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1.
Three new metal alkoxides, [(MMPEP)Al(μ-OCH2C6H4CH2Cl)]2 (1), [(MMPEP-H)Li·(BnOH)]2 (2) and [(MMPEP-H)Li·(HOCH2C6H4CH2Cl)]2 (3) (MMPEP-H2: 2,2′-methylene-bis{4,6-di(1-methyl-1-phenylethyl)phenol}) have been synthesized and characterized. Complex 1 was prepared by the reaction of [(MMPEP)Al(CH3)(Et2O)] with p-(chloromethyl)benzyl alcohol. Followed by the reaction of MMPEP-H2 with nBuLi, BnOH or p-(chloromethyl)benzyl alcohol was added to give complexes 2 and 3, respectively. Complex 1 has shown excellent catalytic activity towards ring-opening polymerization (ROP) of ?-caprolactone. Both complexes 2 and 3 are active for ROP of l-lactide. Block copolymers of poly(?-caprolactone)-b-polyacrylonitrile (PCL-b-PAN) and poly(l-lactide)-b-polyacrylonitrile can be synthesized by combining a technique of atom transfer radical polymerization (ATRP) and ROP using a double-headed initiator. Microphase-separated morphology of PCL-b-PAN has been observed by transmission electron microscopy, indicating the formation of self-assembled nanostructure. 相似文献
2.
High molecular weight di- and triblock copolymers of poly(l-lactide), PLLA, (80 wt%) with a crystallizable flexible second component such as poly(ε-caprolactone), PCL, or poly(oxyethylene), PEO, (20 wt%) were obtained in nearly quantitative yields by ring opening of l-lactide initiated by PCL or PEO hydroxy terminated macromers. The copolymers were characterized by 1H NMR and FTIR spectroscopy and size exclusion chromatography and showed unimodal and narrow molecular weight distributions. X-ray diffraction measurements revealed high crystallinity (38-56%) of the PLLA blocks and gave no clear evidences of PCL or PEO crystallinity. DMTA and DSC techniques showed a melting behaviour of the copolymers (Tm=174-175 °C; ΔHm=19-37 J/g) quite similar to that of PLLA. PCL and PLLA segments are immiscible, while PLLA and PEO segments are partially miscible in the amorphous phase. Stress-strain measurements indicated a ductile behaviour of the copolymers, characterized by lower tensile moduli (225-961 Pa) and higher elongations at break (25-134%) with respect to PLLA. 相似文献
3.
Semi-interpenetrating polymer networks (semi-IPNs) were prepared by reactions of methylenediphenyl 4,4’-diisocyanate (MDI) and hydroxy-terminated 4-arm star-shaped ε-caprolactone oligomers (H4CLOn's) with the degrees of polymerization per one arm, n = 3, 5 and 10 in the presence of poly(l-lactide) (PLA). Morphologies, thermal and mechanical properties of the MDI-bridged H4CLOn (MH4CLOn)/PLA semi-IPNs were evaluated by comparing with those of poly(?-caprolactone) (PCL)/PLA blends. Two tan δ peaks related to MH4CLOn and PLA were observed in a dynamic mechanical curve of the semi-IPN. Although all the semi-IPNs and blends had micro-phase separated morphologies, the phase-separated droplets of MH4CLO5/PLA 50/50 were much finer than those of PCL/PLA 50/50. Differential scanning calorimetry (DSC) analyses revealed that MH4CLO3 and MH4CLO5 are substantially amorphous, while MH4CLO10 is semi-crystalline, and that cold crystallization of the PLA component of MH4CLOn/PLA is more strongly disturbed for the semi-IPN with a smaller n value and more MH4CLOn content. Tensile modulus, toughness and elongation at break of MH4CLO5/PLA 50/50 semi-IPN were much higher than those of PCL/PLA 50/50 blend. 相似文献
4.
Enhancing matrix crystallization has been demonstrated to be an effective method to simultaneously improve the impact toughness and heat resistance of poly(l-lactide) (PLLA) modified with flexible polymers, such as poly(ε-caprolactone) (PCL). Unfortunately, increasing PLLA matrix crystallinity alone cannot guarantee the enhancement of impact toughness in most cases, so other structural parameters should be considered. In this work, taking PLLA/PCL (80/20) blend as an example, the combined roles of matrix crystallization and impact modifier particle size in the toughening have been investigated. PLLA matrix crystallinity was controlled by adding a highly effective nucleating agent and PCL particle size was tailored by varying processing conditions while maintaining constant interfacial adhesion. It is interesting to find that toughening is efficient only if matrix crystallinity and particle size are well matched. With the significant increase of matrix crystallinity, an evident decrease of optimum particle size for toughening PLLA has been identified for the first time. Therefore, suitable particle size is the precondition for highly crystalline matrix to work effectively in the toughening because only small particles (0.3–0.5 μm) are effective in trigger shear yielding mechanism of the matrix needed for good toughness, whereas relatively large particles (0.7–1.1 μm) are only capable of toughening amorphous matrix effectively by initiating multiple crazing of the matrix. Importantly, our findings can be used to well explain the reason for the different roles of matrix crystallization in the toughening of different PLLA blends reported in the literature. Furthermore, the heat resistance of the blend with a highly crystalline matrix is much better than that of the blend with an amorphous one as expected. This work could not only provide a new insight into the synergistic roles of matrix crystallization and modifier particle size in the toughening of PLLA but also set up a universal framework for designing high-performance PLLA products with both good impact toughness and high heat resistance. 相似文献
5.
Poly (ε-caprolactone) (PCL) and poly (l-lactide) (PLA) were prepared by ring-opening polymerization catalyzed by organic amino calcium catalysts (Ca/PO and Ca/EO) which were prepared by reacting calcium ammoniate Ca(NH3)6 with propylene oxide and ethylene oxide, respectively. The catalysts exhibited high activity and the ring-opening polymerization behaved a quasi-living characteristic. Based on the FT-IR spectra and the calcium contents of the catalysts, and based on the 1H NMR end-group analysis of the low molecular weight PCL prepared using catalysts Ca/PO and Ca/EO, it was proposed that the catalysts have the structure of NH2-Ca-O-CH(CH3)2 and NH2-Ca-O-CH2CH3 for Ca/PO and Ca/EO, respectively. The ring-opening polymerization of CL and LA follows a coordination-insertion mechanism and the active site is the Ca-O bond. 相似文献
6.
Two novel magnesium aryloxides have been prepared and their catalytic activities toward ring-opening polymerization (ROP) of ε-caprolactone and l-lactide have been investigated. The reaction of 2,2′-(2-methoxybenzylidene)-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MEMPEP-H2) (1) and 2,2′-methylene-bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MMPEP-H2) with nBu2Mg yield dimeric magnesium complexes [Mg(μ-MEMPEP)(THF)]2 (2) and [Mg(μ-MMPEP)(THF)]2 (3), respectively. Catalytic studies of complexes 2 and 3 illustrate that both 2 and 3 are good catalysts in ε-caprolactone and l-lactide polymerization. Theoretical study of the ROP mechanism of ε-caprolactone catalyzed by 2 demonstrates that the initiator, benzyl alcohol, is activated by the formation of a hydrogen bond with the phenoxy oxygen of MEMPEP2− ligand. 相似文献
7.
A series of copolymers with various compositions were prepared by the ring opening copolymerization of l-lactide (l-LA) and ?-caprolactone (?-CL) using nontoxic magnesium octoate as a catalyst in bulk. The copolymerization process and the influence of transesterification on the chain microstructure were examined by 1H and 13C NMR. A tapered block or gradient copolymer is expected to be formed on the basis of the reactivity difference between l-LA and ?-CL. Two modes of transesterification occurred and played an important role in the redistribution of comonomer sequences but not a completely random distribution. The CLC sequence formed by the second mode of transesterification was observed at the end of reaction. The coefficient of the second mode of transesterification (TII) increased as the feed mole fraction of ?-CL increased. In terms of the overall feed compositions, the LLLr values of lactidyl sequences calculated from the reactivity ratio exceeded the LLLe values determined from the product, however, the LCr values of caproyl sequences were identical or shorter than the LCe values. The thermal properties and crystallinities of the obtained copolymers were investigated by DSC and WAXD. The thermal properties and crystallinities depend on both the composition and the chain microstructure. The l-LA/?-CL copolymer with intermediate composition exhibited some blocky character by DSC. Only single Tg was observed for each copolymer and in agreement with the calculated value from Fox equation, indicating that the amorphous region of the copolymers is miscible. The obtained copolymers can best be described as random copolymers with more or less blocky chain structure. 相似文献
8.
Crystallinity of poly(?-l-lysine) (?-PL) was discussed by analyzing the differences in the 1H spin-spin relaxation times (T2H), the 13C spin-lattice relaxation times (T1C), and the 13C NMR signal shapes between the crystalline and the non-crystalline phases. The observed 1H relaxation curve (free induction decay followed by solid-echo method) showed the sum of Gaussian and exponential decays. Similarly, the observed 13C relaxation curves obtained from the Torchia method were double-exponential. The 13C NMR spectrum of ?-PL was divided into the narrow and the broad lines by utilizing the intrinsic differences in the 1H spin-lattice relaxation times in the rotating-frame between them, which are attributed to the crystalline and the non-crystalline phases, respectively. Even though the crystallinity is obtained from the identical NMR measurements, the estimated values are different with each other. The crystallinity estimated from the T2H differences was 75.8 ± 0.1% at 333 K and 60.7 ± 0.4% at 353 K. From the T1C differences, the value was estimated to be 62 ± 11%. Furthermore, the value estimated from the NMR signal separation was 54 ± 5%. In this study we have explained these discrepancies by the difference in susceptibility among the experiments for the inter-phase, which exists in-between the crystalline and the amorphous phases. Furthermore, the estimated crystallinity was ascertained by the X-ray diffraction experiment. 相似文献
9.
Hydrolytic degradation ability is an intriguing characteristic of poly(l-lactide) (PLLA) and it has been intensively investigated recently. However, the microstructure evolution of PLLA during the early stage of the hydrolytic degradation process is neglected. In this work, amorphous PLLA was hydrolyzed in alkaline media at temperatures from 40 to 60 °C. The variations of weight loss and molecular weight were measured to study the degree of the hydrolytic degradation of PLLA. The effect of hydrolytic degradation on microstructure of the amorphous PLLA was investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscope (FTIR), wide angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). The results clearly proves the occurrence of molecular ordering and the formation of α′-form PLLA, which is greatly related to the hydrolytic degradation conditions. At relatively low hydrolytic degradation temperature (40 and 50 °C), locally ordered structure is provoked, while a large number of α′-form crystallites are induced at relatively high temperature (60 °C). This work is very significant in understanding the microstructure evolution of PLLA during the hydrolytic degradation process. 相似文献
10.
Yodthong Baimark 《Polymer》2009,50(20):4761-4767
Surfactant-free biodegradable porous microspheres of methoxy poly(ethylene glycol)-b-poly(?-caprolactone-co-d,l-lactide) (MPEG-b-PCLDLL) diblock copolymers were prepared by a simple melt dispersion method in water at 80 °C with magnetic stirring. Any organic solvents and surfactants can be neglected for this method. Different CL/DLL ratios in the MPEG-b-PCLDLL were investigated for preparation of the porous microspheres. It was found that microsphere sizes decreased and surface pore sizes increased as the increasing DLL ratio. The pores were well interconnected throughout the microsphere matrices for all MPEG-b-PCLDLLs. The larger pore sizes can be obtained when the PEG was blended with diblock copolymer before preparation of porous blended microspheres. Possible mechanisms for formation of the porous microspheres with and without PEG blending were also proposed. 相似文献
11.
Bor-Hunn Huang 《Polymer》2006,47(19):6622-6629
Three novel sterically hindered zinc aryloxides have been prepared and well characterized. Their catalytic activities toward ring-opening polymerization (ROP) of ?-caprolactone and l-lactide have been investigated. The reaction of 2,2′-ethylidene-bis(4,6-di-tert-butylphenol) (EDBP-H2), 2,2′-(2-methoxybenzylidene)bis(4-methyl-6-tert-butylphenol) (MEBBP-H2) and 2,2′-(2-methoxybenzylidene)bis(4,6-di(1-methyl-1-phenylethyl)phenol) (MEMPEP-H2) with ZnEt2 in THF yields dimeric zinc complexes [(μ-EDBP)Zn(THF)]2 (1), [(μ-MEBBP)Zn(THF)]2 (2) and [(μ-MEMPEP)Zn(THF)]2 (3), respectively. Experimental results show that all three compounds are good catalysts for ROP of ?-caprolactone and l-lactide yielding polymer in a controlled fashion with low polydispersity indexes. 相似文献
12.
The ring-opening copolymerization of l-lactide (l-LA) and RS-β-benzyl malate (MA) was performed in the presence of stannous octoate. Copolymers were successfully synthesized using different feeding doses. 1H NMR analysis revealed that the compositions of the copolymers with high MA contents were similar to the feeding doses. GPC measurements showed that the molecular weight of the copolymers decreased as the MA content increased. The hydrophilicity of these copolymers was remarkably improved after they were hydrogenolyzed over palladium on charcoal, which removed the pendant benzyl groups. These de-protected copolymers had higher glass transition temperatures (Tg) than both the corresponding protected copolymers and the PLLA homopolymer due to the formation of intermolecular hydrogen bonds between the pendant carboxyl groups. The morphology of the copolymers changed from crystalline to amorphous with increasing RS-β-malic acid content. 相似文献
13.
Bismuth (III) subsalicylate, a commercial drug, was used as catalyst for 1,4-butanediol-initiated copolymerizations of ε-caprolactone (εCL) and glycolide (GL). Telechelic copolyesters having two OH-endgroups and predominantly alternating sequences were obtained. These copolyesters are amorphous with glass transition temperatures (Tgs) below −30 °C. In a second series of polymerizations, in situ chain extension with l-lactide (LLA) was performed, whereby A-B-A triblock copolymers were obtained without significant transesterification between A- and B-blocks. Finally, these A-B-A triblock copolymers were transformed into multiblock copolymers by chain extension with 1,6-hexamethylene diisocyanate. The block copolymers were characterized by 1H and 13C NMR spectroscopy, by viscosity, SEC and DSC measurements. 相似文献
14.
The aim of this study was to investigate coaxial electrospun poly(l-lactide-co-?-caprolactone) [PLLACL] nanofibers for the application in nerve tissue engineering. The hypothesis was that the nanofibrous mats fabricated by coaxial electrospun PLLACL could be effective scaffolds for releasing proteins, such as Bovine Serum Albumin (BSA) or/and Nerve Growth Factor (NGF), in a sustained manner. To test the hypothesis, the coaxial electrospun nanofibers with PLLACL as the shell and BSA/NGF as the core were characterized. Morphologies and mechanical properties of nanofibrous mats were examined. BSA released behavior was studied. The results demonstrated that BSA could be sustainedly released from coaxial electrospun PLLACL nanofibers, however, BSA released from mix electrospun nanofibers present the burst release behavior. Bioactivity of released NGF from coaxial electrospun nanofibers was verified by testing the differentiation of rat pheochromocytoma cells (PC12). 相似文献
15.
Poly (β,l-malic acid) (PMLA) was obtained by Physarum polycephalum. The FT-IR and FT-Raman spectra were recorded experimentally and used for normal mode analysis using Wilson GF matrix method and phonon dispersion of PMLA. The non redundant set of internal coordinate are simplified. Urey-Bradley force field approximation was employed in normal mode analysis and to calculate the potential energy distribution (PED) of each fundamental vibration. Apart from detailed assignment, various characteristic features of dispersion curve have also been explained, arising due to internal symmetry in energy momentum space. Predictive values of the intramolecular contribution to the heat capacity of this polymer calculated by the density of states, are also been reported. The thermal degradation of PMLA was investigated in nitrogen atmosphere by thermogravimetric analysis in combination with DTA and FT-IR. The spectra of gases found in the thermal degradation of PMLA are very much similar to the spectra of gases released during decomposition of fumaric acid. 相似文献
16.
Poly(lactic acid) samples rich in α′ or α crystals have been characterized using spectroscopic and thermal methods. Cryogenic infrared and Raman spectroscopy were used to probe the differences in chain conformation and packing. Compared to the α crystal, the α′ crystal has weakened specific carbonyl and methyl interactions. Experimental spectroscopic analysis in conjunction with simulation studies have shown that the α′ crystal has uniform conformational disorder in the Cα-C torsion angle. This disorder in chain conformation and packing leads to different crystalline forms with different stabilities. The difference in thermal stability was quantified by measuring enthalpic change at melting for both crystalline forms. Significantly different values for the two crystalline forms were obtained ( and ). The transformation from the less stable α′ to the more stable α phase has been characterized. This analysis provides an explanation to the double melting peaks usually found in PLLA samples. 相似文献
17.
Conformationally disordered α′-crystals of poly (l-lactic acid) were formed by crystallization of the melt at high supercooling at 95 °C. Analysis of their melting temperature as a function of the crystallinity revealed absence of crystal thickening during isothermal crystallization. Annealing of α′-crystals between the crystallization temperature of 95 °C and their zero-entropy production melting temperature of 150 °C leads to their stabilization, mainly by solid-state reorganization. Heating faster than 30 K s−1 suppresses reorganization and permits superheating of the α′-phase. Consequently, isothermal melting followed by melt-recrystallization becomes accessible. Melting is completed within few hundreds of milliseconds, and melt-recrystallization is about two orders of magnitude faster than crystallization of the isotropic melt at identical temperature. The time required for melting decreases with superheating and increases with the lateral dimension of the lamellar crystals. Laterally extended lamellae require long time for melting of the outer crystal layers, which allows stabilization of the central crystal part. These crystal remnants then serve as seed for immediate recrystallization. In case of complete melting of smaller lamellae, melt-recrystallization is retarded but still distinctly faster than cold- and melt-crystallization, due to incomplete isotropization of the melt. 相似文献
18.
Laser melt electrospinning is a novel technology to produce nonwoven scaffolds for tissue engineering (TE) applications. This solvent-free process is far safer than common solution electrospinning. In this paper, we demonstrated the poly(?-caprolactone) (PCL) fibers diameters could be governed from 3 to 12 μm with changing electrospinning parameters. The various diameters can meet the needs of scaffold properties such as porosity, pore size, etc. Our experiential results also showed that the fibers diameter tended to decrease as laser current increased. The degradation of PCL molecular chains often occurs in the melt electrospinning process due to mechanical scission and thermal degradation. The crystallinity of as-spun PCL fibers was approximately equal to that of the annealing fibers by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). In our experiential, the collected PCL electrospun fibers often fused together to form a three-dimension network structure, which is favorable to mechanical properties. 相似文献
19.
In this work, we investigated the self-assembly behavior of poly(?-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(?-caprolactone) (PCL-b-PEEE-b-PCL) triblock copolymer in epoxy thermosets. The PCL-b-PEEE-b-PCL triblock copolymer was synthesized via the ring-opening polymerization of ?-caprolactone with a hydroxyl-terminated poly(ethylene-co-ethylethylene) as the macromolecular initiator. The hydroxyl-terminated poly(ethylene-co-ethylethylene) was prepared with the hydrogenation reaction of a hydroxyl-terminated polybutadiene. The triblock copolymer was incorporated into the precursors of epoxy to obtain the nanostructured thermosets. It was found that the self-organized nanophases were formed in the mixture before curing reaction and the nanostructures can be further fixed via curing reaction. The self-assembly behavior of the triblock copolymer in epoxy thermosets was investigated by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) shows that the formation of the self-organized nanophase in the thermosets caused that a part of poly(?-caprolactone) subchains were demixed from epoxy matrix with the occurrence of curing reaction; the fractions of demixed PCL blocks were estimated according to the Tg-composition relation of the model binary blends of epoxy and PCL. 相似文献
20.
A film of poly(l-lactic acid) (PLLA) consisting of highly oriented α crystals was uniaxially drawn by tensile force. The effects of the draw ratio (DR), draw temperature (Td), and draw stress on the crystal/crystal transformation from the α- to the β-form crystals were studied. At the initial stage of drawing, the highly oriented α crystals of the starting film transformed into a broader orientation distribution, and significant crystal disorder was introduced. Upon further drawing, the α crystals steadily transformed into β crystals with increasing the DR. For the drawing at a constant Td, the crystal transformation proceeded more efficiently at a higher draw rate and, hence, at a higher draw stress. Furthermore, for the drawing at a constant draw rate, the transformation proceeded with DR most efficiently for the tensile draw at a Td around 140 °C, although the draw stress increased with decreasing the Td. The present result combined with the previous finding in the drawing of PLLA by solid-state extrusion [Macromolecules 36 (2003) 3601] suggests that there is a Td of around 140 °C at which the crystal transformation proceeds most efficiently with DR, suggesting that there are two factors that have opposite effects on the efficiency of the crystal transformation with increasing the Td. However, as a result of the combined effects of the Td and DR on the crystal transformation and the ductility increase with the Td, an oriented film consisting predominantly of β crystals was obtained by tensile drawing at a Td in the range of 140-170 °C to the highest DR achieved at each Td. 相似文献