyl methacrylate(GMA)/methylmethacrylate(MMA)‐b‐butadiene(B)‐b‐GMA/MMA] reactive thermoplastic elastomers: Synthesis and characterization

New block copolymers of the ABA type, where B stands for polybutadiene (PBD) and A for polyglycidylmethacrylate(PGMA), poly(methylmethacrylate(MMA)-co-GMA) and PMMA-b-PGMA, respectively, have been successfully synthesized by using the diadduct of tert-butyllithium (tert-BuLi) to meta-diisopropenylbenzene (m-DIB) as a difunctional initiator. The PBD midblock has been synthesized in a cyclohexane/diethylether (100/6, v/v) mixture at room temperature, whereas the methacrylate outer blocks have been synthesized in a cyclohexane/diethylether/THF (100/6/150, v/v/v) mixture at −78°C. Block copolymers of a very narrow molecular weight distribution (1.10) have been analyzed by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and tensile testing. These materials are phase separated and can exhibit tensile strength up to 22 MPa together with very high elongation at break (1500%).