【作者】 靳春丽；

【导师】 吴林波；

【作者基本信息】 浙江大学 ， 化学工程， 2010， 硕士

【摘要】 可生物降解形状记忆聚合物(Biodegradable shape memory polymers, BSMPs)由于同时具有可生物降解和形状记忆功能,近年来得到广泛关注,尤其在生物医用领域备受欢迎,如用作手术缝合线、骨折内固定等生物医用材料时可实现自动打结或加强固定效果,使用后可生物降解和吸收,无需拆线或二次手术取出。热致BSMPs已有很多的研究报道,并逐渐得到应用。与之相比,光致BSMPs具有形状恢复不依赖于温度、在室温或体温状态下即可恢复形变、可远程控制等特点,在生物医用材料领域也有很好的应用前景,但自2005年Lendlein等首次在Nature上报道光致BSMPs以来,现有的研究均局限于非降解的光致BSMPs,尚不具备生物材料要求的生物降解性和生物相容性。本文旨在设计、合成一种可生物降解且具有良好的生物相容性及光致形状记忆效应的新型功能聚合物—含光响应基团的可生物降解聚酯氨酯,并对其结构、性能和光致形状记忆效应进行深入研究。(1)以肉桂酸甲酯(MC)和二乙醇胺(DEA)为原料,甲醇钠为催化剂,通过氨解反应一步合成出一种光响应的功能单体N,N-二羟乙基肉桂酰胺(BHECA).以FTIR、1H NMR、HLPC、MS、DSC及元素分析等方法对其结构进行了表征和确认。考察了原料配比、温度、催化剂、反应时间对反应转化率的影响,发现随着二乙醇胺量的加大、温度的升高、反应时间的加长及催化剂量的增加,反应的转化率增加,但当温度达到120℃以上时,会有其他副反应发生。在MC:DEA摩尔比1：2,反应温度110℃,催化剂用量为MC的0.6wt%的条件下反应30 min,BHECA产率达93%,纯度达96%。(2)以辛酸亚锡为催化剂,二元醇为引发剂,进行L,L-丙交酯和ε-己内酯的活性开环聚合,得到端羟基的PLLA和PCL。再以BHECA和端羟基PCL、PLLA为原料,以六亚甲基二异氰酸酯(HDI)为偶联剂,通过两步加成聚合反应合成出含光响应基团的可生物降解多嵌段聚酯氨酯,IR、1HNMR证明产物具有预期的结构,肉桂酰胺光响应基团成功引入到聚合物柔性链中。(3)采用差示扫描量热仪(DSC)研究了共聚物的热转变行为,发现大量悬挂肉桂酰氧基团的存在会扰乱链段结构的排列,破坏了PCL链段的结晶性,软段呈现无定形状态,使得链段在室温下运动性增强,从而有利于在室温下进行光机械加工。PLLA链段仍为结晶性,但由于软段的存在其结晶能力减弱；随着PLLA分子量的增大,多嵌段共聚物的熔融温度和熔融焓会随之增大。(4)由于具有软、硬段分相的多嵌段结构,该聚酯氨酯表现出典型的热塑性弹性体的力学行为。其断裂伸长率高达230～530%,并随PCL含量的增大而增大,杨氏模量E随PLLA链段含量增加,在20～230 MPa之间变化,受PCL影响不大,抗张强度σb受多种因素影响,在10-21 MPa变化。(5)该多嵌段聚酯氨酯具有良好的光致形状记忆性能,不同配比的聚合物应变固定率Rf在32～55%,应变回复率Rr在73～98%。结晶型PLLA作为多嵌段共聚物的硬段,起到固定永久形变的作用,且随着PLLA分子量和含量的提高,应变回复率逐渐变大,当PLLA含量在50%以上时,应变回复率Rr在95%以上。柔性PCL链段和BHECA光响应单体共同构成聚合物软段部分,其中悬挂肉桂酰氧基团作为光可逆的分子开关,起到固定临时形变的作用。随着BHECA含量的增大,应变固定率Rf也相应增大,当BHECA含量在20%时,应变固定率可达到50%以上。另外,拉伸应变、辐照强度及时间等对形状记忆性能也有很大影响,辐照越强,形变回复速率越大,但辐照时间太久容易使聚合物氧化变色,反而会使回复率下降,经试验证明,最佳辐照时间在60～90min。温度、循环次数对光致形状记忆效应无明显影响,但循环次数过多,会导致应变回复率下降。更多还原

【Abstract】 Thermally induced biodegradable shape memory polymers (TBSMPs) have been paid much attention in recent years due to their excellent shape-memory function and biodegradability. They have found many application fields, especially in biomedical application such as sutures, bone-fixing materials to facilitate knotting and fixing in surgical operations and to avoid second operation to take them out of the body. With comparison to thermally induced SMPs, light-induced SMPs are characterized by temperature-independent shape memory effect and possible remote light triggering and may find biomedical and other applications. Nondegradable light-induced shape memory polymers were first reported by Lendlein Andreas in 2005. However, biodegradable and biocompatible LSMPs has not yet reported up to now though good biodegradability and biocompatibility are very desirded for biomedical applications.In this study, we aim to design and synthesize a kind of light-induced biodegradable shape memory polymers (LBSMPs)—biodegradable muti-block polyesterurethanes containing pendent photoresponsive cinnamamide group and possessing satisfactory shape memory effect and good biodegradability and biocompatibility.Firstly, N,N-Bis(2-hydroxyethyl)cinnamamide (BHECA), a diol monomer with a pendent photoresponsive cinnamamide group was successfully synthesized in high yield from methyl cinnamate (MC) and diethanolamine (DEA) under mild conditions. The product was characterized with element analysis, FTIR,1H NMR, MS, DSC and HPLC. The reaction was infuenced by ratio of raw materials, temperature and reaction time, etc. The reaction conversion increased with the increasing of the temperature, the dose of catalyst, the quantity of diethanolamine. It leveled off at 110℃,0.6wt% of MC and n(MC:DEA)=1:2, respectively. The reaction conversion can be as high as 99%. BHECA with purity of 96% was synthesized at a yield of 93% at the following conditions:reaction temperature 110℃, n(MC:DEA)=1:2,30min. This ammonolysis approach is characterized by readily available and safe raw material, high yield, easy separation and nonuse of organic solvent.Then biodegradable multiblock polyesterurethanes containing pendent photoresponsive cinnamamide groups were synthesized via a two-step polyaddition reaction using N,N-bis(2-hydroxyethyl) cinnamamide as molecular switch, aliphatic polyester diols as biodegradable soft and hard segments, and diisocyanate as coupling agent. They were characterized by IR,1H NMR, which furtherly confirmed its multi-block structure.The existence of pendent cinnamamide groups disturbed the molecular structure of soft segments and greatly destroyed the crystallinity of PCL. The amorphous nature of the soft segments facilitates to deform of the polymer and to be processed photomechnically at room temperature. However, the hard PLLA segments remained crystallized though the crystallization was depressed to cetain extent due to the existence of the soft segments. The melting temperature and enthalpy increased with PLLA molecular weight.The flexible PCL segments studded with BHECA moieties are amorphous and constitute the soft phase. The crystallized PLLA segments act as physical crosslinks and compose the hard phase. Therefore, the resultant polymers behaved as thermoplastic elastomers at room temperature. The tensile strength, modulus and elongation at break range 10-20 MPa,20-230 MPa and 230%-530%, respectively. The elongation increases with increasing the content of soft PCL segments.The pendent cinnamamide groups work as photoresponsive molecular switches and endow the polymer with light-induced shape memory behavior via reversible [2+2] cycloaddition crosslinking. The Rf, Rr range 32～55% and 73～98%, respectively, with different compositions. The strain fixity rate Rf increases with the content of BHECA moieties and the strain recovery rate Rr increases with PLLA content. The Rf reaches 50% at a BHECA content of 20 wt% and the Rτreaches>95% at PLLA content of 50 wt%.Besides, the shape memory effect was also dependent on the strain, the irradiation time and light density. The recovery rate increased with the light density, while too long irradiation time and large deformation were not favorable to the shape memory behavior. The best irradiation time was 60-90min. Temperature and cycles had no significant influence on shape memory effect, but the Rr will have a large decrease after repeated many times.更多还原