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. (C) 2011 Elsevier Ltd. All rights reserved.