Free Radical Grafting Reaction Research Articles

Biological Activity of a Gallic Acid−Gelatin Conjugate

Goal of the present study was the characterization of the biological properties of a gelatin-gallic acid conjugate (Gel-GA) to evaluate its applicability in biomedicine and pharmacy. The macromolecular conjugate was synthesized by free radical grafting reaction between gelatin and gallic acid (GA) to form a covalent conjugate that was found to retain the antioxidant and enzymatic activities of free GA. In particular, the peroxynitrite scavenging power was found to be consistent with a IC(50) value of 2.17 ± 0.4 mg mL(-1). The enzymatic capacities of GA, which are regarded beneficial for cell functions, are partly retained in the Gel-GA conjugate. In particular, acetylcholinesterase inhibition (IC(50) of 7.1 ± 1.3 mg mL(-1)) implies the conjugate's usefulness in the chemoprevention of Alzheimer's disease, while the inhibition of α-amylase (IC(50) of 9.8 ± 1.1 mg mL(-1)) suggests that the conjugate can be a preferred alternative for inhibition of carbohydrate breakdown and control of glycemic index of food products. Finally, the anticancer activity of Gel-GA was proven in prostate carcinoma and renal cell carcinoma cell lines, confirming the potential of the proposed protein-polyphenol conjugate in medicine.

Preparation and Application of Hybrid SBS Bipolar Membrane in Electro-Generation of HPAc and Succinic Acid

The hybrid SBS-g-(DMAEMA-SiO2)/SBS-g-(AA-StSO3Na-SiO2) bipolar membrane, SBS BPM was prepared by SBS (styrene-butadiene-styrene triblock copolymer) grafted with acrylic acid (AA), sodium sulfonic styene(StSO3Na) through free radical grafting reaction, then the grafting copolymer and γ-mercaptopropyltrimethoxysilane (KH-590) were exposed to UV illumination, and the SiO2 doped anode membrane was obtained through sol–gel reaction of trimethoxysilane group, as similar process the cathode membrane was prepared by SBS grafted with dimethyl amino ethyl methacrylate (DMAEMA) and KH-570. The SBS BPM exhibited good mechanical strength (tensile strength, TS is 1.55MPa) and high temperature tolerance (thermal degradation temperature in N2 is in the range of 230–250°C). The ion exchange capacities (IECs) of SBS-g-(DMAEMA-SiO2) and SBS-g-(AA-StSO3 Na-SiO2) were in the region of 1.42–2.82 mmol/g. The SEM images show that the membrane cross- sections are very smooth where no silica particles could be observed. SBS-g-(DMAEMA-SiO2)/ SBS- g-(AA-StSO3Na-SiO2) bipolar membrane was used as the separator in the electrolysis cell for electro- generation of 2,2-dimethyl-3- hydroxypropionic acid(HPAc) and succinic acid in pairs. The yield of HPAc and the corresponding average current efficiency in the anode chamber were 28.2% and 53.8％, respectively. The yield of succinic acid and the average current efficiency in the cathode chamber were 74.1% and 62.5%, respectively.

PREPARATION OF PNIPAAm GRAFTED COTTON AND ITS THERMAL SENSITIVITY

The thermal sensitive cotton-g-PNIPAAm was prepared through free radical grafting reaction initiated by different initiators including ammonium ceric nitrate(CAN),potassium persulfate(KPS) and hydrogen peroxide/ascorbic acid(H_2O_2/H_2A system).The degrees of grafting(G) achieved by different initiators could be sorted into descent order as following: G(H_2O_2/H_2A)G(KPS)G(CAN).The other factors affecting the degree of grafting,such as the concentration of initiator,reaction time,temperature and the concentration of monomer,were studied.The results showed that the optimal conditions for grafting reaction using H_2O_2/H_2A initiating system were: initiator dosage 7.5 mmol/L(mole ration of H_2O_2to H_2A=1∶0.6),reaction time 1.5 h,monomer concentration 5%～15% and the reaction temperature 25℃.FTIR spectrogram of grafted cotton fiber showed characteristic absorptions of(—CH_3,)(CO,)(—N—H,)(—C—N) and(—CH(CH_3)_2) groups at 2967.5,2857.4,1623.9,1540.3,1457.4 cm~(-1),1385.6 and 1365.4 cm~(-1) giving the evidence for the successful grafting of PNIPAAm onto cotton fiber surface.The extraneous polymer attached to fiber surface can be observed in SEM images of grafted cotton samples.DSC analysis revealed that all grafted cotton fibers had the LCST around 32～33℃ which was very close to the LCST of pure PNIPAAm gel(32.48℃).The raising of grafting degree has little impact on LCST but increases the reversible enthalpy change(ΔH) of the cotton-g-PNIPAAm.In the falling-drop test(AATCC 79) and capillary rise test(FZ/T 01071), the fabric samples of cotton-g-PNIPAAm demonstrated different water absorbing abilities at different temperatures which meant that the cotton fiber had been endowed with thermo sensibility by PNIPAAm grafting.A grafting degree between 25%～45% is suitable for creating high thermo sensitivity.Other grafting degrees out of above range were not suggested.The analysis and discussion about the relationship between ΔH and swelling/shrinking time of cotton-g-PNIPAAm indicated that cotton-g-PNIPAAm reacted to temperature much quickly than pure PNIPAAm gel.

Reactive processing of polymers: Effect of bifunctional and tri-functional comonomers on melt grafting of glycidyl methacrylate onto polypropylene

Two reactive comonomers, divinyl benzene (DVB) and trimethylolpropane triacrylate (TRIS), were evaluated for their role in effecting the melt free radical grafting reaction of the monomer glycidyl methacrylate (GMA) onto polypropylene (PP). The characteristics of the GMA-grafting systems in the presence and absence of DVB or TRIS were examined and compared in terms of the yield of the grafting reaction and the extent of the main side reactions, namely homopolymerisation of GMA (poly-GMA) and polymer degradation, using different chemical compositions of the reactive systems and processing conditions. In the absence of the comonomers, i.e. in a conventional system, high initiator concentrations of peroxides were typically required to achieve the highest possible GMA grafting levels which were found to be generally low. Concomitantly, both poly-GMA and degradation of the polymer by chain scission takes place with increasing initiator amounts. On the other hand, the presence of a small amount of the comonomers, DVB or Tris, in the GMA-grafting system, was shown to bring about a significant increase in the grafting level paralleled by a large reduction in poly-GMA and PP degradation. In the presence of these highly reactive comonomers, the optimum grafting system requires a much lower concentration of the peroxide initiator and, consequently, would lead to the much lower degree of polymer degradation observed in these systems. The differences in the effects of the presence of DVB and that of TRIS in the grafting systems on the rate of the GMA-grafting and homopolymerisation reactions, and the extent of PP degradation (through melt flow changes), were compared and contrasted with a conventional GMA-grafting system.

Improvement of interfacial adhesion between wood and polypropylene in wood–polypropylene composites

N-vinylformamide-grafted polypropylene (VFPP) was successfully synthesized through a free radical grafting reaction. Both polymeric methylene diphenyl diisocyanate (PMDI) and VFPP were effective compatibilizers for increasing both the strength and stiffness of the resulting wood–PP (polypropylene) composites. Both the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the resulting wood–PP composites were further increased when PMDI and VFPP were used together as an integrated compatibilizer system. This new PMDI-VFPP compatibilizer system was comparable to maleic-anhydride-grafted polypropylene in terms of enhancing the strength and stiffness of the wood–PP composites. Study of the fractured surfaces of the wood–PP composites with scanning electron microscopy revealed that this new PMDI-VFPP compatibilizer system greatly improved the interfacial adhesion between wood and PP. This PMDI-VFPP compatibilizer system also greatly reduced the water absorption of the resulting wood–PP composites. In this PMDI-VFPP compatibilizer system, PMDI is proposed to function as a wood-binding domain and VFPP to function as a PP-binding domain. PMDI reacted with the amide group in VFPP, thus forming covalent linkages between PMDI and VFPP.

Determination methods of the grafting yield in glycidyl methacrylate-grafted ethylene/propylene/diene rubber (EPDM-g-GMA): Correlation between FTIR and1H-NMR analysis

A normalized and universally applicable calibration function for the Fourier-transformed infrared (FTIR) quantification of the glycidyl methacrylate (GMA) grafting yield in polymers of known compositions having ethylene block sequences was established. The 1H nuclear magnetic resonance (1H-NMR) spectroscopy results achieved on different GMA-grafted ethylene/propylene/diene rubber (EPDM-g-GMA) and ethylene/GMA copolymers were correlated to their FTIR data to calibrate the relative determination of the FTIR method. Both direct and indirect standardization approaches were followed and evaluated. The calibration deduced was used to investigate the free radical grafting reaction of GMA on EPDM rubber in the melt phase. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2616–2624, 1999

Poly(β‐hydroxynonanoate) and polystyrene or poly(methyl methacrylate) graft copolymers: microstructure characteristics and mechanical and thermal behavior

AbstractActive polymers containing peroxide groups were synthesized via polymerization of styrene or methyl methacrylate with oligo(adipoyl 2,5‐dimethylhexane‐2,5‐diyl peroxide) (OAHP) or oligo(2,5‐dimethylhexane‐2,5‐diyl 4,4′‐azobis(4‐cyanoperoxyvalerate)) (LUAB). Poly(β‐hydroxynonanoate) (PHN) and the active polymer were mixed, and free radical grafting reactions were carried out to optimize mechanical and viscoelastic properties of PHN. The “active” vinyl polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA) were grafted onto PHN chains or cleaved them, depending on the PHN/active polymer mass ratio and the peroxygen content of the active polymer. The increase in tensile strength (f) and strain (ε) was observed to be maximum in graft copolymers having vinyl polymer contents less than 20 wt.‐%. SEM micrographs showed surface topography. Phaseseparated graft copolymers reveal dispersed phase particles, micrometer and submicrometer sized particles, and holes in the micrographs. The SEM observations are also wholly consistent with the glass transition temperature behavior obtained from differential scanning calorimetric (DSC) measurements.

A gel permeation chromatography method to determine grafting efficiency during graft copolymerization

A new method of measuring the efficiencies of free radical grafting reactions is presented. This technique utilizes the compositional analysis capability of dual-detector (ultraviolet and refractive index) gel permeation chromatography (g.p.c.) in which the mixture of polymers resulting from the graft copolymerization reaction is also subjected to separation by molecular size. Samples of the reaction mass drawn from a reactor are diluted with g.p.c. eluent and injected directly into the chromatograph without any other preparative step. Grafting efficiency, graft ratio, molecular weight distributions and the frequency of graft chains along the backbone polymer are simultaneously determined. Low molecular weight diluents (residual monomer, solvent, initiator, etc.) are readily separated from the polymer within the chromatograph, allowing for the determination of the fractional conversion of graft monomer (to grafted and ungrafted polymer) from the same analysis. This simple technique overcomes the need to separate or purify the polymer mixture prior to analysis, as required for most other methods. Experimental results are presented for the grafting of styrene onto cis -polybutadiene. Gelled samples cannot be analysed by this new technique.

Exchange and free radical grafting reactions in reactive extrusion

AbstractThe potential of two types of reactions for reactive extrusion was evaluated in our laboratory: exchange reactions of copolyesters and free radical grafting of monomers onto polyolefins. Specifically, the alcoholysis of ethylene and vinyl acetate copolymers, the transesterification of ethylene and alkyl acrylate copolymers (EAA) and the aminolysis of alkyl acrylate copolymers were investigated as the exchange reactions while the grafting of maleic anhydride (MA) onto polypropylene (PP) as the free radical reactions. The exchange reactions are very slow without catalysts. Tin derivatives, such as dibutyl tin dilaurate (DBTDL) and dibutyl tin oxide (DBTO), are good catalysts for the alcoholysis and the transesterification, but not for the aminolysis. For the latter, tautomeric compounds, such as 2‐pyridone and 2‐mercaptopyridone, are efficient. Comparative kinetic studies showed that, for all the three exchange reactions, the reacting medium (solution or the homogeneous melt) does not affect their reaction mechanisms nor their intrinsic rate constants. Additionally, mechanical mixing does not contribute to the overall reactions. As for the free radical grafting of MA, the presence of electron‐donating monomers and styrene (ST) in particular was shown to be very effective in improving the grafting yield while minimising the degradation of PP. This was proven to be due to the formation of a charge transfer complex between MA and such a monomer.