生物降解聚合物论文：聚乳酸的扩链与支化反应

1、生物降解聚合物论文：聚乳酸的扩链与支化反应【中文摘要】聚（l-乳酸）是一种以可再生植物资源为原料的生 物降解高分子材料，具有良好的生物降解性、生物相容性、生物吸收 性及力学性能，在生物医用材料、纤维、包装材料等领域有着良好的 应用前景。因此，聚乳酸的研究与开发已成为可生物降解高分子材料 领域的热点。而高效、低成本地获得高分子量的聚乳酸、并使其发生 部分支化以改善力学性能,是聚乳酸材料研究开发中的重要方向之一 为此,本文提出一种新的熔融缩聚/扩链方法,即用熔融缩聚得到的 端竣基聚乳酸预聚物与二缩水甘油酯进行扩链反应制备高分子量的 具有支化结构的聚乳酸。首先,通过在snc12 2h20/tsa双组

2、分催化 剂催化乳酸熔融缩聚的过程中添加一定量的丁二酸酹,制备得数均分 子量（mn）为1000-20000,端竣基含量高于98%的结晶性聚乳酸预聚 物。当mnw2000时，聚乳酸预聚物结晶速度慢，难以结晶；当mn>4000 时，则很容易结晶，随着分子量从4000增人到10000,其结晶度由27% 上升至40%。其次,采用二缩水甘油酯与端竣基聚乳酸预聚物进行扩 链反应，并用三检测器凝胶渗透色谱技术对聚乳酸扩链产物的链结构 （分子量及其分布、特性粘数、支化因子）进行表征,考察了预聚物 分子量、扩链反应温度、环氧/竣基摩尔比、真空度等因素对扩链反 应及扩链产物链结构的影响。在扩链过程中，聚乳酸预

3、聚物的端竣基 与二缩水甘油酯的环氧基反应迅速，因而可在很短的吋间内提高聚乳 酸重均分子量；但rtr丁存在竣基和环氧基与生成的侧疑基的副反应， 在扩链的同吋也产生支化结构,分了量分布明显变宽，甚至产生凝胶。 预聚物分子量、反应温度、环氧基/竣基摩尔比显著影响扩链反应和 扩链产物链结构。采用合适分子量(mn 6000)的预聚物、提高反应 温度、提高环氧/竣基摩尔比，有利于提高扩链产物分子量；随着预聚 物分子量减小、反应温度升高或环氧/竣基摩尔比偏离1/1,扩链产 物分子量支化程度增大、分子量分布变宽，乃至产生凝胶。在真空下 反应，会进一步促进支化反应的发生和支化结构的形成。进一步对聚 乳酸扩链产物

4、的结晶性进行了研究。扩链剂结构的引入和支化结构的 产生,导致扩链产物的结晶性下降，但仍具有结晶性。支化程度越高， 结晶性下降越明显。采用更高分子量的预聚物扩链，所得的扩链产物 具有更好的结晶性。端竣基聚乳酸预聚物与1, 3-苯基-双(2-恶呼咻) 扩链制得线性扩链产物，其结晶性优于二缩水甘油酯扩链产物，但与 预聚物相比,仍有明显下降。综上，采用mn为6000-20000的端竣基聚 乳酸与二缩水廿油酯在环氧/竣基摩尔比1、160°c下反应30 min,可 制得 mw 9.0-21.5 万、pdt 4. 88-9. 18、支化因子 0.27-0.79、结晶 度3. 7-10. 7%的扩链

5、聚乳酸，经充分结晶后，其结晶度可提高到 20-30%o【英文摘要】poly (l-lactic acid) (plla) is a biodegradable polymer produced from renewable biobased resources due to its biodegradabi1ity, biocompatibility and good mechanical properties, it has tremendous market potential in biomaterials, fibers, disposable commodities and pack

6、age materials so, plla has attracted many researchers? and companies? attention in biogegradable area how to obtain high molecular weight plla via an efficient and low-cost way, and how to introduce branching into its chain to improve its mechanical properties, especially melt strength, are key poin

7、ts in its synthesis and modification. in this article, crystalline dicarboxylated plla prepolymer was first synthesized and then reacted with diglycidylester as a chain extender via the so-called melt polycondensation-chain extension method, high molecular weight pllas wi th branched long chains wer

8、e prepared .firstly, dicarboxylated pllas with number average molecular weight (mi) of 1000-20000 g. mol-1 were synthesized via melt polycondensation of l-lactic acid in the presenee of a small amount of succinic anhydride (sad), using tin( ii) chloride and toluene-4-sulfonic acid as a binary cataly

9、st (snct2/tsa). the terminal c00ii percentage reaches over 98% and the molecular weight can be controlled by molar ratio of lla to sad thermal transition behaviors of the prepolymer depends on its molecular weight. it crystallizes slowly at mnw2000, but quickly at mn $4000. the crystal 1 inity incre

10、ases from 27% to 40% when the mn grows from 4000 to 10000. secondly, dicarboxylated pllas were chain extended with diglycidylester and the chain structures of the chain extended products were characterized by three-detector gpc the effects of mn of prepolyme, r epoxy/carboxyl mo 1 ar ratio, reaction

11、 temperature and pressure on the chain extenstion reaction and on the chain structures of chain extended products were investigated. the reaction between the epoxy groups in diglycidylester and the carboxyl groups in prepolymer took place rapidly during chain extension, so the molecular weight of ch

12、ain extended plla grew rapidly to high value in short time meanwhile, side reations between carboxyl/epoxy and side hydroxyl formed during chain extension ocuured too, leading to the formation of branched chains, together with broadening of molecular weight distribution and even with gellation. the

13、mn of prepolymer, epoxy/carboxyl molar ratio and reaction temperature exhibited significant effects on the chain extenstion reaction and on the chain structures of chain extended pllas chainextending prepolymer with propriate molecular weight (ca mn 6000) at higher epoxy/carboxyl ratio and higher te

14、mperature was beneficial to the growth of the molecular weight lower mn of prepolymer, epoxy/carboxyl molar ratio other than 1/1 and higher reaction temperature led to enhanced branching, broader mwd and even gellation. reaction under vacuum also enhaneed the branchingto certain extent.the crystalli

15、zation of the chain extendedpllas was further studied. the chain extended pllas were crystallizable but their crystallizability was decresed with comparison to their prepolymers because of introduction of chain extender moiety and formation of branching. the higher extent of branching, the less the

16、crystallizability. so chain extended pllas prepared from prepolymer with higher mn has better crystallizability. for comparison, linear chain extended pllas were prepared using 1, 3-phenyl-bis (2-oxazoline) as chain extender. tt has better crystal 1izabi1ity than the branched counterpart, but is sti

17、ll interior to the prepolymer in the end, when dicarboxylated plla prepolymers with mn of 6000-10000 were chain extended with diglycidylester at optimized conditions, i.e., at epoxy/cooh ratio of 1 and 160 °c for 30 min, branchd pllas with mw of 90, 000-215, 000, pdt of 4. 889. 18, branchi ng f

18、actor of 0. 27-0. 79 and crystallinity of 3.7一10. 7% were successfully synthesized. after sufficient isothermal cold crystallization, the crystallinity can reach 20-30%【关键词】生物降解聚合物 聚乳酸扩链结晶支化【英文关键诃】biodegradable polymers卩oly (l-lacticacid)chain extensioncrystallizationbranching【目录】聚乳酸的扩链与支化反应致谢4-5 摘要5-7 abstract 7-8 冃录 9-11 第 1 章绪论11-331.1前言11-131.2文献综述13-301.2. 1聚乳酸的结构、性能和应用13-151.2.2聚乳酸的合成方法15-211.2.3扩链