含悬挂羧基手臂聚乳酸材料的合成与血小板粘附性研究

制备了乳酸-β-苹果酸共聚物,并在此基础上进一步修饰合成了含悬挂羟基(PLMAHE)以及悬挂羧基(PCA-PLA)的聚乳酸共聚物,利用原子力显微镜及环境扫描电镜,观察了聚合物膜的表面形貌以及粘附在聚合物膜上的血小板数量与形态.结果表明含悬挂羟基材料表面粘附血小板时发生聚集并有伪足生成,含悬挂羧基材料表面血小板粘附数量较少且形态正常,有望成为优良的抗凝血材料.     

聚乳酸-b-聚(N~ε-苄氧羰基-L-赖氨酸)-b-聚乙二醇的合成与表征

用端氨基聚乳酸做引发剂,在DMF中引发Nε-苄氧羰基-L-赖氨酸酐(Lys(Z)-NCA)聚合,合成了端氨基聚(Nε-苄氧羰基-L-赖氨酸)-b-聚乳酸两嵌段共聚物.以端羧基聚乙二醇经NHS活化与端氨基聚(Nε-苄氧羰基-L-赖氨酸)-b-聚乳酸偶联,合成了聚(乳酸-b-Nε-苄氧羰基-L-赖氨酸-b-乙二醇)三嵌段聚合物.利用IR、1H-NMR、GPC和TEM对它们的结构、形态进行了表征,结果表明,所合成的分子量可控、分子量分布窄(Mw/Mn=1.07)的嵌段共聚物,酰化反应产率达70%以上.同时聚乙二醇和Nε-苄氧羰基-L-赖氨酸被引入到聚乳酸主链中,在聚合物侧链脱保护后有望改善聚乳酸的细胞亲和性。     

Light olefins/paraffins sorption in poly(lactic acid) films

The sorption behavior of small molecules like ethane and ethylene in poly (lactic acid) (PLA) was studied in the temperature interval from 283 to 313 K using a Quartz Crystal Microbalance (QCM). The effect of the polymer structure on the solubility selectivity of PLA films with respect to these two gases was studied using polymer with two different L:D ratios (98:2 and 80:20). Furthermore, the polymer films were submitted to different thermal treatments to address the influence of crystallinity and morphology of the noncrystalline fraction on the sorption behavior. The sorption results obtained indicate that ethylene solubility coefficient in annealed PLA 98:2 is about 26% higher than that of ethane and 41% higher in PLA 98:2 melted. The dual‐mode sorption model describes well the sorption isotherms behavior, which is concave concerning the pressure axis. The fully amorphous PLA presents the better selectivity for the studied gases, since the crystallinity seems to produce a negative effect on the selectivity. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1312–1319, 2008     

Improvement of compatibility,mechanical, thermal and dielectric properties of poly(lactic acid) and poly(butylene adipate-co-terephthalate) blends and their composites with porous clay heterostructures from mixed surfactant systems

In this study, nanocomposite poly(lactic acid) and poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends were prepared through polymer blending in the presence of multi-functional epoxy as a compatibilizer that could react with epoxy group and terminated end group of two phases to increase interfacial adhesion between PLA and PBAT and improve the toughness of PLA. The effects of porous clay heterostructure from mixed CTAB:CTAC surfactant in the mole ratio of 1:2 (B1C2-PCH) were also investigated. The elongation at break of the blends reached 38%, which was eight times that of neat PLA. The cryo-fractured surface demonstrated the interfacial adhesion caused by the interaction of the epoxy group of the reactive compatibilizer with the terminal carboxyl and hydroxyl groups of PLA and PBAT. Moreover, PBAT reduced the crystallization rate and percent crystallinity of the PLA matrix and further decreased when compatibilizer was used. Alternatively, B1C2-PCH accelerated the heterogeneous nucleation and crystallization of the nanocomposite films. After adding small amount of B1C2-PCH, the nanocomposite films demonstrated excellent dielectric properties. Therefore, the improvement of PLA/PBAT nanocomposite blends are capable to be further developed as polymeric capacitor films.     

XPS and wettability characterization of modified poly(lactic acid) and poly(lactic/glycolic acid) films

Poly(lactic acid) (PLA) and poly(lactic/glycolic acid) copolymers (PLGA) are biodegradable drug carriers of great importance, although successful pharmaceutical application requires adjustment of the surface properties of the polymeric drug delivery system to be compatible with the biological environment. For that reason, reduction of the original hydrophobicity of the PLA or PLGA surfaces was performed by applying a hydrophilic polymer poly(ethylene oxide) (PEO) with the aim to improve biocompatibility of the original polymer. PEO-containing surfaces were prepared by incorporation of block copolymeric surfactants, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic), into the hydrophobic surface. Films of polymer blends from PLA or PLGA (with lactic/glycolic acid ratios of 75/25 and 50/50) and from Pluronics (PE6800, PE6400, and PE6100) were obtained by the solvent casting method, applying the Pluronics at different concentrations between 1 and 9.1% w/w. Wettability was measured to monitor the change in surface hydrophobicity, while X-ray photoelectron spectroscopy (XPS) was applied to determine the composition and chemical structure of the polymer surface and its change with surface modification. Substantial reduction of surface hydrophobicity was achieved on both the PLA homopolymer and the PLGA copolymers by applying the Pluronics at various concentrations. In accordance with the wettability changes the accumulation of Pluronics in the surface layer was greatly affected by the initial hydrophobicity of the polymer, namely, by the lactide content of the copolymer. The extent of surface modification was also found to be dependent on the type of blended Pluronics. Surface activity of the modifying Pluronic component was interpreted by using the solubility parameters.     

三臂PPO-PDLA-PLLA 嵌段共聚物的制备与结构及其立构复合体的结晶行为

以环氧丙烷聚醚三元醇(PPO)为起始剂, 开环聚合D 型丙交酯(DLA), 合成三臂环氧丙烷聚醚三元醇-聚右旋乳酸(PPO-PDLA)嵌段预聚体. 采用端基活化技术对预聚体进行端羟基活化, 再与L 型丙交酯(LLA)进行逐步开环聚合,合成了不同分子量的三臂环氧丙烷聚醚三元醇-聚右旋乳酸-聚左旋乳酸(PPO-PDLA-PLLA)嵌段共聚物. 采用红外(FTIR)、核磁(NMR)和凝胶渗透色谱(GPC)等对三臂PPO-PDLA-PLLA 嵌段共聚物的测试表明, 合成的嵌段共聚物分子链具有很高的立构规整度; 通过调节LLA 单体与PPO-PDLA 预聚体的投料比, 不仅可控制产物的分子序列结构, 而且样品的数均分子量可大于100 kDa. 差示扫描量热仪(DSC)和广角X 射线衍射(WAXD)结果显示, 三臂PPO-PDLAPLLA嵌段共聚物的异构体链段分子间生成立构复合晶体, 其熔点约为200 ℃, 且没有PLLA 均聚物链段结晶现象. 实验结果表明, 这是一类具有实际应用价值的新型耐热聚乳酸(PLA)材料.     

Toughening of poly(lactic acid) by ethylene-co-vinyl acetate copolymer with different vinyl acetate contents

The well-known bio-based and biocompostable poly(lactic acid), PLA, suffers from brittleness and a low heat distortion temperature. In this paper, we address a possible route to make PLA tough(er) by blending with ethylene-co-vinyl acetate (EVA) with different vinyl acetate contents. The compatibility and phase morphology of the PLA/EVA blends was controlled by the ratio of vinyl acetate and ethylene in the random copolymers. Tough PLA/EVA blends with increased impact toughness, up to a factor of 30, were obtained with a maximum toughness at a vinyl acetate content of approximately 50 wt.%. The local deformation mechanism was well studied by TEM, SAXS and SEM. It revealed that internal rubber cavitation in combination with matrix yielding is the dominant toughening mechanism for the PLA/EVA blends under both impact and tensile testing conditions.     

Tough crystalline blends of polylactide with block copolymers of ethylene glycol and propylene glycol

The effect of crystallinity of polylactide (PLA) on the structure and properties of tough PLA blends with PEG-b-PPG-b-PEG block copolymers was studied. PLA was melt blended with a set of the copolymers with varying ratio of the hydrophilic (PEG) and hydrophobic (PPG) blocks. Although the blend phase structure depended on the copolymer molar mass and PEG content, as well as on the copolymer concentration in the blend, crystallinity also played an important role, increasing the copolymer content in the amorphous phase and enhancing phase separation. The influence of crystallinity on the thermal and mechanical properties of the blends depended on the copolymer used and its content. The blends, with PLA crystallinity of 25 ÷ 34 wt%, exhibited relatively high glass transition temperature ranging from 45 to 52 °C, and melting beginning above 120 °C. Although with a few exceptions crystallinity worsened the drawability and toughness, these properties were improved with respect to neat crystalline PLA in the case of partially miscible blends, in which fine liquid inclusions of the modifier were dispersed in PLA rich matrix. About 20-fold increase of the elongation at break and about 4-fold increase of the tensile impact strength were reached at a small content (10 wt%) of the modifier. Moreover, crystallinity decreased oxygen and water vapor transmission rates through neat PLA and the blend, and the barrier property for oxygen of the latter was better than that of neat polymer.     

Physicochemical evaluation of PLA nanoparticles stabilized by water-soluble MPEO-PLA block copolymers

Different water-soluble MPEO-PLA diblock copolymers with various alpha-methoxy-omega-hydroxyl polyethylene (MPEO) and poly(lactic acid) (PLA) block lengths have been synthesized. Their surface-active properties were evidenced by surface tension (water/air) measurements. In each case the surface tension leveled down above a critical polymer concentration, which was attributed to the formation of a dense polymer layer at the liquid-air interface. The applicability of copolymers as emulsion stabilizers in the preparation of PLA nanospheres by an o/w emulsion/evaporation technique was then investigated. Four copolymers presenting sufficient water solubility and good surfactive properties were used to prepare PLA nanospheres with MPEO chains firmly anchored at the particle surface. The effect of polymer concentration in emulsion on particle size and surface coverage was examined. Whatever the copolymer characteristics, it was found that the optimal concentration to obtain a large amount of MPEO at the particle surface was similar (around 2 g/l). The effect of the copolymer composition on MPEO layer characteristics and on colloidal stability was also evaluated. The conformation of MPEO blocks at the PLA particle surface is discussed in relation to the layer thickness and the surface area occupied per molecule.     

Synthesis of novel graft polyhydroxyalkanoates

Graft copolymers were synthesized by direct condensation of methoxy-poly(ethylene glycol) (MePEG) or methoxy-poly(lactic acid) (MePLA) onto a reactive polyhydroxyalkanoate (PHA) backbone in organic solvent. Side carboxylic groups of the PHA were coupled with end hydroxyl groups of MePEG or MePLA in the presence of N,N′-dicylohexylcarbodiimide (DCC). Graft copolymers were characterized by ¹H NMR spectroscopy and size exclusion chromatography (SEC). NMR spectra of PHA-g-PEG and PHA-g-PLA showed the presence of significant amounts of PEG and PLA, respectively. No noticeable unreacted PEG or PLA were detected in SEC chromatograms. Grafting of hydrophilic polymers chains as PEG or biodegradable oligomers as PLA onto PHA backbone will generate polyesters with a more rapid water uptake and faster biodegradation rates. These PHA polymers conjugates could be interesting for bioactive agent delivery systems.     

生物可降解材料聚乳酸结晶行为研究进展

聚乳酸是一种具有良好生物相容性、可生物降解的热塑性脂肪族聚脂,是一种环境友好材料。聚乳酸的结晶性能对其力学性能和降解速率有着重要的影响,因而其结晶行为也逐渐成为人们研究的热点。本文针对聚乳酸的结晶行为综述了聚乳酸及其共混、共聚体系的最新研究进展。     

The influence of process parameters on the characteristics of polyhydroxyalkanoates produced by mixed cultures

The characterization of polyhydroxyalkanoates (PHA) produced by mixed cultures is fundamental for foreseeing the possible final applications of the polymer. In this study PHA produced under aerobic dynamic feeding (ADF) conditions are characterized. The PHA produced shows a stable average molecular weight ([symbol: see text]) in the range (1.0-3.0) x 10(6), along three years of reactor operation. Attempts to improve the amount of PHA produced did not introduce significant variations on the values [symbol: see text]. Along this period, the polydispersity indices (PDI) were between 1.3 and 2.2. The use of different carbon sources allowed the tailoring of polymer composition: homopolymers of poly(3-hydroxybutyrate), P(3HB), were obtained with acetate and butyrate, whereas a mixture of acetate and propionate, and propionate and valerate, gave terpolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 2-methyl-3-hydroxyvalerate (2M3HV). All of these PHA had [symbol: see text] between 2.0 x 10(6) and 3.0 x 10(6). Thermal characterization of the produced polymers showed values of glass transition temperature, melting temperature, melting enthalpy, and crystallinity slightly lower than those obtained for PHA from pure cultures. The introduction of a purification step during the polymer extraction process allowed the elimination of possible contaminants but did not significantly improve the polymer quality.     

High-speed monitoring of the crystallinity change in poly(lactic acid) during photodegradation by using a newly developed wide area NIR imaging system (Compovision)

We aimed to achieve wide area rapid monitoring of the crystallinity change in poly(lactic acid) (PLA) during photodegradation caused by ultraviolet (UV) light by using a newly developed near-infrared (NIR) camera (Compovison). Several kinds of PLA samples with different crystallinities and their blends with poly[(3)-(R)-hydroxybutyrate] were prepared. Their two-dimensional NIR spectra in the 1,000–2,350-nm region were measured by Compovision at a 5-min interval during photolysis. An intensity decrease of the band in the 1,900-1,925-nm region due to the second overtone of the C = O stretching vibration of PLA was observed during photolysis. This suggests that an anhydride carbonyl is produced during photolysis. The NIR image of the crystallinity change monitored by the band at 1,917 nm in the standard normal variate spectra clearly shows the inhomogeneity of crystal evolution. A logarithmic increase was observed for all identified areas in the PLA film; however, the time to reach the maximum crystallinity was slightly different according to the initial crystallinity of the sample. It is likely that the initial crystallinity of the sample influences the degradation speed more than the degradation amount. These imaging results have provided fundamental chemical insights into the photolytic process for PLA, and at the same time they have demonstrated that the two-dimensional spectral data obtained by Compovision are useful for process monitoring of polymers.     

1,3-PBO扩链改性端羧基聚乳酸的性能表征

以乳酸为原料、辛酸亚锡为催化剂,采用梯度升温法,在170℃、0.098 MPa条件下直接熔融缩聚合成端羧基共聚物P(LA/SA).将其用2,2-(1,3-亚苯基)-二噁唑啉(1,3-PBO)扩链,按n(—COOH)/n(—oxazoline)=1∶1.4比例加入1,3-PBO,在150℃,0.098 MPa条件下反应15 min制得聚酰胺酯(PEA).采用GPC、FTIR、1H-NMR、DSC、XRD、TGA、SEM等手段对聚合物的结构进行了表征和性能测试.结果表明,与P(LA/SA)相比,扩链产物相对分子质量大幅度提高,重均分子量达36×104;产物Tg比PLA升高,材料的刚性增强;产物热稳定性能提高,为一步分解;产物结晶度较P(LA/SA)降低,其柔韧性较P(LA/SA)增强,但相对于PLA有所降低.     

Crystallinity and dimensional stability of biaxial oriented poly(lactic acid) films

Transparent biaxial oriented poly(lactic acid) (BOPLA) films with improved dimensional stability were successfully prepared by controlling the crystallization of poly(lactic acid) (PLA). The crystalline morphology of PLA films can be manipulated by changing certain processing parameters, such as stretch ratio, heat setting temperatures, and heat setting time. Optical and mechanical properties as well as dimensional stability of the resulting polymer films are governed by their crystallinity and crystalline morphology. Crystallization behavior and kinetics of PLA, therefore, were investigated using wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC) techniques. Mechanical properties and the dimensional stability of the biaxial oriented PLA films were obtained and correlated with their processing conditions. Poly(lactic acid) films prepared by melt extrusion methods have great potential for food packaging, shrink labeling and protective film applications. However, shrinkage at elevated processing temperature should be minimized to avoid puckering of the polymer film. Shrinkage of less than 2% was achieved for a BOPLA film stretched 300% in both directions at 75 °C and then annealed at 160 °C for 30 s. Fabrication, properties, and potential applications of a series of biodegradable films will be described.     

Use of microperlite in direct polymerization of lactic acid

PLA is one of the most frequently used biodegradable polymers. In this work, PLA was synthesized by direct condensation polymerization of lactic acid in the presence of microperlite to obtain enhanced thermal stability of PLA polymer. Molecular weights of the synthesized polymers were determined by GPC. Chemical structure analyses was done by FTIR. The degree of crystallinity was evaluated by DSC and XRD. Thermal stability of polymers was investigated by DSC and TGA. It has been observed that the existence of perlite has significantly increased the crystallinity and degradation temperature, therefore, enhanced the thermal stability of the PLA.     

Microbial synthesis and characterization of polyhydroxyalkanoates with fluorinated phenoxy side groups from Pseudomonas putida

Microbial poly(3-hydroxyalkanoates) (PHAs) with fluorinated phenoxy side groups were produced by Pseudomonas putida when fluorophenoxyalkanoic acids were used as carbon sources. 11-(2-Fluorophenoxy)undecanoic acid (2FPUDA), 11-(3-fluorophenoxy)undecanoic acid (3FPUDA), 11-(4-fluorophenoxy)undecanoic acid (4FPUDA), 11-(2,4-difluorophenoxy)undecanoic acid (2,4DFPUDA), 11-(2,4,6-trifluorophenoxy)undecanoic acid (2,4,6TFPUDA), and 11-(2,3,4,5,6-pentaflurophenoxy)undecanoic acid (2,3,4,5,6PFPUDA) were used as carbon sources in the present study. When cells were grown with 2,4DFPUDA, the production of homo poly(3-hydroxy-5-(2,4-difluorophenoxy)pentanoate) was confirmed by NMR and GC/MS analyses. Fluorine atoms inserted into the side chain of the PHA dramatically affected its physical properties. In marked contrast to medium chain length (MCL) PHA, this fluorinated PHA was opaque, cream colored, and possessed greater crystallinity and a higher melting point (∼100 °C) than did the other MCL PHAs. Surface contact angle evaluation revealed that the PHA with two fluorine atoms possessed water-shedding properties. The number of substituted fluorine atoms in the carbon source affected cell growth and difluorine-substituted phenoxyalkanoic acids reduced cell growth, and polymer production compared to non-substituted phenoxyalkanoic acids. No polymeric materials were obtained using either 2,4,6TFPUDA or 2,3,4,5,6PFPUDA.     

Random copolymerization of macromonomers as a versatile strategy to synthesize mixed-graft block copolymers

The random copolymerization of norbornene-functionalized macromonomers was explored as a method of synthesizing mixed-graft block copolymers (mGBCPs). The copolymerization kinetics of a model system of polystyrene (PS) and poly(lactic acid) (PLA) macromonomers was first analyzed, revealing a gradient composition of side chains along the mGBCP backbone. The phase separation behavior of mGBCPs with PS and PLA side chains of various backbone lengths and side chain molar ratios was investigated, and increasing the backbone length was found to stabilize the phase-separated nanostructures. The graft architecture was also demonstrated to improve the processability of the mGBCP, compared to a linear counterpart. Investigations of mGBCPs comprised of polydimethylsiloxane and poly(ethylene oxide) side chains exemplified the diverse self-assembled morphologies, including a Frank-Kasper A15 phase, that can be obtained with mGBCPs synthesized by random copolymerization of macromonomers. Lastly, a ternary mGBCP was synthesized by the copolymerization of three macromonomers.     

Synthesis and enzymatic hydrolysis of lactic acid–depsipeptide copolymers with functionalized pendant groups

Since poly(lactic acid) is the biodegradable polyester having low immunogenicity and good biocompatibility, it is utilized as a medical material. However, poly(lactic acid) is a water-insoluble crystalline polymer having no reactive side-chain group. Thus, the use of poly(lactic acid) is limited. To modify the properties of poly(lactic acid) and to introduce the functionalized pendant groups to poly(lactic acid), we synthesized two kinds of lactic acid-depsipeptide copolymers with reactive pendant groups, namely poly[LA-(Glc-Lys)] and poly[LA-(Glc-Asp)]. This was done through ring-opening copolymerizations of L-lactide with the corresponding protected cyclodepsipeptides, cyclo[Glc-Lys(Z)] and cyclo[Glc-Asp(OBzl)], and subsequent deprotection of benzyloxycarbonyl and benzyl groups, respectively. By changing the mole fraction of the corresponding depsipeptide units, the solubility, thermal transition and degradation behavior of the modified poly(lactic acid) could be varied. © 1997 John Wiley & Sons, Inc.     

Synthesis,characterization of layered double hydroxide‐poly(methylmethacrylate) graft copolymers via activators regenerated by electron transfer for atom transfer radical polymerization and its effect on the performance of poly(lactic acid)

Layered double hydroxide‐poly(methylmethacrylate) (LDH‐PMMA) graft copolymers were prepared via activators regenerated by electron transfer for atom transfer radical polymerization. The results showed that the hydrophobicity of LDH‐PMMA was improved by the incorporation of hydrophilic groups. Moreover, poly(lactic acid) (PLA)/LDH‐PMMA nanocomposites were prepared by melt blending to enhance the performances of PLA. The crystallization and mechanical properties of the PLA/LDH‐PMMA nanocomposites were studied by differential scanning calorimetry, tensile testing, and polarized optical microscopy, respectively. Results of mechanical testing showed that the tensile strength, elongation at break, and impact strength of PLA/LDH‐PMMA nanocomposites were increased by 5.64%, 37.95%, and 49.70%, respectively, compared with PLA. The differential scanning calorimetry results indicated that LDH‐PMMA eliminated the cold crystallization of PLA matrix and improved the crystallinity of PLA by 37.26%. The polarized optical microscopy of PLA/LDH‐PMMA nanocomposites demonstrated that LDH‐PMMA increased the crystallization rate of PLA. It was also found that the rheological behaviors of the PLA nanocomposites were significantly enhanced. Based on these results, a new choice for modified LDHs was provided and used as a nucleating agent to improve the properties of PLA.