Effects of residual monomer on the degradation of DL-lactide polymer

The effects of remaining monomer on hydrolysis of poly(DL -lactide) were examined by adding different amounts of monomer to purified polymer samples. The existence of monomer in the polymerization products was found to enhance hydrolytic degradation of the polymer. A porous texture was observed on the SEM photographs of degraded materials, which led to the conclusion that the remaining monomer enabled water molecules to gain better access to the polymer matrix through this porous structure. The effects of molecular weight and chemical composition of polylactides on the hydrolytic degradation were also studied. Poly(DL -lactic acid) with higher molecular weights showed longer retention of the initial properties such as molecular weight and tensile strength. Copolymerization of DL -lactide with glycolide enhanced the hydrolysis, probably because of increased hydrophilicity of the polymers. © 1998 SCI.     

Crystalline,Thermal, and Biodegradable Properties of Poly(L-Lactic Acid)/Poly(D-Lactic Acid)/POSS Melt Blends

A ternary nanocomposite consisting of poly(L-lactic acid) (PLLA), poly(D-lactic acid) (PDLA), and epoxy cyclohexyl polyhedral oligomeric silsesquioxane (e-POSS) was prepared by reactive blending method. Scanning electron microscopy revealed that the feeding of three compositions in batches, i.e., PDLA incorporation at different times, was more beneficial for the even dispersion of POSS in matrix. POSS introduction improved the homocrystallinity and stereocomplex of the blends. Rheological properties and heat resistance were enhanced, which indicated potential extensive application of PLLA-based materials. The optimization of degradation stability in saline buffer was attributed to the various hydrophobic properties of blends caused by POSS structure.     

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems

Thermally induced phase separation in poly(lactic acid)/dialkyl phthalate systems was investigated. Poly(DL ‐lactic acid) (PDLLA) and poly(L ‐lactic acid) (PLLA) with different molecular weights were used. A series of dialkyl phthalates, with different numbers of carbon atoms in the alkyl chain, were employed as solvents to control the interaction between polymer and solvent. The liquid–liquid phase‐separation temperature of the poly(lactic acid) solutions decreased systematically with a shorter alkyl chain in the phthalate. Based on the interaction between polymer and solvent and the molecular weight of polymer influencing liquid–liquid phase‐separation temperature significantly but crystallization temperature only slightly, proper thermal conditions were employed to investigate competitive phase separation and crystallization in PLLA solutions. Factors that can influence the final morphology of PLLA solutions were examined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2224–2232, 2003     

In vitro degradation and release profiles of poly‐DL‐lactide‐poly(ethylene glycol) microspheres with entrapped proteins

Poly‐DL ‐lactide (PLA) and poly‐DL ‐lactide‐poly(ethylene glycol) (PELA) were produced by bulk ring‐opening polymerization using stannous chloride as initiator. PLA, PELA microspheres, and PELA microspheres containing the outer membrane protein (OMP) of Leptospira interrogans with the size of 1.5–2 μm were prepared by a solvent evaporation process. In vitro degradation and release tests of PLA, PELA, and OMP‐loaded PELA microspheres were performed in pH 7.4 buffer solution at 37°C. Quantitatively, the degree of degradation was monitored by detecting the molecular weight reduction, by evaluating the mass loss and the apparent degradation rate constant, and by determining the intrinsic viscosity and poly(ethylene glycol) content of retrieved polymer, while the release profile was assessed by measuring the amount of protein presented in the release medium at various intervals. Qualitatively, the morphological changes of microspheres were observed with scanning electron micrography. The observed relative rates of mass loss versus molecular weight reduction are consistent with a bulk erosion process rather than surface erosion for PELA microspheres. The introduction of hydrophilic poly(ethylene glycol) domains in copolymer PELA and the presence of OMP within microspheres show critical influences on the degradation profile. The OMP‐loaded PELA microspheres present triphasic release profile and a close correlation is observed between the polymer degradation and the OMP release profiles. It is suggested that the polymer degradation rate, protein diffusion coefficient, and the water‐swollen structure of microspheres matrix commonly contribute to the OMP release from PELA microspheres. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 140–148, 2000     

Structural changes of polylactic‐acid (PLA) microspheres under hydrolytic degradation

Low molecular‐weight polylactic acid (PLA) was obtained by direct polycondensation of a mixture of 95% l and 5% d ‐lactic acid isomers, without catalyst, at 195°C. This polymer was used for the synthesis of microspheres by emulsion–solvent evaporation method. Gel Permeation Chromatography (GPC), X‐ray Scattering (XRD), Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM) techniques were applied to follow morphological and structural changes of particles along in vitro degradation at 37°C. The original microspheres were amorphous but could crystallize partially upon heating. Samples stored in a humid environment exhibited an increase in the crystallization capability upon heating. Initial smooth‐surface microspheres were transformed to porous particles at the time of degradation at pH = 7 (37°C). The shape of mass loss vs. time curve supports the presence of a heterogeneous bulk degradation process. After hydrolytic degradation the residual particles showed a molecular weight decrease and a crystallinity increase. After 90 days the crystallinity attained a value of 53%. The X‐ray diffraction spectrum indicated the formation of a crystalline oligomeric structure. Crystallization of low molecular weight species will not enable the desired PLA absorption in drug delivery systems. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1223–1230, 1999     

生物医用材料聚L-乳酸的生物相容性及降解性能研究

通过DSC、SEM、TGA等分析手段对合成得到的聚L-乳酸(PLLA)进行了细胞种植、动物体内包埋及热降解实验,其生物相容性及体内、体外降解情况。实验证明PLLA材料具有良好的生物相容性和组织相容性。用其薄膜埋植于兔子皮下,兔子的生存状态及生长良好;其薄膜可为细胞在其表面上生长、增殖、分泌基质提供良好的微环境。PLLA材料分子量越大降解速度越慢,且体内降解的速度要比体外降解的速度快。     

Low molecular weight polyacrylic acid with pendant aminomethylene phosphonic acid groups

Low molecular weight poly(acrylic acid‐co‐vinyl aminomethylene phosphonic acid)s were prepared by consecutively applying the Hofmann degradation and the Mannich reaction to polyacrylamide and poly(acrylamide‐co‐acrylic acid)s. ¹H‐NMR, ³¹P‐NMR, and microanalysis were used for structural analyses. These polymers were tested as anti‐scalent and they showed better anti‐scalent effect than commercial poly(acrylic acid)s. The scale inhibition properties of copolymers increased with increasing amount of aminomethylene phosphonic acid groups. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 870–874, 2000     

On the Optical Activity of Poly(l-lactic acid) (PLLA) Oligomers and Polymer: Detection of Multiple Cotton Effect on Thin PLLA Solid Film Loaded with Two Dyes

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(l-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of π-conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with π-conjugated dyes for molecular electronics studies.     

Characterization of the mechanical properties,crystallization, and enzymatic degradation behavior of poly(butylene succinate‐co‐ethyleneoxide‐co‐DL‐lactide) copolyesters

A series of aliphatic biodegradable poly (butylene succinate‐co‐ethyleneoxide‐co‐DL ‐lactide) copolyesters were synthesized by the polycondensation in the presence of dimethyl succinate, 1,4‐butanediol, poly(ethylene glycol), and DL ‐oligo(lactic acid) (OLA). The composition, as well as the sequential structure of the copolyesters, was carefully investigated by ¹H‐NMR. The crystallization behaviors, crystal structure, and spherulite morphology of the copolyesters were analyzed by differential scanning calorimetry, wide angle X‐ray diffraction, and polarizing optical microscopy, respectively. The results indicate that the sequence length of butylene succinate (BS) decreased as the OLA feed molar ratio increasing. The crystallization behavior of the copolyesters was influenced by the composition and sequence length of BS, which further tuned the mechanical properties of the copolyesters. The copolyesters formed the crystal structures and spherulites similar to those of PBS. The incorporation of more content of ethylene oxide (EO) units into the copolyesters led to the enhanced hydrophilicity. The more content of lactide units in the copolyesters facilitated the degradation in the presence of enzymes. The morphology of the copolyester films after degradation was also studied by the scanning electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Poly(L-lactide)-degrading activity of a newly isolated bacterium

A new strain exhibiting poly(L -lactic acid) (PLLA)-degrading activity was isolated from the compost loaded with low-molecular weight PLLA. The strain was rod-shaped gram positive bacterium and was identified to be Bacillus licheniformis by the 16S rDNA sequence analysis. It degraded not only low-molecular weight PLLA but also other PLLAs having higher molecular weight. The lower the molecular weight of PLLA, the faster the biodegradation rate. And thereby 45% and 81% of PLLAs with weight average molecular weight of 256,000 and 5,000, respectively, were metabolized into CO₂ after 40 days of biodegradation at 58°C in the sterilized compost inoculated with the bacterium. According to the 16S rDNA sequence analysis, B. licheniformis PLLA-2 belonged to Bacillus spp. phylogenetically. However, there existed almost no phylogenetic relationship between B. licheniformis PLLA-2 and the previously reported PLLA-degrading strains. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of low molecular weight compounds with hydroxyl groups on properties of poly(L-lactic acid)

The effects of low molecular weight compounds with hydroxyl groups on the properties of poly(L -lactic acid) (PLLA) were investigated. The specific interaction between PLLA and 4,4′-thiodiphenol (TDP) was investigated by Fourier transform IR spectroscopy. The spectra of the blends suggested that there were interassociated hydrogen bonds between the PLLA chains and TDP molecules. The thermal and dynamic mechanical properties of PLLA/TDP blends were investigated by differential scanning calorimetry and dynamic mechanical thermal analysis, respectively. The results revealed that the thermal and dynamic mechanical properties of PLLA were greatly modified through blending with TDP and that PLLA/TDP blends possessed eutectic phase behavior. The effects of the thermal history on the formation of hydrogen bonds and the thermal and mechanical properties were evaluated. It was found that the properties of the blends were strongly dependent on the thermal history. In addition to TDP, PLLA blends with other low molecular weight hydroxyl compounds, including aromatic and aliphatic compounds, were also characterized. The effects of the chemical structure of the low molecular weight compounds on the properties of PLLA were discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 640–649, 2001     

Biodegradable blends of high molecular weight poly(ethylene oxide) with poly(3‐hydroxypropionic acid) and poly(3‐hydroxybutyric acid): a miscibility study by DSC,DMTA and NMR spectroscopy

The miscibility of high molecular weight poly(ethylene oxide) blends with poly(3‐hydroxypropionic acid) and poly(3‐hydroxybutyric acid) (P(3HB)) has been investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and high‐resolution solid state ¹³C nuclear magnetic resonance (NMR). The DSC thermal behaviour of the blends revealed that the binary blends of poly(ethylene oxide)/poly(3‐hydroxypropionic acid) (OP blends) were miscible over the whole composition range while the miscibility of poly(ethylene oxide)/poly(3‐hydroxybutyric acid) blends (OB blends) was dependent on the blend composition. OB blends were found to be partly miscible at the middle P(3HB) contents (25 %, 50 %) and miscible at other P(3HB) contents (10 %, 75 % and 90 %). Single‐phase behaviour for OP blends and phase separation behaviour for OB blends were observed from DMTA. The results from NMR spectroscopy revealed that the two components in the OP50 blend were intimately mixed on a scale of about 35 nm, while the domain sizes in the OB blend with a P(3HB) content of 50 % were larger than about 32 nm. © 2000 Society of Chemical Industry     

聚乳酸的合成及应用

综合分析了聚乳酸的合成方法和应用概况,重点阐述了间接开环聚合的机理,以及直接缩聚反应提高聚乳酸分子质量的最新进展概况。对聚乳酸的应用现状及应用前景进行了归纳分析,提出了聚乳酸研究的发展方向及重点应用领域。     

Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol)

Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1495–1505, 1997     

High molecular weight poly( -lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly( -lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.     

Synthesis and characterization of poly(acrylate amic acid) and its application as negative‐tone photosensitive polyimides

The dianhydride monomer 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride and two diamine monomers, 4,4′‐diamino‐3,3′‐biphenyldiol (HAB) and 2,4‐diaminophenol dihydrochloride (DAP), were used to synthesize a series of poly(hydroxyl amic acid). Further functionalization by grafting acrylate groups yields the corresponding poly(acrylate amic acid) that underwent a crosslinking reaction on exposure to UV‐light and was used as a negative‐tone photosensitive polyimide (PSPI). The analysis of chemical composition and molecular weight of these poly(amic acid)s determined by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography revealed that the molecular weight of the poly(hydroxyl amic acid) increased with the molar content of HAB in the feedstock, because HAB exhibited higher polymerization reactivity than DAP. Moreover, the degree of grafting acrylate groups onto poly(hydroxyl amic acid) was determined by ¹H‐NMR spectroscopy. The photoresist was formulated by adding 2‐benzyl‐2‐N,N‐dimethylamino‐1‐(4‐morpholinophenyl) butanone (IRG369) and isopropylthioxanthone as a photoinitiator, tetra(ethylene glycol) diacrylate as a crosslinker, and tribromomethyl phenyl sulfone as a photosensitizer. The PSPI precursor exhibited a photosensitivity of 200 mJ/cm² and a contrast of 1.78. A pattern with a resolution of 10 μm was observed in an optical micrograph after thermal imidization at 300°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

In vitro degradation of poly(L-lactic acid) fibers produced by melt spinning

In vitro degradation of poly(L -lactic acid) fibers was investigated for a period of 16 weeks in Ringer solution at 37°C. Two sets of fibers, with similar initial mechanical properties, molar mass, and crystallinity content, but markedly different in diameter (72 and 120 μm) were studied. Viscometric molar mass decreased during the immersion time at a faster rate for the thinner fibers compared to the thicker ones. As a consequence, the fiber mechanical properties changed; the elastic modulus was only slightly affected by the molar mass decrease whereas ultimate mechanical properties (stress and strain at break) showed a strong decrease. A quantitative correlation between tensile strength and viscometric-average molar mass was attempted. A possible explanation of the faster degradation rate of the thinner fibers was proposed on the basis of the higher surface/volume ratio and water uptake. Dynamic mechanical properties were also measured as a function of immersion time. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 213–223, 1997     

Effect of hydrolytic degradation and dehydration on the microstructure of 50:50 poly(glycolide-co-D,L-lactide)

The effect of hydrolytic degradation on the microstructure of unoriented, random 50: 50 poly(glycolic acid-co-D ,L -lactic acid) was examined using simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). Samples were degraded in phosphate-buffered saline solution at 37·5°C and studied wet and after dehydration. There was no evidence of crystalline material within the sample at any stage of degradation or dehydration from either X-ray scattering or thermal analysis. Thus, chain scission does not enable crystallization of the copolymer, and the glycolic acid and lactic acid fragments formed on degradation do not crystallize, even when the samples are dehydrated. Because such fragments are clearly formed (Hakkarainen, M., Albertsson, A. C. & Karlsson, S., Polym. Deg. Stab., 52 (1996) 283), and because they are crystalline in the dry state, it must be assumed either that these species are not present in any quantity in the degrading sample and that they diffuse easily from the bulk into the surrounding medium, or that the bulk polymer prevents them from crystallizing. SAXS gave evidence of small voids within the structure. Unlike dehydrated degraded semi-crystalline samples, there is no evidence for voiding on a macroscopic scale. The number and size of the small voids in the dehydrated samples rises with degradation. The voids close as samples are heated above the glass transition temperature and the amorphous chains gain mobility. The glass transition, although clearly visible in the undegraded samples, becomes less visible by DSC on degradation. After 28 days’ degradation, there is some evidence that the structure begins to close up, perhaps as a result of reduced viscosity arising from the increased fraction of low molecular weight material. © 1998 SCI.     

生物降解材料聚乳酸的直接法合成与表征

分别以外消旋乳酸(D,L-LA)和左旋乳酸(L-LA)为原料,通过熔融聚合法直接合成了生物降解材料聚外消旋乳酸(PDLLA)和聚左旋乳酸(PLLA),并用特性粘度[η]、凝胶渗透色谱(GPC)、傅立叶红外光谱(FTIR)、核磁共振氢谱(1H NMR)、差热分析(DSC)、X-射线衍射等手段.对PLLA、PDLLA的相对分子质量、结构、性能等进行了系统的表征与比较,发现相同合成条件下PLLA的相对分子质量、熔融温度、熔融热、结晶度等明显比PDLLA高。     

Thermal degradation and biodegradability of poly (lactic acid)/corn starch biocomposites

Thermal degradation and biodegradability of poly (lactic acid) (PLA) and poly (lactic acid)/corn starch (PLA/CS) composites with and without lysine diisocyanate (LDI) were evaluated by thermogravimetric analysis measurement and enzymatic degradation using Proteinase K and burial tests, respectively. Thermal stability was decreased by addition of CS and the composites with LDI showed higher thermal degradation temperature than those without LDI. In enzymatic biodegradation, the weight remaining of all samples decreased almost linearly with time. The addition of CS resulted in a faster rate of degradation and the composites with LDI were more difficult to degrade than those without it. In the composite without LDI, the degradation was faster at the interface between PLA and CS, showing deep and wide clearance, but degradation starting at the interface was not clearly observed in the composite with LDI. There was no considerable difference in molecular weight and distribution of the samples after enzymatic degradation. The lactic acid content of the water‐soluble product obtained after enzymatic degradation increased with degradation time. In burial tests, pure PLA was little degraded but the composites gradually degraded. The degradation of the composite without LDI was faster than that of the composite with LDI. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3009–3017, 2006