New optically active poly(amide-imide)s from N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)bis-l-phenyl alanine and aromatic diamines: synthesis and characterization

In this work, new optically active poly(amide-imide)s (PAIs) having bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic diimide groups were prepared by the reaction of N,N′-(bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic)bis-l-phenyl alanine (4) as a diacid monomer with various readily available aromatic diamines. Triphenyl phosphite (TPP)/pyridine (Py) in the presence of calcium chloride (CaCl₂) and N-methyl-2-pyrrolidone (NMP) were successfully applied for direct polycondensation. The diacid (4) was synthesized by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (1) with l-phenyl alanine (2) in acetic acid solution. The resulting new polymers were obtained in good yields, inherent viscosities ranging between 0.29 and 0.48 dLg⁻¹ and were characterized with elemental analysis, FT-IR, ¹H-NMR spectroscopy, specific rotation, and thermal gravimetric analysis (TGA, DTG) techniques. Thermogravimetric analysis indicated that the residual weight percent of polymers at 600 °C was between 53.80 and 56.21%, which show these are moderately thermally stable. In addition because of existence of chiral center and optical activity of these polymers, they have potential to be used as chiral stationary phase in chromatography technique for the separation of racemic mixtures.     

New photosensitive and optically active organo-soluble poly(amide–imide)s from N,N′-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids and 1,5-bis(4-aminophenyl)penta-1,4-dien-3-one: synthesis and characterization

A new series of N,N′-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids 3a–g were synthesized by the condensation reaction of bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride 1 with two equimolars of various amino acids such as L-alanine 2a, L-valine 2b, L-leucine 2c, L-isoleucine 2d, L-phenyl alanine 2e, L-2-aminobutyric acid 2f and L-histidine 2g in an acetic acid solution. Also 1,5-bis(4-aminophenyl)penta-1,4-dien-3-one 7 was synthesized by using a two-step reaction. At first 1,5-bis(4-nitrophenyl)penta-1,4-dien-3-one 6 was prepared from the reaction of two equimolars 4-nitrobenzaldehyde 5 and one equimolar acetone 4 in ethanol and NaHCO₃ and dinitro compound 6 was reduced by using Na₂S. Then seven new photosensitive and optically active organo-soluble poly(amide–imide)s (PAIs) 8a–g with good inherent viscosities were synthesized from the direct polycondensation reaction of new N,N′-(bicyclo[2,2,2]oct-7-ene-tetracarboxylic)-bis-L-amino acids 3a–g with 1,5-bis(4-aminophenyl)penta-1,4-dien-3-one 7 by two different methods such as direct polycondensation in a medium consisting of N-methyl-2-pyrrolidone (NMP)/triphenyl phosphite (TPP)/calcium chloride (CaCl₂)/pyridine (py) and direct polycondensation in a tosyl chloride (TsCl)/pyridine (py)/N,N-dimethylformamide (DMF) system. The polymerization reactions produced a series of photosensitive and optically active organo-soluble PAIs with high yield and good inherent viscosity. The resulted polymers were fully characterized by means of FTIR and ¹H-NMR spectroscopy, elemental analyses, inherent viscosity, specific rotation, solubility tests, UV-vis spectroscopy, differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), and derivative of thermaogravimetric (DTG). These macromolecules exhibited maximum UV-vis absorption at around 370 and 265 nm in a DMF solution.     

Synthesis and properties of polyesterimides containing a bicyclo-octene ring

New polyesterimides containing a bicyclo-octene ring were synthesized by the polycondensation reaction of N,N′-dicarboxymethyl(bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid diimide)dimethylester and N,N′-dicarboxyphenyl(bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid diimide)dimethylester with various aliphatic diols. These polymers thus obtained are soluble in m-cresol, dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethylsulfoxide (DMSO) except those from ethylene glycol. The polymers showed thermal stability above 350°C.     

<Emphasis Type="SmallCaps">l</Emphasis>-Aspartic acid incorporated optically active poly(amide-imide)s: synthesis and characterization

N-trimelliticimido-l-aspartic acid (1) was prepared from the reaction of trimellitic anhydride with l-aspartic acid in a mixture of glacial acetic acid and pyridine solution (3/2 ratio) under refluxing conditions. The solution polycondensation of the corresponding activated monomer with eight aromatic diamines were carried out in DMAc. The resulting poly(amide-imide)s were obtained in quantitative yields, showed admirable inherent viscosities (0.20–0.36 dl g⁻¹), good optical activity (+7.32o to +15.24o), and were readily soluble in polar aprotic solvents. They start to decompose (T _10%) above 170 °C and display glass-transition temperatures at 120–237 °C. All of the above polymers were fully characterized by UV, FT–IR, and ¹HNMR spectroscopy, elemental analysis, thermogravimetric analyses, DSC, inherent viscosity measurement, and specific rotation.     

Synthesis and characterization of new optically active and photolable poly (amide-imide)s from N,N ′-(3,3′,4,4′-benzophenonetetracarboxylic)-3,3′,4,4′-diimido-di-L-methionine and different diamines

Summary N,N^′-(3,3^′,4,4^′-benzophenonetetracarboxylic)-3,3^′,4,4^′-diimido-di-L-methionine (3) was prepared from the reaction of 3,3^′,4,4^′-benzophenonetetracarboxylic-3,3^′,4,4^′-dianhydride (1) with L-methionine (2) in a solution of (glacial acetic acid/pyridine) at refluxing temperature. The phosphorylation polycondensation of the diimide-diacid monomer (3) with 1,3-phenylenediamine (4a), 1,4-phenylenediamine (4b), 2,6-diaminopyridine (4c), 3,5-diaminopyridine (4d), 4,4^′-diaminobiphenyl (4e) and 4,4^′-diaminodiphenylsulfone (4f) was carried out in N-methyl-2-pyrolidone (NMP). The resulting poly (amide-imide)s showed admirable moderate inherent viscosities (0.23–0.48 dl g^-1), good thermal stability and improved optical activity. All of the above compounds were fully characterized by IR spectroscopy, elemental analysis and specific rotation. Some structural characterization and physical properties of these new poly (amide-imide)s are presented.     

Nanoscale blending of aliphatic and aromatic polyimides: A clue for forming semi-molecular composites and in-situ generation of copolyimide fractions

Summary Nanoscale blending of aromatic and aliphatic polyimides has been attempted by employing corresponding poly(amic acid) precursors in order to elucidate clues for achieving a semi-molecular composite film. Pyromellitic dianhydride (PMDA) and 4,4’-oxydianiline (ODA) were used to make the precursor polymer of aromatic polyimide (PMDA-ODA PI) as a semi-rigid rod-like component, whilst bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BOCA) and 4,4’-methylenebis(cyclohexylamine) (MCA) were used to prepare the precursor of aliphatic polyimide (BOCA-MCA PI) as a flexible coil-like component. The weight ratio of aromatic to aliphatic polyimides was varied from 100:0: to 0:100 by 10 wt % gap for monitoring the critical composition upon nanostructure changes. The micro/nanostructure of composite films was characterized by using small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD), while the evolution and thermal property of semi-molecular composites were studied by using FT-IR spectroscopy and dynamic mechanical thermal analysis (DMTA). The result showed that the composite films exhibited a single glass transition behavior, which is ascribed to the molecular level mixing, in the presence of copolyimide fractions.     

Structural Diversity of Mercury(II) Halide Complexes Containing Bis-pyridyl-bis-amide with Bulky and Angular Backbones: Ligand Effect and Metal Sensing

Hg(II) halide complexes [HgCl₂] 2L¹ [L¹ = N,N’-bis(3-pyridyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide), 1, [HgBr₂(L¹)]_n, 2, [HgI₂(L¹)], 3, [Hg₂X₄(L²)₂] [X = Cl, 4, Br, 5, and I, 6; L² = N,N’-bis(4-pyridylmethyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide] and {[HgX₂(L³)]⋅H₂O}_n [X = Cl, 7, Br, 8 and I, 9; L³ = 4,4′-oxybis(N-(pyridine-3-yl)benzamide)] are reported and structurally characterized using single-crystal X-ray diffraction analyses. The linear HgCl₂ units of complex 1 are interlinked by the L¹ ligands through Hg---N and Hg---O interactions, resulting in 1D supramolecular chains. Complex 2 shows 1D zigzag chains interlinked through the Br---Br interactions to form 1D looped supramolecular chains, while the mononuclear [HgI₂L²] molecules of 3 are interlinked through Hg---O and I---I interactions, forming 2D supramolecular layers. Complexes 4–6 are isomorphous dinuclear metallocycles, and 7–9 form isomorphous 1D zigzag chains. The roles of the ligand type and the halide anion in determining the structural diversity of 1–9 is discussed and the luminescent properties of 7–9 evaluated. Complexes 7–9 manifest stability in aqueous environments. Moreover, complexes 7 and 8 show good sensing towards Fe³⁺ ions with low detection limits and good reusability up to five cycles, revealing that the Hg-X---Fe³⁺ (X = Cl and Br) interaction may have an important role in determining the quenching effect of 7 and 8.     

Biocatalytic synthesis of some chiral drug intermediates by oxidoreductases

Chiral intermediates were prepared by biocatalytic processes with oxidoreductases for the chemical synthesis of some pharmaceutical drug candidates. These include: (i) the microbial reduction of 1-(4-fluorophenyl)-4-[4-(5-fluoro-2-pyrimidinyl)-1-piperazinyl]-1-butanone (1) to R-(+)-1-(4-fluorophenyl)-4-[4-(5-fluoro-2-pyrimidinyl)-1-piperazinyl]-1-butanol (2) [R-(+)-BMY 14802], an antipsychotic agent; (ii) the reduction of N-4-(1-oxo-2-chloroacetyl ethyl) phenyl methane sulfonamide (3) to the corresponding chiral alcohol (4), an intermediate for d-(+)-N-4-{1-hydroxy-2-[(-methylethyl)amino]ethyl}phenyl methanesulfonamide [d-(+) sotalol], a β-blocker with class III antiarrhythmic properties; (iii) biotransformation of Nɛ-carbobenzoxy (CBZ)-l-lysine (7) to Nɛ-CBZ-l-oxylysine (5), an intermediate needed for synthesis of (S)-1-[6-amino-2-{[hydroxy(4-phenylbutyl)phosphinyl]oxy}1-oxohexyl]-l-proline (ceronapril), a new angiotensin converting enzyme inhibitor (6) and (iv) enzymatic synthesis of l-β-hydroxyvaline (9) from α-keto-β-hydroxyisovalerate (16). l-β-Hydroxyvaline (9) is a key chiral intermediate needed for the synthesis of S-(Z)-{[1-(2-amino-4-thiazolyl)-2-{[2,2-dimethyl-4-oxo-1-(sulfooxy)-3-azetidinyl] amino}-2-oxoethylidene]amino}oxyacetic acid (tigemonam) (10), an orally active monobactam.     

A Feeding Stimulant for Manduca sexta from Solanum surattenses

The acceptance of Solanum surattenses as a host plant for the larvae of Manduca sexta was explained by the presence of feeding stimulants in foliage. Bioassay-guided fractionation of plant extracts resulted in the isolation of a highly active compound (1), which was identified as a furostan derivative {26-O-β-d-glucopyranosyl-(25R)-furosta-5-ene-3-β-yl-O-α-l-rhamnopyranosyl-(1″-2′)-O-α-l-rhamnopyranosyl-(1′″-3″)-O-β-d-glucopyranoside}. This compound has the same steroidal core substructure as that in a stimulant (indioside D) previously identified from potato foliage. However, the sugar substituents attached to the core are different.     

Direct Polyamidation of N,N’-(4,4’-Hexafluoroisopropy-lidendiphthaloyl)-bis-L-isoleucine with Different Aromatic Diamines via Vilsmeier Adduct Derived from Tosyl Chloride and N,N-Dimethylformamide

Summary Various approaches have been carried out in the synthesis of poly(amide-imide)s. A well-developed solution polycondensation method has been used to prepare such copolymers either from a dianhydride containing a preformed amide group with a diamine or from a dicarboxylic acid containing a preformed imide ring with a diamine. Direct polycondensations of carboxylic acids and aromatic diamines can be a more useful technique for synthesis of poly(amide-imide)s PAIs. In this work, direct polymerization reaction of N,N’-(4,4’-hexafluoroisopropylidendiphthaloyl)-bis-L-isoleucine with several aromatic diamines such as 4,4’-diaminodiphenylsulphone (4a), 4,4’-diaminodiphenylmethane (4b), 4,4’-diaminodiphenylether (4c), 1,4-phenylenediamine (4d), 4,4’-diaminobiphenyl (4e), 1,3-phenylenediamine (4f), 2,4-diaminotoluene (4g), was performed in the presence of tosyl chloride (TsCl)/dimethylformamide (DMF)/pyridine (Py) as a condensing agent. The resulting PAIs were obtained in high yield and inherent viscosity. Some structural characterization and physical properties of these polymers have been studied and will be reported.     

Synthesis and properties of poly(amide-imide)s based on 1,5-bis(4-trimellitimido)naphthalene

1,5-Bis(4-trimellitimido)naphthalene (II) was prepared by the condensation reaction of 1,5-naphthalenediamine and trimellitic anhydride. A series of aromatic poly(amide-imide)s (IV _a–o) was synthesized by the direct polycondensation of the diimide-diacid (II) and various aromatic diamines (III _a–o). The reaction utilized triphenyl phosphite and pyridine as condensing agents in the presence of calcium chloride in N-methyl-2-pyrrolidone (NMP). The inherent viscosities of the resulting poly(amide-imide)s were in the range of 0.55∼1.39 dL/g. These polymers were generally soluble in polar solvents, such as N,N-dimethylacetamide (DMAc), NMP, N,N-dimethylformamide (DMF). Flexible and tough poly(amide-imide) films were obtained by casting from a DMAc solution and had tensile strengths of 90∼145 MPa, elongations to break of 5∼13 %, and initial moduli of 2.29∼3.73 GPa. The glass transition temperatures of some poly(amide-imide)s were recorded in the range of 206∼218 °C, and most of the polymers did not show discernible glass transition on their DSC traces. The 10% weight loss temperatures were above 522 °C in nitrogen and above 474 °C in air atmosphere.     

New cerebrosides from the basidiomycete <Emphasis Type="Italic">Cortinarius tenuipes</Emphasis>

Five cerebrosides (1–5), including three new ones named cortenuamide A (1), cortenuamide B (2), and cortenuamide C (3), were isolated from the fruiting bodies of the basid-iomycete Cortinarius tenuipes. The structures of those compounds were elucidated as (4E,8E)-N-d-2′-hydroxytetracosanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (1), (4E,8E)-N-d-2′-hydroxytricosanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8 sphingadienine (2), (4E, 8E)-N-d-2′-hydroxydocosanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (3), (4E, 8E)-N-d-2′-hydroxyoctadecanoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (4), and (4E, 8E)-N-d-2′-hydroxypalmitoyl-1-O-β-d-glycopyranosyl-9-methyl-4,8-sphingadienine (5) by spectral and chemical methods.     

Synthesis and characterization of heterocyclic,and optically active poly(amide-imide)s by phosphorylation polycondensation

Summary N,N′-Pyromelliticdiimido-di-L-methionine (1), N,N′-Pyromelliticdiimido-di-L-alanine (2), N,N′-Pyromelliticdiimido-di-L-phenylalanine (3) , and N,N′-Pyromelliticdiimido-di-L-leucine (4) were prepared from the reaction of Pyromellitic dianhydride with corresponding L-amino acids in a mixture of glacial acetic acid and pyridine solution (3/2 ratio) under refluxing conditions. The phosphorylation polycondensation of the corresponding diimide-diacid monomers with 4-phenyl-2,6-bis(4-aminophenyl) pyridine (6) or 4-(p-methylthiophenyl)-2,6-bis(4-aminophenyl) pyridine (8) were carried out in N-methyl-2-pyrolidone (NMP). The resulting poly (amide-imide)s were obtained in quantitative yields, showed admirable inherent viscosities (0.20-0.97 dl g^-1), were soluble in polar aprotic solvents, showed good thermal stability and high optical purity. The synthetic compounds were characterized by IR, MS, ¹H NMR and ¹³C NMR spectroscopy, elemental analysis and specific rotation.     

A new ceramide from the basidiomycete Russula cyanoxantha

A new phytosphingosine-type ceramide (1) was isolated along with nine other compounds—5α,8α-epidioxy-(22E,24R)-ergosta-6,22-dien-3β-ol, 5α,8α-epidioxy-(24S)-ergosta-6-en-3β-ol, (24S)-ergosta-7-ene-3β,5α,6β-triol,(22E,24R)-ergosta-7, 22-dien-3β,5α,6β-triol, inosine, adenine, l-pyroglutamic acid, fumaric acid, and d-allitol from the ethanol and chloroform/methanol extract of the fruiting bodies of the basidiomycete Russula cyanoxanotha (Schaeff.) Fr. The structure of (1) was established as (2S,3S,4R,2′R)-2-(2′-hydroxytetracosanoylamino) octadecane-1,3,4-triol by means of spectroscopic and chemical methods.     

Thermostable soluble aromatic poly(amide-imide)s having hexafluoroisopropylidene and ether links in the main chain

An imide-containing dicarboxylic acid, 2,2-bis[4-(4-trimellitimidophenoxy)phenyl]-hexafluoropropane (I), was prepared by the condensation of 2,2-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane and trimellitic anhydride. A series of new hexafluoroisopropylidene-containing poly(amide-imide)s having inherent viscosities of 0.64–1.44 dL/g were prepared by the direct polycondensation of diimide-diacid I with various long-chain aromatic diamines using triphenyl phosphite and pyridine as condensing agents in N-methyl-2-pyrrolidone in the presence of calcium chloride. Most of the resulting poly(amide-imide)s were noncrystalline and showed good solubility in polar organic solvents. Almost all polymers afforded transparent, flexible, and tough films. The 10 % weight loss temperatures of these polymers were all above 499 °C, and the glass transition temperatures were in the range of 203–277 °C.     

Copolyimides with trifluoromethyl or methoxy substituents. NMR characterization

In the first stage, a series of aromatic diamine compounds such as 2-methoxy-5,4′-diaminodiphenyl ether (ODAOMe) and 2-trifluomethyl-4,4′-diaminodiphenyl ether (ODACF₃) were synthesized. These aromatic diamines and 4,4′-diaminodiphenyl ether (ODA) were then used to prepare copolyimides with 4,4′-oxydiphthalic anhydride (ODPA) and bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA). Both chemical composition and the arrangements of repetitive units were characterized by ¹H and ¹⁹F NMR. It was shown that solubility and thermal stability are related to the BCDA fraction in the copolymers and to the chemical structure of the diamine.     

Synthesis and gas permeability of poly(<Emphasis Type="Italic">p</Emphasis>-phenyleneethynylene)s having bulky alkoxy or alkyl groups

Dipropynylbenzene with branched alkoxy and alkyl groups [CH₃C≡CRC₆H₂RC≡CCH₃, R = 2-methylpropoxy (1a), 3-methylbutoxy (1b), 4-methylpentoxy (1c), cyclohexylmethoxy (1d), 2-ethylhexoxy (1e), 2-octoxy (1f), 2-ethylhexyl (1g), and 2-octyl (1h)] were polymerized with Mo(CO)₆ in the presence of 4-(trifluoromethyl)phenyl to afford poly(2,5-di(alkoxy or alkyl)-p-phenyleneethynylene)s (2a–h). Polymer 2a was insoluble in any solvents, but the other polymers (2b–h) were soluble in common organic solvents. The polymers with relatively long side chains (2e–h) had high molecular weight over 1.6 × 10⁴ and gave free-standing membranes by solution-casting method. The densities of membranes of 2e–h were 0.914–0.998, and their fractional-free volume values were relatively large (0.094–0.158). The oxygen permeability coefficients of membranes of 2e–h were 18.4, 12.7, 4.85, and 19.3 barrers, respectively. It was found that poly(p-phenyleneethynylene) with 2-octyl side groups, which have the branch at the nearest position from main chain, exhibited the highest gas permeability.     

Synthesis and characterization of biodegradable poly(ε-caprolactone)/poly(γ-benzyl <Emphasis Type="SmallCaps">l</Emphasis>-glutamate) block copolymer

A biodegradable poly(ε-caprolactone)/poly(γ-benzyl l-glutamate) (PCL-b-PBLG) block copolymer was synthesized by ring-opening polymerization of N-carboxy-γ-benzyl l-glutamate anhydride (BLG-NCA) with amine-terminated poly(ε-caprolactone) (PCL-NH₂) as a macroinitiator. The PCL-NH₂ was prepared by deprotection of a PCL-CH₂CH₂NHBoc, which was obtained by ring-opening polymerization of ε-caprolactone (ε-CL) initiated by Boc-aminoethanol (HOCH₂CH₂NHBoc) using stannous octanoate as catalyst under microwave irradiation. The structures of the block copolymers were determined by IR, ¹H NMR, and GPC measurements. The results prove that BLG-NCA can be initiated by PCL-NH₂ to produce PCL-b-PBLG block copolymers.     

Synthesis and properties of aromatic polyimides based on ether-sulfone-diamines

Two diamine monomers, 4,4′-[sulfonylbis(1,4-phenyleneoxy)]dianiline (III _a ) and 4,4′-[sulfonylbis(2,6-dimethyl-l,4-phenyleneoxy)]dianiline (III _b ), were prepared by an aromatic nucleophilic substitution of 4,4′-sulfonyldiphenol (I _a ) and 4,4′-sulfonylbis(2,6-dimethylphenol) (I _b ) with p-chloronitrobenzene in the presence of potassium carbonate, followed by hydrazine catalytic reduction of the intermediate dinitro compounds. The diamines III _a and III _b were used as monomers with various aromatic tetracarboxylic dianhydrides (IV _a–f ) to synthesize polyimides. The polymerization was conducted in two steps via the formation of a poly(amic acid) precursor followed by thermal cyclodehydration. The poly(amic acid)s had inherent viscosities above 0.87 and up to 2.56 dL/g. Most poly(amic acid)s could be coated and thermodehydrated into flexible and transparent polyimide films. The polyimides derived from the dianhydrides containing-O-and-SO₂-or-C(CF₃)₂-bridging groups between the phthalic anhydride units were soluble in some organic solvents such as N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF). The glass transition temperatures (T_g) of the polyimides were in the range from 254 to 300 °C. The methyl-substituted polyimides exhibited slightly higher solubility and higher T_g compared to the corresponding unsubstituted polyimides. Thermogravimetric analysis (TG) showed that the polyimides containing methyl substitutents started to lose weight around 450 °C and the unsubstituted ones started to lose weight around 550 °C.     

Preparation and thermo-oxidative degradation of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)/poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)-grafted SiO<Subscript>2</Subscript> nanocomposites

Poly(l-lactic acid)/poly(l-lactic acid)-grafted SiO₂ nanocomposites were prepared by in situ melt polycondensation, in which “free” poly(l-lactic acid) and poly(l-lactic acid)-grafted SiO₂ nanoparticles were formed simultaneously. The maximum values of grafting ratio and grafting efficiency of poly(l-lactic acid) were up to 37.67% and 26.60%, respectively. In the polycondensation system, SiO₂ content was a critical parameter of getting nanocomposites with uniformly dispersed SiO₂ nanoparticles. At lower SiO₂ content, Mn of grafted poly(l-lactic acid) was close to that of “free” poly(l-lactic acid), and poly(l-lactic acid)-grafted SiO₂ nanoparticles could be well dispersed in poly(l-lactic acid) matrix. While at higher SiO₂ content, Mn of “free” poly(l-lactic acid) and grafted poly(l-lactic acid) decreased seriously, especially GPC curves of “free” poly(l-lactic acid) exhibited two peaks due to the aggregation of SiO₂ nanoparticles during the polycondensation process. The grafting ratio and SiO₂ content exhibited a clear effect on the thermo-oxidative degradation of nanocomposites. The existence of poly(l-lactic acid)-grafted SiO₂ nanoparticles dramatically improved the thermo-oxidative stability of poly(l-lactic acid). Compared with that of pure poly(l-lactic acid), T _g, T _c, and T _m of nanocomposites varied slightly.