光引发接枝聚合调控水凝胶表面疏水性能

利用光引发表面聚合的方法在水凝胶表面接枝疏水基团，赋予水凝胶表面疏水性能，其原理是基于TypeⅡ型光引发剂的夺氢光引发机理，夺取水凝胶高分子链中叔胺邻位碳原子上的氢原子，使得该碳原子成为自由基，引发丙烯酸十八酯增长聚合，从而在水凝胶表面以化学键铆接上一层疏水的高分子层。通过红外（FT-IR）、接触角和水滴渗入时间测试，探讨了光引发接枝条件对水凝胶表面疏水性能的影响，结果表明：在水凝胶中加入含有叔胺基团的甲基丙烯酸二甲氨基乙酯作为TypeⅡ型光引发的助引发剂和接枝位点，与疏水单体丙烯酸十八酯发生聚合反应可以形成稳固的疏水层，有效增强水凝胶的疏水性；采用N，N'-亚甲基双丙烯酰胺（BIS）交联剂能使疏水层形成交联网络结构，提高接枝层的致密性和疏水性，对水滴的渗入起到更好的阻碍作用。

Grafting of a hydrophobic layer on hydrogel surfaces via Type II photopolymerization

Hydrogels, which usually comprise hydrophilic polymers and water, are generally able to act as biomaterials, due to their high water content, soft nature, and 3D porous structure. However, the surface of many biological tissues is hydrophobic. In this work, a hydrophobic polymer layer was grafted on the surface of a hydrogel through Type Ⅱ photopolymerization in an attempt to increase the hydrophobic properties of the hydrogel surface. Isopropyl thioxanthone (ITX) is a Type Ⅱ photoinitiator, with an excitation wavelength of 405 nm. ITX exhibits no triggering activity but abstracts H atoms from amines and the amines are the final radicals initiating photopolymerization. Through this photo-grafting method, a hydrophobic polymer, poly(octadecyl acrylate) was grafted on the surface of a hydrogel. A cross-linking polymer layer can be formed by using BIS cross-linking agent, which increases compactness and the hydrophobic properties of the polymerized surface, thus effectively blocking infiltration of water drops. The conversion of the photopolymerization was monitored by FT-IR and the effect of varying the photo-grafting conditions on the surface hydrophobic properties of the hydrogel was studied by the measuring the contact angle and infiltration time of water drops. The results show that the layer of poly(octadecyl acrylate) effectively improves the hydrophobic properties of the hydrogel.