【作者】 魏正方；

【导师】 范仲勇；

【作者基本信息】 复旦大学 ， 材料物理与化学， 2010， 博士

【摘要】 通过柔性聚乙二醇(MePEG)或低不饱和度聚醚多元醇(PPO)与左旋聚乳酸(PLLA)进行共聚改性,合成了一系列不同分子量的线型结晶-结晶MePEG-b-PLLA嵌段共聚物或三枝链非晶-结晶PPO-b-PLLA嵌段共聚物。在PEG晶态或PPO非晶态等受限条件下,研究了PLLA链段的结晶机制及结晶动力学和晶体形貌。基于聚合物成核-生长结晶理论,对可结晶PLLA链段在三枝链非晶态PPO链段受限作用下的结晶行为进行了研究。探讨嵌段共聚物的复杂结晶行为。从材料的微观凝聚态结构、结晶热力学、动力学等角度研究新型可降解PLLA基聚合物功能材料结构与性能的关系。并在此基础上,开发了新型环境友好可降解PPO-b-PLLA聚醚酯形状记忆新材料,对这类新型绿色可降解的聚醚酯形状记忆材料的性能进行了试验研究和理论初探。在下述几个方面,文中着重进行了系统的理论和实验研究：选择MePEG为大分子起始剂,通过与L-丙交酯开环聚合,合成了不同PLLA链段序列长度的MePEG-b-PLLA线型嵌段共聚物。通过实验温度的控制,可得到单组分结晶或双结晶的不同受限条件下聚合物凝聚态结构。在PEG结晶的条件下,PLLA链段生长的晶粒与PLLA均聚物的晶型相同,属于正交晶系。但是,PLLA晶粒的侧向尺寸远低于PLLA均聚物晶粒的侧向尺寸。通过精心设计双结晶层膜样品的制备和测试,减少线型MePEG-b-PLLA嵌段共聚物链间缠结,人为调控聚合物链的受限程度。与本体样品相比,双层膜PLLA晶体的侧向尺寸比本体样品中PLLA晶体的侧向尺寸大。在分子受限状态条件设计中,以PPO大分子起始剂,引发L-丙交酯开环聚合,分别合成了不同组成的三枝链PPO-b-PLLA嵌段共聚物。同时,设计合成了三枝链PLLA均聚物和线型PPO-b-PLLA嵌段共聚物为对比研究对象。对PPO-b-PLLA嵌段共聚物的冷结晶行为和晶体结构进行了测试研究。测试结果表明聚合物链构型对PPO-b-PLLA嵌段共聚物的结晶行为有着显著的影响。当PPO链段序列长度一定,三枝链PPO-b-PLLA嵌段共聚物的冷结晶峰值温度、熔点及熔融焓随PLLA链段序列长度的减小而降低。当PLLA链段序列长度一定,随着PPO链段序列长度的增加,共聚物的熔点及熔融焓增加,晶体完善度提高。再者,三枝链PPO-b-PLLA嵌段共聚物中PLLA链段冷结晶的晶体仍归属于正交晶系。文中详细地研究了聚合物链构型及链段序列长度对PPO-b-PLLA嵌段共聚物结晶热力学和动力学的影响。采用Lauritzen-Hoffman理论分析了PLLA链段序列长度对三枝链PPO-b-PLLA嵌段共聚物结晶动力学上的影响。发现三枝链PPO-b-PLLA嵌段共聚物的Regime II与Regime III的转变温度与链段的组成和序列长度有关,不同样品的转变温度发生在111℃-125℃之内。再者,三枝链PPO-b-PLLA嵌段共聚物的等温结晶活化能、成核参数、端表面折叠自由能及表面折叠功均高于三枝链PLLA均聚物的相应值,说明三枝化链构型聚合物结晶的的复杂性。实验揭示了非晶态PPO链段对PLLA链段的晶体生长具有增塑作用,对PLLA链段的成核具有一定的受限作用。对三枝链和线型PPO-b-PLLA嵌段共聚物的熔体非等温结晶行为及熔融行为进行了研究,分别采用Jeriorny理论、Ozawa方法和Mo方法对PPO-b-PLLA共聚物非等温结晶动力学过程进行了理论处理,并采用Arrhenius方程计算得到熔体非等温结晶表观活化能,验证了等温结晶实验现象与结论。在形态学方面,采用热台偏光显微镜(POM)观察了三枝链PPO-b-PLLA嵌段共聚物的熔体结晶形貌。不同序列长度的PLLA链段对共聚物结晶形貌有显著影响,且有很强的温度依赖性,在不同过冷度下先后生成了环带球晶。采用原子力显微镜(AFM)观察了环带球晶中片晶的堆砌方式。环带球晶表面凸起部分呈现为纤维状堆积,凹陷部分呈现为螺旋位错状堆积。由此推测该环带球晶是由于片晶的不同取向造成的。对蚀刻后球晶的扫描电镜(SEM)观察表明球晶以"branching"(枝化)模式生长。此外,还采用AFM观察了共聚物在几何空间受限条件下的结晶行为的影响,即研究超薄膜厚度样品的晶体形貌。在薄膜厚度约为1μm时,结晶形成由扩散控制生长机制的树枝状晶体。且树枝状晶体形貌具有强烈的结晶温度依赖性,在105℃和110℃结晶温度下分别呈现出向日葵晶体和六方状晶体。当薄膜厚度降低为200 nm时,晶体形态则呈树枝状发散、束状堆砌。进一步降低薄膜厚度为100 nm时,晶体则呈现为具有一定方向性和有序性片晶堆砌排列的堆积形态,呈“岛”状分布。揭示了聚合物薄膜低维受限条件下晶体的分布与尺寸。作为一种具有很强潜在应用前景的新型生物可降解嵌段共聚物材料,文中采用异氰酸酯(TDI)为交联剂制备了PPO-b-PLLA聚醚酯形状记忆材料。在形状记忆性能方面,研究了结晶对材料形状记忆性能的影响,揭示了此类形状记忆材料的结构与性能的内在联系。通过对PLLA链段结晶过程和晶体结构的控制,可得到不同结构和不同形状记忆性能的新型可生物降解形状记忆聚醚酯材料。更多还原

【Abstract】 A series of linear crystalline-crystalline and triarm amorphous-crystalline diblock copolymers with various molecular weight were synthesized by ring-opening polymerization of L-lactide (L-LA) using monomethoxy poly(ethylene glycol) (MePEG) or low unsaturated poly(propylene oxide) (PPO) as macromolecular initiator. The crystallization processes and crystallization kinetics of the PLLA blocks were investigated under different confined condition formed by crystalline PEG or amorphous PPO of copolymers samples. Based on the polymer nucleation-growth theory, the crystallization behaviors of PLLA block was investigated under the confinement condition formed by triarm amorphous PPO, in which the complicated crystallization behaviors was discussed. From the viewpoint of the condensed structure of polymers, thermodynamics and crystallization kinetics, the relationships between the structure and properties of novel PLLA matrix copolymers functional materials were investigated. The newly environmentally friendly and biodegradable shape memory materials (SMP) of PPO-b-PLLA poly (ether-ester) were developed. The properties of poly (ether-ester) SMP were investigated from the aspect of experiment results. The main contents of the thesis are as follows:Linear MePEG-b-PLLA copolymers with various PLLA block lengths were synthesized by ring-opening polymerization of L-lactide in the presence of MePEG macroinitiator, using Sn(Oct)2 as catalyst. The condensed structure formed with the crystallization of one block or two blocks can be obtained by controlling the experimental temperatures. The crystals of the PLLA blocks under crystalline PEG corresponded to a form crystal with the orthorhombic unit cell, which is as same as that of PLLA homopolymer. However, the lateral sizes of the PLLA crystals were much smaller than that of PLLA homopolymer. The entanglements between MePEG-b-PLLA copolymers chains decreased by preparation the bilayer films. The lateral sizes of the PLLA crystals from the bilayer films were much larger than values of the bulk samples.For the samples confined by configuration of polymer chains, triarm PPO-b-PLLA copolymers with different compositions were synthesized by ring-opening polymerization of L-lactide in the presence of PPO macroinitiator, using Sn(Oct)2 as catalyst. Meanwhile, triarm PLLA homopolymer and linear PPO-b-PLLA copolymers were also synthesized for experiments. The crystallization behaviors from glass states and the crystal structure of PPO-b-PLLA copolymers were investigated. The results indicated that the segment structure had obvious effect on the cold crystallization behaviors of PPO-b-PLLA copolymers. The cold crystallization peak temperatures, melting temperatures and melting enthalpy of triarm PPO-b-PLLA copolymers with fixed PPO block length decreased with decreasing the PLLA block length. Meanwhile, the melting temperatures, melting enthalpy of triarm PPO-b-PLLA copolymers with fixed PLLA block length increased with increasing the PPO block length. In addition, crystals formed in the cold crystallization behavior corresponding to the a form crystals with the orthorhombic unit cell.The effects of the segment structure and the block lengths on the crystallization kinetics and thermodynamics of PPO-b-PLLA copolymers were investigated. The effect of various PLLA block lengths on the crystallization kinetics of triarm PPO-b-PLLA copolymers was investigated and analyzed with nucleation and growth theory by Lauritzen-Hoffman. The crystallization kinetics of triarm copolymers indicated that the regime transition temperature from regime II to regime III depended on the compositions and various block length of copolymers. The transition temperatures of different samples were in the range of 111℃-125℃, respectively. The calculated values of isothermal crystallization activation energy, nucleation constant and the fold surface free energy of triarm copolymers were higher than that of triarm PLLA homopolymer, which suggested the complication of the crystallization behavior in the polymers with star shape structure. The result implies that the amorphous PPO block not only had effect on the plasticization but also the confined effect on the nucleation and crystals growth of triarm copolymers. Furthermore, nonisothermal crystallization behaviors and subsequent melting behavior of triarm and linear of PPO-b-PLLA copolymers were also investigated. Nonisothermal crystallization kinetics was analyzed with Jeriorny, Ozawa and Mo method, respectively. The values of nonisothermal activation energy of triarm PPO-b-PLLA copolymers were obtained by Arrhenius equation and exhibited the same trend with the analysis of melt isothermal crystallization, which results further demonstrated the isothermal crystallization experiments and conclusions.In the morphological researches, the spherulite morphologies of triarm PPO-b-PLLA copolymers were observed by polarized optical microscopy (POM) with hot-stage. Different PLLA block lengths and the crystallization temperature had obvious effect on the crystals morphologies of triarm PPO-b-PLLA copolymers. The spherulites with concentric extinction banded textures were observed under various supercooling degrees. The clusters of the lamella in the banded spherulites were observed using atomic forced microscope (AFM). The protrude part of the banded spherulites was built up with fiber-orientation lamella, while the depressed part built up with the stacks of lamellae with screw dislocations. From such phenomenon, it can be speculated that the formation of the banded spherulites were attributed to different orientation of the lamella. The spherulites after etching were observed with scanning electron microscope (SEM), which growth obeyed the mechanisms of "branching" model. In addition, the crystals morphologies of triarm PPO-b-PLLA copolymer in the ultra thin films under geometrical confined environment were investigated by AFM. With the film thickness of 1μm, the dendrite can be observed, of which the crystal growth was controlled by diffusion mechanism. Moreover, the morphology of the dendrite strongly depended on the crystallization temperatures. The crystals of sunflower-shape and hexagonal-shape were observed at 105℃and 110℃, respectively. As the thickness of the film decreased to 200 nm, the crystal morphology exhibited the dendritic shape, which was built up with the stacks of micro-bind lamella. As the thickness of the film decreased to 100 nm, crystals with oriented lamellas can be observed and exhibited "island" distributing. The results indicated the distribution and the size of crystals in the thin films under low dimensional confinement.As one of the novel biodegradable diblock copolymers materials, the shape memory (SMP) materials of crosslinked PPO-b-PLLA copolymers were synthesized using Sn(oct)2 as a catalytic and isocyanate (TDI) as a crosslink agent. The effect of the crystallization on the shape memory parameters was investigated, which results elucidated the relationships between the structure and properties of such SMP materials. A series of novel biodegradable poly(ether-ester) SMP materials with different molecular configuration and shape memory properties can be obtained by adjusting the crystallization process and the crystal structures of PLLA segments.更多还原