木质纤维素基可降解高分子的合成与性能研究

Renewable and degradable polymers is key to address oil depletion and ‘white pollution’. Even though lignocellulose is abundant and there are many types of lignocellulose-derived aldehydes, its usage is limited due to the lack of polymerizable monomers and highly efficient polymerization methods. Based on the applicant’s extensive work on the coordination ring-opening polymerization, we noticed that the distinctive features of a good catalyst for coordination ring-opening polymerization are applicable to Tishchenko aldehyde disproportionation reaction — a subtle balance between electrophilic and nucleophilic. In this project, we plan to design and synthesize a range of lignocellulose-derived dialdehydes. Then, a range of organometallic catalysts will be prepared and screened based on their catalytic activity on Tishchenko polymerization. Thereafter, the reaction mechanism will be investigated to establish a primary theory. Highly active catalysts will then be applied to polymerize lignocellulose-derived dialdehyde monomers to afford renewable and degradable polyesters. Additionally, copolymerization with other renewable monomers, such as epoxides, cyclic anhydrides and lactones, will be conducted to investigate the selective catalysis upon a mixed monomer feedstock. This is to afford renewable polyesters with various chain architecture (e.g. block, alternative and gradient, etc.) as well as demonstrate the feasibility of modification on material properties, aiming to produce renewable and degradable polymers with comparable material properties to conventional petro-based polymers. The life cycle of promising polymer candidates will be assessed to provide preliminary data on sustainability. This project will provide approaches and theories on the synthesis of renewable monomers, catalyst design, and the mechanism of Tishchenko polymerization as well as examples of renewable and degradable polymeric materials.

可再生可降解高分子对于应对石油短缺及‘白色污染’问题具有重要意义。木质纤维素储量丰富且其醛类衍生物种类繁多，然而缺乏可聚合的单体和高效的聚合方法。申请人前期研究表明，配位开环聚合对有机金属催化剂的要求与季先科二醛歧化成酯反应类似，即要求活性中心既有亲电性又有亲核性。本项目拟设计并合成一系列木质纤维素基二醛类单体，构建并筛选能高效催化季先科聚合的有机金属催化剂并阐明聚合机理，然后利用这些单体制备可再生可降解聚酯。同时，与其他环氧、环酸酐和内酯类可再生单体共聚，研究催化剂在多元单体共聚时的选择性，制备多种链结构（例如，嵌段、交替及梯度等）的可再生聚酯，并实现对材料性能的调控，以设计出在材料性能上可替代石油基高分子的可再生、可降解高分子，并采用生命周期评估的方法对其可持续性进行初步的评估。该项目可望在单体和催化剂设计、聚合机理等方面为合成可再生可降解高分子材料提供理论基础及实际范例。

可再生可降解高分子对于应对石油短缺及‘白色污染’问题具有重要意义。木质纤维素储量丰富且其醛类衍生物种类繁多，然而缺乏可聚合的单体和高效的聚合方法。本项目设计并合成一系列木质纤维素基二醛类单体并构建了一种基于席夫碱动态化学键的完全生物基类玻璃高分子。由于具有较高的芳烃含量（59.2 ~ 61.3 wt%），该类玻璃高分子具有几乎媲美传统热固性高分子的机械性能[（σ = 58.0 MPa；E’ = 3.07 GPa）]。且即使在实际加工条件下，该材料也表现出优异的热稳定性。同时，本项目研究了该材料的闭环可回收性。通过常用的方式（例如热机械回收和化学回收），其均表现出优异的可回收性。即使经过三个热压循环，其拉伸强度的恢复率仍高于 84%。该恢复率甚至优于许多商业化的可再加工的热塑性塑料。此外，该完全生物基类玻璃高分子可在温和酸性条件下完全降解。该特点显著地提高了其环境友好性以及可回收性。综上，本课题构建了一种基于木质素衍生单体的类玻璃高分子材料，其热/机械性能几乎与传统热固性材料相当，且可通过工业上成熟的方法实现闭环回收，显示出替代传统热固性材料的巨大潜力。