The Ring-opening Polymerization of D, L-Lactide Initiated with Stannous Octoate

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).

Poly(L-lactide)-Poly(ethylene glycol) Multiblock Copolymers: Synthesis and Properties

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.

NON-ISOTHERMAL CRYSTALLIZATION OF POLY(L-LACTIDE)(PLLA) UNDER QUIESCENT AND STEADY SHEAR CONDITIONS

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.

Montmorillonite/Poly(L-Lactide)microcomposite spheres as reservoirs of antidepressant drugs and their controlled release property

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.

A Series of Rare Earth Phenolates Substituted by Alkyl Groups for D,L-Lactide Ring-Opening Polymerization

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.

Measurement of Monomer Reactivity Ratios of D,L-3-Methylglycolide with Glycolide or D,L-Lactide

For monomer reactivity ratios study, the copolymerization of D,L-3-methylglycolide (MG) with glycolide (GA) or D,L-lactide (LA) was carried out in bulk to a certain low conversion in the presence of stannous octoate at 140 degrees C. The copolymer compositions were determined by H-1 NMR spectroscopy. The monomer reactivity ratios were evaluated by Fineman-Ross method, Kelen-Tudos method and linear least-squares method. The monomer reactivity ratios of D,L-3-methylglycolide and glycolide or D,L-lactide are r(mg)= 0.73, r(ga)= 1.47; r(mg)= 1.71, r(la)= 0.92, respectively.

Research in the Degradation and Antifouling Performance of Copolyesters of L-Lactide and ε-Caprolactonen

Block copolyesters of L-lactide and ε-caprolactone were synthesized by melt copolymerization of ε-caprolactone and L-lactide.The degradation performance of copolyesters was investigated by quartz crystal microbalance with dissipation(QCM-D).Diisocyanate terminated copolyesters could obtain via the reaction of copolyesters and diisocyanate.Diisocyanate terminated copolyesters could react with polyol resin to prepare degradable polyurethane which can be used in antifouling coatings.In this paper,we also discussed the degradation products release action and antifouling performance of the copolyesters film.

NOVEL COMPOSITES OF POLY(L-LACTIDE)AND SURFACE MODIFIED BIOACTIVE SiO_2-CaO-P_2O_5 GEL NANOPARTICLES:MECHANICAL AND BIOLOGICAL PROPERTIES

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.

Synthesis and Characterization of Poly(L-lactide-co-ε-caprolactone) Copolymers

A series of random and block poly（ L-lactide-co-e-caprolactone ） （ PCLA ） copolymers whh different composition are prepared using stannous octaoate as catalyst.The effects of the amount of initiator on the intrinsic viscosity have been investigated. The structure of the PCLA copolymers is characterized by means of nuclear magnetic resonance（ NMR ）, Fourier transform infrared spectrum （ FTIR ）, differential scanning calorimetry （ DSC ） and X- ray diffraction （ XRD ） methods. It is shown that the synthesis condition and the composition of copolymers obrious influence on the structure of PCLA copolymers. Hydrolytic degradation of the copolymers in a PBS solution of pH 7.4 at 37.0℃ shows that the copolymers of different composhions degrade at different rates.

Surface-modified Biphasic Calcium Phosphate/Poly (L-lactide) Biocomposite

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.

The copolymerization of L-lactide andε-caprolactone using magnesium octoate as a catalyst

Copolymerizations of L-lactide （L-LA） and ε-caprolactone （ε-CL） were conducted in bulk using magnesium octoate as a catalyst. The reactivity ratios of L-LA and ε-CL were determined to be rL=23 and rc=0.22, respectively. The sequence analyses of the copolymers were performed on ^13C NMR. An increase in the reaction temperature enhances the role of transesterification and the extent of randomness.

Poly (L-lactide-co-e-caprolactone)/Functionalized CNTs Nanocomposite,Thermal and Mechanical Properties

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.

SYNTHESIS,CHARACTERIZATION AND NANOPARTICLE FORMATION OF STAR-SHAPED POLY(L-LACTIDE)WITH SIX ARMS

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...

STABILIZATION, REFORMATION AND MELTING OF POLY(L-LACTIDE) CRYSTALLITES

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.

THE RING-OPENING POLYMERIZATION OF D,L-LACTIDE WITH ONE COMPONENT RARE EARTH CATALYST

(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.

Toughening of Poly (L-lactide) with Branched Multiblock Poly (ε-caprolactone)/poly (D-lactide) Copolymers

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.

Supercritical Fluid Impregnation of Essential Bark Oil in Copolymers of L-Lactide with 7-Membered Cyclic Compounds

In order to develop a novel controlled-release material, we previously attempted to impregnate poly(L-lactide) (poly(L-LA)), poly(L-LA-ran-CL) (CL: ε-caprolactone) or poly(L-LA-ran-TEMC) (TEMC: tetramethylene carbonate) with low boiling point, organic useful compounds using supercritical carbon dioxide (scCO2) as the solvent. In this work, the factors influencing impregnation of poly (L-LA) random copolymers with useful compounds were investigated under scCO2 using the copolymers previously used. The influence of temperature, pressure, and time on the impregnation contents of the useful compounds on the copolymers was evaluated. The polymer used, which is a base of this material, was poly(L-LA-ran-CL), poly(L-LA-ran-TEMC), or poly(L-LA-ran-DXO) (DXO: 1,5-dioxepan-2-one). Statistical random copolymers of L-LA with CL, TEMC, or DXO were synthesized using Sn(oct)2 as a catalyst at 150°C for 24 h without solvent. Preparation of the controlled-release materials was carried out using essential bark oil from Thujopsis dolabrata var. hondae and synthetic L-LA random copolymers as a base material under scCO2. The impregnation experiment, which investigated the influence of pressure, was conducted in the range of 10 to 20 MPa. The influence of temperature on impregnation was carried out at 40°C to 100°C. Impregnation time was varied from 1 to 5 h. The pressure of essential oil impregnated into poly(L-LA) random copolymers was the highest at 14 MPa. In the influence of temperature on impregnation, the amount of essential oil increased with increasing temperature.

Development of Chitosan/Poly(L-Lactide)/Multiwalled Carbon Nanotubes Scaffolds for Bone Tissue Engineering

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.