Abstract
Copolymers of polyester were made with two spiro orthocarbonates: cyclohexane and cyclohexene. They were also used to make unidirectional carbon fibre composites, and the properties of polymers and composites were compared with those made with a low profile additive (a copolymer of methyl and allyl methacrylates). The copolymers were not effective in reducing the shrinkage stress of the resin, except through a reduction in glass transition temperature. They gave composites with poor properties. The low profile additive was effective in reducing the shrinkage volume, but at the cost of a reduction in tensile strength. It did not affect the shrinkage stress very much, and did not have much effect on composite properties. Thus, while it is advantageous to use low profile additives with reinforced polyesters, it is not beneficial to use spiro orthocarbonate expanding monomers. Overall, the three papers in this series strongly suggest that, while controlling shrinkage stress may well be useful, it cannot be realized to any useful extent by using expanding monomers.
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