We measured dynamic shear moduli of poly(macromonomer)s of an increased backbone chain length and those bearing branch chains of increased branch length up to the critical molecular weight for the intermolecular chain entanglement, M c, of a linear polystyrene as functions of frequency and temperature using a parallel-plate rheometer. The poly(macromonomer)s were prepared from ω-methacryloyloxyethyl polystyrene macromonomers (MA-PSt)s or ω-vinylbenzyl polystyrene macromonomers (VB-PSt)s. It was revealed that a great increase in the backbone length caused the poly-(macromonomer)s to show a weak rubbery plateau region in the master curves of the storage modulus G′, where the molecular weights of the branch chains were smaller than Mc. The plateau modulus was much lower than that observed for the linear polystyrenes. On the other hand, the poly(macromonomer)s with polystyrene branches are nearly equal to the Mc, and a very short backbone chain showed a clear rubbery plateau region. The glass transition temperature of poly(macromonomer)s in the region without the chain entanglement decreased with decreasing branch length but remained almost constant over the wide range of the backbone length.

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