The Syntheses and Properties of Poly(L- Lactide)

Poly (L-lactide) was prepared by bulk polymerization ofL-lactide at 140°C in the presence of stannous octoate. The polymer products were characterized by number average molecular weight Mn, weight average molecular weight Mw and molecular weight distribution MWD (M w/M n) respectively. The results showed that stannous octoate was a high effective catalyst, and coordinated insertion mechanism of the reaction was proposed.

Biodegradation of Absorbable Hydroxyapatite/Poly-DL-lactide Composites in Different Environment

To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapatite/ poly DL lactide (HA/PDLLA) composites were investigated in vitro and in vivo.HA/PDLLA rods were immersed in phosphate buffered saline,or implanted in muscle and bony tissue for 52 weeks.Scanning electron microscopic and histological studies were done.The degradation rate was the slowest in vitro,slower in muscle tissue and fast in bone.In vitro, the composites degraded heterogeneously and a hollow structure was formed.In bone,the limited clearing capacity leads to the accumulation of oligomeric debris,which contribute totally to the autocatalytic effect.So,the fastest degradation and intense tissue response were seen.In muscle tissue,oligomeric debris migrated into vicinal fibers over a long distance from the original implant cavity and the tissue reactions were,however, quite moderate.For the same size organic/inorganic composite,the environment where it was placed is the major factor in determining its biodegradation process and cellular reaction.In living tissue,factors such as cells,enzymes and mechanical stress have an obvious influence on the biodegradation and biological process at the tissue/implant interface.The biocompatibility of the HA/PDLLA composites is enhanced with the incorporating of the resorbable HA microparticles.

MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF BIODEGRADABLE BLEND OF POLY(β—HYDROXYBUTYRATE)AND POLY(D,L—LACTIDE)—CO—POLY(ETHYLENE GLYCOL)

Studies on the miscibility of PHB/PELA blends showed that PHB and PELA were miscible in amorphous state.The crystallization behavior of PHB in the blend was strongly de- pendent on the addition of PELA component.

MISCIBILITY AND MORPHOLOGICAL STRUCTURE OF BIODEGRADABLE BLEND OF POLY(β—HYDROXYBUTYRATE)AND POLY(D,L—LACTIDE)

The poly(β-hydroxybutyrate)/poly(d,1-lactide)(PHB/PLA)blend was found to be immiscible,the melting point and the phase crystallinity of PHB were independent of the blend composition.Comparing with plain PHB,the blend exhibited the crystallization change and a certain improvement of the mechanical property.

Zinc Complexes of New Chiral Aminophenolate Ligands: Synthesis, Characterization and Reactivity toward Lactide

The syntheses of a library of new chiral aminophenolate bidentate O,N-type ligands HOC6H4(2-R- 4-R′)CH2N(Me)CH(Me)C6H5 [R = R′ = But, 1;R = R′ = Pent, 2;R = But, R′ = Me, 3;R = Me, R′ = But, 4;R = R′ = Me, 5] and tridentate O,N,O-type ligands HOC6H4(2,4-But)CH = NCH(R′′)C6H5 [R′′ = Me, 6;R′′ = CH2OMe, 7] are reported. These ligands were characterized by elemental analysis, nuclear magnetic resonance spectroscopy (1H & 13C), and single crystal X-ray diffraction. These ligands serve as chiral auxiliaries for inorganic chemists to design chiral metal-based complexes for asymmetric catalysis and stereoselective polymerization reactions. Three new heteroleptic zinc complexes based on these ligands have been synthesized in moderate yields via a ligand-exchange transamination reaction between homoleptic [Zn(N(SiMe3)2)2] and one equivalent of corresponding ligands to afford [L3ZnN- (SiMe3)2] (3a), [L4ZnN(SiMe3)2] (4a), and [L7ZnN(SiMe3)2] (7a). Solvent-free polymerization of raclactide at 130°C using these zinc compounds yielded atactic polylactides with Mw 10,000 g/mol and narrow polydispersity of 1.3.

Preparation and Swelling Behavior of L-Lactide Interpenetrating Networks

Novel triblock copolymers of poly (L-lactide)-poly (ethylene glycol)-sebacate-poly (ethylene glycol)-poly (L-lactide) were synthesized by Ring-Opening Polymerization of different ratios of L-lactide with other three pre-prepared poly (ethylene glycol)-sebacate-poly (ethylene glycol) polymers, coded A, B and C which had different poly (ethyleneglycol) chain lengths. The copolymers were characterized by FTIR and 1H NMR spectroscopy, which indicated that the reaction of ROP took place and led to producing nine triblock copolymers having new different lactide chain lengths (n = 10, 25 and 50), AL10, AL25, AL50,BL10, BL25, BL50, CL10, CL25, and CL50. Nine polymer networks were also prepared from copolymers with sodium alginate S1 - S9 and finally mixed with a solution of hydroxyl ethyl cellulose to form SH1 - SH9.

Lightweight,Strong and High Heat-Resistant Poly(lactide acid)Foams via Microcellular Injection Molding with Self-Assembly Nucleating Agent

Poly(lactide acid)(PLA)foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams,such as polystyrene(PS)foams.Nevertheless,PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength.In this study,a high-performance PLA foam with well-defined cell morphology,exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding(MIM)process.Differential scanning calorimetry(DSC)results revealed that the added hydrazine-based nucleating agent(HNA)significantly increased the crystallization temperature and accelerated the crystallization process of PLA.Remarkably,the addition of a 1.5 wt%of HNA led to a significant reduction in PLA’s cell size,from 43.5µm to 2.87µm,and a remarkable increase in cell density,from 1.08×10^(7)cells/cm^(3)to 2.15×10^(10)cells/cm^(3).This enhancement resulted in a final crystallinity of approximately 55.7%for the PLA blend foam,a marked improvement compared to the pure PLA foam.Furthermore,at 1.5 wt%HNA concentration,the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improvements of 136%and 463%,respectively.Additionally,the Vicat softening temperature of PLA blend foam increased significantly to 134.8°C,whereas the pure PLA foam exhibited only about 59.7℃.These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance,which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications.

Chemical upcycling of poly(lactide) plastic waste to lactate ester,lactide and new poly(lactide) under Mg-catalysis condition

Chemical upcycling of end-of-life poly(lactide) plastics to lactide,lactate ester and new poly(lactide)has been achieved by using magnesium bis[bis(trimethylsilyl)amide][Mg(HMDS)_(2)]as promoter.Mg(HMDS)2 showed high efficiency in L-lactide polymerization and poly(lactide) depolymerization.Mg(HMDS)_(2)/Ph_(2) CHOH catalytic system displayed high ring-opening selectivity and the characteristic of immortal polymerization.Taking advantage of transesterification,depolymerizations of end-oflife poly(lactide) plastics to lactate ester (polymer to value-added chemicals) and lactide (polymer to monomer) were achieved with high yields.Besides,a new“depolymerization-repolymerization”strategy was proposed to directly transform poly(lactide) into new poly(lactide).This work provides a theoretical basis for the design of polymerization and depolymerization catalysts and promotes the development of degradable polymers.

Mechanically Robust Polylactide Fibers with Super Heat Resistance via Constructing in situ Nanofibrils

All-PLA fibers with excellent comprehensive performance and recycling convenience are realized efficiently.High molecular weight poly(D-lactide)(HPDLA)is incorporated into poly(L-lactide)(PLLA)matrix to construct in situ nanofibrils structure by taking advantages of the microphase separation between HPDLA and PLLA.The tensile strength of HPDLA/PLLA composite fibers(HDL-8)is enhanced from 2.1 cN/dtex of neat PLLA-8 fibers up to 2.9 cN/dtex.Its boiling water shrinkage(BWS)and shrinkage in hot air(HAS)significantly decrease to 7.8%and 2.8%,respectively.The abundance of in situ nanofibrils creates a grille-like structure that is crucial for both heat and hydrolysis resistance.More strikingly,a hybrid shish-kebab structure induced by the in situ nanofibrils serves as a mechanical reinforcement.This work paves a new way for heat resistance and self-reinforcement modification of PLA materials.

Polymerization of lactide and synthesis of block copolymer catalyzed by copper(Ⅱ) Schiff base complex

In the present investigation, the novel copper Schiff base complex was synthesized and its catalytic activity was evaluated for the ring-opening polymerization （ROP） of lactide and block polymerization of poly（lactide） with po/y（ethylene glycol）methyl ether,

Synthesis and characterization of aminophenolate-ligated rare-earth metal amide complexes and their catalytic activity for lactides polymerization

Amine elimination of Ln[N(SiMe3)2]3(μ-Cl)Li(THF)3 with aminophenol H[ON]{H[ON]=2-(CH2 NC5 H10)-4,6-tBu2-C6 H3OH}in 1:2 molar ratio in THF gave the monometallic rare-earth metal amide complexes[ON]2 LnN(SiMe3)2(Ln=Yb(1),Y(2),Gd(3),Sm(4),Nd(5))in 57%-73%isolated yields.All these complexes were characterized by elemental analysis.The molecular structures of complexes 1-4 were determined by single crystal X-ray diffraction.These complexes are highly active for L-Iactide polymerization to give high molecular weight polymers with unimodal molecular weight distributions.In addition,these complexes can also initiate rac-lactide polymerization with high activity to afford heterotactic-rich polylactides.

Effect of Plasticizer Poly(Ethylene Glycol)on the Crystallization Properties of Stereocomplex-Type Poly(Lactide Acid)

The effects of the plasticizer poly（ethylene glycol） （PEG） on crystallization properties of equimolar poly（L-lactide） （PLLA）/poly（D-lactide） （PDLA） blends were investigated. Forma- tion of the stereocomplex-type poly（lactide acid） （sc-PLA） crystallites was confirmed by Wide-angle X-ray diffraction （WAXD） and differential scanning calorimetry （DSC） analyses. Sc-PLA crystallites without any homochiral poly（lactide acid） （hc-PLA） formed, as the result of the incorporation of the plasticizer PEG （more than or equal to 10%（wt）） at a processing temperature （240 ℃）. More-over, when the Mw of PEG reached 1 000 g · mol^-1, the crystal- lizability of stereocomplex crystallites was the best. Isothermal crystallization kinetics further revealed that PEG could accelerate the crystallization rate of sc-PLA, with the optimum crystallization kinetic parameters being obtained at 10% （wt） PEG. Several crys- tallization kinetics equations were applied to describe the effect of PEG on the crystallization behavior of sc-PLA. The influence of PEG on the spherocrystal morphologies of sc-PLA was also inves- tigated using polarized optical microscopy.

Salen-iron Complexes: Synthesis, Characterization and Their Reactivity with Lactide

Schiff-base metal complexes as efficient catalysts are widely used in ring-opening polymerization of cycle esters. The salen Fe complexes were formed with their excellent biocompatibility and less toxicity. A series of salen Fe complexes were designed in this work in order to study the activity and control of polymerization of lactide. The salen Fe complexes＇ activities changed with the ligands configuration and substituent groups.

CRYSTALLIZATION BEHAVIOR OF POLYLACTIDE ON HIGHLY ORIENTED POLYETHYLENE THIN FILMS

The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130℃ were investigated by means of optical microscopy, AFM and X-ray diffraction. The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably, which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition. The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals. It is further demonstrated that except for the different crystal orientation, the PE does not influence the crystalline modification and crystallinity of the PLA.

Enolic Schiff Base Zinc Amide Complexes： Highly Active Catalysts for Ring-Opening Polymerization of Lactide and ε-Caprolactone

A series of zinc silylamido complexes based upon NNO tridentate enolic Schiff base framework have been synthesized and characterized. These complexes were tested for the ring opening polymerization of lactide and e-caprolactone, exhibiting notably high activity at ambient temperature, The influence of imine bridge length and substituents of diketone over the course of polymerization was investigated in details. Remarkably, 4a was confirmed to be a rare example of exceedingly active and robust zinc catalysts, achieving major transformation of lactide under extremely low loading （0.025 mol%） within 18 rain. The influence of various monomers as well as the polymerization mechanism have also been discussed.

Anilido-imine Zinc Complexes： Efficient Catalysts for Ring-opening Polymerization ofL-Lactide

A series of anilido-imine zinc complexes ortho-C6H4（CH：NAr）（NAr）ZnEt[Ar=2,6-Me2C6H3（2a）; Ar=2,6-Et2C6H3（2b）] was synthesized, characterized and used as catalysts for the ring-opening polymerization of L-lactide in the presence of benzyl alcohol. The effects of the structures of catalysts and reaction conditions on the reactivity were investigated. The polymerization of L-lactide initiated by each of these complexes was found to take place with a controlled manner.

Synthesis and Hydrophilic Performance of Poly(Lactic Acid)-Poly(Ethylene Glycol) Block Copolymers

Lactide was synthesized using lactic acid and stannous octoate as raw material and catalyst, respectively. Poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) was prepared by lactide and poly (ethylene glycol) (PEG) via ring-opening polymerization. The most appropriate technological conditions of synthesis of lactide were researched in the paper. The copolymers were measured by Infrared spectroscopy (IR) and 1H nuclear magnetic resonance (1H NMR). The results proved that the lactide and PLA-PEG were synthesized successfully. Hydrophilic performance of the copolymer was measured by a water contact angle tester after prepared into a flat membrane. The water contact angle changed from 81.5? to 71.6?, which proved that the hydrophily of PLA-PEG was better than PLA.

Synthesis of L-Aspartic Acid and Lactone Copolymers

Biodegradable poly(alc-alt-Asp) was synthesized by ring-opening polymerization of the monomer 3-(S)-[(benzyloxycarbonyl)methyl] -morpholine-2, 5-dione and subsequent catalytic hydrogenation. Copolymers of the monomer with glycolide, D,L-lactide and L-lactide were also prepared.

Stride Strategy to Enable a Quasi-ergodic Search of Reaction Pathways Demonstrated by Ring-opening Polymerization of Cyclic Esters

Coordination-insertion ring-opening polymerization(ROP)of cyclic esters is an industrial way to synthesize polyesters,which are widely applied in biomedical and environment-benign fields.However,the rate-determining transition state(TS)identified by the conventional reaction pathways(pathway A and pathway B)presented in the literature did not well describe the structure-reactivity relationship.The misidentification of the rate-determining TS might arise from the less ergodicity in the search of reaction pathways.Herein,we suggested a stride strategy based on the insight that even a partial double bond is rotatable at the catalysis temperature.As a result,we revealed a new reaction pathway,pathway C with a torsion transition state TSC2,by density functional theory(DFT).We also carried out kinetic experiments of ROP of D-lactide(D-LA),L-lactide(L-LA),ε-caprolactone(CL),andδ-valerolactone(VL),using poly(ethylene glycol)as the initiator and stannous octoate as the catalyst.The excellent linearity between the calculated free energy barriers and logarithms of the experimental kinetic constants of the two kinds of lactide and lactone monomers,was established,validating the quasi-ergodic search of reaction pathways and the scaling predicted by transition state theory.The linearity was highly predictive for the other lactide and lactone monomers,demonstrated by glycolide(GA)and trimethylene urethane(TU).

The Stereocomplex Formation and Phase Separation of PLLA/PDLA Blends with Different Optical Purities and Molecular Weights

In this study, the poly（L-lactide）/poly（D-lactide） （PLLA/PDLA） blends with different optical purities of PLLA and various molecular weights of PDLA are prepared by solution mixing, and the stereocomplex formation and phase separation behaviors of these blends are investigated. Results reveal that optical purity and molecular weight do not vary the crystal structure of PLA stereocomplex （sc） and homochiral crystallites （hc）. As the optical purity increasing in the blends, the melting temperature of sc （Tsc） and the content of sc （AHsc） increased, while the melting temperature of hc （Thin） hardly changes, although the content ofhc （AHhm） decreased gradually. The Tsc and AHsc are also enhanced as the molecular weight of PDLA reduces, and the AHhm reduces rapidly even though the Thin does not vary apparently. With lower optical purities of PLLA and higher molecular weights of PDLA, three types of crystals form in the blends, i.e., PLA sc, PLLA hc and PDLA hc. As molecular weight decreases and optical purity enhances, the crystal phase decreases to two （sc and PDLA hc）, and one （sc） finally. This investigation indicates that the phase separation behavior between PLLA and PDLA in the PLLA/PDLA blends not only depends on molecular weights, but also relies on the optical purities of polymers.