光固化收缩应力和聚合动态的耦合测试研究

Coupled tests of shrinkage stress and polymerization kinetics during photopolymerization

光聚合反应是一种复杂的物理化学反应。在特定光照下,光引发剂分解为活性自由基,引发液态聚合物单体进行链式聚合反应,形成固态高分子聚合物。在聚合过程中,随着聚合转化率(已反应单体占总单体的比例)的增加,材料的体积发生一定程度的收缩,致使材料内部和界面上产生收缩应力。在实际应用中,收缩应力会造成界面的破坏和材料的断裂等问题,因此探究转化率与收缩应力之间的动态关系,进而控制收缩应力的发展至关重要。本文基于近红外光谱测试原理和悬臂梁原理,搭建了光聚合反应中转化率和收缩应力的实时耦合测试平台(测试频率可达10Hz)。将牙科复合树脂作为实验材料,研究了不同浓度颗粒填充对光固化树脂聚合反应的影响,发现填充物浓度的增加提高了复合树脂的转化率,进而增大了体系的收缩应力。收缩应力/聚合动态的耦合测试平台可为研究光聚合动态过程提供有力的实验工具,其实验数据也可为揭示收缩应力发展的动态机制和优化光聚合产物的力学性能提供参考。

Photopolymerization is a complex chemical and physical reaction.Under a specific light irradiation,photoinitiators decompose into active free radicals,which initiate the polymer chain growth and transform liquid monomers into solid polymer products.During the photopolymerization process,as the degree of conversion(i.e.,the ratio of reacted monomers to the total monomers)increases,the volume of the material decreases,leading to the development of shrinkage stress within the material and at the material/substrate interface.In practice,the shrinkage stress can induce adverse effects such as interfacial damage and material fracture.Therefore,in order to effectively control the development of the shrinkage stress,it is crucial to explore the dynamic correlations between the degree of conversion and the shrinkage stress.In this study,we have built a cantilever-beam based setup combined with in-situ near-infrared spectroscopy and realized simultaneous and synchronous measurement of the degree of conversion and shrinkage stress during photopolymerization.Both parameters can be measured in real time at a high frequency of up to 10Hz.By adopting typical dental resins(Bis-GMA/TEGDMA compound)as the testing materials,we have studied the effects of incorporating nano-silica nanoparticles on the polymerization kinetics of the dental resins.The degree of conversion of the composite resin is found to increase with the increase of the nanoparticle content,which consequently leads to an increase in the elastic modulus and hardness.As a result,the final shrinkage stress of the composite also increases as more nanoparticles are incorporated into the resins.The coupled testing setup for the shrinkage stress and polymerization kinetics is believed to provide a powerful tool for studying the dynamics of photopolymerization.Experimental data captured from this setup are helpful in revealing the mechanisms of the shrinkage stress development and can guide the design of photopolymers with superior mechanical properties.