高分子量DL-丙交酯的合成及热降解

研究了聚ＤＬ－丙交酯（ＰＤＬＬＡ）的合成及热降解性能。发现影响聚合物分子量的关键因素是单体的重结晶、引发剂的浓度以及安瓿瓶在封管时的干燥和真空度。采用ＤＳＣ、ＴＧＡ分析了ＰＤＬＬＡ的玻璃化转变和热分解。ＰＤＬＬＡ是热不稳定聚合物,影响其热稳定性的主要因素是残留单体、催化剂和低聚物的含量,将聚合物溶解沉淀处理可以延缓其热解速度,提高它的热稳定性。     

高分子量外消旋聚乳酸的合成、表征及工艺优化

通过丙交酯开环聚合制备了高分子量的外消旋聚乳酸(PDLLA),研究了反应温度、反应时间以及催化剂与单体的物质的量之比对PDLLA数均分子量的影响,获得了优化的聚合工艺条件。采用凝胶渗透色谱(GPC)、傅里叶红外光谱(FT-IR)、核磁共振波谱(NMR)、扫描电镜(SEM)、差示扫描量热(DSC)、热重分析(TGA)、电子万能试验机等对所制备聚乳酸的数均分子量、化学结构、热性能、力学性能进行了表征,并研究了PDLLA膜的降解性能及与小鼠成纤维(L929)细胞的生物相容性。根据正交实验结果,当催化剂与单体的物质的量之比为2.04∶5 000、反应温度为135℃、聚合时间为4.5 h时,可得到数均分子量为2.01×105的PDLLA。如果综合考虑单体转化率,则反应时间可选为6.0 h。制备得到的PDLLA的拉伸强度为(39.91±1.34) MPa,断裂伸长率为3.94%±0.54%,弹性模量为(1.68±0.34) GPa。PDLLA降解初期缓慢,降解220 d之后,降解速率迅速增加。体外生物相容性实验表明,PDLLA膜可促进L929细胞的增殖。     

低毒锌类催化剂制备聚乳酸的研究

采用低毒锌类催化剂制备了一系列具有高分子量、不同光学纯度及热力学性质的聚乳酸材料. 以金属锌作催化剂制备丙交酯, 研究了不同裂解温度对产物光学纯度的影响. 随后在低毒催化剂乳酸锌的作用下使丙交酯开环聚合, 进一步研究了单体的光学纯度对聚乳酸立体规整性的影响, 以及聚合过程中的结晶对聚合物分子量和热力学行为的影响. 并用旋光仪、核磁共振氢谱(1H NMR)、凝胶渗透色谱(GPC)、差示扫描量热分析(DSC)等方法对产物进行表征. 结果表明, 合适的裂解温度有利于合成高光学纯度的丙交酯; 在低毒乳酸锌的催化作用下, 高光学纯度的单体以及聚合过程中的结晶都有利于制备高分子量聚乳酸.     

高分子量聚L-乳酸热降解回收L-丙交酯

本文综述了高分子量聚L-乳酸(Poly(L-lactide), PLLA)经热降解直接回收L-丙交酯的研究进展。纯PLLA的热降解为无规反应,经添加金属类催化剂后,PLLA则可获得以L-丙交酯为主的热降解产物。本文介绍了聚乳酸热降解的反应机理,详细阐述了添加的金属催化剂的种类,及其催化PLLA热降解生成L-丙交酯及发生消旋化作用的机理。经PLLA热降解直接回收L-丙交酯技术的研究,可缩短PLLA再循环使用周期,既降低生产成本,又充分利用资源,达到促进发展循环经济的目的。     

乙酰丙酮铁催化丙交酯开环聚合的研究

以乙酰丙酮铁 [Fe(acac) 3]为催化剂进行D ,L 丙交酯的开环聚合及在聚乙二醇 (PEG)存在下的开环共聚 ,研究了催化剂用量、反应温度和反应时间对聚合反应的影响以及PEG用量对共聚反应的影响 ,并探讨了丙交酯开环聚合机理 .结果表明 ,Fe(acac) 3是按配位 插入机理催化丙交酯开环聚合的 ;在本文的聚合条件下 ,大部分聚合的单体转化率都达 90 %以上 ,聚合产物的粘均分子量最高可达 6 6 0 0 0 ,均显示出较好的催化性能 .在PEG存在下 ,PEG作为引发剂参入了丙交酯的开环聚合 ,D ,L 丙交酯是沿着PEG分子两端开环聚合的 ,分子链的链端结构是以羟基为端基的乳酰基结构单元 ,Fe(acac) 3有促进PEG参与聚合成酯的作用 .     

稀土配位催化合成聚乳酸

本文开发了合成聚乳的一类新型催化剂, 它是由稀土化合物-三烷基铝-水组的配位催化剂。试验表明稀土配位催化剂可以使丙交酯在甲苯溶液中以高转化率聚合, 得到分子量可控的聚乳酸。并研究了稀土元素种类、不同配位基团及聚合条件变化对丙交酯开环聚合的影响。     

醇铁化合物引发丙交酯开环聚合的研究

分别以乙醇铁、正丙醇铁、异丙醇铁、正丁醇铁为引发剂进行D,L-丙交酯和L-丙交酯的本体开环聚合,研究了在130℃的聚合温度下引发剂用量和聚合时间对聚合反应的影响.结果表明这些醇铁化合物对丙交酯开环聚合都有较好的引发作用;聚合36h,单体转化率可达90%以上.单体转化率在引发剂/单体摩尔比为1/1000时最高,然后随引发剂用量增加和聚合时间延长而降低.乙醇铁表现出最高的引发活性,聚合产物的相对粘均分子量最高可达7·28×104[聚(D,L-丙交酯)]和19·00×104[聚(L-丙交酯)].醇盐配体对聚合产物的分子量和分子量分布影响显著,随醇铁配体体积增大,聚合产物的分子量逐渐降低,分子量分布也逐渐加宽.1H和13C-NMR分析表明醇铁对L-丙交酯的开环聚合没有发生消旋化,对D,L-丙交酯的开环聚合有一定的等规加成选择性.MALDI-TOF MS分析指出D,L-丙交酯在开环聚合过程中发生了分子间的酯交换反应,用13C-NMR评价了各醇铁引发体系在聚合过程中的酯交换程度.但基于谱峰分辨原因,醇铁配体对立构加成选择性和酯交换的影响的规律性不明显.     

低左旋度聚丙交酯的分子结构及体外降解行为研究

以辛酸亚锡为催化剂,135℃下低左旋度的l-丙交酯([a]_(Na)~(25)=—231°)开环聚合制备了低左旋度聚(l-丙交酯)[l-PLLA]([a]_(CHCl_3)~(25)=-119.7°),并用同核去偶~1H-NMR谱表征其分子链结构。用成纤模压法制备了该聚合物的棒材(φ=3.2mm)试样,研究了其在37℃的模拟体液(SBF)中的降解行为。结果表明,l-PLLA具有良好的力学性能,其初始弯曲强度(σ_b)、剪切强度(σ_s)以及弯曲模量(E_b)虽比聚(l-丙交酯)(PLLA)低,但均比聚(dl-丙交酯)(PDLLA)高得多,且材料表现出很好的韧性,呈非晶态,其分子量下降速率和失重速率都介于PLLA和PDLLA之间,可望是一种良好的骨折内固定材料。     

静电纺丝法制备胆固醇-g-聚乳酸液晶/ 聚乳酸复合纳米纤维膜

以辛酸亚锡为催化剂, 胆固醇(CHOL)为共引发剂引发D,L-丙交酯开环聚合, 制备了胆固醇-g-聚(D,L-乳酸)(CHOL-g-PDLLA)低聚物, 采用偏光显微镜(POM)和差示扫描量热(DSC)方法考察了其液晶特性. 通过静电纺丝技术制备了CHOL/PDLLA和CHOL-g-PDLLA /PDLLA复合纳米纤维膜, 对其形貌、界面相容性、孔隙率、拉伸性能和细胞相容性进行了研究. 结果表明, CHOL-g-PDLLA为一种热致胆甾型液晶, 液晶温度区间为21.8~74.5 ℃; CHOL-g-PDLLA/PDLLA复合纳米纤维膜的纤维形态良好, 表面均匀光滑, 孔隙率在70%~75%之间, 且其界面相容性优于相应的CHOL/PDLLA. 随着CHOL和CHOL-g-PDLLA含量的增加, 复合纳米纤维膜的拉伸强度逐渐下降, 但CHOL-g-PDLLA/PDLLA复合纳米纤维膜的拉伸强度显著大于CHOL/PDLLA. 体外骨髓间充质干细胞培养结果显示, CHOL-g-PDLLA/PDLLA复合纳米纤维膜具有良好的细胞相容性, 且优于相应的PDLLA和CHOL/PDLLA纳米纤维膜.     

低分子量结晶性丙交酯/乙交酯与己内酯/乙交酯共聚物热转变温度的组成与分子量依赖性

以1,4-丁二醇为引发剂、辛酸亚锡为催化剂,通过L-丙交酯(LLA)、乙交酯(GA)、ε-己内酯(CL)的开环共聚,制得了低分子量的端羟基结晶性LLA/GA共聚物(PLLGA)和CL/GA共聚物(PCG),分别以FTIR1、H-NMR、GPC、DSC对其微结构和热转变温度进行了表征,重点考察了其热转变温度的组成、分子量依赖性.结果表明,利用辛酸亚锡/二元醇引发开环聚合,通过改变单体配比和单体/引发剂配比,可方便地调控共聚物的组成和分子量;通过改变共聚物的组成和分子量,可在较宽的范围内调节共聚物的热转变温度,并得到了玻璃化温度和熔点与组成、分子量之间定量的经验关系式.     

Biodegradable Polymers for Orthopedic Applications: Synthesis and Processability of Poly (l-Lactide) and Poly (Lactide-co-€-Caprolactone)

Abstract

The synthesis of poly(l-lactide) (PLLA), poly(l-lactide-co-e-caprolactone), and poly(DL-lactide-co-e-caprolactone) by ring-opening bulk polymerization was investigated. Polymerization temperature had a significant effect on the PLLA molecular weight. At 184°C a polymer with a molecular weight of only 10 × 10⁴ resulted. This was lower by a factor of 2 than that obtained at 103 and 145°C. The stannous octoate (SnOct) concentration, with a monomer/SnOct molar ratio in the range of 1,000 to 10,000, was not found to have a significant effect on the PLLA molecular weight. A heterogeneous structure in polymerized PLLA was observed. The intrinsic viscosity of poly(lactide-co-€-caprolactone), obtained at 130°C, monomer/SnOct molar ratio 5,000, and polymerization time of 30 hours, decreased with increasing €-caprolactone content within the first 9 wt% and then leveled off. Die-drawing of PLLA cylinders, for the purpose of increasing the polymer's mechanical strength, was unsuccessful due to the brittleness of the polymer. The drawability of poly(l-lactide), however, was greatly improved by copolymerization with €-caprolactone. With only 3 wt% of €-caprolactone, for example, the tensile strength of die-drawn poly(l-lactide-co-e-caprolactone) was increased by a factor of more than 3. Polymer processing temperature was also investigated. The requirement for low processing temperatures in melt manufacture of controlled release matrix devices containing thermal sensitive drugs was accomplished by three methods: through the use of low molecular weight poly(DL-lactide), adding (DL-lactic) acid oligomer to high molecular weight PDLLA, and copolymerizing DLLA with €-caprolactone. The glass transition temperatures of the modified high molecular weight PDLLA decreased significantly. Melt extrusion below 100°C could be performed.     

Improved hydrolytic stability of poly(dl-lactide) with epoxidized soybean oil

The multi-arm star polymer (ESOPLA) was obtained by ring-opening polymerization of dl-lactide using multifunctional epoxidized soybean oil (ESO) as an initiator in the presence of a stannous actuate (SnOct₂) catalyst. Gel permeation chromatography with multi-angle laser light scattering (GPC-MALLS), FTIR, ¹H NMR, thermal analysis and in vitro degradation were used to qualitatively characterize the synthesized polymers. The results revealed that ESO plays an important role in increasing the molecular weight, polymerization rate and monomer conversion rate. Degradation analysis demonstrated that the decrease in molecular weight and the weight loss ratio of the star-shaped ESOPLA were lower than that of linear poly(dl-lactide) (PDLLA). The surface topography of pre- and post-degradation materials was characterized by scanning electron microscopy (SEM). These SEM images showed that the linear PDLLA films underwent water erosion more readily than the star-shaped polymer films.     

高分子量聚对二氧环己酮改进聚DL-乳酸柔韧性的研究

为了提高DL-聚乳酸(PDLLA)的柔韧性,将10～20wt%不同比例的由本课题组自主合成的高分子量聚对二氧环己酮(PPDO)加入到PDLLA基体中,对共混物的微观两相形态、力学性能、热学性能和表面性质、降解性能等物化性质进行了研究.实验结果表明,PPDO加入后,在PDLLA/PPDO共混物的柔韧性得到显著提高的同时,共混物表面亲水性相应提高,降解速率也随之加快.     

八甲基环四硅氧烷正离子细乳液开环聚合动力学

以十二烷基苯磺酸钠(SDBS)为乳化剂,硫酸或盐酸为催化剂,八甲基环四硅氧烷(D4)为单体,十六烷为共稳定剂,超声预乳化,制备了聚硅氧烷细乳液,研究了超声时间、催化剂用量、乳化剂用量和温度对聚合动力学的影响.结果表明,在一定酸度范围内,聚合速度与硫酸浓度0.81次方、与盐酸浓度1.02次方、与乳化剂浓度-0.66次方成正比,反应的表观活化能为40.56kJ/mol.     

镧配位催化N-十八烷基马来酰亚胺均聚合

N-取代马来酰亚胺聚合物中的酰亚胺环为平面五元环结构,阻碍了酰亚胺单元绕聚合物主链的旋转,限制了聚合物主链的运动,使聚合物的热性能和化学稳定性得到了很大的提高．近些年来,有关N-取代马来酰亚胺均聚合研究的报道已经有很多,但大多采用自由基聚合方法和负离子聚合方法,采用配位催化聚合方法很少．     

Cyclopolycondensations. VII. Preparation of aromatic poly(ureido acids) by the low-temperature solution polymerization and cyclodehydration to fully aromatic polyquinazolinediones

Fully aromatic polyquinazolinediones (IV) of high molecular weight were obtained by thermal cyclodehydration of aromatic poly(uredio acids) (III) prepared by the polyaddition reaction of 4,4′-diaminobiphenyl-3,3′-dicarboxylic acid (I) with aromatic diisocyanates (II). From the kinetic study of reactions of model systems (anthranilic acid with phenyl isocyanate) in the presence of a variety of basic catalysts, it was established that tertiary amines had the highest catalytic activity for the formation of ureido linkage. The optimum polymerization conditions were determined by the study of reaction variables such as monomer concentration, polymerization temperature, monomer ratio, and catalyst concentration. The effect of polarity and purity of organic solvents and reactants was also studied.     

Influence of preparative conditions on molecular weight and stereoregularity distributions of polypropylene

The influence of preparative conditions on the molecular weight and stereoregularity distributions of polypropylene was investigated. The stereoregularity distribution is narrowed by using a highly stereospecific catalyst, by decreasing the polymerization temperature, and for the three-component catalyst by keeping the mole proportion of the electron-donating third component at 0.5. The molecular weight distribution can be narrowed by using a highly stereospecific catalyst, a high monomer concentration, and a high polymerization temperature, and by having a lower conversion, particularly at low monomer concentration. The possibility of long-chain branching in polypropylene was indicated by data from the fractionation of tritium-labeled polymers.     

异戊二烯在Nd(naph)_3-Al(i-Bu)_3-Al_2(C_2H_5)_3Cl_3催化体系作用下聚合动力学

本文研究了异戊二烯在稀土催化剂作用下聚合动力学的一般规律。通过稳态处理及分段聚合证明,体系的活性中心数目基本稳定。聚合转化率低于50％时,聚合速率与单体浓度呈一级关系,同催化剂浓度为1.7级关系。聚合表观活化能为9.0千卡/克分子。聚合物的特性粘数随转化率增加而增大的事实,说明本体系具有某些“活性”聚合的特性。