不同分子链微结构聚乳酸—聚三亚甲基碳酸酯共聚物的降解行为研究
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摘要
大多数的可生物降解材料都是脂肪族聚酯,它们具有良好的生物相容性,而且对环境无污染,在生物医学领域如手术缝合线,药物控制释放载体以及组织工程材料等方面得到了广泛的应用,是二十一世纪理想的绿色环保材料。通过在聚L-乳酸(PLLA)的链段中引入聚三亚甲基碳酸酯(PTMC),可以改善PLLA的降解速率和力学性能,同时还可以减轻PLLA降解过程中产生的大量酸性物质带来的炎症反应,减少患者的痛苦,缩短病患的恢复期。可降解材料的生物降解行为研究,不仅具有重要的理论价值,对于实际应用也具有重要的指导意义。
本论文研究了一系列PLLA-PTMC共聚物。其中,Cop1、Cop2和Cop3是在110℃反应了72h后的产物,而Cop4和Cop5是在180℃反应50min和80min后得。样品放入pH=7.4,37℃的磷酸盐缓冲溶液进行降解实验,对聚合物的降解行为进行了跟踪测试。采用~1H NMR、~(13)C NMR、GPC、DSC、WAXD、FI-IR等分析测试方法对共聚物进行合成表征以及降解行为的研究。
结果表明,Cop1、Cop2和Cop3为半结晶态共聚物,而Cop4和Cop5为无规共聚物,其中LLA和TMC单元含量相同的无规共聚物Cop4在降解中仍然保持了无规的特性,而LLA含量较高的无规共聚物Cop5由于含有较多的长链段LLA序列,因此在降解过程中发生了结晶行为。对于初始状态为半结晶形态的共聚物Cop1～Cop3,降解优先发生在无定型区域。不同形态的共聚物在降解过程中呈现了不同的化学组成,链段微观结构以及不同的形态变化,我们可以通过改变共聚物组成与链结构来调节材料的亲疏水性能和降解速率,为生物医药和组织工程领域的研究提供了一种有意义的载体材料。
Ring-opening copolymerization of L-lactide(LLA) and 1,3-trimethylene carbonate(TMC) blends with LLA/TMC feed ratios from 90/10 to 50/50 was realized at 110℃or at 180℃for various time periods,using low toxic zirconium(Ⅳ) acetylacetonate(Zr(Acac)_4) as initiator.The resulting copolymers exhibit different chain microstructures.Copolymers obtained at 110℃exhibit a gradient chain structure with the presence of long lactidyl sequences next to very short ones,and are thus semi-crystalline.In contrast,copolymers obtained at 180℃are amorphous because of a more random chain microstructure with the presence of larger amounts of medium sequences.Degradation of the copolymers was carried out in a pH 7.4 phosphate buffer at 37℃.Analytical techniques such as ~1H-NMR、~(13)C-NMR、DSC、GPC and WAXD were used to monitor the degradation.Initially amorphous copolymers can remain amorphous during degradation because of the highly random units distribution,and equivalent LLA and TMC contents.However,initially amorphous copolymers containing larger amounts of lactidyl units are able to crystallize during degradation because of the presence of relatively long LLA blocks. Insofar as initially semi-crystalline copolymers are concerned,degradation occurs preferentially in the amorphous zones.Therefore,various degradation behaviors and degradation rates can be obtained by varying the chemical composition,chain microstructure and morphology of PLLA-PTMC copolymers.
本论文研究了一系列PLLA-PTMC共聚物。其中,Cop1、Cop2和Cop3是在110℃反应了72h后的产物,而Cop4和Cop5是在180℃反应50min和80min后得。样品放入pH=7.4,37℃的磷酸盐缓冲溶液进行降解实验,对聚合物的降解行为进行了跟踪测试。采用~1H NMR、~(13)C NMR、GPC、DSC、WAXD、FI-IR等分析测试方法对共聚物进行合成表征以及降解行为的研究。
结果表明,Cop1、Cop2和Cop3为半结晶态共聚物,而Cop4和Cop5为无规共聚物,其中LLA和TMC单元含量相同的无规共聚物Cop4在降解中仍然保持了无规的特性,而LLA含量较高的无规共聚物Cop5由于含有较多的长链段LLA序列,因此在降解过程中发生了结晶行为。对于初始状态为半结晶形态的共聚物Cop1～Cop3,降解优先发生在无定型区域。不同形态的共聚物在降解过程中呈现了不同的化学组成,链段微观结构以及不同的形态变化,我们可以通过改变共聚物组成与链结构来调节材料的亲疏水性能和降解速率,为生物医药和组织工程领域的研究提供了一种有意义的载体材料。
Ring-opening copolymerization of L-lactide(LLA) and 1,3-trimethylene carbonate(TMC) blends with LLA/TMC feed ratios from 90/10 to 50/50 was realized at 110℃or at 180℃for various time periods,using low toxic zirconium(Ⅳ) acetylacetonate(Zr(Acac)_4) as initiator.The resulting copolymers exhibit different chain microstructures.Copolymers obtained at 110℃exhibit a gradient chain structure with the presence of long lactidyl sequences next to very short ones,and are thus semi-crystalline.In contrast,copolymers obtained at 180℃are amorphous because of a more random chain microstructure with the presence of larger amounts of medium sequences.Degradation of the copolymers was carried out in a pH 7.4 phosphate buffer at 37℃.Analytical techniques such as ~1H-NMR、~(13)C-NMR、DSC、GPC and WAXD were used to monitor the degradation.Initially amorphous copolymers can remain amorphous during degradation because of the highly random units distribution,and equivalent LLA and TMC contents.However,initially amorphous copolymers containing larger amounts of lactidyl units are able to crystallize during degradation because of the presence of relatively long LLA blocks. Insofar as initially semi-crystalline copolymers are concerned,degradation occurs preferentially in the amorphous zones.Therefore,various degradation behaviors and degradation rates can be obtained by varying the chemical composition,chain microstructure and morphology of PLLA-PTMC copolymers.
引文
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