Newly Synthesized Urethane Monomers: co-polymerizations with BisGMA and BisEMA

Objectives: With the longer-term goal of designing new heterogeneous copolymer systems, the current study focuses on development of new mono- and di-methacrylate monomers with extended aliphatic structures. The relationship between monomer structure and its homo- or co-polymerization kinetics is examined here. Methods: Several versions of isostearyl methacrylate (ISMA), which differ in degree of branching and whether a urethane linkage was included, were synthesized. A urethane-containing analog of lauryl methacrylate (LMA) was also prepared. Crosslinkable monomers, batyl dimethacrylate (BDMA) and ricinoleyl dimethacrylate (RDMA) were synthesized and both were semi-crystalline due to extended aliphatic structures. Photo-activated homopolymerizations of the experimental monomers and their co-polymerizations with equimolar amounts of BisGMA or ethoxylated bisphenol A dimethacrylate (BisEMA) were monitored by real-time near-infrared spectroscopy and conducted at 60°C, at which point all the monomers are in the liquid state, and at room temperature (RT). Results: Introduction of urethane functionality into LMA enhanced the maximum rate of reaction (RPmax) and final conversion. While many of the homopolymers reached 100% conversion at 60°C, only the urethane ISMA with the low degree of branching reached quantitative conversion at RT. At 60°C, nearly all the co-polymerizations with BisEMA proceeded to complete conversion, whereas BisEMA alone reached 82.2±2.0%. The highly branched non-urethane ISMA could not mix with BisGMA even at elevated temperature; otherwise, the final conversion values for the BisGMA copolymers ranged from ~90-98% with BisGMA homopolymer achieving 64.9±2.0%. The BisGMA/BDMA copolymerization produced the highest RPmax. At RT, copolymerizations with BisEMA yielded conversions of 80-98% with the BisEMA homopolymer reaching 65.8±0.4%. With BisGMA, which only reached 38.1±1.0% conversion alone, copolymer conversion was improved considerably to 70-80%. Conclusions: Presence of urethane functionality increases monomer reactivity and compatibility with BisGMA. Aliphatic branching reduces co-monomer compatibility while restricting crystallization potential. The experimental monomers, including the dimethacrylates, contribute to high conversion co-polymers. Support: NIH/NIDCR-2R01DE14227