Photo-Reactive Nanogel as a Means to Tune Properties during Polymer Network Formation.
Photo-Reactive Nanogel as a Means to Tune Properties during Polymer Network Formation.
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DOI：
10.1039/c3py00870c
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发表时间：
2014-01-07
影响因子：
4.6
通讯作者：
Stansbury JW
中科院分区：
文献类型：
--
作者：
Liu J;Rad IY;Sun F;Stansbury JW
通过可逆加成-断裂链转移(RAFT)过程合成了具有光引发剂功能的光反应纳米凝胶。在没有额外的自由引发剂的情况下，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粒子的第二单体(即二甲基丙烯酸酯)的聚合。由于RAFT官能团的存在以及所有引发点最初都位于纳米凝胶结构内的事实，可以通过对从纳米凝胶到本体基质的聚合进行排序来延迟凝胶化。在纳米凝胶填充树脂体系的聚合过程中，凝胶转化率从传统的链生长聚合的约2%逐渐延迟到含有20wt%纳米凝胶添加剂的相同单体的18%。由于网络形成机制的改变，纳米凝胶修饰体系的应力发展也有明显的延迟，最终应力大大降低。与含有均匀分布的自由引发剂的无纳米凝胶的二甲基丙烯酸酯对照相比，纳米凝胶含量大于10wt%的光聚合物保持了弯曲模量和机械强度的结果。光反应纳米凝胶似乎有一个关键的颗粒间距，它提供了有效的光聚合，同时提供了延迟的凝胶和大量的应力降低。
Photo-reactive nanogels with an integrated photoinitiator-based functionality were synthesized via 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.