聚左旋乳酸/聚氧化乙烯共混物的拉伸行为及结构转变

采用熔融共混方法制备了聚左旋乳酸(PLLA)和超高分子量聚氧化乙烯(PEO)共混物, 通过差示扫描量热(DSC)、 扫描电子显微镜(SEM)和二维广角X射线散射(2D-WAXS)等方法系统研究了PEO的加入对不同温度下PLLA拉伸行为及拉伸过程中微观结构变化的影响. 结果表明, PLLA/PEO共混物为非均相体系, PEO粒子均匀分布在PLLA中形成两相结构. PEO的加入能够显著降低PLLA的玻璃化转变温度(T_g), 在25～60 ℃范围内显著提高PLLA的拉伸性能. 在60 ℃拉伸时, PEO的加入提高了PLLA在拉伸过程中的结晶和形变能力. 在80 ℃拉伸时, 共混物的拉伸断裂伸长率下降, 但共混物的结晶速度仍高于纯PLLA样品.     

Preparation and Characterization of Poly(D,L-Lactide) (PLA) and Poly(D,L-Lactide)-Poly(Ethylene Glycol) (PLA-PEG) Nanocapsules Containing Antitumoral Agent Methotrexate

Summary: The aims of the present work were to prepare and characterize nanocapsules containing antitumoral agent methotrexate (MTX) from poly(D ,L -lactide) (PLA) and poly(D ,L -lactide)-poly(ethylene glycol) diblock copolymer (PLA-PEG) with the purpose of administrating this drug by topical ocular route for primary ocular lymphoma treatment. Nanocapsules were prepared by the interfacial deposition of preformed polymer. The influences of the initial amount of MTX on the encapsulation efficiency, drug recovery and drug content, as well as the physicochemical properties of the particles were evaluated. The particle mean diameters were 246 and 146 nm, and zeta potential values were −38.8 and −33.6 mV, for the MTX-loaded nanocapsules prepared from PLA and PLA-PEG, respectively. The methotrexate content in the particles increased with the increasing in the drug amount added to the formulations, but the drug recovery decreased significantly. After 4 h of in vitro release, 28 and 86% of MTX was released from PLA and PLA-PEG nanocapsules, respectively.     

制备聚(L-乳酸-co-乙醇酸）/聚D-乳酸共混物立构复合物的新方法

首次以高分子量的聚(L-乳酸-co-乙醇酸）(PLLGA）和D-聚乳酸（PDLA)［m(PLLGA) : m(PDLA)=3:1, c 50 mL·g^-1］为原料,氯仿为溶剂,等体积的甲醇为沉淀剂,于50 ℃蒸发4 h形成了PLLGA和PDLA的立构复合物（sc-PLA）,其结构和性能经XRD, DSC和TGA表征。结果表明：sc-PLA的结晶度达96.2%,热失重5%温度为342 ℃（PLLGA为304 ℃）。     

Biodegradable ultra high strength poly(L-lactide) rods for bone fixation

The hydrostatic molecular orientation technique was used to explore the highest mechanical improvements achievable for poly-L-lactide (PLLA). The mechanical attributes of these materials designed for bone fracture fixation devices, i.e. bending strength and modulus were measured and compared with those prepared by stretching method. The starting samples were prepared by conventional melt extrusion at 200 °C followed by hydrostatic extrusion at 140 °C using glycerin filled extruder. Uniaxially stretched rods were prepared by drawing in silicon oil at 120 °C. The physical properties of these rods are inadequate as mechanical supports in the dynamic healing process of the bone. Moreover, they underwent a marked strength deterioration when immersed in aqueous buffered solution for 90 days. On the other hand, the hydrostatic extrusion technique produced rods with progressively higher bending strength that showed only a small drop after 90 days hydrolytic degradation. Micrographs suggested a superior molecular orientation and packing, which could be associated with the improved performance. The hydrostatic extrusion technique proved to be a safe and effective approach for strengthening biodegradable polymeric materials for dynamic mechanical support in orthopedic medical devices.     

Transcrystalline Morphology of an in situ Microfibrillar Poly(ethylene terephthalate)/Poly(propylene) Blend Fabricated through a Slit Extrusion Hot Stretching‐Quenching Process

Summary: Isotactic poly(propylene) (iPP) transcrystallites are obtained in in situ microfibrillar polyethylene terephthalate (PET)/iPP blends during a slit extrusion‐hot stretching‐quenching process. Based on morphological information from X‐ray scattering and microscopy, three nucleation origins are proposed in microfibrillar reinforced blends under an elongational flow field: (a) the classical row nuclei model; (b) fiber nuclei; (c) nuclei induced by fiber assistant alignment. The last model provides a natural explanation for the case that transcrystallites only occur in some microfiber reinforced blends under flow rather than without the external field.

AFM image for the transcrystalline layer of the microfibrillar blend.     

光学纯度对聚左旋乳酸结晶与熔融行为的影响

通过示差扫描量热仪(DSC)和广角X射线衍射仪(WAXD)研究了聚左旋乳酸(PLLA)的光学纯度(91.6%、93.3%、94.0%、97.0%、98.4%)对聚乳酸结晶和熔融行为的影响。 在非等温结晶过程中,随着光学纯度的提高,聚乳酸的结晶峰值温度、熔点、熔融焓均提高。 在等温结晶过程中,PLLA的半结晶时间(t_1/2)随着光学纯度的增加而减少,在结晶温度100~110 ℃区间内半结晶时间均达到最小值;含有不同光学纯度PLLA的Avrami指数n≈3,表明光学纯度的变化不能改变聚乳酸以三维球晶生长的异相成核机理。 随着光学纯度的增加,聚乳酸δ-晶型转变为α-晶型的临界温度升高。 聚乳酸的结晶和熔融行为对光学纯度具有依赖性。     

Stereoselective Interaction between Isotactic and Optically Active Poly(lactic acid) and Phenyl‐Substituted Poly(lactic acid)

Isotactic and optically active poly(D ‐lactic acid) (PDLA) and phenyl‐substituted poly(lactic acid)s (Ph‐PLAs), i.e., poly(D ‐phenyllactic acid) (Ph‐PDLA) and poly(L ‐phenyllactic acid) (Ph‐PLLA), were synthesized and stereospecific interactions between the synthesized polymers were investigated by their thermal properties and crystallization behavior using differential scanning calorimetry (DSC). The DSC measurements indicated that PDLA is miscible with Ph‐PLAs and that the attractive interaction between PDLA and L ‐configured Ph‐PLA is higher than that between PDLA and D ‐configured Ph‐PDLA. In other words, the latter result means that poly(lactic acid) (PLA) has a higher stereoselective attractive interaction with Ph‐PLA with the reverse configuration than with Ph‐PLA of the same configuration. These results strongly suggest that PLA‐based materials with a wide variety of physical properties and biodegradability can be fabricated by blending them with substituted PLAs with the reverse and same configurations.

     

Poly(methyl malate) nanoparticles: formation, degradation, and encapsulation of anticancer drugs

PMLA nanoparticles with diameters of 150-250 nm are prepared, and their hydrolytic degradation is studied under physiological conditions. Degradation occurs by hydrolysis of the side chain methyl ester followed by cleavage of the main-chain ester group with methanol and L-malic acid as the final degradation products. No alteration of the cell viability is found after 1 h of incubation, but toxicity increases significantly after 3 d, probably due to the noxious effect of the released methanol. Anticancer drugs temozolomide and doxorubicin are encapsulated in the NPs with 20-40% efficiency, and their release is monitored using in vitro essays. Temozolomide is fully liberated within several hours, whereas doxorubicin is steadily released from the particles over a period of 1 month.     

Poly(lactic acid) Synthesis in Solution Polymerization

The step-growth polymerization of L-lactic acid in solution was studied in this work. In order to attain a polymer with high molecular weight, the water formed during the polymerization must be continuously removed. The use of organic solvents with high boiling point, drying agents and reduced pressure led to poly(lactic acid) (PLA) with high molecular weight, directly from the monomer. Tin (II) chloride dihydrate, SnCl₂.2H₂O, was the best of the catalysts tested as it allowed achieving PLA with a molecular weight close to 80 000 g.mol⁻¹. However, the stereoregurarity control is a severe problem in PLA synthesis by step-growth due to transesterification reactions, which lead to an inversion of the conformation and a decrease of the optical purity of the polymer. Specific rotation measurements were used in this work and showed to be a powerful technique to evaluate the racemization extent. The thermal stability of the PLA samples was evaluated by DSC which exhibits a thermal behaviour similar to the commercial Polylactide.     

Accelerated Microbial Degradation of Poly(L-lactide)

Acceleration of the biodegradation of poly(L -lactide) (PLA) was studied. We found that the degradation rate of high molecular weight (1.3×10⁵) PLA film was greatly increased by the addition of gelatin into the culture medium of the microorganisms. 100 mg of PLA film was almost completely degraded by the fungus, Tritirachium album (eukaryotic microorganisms), and by an actinomycete, Saccharothrix waywayandensis (prokaryotic microorganisms). In addition to gelatin, various insoluble proteins, peptides and amino acids also accelerate the biodegradation of PLA. Silk fibroin was the best inducer for the production of PLA-degrading enzymes of an actinomycete, Amycolatopsis orientalis.     

Biodegradable Composites of Poly(lactic acid) with Cellulose Fibers Polymerized by Aluminum Triflate

Biodegradable polymer composites consisting of poly(lactic acid) (PLA) and cellulose fibers (CF) were prepared by our newly developed method. L-Lactic acid (LA) was reacted by ring-opening polymerization with aluminum triflate as a catalyst, glycerol as an initiator and CF as a filler, in simple plastic tubes at 100 °C for 6 hours. By this method, CF could be mixed with the polymer matrix easily and homogeneously. The molecular weight and molecular weight distribution of the PLA matrix were determined by gel permeation chromatography (GPC). The M_n of the composite samples decreased from 6200 to 2800 with increasing CF content. The molecular weight distribution of composites was around 2.5 regardless of the CF content. Biodegradation of samples was determined by measuring the results from the Microbial Oxidative Degradation Analyzer (MODA) and the weight loss in compost. Biodegradation of composite samples of PLA with CF increases with increasing CF content as measured by the MODA. Apparent density of composite samples was calculated by using the weight and sizes of column shape specimens. The density of the composite samples was a bit lower than that of PLA pure samples without CF. Mechanical properties such as the elastic modulus and strength were investigated by compression tests using column shape specimens. For the sample with filter paper as CF, the strength of composite samples increases with increasing CF content.     

Thermoreversible gelation of poly(ethylene oxide) biodegradable polyester block copolymers. II

Poly(ethylene oxide)-b-poly(L-lactic acid) (PEO-PLLA) diblock copolymers were synthesized via a ring opening polymerization from poly(ethylene oxide) and l -lactide. Stannous octoate was used as a catalyst in a solution polymerization with toluene as the solvent. Their physicochemical properties were investigated by using infrared spectroscopy, ¹H-NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry, as well as the observational data of gel-sol transitions in aqueous solutions. Aqueous solutions of PEO-PLLA diblock copolymers changed from a gel phase to a sol phase with increasing temperature when their polymer concentrations are above a critical gel concentration. As the PLLA block length increased, the gel-sol transition temperature increased. For comparison, diblock copolymers of poly(ethylene oxide)-b-poly(l -lactic acid-co-glycolic acid) [PEO-P(LLA/GA)] and poly(ethylene oxide)-b-poly(dl -lactic acid-co-glycolic acid) [PEO-P(DLLA/GA)] were synthesized by the same methods, and their gel-sol transition behaviors were also investigated. The gel-sol transition properties of these diblock copolymers are influenced by the hydrophilic/hydrophobic balance of the copolymer, block length, hydrophobicity, and stereoregularity of the hydrophobic block of the copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2207–2218, 1999     

Crystal Transformation and Development of Tensile Properties upon Drawing of Poly(L-lactic acid) by Solid-State Coextrusion: Effects of Molecular Weight

Melt-crystallized films of poly(L -lactic acid) (PLLA) with M_v in the range of 3.8 ∼ 46 × 10⁴ consisting of α-form crystals were uniaxially drawn by solid-state coextrusion. The effects of M_v, extrusion draw ratio (EDR), and extrusion temperature (T_ext) on the crystal/crystal transformation from α- to β-form crystals and the resultant tensile properties of drawn products were studied. The crystal transformation proceeded with EDR and more rapidly for the higher M_v's. Furthermore, the crystal transformation proceeded most rapidly with EDR at a T_ext around 130 °C, independently of the M_v's. As a result of the optimum combination of processing variables influencing the the crystal transformation (M_v, T_ext, and drawability), highly oriented films consisting of β-form crystals alone were obtained by coextrusion of higher M_v samples at T_ext's slightly below the melting temperature (150 ∼ 170 °C) and at higher EDR's > 11. Both the tensile modulus and strength increased rapidly with EDR. The modulus at a given EDR was slightly higher for the samples with higher M_v's. In contrast, the strength at a given EDR was remarkably higher for the higher M _v's. The highest tensile modulus of 8.0 GPa and strength of 500 MPa were obtained with the sample of the highest M_v of 46 × 10⁴ coextruded at 170 °C to the highest EDR of 14.     

聚天冬氨酸的合成研究

以L-天冬氨酸为原料,磷酸为催化剂,在不同溶剂中进行缩聚反应,合成中间体聚丁二酰亚胺(PSI),当混合溶剂为m三甲苯／m环丁砜=7／3时,可得到较高分子量的PSI。当催化剂与单体的质量比为0．14时,分子量达到最大值。将PSI碱解得到聚天冬氨酸。     

癸二酸己二醇酯/己二酸二醇酯共聚物的合成及热性能

癸二酸己二醇酯/己二酸二醇酯共聚物的合成及热性能;直接聚合;可降解聚合物     

Preparation of Clickable Poly(3‐hydroxyalkanoate) (PHA): Application to Poly(ethylene glycol) (PEG) Graft Copolymers Synthesis

A new synthesis of amphiphilic biodegradable copolymers consisting of hydrophobic poly(3‐hydroxyalkanoate) (PHA) backbone and hydrophilic poly(ethylene glycol) (PEG) units as side chains is described. Poly[(3‐hydroxyoctanoate)‐co‐(3‐hydroxyundecenoate)] (PHOU) was first methanolyzed and its unsaturated side chains were quantitatively oxidized to carboxylic acid. Esterification with propargyl alcohol led to an alkyne‐containing “clickable” PHA in 71% conversion. Its reactivity was successfully demonstrated by grafting azide‐terminated PEG chains of 550 and 5 000 g · mol⁻¹, respectively. All products were fully characterized using GPC, ¹H, and COSY NMR.

     

Poly(methyl methacrylate)-induced Microstructure and Hydrolysis Behavior Changes of Poly(L-lactic acid)/Carbon Nanotubes Composites

Poly(L-lactic acid)(PLLA)-based composites exhibit wide applications in many fields.However,most of hydrophilic fillers usually accelerate the hydrolytic degradation of PLLA,which is unfavorable for the prolonging of the service life of the articles.In this work,a small quantity of poly(methyl methacrylate)(PMMA)(2 wt%-10 wt%)was incorporated into the PLLA/carbon nanotubes(CNTs)composites.The effects of PMMA content on the dispersion of CNTs as well as the microstructure and hydrolytic degradation behaviors of the composites were systematically investigated.The results showed that PMMA promoted the dispersion of CNTs in the composites.Amorphous PLLA was obtained in all the composites.Largely enhanced hydrolytic degradation resistance was achieved by incorporating PMMA,especially at relatively high PMMA content.Incorporating 10 wt%PMMA led to a dramatic decrease in the hydrolytic degradation rate from 0.19%/h of the PLLA/CNT composite sample to 0.059%/h of the PLLA/PMMA-10/CNT composite sample.The microstructure evolution of the composites was also detected,and the results showed that no crystallization occurred in the PLLA matrix.Further results based on the interfacial tension calculation showed that the enhanced hydrolytic degradation resistance of the PLLA matrix was mainly attributed to the relatively strong interfacial affinity between PMMA and CNTs,which prevented the occurrence of hydrolytic degradation at the interface between PLLA and CNTs.This work provides an alternative method for tailoring the hydrolytic degradation ability of the PLLA-based composites.     

Biodegradable Poly(ester hydrazide)s via Enzymatic Polymerization

Summary: The reaction of hydrazine with ethyl glycolate results in 1,2‐bisglycoylhydrazine, a monomer that was used for the lipase‐catalyzed synthesis of biodegradable poly(ester hydrazide)s. The polymers derived from the hydrazide‐containing monomer and vinyl‐activated adipic, suberic, and sebacic acid, respectively, showed low melting temperatures of 136 to 141 °C and are thermally stable up to 300 °C. The aliphatic poly(ester hydrazide)s (PEHs) are highly crystalline, as proven by polarization microscopy and atomic force microscopy. Further, the PEHs represent the first described biodegradable poly(hydrazide)s. They degrade in the presence of lipase at 37 °C within a few weeks.

Synthetic route to poly(ester hydrazide)s.