The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide...The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide-angle X-ray diffraction (WAXD). The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.展开更多
A newly synthesized aromatic sulfonate compound,complex 2 with formula of K2[H3COOC-C6H3(SO3)2]·2H2O(methyl 3,5-disulfo-benzoate dipotassium dihydrate) was synthesized and characterized by elemental analysis,...A newly synthesized aromatic sulfonate compound,complex 2 with formula of K2[H3COOC-C6H3(SO3)2]·2H2O(methyl 3,5-disulfo-benzoate dipotassium dihydrate) was synthesized and characterized by elemental analysis,infrared(IR) spectrometry,nuclear magnetic resonance(NMR) and crystal structure measurement.Single-crystal X-ray diffraction(XRD) revealed that complex 2 crystallized in the triclinic system with space group P(i).Complex 2 was used as nucleating agent for poly(L-lactide)(PLLA).The crystallization of PLLA with powder of complex 2 was investigated by means of differential scanning calorimetry(DSC) and polarized optical microscopy (POM).The results prove that complex 2 was effective as nucleating agent for PLLA.It could accelerate crystallization by reducing the induction time and increasing the density of nuclei in the crystallization process.The half-time of crystallization(t0.5) for pure PLLA was about 8 times longer than that of PLLA sample with 1.0%(mass fraction) of complex 2.展开更多
Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The e...Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The effects of molar ratios of both monomer to initiator and monomer to catalyst on the molecular weights of as-synthesized sPLLA polymers were in detail investigated.The molecular weights of sPLLA polymers linearly increased with the molar ratio of monomer to initiator,and the molecular weight dist...展开更多
The large size of the crystallites in poly(L-lactide) and the low growth rate enable detailed time- and temperaturedependent X-ray scattering studies of the ordering processes to be carded out. A layer located inter...The large size of the crystallites in poly(L-lactide) and the low growth rate enable detailed time- and temperaturedependent X-ray scattering studies of the ordering processes to be carded out. A layer located intermediate between crystals and melt-like regions is observed which finally takes on crystalline order. Recrystallization processes during heating change the complete stack structure rather than the crystallites individually and produce voids in the stacks, Establishment of a new stable structure after a temperature jump in the melting range can be followed in time. DSC experiments indicate times of melting of the order of minutes.展开更多
We have investigated the crystallization and morphological behaviors of poly(ε-caprolactone)-b-poly(L-lactide) (PCL-b-PLLA) in its autophobic dewetted ultrathin films (-11 nm) using atomic force microscopy (...We have investigated the crystallization and morphological behaviors of poly(ε-caprolactone)-b-poly(L-lactide) (PCL-b-PLLA) in its autophobic dewetted ultrathin films (-11 nm) using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The autophobic dewetting process creates a well defined film geometry containing an extremely thin wetting layer (-4.5 nm) with densely distributed micrometer droplets atop, which re- stricts the primary nucleation process to occurring only in the droplets. In addition to the normally encountered flat-on lamellae, the growth of edge-on lamellae in such a thin wetting layer has been observed on both of two crys- tallization paths. In thermal crystallization, flat-on lamellae are favored at small supercoolings while edge-on la- mellae appear at very large supercoolings both in the droplets and the wetting layer. For cold crystallization, the edge-on lamellae can form easily in the droplets and grow into the wetting layer even at very small supercoolings. These observations are explained on the basis that the nucleation and lamellar orientation are strongly affected by the film geometry, the crystallization paths, and the applied supercoolings.展开更多
Poly (lactic acid) (PLA) was synthesized by microwave-assisted ring-opening polymerization of D, L-lactide with stannous octanoate (SnOct(2)) as catalyst. Its weight-average molar mass (M-w) ranged from 39000 to 67000...Poly (lactic acid) (PLA) was synthesized by microwave-assisted ring-opening polymerization of D, L-lactide with stannous octanoate (SnOct(2)) as catalyst. Its weight-average molar mass (M-w) ranged from 39000 to 67000 and the polydispersity index from 1.3 to 1.7. The polymerization rate was much faster than that of the conventional thermal polymerization. A degradation of newly formed PLA in reaction mixture by microwave irradiation was observed.展开更多
Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as ...Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as better miscibility between the two components, low crystallinity and better hydrophilicity, which can be modulated by adjusting the block lengths of the two components.展开更多
The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw ...The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw respectively. The results indicated that five variables, namely purity of monomer, initiator to monomer ratio, vacuum level, polymerization temperature and polymerization time had different influences on the molecular weight and molecular weight distribution of poly(D. L-lactide).展开更多
Poly(d,l-lactide-co-p-dioxanone) (P(LA-co-PDO)) copolymers with different chain microstructures were synthesized by onestep or two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (...Poly(d,l-lactide-co-p-dioxanone) (P(LA-co-PDO)) copolymers with different chain microstructures were synthesized by onestep or two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (PDO) monomers using stannous octoate [Sn(Oct)2]/n-dodecanol as the initiating system. The average sequence lengths of the lactidyl (LLA) and dioxanyl (LpDo) units were calculated from the ^1H NMR spectra. It was found that both LLA and Lpoo values from the two-step syntheses were significantly longer than those from the corresponding one-step syntheses, indicating more blocky structure achieved for the twostep copolymers. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline, while the one-step copolymers were completely amorphous. In conclusion, the crystallinity of P(LA-co-PDO) copolymers could be adjusted conveniently to meet specific applications by changing the microstructure of the copolymers via different polymerization routes.展开更多
This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MP...This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MPs)for oral controlled drug delivery.The XRD patterns,thermal and spectroscopic analyses indicated intercalation of drugs into the MMT interlayer that was stabilized by electrostatic interaction.No significant changes in structural and functional properties of drugs were found in the MMT layers.In vitro drug release studies showed controlled release pattern.展开更多
Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides' structure and catalytic activity in the ring-opening polymerization of D,L-lac...Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides' structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates' catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents' number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.展开更多
(D, L)-Lactide (LA) was first polymerized with one component of rare earth catalysts [Nd(naph)(3), Nd(oct)(3), Nd(O-iPr)(3), Nd(AcAc)(3), Y(AcAc)(3), Sm(AcAc)(3), Er(AcAc)(3))] respectively in solution and in melt sta...(D, L)-Lactide (LA) was first polymerized with one component of rare earth catalysts [Nd(naph)(3), Nd(oct)(3), Nd(O-iPr)(3), Nd(AcAc)(3), Y(AcAc)(3), Sm(AcAc)(3), Er(AcAc)(3))] respectively in solution and in melt state. The effects of [Cat]/[La] molar ratio, solvents, polymerization time, temperature, various rare earth Elements and ligands were investigated in detail. The results showed that both the conversion of polymerization and the molecular weight (MW) of poly (D, L-Lactide) (PLA) in melt polymerization are higher than that in solution polymerization, but the polymerization rate in melt was lower than in solution. The molecular weight distribution (MWD) of PLA is broader with increasing temperature. X-ray study indicated that PLA obtained by Nd(AcAc)(3) in melt polymerization is an amorphous polymer.展开更多
Multiwalled carbon nanotubes(MWCNTs) grafted with poly(L-lactide-e-caprolactone)(PCLA) were synthesized by ring opening polymerization reaction and used as a reinforcement for neat PCLA.Scanning electron microscopy(SE...Multiwalled carbon nanotubes(MWCNTs) grafted with poly(L-lactide-e-caprolactone)(PCLA) were synthesized by ring opening polymerization reaction and used as a reinforcement for neat PCLA.Scanning electron microscopy(SEM) revealed that the applied tensile load on the composite was transferred to the MWNT-OH-g-PCLA,loading to a strain failure of the MWCNTs rather than an adhesive failure between the MWCNTs and the matrix.展开更多
Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface mod...Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.展开更多
Biphasic calcium phosphate (BCP) powders were prepared by hydrolyzation proc-ess and surface-modified by directly grafted L-lactide (LLA) onto the surface of BCP through a chemical linkage. The grafting ratio of o...Biphasic calcium phosphate (BCP) powders were prepared by hydrolyzation proc-ess and surface-modified by directly grafted L-lactide (LLA) onto the surface of BCP through a chemical linkage. The grafting ratio of organic groups was 9 wt%. After surface modification, the surface of BCP powders was covered by the lamella-shaped crystal. Poly (L-lactide) was mixed with BCP to form the BCP/PLLA biocomposite. Modified BCP (mBCP) particles could be uniformly dis-persed in PLLA matrix. The compressive strength of the mBCP/PLLA composite is 115 MPa, 28% higher than that of unmodified-BCP/PLLA composite. The improved mechanical strength is attributed to the enhanced adhesion between the inorganic BCP filler and the organic PLLA matrix.展开更多
A total biodegradable elastomer,branched multiblock poly( ε-caprolactone)/poly( D-lactide)( BMCD) was prepared using 3-isocyanatopropyltriethoxysilane( IPTS) as a coupling agent.To improve the toughness of poly( L-la...A total biodegradable elastomer,branched multiblock poly( ε-caprolactone)/poly( D-lactide)( BMCD) was prepared using 3-isocyanatopropyltriethoxysilane( IPTS) as a coupling agent.To improve the toughness of poly( L-lactide)( PLLA),PLLA/BMCD blends were prepared via a simple solvent evaporation method at various BMCD loadings. Tensile test showed that the elongation at break of PLLA blends increased to 50. 97% and104. 55% at the loadings of 5% and 7%( mass fraction) BMCD respectively, with no sacrifice of their biodegradability. This approach allowed for simultaneous control of mechanical and biodegradable properties of PLLA with a few additives in actual production. Furthermore, UV-VIS test showed that the light transmittance of the films at the loadings of 5%( mass fraction)BMCD was almost the same as pure PLLA at 400 nm.展开更多
Methoxy poly(ethylene glycol)-poly(D,L-lactide) block copolymers (PEG-PLA) were prepared through ring-opening polymerization.The oil in water suspension method was used to prepare block copolymer micelles. The critica...Methoxy poly(ethylene glycol)-poly(D,L-lactide) block copolymers (PEG-PLA) were prepared through ring-opening polymerization.The oil in water suspension method was used to prepare block copolymer micelles. The critical micelle concentration (CMC) by fluorescence spectroscopy was 0.0056 mg·ml -1 . The physical state of the inner core region of micelles was characterized with 1HNMR. The size of indomethacin (IMC) loaded micelles measured by dynamic light scattering (DLS) showed narrow monodisperse size distribution and the average diameters were less than 50 nm. In addition, the nanoparticles with relatively high drug loading content (DLC) were obtained.展开更多
This work focuses to improve the mechanical properties and investigates the growth of osteoblasts on a degradable chitosan/poly(L-lactide)/carbon nanotubes composite for tissue engineering. The morphological and mecha...This work focuses to improve the mechanical properties and investigates the growth of osteoblasts on a degradable chitosan/poly(L-lactide)/carbon nanotubes composite for tissue engineering. The morphological and mechanical properties characterizations were performed using scanning electronic microscopy (SEM) and rheometrics analysis system (RSA). Osteoblasts differentiation was determined by alkaline phosphatase activity, total number cells by an Alamar Blue assay, cell attachment and proliferation were visualized qualitatively using SEM, mineralization was characterized by transformed infrared spectroscopy, energy dispersive spectroscopy, and X-ray diffraction. The results suggest that the chitosan/poly(L-lactide)/multiwalled carbon nanotubes composites exhibit the ability to promote cell adhesion, proliferation, and differentiation on their surface.展开更多
基金supported by the National Natural Science Foundation of China(No.50527301)
文摘The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide-angle X-ray diffraction (WAXD). The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s^-1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.
基金Supported by the National Natural Science Foundation of China(Nos.51203155,51173183,21004061,51021003) and the National High Technology Recearch Development Program of China(No.2011AA02A202).
文摘A newly synthesized aromatic sulfonate compound,complex 2 with formula of K2[H3COOC-C6H3(SO3)2]·2H2O(methyl 3,5-disulfo-benzoate dipotassium dihydrate) was synthesized and characterized by elemental analysis,infrared(IR) spectrometry,nuclear magnetic resonance(NMR) and crystal structure measurement.Single-crystal X-ray diffraction(XRD) revealed that complex 2 crystallized in the triclinic system with space group P(i).Complex 2 was used as nucleating agent for poly(L-lactide)(PLLA).The crystallization of PLLA with powder of complex 2 was investigated by means of differential scanning calorimetry(DSC) and polarized optical microscopy (POM).The results prove that complex 2 was effective as nucleating agent for PLLA.It could accelerate crystallization by reducing the induction time and increasing the density of nuclei in the crystallization process.The half-time of crystallization(t0.5) for pure PLLA was about 8 times longer than that of PLLA sample with 1.0%(mass fraction) of complex 2.
基金This work was financially supported by the National Natural Science Foundation of China(No.20404007)and many thanks for the assistance of Instrumental Analysis Center of SJTU.
文摘Well-defined star-shaped poly(L-lactide)with six arms(sPLLA)was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125~C.The effects of molar ratios of both monomer to initiator and monomer to catalyst on the molecular weights of as-synthesized sPLLA polymers were in detail investigated.The molecular weights of sPLLA polymers linearly increased with the molar ratio of monomer to initiator,and the molecular weight dist...
基金This work was supported by the Deutsche Forschungsgemeinschaft. Thanks are also due to the Fonds der Chemischen Industrie for financial help.
文摘The large size of the crystallites in poly(L-lactide) and the low growth rate enable detailed time- and temperaturedependent X-ray scattering studies of the ordering processes to be carded out. A layer located intermediate between crystals and melt-like regions is observed which finally takes on crystalline order. Recrystallization processes during heating change the complete stack structure rather than the crystallites individually and produce voids in the stacks, Establishment of a new stable structure after a temperature jump in the melting range can be followed in time. DSC experiments indicate times of melting of the order of minutes.
文摘We have investigated the crystallization and morphological behaviors of poly(ε-caprolactone)-b-poly(L-lactide) (PCL-b-PLLA) in its autophobic dewetted ultrathin films (-11 nm) using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The autophobic dewetting process creates a well defined film geometry containing an extremely thin wetting layer (-4.5 nm) with densely distributed micrometer droplets atop, which re- stricts the primary nucleation process to occurring only in the droplets. In addition to the normally encountered flat-on lamellae, the growth of edge-on lamellae in such a thin wetting layer has been observed on both of two crys- tallization paths. In thermal crystallization, flat-on lamellae are favored at small supercoolings while edge-on la- mellae appear at very large supercoolings both in the droplets and the wetting layer. For cold crystallization, the edge-on lamellae can form easily in the droplets and grow into the wetting layer even at very small supercoolings. These observations are explained on the basis that the nucleation and lamellar orientation are strongly affected by the film geometry, the crystallization paths, and the applied supercoolings.
文摘Poly (lactic acid) (PLA) was synthesized by microwave-assisted ring-opening polymerization of D, L-lactide with stannous octanoate (SnOct(2)) as catalyst. Its weight-average molar mass (M-w) ranged from 39000 to 67000 and the polydispersity index from 1.3 to 1.7. The polymerization rate was much faster than that of the conventional thermal polymerization. A degradation of newly formed PLA in reaction mixture by microwave irradiation was observed.
基金The authors are Indebted to the National Basic Science Rescarch and Development Grants(973)(No.1999054306).
文摘Poly (L-lactide)-poly(ethylene glycol) multiblock copolymers with predetermined block lengths were synthesized by polycondensation of PLA diols and PEG diacids. These copolymers presented special properties, such as better miscibility between the two components, low crystallinity and better hydrophilicity, which can be modulated by adjusting the block lengths of the two components.
基金Funded by the Key Project of the Ministry of Science and Technology (No. 96 - 920 - 20 - 21)
文摘The ring-opening polymerization of D, L-lactide in the melt was systematically investigated by using stannous octoate as the initiator. The molecular weight of poly (D, L-lactide) was characterized with M,. Mn and Mw respectively. The results indicated that five variables, namely purity of monomer, initiator to monomer ratio, vacuum level, polymerization temperature and polymerization time had different influences on the molecular weight and molecular weight distribution of poly(D. L-lactide).
基金supported by the National Natural Sciences Fund of China(No.50603025)the Opening Project of State Key Laboratory of Polymer Materials Engineering(Sichuan University).
文摘Poly(d,l-lactide-co-p-dioxanone) (P(LA-co-PDO)) copolymers with different chain microstructures were synthesized by onestep or two-step bulk ring-opening polymerizations of d,l-lactide (LA) and p-dioxanone (PDO) monomers using stannous octoate [Sn(Oct)2]/n-dodecanol as the initiating system. The average sequence lengths of the lactidyl (LLA) and dioxanyl (LpDo) units were calculated from the ^1H NMR spectra. It was found that both LLA and Lpoo values from the two-step syntheses were significantly longer than those from the corresponding one-step syntheses, indicating more blocky structure achieved for the twostep copolymers. Corresponding to this difference in microstructure, the two-step copolymers were semi-crystalline, while the one-step copolymers were completely amorphous. In conclusion, the crystallinity of P(LA-co-PDO) copolymers could be adjusted conveniently to meet specific applications by changing the microstructure of the copolymers via different polymerization routes.
基金Authors are thankful to Director,CSMCRI,Bhavnagar for pro-viding necessary infrastructure facilities and the Council of Scientific and Industrial Research,Government of India,New Delhi,India(CSIR)for Senior research fellowship awarded to BDK,and funding under Network Project:NWP 0010.
文摘This work evaluates intercalation of Nortriptyline(NT)and Venlafaxine(VFX)in an interlayer gallery of Na^(+)-MMT(Montmorillonite),which was further compounded with Poly(LLactide)(PLLA)to form microcomposite spheres(MPs)for oral controlled drug delivery.The XRD patterns,thermal and spectroscopic analyses indicated intercalation of drugs into the MMT interlayer that was stabilized by electrostatic interaction.No significant changes in structural and functional properties of drugs were found in the MMT layers.In vitro drug release studies showed controlled release pattern.
基金Funded by the Natural Science Foundation of Shanxi Province (No.2006011069)the Opening Foundation of Key Laboratory of Shanxi Province (No.2009011059-7)
文摘Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides' structure and catalytic activity in the ring-opening polymerization of D,L-lactide has also been investigated.The catalytic activity of all rare earth aryloxides,characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated.The results showed that both phenolates' catalytic activities and polymerization characteristics changed regularly,keeping in good concordance with variations in substitutents' number on phenol and structure of aryloxide ligands.The stronger ability of electron-donation of alkyl groups,the higher catalytic activity.Moreover,the more numbers of substituted alkyl on phenyl ring,the higher catalytic activity.The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.
基金This work was supported by the National Natural Science Foundation of China and the Laboratory of Rare-earth Chemistry and Physics,Changchun Institute of Applied Chemistry,Academia Sinica
文摘(D, L)-Lactide (LA) was first polymerized with one component of rare earth catalysts [Nd(naph)(3), Nd(oct)(3), Nd(O-iPr)(3), Nd(AcAc)(3), Y(AcAc)(3), Sm(AcAc)(3), Er(AcAc)(3))] respectively in solution and in melt state. The effects of [Cat]/[La] molar ratio, solvents, polymerization time, temperature, various rare earth Elements and ligands were investigated in detail. The results showed that both the conversion of polymerization and the molecular weight (MW) of poly (D, L-Lactide) (PLA) in melt polymerization are higher than that in solution polymerization, but the polymerization rate in melt was lower than in solution. The molecular weight distribution (MWD) of PLA is broader with increasing temperature. X-ray study indicated that PLA obtained by Nd(AcAc)(3) in melt polymerization is an amorphous polymer.
基金Funded by the National Basic Research Program of China(No.2006CB708609)the Development Program for Outstanding Young Teachers in HIT (HITQNJS.2007.015)
文摘Multiwalled carbon nanotubes(MWCNTs) grafted with poly(L-lactide-e-caprolactone)(PCLA) were synthesized by ring opening polymerization reaction and used as a reinforcement for neat PCLA.Scanning electron microscopy(SEM) revealed that the applied tensile load on the composite was transferred to the MWNT-OH-g-PCLA,loading to a strain failure of the MWCNTs rather than an adhesive failure between the MWCNTs and the matrix.
基金supported by the National Natural Science Foundation of China(Nos.50425309,0711351501,50733033)National Fund for Distinguished Young Scholar(No.50425309).
文摘Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.
基金Funded by the Research Fund for the Doctoral Program of Higher Education of China (No. 20060610024)
文摘Biphasic calcium phosphate (BCP) powders were prepared by hydrolyzation proc-ess and surface-modified by directly grafted L-lactide (LLA) onto the surface of BCP through a chemical linkage. The grafting ratio of organic groups was 9 wt%. After surface modification, the surface of BCP powders was covered by the lamella-shaped crystal. Poly (L-lactide) was mixed with BCP to form the BCP/PLLA biocomposite. Modified BCP (mBCP) particles could be uniformly dis-persed in PLLA matrix. The compressive strength of the mBCP/PLLA composite is 115 MPa, 28% higher than that of unmodified-BCP/PLLA composite. The improved mechanical strength is attributed to the enhanced adhesion between the inorganic BCP filler and the organic PLLA matrix.
基金National Natural Science Foundation of China(No.51503029)National Institute of Food and Agriculture of U.S.Department of Agriculture,U.S.(No.NEB 37-037)Agricultural Research Division at the University of Nebraska-Lincoln,U.S
文摘A total biodegradable elastomer,branched multiblock poly( ε-caprolactone)/poly( D-lactide)( BMCD) was prepared using 3-isocyanatopropyltriethoxysilane( IPTS) as a coupling agent.To improve the toughness of poly( L-lactide)( PLLA),PLLA/BMCD blends were prepared via a simple solvent evaporation method at various BMCD loadings. Tensile test showed that the elongation at break of PLLA blends increased to 50. 97% and104. 55% at the loadings of 5% and 7%( mass fraction) BMCD respectively, with no sacrifice of their biodegradability. This approach allowed for simultaneous control of mechanical and biodegradable properties of PLLA with a few additives in actual production. Furthermore, UV-VIS test showed that the light transmittance of the films at the loadings of 5%( mass fraction)BMCD was almost the same as pure PLLA at 400 nm.
文摘Methoxy poly(ethylene glycol)-poly(D,L-lactide) block copolymers (PEG-PLA) were prepared through ring-opening polymerization.The oil in water suspension method was used to prepare block copolymer micelles. The critical micelle concentration (CMC) by fluorescence spectroscopy was 0.0056 mg·ml -1 . The physical state of the inner core region of micelles was characterized with 1HNMR. The size of indomethacin (IMC) loaded micelles measured by dynamic light scattering (DLS) showed narrow monodisperse size distribution and the average diameters were less than 50 nm. In addition, the nanoparticles with relatively high drug loading content (DLC) were obtained.
文摘This work focuses to improve the mechanical properties and investigates the growth of osteoblasts on a degradable chitosan/poly(L-lactide)/carbon nanotubes composite for tissue engineering. The morphological and mechanical properties characterizations were performed using scanning electronic microscopy (SEM) and rheometrics analysis system (RSA). Osteoblasts differentiation was determined by alkaline phosphatase activity, total number cells by an Alamar Blue assay, cell attachment and proliferation were visualized qualitatively using SEM, mineralization was characterized by transformed infrared spectroscopy, energy dispersive spectroscopy, and X-ray diffraction. The results suggest that the chitosan/poly(L-lactide)/multiwalled carbon nanotubes composites exhibit the ability to promote cell adhesion, proliferation, and differentiation on their surface.