Bulk Structure and Rheological Properties of Poly (macromonomer)s Associate with Multibranched Structure of High Branch Density

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Dynamic shear moduli of multibranched polystyrenes were measured as functions of frequency and temperature using a parallel-plate rheometer to investigate the effect of the multibranched structure of polymer molecules on the rheological properties. The multibranched polystyrenes are poly(macromonomer)s of omega-methacryloyloxyethyl polystyrene macromonomers (MA-PSt)s and statistical copolymers of the MA-PSt with methyl methacrylate (MMA) monomer. The dynamic shear moduli of a linear polystyrene were also measured under the same conditions for comparison. The master curve of the storage dynamic shear modulus G' for the poly(macro-monomer)s did not show the so-called plateau region and the G' gradually decreased from the edge of the glass transition region to the terminal zone. In this region, the loss modulus G" was always larger than G'. The plateau region became clear in the copolymers with less branch density. These results indicate that the intermolecular chain entanglement is restricted in the poly(macromonomer) system due to the multibranched structure of high branch density. Film forming properties of the branched polymers such as brittleness are consistent with the results of rheological properties, thus, can be ascribed to the absence of the intermolecular chain entanglement.