生物可降解脂肪族聚酯的制备、表征与性能研究
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摘要
生物可降解脂肪族聚酯——聚乳酸(PLA)、聚-3-羟基丁酸酯(P3HB)、聚ε-己内酯(PCL)以及它们的共聚物,是目前研究和应用最为广泛的生物医用材料之一。脂肪族聚酯主要由环状内酯开环聚合制备,而聚合过程中使用的催化剂/引发剂显著影响聚合产物的分子量、微观结构和性能;同时,用作生物医用材料,其使用安全性,特别是所用催化剂的毒性,越发受到关注。因此,催化剂的有效性和安全性显得突出地重要,吸引人们不断地努力研究和开发高效、安全的内酯开环聚合的催化剂来制备脂肪族聚酯。
本论文研究了环烷氧锡、二丁基镁、辛酸镁、辛酸亚锡等化合物催化或引发L-、DL-丙交酯、β-丁内酯、ε-己内酯等内酯开环聚合,制备了一系列的脂肪族聚酯,采用~1HNMR、~(13)CNMR、FT-IR、GPC、DSC和XRD等手段分析和表征了聚合物化学结构和性能,并研究了聚合产物微观结构与性能的关系。
1.合成了两种结构确定的环烷氧锡化合物SnA和SnB作为β-丁内酯(β-BL)开环聚合的引发剂,制得了高分子量的聚-3-羟基丁酸酯(P3HB)。聚合物分子量依赖于单体引发剂配比(M/I),当M/I=10000时获得最高分子量M_n为25万,M_w为38万,伸长率达1100%,断裂强度23MPa。聚合温度降低,引发剂活性降低,聚合速率下降,间同组分增加。采用膨胀计法研究了环烷氧锡SnB引发β-丁内酯聚合动力学,表明链增长反应对单体浓度和引发剂浓度的反应级数分别为1和0.56。采用~(13)CNMR分析了聚合物微观结构,二单元组序列结构分析表明所得P3HB以间同结构为主,在60%-80%之间,并求得两种引发剂SnA和SnB所得P3HB的间同全同结构活化能差值分别为-11和-13 KJ/mol,三单元组序列结构分析符合链端立构控制的Bernoulli模型。
2.考查了二丁基镁引发β-丁内酯溶液聚合动力学,表明对单体和引发剂均为一级反应,求得反应活化能为30 kJ/mol。聚合物端基分析表明,聚合链一端为来自引发剂的丁基,另一端为来源于消除反应的丁烯酸酯或来自水解后的羟基,证明引发和增长过程是单体酰氧键断裂而不是烷氧键断裂插入增长链中,在此基础上提出了二丁基镁引发β-丁内酯聚合增长机理。
3.以二丁基镁为催化剂、聚乙二醇为引发剂,成功地制得了一系列不同嵌段长度的聚ε-己内酯-聚乙二醇-聚ε-己内酯两亲三嵌段共聚物。结晶性和热性能测试结果表明,共聚物PCL/PEG两段相对长度或组成比例显著影响共聚物的结晶性和熔融行为,处在中间链段PEG的结晶行为受到两端PCL链段的限制,而PEG对PCL结晶影响较小;PEG段只有相对于PCL足够长时才能结晶,且当PEG段较长时,共聚物出现共结晶和共熔融现象。
4.研究了辛酸镁催化DL-或L-丙交酯和ε-己内酯开环聚合,表明辛酸镁对内酯开环聚合具有良好的活性,成功地制得了一系列不同单体配比的共聚物。K-R法估算出L-丙交酯和ε-己内酯竞聚率分别为r_(LA)=23和r_(CL)=0.22,共聚单体竞聚率相差较大表明将形成渐变型共聚物。而~(13)CNMR微观结构分析表明,共聚过程中酯交换反应显著改变了共聚物序列结构及分布,使得平均序列长度降低,趋向无规共聚物。
共聚物组成显著影响单元序列长度,各序列长度随相应单体加入量增加而增长。共聚物单元序列分布随共聚物投料比、反应时间和温度而改变,趋向于无规分布。反应初期主要是一级酯交换反应,二级酯交换反应导致的CLC序列结构在反应后期才观察到。
考察了LA构型对共聚合酯交换反应、无规化和共聚物微观链结构与性能的影响,DL-LA比L-LA的二级酯交换系数(T_Ⅱ[CLC])稍低,相应的单元序列长度稍长,游程数R稍小,结果表明与ε-CL共聚合,DL-LA发生酯交换反应和无规化程度比L-LA相对要小。
共聚物热性能和结晶性分析结果表明,共聚物结晶性与单元性质和序列长度密切相关。所有共聚物只观察到一个玻璃化转变温度T_g,符合无规共聚物的Fox方程,说明所得共聚物为无规共聚物,或者说包含有相容性嵌段成分的共聚物。
5.考察了月桂醇作为分子量控制剂对合成聚乳酸分子量的影响。实验结果表明,月桂醇是一种良好的分子量控制剂,加入分子量控制剂是一种很好的控制聚乳酸分子量的手段,可以通过改变月桂醇的加入量来控制聚合物的分子量。以辛酸亚锡为催化剂、月桂醇为分子量控制剂催化DL-丙交酯、L-丙交酯和乙交酯在高真空条件下本体开环聚合,制得了不同分子量的乳酸均聚物(PLA)和不同配比的丙交酯乙交酯共聚物(PLGA)。
6.考察了所制备的聚乳酸均聚物和乳酸乙醇酸共聚物薄膜在汉克斯人工模拟体液中降解行为,筛选了适合作为冠脉支架表面载药涂层的聚合物。试验结果表明:PLGA降解速度可以通过调节共聚物的组成和分子量来控制,随着乙交酯含量的增加,共聚物PLGA的降解速率逐渐加快,乙交酯含量为30%-40%的PLGA一个月内降解可达60%～80%,符合冠脉支架表面载药涂层的降解速率要求,适宜用作该涂层材料。
Aliphatic polyesters such as polylactide(PLA),poly-3-hydroxybutyrates(P3HB), poly(ε-caprolactone)(PCL)and their copolymers are the most intensively studies and widely used as biodegradable medical materials.Continuous efforts have been devoted to the development of new catalysts and initiators for the ring opening polymerization of lactide and lactones.
In the present thesis,ring opening polymerizations of DL-lactide,L-lactide,glycolide, (R,S)-β-butyrolactone andε-caprolactone have been carried out by using stannous octoate, cyclic tin alkoxides,dibutylmagnesium and magnesium octoate as catalysts or initiators.The structure and properties of homopolymers and copolymers were characterized and analyzed by ~1HNMR,~(13)CNMR,FT-IR,GPC,DSC and XRD.The detailed results and conclusions are as follows:
1.Two well-designed cyclic tin alkoxides(SnA and SnB)were used as initiators for the ring opening polymerization of(R,S)β-butyrolactone(β-BL)to prepare high molecular weight P3HB.Polymerizations ofβ-BL were successfully carried out using high vacuum technique, being molar ratio of monomer to initiator(M/I)above 5 000 or around 20℃.Molecular weight of the polymer is largely dependent on an amount of initiator and inversely proportional to that.The kinetics ofβ-BL polymerization initiated with SnB was investigated at various M/I using dilatometer.The results showed that chain propagation rate forβ-BL polymerization was first order in monomer concentration and 0.56 order in initiator concentration,respectively.Analysis of diad sequence distributions at various polymerization temperatures for SnA and SnB showed the activation energy of ca.-11 and -13 kJ/mol for syndiotactic versus isotactic diad formation.Triad stereosequence distributions of P3HB samples agreed well with the Bernoullian statistical model of chain-end control.
2.The kinetics ofβ-BL polymerization imitated by dibutylmagnesium(Bu_2Mg)was examined and showed a first order both in monomer concentration and initiator concentration. The value of activation energy obtained for Bu_2Mg-initiatedβ-BL polymerization is ca.30 KJ/mol.The end group analysis suggested that monomer inserted into the growing chains proceeding through the coordination-insertion mechanism based on the acyl-oxygen bond scission rather than the alkyl-oxygen bond cleavage of theβ-BL ring.A possible mechanism for the initiation and propagation procedures ofβ-BL polymerization with Bu_2Mg was proposed.
3.Two series of poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone)(PCL-PEG-PCL)triblock copolymers with different lengths of each block were synthesized successfully by ring opening polymerization ofε-CL using Bu_2Mg as catalyst and PEG as macroinitiator in 1,4-dioxane solution at 70℃.The triblock structure and molecular weight of the copolymers were analyzed and confirmed by ~1H NMR,~(13)C NMR,FT-IR and GPC.The crystallization and thermal properties of the copolymers were investigated by WAXD and DSC.The results illustrated that the crystallization and melting behaviors of the copolymers were depended on the copolymer composition and the relative length of each block in copolymers.The crystallization of PEG block was strongly restricted by the crystallization of the lateral PCL blocks,whereas the crystallization of PCL blocks was not suppressed by the middle PEG block.
4.Ring opening copolymerization of L- or DL-LA withε-CL catalyzed by magnesium octoate were investigated in bulk.The reactivity ratios of L-LA andε-CL were measured to be r_(LA)= 23 and r_(CL)= 0.22,respectively,using the Fineman-Ross method.The results(r_(LA)＞1 and r_(CL)＜1)imply that L-LA monomer added preferentially into the copolymer chain end in the first step of the reaction,resulting in the formation of long blocks of lactidyl unit in the polymer chain.Two modes of transesterification occurred during the copolymerization process and played an important role in the redistribution of comonomer sequences.The repeat unit sequence distribution of the copolymers was varied more or less toward a random sequence distribution by variation in the comonomer feed ratio,reaction time and temperature. The copolymer composition has a profound influence on their average block length, increasing as the relative proportions of the corresponding ective monomers increased.
The effect of lactide configuration on the transesterification and randomization of the copolymer chain microstructure was determined.The DL-lactide-based copolymers have a more blocky structure and lower transesterification coefficient of the second mode than those containing L-lactide.It is less sensitive to transesterification reactions in the case of DL-LA. The thermal properties and crystallization of the copolymers were investigated by DSC and XRD.The results showed that a close relationship between copolymer crystallinity and the length of the copolymer sequences.All copolymers exhibited a single T_g determined from the second heating scan.The experimental T_gs were in agreement with the calculated values from Fox equation.It can be concluded that the copolymers are random,or comprise a mixture of compatible block copolymers.
5.A series of poly(DL-lactide)(PDLLA),poly(L-lactide)(PLLA)and poly(L-lactide-co-glycolide)(PLGA)with various molecular weights and various copolymer composition were prepared via ring-opening polymerization of DL-lactide or L-lactide and glycolide catalyzed by stannous octoate in vacuum.The molecular weight of these polymers was controlled by using a molecular weight controller,lauryl alcohol.The number-average molecular weight of PDLLA,ranging from 14800 to 63300 Da,was controlled by the amount of molecular weight controller used.The effect of the amount of molecular weight controller on the polymer molecular weight was studied.The results indicated that the polymer molecular weight has a log-log linear relationship with the amount of lauryl alcohol.
6.The resulting PDLLA,PLLA and PLGA were further investigated with respect to their degradation behaviors.The biodegradation rate of polymers films in Hank's solution were monitored by the changes of weight loss,inherent viscosity and morphology of the samples.PLGA containing a higher content of glycolide degraded faster than those containing a lower content of glycolide.The results demonstrated that the degradation rate of PLGA could be adjusted by changing the compositions and molecular weight of the copolymer and enhanced with the glycolide content increasing.The results indicated that the PLGA copolymer containing glycolide from 30 to 40%is a potential material as coating on drug elusion stents.
本论文研究了环烷氧锡、二丁基镁、辛酸镁、辛酸亚锡等化合物催化或引发L-、DL-丙交酯、β-丁内酯、ε-己内酯等内酯开环聚合,制备了一系列的脂肪族聚酯,采用~1HNMR、~(13)CNMR、FT-IR、GPC、DSC和XRD等手段分析和表征了聚合物化学结构和性能,并研究了聚合产物微观结构与性能的关系。
1.合成了两种结构确定的环烷氧锡化合物SnA和SnB作为β-丁内酯(β-BL)开环聚合的引发剂,制得了高分子量的聚-3-羟基丁酸酯(P3HB)。聚合物分子量依赖于单体引发剂配比(M/I),当M/I=10000时获得最高分子量M_n为25万,M_w为38万,伸长率达1100%,断裂强度23MPa。聚合温度降低,引发剂活性降低,聚合速率下降,间同组分增加。采用膨胀计法研究了环烷氧锡SnB引发β-丁内酯聚合动力学,表明链增长反应对单体浓度和引发剂浓度的反应级数分别为1和0.56。采用~(13)CNMR分析了聚合物微观结构,二单元组序列结构分析表明所得P3HB以间同结构为主,在60%-80%之间,并求得两种引发剂SnA和SnB所得P3HB的间同全同结构活化能差值分别为-11和-13 KJ/mol,三单元组序列结构分析符合链端立构控制的Bernoulli模型。
2.考查了二丁基镁引发β-丁内酯溶液聚合动力学,表明对单体和引发剂均为一级反应,求得反应活化能为30 kJ/mol。聚合物端基分析表明,聚合链一端为来自引发剂的丁基,另一端为来源于消除反应的丁烯酸酯或来自水解后的羟基,证明引发和增长过程是单体酰氧键断裂而不是烷氧键断裂插入增长链中,在此基础上提出了二丁基镁引发β-丁内酯聚合增长机理。
3.以二丁基镁为催化剂、聚乙二醇为引发剂,成功地制得了一系列不同嵌段长度的聚ε-己内酯-聚乙二醇-聚ε-己内酯两亲三嵌段共聚物。结晶性和热性能测试结果表明,共聚物PCL/PEG两段相对长度或组成比例显著影响共聚物的结晶性和熔融行为,处在中间链段PEG的结晶行为受到两端PCL链段的限制,而PEG对PCL结晶影响较小;PEG段只有相对于PCL足够长时才能结晶,且当PEG段较长时,共聚物出现共结晶和共熔融现象。
4.研究了辛酸镁催化DL-或L-丙交酯和ε-己内酯开环聚合,表明辛酸镁对内酯开环聚合具有良好的活性,成功地制得了一系列不同单体配比的共聚物。K-R法估算出L-丙交酯和ε-己内酯竞聚率分别为r_(LA)=23和r_(CL)=0.22,共聚单体竞聚率相差较大表明将形成渐变型共聚物。而~(13)CNMR微观结构分析表明,共聚过程中酯交换反应显著改变了共聚物序列结构及分布,使得平均序列长度降低,趋向无规共聚物。
共聚物组成显著影响单元序列长度,各序列长度随相应单体加入量增加而增长。共聚物单元序列分布随共聚物投料比、反应时间和温度而改变,趋向于无规分布。反应初期主要是一级酯交换反应,二级酯交换反应导致的CLC序列结构在反应后期才观察到。
考察了LA构型对共聚合酯交换反应、无规化和共聚物微观链结构与性能的影响,DL-LA比L-LA的二级酯交换系数(T_Ⅱ[CLC])稍低,相应的单元序列长度稍长,游程数R稍小,结果表明与ε-CL共聚合,DL-LA发生酯交换反应和无规化程度比L-LA相对要小。
共聚物热性能和结晶性分析结果表明,共聚物结晶性与单元性质和序列长度密切相关。所有共聚物只观察到一个玻璃化转变温度T_g,符合无规共聚物的Fox方程,说明所得共聚物为无规共聚物,或者说包含有相容性嵌段成分的共聚物。
5.考察了月桂醇作为分子量控制剂对合成聚乳酸分子量的影响。实验结果表明,月桂醇是一种良好的分子量控制剂,加入分子量控制剂是一种很好的控制聚乳酸分子量的手段,可以通过改变月桂醇的加入量来控制聚合物的分子量。以辛酸亚锡为催化剂、月桂醇为分子量控制剂催化DL-丙交酯、L-丙交酯和乙交酯在高真空条件下本体开环聚合,制得了不同分子量的乳酸均聚物(PLA)和不同配比的丙交酯乙交酯共聚物(PLGA)。
6.考察了所制备的聚乳酸均聚物和乳酸乙醇酸共聚物薄膜在汉克斯人工模拟体液中降解行为,筛选了适合作为冠脉支架表面载药涂层的聚合物。试验结果表明:PLGA降解速度可以通过调节共聚物的组成和分子量来控制,随着乙交酯含量的增加,共聚物PLGA的降解速率逐渐加快,乙交酯含量为30%-40%的PLGA一个月内降解可达60%～80%,符合冠脉支架表面载药涂层的降解速率要求,适宜用作该涂层材料。
Aliphatic polyesters such as polylactide(PLA),poly-3-hydroxybutyrates(P3HB), poly(ε-caprolactone)(PCL)and their copolymers are the most intensively studies and widely used as biodegradable medical materials.Continuous efforts have been devoted to the development of new catalysts and initiators for the ring opening polymerization of lactide and lactones.
In the present thesis,ring opening polymerizations of DL-lactide,L-lactide,glycolide, (R,S)-β-butyrolactone andε-caprolactone have been carried out by using stannous octoate, cyclic tin alkoxides,dibutylmagnesium and magnesium octoate as catalysts or initiators.The structure and properties of homopolymers and copolymers were characterized and analyzed by ~1HNMR,~(13)CNMR,FT-IR,GPC,DSC and XRD.The detailed results and conclusions are as follows:
1.Two well-designed cyclic tin alkoxides(SnA and SnB)were used as initiators for the ring opening polymerization of(R,S)β-butyrolactone(β-BL)to prepare high molecular weight P3HB.Polymerizations ofβ-BL were successfully carried out using high vacuum technique, being molar ratio of monomer to initiator(M/I)above 5 000 or around 20℃.Molecular weight of the polymer is largely dependent on an amount of initiator and inversely proportional to that.The kinetics ofβ-BL polymerization initiated with SnB was investigated at various M/I using dilatometer.The results showed that chain propagation rate forβ-BL polymerization was first order in monomer concentration and 0.56 order in initiator concentration,respectively.Analysis of diad sequence distributions at various polymerization temperatures for SnA and SnB showed the activation energy of ca.-11 and -13 kJ/mol for syndiotactic versus isotactic diad formation.Triad stereosequence distributions of P3HB samples agreed well with the Bernoullian statistical model of chain-end control.
2.The kinetics ofβ-BL polymerization imitated by dibutylmagnesium(Bu_2Mg)was examined and showed a first order both in monomer concentration and initiator concentration. The value of activation energy obtained for Bu_2Mg-initiatedβ-BL polymerization is ca.30 KJ/mol.The end group analysis suggested that monomer inserted into the growing chains proceeding through the coordination-insertion mechanism based on the acyl-oxygen bond scission rather than the alkyl-oxygen bond cleavage of theβ-BL ring.A possible mechanism for the initiation and propagation procedures ofβ-BL polymerization with Bu_2Mg was proposed.
3.Two series of poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone)(PCL-PEG-PCL)triblock copolymers with different lengths of each block were synthesized successfully by ring opening polymerization ofε-CL using Bu_2Mg as catalyst and PEG as macroinitiator in 1,4-dioxane solution at 70℃.The triblock structure and molecular weight of the copolymers were analyzed and confirmed by ~1H NMR,~(13)C NMR,FT-IR and GPC.The crystallization and thermal properties of the copolymers were investigated by WAXD and DSC.The results illustrated that the crystallization and melting behaviors of the copolymers were depended on the copolymer composition and the relative length of each block in copolymers.The crystallization of PEG block was strongly restricted by the crystallization of the lateral PCL blocks,whereas the crystallization of PCL blocks was not suppressed by the middle PEG block.
4.Ring opening copolymerization of L- or DL-LA withε-CL catalyzed by magnesium octoate were investigated in bulk.The reactivity ratios of L-LA andε-CL were measured to be r_(LA)= 23 and r_(CL)= 0.22,respectively,using the Fineman-Ross method.The results(r_(LA)＞1 and r_(CL)＜1)imply that L-LA monomer added preferentially into the copolymer chain end in the first step of the reaction,resulting in the formation of long blocks of lactidyl unit in the polymer chain.Two modes of transesterification occurred during the copolymerization process and played an important role in the redistribution of comonomer sequences.The repeat unit sequence distribution of the copolymers was varied more or less toward a random sequence distribution by variation in the comonomer feed ratio,reaction time and temperature. The copolymer composition has a profound influence on their average block length, increasing as the relative proportions of the corresponding ective monomers increased.
The effect of lactide configuration on the transesterification and randomization of the copolymer chain microstructure was determined.The DL-lactide-based copolymers have a more blocky structure and lower transesterification coefficient of the second mode than those containing L-lactide.It is less sensitive to transesterification reactions in the case of DL-LA. The thermal properties and crystallization of the copolymers were investigated by DSC and XRD.The results showed that a close relationship between copolymer crystallinity and the length of the copolymer sequences.All copolymers exhibited a single T_g determined from the second heating scan.The experimental T_gs were in agreement with the calculated values from Fox equation.It can be concluded that the copolymers are random,or comprise a mixture of compatible block copolymers.
5.A series of poly(DL-lactide)(PDLLA),poly(L-lactide)(PLLA)and poly(L-lactide-co-glycolide)(PLGA)with various molecular weights and various copolymer composition were prepared via ring-opening polymerization of DL-lactide or L-lactide and glycolide catalyzed by stannous octoate in vacuum.The molecular weight of these polymers was controlled by using a molecular weight controller,lauryl alcohol.The number-average molecular weight of PDLLA,ranging from 14800 to 63300 Da,was controlled by the amount of molecular weight controller used.The effect of the amount of molecular weight controller on the polymer molecular weight was studied.The results indicated that the polymer molecular weight has a log-log linear relationship with the amount of lauryl alcohol.
6.The resulting PDLLA,PLLA and PLGA were further investigated with respect to their degradation behaviors.The biodegradation rate of polymers films in Hank's solution were monitored by the changes of weight loss,inherent viscosity and morphology of the samples.PLGA containing a higher content of glycolide degraded faster than those containing a lower content of glycolide.The results demonstrated that the degradation rate of PLGA could be adjusted by changing the compositions and molecular weight of the copolymer and enhanced with the glycolide content increasing.The results indicated that the PLGA copolymer containing glycolide from 30 to 40%is a potential material as coating on drug elusion stents.
引文
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