Liu Jiancheng, Rad Ima Y, Sun Fang, Stansbury Jeffrey W
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80309, United States.
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, PR China ; College of Science, Beijing University of Chemical Technology, Beijing 100029, PR China.
Polym Chem. 2014 Jan 7;5(1). doi: 10.1039/C3PY00870C.
Photo-reactive nanogels with an integrated photoinitiator-based functionality were synthesized a Reversible Addition-Fragmentation Chain Transfer (RAFT) process. Without additional free initiators, this nanogel is capable of radical generation and initiating polymerization of a secondary monomer (i.e. dimethacrylate) that infiltrates and disperses the nanogel particles. Due to the presence of RAFT functionality and the fact that all initiating sites are initially located within the nanogel structure, gelation can be delayed by sequencing the polymerization from the nanogel to the bulk matrix. During polymerization of a nanogel-filled resin system, a progressive delay of gelation conversion from about 2 % for conventional chain growth polymerization to 18 % for the same monomer containing 20 wt% nanogel additive was achieved. A significant delay of stress development was also observed with much lower final stress achieved with the nanogel-modified systems due to the change of network formation mechanics. Compared with the nanogel-free dimethacrylate control, which contained uniformly distributed free initiator, the flexural modulus and mechanical strength results were maintained for the photopolymers with nanogel contents greater than 10 wt%. There appears to be a critical interparticle spacing of the photo-reactive nanogel that provides effective photopolymerization while providing delayed gelation and substantial stress reduction.
通过可逆加成-断裂链转移（RAFT）过程合成了具有基于光引发剂的集成功能的光反应性纳米凝胶。无需额外的游离引发剂，这种纳米凝胶能够产生自由基并引发渗透和分散纳米凝胶颗粒的第二单体（即二甲基丙烯酸酯）的聚合。由于存在RAFT功能且所有引发位点最初都位于纳米凝胶结构内，通过对从纳米凝胶到本体基质的聚合进行排序，可以延迟凝胶化。在纳米凝胶填充树脂体系的聚合过程中，实现了凝胶化转化率的逐步延迟，从传统链式增长聚合的约2%延迟到含有20 wt%纳米凝胶添加剂的相同单体的18%。由于网络形成机制的变化，还观察到应力发展的显著延迟，纳米凝胶改性体系的最终应力要低得多。与含有均匀分布游离引发剂的不含纳米凝胶的二甲基丙烯酸酯对照相比，纳米凝胶含量大于10 wt%的光聚合物的弯曲模量和机械强度结果得以保持。似乎存在一个光反应性纳米凝胶的临界颗粒间间距，它能提供有效的光聚合，同时延迟凝胶化并大幅降低应力。
