Influence of Grafted Chain Length of a Phenolic Copolymer on Its Complex Formation with Poly(vinyl Pyrrolidone) and Poly(ethylene Oxide)

A phenolic copolymer has been grafted with oligomers of different chain lengths. Polymer-polymer complexation has been studied between graft copolymers and nonionic polymers, such as polyvinyl pyrrolidone) and poly(ethylene oxide), in an acetone-methanol mixture by several methods, e.g., viscosity, conductance, and apparent pH measurements. A distinct stepwise complexation between PVP and graft copolymers has been observed. The length of the side chain also seemed to influence interpolymer complex formation. Some of these observations have been interpreted with reference to the actual structure of the graft copolymers.     

Complexes of Chlorin e6 with Pluronics and Polyvinylpyrrolidone: Structure and Photodynamic Activity in Cell Culture

Polymeric carriers are extensively used in photodynamic therapy (PDT) for increase of efficacy of photosensitizers. Here, we report the influence of nine Pluronic copolymers on phototoxicity of chlorin e6 (Ce6), in particular 5‐ to 7‐fold rise in the phototoxicity caused by hydrophilic Pluronics F127, F108, F68 and F87 and practically no influence on Ce6 of more hydrophobic polymers. The revealed value of 0.2 mg mL^?1 of Pluronic F127 concentration sufficient for half‐of‐maximal increase of Ce6 photodynamic activity proved to be close to 0.16 mg mL^?1 inherent in well‐documented carrier poly(N‐vinylpyrrolidone) (PVP). The dissociation constants of Ce6 complexes with Pluronic F127 and PVP that were estimated from UV spectra were 0.252 and 0.036 mg mL^?1, respectively, indicating higher stability of Ce6 complex with PVP. According to the results of ¹H‐NMR studies of Ce6 complexes, the porphyrin interacts not only with hydrophobic regions but also with hydrophilic sides of both polymers.     

Synthesis and in vitro degradation of poly(N‐vinyl‐2‐pyrrolidone)‐based graft copolymers for biomedical applications

This work is devoted to the design of a novel family of hydrosoluble biomaterials: poly(N‐vinyl‐2‐pyrrolidone) (PVP)‐based graft copolymers. A synthesis route has been elaborated in which ω‐functionalized PVP is prepared via chain‐transfer radical polymerization, end‐group modified, and subsequently grafted onto a polyhydroxylated backbone, typically dextran or poly(vinyl alcohol). The resulting graft copolymer biomaterials are designed for use in various biomedical applications, particularly as materials with a stronger potential for plasma expansion than already existing products have. The graft copolymers are potentially degradable because the PVP grafts are connected to the polyol backbone via a hydrolytically labile carbonate or ester linkage. The degradation of the graft copolymers was performed in vitro over a period of 6 weeks. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3652–3661, 2002     

Effect of water-soluble polymers, polyethylene glycol and poly(vinylpyrrolidone), on the gelation of aqueous micellar solutions of Pluronic copolymer F127

The micellization of F127 (E(98)P(67)E(98)) in dilute aqueous solutions of polyethylene glycol (PEG6000 and PEG35000) and poly(vinylpyrrolidone) (PVP K30 and PVP K90) is studied. The average hydrodynamic radius (r(h,app)) obtained from the dynamic light scattering technique increased with increase in PEG concentration but decreased on addition of PVP, results which are consistent with interaction of the micelles with PEG and the formation of micelles clusters, but no such interaction occurs with PVP. Tube inversion was used to determine the onset of gelation. The critical concentration of F127 for gelation increased on addition of PEG and of PVP K30 but decreased on addition of PVP K90. Small-angle X-ray scattering (SAXS) was used to show that the 30 wt% F127 gel structure (fcc) was independent of polymer type and concentration, as was the d-spacing and so the micelle hard-sphere radius. The maximum elastic modulus (G(max)(')) of 30 wt% F127 decreased from its value for water alone as PEG was added, but was little changed by adding PVP. These results are consistent with the packed-micelles in the 30 wt% F127 gel being effectively isolated from the polymer solution on the microscale while, especially for the PEG, being mixed on the macroscale.     

Suspension Graft Polymerization of Methyl Methacrylate onto Selected Backbones

Methyl methacrylate was grafted onto poly(vinyl oxazoline ester) and poly(stearyl methacrylate) by a chain transfer suspension polymerization method to produce specialty polymeric products. These graft polymers should find application in powder coating, toner resin, and for encapsulating electronic components.     

Pre-irradiation induced emulsion graft polymerization of acrylonitrile onto polyethylene nonwoven fabric

Acrylonitrile has been widely used in the modification of polymers by graft polymerization. In the present work, pre-irradiation induced emulsion graft polymerization method is used to introduce acrylonitrile onto PE nonwoven fabric instead of the traditional reaction in organic solvents system. The degree of grafting (DG) is measured by gravimetric method and the kinetics of the graft polymerization is studied. The existence of the graft chains is proven by Fourier transform infrared spectroscopy (FT-IR) analysis. Thermal stability of the grafted polymer is measured by Thermogravimetric analysis (TGA).     

Solution properties of chlorinated polypropylene and maleic anhydride grafted chlorinated polypropylene

The solution behaviors of the chlorinated polypropylene (CPP) and its grafted polymers (CPP-g-MAH) were systematically studied to characterize their polar change with grafting maleic anhydride (MAH) onto the chain of CPP. The molecular weights of the polymers were determined with light scattering measurements, and the Mark–Houwink equation of CPP in toluene was also obtained. The result showed that the Mark–Houwink equation of CPP was suitable for estimating the molecular weight of the polydisperse samples of CPP and not suitable to CPP-g-MAH because the molecular polarity of the graft polymers had changed with grafting MAH onto CPP. The solubility result of CPP and CPP-g-MAH in various solvents indicated that the polarity of CPP gradually increased with grafting MAH onto its chain, which would cause the solubility of poorly hydrogen bonded solvents for CPP-g-MAH to gradually become poor, whereas that of moderately hydrogen bonded solvents for the polymers becomes better with an increase of the MAH graft content. This is consistent with the results of their dilution ratio and solubility parameter. Stabilities of the 344^# resin–CPP-g-MAH–toluene solutions showed that the miscibility of CPP-g-MAH and 344^# resin was improved with increase of the MAH grafted content.     

Synthesis, characterization and biodegradation of butanediamine-grafted poly(dl-lactic acid)

Novel butanediamine-grafted poly(dl-lactic acid) polymers (BDPLAs) were synthesized via a series of chemical bulk modifications in this study. Briefly, maleic anhydride (MAH) was first grafted onto the side chain of poly(dl-lactic acid) (PDLLA) molecules via melt free radical copolymerization using benzoyl peroxide (BPO) as initiator to get maleic anhydride-grafted PDLLA polymers (MPLAs); thereafter butanediamine (BDA) was immobilized onto grafted anhydride groups in MPLAs via N-acylation reaction to obtain the desired BDPLAs. Gel permeation chromatography with multi-angle laser light scattering (GPC-MALLS), FT-IR, ¹³C NMR and XPS were employed to qualitatively characterize these synthesized polymers. Rhodamine-carboxyl interaction method and ninhydrin reaction were further used to quantitatively determine the graft ratio of MAH (MAH%) in MPLAs and the graft ratio of BDA (BDA%) in BDPLAs, respectively. The degradations of BDPLAs, PDLLA and MPLAs were investigated by observation of the changes of the pH value of incubation medium, molecular weight and weight loss ratio for a time interval of 12 weeks in vitro, respectively. The results revealed that grafting butanediamine onto PDLLA has weakened or neutralized the acidity of PDLLA degradation products. A uniform degradation of BDPLAs was observed in comparison with an acidity-induced auto-accelerating degradation featured by PDLLA and MPLAs. The biodegradation behaviors of BDPLAs are tunable by controlling the content of BDA. BDPLAs might be a new derivative of PDLLA-based biodegradable materials for medical applications without acidity-caused irritations and acidity-induced auto-accelerating degradation behavior as that of PDLLA.     

Vinyl Polymerization Initiated by Reducing Compounds of Transition Metals. XI. Two-step Selective Graft Copolymerization

Grafting of methyl methacrylate onto poly(methyl-4-vinylbenzyl-sulfoxide-co-trichloroethyl methacrylate) is initiated by molybdenum (III) chloride in ethylene chloride. In a second step the obtained graft copolymers are grafted with styrene in the presence of chromium(II) acetate and morpholinocyclohexene in dimethylformamide. By this stepwise selective graft copolymerization technique, polymers can be tailored to give the required properties.     

Polypropylene Modification by the Radiation Graft Polymerization of N-Vinylcaprolactam

The radiation graft polymerization of N-vinylcaprolactam onto polypropylene films was studied. The radiation graft polymerization was performed with preirradiation in air (peroxide method) or using a direct method in aqueous solutions and organic solvents. The effects of radiation dose, reaction time, monomer concentration, and homopolymerization inhibitor on the radiation graft polymerization were studied. It was found that the radiation graft polymerization from a monomer emulsion in water occurred at the highest rate. The IR spectra of grafted polymers were obtained. With the use of differential scanning calorimetry and equilibrium swelling in water, it was found that the modified polymers of polypropylene with grafted poly(N-vinylcaprolactam) chains exhibited thermoresponsive properties.     

Photografting of vinyl polymers onto ultrafine inorganic particles: Photopolymerization of vinyl monomers initiated by AZO groups introduced onto these surfaces

The photografting of polymers onto ultrafine inorganic particles, such as silica and titanium oxide, initiated by azo groups introduced onto these surfaces was investigated. The introduction of azo groups onto the particles was achieved by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with surface isocyanate groups, which were introduced by the treatment with tolylene 2,4-diisocyanate. It was found that the photopolymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole, is initiated by ultrafine particles having azo groups. The corresponding polymers were effectively grafted onto these surfaces through the propagation of the polymer from the surface radicals formed by the photodecomposition of the azo groups: e.g., the percentage of grafting of PMMA and polystyrene onto silica was reached to 112 and 176%, respectively. The percentage of grafting onto silica in the graft polymerization initiated by photodecomposition of surface azo groups was much larger than that initiated by thermal decomposition. Polymer-grafted ultrafine particles thus obtained gave a stable colloidal dispersion in good solvents for the grafted chain. © 1994 John Wiley & Sons, Inc.     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. III. The grafting and in vitro degradation of chemically crosslinked poly(1,5‐dioxepan‐2‐one)

Acrylamide was graft polymerized onto the surface of a chemically crosslinked and amorphous biodegradable polyester, poly(1,5‐dioxepan‐2‐one). Electron beam irradiation at a dose of 5 Mrad was used to generate the initiating species in the polyester. The degradation behavior in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated, and acrylamide‐grafted polymer. Differences in weight loss performance were observed between virgin and treated polymers. The acrylamide‐grafted poly(1,5‐dioxepan‐2‐one) was totally degraded after 43 weeks as compared to 48 weeks for the irradiated and 55 weeks for the virgin polymer. On the other hand, the treated polymers showed a higher resistance to degradation in terms of weight loss during the intermediate part of the degradation, i.e., between about 5 and 35 weeks. After this period, the irradiated and particularly the acrylamide grafted poly(1,5‐dioxepan‐2‐one) degraded much more rapidly than the virgin polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1659–1663, 1999     

Mediated melt functionalization of polypropylene

This work investigated the ability of several kinds of molecules to mediate the melt functionalization of polypropylene. N-Bromosuccinimide, nitroxides, iniferters, thiols and RAFT chain transfer agents were tested as potential mediators. The grafting of maleic anhydride onto polypropylene was carried out with and without mediator and the grafted polymers are discussed in terms of graft content, graft structure and molecular weights.     

Grafting of polymers with controlled molecular weight onto ultrafine silica surface

To graft polymers with controlled molecular weight and narrow molecular weight distribution, the grafting of polymers onto ultrafine silica surface by the termination of living polymer cation with amino groups introduced onto the surface was investigated. The introduction of amino or N-phenylamino groups onto the silica surface was achieved by the treatment of silica with γ-aminopropyltriethxysilane or N-phenyl-γ-aminopropyltrimethoxysilane. It was found that these amino groups on silica are readily reacted with living poly(isobutyl vinyl ether) (polyIBVE), which was generated with CF₃COOH/ZnCl₂ initiating system, and polyIBVE with controlled molecular weight and narrow molecular weight distribution is grafted onto the surface. By the termination of living poly(2-methyl-2-oxazoline), which was generated with methyl p-toluenesulfonate initiator, with amino groups on silica, polyMeOZO was also grafted onto the surface. The percentage of grafting of polymer onto the silica surface decreased with increasing molecular weight of the living polymer, because the steric hindrance of silica surface increases with increasing molecular weight of living polymer. Polymer-grafted silica gave a stable dispersion in a good solvent for grafted chains. © 1995 John Wiley & Sons, Inc.     

Physicomechanical properties of grafted polymers obtained by radiation-induced polymerization by radical and ionic mechanisms

The radiation-induced grafting of acrylonitrile, 4-vinylpyridine, and styrene was carried out by both radical and ionic mechanisms. Grafted polymers with equal percentages of graft were obtained by the radical and ionic propagation of the grafted chains. The molecular weight of homopolymers has been determined. The thermomechanical properties of the graft polymers were investigated. The yield temperatures for the graft polymers obtained by ionic propagation of the grafted chains is higher than that of graft polymers obtained by a radical mechanism. This is attributed to the higher molecular weight of the grafted chains obtained by the radiation-induced grafting by the ionic mechanism. The radiation-induced grafting of polyacrylonitrile increases significantly the thermal stability of polyethylene. The differential thermal analysis shows no marked differences in properties of the polymers.     

Nucleic acid base grafted polyethylenimine. Cytosyl pendant groups: Elucidation of structure with solution spectroscopy

In a previous paper, potassium 2-(cytos-1-yl)propanoate was grafted onto polyethylenimine of various molecular weights. These water-soluble polynucleotide analogs exhibited remarkable properties in their solution ultraviolet spectra. High hypochromicity values of 50% and 54% have been observed in alkaline aqueous solution and 50% trifluoroethanol solution, respectively. Percent hypochromicity value was observed to be directly proportional to percent graft. Red shift and hyperchromicity as a function of pH were observed for both the monomer model and the graft polymers. Light-scattering experiments on nucleic acid base grafted hydrophilic polymer backbones were carried out. Radius of gyration and second virial coefficient values indicated stiff macromolecules, rodlike in nature. Therapeutic potential of cytosyl grafted polyethylenimine was suggested by the results from continuous mixing experiments with polyinosinic acid and polyguanylic acid. Job plots showed enhanced hypochromicity, whose magnitude was dependent upon the polynucleotide and the base-base distance.     

An infrared spectroscopy study of PES PVP blend and PES-g-PVP copolymer

Systematic study of FTIR spectra was carried out on the PES/PVP blends and PES-g-PVP copolymers. In the blends, no shift of carbonyl group absorbance was observed. In the copolymers, there was an occurrence of blue-shift that increases with the grafting degree, which can be used as a compelling evidence of PVP being grafted onto PES. This phenomenon was interpreted from the stereo-hindrance effect. Besides, as the intensity of carbonyl group absorbance increased proportionally with the degree of grafting obtained by elementary analysis, FTIR, a simple and easy tool, became feasible for the quantitative determination of PVP content in the graft copolymers. Calibration curves with high correlation coefficient were established from which the quantitative relationship between the intensity of carbonyl group absorbance normalized by a chosen internal reference and the grafting degree can be obtained.     

Zwitterionically modified hydroxypropylcellulose for biomedical applications

Novel polyelectrolytes have been synthesized by grafting sulfobetaine side chains onto hydroxypropylcellulose backbone. Polymers with various degrees of grafting have been obtained. The polymers do not interact with model anionic, cationic and zwitterionic surfactants as found in fluorescence studies using pyrene as a molecular probe. Dynamic light scattering (DLS) studies indicated that in the graft polymer solution two types of polymers are present. The films were formed from the grafted polymers. Using atomic force microscopy (AFM) technique it was found that they are resistant to the adhesion of proteins and can be used for the preparation of antiadhesive surfaces which may find biomedical applications.     

Debundling of multiwalled carbon nanotubes in N,N-dimethylacetamide by polymers

Structure and properties of the dispersions of multiwalled carbon nanotubes (MWCNTs) in N,N-dimethylacetamide (DMAc) with different dispersing polymers: polyvinylpyrrolidone (PVP), poly(ethyleneoxide), triblock copolymers poly(ethyleneoxide)-b-poly(propyleneoxide)-b-poly(ethyleneoxide) (Pluronic F127 and Pluronic F108), ethylenediamine tetrakis(ethoxylate-b-propoxylate) tetrol, and ethylenediamine tetrakis(propoxylate-b-ethoxylate) tetrol (Tetronic) of different molecular weights were studied. All studied polymers were shown to be able to disperse MWCNT in DMAc, and MWCNT dispersions appear free of aggregates by visual inspection even after 3 months of keeping at room temperature. Dispersions were characterized by UV–VIS absorption spectroscopy and dynamic light scattering measurements. PVP was found to be the best dispersing polymer for MWCNT in DMAc. It was shown that the yield of the dispersed MWCNT and the average particle size of the MWCNT in DMAc depend on the chemical nature, molecular weight of the dispersing polymer, and solvent quality. The difference in dispersive capacity of the studied polymers is attributed to different dispersion mechanisms for PVP (“polymer wrapping” model) and for other studied dispersing polymers (“loose adsorption” model), which have different efficiencies in DMAc. It was revealed that an increase of dispersing polymer (PVP) concentration at the range of 4.7–37.6 g l^?1 results in an average particle size enlargement and MWCNT final concentration reduction.     

Synthesis of poly(vinyl alcohol) containing asymmetric nucleic acid base derivatives as grafted pendants

The preparations of new model polymers of polynucleotides with linear poly(vinyl alcohol) (PVA) backbones and an optically active nucleic acid base derivative as a pending side chain are described. (±)-, (+)-, and (?)-2-(thymin-1-yl)propionic acid were grafted onto PVA through ester bonds by direct coupling with dicyclohexylcarbodiimide (DCC) in the presence of highly active catalyst 4-pyrrolidinopyridine (PPY) to give optically active graft polymers. The corresponding monomer and dimer models have been prepared.