Three series of neat resins, based on methacrylates or dimethacrylates modified with 1-[3-(methacryl)propyl]-3,5,7,9,11,13,15-heptacyclopentylpentacyclo[9.5.113,9.15,15.17,13]octasiloxane (Methacryl-POSS or POSS-MA), were evaluated. Incorporation of POSS-MA into the polymeric matrix was accomplished in three ways: (a) resins series I was formulated with one-pot copolymerization of a bis-GMA/diluent monomer with POSS-MA; (b) the copolymer of 2-hydroxylethyl methacrylate (HEMA) and POSS-MA, with a weight ratio of 1 : 1, was first made, then the copolymer hydroxyl groups were converted into methacrylate groups to get a macromer; finally the macromer was copolymerized with bis-GMA/diluents to formulate the second series of neat resins; (c) copolymer of POSS-MA and t-butyl methacrylate (t-BMA) or 2-ethylhexyl methacrylate (EHMA) were first made, then they were combined with a mixture of bis-GMA and the corresponding diluent to make the third kind of neat resins. The amount of POSS incorporated into the neat resin matrix was controlled at 5, 10 and 15 wt%. Incorporating only 5 wt% substantially reduced the shrinkage of the prepared neat resins. The percentage of methacrylate-functionalized POSS monomer in the bis-GMA/diluent base, was compared to neat resins prepared without the POSS. The mechanical properties of neat resin having POSS were improved for approaches (b) and (c), but remained at the same level as the neat resins without POSS for approach (a). The results show that miscibility between the POSS component and the matrix, especially the diluent, plays a very important role in the improvement of the properties of the formulated thermosets. Copyright © 2001 John Wiley & Sons, Ltd.
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