Effect of substituents in the styrene ring on the dynamic mechanical relaxations of a styrene‐crosslinked unsaturated polyester resin

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Abstract
The dynamic mechanical properties of a series of polyester resins made from a maleic/phthalic anhydride‐based unsaturated polyester crosslinked with each of styrene, 4‐methyl styrene, 4‐ethyl styrene, 4‐n‐butyl styrene, 4‐isopropyl styrene, tertiary butyl styrene, 4‐chlorostyrene, and 3,4‐dichlorostyrene were studied. The order of the α transition temperatures was as expected from that for the homopolymers, except in the case of the chlorostyrenes, for which dipolar interactions with the polyester chain may be important. The styrene bridges appeared to be involved in a steric interaction (and in the case of the chlorostyrenes, a dipolar interaction) with the β relaxing ester species. It is suggested that both the γ and γ′ relaxations involve similar interactions between the matrix and the relaxing moieties. For the 4‐n‐butyl styrene resin, an additional relaxation below −170°C was observed, and is ascribed to relaxation of the n‐butyl group.