Department of Chemical and Biological Engineering, Engineering Center, ECCH 111, University of Colorado, Boulder, CO 80309-0424, USA.
Dent Mater. 2010 Oct;26(10):1010-6. doi: 10.1016/j.dental.2010.06.007. Epub 2010 Jul 22.
The aim is to demonstrate significant polymerization shrinkage stress reduction in model resins through incorporation of addition-fragmentation chain transfer moieties that promote network stress accommodation by molecular rearrangement. Monomers containing allyl sulfide linkages are incorporated to affect the shrinkage stress that arises during photopolymerization of model resins that contain an initiator and dimethacrylates. Radical-mediated allyl sulfide addition-fragmentation is enabled during polymerization. We hypothesize that allyl sulfide incorporation into methacrylate polymerizations promotes stress relaxation by enabling network adaptation.
A 1:2 mixture of tetrathiol and allyl sulfide-containing divinyl ethers is formulated with glass-forming dimethacrylates and compared to controls where the allyl sulfide is replaced with a propyl sulfide that is incapable of undergoing addition-fragmentation. Simultaneous shrinkage stress and functional group conversion measurements are performed. The T(g) is determined by DMA.
Increasing allyl sulfide concentration reduces the relative stress by up to 75% in the resins containing the maximum amount of allyl sulfide. In glassy systems, at much lower allyl sulfide concentrations, the stress is reduced by up to 20% as compared to propyl sulfide-containing systems incapable of undergoing addition-fragmentation chain transfer.
Shrinkage stress reduction, typically accompanying free-radical polymerization, is a primary focus in dental materials research and new product development. Allyl sulfide addition-fragmentation chain transfer is utilized as a novel approach to reduce stress in ternary thiol-ene-methacrylate polymerizations. The stress reduction effect depends directly on the allyl sulfide concentration in the given ternary systems, with stress reduction observed even in systems possessing super-ambient T(g)s and low allyl sulfide concentrations.
本研究旨在通过引入可通过分子重排促进网络应力适应的加成-断裂链转移基团，来降低模型树脂中的显著聚合收缩应力。将含有烯丙基硫醚键的单体引入到含有引发剂和二甲基丙烯酸酯的模型树脂的光聚合中，以影响收缩应力。聚合过程中可实现自由基介导的烯丙基硫醚加成-断裂。我们假设，将烯丙基硫醚引入甲基丙烯酸酯聚合中，可通过促进网络适应性来实现应力松弛。
用四硫醇和含烯丙基硫醚的二乙烯基醚以 1:2 的比例与玻璃化形成的二甲基丙烯酸酯配制成混合物，并与对照组进行比较，对照组中的烯丙基硫醚被不能进行加成-断裂的丙基硫醚取代。同时进行收缩应力和官能团转化率的测量。通过 DMA 确定 Tg。
在含有最大量烯丙基硫醚的树脂中，增加烯丙基硫醚的浓度可使相对应力降低多达 75%。在玻璃态体系中，与不能进行加成-断裂链转移的含丙基硫醚体系相比，在低得多的烯丙基硫醚浓度下，应力降低了 20%。
收缩应力的降低是牙科材料研究和新产品开发的主要关注点，通常伴随着自由基聚合。烯丙基硫醚加成-断裂链转移被用作一种降低三元硫醇-烯-甲基丙烯酸酯聚合中应力的新方法。应力降低效果直接取决于给定三元体系中的烯丙基硫醚浓度，即使在具有超环境 Tg 和低烯丙基硫醚浓度的体系中也观察到了应力降低。
