Triblock Copolymer Based Thermoreversible Gels. 3. Effect of Stereocomplexation with iPMMA

Abstract

Thermoreversible gelation of syndiotactic poly(methyl methacrylate) (sPMMA)−polybutadiene (PBD)−sPMMA, triblock copolymers in o-xylene has been studied in the presence of isotactic PMMA (iPMMA) in a large range of syndio/iso mixing ratio (s/i). Differential scanning calorimetry (DSC) shows that two types of association contribute to the gel formation, i.e., the self-aggregation of the sPMMA outer blocks and the stereocomplexation of the sPMMA outer blocks with iPMMA. At low iPMMA contents (s/i = 30/1), self-association of the outer blocks accounts for the gelation process, although stereocomplexation occurs. Stereocomplexation becomes the dominant gelation mechanism at a high enough iPMMA content (s/i = 2/1). Thus, gelation is observed at a copolymer concentration as low as 1 wt %. The time dependence of the storage (G‘) and loss (G‘‘) moduli has been measured in the 0.08−1Hz frequency range in order to probe the gelation process. At the gel point, where the loss angle (tan δc = G‘‘/G‘) is independent of ...