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71.
固体超强酸SO4^2—/ZnO—SnO2/La^3+催化合成丙交酯 总被引:2,自引:0,他引:2
研究了在乳酸合成丙交酯的实验中,以三种不同类型金属氧化物(ZnO,SnO2,La2O3)的固体超强酸作催化剂对反应产物收率,反应温度和时间的影响。实验表明,双金属固体超强酸SO2-4/ZnO-SnO2/La3+催化效果最佳。使用该催化剂,减压(5 0×103Pa)条件下在120~130℃下脱水2h生成乳酸低聚物。然后在150~210℃下分解低聚物,收集丙交酯,反应时间90min。丙交酯的平均收率达58%。 相似文献
72.
Crystallization, spherulite growth, and structure of blends of crystalline and amorphous poly(lactide)s 总被引:1,自引:0,他引:1
The effects of incorporated amorphous poly(dl-lactide) (PDLLA) on the isothermal crystallization and spherulite growth of crystalline poly(l-lactide) (PLLA) and the structure of the PLLA/PDLLA blends were investigated in the crystallization temperature (Tc) range of 90-150 °C. The differential scanning calorimetry results indicated that PLLA and PDLLA were phase-separated during crystallization. The small-angle X-ray scattering results revealed that for Tc of 130 °C, the long period associated with the lamellae stacks and the mean lamellar thickness values of pure PLLA and PLLA/PDLLA blend films did not depend on the PDLLA content. This finding is indicative of the fact that the coexisting PDLLA should have been excluded from the PLLA lamellae and inter-lamella regions during crystallization. The decrease in the spherulite growth rate and the increase in the disorder of spherulite morphology with an increase in PDLLA content strongly suggest that the presence of a very small amount of PDLLA chains in PLLA-rich phase disturbed the diffusion of PLLA chains to the growth sites of crystallites and the lamella orientation. However, the wide-angle X-ray scattering analysis indicated that the crystalline form of PLLA remained unvaried in the presence of PDLLA. 相似文献
73.
Ahmed Bakry Andrea Martinelli Mariano Bizzarri Alessandra Cucina Lucio D'Ilario Iolanda Francolini Antonella Piozzi Sara Proietti 《Polymer International》2012,61(7):1177-1185
The aim of the present work was to study the possibility of building a porous scaffold for tissue engineering with a new bottom‐up approach, obtained by assembling two‐dimensional‐micro, one‐dimensional‐nano sized poly(L ‐lactide) lamellar single crystals. This choice was dictated by the fact that polymer single crystals have structural and morphological features which can be exploited for chemical surface modifications to give a system characterized by a high specific active surface area. Indeed, the outermost amorphous regions can undergo functionalization reactions easily, whereas the inner, relatively inaccessible and inert crystalline core ensures morphological and mechanical stability. The assembling method employed to give the porous structures is based on a mould pressing, salt leaching technique and was found to be facile and versatile. In the first part of this paper we report the experimental results obtained to find the best conditions to achieve a suitable frame in terms of morphology, porosity and mechanical properties. In the second part of the paper, we describe the biological tests performed by using mouse fibroblasts seeded onto scaffolds prepared from pristine and surface hydrolysed lamellae. The results show that the samples obtained are suitable for sustaining cells which can proliferate and reach the inner pores of the scaffold containing hydrolysed single crystals much better than those prepared from pristine lamellae. Copyright © 2012 Society of Chemical Industry 相似文献
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75.
Scott J. Moravek Mohammad K. Hassan David J. Drake Tim R. Cooper Jeffrey S. Wiggins Kenneth A. Mauritz Robson F. Storey 《应用聚合物科学杂志》2010,115(3):1873-1880
Degradable thermoplastic polyurethane (TPU) elastomers incorporating poly(D ,L ‐lactide‐co‐glycolide) (PLGA) were synthesized and characterized. The soft segments consisted of a mixture of poly(butylene adipate) (PBA) and PLGA with PBA/PLGA ratios of 100/0, 75/25, and 50/50 wt %. Two PLGA polyesters were used. BD‐PLGA was initiated from butanediol; whereas BHMBA‐PLGA was initiated from 2,2‐bis‐(hydroxymethyl)butanoic acid. The hard segments consisted of dicyclohexylmethane‐4,4′‐diisocyanate (H12MDI) and 1,4‐butanediol (BD). The hard segment content, expressed as the weight ratio of BD to polyol used in the TPU formulation, was set either at 8 or 12% (31.2 or 38.1% hard segment by weight, respectively). In all cases initial [NCO]/[OH] ratio was 1.03. The tensile modulus of the TPUs ranged from 9 to 131 MPa and ultimate strains ranged from 100 to 750%. DMA was used to probe the thermomechanical transitions of the TPUs and indicated useful application temperatures from well below zero up to 60–80°C depending on the formulation. Hydrolytic degradation of the TPUs was tested in seawater at 37°C. All of the PLGA‐containing TPUs showed enhanced degradation compared to those with only PBA as the soft segment. The latter compositions remained essentially unchanged throughout the test while the PLGA‐containing TPUs lost as much as 45% of their initial mass in 153 days. Molecular weights of TPUs containing degradable polyols were lower than those derived from 100% PBA polyol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
76.
A series of hyperbranched poly(amine‐ester)‐co‐D ,L ‐lactide (HPAE‐co‐PLA) copolymer were synthesized by ring‐opening polymerization of D ,L ‐lactide with Sn(Oct)2 as catalyst to a fourth generation branched poly(amine‐ester) (HPAE‐OHs4). The chemical structures of copolymers were determined by FTIR, 1H‐NMR, 13C‐NMR, and TGA. Double emulsion (DE) and nanoprecipitation (NP) method were used to fabricate the nanoparticles of these copolymers encapsulating bovine serum albumin (BSA) as a model. DSC thermo‐grams indicated that the nanoparticles with BSA kept stable below 40°C. Different factors which influence on particular size and encapsulation efficiency (EE) were investigated. Their EE to BSA could reach 97.8% at an available condition. In vitro release behavior of NPs showed a continuous release after a burst release. The stability maintenance of BSA in the nanoparticle release in vitro was also measured via circular dichroism and fluorescence spectrometry. The results showed that the copolymer nanoparticles have a promising potential in protein delivery system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
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Osteomyelitis is the inflammation of bone which is treated by a high dose of antibiotics given intravenously for 4–6 weeks. However, at present locally administered antibiotic such as gentamicin poly (methyl methacrylate) (PMMA) bead is nonbiodegradable and a secondary surgery is often inevitable. This study described the biodegradable material poly‐D , L ‐lactide (PLA) with 80 kDa molecular weight that could be used as a potential antibiotic carrier for local drug release. PLA was first dissolved in tetrahydrofuran followed by blending with levofloxacin (LFX) in a physical way. The blend was then molded into beads. The optimized weight ratio between PLA and LFX was designated as 45 : 15. Glass transition temperature and surface ultramicrostructure of the beads were measured. In vitro tests of drug release and bacteriostasis demonstrated that the PLA–LFX beads released high concentrations of antibiotic for the period of time (i.e., 6 weeks), which is needed to treat bone infection. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
80.
Linear (1‐arm) and star‐shaped (4‐, 6‐, and 16‐arm) poly(D,L ‐lactide)s (PDLLs) were synthesized by ring‐opening polymerization in bulk of D,L ‐lactide monomer. Hydroxyl end‐group compounds and stannous octoate were used as the initiator and catalyst, respectively. The intrinsic viscosity and glass transition temperature (Tg) of the PDLLs decreased steadily as the branch arm number increased for similar molecular weights. However, the intrinsic viscosity and Tg values of the linear PDLL were less than the star‐shaped PDLL for similar each PDLL arm lengths. Ibuprofen, a poorly water soluble model drug was entrapped in the PDLL microspheres. All drug‐loaded PDLL microspheres were prepared by the oil‐in‐water emulsion solvent evaporation method, were spherical in shape, and had a smooth surface with fine dispersibility. In vitro drug release behaviors indicated that the drug release from the microspheres with higher branch arm number was faster than from those with lower branch arm number. Moreover, the drug release from the star‐shaped PDLL microspheres was slower than that of the linear PDLL microspheres for similar PDLL arm lengths. The drug release behavior could be adjusted through both the branch arm number and arm length of PDLL. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献