Department of Chemistry and Macromolecules Innovation Institute , Virginia Tech , Blacksburg , Virginia 24061 , United States.
ACS Appl Mater Interfaces. 2018 Aug 8;10(31):26662-26668. doi: 10.1021/acsami.8b08480. Epub 2018 Jul 31.
Dynamically cross-linkable bottlebrush polymer adhesives were synthesized by the grafting-from strategy through a combination of ring-opening metathesis polymerization (ROMP) and photoiniferter polymerization. A norbornene-containing trithiocarbonate was first polymerized by ROMP to form the bottlebrush polymer backbone; this was followed by blue-light-mediated photoiniferter polymerization of butyl acrylate initiated by the poly(trithiocarbonate) to form the bottlebrush polymer. This strategy afforded well-defined bottlebrush polymers with molar masses in excess of 11 000 kg/mol. For un-cross-linked bottlebrush polymers, 180° peel tests revealed a cohesive failure mode and showed similar peel strengths (∼30 g/mm) regardless of the backbone polymer degree of polymerization (DP). The bottlebrush polymers were then treated with butylamine to remove the trithiocarbonate, liberating thiols on each side-chain terminus. In the presence of oxygen, these thiols readily cross-linked via disulfide bond formation. The cross-linked bottlebrush polymers with a backbone DP of 400 showed a greater than sixfold improvement in peel strength, whereas those with a backbone DP of 100 exhibited a twofold enhancement compared with un-cross-linked samples along with a change to adhesive failure. Triphenylphosphine readily reduced the disulfide bonds, effectively removing all cross-links in the bottlebrush network and allowing for recasting of the adhesive, which showed similar adhesive and rheological properties to the original un-cross-linked samples.
通过开环易位聚合 (ROMP) 和光引发剂聚合相结合的方法，采用接枝法合成了可动态交联的瓶刷聚合物胶黏剂。首先通过 ROMP 聚合含降冰片烯的三硫代碳酸酯，形成瓶刷聚合物的主链；随后，在蓝光的介导下，通过聚（三硫代碳酸酯）引发丙烯酸丁酯进行光引发剂聚合，形成瓶刷聚合物。该策略得到了具有超过 11000kg/mol 摩尔质量的定义明确的瓶刷聚合物。对于未交联的瓶刷聚合物，180°剥离测试显示出内聚失效模式，并且无论主链聚合物的聚合度 (DP) 如何，剥离强度（约 30g/mm）相似。然后用丁胺处理瓶刷聚合物以去除三硫代碳酸酯，在每个侧链末端释放硫醇。在氧气存在下，这些硫醇通过二硫键形成很容易交联。具有 400 的 DP 的交联瓶刷聚合物的剥离强度提高了六倍以上，而 DP 为 100 的交联瓶刷聚合物与未交联的样品相比，剥离强度提高了两倍，并且发生了从内聚到黏附的失效模式转变。三苯基膦很容易还原二硫键，有效地去除瓶刷网络中的所有交联，并允许重新铸造胶黏剂，其表现出与原始未交联样品相似的黏附性和流变性能。
