DYNAMIC-MECHANICAL ANALYSIS OF AMORPHOUS-PHASE ORGANIZATION IN ACRYLIC POLYMERS

Factors affecting polymer network organization were studied in highly crosslinked acrylics of the type used in dental adhesive resins. The v ariables tested were comonomer content and processing conditions. BisE MA 2,-bis[4-(2-methacryloyloxyethoxy)-phenyl]propane) and BisEMA + TEG DMA (triethyleneglycol dimethacrylate) were cured with and without 25% comonomer. Comonomers had characteristics that are expected to influe nce intrachain organization in amorphous phases: TEGDMA, crosslinking; methyl methacrylate (MMA), monomer conversion; isobornyl methacrylate (IBM), low cure shrinkage; tetrahydrofurfuryl methacrylate (THFM), an tiplasticization. Dynamic mechanical analysis temperature scans were r un at 0.1 Hz 2h or 24h after ambient cure, or 24h postcure after heati ng at 75 degrees or 125 degrees C. After 24h, tan delta maxima occurre d in ranges centering on approximately - 30 degrees, 75 degrees and 15 0 degrees C (T-g). Heating at 125 degrees C nearly eliminated all peak s except T-g, reduced tan delta peaks and increased T-g by 0-14 degree s. T-g increased in the order: TEGDMA>125 degrees C>IBM>MMA>75 degrees C>2h>24h>THFM. The ability to crosslink, and postcure heating at 125 degrees C, were the more important factors found to increase intrachai n organization in amine-promoted, unfilled BisEMA resins of the type u sed in dental sealants, luting cements and bulk-filling resin composit e materials.