生物降解聚合物優(yōu)秀論文：聚乳酸的擴(kuò)鏈與支化反應(yīng)

1、生物降解聚合物優(yōu)秀論文：聚乳 酸的擴(kuò)鏈與支化反應(yīng)作者:日期:生物降解聚合物論文：聚乳酸的擴(kuò)鏈與支化反應(yīng)【中文摘要】聚（L-乳酸）是一種以可再生植物資源為原料的生 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 性及力學(xué)性能，在生物醫(yī)用材料、纖維、包裝材料等領(lǐng)域有著良好的 應(yīng)用前景。因此，聚乳酸的研究與開(kāi)發(fā)已成為可生物降解高分子材料 領(lǐng)域的熱點(diǎn)。而高效、低成本地獲得高分子量的聚乳酸、并使其發(fā)生 部分支化以改善力學(xué)性能，是聚乳酸材料研究開(kāi)發(fā)中的重要方向之一 為此，本文提出一種新的熔融縮聚/擴(kuò)鏈方法，即用熔融縮聚得到的 端竣基聚乳酸預(yù)聚物與二縮水甘油酯進(jìn)行擴(kuò)鏈反應(yīng)制備高分子量的 具有支

2、化結(jié)構(gòu)的聚乳酸。首先，通過(guò)在SnCl2 2H2O/TS頗組分催化 劑催化乳酸熔融縮聚的過(guò)程中添加一定量的丁二酸酊，制備得數(shù)均分子量（Mn為1000-20000，端竣基含量高于98%勺結(jié)晶性聚乳酸預(yù)聚 物。當(dāng)Mrnc 2000時(shí)，聚乳酸預(yù)聚物結(jié)晶速度慢，難以結(jié)晶；當(dāng)Mn>4000 時(shí)，則很容易結(jié)晶，隨著分子量從4000增大到10000,其結(jié)晶度由27% 上升至40%其次,采用二縮水甘油酯與端竣基聚乳酸預(yù)聚物進(jìn)行擴(kuò) 鏈反應(yīng)，并用三檢測(cè)器凝膠滲透色譜技術(shù)對(duì)聚乳酸擴(kuò)鏈產(chǎn)物的鏈結(jié)構(gòu)（分子量及其分布、特性粘數(shù)、支化因子）進(jìn)行表征，考察了預(yù)聚物分子量、擴(kuò)鏈反應(yīng)溫度、環(huán)氧/竣基摩爾比、真空度等因素對(duì)擴(kuò)鏈

3、反 應(yīng)及擴(kuò)鏈產(chǎn)物鏈結(jié)構(gòu)的影響。在擴(kuò)鏈過(guò)程中，聚乳酸預(yù)聚物的端竣基 與二縮水甘油酯的環(huán)氧基反應(yīng)迅速，因而可在很短的時(shí)間內(nèi)提高聚乳 酸重均分子量；但由于存在竣基和環(huán)氧基與生成的側(cè)羥基的副反應(yīng)，在擴(kuò)鏈的同時(shí)也產(chǎn)生支化結(jié)構(gòu)，分子量分布明顯變寬，甚至產(chǎn)生凝膠。預(yù)聚物分子量、反應(yīng)溫度、環(huán)氧基/竣基摩爾比顯著影響擴(kuò)鏈反應(yīng)和 擴(kuò)鏈產(chǎn)物鏈結(jié)構(gòu)。采用合適分子量(Mn 6000)的預(yù)聚物、提高反應(yīng) 溫度、提高環(huán)氧/竣基摩爾比，有利于提高擴(kuò)鏈產(chǎn)物分子量；隨著預(yù)聚 物分子量減小、反應(yīng)溫度升高或環(huán)氧/竣基摩爾比偏離1/1,擴(kuò)鏈產(chǎn)物分子量支化程度增大、分子量分布變寬，乃至產(chǎn)生凝膠。在真空下 反應(yīng)，會(huì)進(jìn)一步促進(jìn)支化反應(yīng)的發(fā)生

4、和支化結(jié)構(gòu)的形成。進(jìn)一步對(duì)聚 乳酸擴(kuò)鏈產(chǎn)物的結(jié)晶性進(jìn)行了研究。擴(kuò)鏈劑結(jié)構(gòu)的引入和支化結(jié)構(gòu)的 產(chǎn)生，導(dǎo)致擴(kuò)鏈產(chǎn)物的結(jié)晶性下降，但仍具有結(jié)晶性。支化程度越高， 結(jié)晶性下降越明顯。采用更高分子量的預(yù)聚物擴(kuò)鏈，所得的擴(kuò)鏈產(chǎn)物具有更好的結(jié)晶性。端竣基聚乳酸預(yù)聚物與1,3-苯基-雙(2-惡噪咻) 擴(kuò)鏈制得線性擴(kuò)鏈產(chǎn)物，其結(jié)晶性優(yōu)于二縮水甘油酯擴(kuò)鏈產(chǎn)物，但與 預(yù)聚物相比，仍有明顯下降。綜上，采用Mn為6000-20000的端竣基聚 乳酸與二縮水甘油酯在環(huán)氧/竣基摩爾比1、160c下反應(yīng)30 min,可 制得 Mw 9.0-21.5 萬(wàn)、PDI 4.88-9.18、支化因子 0.27-0.79、結(jié)晶 度3.7

5、-10.7%的擴(kuò)鏈聚乳酸，經(jīng)充分結(jié)晶后，其結(jié)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 biodegradability, biocompatibility and good mechanical properties, it has tremendous market potential in biomaterials, fibers, disposable commodities

6、and package materials. So, PLLAhas 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 str

7、ength, are key points 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 molecularweight PLLAs with branch

8、ed long chains were prepared.Firstly, dicarboxylatedPLLAs with number average molecular weight (Mi)of 1000-20000 g.mol-1 were synthesized via melt polycondensation of L-lactic acid in the presence of a small amount of succinic anhydride (SAD), using tin( H) chloride and toluene-4-sulfonic acid as a

9、binary catalyst (SnCI2/TSA). The terminal COOH 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 Mn < 2000, but quickly at Mn >4000. The

10、crystallinity increases from 27% to 40% when the Mngrows from 4000 to 10000.Secondly, dicarboxylated PLLAswere chain extended with diglycidylester and the chain structuresof the chain extended products were characterized by three-detector GPC. The effects of Mn of prepolyme, r epoxy/carboxyl molar r

11、atio, reaction 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 molecula

12、r weight of chain extended PLLAgrew 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 g

13、ellation. The Mnof 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. Chain-extending prepolymer with propriate molecular weight (ca. Mn 6000) at higher epoxy/carboxyl rat

14、io and higher temperature 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 enhanced the branchingto certain ext

15、ent.The crystallization of the chain extended PLLAs 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 branch

16、ing, the less the crystallizability. So chain extended PLLAs prepared from prepolymer with higher Mn has better crystallizability. For comparison, linear chain extended PLLAswere prepared using 1,3-phenyl-Bis(2-oxazoline) as chain extender. It has better crystallizability than the branched counterpa

17、rt, but is still interior to the prepolymer.In the end, when dicarboxylated PLLA prepolymers with Mnof 6000-10000 were chain extended with diglycidylester at optimized conditions, i.e., at epoxy/COOH ratio of 1 and160 C for 30 min, branchd PLLAs with Mwof 90, 000-215,000, PDI of 4.88-9.18, branching

18、 factor of 0.27-0.79 and crystallinity of 3.7-10.7% were successfully synthesized. After sufficient isothermal cold crystallization, the crystallinity can reach 20-30%.【關(guān)鍵詞】生物降解聚合物聚乳酸擴(kuò)鏈結(jié)晶支化【英文關(guān)鍵詞】Biodegradable polymers Poly(L-lactic acid) Chain extension Crystallization7Branching【目錄】聚乳酸的擴(kuò)鏈與支化反應(yīng)致謝 4-5摘要