共沸缩聚-解聚法高效合成乙交酯

乙交酯是聚羟基乙酸的单体,乙交酯的合成直接影响聚羟基乙酸的合成。一般用羟基乙酸(酯)制备乙交酯,但是,制备乙交酯的缩聚过程需要真空高温的条件,消耗大量的能量。共沸缩聚-解聚法制备乙交酯的缩聚过程,具有条件温和、无催化剂、溶剂可回收的优点。羟基乙酸通过共沸缩聚-解聚法得到乙交酯。用X-射线粉末衍射、红外分析、差热分析等方法对聚羟基乙酸低聚物进行了表征。结果表明：羟基乙酸制备的聚羟基乙酸低聚物是一种半结晶聚合物,聚羟基乙酸低聚物解聚得到产率为81.26%和纯度为89.29%的乙交酯,并且解聚反应残渣可以重复利用来制备乙交酯。     

聚羧基乙酸及其共聚物

对聚羧基乙酸及其共聚物的合成方法，生物降解性，生物相容性，力学性能，共聚改性等方面的研究进展做了综述，并讨论了聚羟基乙酸类材料的医学应用现状及前景。     

高压下开环聚合制备聚羟基乙酸的工艺研究

从乙交酯(GA)单体出发,以二水合氯化亚锡(SnCl2.2H2O)为催化剂,在高压条件下,进行开环聚合制备高分子量的生物可降解材料聚羟基乙酸(PGA);通过一系列的单因素实验研究了乙交酯的纯度、聚合压力、催化剂用量、聚合时间等因素对聚羟基乙酸相对重均分子量(Mw)的影响规律,根据单因素实验的结果设计并进行了正交试验。采用STATISTICA6.0对正交试验的数据进行分析,得出最优工艺:反应温度196.5℃,反应时间3.5h,催化剂用量n(cat.)/n(GA)=1.7×10-5。进行该工艺验证实验,制备了相对重均分子量可以达到1.61×105的聚羟基乙酸。     

侧链含炔丙基的PLGA-PEG-PLGA三嵌段共聚物的合成与表征

通过简单易行的技术路线合成了炔丙基化乙交酯单体,以1,4-二甲氨基吡啶为催化剂,亲水性和生物相容性良好的聚乙二醇为大分子引发剂,在较滥条件下引发炔丙基化乙交酯和丙交酯的开环共聚,制备了侧链含炔丙基的聚(乳酸-羟基乙酸)-聚乙二醇-聚(乳酸-羟基乙酸)(PLGA-PEG-PLGA)三嵌段共聚物,并对产物的组成与结构进行了表征.为生物孤犊触乳聚酯的分子修饰、生物相容性的提高探索一条简单而有效的途径     

用三辛胺和正辛醇络合萃取羟基乙酸的机理研究

以三辛胺和正辛醇为萃取剂,对羟基乙酸进行萃取分离,通过萃取有机相红外谱图的分析,得出络合萃取过程中羟基乙酸与萃取相之间的成键机理为离子缔合与氢键结合。然后,根据萃取中存在的络合萃取平衡、物理萃取平衡和电离平衡,推导出羟基乙酸分配系数模型公式。将达到平衡时的油水两相羟基乙酸浓度值与分配系数的模型公式相结合,得出萃取形成的络合物中,羟基乙酸与三辛胺的结合比例为1∶1和2∶1。     

聚(乳酸-羟基乙酸)共聚物涂层的释药性能

以乙酸乙酯为溶剂,配制聚(乳酸-羟基乙酸)共聚物(PLGA)雷帕霉素溶液,利用滴涂法在316L不锈钢表面制备PLGA载药涂层。于37℃磷酸盐缓冲液(PBS)中进行体外动态药物释放,并用紫外-可见分光光度计测定药物释放量。结果表明:PLGA涂层中PLGA分子量越小,羟基乙酸(GA)含量越高,药物释放越快;药物释放量与滴涂量呈线性关系,药物释放率与滴涂量的倒数呈线性关系;涂层中药物含量增加,其释放量也随之增加,而药物释放率先增加后降低。     

乙酸存在下磷酸铁催化对甲酚气相选择性氧化

 在乙酸存在和空气气氛下,以磷酸铁为催化剂进行了对甲酚气相选择氧化生成对羟基苯甲醛和对羟基苯甲醇的反应. 考察了不同乙酸/对甲酚比和反应温度对反应产物分布的影响. 结果表明,加入乙酸可抑制目标产物深度氧化,促进气相反应中高选择性地生成对羟基苯甲醛和对羟基苯甲醇. 在反应温度为250 ℃,乙酸/对甲酚比为0.9,催化剂用量为0.35 g和对甲酚流速为1.92 g/h时,生成对羟基苯甲醛的选择性为34.4%,生成对羟基苯甲醇的选择性为65.6%.     

笼形聚偕胺肟树脂对羧酸的吸附作用

研究了碱处理笼形聚偕胺肟树脂（ＢＣＡＯ）对饱和一元脂肪酸、二元脂肪酸、不饱和脂肪酸、α－取 代乙酸和羟基羧酸的吸附作用。发现ＢＣＡＯ对羧酸强烈吸附。一元羧酸在ＢＣＡＯ上以多分子层吸附占优势,二元和三元羧酸则以单分子层吸附为主要特征;后者作为阴离子聚体吸着在ＢＣＡＯ表面,形成了对外来的羧酸阴离子起排斥作用的离子场。     

多种形貌和晶型8-羟基喹啉铜微纳米材料的简易合成

以8-羟基喹啉和乙酸铜为主要原料,通过简单调控醇水介质和熟化时间,液相沉淀法快速合成出大量不同形貌和晶型的8-羟基喹啉铜微纳米材料.采用SEM,XRD,UV-Vis,FT-IR对产物进行表征.结果表明,以8-羟基喹啉盐酸水溶液与乙酸铜水溶液反应,合成了直径40～130nm的棒状α型二水合8-羟基喹啉铜沉淀物.以8-羟基喹啉乙醇溶液与乙酸铜乙醇溶液反应,获得了厚度约300nm的三维(3D)板条束状α型无水8-羟基喹啉铜微纳米结构.若采用8-羟基喹啉乙醇溶液与乙酸铜的乙醇/水溶液反应,当体系醇/水体积比为3∶1时,随着熟化时间的延长,产物由亚稳的α型和γ型晶相向稳定的β型晶相转变,形貌从胡须束状/菱片状混合结构转变为纳米棒状/菱片状混合结构,50min熟化后最终形成菱片状β型二水合8-羟基喹啉铜及其四角星形自组装体.     

水溶性香豆素荧光底物的制备及在液滴数字式检测中的应用

4-甲基伞形酮磷酸酯(4-MUP)是一类重要的荧光底物, 由于具有较高的疏水性, 荧光信号易在液滴间扩散而限制了其在液滴微流控芯片领域中的应用. 本文首先通过修饰7-羟基香豆素-4-乙酸, 制备了具有较高水溶性的新型底物分子7-二羟基磷酸酯香豆素-4-乙酸甲酯; 进而以7-二羟基磷酸酯香豆素-4-乙酸甲酯为底物, 以球刷酶(荷载大量碱性磷酸酶的聚电解质纳米颗粒, SP-AKP)为模式酶, 建立了基于液滴微流控的单SP-AKP数字式检测体系. 结果表明, 该水溶性香豆素荧光底物具有与传统4-MUP底物相似的荧光光谱和酶催化性能. 传统4-MUP酶促荧光产物5 min即在液滴中发生明显扩散, 而该水溶性香豆素荧光底物酶催化后产生的荧光产物7-羟基香豆素-4-乙酸甲酯在24 h后仍未观察到明显扩散现象, 具有优异的抑制荧光扩散性能. 在基于液滴微流控芯片的单SP-AKP数字式检测中, 对SP-AKP的检测限可达29.9 amol/L, 同时有效提升了检测时间的可操作性与数字式信号读取的准确性. 新型水溶性香豆素荧光底物有望替代4-MUP应用于以基于液滴数字式超敏生物检测为代表, 在液滴分区实现酶促反应进行超灵敏检测的众多检测领域中.     

Hierarchically structured polyglycolide – a biomaterial mimicking natural bone

Polyglycolide (poly(hydroxyacetic acid)) with wide variability of pore size can be prepared by combination of a solid-state polymerization reaction and addition of sodium chloride crystals. The solid state reaction leads to a composite of polyglycolide and NaCl. The latter can be washed out with water leaving behind porous polyglycolide with interconnected pores in the micrometer range. To achieve a higher porosity and to induce larger pores, additional coarse sodium chloride was added before polymerization. This opens a way to functionally graded polyglycolide resembling natural bone that should have a potential as bone substituting material.     

New high-yield,one-step synthesis of polyglycolide from haloacetic acids

In a new, one-step synthesis, polyglycolide was prepared by the reaction of bromo- or chloroacetic acid with triethylamine in a nitromethane solution. It was discolored, by iodoacetic acid possibly as a result of iodine formed by the decomposition of triethylammonium iodide. The structure of polyglycolide was characterized by hydrolysis, ¹H-NMR and IR spectra, and x-ray powder diffraction, which indicated partial crystallinity. A mechanism is proposed for the formation of polyglycolide. A lower limiting value of the number-average molecular weight of 10⁴ was determined by cryoscopy in 1,3-dinitrobenzene for polyglycolide prepared from bromoacetic acid; the measurement was inaccurate because of the low solubility of the polymer. No significant effect of solvent (acetone, ether, or chloroform) on yield or melting point was observed; a higher yield was obtained in nitromethane. The polymer obtained with tri-n-propylamine and bromoacetic acid had properties similar to that obtained with triethylamine. No polymer was obtained with N,N-dimethylaniline and bromoacetic acid or with triethylamine and bromoacetic acid in aqueous solution.     

Modification of chitosan via grafting of glycolic acid followed by polycondensation during heat treatment

The modification of chitosan via grafting of glycolic acid and subsequent polycondensation during heat treatment have been studied. The formation of copolymers, the degree of amidization of amino groups, and the length of side polyglycolide chains are investigated by IR spectroscopy and gravimetry. The structural features and surface behavior of the films based on chitosan modified by poly(glycolic acid) are examined by X-ray diffraction and AFM. The grafting of side polyglycolide chains leads to marked changes in the chitosan structure. The study of the sorption behavior of the films based on the modified chitosan confirms the hydrophobization of chitosan via grafting of poly(glycolic acid).     

A Single Crystal Study of a Solid-state Polymerization Reaction

Halogenoacetates are known to undergo a solid-state elimination reaction to metal halide and poly(hydroxyacetic acid), polyglycolide. Earlier studies have shown that the reaction takes place exclusively in the solid-state without the occurrence of liquid intermediates. Single crystals of sodium chloroacetate and silver chloroacetate were reacted and studied with X-ray diffractometry, scanning electron microscopy and thermomicroscopy. The results show that the reaction leads from single crystals to a composite of polyglycolide and metal halide. Neither the salt nor the polymer exhibit a preferred crystallographic orientation, therefore it must be concluded that the crystal lattice is not preserved during the reaction.This revised version was published online in November 2005 with corrections to the Cover Date.     

An Atomistic Modeling and Quantum Mechanical Approach to the Hydrolytic Degradation of Aliphatic Polyesters

This paper reports computational simulations at two different scales employed to investigate the hydrolytic degradation of two homopolyesters: polyglycolide, PGA and poly(L-lactide), PLLA. Atomistic bulk models were used to investigate the dry and various hydrated states of the two systems. In addition, the first moments of contact between the polymers and water were studied employing atomistic interface models. A higher affinity of water to polyglycolide in comparison with poly(L-lactide) was observed, while diffusion of water was found to be lower in the first polymer. Quantum chemical calculations for the first step of the water-assisted hydrolysis revealed a higher resistance to hydrolytical scission of the L-lactyl units in comparison to glycolyl units.     

An in situ IR-spectroscopic study of the solid-state formation reaction of polyglycolide

The thermal elimination of NaCl from sodium chloroacetate, a polymerization reaction that takes place between 150 and 200C in the solid state, leads quantitatively to the simplest polyester, polyglycolide. Byin situ IR-spectroscopy, we have shown that the reaction proceeds smoothly and directly without intermediates or by-products. The endgroups of the polymeric product — ionised carboxylate groups (-COONa) and hydrogen-bonded alcohol groups (–COH) — are clearly detectable. It is therefore concluded that the polymer forms extended chains, not rings, during the course of this solid-state reaction. That corresponds well with the idea of a polymerization reaction in the solid state. However, this experiment does not exclude the formation of polyglycolide rings as further product because they do not contain any terminating groups.M. E. and H. K. thank Prof. A. Reller, Hamburg, for generous support. Dr. G. Sankar, London, is acknowledged for experimental assistance. This work was supported by the Deutsche Forschungsgemeinschaft (Bonn, Germany), the Fonds der Chemischen Industrie (Frankfurt/Main, Germany) and the Engineering and Physical Sciences Research Council (UK).     

Synthesis and characterization of degradable electrically conducting copolymer of aniline pentamer and polyglycolide

A novel block copolymer of polyglycolide (PGA) and aniline pentamer that is electro-active and degradable was synthesized. The copolymer was prepared by low-temperature polycondensation between carboxyl-capped aniline pentamer and hydroxyl-capped PGA, with N,N′-dicyclohexylcarbodiimide (DCC) as dehydrating agent. The structures of monomers and the copolymer were characterized by IR, ¹H NMR. The chemical redox process of the as-prepared copolymer was studied by UV-vis spectra and cyclic voltammetry (CV). Thermal analysis and the study of degradation show that the copolymer has good thermal stability and degradability.     

Kinetics and mechanism of biodegradation of (co)polyglycolide sutures

Biodegradation in vivo of modified and unmodified PG (polyglycolide) and PGL (copolymer glycolide — L — lactide) monofilament sutures were studied using ¹H- NMR, wide and small angle X-ray scattering, differential scanning calorimetry (DSC), electron microscopy (EM), Fourier transform (FT) Raman spectroscopy methods. It was found that the process includes a steady-state and accelerated stages of biodegradation. The suture biostability depends on polymer morphology changing widely over the suture draw ratio. The modification of polymer chain results in an increase in suture useful lifetime without significant changes of complete polymer degradation time. It was also established the important role of weak intermolecular hydrogen bonds such as CH–-O=C in the suture stability.     

Synthesis and characterization of biodegradable-cum-crosslinkable well-defined polyesters via chain-growth polycondensation in solid-liquid phase

Well-defined aliphatic polyesters, polyglycolide (PGA), polylactide (PLA) and their copolymers (PLGA) were prepared by chain-growth polycondensation of potassium 2-bromocarboxylates in solid-liquid phase. The polymerization proceeded in a living fashion without any side reactions. The degrees of polymerization (D_p) of polyesters was in agreement with the feed ratio of monomer to initiator. The polymer, which was only composed of heptamer, octamer and nonamer, possessed a narrow molecular weight distribution. Furthermore, the end groups of polymers, such as allyl and phenyl units, were directly yielded during the polymerization for the further modifying and crosslinking. The synthesized polyesters with allyl end groups were successfully crosslinked, and the products possessed biodegradability in phosphate buffer solution at 37 °C.     

Application of R.O.P. in polymerization of furanic oligoesters with cyclic esters: Synthesis,characterization and degradation

Furano-Aliphatic copolyesters, such as poly(propylene furanic)-co-(polycaprolactone) (PPF-co-PCL), Poly(propylene furanic)-co-(polylactide) (PPF-co-PLA) and Poly(propylene furanic)-co-(polyglycolide) (PPF-co-PGA) were prepared by ring opening polymerization (R.O.P.) using monomers derived from renewable resources. These copolyesters were characterized by ¹H-NMR, DSC and TGA. The degree of randomness determined by ¹H-NMR is close to 1, reflecting a random distribution, sometimes less than one. This indicates that these polyesters have a character to block. The hydrolytic degradation of polymers was performed at pH 4.35 at 37°C over a period of four weeks. The oxidative degradation proved a mass loss of about 50%.