Delayed Gelation Through Chain-Transfer Reactions: Mechanism For Stress Reduction In Methacrylate Networks.

Chain-transfer reactions from thiols to methacrylates are expected to delay gelation and possibly reduce stress at the bonded interface of dental restorations. Thiol additives with varying structures were combined with a dimethacrylate commonly used in dental materials. Polymerization stress/modulus development were monitored by a tensometer/rheometer, respectively, both coupled with RT-NIR. For all thiol-modified materials, conversion and modulus were 5-25 % higher than the control, and maximum reaction rate was 25-50 % lower. Gel point conversions were 12-22 % (control=5 %), and deceleration was observed at later stages in conversion (30-60 %; control=15 %). Consequently, even with increased conversion/modulus, stress values were either equal or reduced compared to the control. This approach does not require any modification in the bonding/photoactivation procedures, and seems promising for stress management not only in polymeric dental materials, but also for other applications of glassy, crosslinked photopolymers, as long as thiol volatility is addressed.