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

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 selfassociation 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.