<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 of poly(ethylene adipate-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) copolymers via ring opening polymerization

Poly(ethylene adipate-co-l-lactic acid) (PLEA) copolymers were prepared via ring opening polymerization from l-lactide and hydroxyl terminated poly(ethylene adipate) prepolymer as starting materials. The composition and microstructure of the PLEA copolymers were characterized by nuclear magnetic resonance (¹H NMR) spectra. Results confirmed the incorporation of lactic acid segments into the chain of PLEA copolymers as well as the existence of ester exchange reaction. The thermal behaviors and thermal stability of the resultant PLEA copolymers were evaluated by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA), respectively; and the crystal structure was confirmed by using wide-angle X-ray diffraction (WAXD). Results showed that those properties of the PLEA copolymers showed high dependence on the composition of the copolymers.     

Changes in the crystallinity and mechanical properties of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)/poly(butylene succinate-<Emphasis Type="Italic">co</Emphasis>-<Emphasis Type="SmallCaps">l</Emphasis>-lactate) blend with annealing process

Biodegradable polymer blends of poly(l-lactic acid) (PLLA) and poly(butylene succinate-co-l-lactate) (PBSL) at various blending ratios are prepared. The blending of PLLA with PBSL results in an increase in the ductility and thermal stability of the blend. However, flexural strength and modulus, as well as loss modulus, decrease with an increase in PBSL content. Annealing is employed to increase blend crystallinity and subsequently improve the mechanical properties of the PLLA/PBSL blend. The influences of annealing time on the crystal modification, thermal properties, and mechanical properties of the PLLA/PBSL blend are investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and three-point bending test, respectively. Crystalline peaks are found in the XRD patterns of all annealed samples. DSC analysis reveals that the degree of crystallinity is enhanced with an increase in annealing time. The flexural modulus also increases with annealing time due to the change in crystalline phases. However, longer periods of annealing, especially over 20 h, result in thermal degradation and subsequently reduce the modulus value of the PLLA/PBSL blend.     

Thermal and phase-separation behavior of injection-molded poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)/poly(<Emphasis Type="SmallCaps">d</Emphasis>-lactic acid) blends with moderate optical purity

l-Lactide-rich poly(l-lactide) (LR-PLLA)/d-lactide-rich poly(d-lactide) (DR-PDLA) blends with moderate optical purity were prepared by conventional extrusion and followed by injection-molding process in this study. Thermal properties, crystalline structure, spherulite morphology, melt degradability, and thermal mechanical property were investigated by means of DSC, WAXD, POM, TG, and DMA. In comparison with LR-PLLA/DR-PDLA blends with higher optical purity, stereocomplex with less perfect structure was partially formed from the LR-PLLA/DR-PDLA blends with various compositions and showed lower melting temperature. Surprisingly, double melting peaks have appeared in blends with 40 or 50 wt% DR-PDLA. Annealing at higher temperature for blends with 50 wt% DR-PDLA resulted in three melting peaks. It is assumed that the optical purity would play a critical role, thus, producing limited amount of stereocomplex with less imperfect structure. Annealing would also induce the micro-phase separation behavior in LR-PLLA/DR-PDLA blends and significantly influence the thermal and degradable properties of blends.     

<Emphasis Type="SmallCaps">l</Emphasis>-DOPA Increases Lignification Associated with <Emphasis Type="BoldItalic">Glycine max</Emphasis> Root Growth-Inhibition

l-3,4-dihydroxyphenylalanine (l-DOPA), an allelochemical exuded from the roots of velvet bean [Mucuna pruriens (L.) DC. var. utilis], presents a highly inhibitory action to plant growth. The effects of l-DOPA on phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and peroxidase (POD, EC 1.11.1.7) activities, and phenolic compound and lignin content in soybean [Glycine max (L.) Merr.] roots were investigated to determine the possible phytotoxic mechanism. Three-day-old seedlings were cultivated in half-strength Hoagland nutrient solution (pH 6.0), without or with 0.1 to 1.0 mM l-DOPA in a growth chamber (25°C, 12-hr light to 12-hr darkness photoperiod, irradiance of 280 μmol m⁻² s⁻¹) for 24 hr. In general, the length, fresh weight, and dry weight of the roots decreased, whereas PAL and POD activities and phenolic compound and lignin content increased after l-DOPA treatments. Results showed the susceptibility of soybean to l-DOPA and reinforce the role of this nonprotein amino acid as a strong allelochemical. The present findings also suggest that l-DOPA-induced inhibition in soybean roots may be because of a cell wall stiffening process related to the formation of cross-linking between cell wall polymers linked to lignin production.     

Poly(imide-amide)s and poly(imide-esters)s based on silarylene units containing (<Emphasis Type="SmallCaps">l</Emphasis>)-alanine moiety: synthesis and characterization

Optically active poly(imide-amide)s (PIAs) and poly(imide-ester)s (PIEs) containing two silicon atoms in the main chain and l-alanine as chiral residue, were synthesized. The former were prepared by direct polycondensation between two dicarboxilic acids and bis(4-aminophenyl)dipenylsilane according to the triphenyl phosphate method. PIEs were synthesized with bis(4-hydroxyphenyl)dimethyl o ethylmethylsilane, according to the tosyl chloride method. Monomers and polymers were characterized by IR and ¹H, ¹³C, and ²⁹Si NMR spectroscopy and elemental analysis, and the results were in agreement with the proposed structures. PIAs and PIEs showed low values of η_inh, indicative of low molecular weight species, probably of oligomeric nature. Polymers were soluble in polar aprotic solvents and also in common solvents such as CH₂Cl₂, CHCl₃, and acetone, due to the effect of both, the polarity of the Si–C bond and the presence of an aliphatic residue provided by the l-alanine amino acid. The glass transition temperatures (T _g) of the PIAs were higher than those obtained for PIEs, due to the higher flexibility of the ester group. The thermal decomposition temperatures (TDT) were lower than 400 °C and dependent of the polymer structure.     

One-Pot Green Synthesis and Bioapplication of<Emphasis Type="SmallCaps">l</Emphasis>-Arginine-Capped Superparamagnetic Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles

Water-soluble l-arginine-capped Fe₃O₄ nanoparticles were synthesized using a one-pot and green method. Nontoxic, renewable and inexpensive reagents including FeCl₃, l-arginine, glycerol and water were chosen as raw materials. Fe₃O₄ nanoparticles show different dispersive states in acidic and alkaline solutions for the two distinct forms of surface binding l-arginine. Powder X-ray diffraction and X-ray photoelectron spectroscopy were used to identify the structure of Fe₃O₄ nanocrystals. The products behave like superparamagnetism at room temperature with saturation magnetization of 49.9 emu g⁻¹ and negligible remanence or coercivity. In the presence of 1-ethyl-3-(dimethylaminopropyl) carbodiimide hydrochloride, the anti-chloramphenicol monoclonal antibodies were connected to the l-arginine-capped magnetite nanoparticles. The as-prepared conjugates could be used in immunomagnetic assay.     

Role of Catechol Structure in the Adsorption and Transformation Reactions of <Emphasis Type="SmallCaps">l</Emphasis>-D<Emphasis Type="SmallCaps">opa</Emphasis> in Soils

3-(3′,4′-Dihydroxyphenyl)-l-alanine (l-DOPA), which is synthesized in velvet bean (Mucuna pruriens), inhibits plant growth. The concentration of l-DOPA in soil is reduced by adsorption and transformation reactions, which can result in the reduction of its plant-growth-inhibitory activity. To determine which part of the l-DOPA structure is involved in the adsorption and soil transformation reactions, we compared the kinetics of l-DOPA disappearance in a volcanic ash soil with that of l-phenylalanine (3-phenyl-l-alanine) and l-tyrosine (3-(4′-hydroxyphenyl)-l-alanine), compounds that are similar in structure to l-DOPA but do not have a catechol (o-dihydroxybenzene) moiety. l-Phenylalanine and l-tyrosine were not adsorbed and transformed in the soil at equilibrium pH values between 4 and 7. These results suggest that the adsorption and transformation reactions of l-DOPA in the soil involve the catechol moiety and not the amino and carboxylic acid groups, which are common to all three compounds. Like l-DOPA, (+)-catechin, another allelochemical that contains a catechol moiety, underwent adsorption and soil transformation reactions. Thus, we concluded that the concentrations of allelochemicals bearing a catechol moiety in soils will decrease rapidly owing to adsorption and transformation reactions, and this decrease will be faster in soils with a high pH value or high adsorption ability. Owing to this decrease in concentration, allelopathic phenomena may not occur.     

Enhanced mechanical and photoluminescence effect of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) reinforced with functionalized multiwalled carbon nanotubes

The poly(l-lactide) (PLLA) biocompatible and biodegradable polymer was reinforced with functionalized Multiwalled carbon nanotubes (MWCNTs) to overcome on insufficient mechanical properties of this polymer for high load bearing applications. To fully realize the potential of MWCNTs for this purpose, they have to be homogeneously dispersed in polymer matrix and have efficient load transfer across the MWCNTs/polymer interface. The pristine MWCNTs (pMWCNTs) were functionalized, at first, by Friedel–Crafts acylation, which introduced the aromatic amine groups on the sidewall of MWCNTs (MWCNT–NH₂) without shortening or cutting of pMWCNTs. And then, the PLLA chains covalently grafted from the sidewall of MWCNT–NH₂ by in situ ring-opening polymerization of l-lactide oligomers using stannous octanoate as the initiating system. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy spectra revealed that the PLLA chains grafted form the sidewall of MWCNTs strongly. The surface morphology of pristine and PLLA-grafted MWCNTs (MWCNT-g-PLLAs) was characterized by scanning electron microscopy and transmission electron microscopy. The tensile test of prepared composites of PLLA with various concentrations of MWCNT-g-PLLAs show a significant increment in tensile strength and elongation at failure of composites with increasing the concentration of MWCNT-g-PLLAs in composites. Also, it is found that the MWCNT-g-PLLAs increased the photoluminescence effect of PLLA and widened the luminescence region of PLLA.     

Synthesis of poly(lactic acid) by heterogeneous acid catalysis from <Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid

Poly(lactic acid) (PLA) is an important polymer because of its significant biocompatibility and biodegradability. Supported H₃PW₁₂O₄₀ (H₃PW) on activated carbon was utilized for the catalytic polymerization of D,L-lactic acid, resulting in blends of PLA. The stability of the polymer was monitored by thermogravimetry (TGA), and the decomposition temperature (T_d) was used to determine the optimal production conditions (i.e., temperature of 180 °C for 15 h; 0.1 wt. % catalyst; 20 wt. % H₃PW/carbon calcined at 400 °C). The best catalyst was reused three times with good activity and recovery (95 %) and was analyzed to confirm the consistency of its Keggin structure, dispersion, and acidity, which are important parameters that affect the catalyst’s activity. The obtained polymer was characterized by gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FT-IR), ¹H/¹³C nuclear magnetic resonance (NMR) spectroscopy, specific optical rotation ([α]_D ²⁵), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The average molar mass of the polymer was 17,400 g mol^?1. Blends of poly(lactic acid) with 85 % poly(L-lactic acid) stereospecific isomer were obtained.

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Graphical Abstract Stereoselective synthesis of 85 % PLLA from polymerization of d,l-lactic acid using 12-tungstophosphoric acid supported on carbon as a catalyst

     

Preparation of thermally stable and optically active organosoluble aromatic polyamides containing <Emphasis Type="SmallCaps">l</Emphasis>-leucine amino acid under green conditions

An optically active bulky dicarboxylic acid (2S)-4-[(4-methyl-2-phthalimidylpentanoylamino)benzoylamino]isophthalic acid (1), was synthesized in five step starting from l-leucine and phthalic anhydride. A set of new aromatic polyamides containing (N-phthaloyl-l-leucine) units was synthesized by the direct one-pot phosphorylation polycondensation of diacid 1 with various aromatic diamines in the presence of different imidazolium salts and triphenyl phosphite (TPP) without adding extra compounds (Method I). This method was compared with a classical method in a medium consisting of TPP, N-methyl-2-pyrrolidinone, pyridine, and calcium chloride (Method II) and the results are comparable. The polymers were produced with high yields and from moderate to high inherent viscosities (0.43–0.81 dL g⁻¹). Amino acid existence in this backbone results in optically active polymers. The chemical structures of some of these polymers were characterized by ¹H-NMR and elemental analysis, and all of them with FT-IR and specific rotation tools. By introduction of bulky and flexible clusters in these new polyamides pendent group; make them soluble in most polar aprotic solvents.     

Oxidation kinetics of linoleic acid in the presence of saturated acyl <Emphasis Type="SmallCaps">l</Emphasis>-ascorbate

The oxidation processes of linoleic acid (LA) in the presence of l-ascorbic acid or saturated acyl l-ascorbate additives were measured at various temperatures and molar ratios of the additive to LA. Higher oxidative stability of LA was observed at higher additive levels for all additives. The addition of the ascorbates lengthened the induction period for the oxidation of LA. An autocatalytic kinetic rate equation was used to model the oxidation processes of LA mixed with the ascorbates, and the dependence of the rate constant, k, on acyl-chain carbon number was determined. At any temperature, the use of ascorbate additives decreased the k value for LA, and there was a slight tendency for k values to decrease with increasing acyl-chain length. The apparent activation energy, E _a, and the frequency factor, k ₀, for the rate constant were determined from Arrhenius plots. The calculated E _a and k ₀ values also decreased with increasing ascorbate acyl-chain length.     

Continuous production of acyl <Emphasis Type="SmallCaps">l</Emphasis>-ascorbates using a packed-bed reactor with immobilized lipase

Saturated acyl (6-O-caproyl, lauroyl, and myristoyl) and unsaturated acyl (6-O-oleoyl, linoleoyl, and arachidonoyl) l-ascorbates were continuously synthesized at 50°C using a system where a column packed with ascorbic acid powder and a packed-bed reactor with an immobilized lipase from Candida antarctica were connected in series. A productivity of 1.6–1.9 kg/L reactor·d was achieved for at least 11 d. The surface tension of the caproyl or lauroyl l-ascorbate in aqueous solution was measured at various temperatures and pH to estimate the critical micelle concentration (CMC) of the acyl l-ascorbate. The CMC values were independent of temperature but dependent on the pH. The value of the caproyl ascorbate increased with an increase in pH.     

<Emphasis Type="Italic">Meso</Emphasis>-Tetra-(3,5-Dibromo-4-Hydroxydroxyphenyl) Porphyrin Copper (II) Self-Assembled Modified Gold Electrode Through <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine: The Preparation,Electrochemical Behavior and its Application

In this study, a sensor for the sensitive determination of ascorbic acid (AA) has been fabricated based on meso-tetra-(3,5-dibromo-4-hydroxydroxyphenyl) porphyrin copper (II) (T(DBHP)P-Cu) modified Au electrode through l-cysteine (l-cys). Firstly, l-cys modified Au electrode was prepared through self-assembled technology. Then T(DBHP)P-Cu was adsorbed on l-cys/Au through covalent binding. The fabrication process and electrochemical behavior of T(DBHP)P-Cu/l-cys/Au were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that AA exhibited good electrochemical activity at T(DBHP)P-Cu/l-cys/Au. The oxidation peak current increased linearly with AA concentration in the range of 1.00 × 10⁻³–1.02 × 10⁻⁵ mol L⁻¹ with a detection limit of 5.41 × 10⁻⁷ mol L⁻¹. Additionally, the modified electrode could be applied to the detect AA in practical samples.     

Elevation of flow temperature of poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) gel by controlling its morphology and crystal form

Complex crystals (ε-crystals) of poly(l-lactic acid) (PLLA) with solvents such as N,N-dimethylformamide (DMF) induce gelation of PLLA by forming fibrous structure. Three procedures to elevate the flow temperature of the PLLA gel were described: formation of an additional network by immersion of a DMF solution of PLLA with lower molecular weight, changing the crystal form from ε-crystal to α-crystal by heating the gel at 46 °C, and increasing the concentration of the solution to form the gel followed by heating. Field emission electron microscopy and X-ray diffraction measurements were carried out to elucidate the structural change and driving force of the elevation of the flow temperature. Densification of the fibrous structure and change of the crystal form from ε-crystals to α-crystals with lower solubility at higher temperatures were observed in the gel after the formation of an additional network by immersion in a DMF solution of PLLA. The procedure to elevate the flow temperature, which has been developed in this study, can broaden the application of PLLA gels.     

A Calcium(II)-Based <Emphasis Type="SmallCaps">l</Emphasis>-Arginine for ATP Binding and Hydrolysis

The supramolecular recognition of Ca(II) and N _α-4-tosyl-l-arginine methyl ester hydrochloride (TAME) with ATP were investigated using ¹H and ³¹P NMR spectra. In the Ca(II)–ATP–TAME ternary system, Ca²⁺ and TAME bind with ATP via the phosphate chain and adenine ring of ATP. The binding forces are mainly electrostatic and cation (Ca²⁺)–π and π–π stacking interaction. Furthermore, the hydrolysis of ATP catalyzed by Ca(II) and TAME was studied at pH 7.0 and 60 °C using ³¹P NMR spectra. Kinetics studies show that the ATP hydrolysis rate constant is 0.1035 h⁻¹ in the Ca(II)–TAME–ATP ternary system, whereas the value is 8.5 × 10⁻³ h⁻¹ under the same conditions without TAME and Ca²⁺. The Ca(II) ions and TAME accelerate the ATP hydrolysis process about 12-fold. The proposed mechanism of ATP hydrolysis catalyzed by Ca²⁺–TAME occurs through an addition–elimination reaction sequence. These results can help us get more useful information at the molecular level about the key amino acid residue(s) and metal ions that serve as cofactors in the ATPase effect on ATP hydrolysis/synthesis.     

Graphene nanoplatelets dispersion in poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid): preparation method and its influence on electrical,crystallinity and thermomechanical properties

Poly(l-lactic acid) (PLLA)/graphene nanoplatelets (GnP) nanocomposites were prepared through solvent casting and coagulation methods. The better dispersion of graphene was achieved by ultrasounds and its effect on crystallinity, thermomechanical and electrical properties of PLLA were studied and compared in both methods. Differential scanning calorimetry (DSC) was used to investigate the crystallinity of PLLA and its composites. Field emission gun scanning electron microscope (FEG-SEM) and wide-angle X-ray scattering (WAXS) were employed to characterize the microstructure of PLLA crystallites. Dynamic mechanical thermal analysis (DMTA) was performed to study the thermomechanical properties of the nanocomposites. FEG-SEM images illustrated finer dispersion of GnP in samples obtained by coagulation method with respect to solvent casting method. Graphene imparted higher electrical conductivity to nanocomposites obtained by solvent casting under ultrasound due to better formation of graphene network. DSC thermograms and their resulting data showed positive effects of GnP on crystallization kinetics of PLLA in both methods enhanced by the nucleating effect of graphene particles. Meanwhile, the effect of GnP, as nucleating agent, was more prominent in samples produced by coagulation method without utilization of ultrasounds. WAXS patterns represented the same characteristic peaks of PLLA in nanocomposite specimens suggesting similar crystalline structure of PLLA in presence of graphene, and the intensified peaks of nanocomposites compared to neat PLLA confirmed the DSC results regarding its improved crystallinity. Graphene increased storage modulus in rubbery region and glass transition temperature of nanocomposites in the coagulation method due to restricted mobility of PLLA chains.     

Synthesis,characterization of star-shaped copolymers of <Emphasis Type="SmallCaps">l</Emphasis>-lactide and epoxidized soybean oil

Biodegradable star-shaped PLLA–ESO copolymers were synthesized by the bulk copolymerization of l-lactide (l-LA) and epoxidized soybean oil (ESO) with stannous octanoate as the catalyst. Effects of molar ratios of monomer to catalyst, and various amounts of ESO on copolymerization were studied. The resulting copolymers were characterized by FTIR, ¹H NMR, GPC, etc., which confirmed the successful synthesis of star-shaped copolymers of l-LA and ESO. The thermal and mechanical properties of samples were also investigated by means of DSC, TGA and tensile testing. The results showed that the PLLA–ESO copolymers possed lower glass transition temperature, melting point, crystallinity, and maximum decomposition temperature than those of neat polylactide. Tensile testing demonstrated that PLLA–ESO copolymer had better ductility than linear PLLA. It was also found that the amount of catalyst almost had no influence on the weight average molecular weight of PLLA–ESO copolymers, but which could be controlled by variation of molar ratios of l-LA to ESO.     

Morphologies and structures in poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-<Emphasis Type="Italic">b</Emphasis>-ethylene oxide) copolymers determined by crystallization,microphase separation,and vitrification

Morphologies and structures determined by crystallization of the blocks, microphase separation of the copolymers, and vitrification of PLLA block in poly(l-lactide-b-ethylene oxide) (PLLA-b-PEO) copolymers were investigated using microscopic techniques and synchrotron small angle X-ray scattering. The PLLA-b-PEO copolymer films were crystallized from two different annealing processes: melt crystallization (process A) or crystallized from glass state of PLLA block after quenching from melt state (process B). The relationship between the crystalline morphology and microstructure of the copolymers were explored using SAXS. The morphology and phase structure are predominated by crystallization of PLLA block, and greatly influenced by microphase separation of the copolymers. In process B, lozenge-shape and truncated lozenge-shaped PLLA crystals of nanometer scale can be observed. The crystalline morphology is markedly affected by the microstructure formed during the annealing process. Star-shaped morphologies stacked with PLLA single crystals were observed.     

Thermo-oxidative stability of poly(methyl methacrylate)/poly(methyl methacrylate)-grafted SiO2 nanocomposites

Thermo-oxidative stability of PMMA-grafted SiO₂ and PMMA/PMMA-grafted SiO₂ nanocomposites was investigated by conventional non-isothermal gravimetric technique. It was interesting to find that PMMA-grafted SiO₂ nanoparticles exhibited higher thermo-oxidative stability than that of PMMA. The apparent activation energy of PMMA-grafted SiO₂ nanoparticles increased with the grafting ratio of PMMA from SiO₂, which was estimated by Kissinger method. This indicates that the strong interactions existing between the grafted chains are responsible for the enhanced thermo-oxidative stability of PMMA-grafted SiO₂ nanoparticles. However, the grafting ratio of PMMA from SiO₂ in nanoparticles has only limited effect on the thermo-oxidative stability of PMMA/PMMA-grafted SiO₂ nanocomposites due to a much lower content of grafted PMMA in the nanoparticles relative to PMMA. The increased thermo-oxidative stability of PMMA/PMMA-grafted SiO₂ nanocomposites is possibly resulted from the increased SiO₂ content in the nanocomposites, in which the grafting ratio of PMMA in PMMA-grafted SiO₂ nanoparticles is kept almost as a constant. The glass transition temperature (T _g) of PMMA/PMMA-grafted SiO₂ nanocomposites is about 25 °C and is higher than that of PMMA. The grafting ratio of PMMA from SiO₂ in the nanoparticles has no qualitative effects on the T _g of the nanocomposites.