纤维素-树脂酸接枝共聚物大分子结构设计机理及性能研究

Application of cellulose on release material largely relies on the macromolecular architecture design. In our previous work, resin acid monomer was confirmed to polymerize by controlled/living polymerization and used to synthesized the star-shaped resin acid polymer-grafted lignin composites by "grafting from" ATRP. The results indicated that the structure and properites of resin acid and ligin could be combined by atom transfer radical polymerization (ATRP). Herein in this proposed research project, cellulose and ethyl cellulose are to be used as starting material and transformed into ATRP macrointiator in first step respectively. And then resin acid, as the most important renewable product with its characteristic bulky hydrophenanthrene structure obtained from pine trees, is to be ultilized as an modifying agent. Three vinyl monomers derived from resin acid will be sythesized according to our previous work and employed to prepare cellulose-(resin acid) graft copolymer and ethyl cellulose-(resin acid) graft copolymer by ATRP. The mophologies of these graft copolymers are expected to be bulky polymer brush due to the hydrophenanthrene structure of resin acid based monomer. The macromolecular design principles for these graft copolymers will be intensively explored. In addition, effects of number of ATRP initiate site, resin acid's bulky hydrophenanthrene structure, side chain length and structure of resin acid based monomer on the physical properties of these graft copolymers including solubility, crystallization, thermal and mechanical properties, and self-assembly capability will also be evaluated in order to reveal the correlation between micro structure and properties. For further analysis of the effect of resin acid's bulky hydrophenanthrene structure on the morpology and physical properties of cellulose-(resin acid) composite, resin acid will also be introducted into cellulose by conventional esterification reactions. We believe that the synthetic strategy in our research can be utilized in the preparation of other novel polysaccharide based biomaterials by combining resin and its functional derivatives.

纤维素大分子结构设计是其在缓释材料上的应用基础。前期工作采用原子转移自由基聚合（ATRP）聚合方法合成了三维星状木质素-树脂酸共聚物，显示很好的结构控制性。本项目将在此基础上，以纤维素和乙基纤维素为原料，先合成基于纤维素（乙基纤维素）大分子引发剂，然后采用ATRP聚合方法将具有三环菲结构的树脂酸基单体接到纤维素（乙基纤维素）中，制备出巨型刷状纤维素（乙基纤维素）-g-树脂酸接枝共聚物，并研究此类接枝共聚物分子结构的控制机理。与此同时，采用直接酯化法将树脂酸与纤维素复合，研究引发剂引发点数量、树脂酸的三环菲骨架、侧链长度和树脂酸单体结构对纤维素（乙基纤维素）-g-树脂酸接枝共聚物结晶度、溶解性和疏水性等物理性能以及自组装后微观形貌的影响，揭示纤维素（乙基纤维素）-g-树脂酸接枝共聚物微观结构与宏观性能的关系，为进一步探讨树脂酸及其功能性衍生物在纤维素类生物质材料中的应用奠定理论基础。

纤维素和树脂酸都是重要的可再生资源，随着石油资源的日益枯竭和对于环境污染问题的日益关注，高效开发和利用可再生资源变得尤为重要。本项目以纤维素（乙基纤维素）和树脂酸基单体为原料，采用原子转移自由基聚合（ATRP）反应将树脂酸基单体与纤维素（乙基纤维素）大分子复合，制备出巨型刷状纤维素（乙基纤维素）-g-树脂酸接枝共聚物，研究引发剂引发点数量、树脂酸的三环菲骨架、侧链长度和树脂酸单体结构对纤维素（乙基纤维素）-g-树脂酸接枝共聚物结晶度、溶解性和疏水性等物理性能以及自组装后微观形貌的影响，研究纤维素（乙基纤维素）-g-树脂酸接枝共聚物微观结构与宏观性能的相互关系。研究发现（1）纤维素ATRP引发剂引发点的数量可以通过制备过程中2-溴代异丁酰溴与纤维素上羟基比例来调控；（2）受树脂酸结构的影响，过高的引发点密度降低了树脂酸单体接枝纤维素的接枝率；（3）树脂酸基单体ATRP聚合法接枝纤维素过程中，接枝共聚物的分子量随单体转化率的增加呈线性增长，接枝共聚物的分子结构可控；（4）激光光散射（LLS）测试证实，乙基纤维素接枝共聚物在四氢呋喃中呈蠕虫状或是棒状构象；（5）纤维素（乙基纤维素）-g-树脂酸接枝共聚物的玻璃化转变温度可以通过树脂酸基单体的结构进行调节；（6）树脂酸结构引入纤维素侧链赋予纤维素刷状共聚物优越的成膜性能、疏水性能和紫外吸收性能；（7）柔性单体（如丙烯酸丁酯和源于自天然脂肪酸的甲基丙烯酸十二烷基酯）的引入，赋予纤维素-g-树脂酸接枝共聚物热塑性弹性性能；（8）通过调整侧链聚合物单体组成可以调整接枝共聚合物的玻璃化转变温度（-60-50℃）；（9）拉伸应力-应变和蠕变柔量测试显示了接枝共聚物具有良好的力学性能，当单体：引发剂投料摩尔比为1000：1时，接枝聚合物样品屈服应力在0-2.5 MPa之间，杨氏模量最高为99 MPa，弹性应变之间恢复值在50%至85%，断裂时都有大的应力形变（500%或以上），具有弹性体材料特征;（10）AFM、SAXS显示聚合物没有相分离；通过本项目的研究，揭示了纤维素与树脂酸基聚合物复合分子微观结构和宏观弹性性能的关系，并发现纤维素基弹性材料在一些领域具有部分替代石油基产品的潜力，项目研究所取得的成果将为开发新型纤维素基和树脂酸基材料提供理论依据与技术支持。