Triblock and star-block copolymers of N-(2-hydroxypropyl)methacrylamide or N-vinyl-2-pyrrolidone and D,L-lactide: synthesis and self-assembling properties in water

Novel A-B-A triblock and star-block amphiphilic copolymers, i.e. poly(N-(2-hydroxypropyl)methacrylamide)-block-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)metha-crylamide), poly(N-vinyl-2-pyrrolidone)-block-poly(D,L-lactide)-block-poly(N-vinyl-2-pyrrolidone), star-poly(D,L-lactide)-block-poly(N-(2-hydroxypropyl)methacrylamide) and star-poly(D,L-lactide)-block-poly(N-vinylpyrrolidone), were synthesized and characterized. These polymers were prepared by free radical polymerization of N-(2-hydroxypropyl)methacrylamide and N-vinyl-2-pyrrolidone in the presence of either poly(D,L-lactide) dithiol or star-poly(D,L-lactide) tetrakis-thiol, both biodegradable macromolecular chain-transferring agents. All copolymers self-assembled in aqueous solution to form supramolecular aggregates of 20–180 nm in size. The critical aggregation concentration of the copolymers ranged from 5 to 24 mg/L, depending on their hydrophobicity. The partition equilibrium constant of pyrene in the hydrophobic core of micelles was between 0.71×10⁵ and 1.63×10⁵. The triblock copolymer micelles were loaded with two model poorly water-soluble drugs, namely, indomethacin (1.5–16.4% w/w) and paclitaxel (0.4–1.5% w/w), by a dialysis procedure. These triblock and star-block copolymers could prove useful as nanocarriers for the solubilization and delivery of hydrophobic drugs.     

Preparation,Characterization and Biodegradation Characteristics of Poly(adipic anhydride-co-D,L -lactide)

Poly(adipic anhydride-co-D ,L -lactide) (P(AA-LA)) has been synthesized by ring-opening polymerization of adipic anhydride (AA) and D ,L -lactide (LA) using stannous octoate as catalyst in bulk and in solution. The copolymers were characterized by IR, nuclear magnetic resonance, gel permeation chromatography and differential scanning calorimetry. The physical properties can be tailored by varying the copolymer compositions, and showed low glass transition temperature, melting temperature and good solubility in common solvents. In vitro tests showed that after rapid weight loss in the first day, a constant degradation rate was observed. The release profiles of model drugs, bovine serum albumin and norethindrone over 16 days followed closely that of the degradation of copolymers containing higher amounts of AA (AA>64mol%), suggesting that the release mechanism was controlled predominantly by surface erosion. However, a large deviation from the close correlation of polymer degradation and drug release was observed for copolymers containing lower amounts of AA (<30mol%). These materials may be useful in protein delivery systems. © 1997 SCI.     

有机锡化合物引发D,L-丙交酯的开环聚合

D,L-丙交酯在有机锡化合物四苯基锡(Ph4Sn)、三正丁基醋酸锡(Bu3SnOAc)、辛酸亚锡(SnOct2)等催化剂引发下开环聚合,得到高分子量的聚D,L-乳酸,讨论了聚合单体D,L-丙交酯纯度、聚合温度、聚合时间、聚合体系真空度以及引发剂有机锡催化剂与聚合单体D,L-丙交酯的比例对聚D,L-乳酸合成的影响,通过红外光谱和核磁共振光谱对聚D,L-乳酸的结构进行了表征。实验结果表明,D,L-丙交酯开环聚合反应的较佳工艺路线是:D,L-丙交酯重结晶5次,聚合温度140℃,聚合时间24 h,聚合体系真空度13.3~133.3 Pa,引发剂有机锡催化剂与单体D,L-丙交酯比例0.2‰~0.5‰,此时聚D,L-乳酸的粘均分子量最高,分别达到32.46×104,33.43×104和41.36×104。     

氮气鼓泡法制备L-丙交酯的新工艺

用氮气鼓泡法成功制得了L-丙交酯,此工艺路线中,氮气温度对丙交酯的生成至关重要,所得L-丙交酯粗品的纯度和产率比减压蒸馏所得L-丙交酯粗品的纯度和产率要高;用填料装置可完全吸收丙交酯;用活性炭对L-丙交酯粗品进行脱色比用沉淀法脱色效果好,收率较高。     

Thermal degradation behavior and kinetic analysis of poly(L-lactide) in nitrogen and air atmosphere

The non-isothermal and isothermal degradation behaviors and kinetics of poly(L-lactide) (PLLA) were studied by using thermogravimetry analysis (TGA) in nitrogen and air atmosphere, respectively. At lower heating rate ((5–10)°C/min), PLLA starts to decompose in air at lower temperature than those in nitrogen atmosphere; however, at higher heating rate ((20–40)°C/min), the starting decomposition temperature in air are similar to those in nitrogen atmosphere, not only showing that PLLA has better thermal stability in nitrogen than in air atmosphere, but also suggesting that the faster heating rate will decrease the decomposition of PLLA in thermal processing. Whether in air or in nitrogen atmosphere, the decomposition of PLLA has only one-stage degradation with a first-order decomposed reaction, suggesting that the molecular chains of PLLA have the similar decomposed kinetics. The average apparent activation energy of non-isothermal thermal degradation (Ē_non) calculated by Ozawa theory are 231.7kJ·mol⁻¹ in air and 181.6kJ·mol⁻¹ in nitrogen; while the average apparent activation energy of isothermal degradation (Ē_iso) calculated by Flynn method are 144.0kJ·mol⁻¹ in air and 129.2kJ·mol⁻¹ in nitrogen, also suggesting that PLLA is easier to decompose in air than in nitrogen. Moreover, the decomposed products of PLLA are also investigated by using thermogravimetry-differential scanning calorimetry-mass spectrometry (TG-DSC-MS). In air atmosphere the volatilization products are more complex than those in nitrogen because the oxidation reaction occurring produces some oxides groups.     

Polymer/carbon based composites as electromagnetic interference (EMI) shielding materials

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.     

不同催化体系下L-丙交酯的合成及表征研究

以乳酸为单体,采用先缩聚后解聚的方法制备了L-丙交酯。首先通过正交实验较系统的研究了合成工艺,包括三种不同催化剂(锌粉、乙酸铜及辛酸亚锡)用量、脱水温度及裂解温度对产物收率的影响；进而考察了提纯方法对丙交酯最终产率及杂质(乳酸、水)含量的影响,并利用红外、热分析及核磁共振技术对产物结构进行了详细表征。结果表明,在辛酸亚锡催化下,脱水及裂解温度分别为130℃及190℃时,L-丙交酯单体的产率达到80%；通过多次重结晶可以得到较高纯度产物。     

L-丙交酯与ε-己内酯共聚物微观结构与热力学性能研究

以辛酸亚锡作为催化剂催化L-丙交酯（L-LA）和ε-己内酯(ε-CL)的本体开环共聚合。通过改变聚合单体投料比,合成了不同组分的系列共聚物。根据共聚物的核磁共振氢谱（1H-NMR）结果,利用伯努利统计法计算出了共聚物理论和实验嵌段平均长度。结果表明,随着共聚物中己内酰摩尔含量从0.1增加到0.5,共聚物中的双乳酰实验嵌段平均长度(LeLL)从20.0下降到4.2,己内酰实验嵌段平均长度(LeC)从2.4增加到4.2。根据共聚物的差示扫描量热分析的测试数据,考察了共聚物的热力学性能。结果表明,随着共聚物中己内酰摩尔含量的增加,共聚物的熔点（Tm）从161.3 ℃下降到120.5 ℃,熔融焓（△Hm）从31.5 J/g下降到8.0 J/g,玻璃化转变温度（Tg）从51.5 ℃下降到-3.2 ℃。     

软骨细胞在聚乳酸支架中的体外生长行为

采用明胶和氯化钠颗粒作为致孔剂,使用溶剂浇铸／颗粒沥滤法制备了高孔隙率、孔间连通和高机械性能的聚乳酸支架,采用软骨细胞体外培养研究了这两种多孔支架对细胞生长性能的影响．结果表明,软骨细胞在以明胶颗粒为致孔剂制备的多孔支架中的相对数量和GAG的分泌量更多,细胞的活性更高。     

等离子体处理偶联胶原提高聚乳酸材料的细胞相容性

本研究通过结合氨气等离子体处理以及胶原改性的方法来改善聚乳酸材料的细胞相容性。水接触角分析表明氨气等离子体处理可以改善聚乳酸材料的亲水性,促进细胞的粘附。光学显微镜以及扫描电镜的分析结果表明,氨气等离子体处理后通过胶原改性可以进一步促进细胞在聚乳酸材料表面的生长。并且,与涂覆胶原相比,偶联胶原可以更好地使胶原蛋白固定在聚乳酸材料表面,从而表现出更好的细胞相容性。