Grafting reactions onto polyorganophosphazenes. V. Photostabilization of poly[bis(4-benzylphenoxy)-phosphazene] by light-induced grafting copolymerization of acrylate polymers containing pendant HALS moieties

The light-induced grafting reaction of acrylate monomers containing hindered piperidine groups (HALS) onto poly[bis(4-benzylphenoxy)phosphazene] is described as a function of several different experimental parameters, i.e., type of photoinitiator (benzophenone or benzoin ethyl ether), monomer concentration, solvent composition, light intensity, and swelling of the polyphosphazene films. The obtained phosphazene-g-HALS-containing acrylate-grafted copolymers, irradiated with light of wavelength longer than 300 nm under accelerated photooxidative conditions to test the photostabilizing ability of the grafted HALS groups, showed that the hindered piperidine groups grafted onto the polyphosphazene matrix are able to considerably depress the damage caused to the poly[bis(4-benzylphenoxy)phosphazene] films during light exposure. The efficiency of this process seems to be related to the amount of HALS residues grafted onto the phosphazene substrates. © 1996 John Wiley & Sons, Inc.     

Functionalization of polyorganophosphazenes. VII. Photooxidative stabilization of aryloxy-substituted polyorganophosphazenes induced by grafting HALS groups through anhydride moieties

In this article, the general procedure for stabilizing polyorganophosphazenes against the damage induced in these substrates by photooxidation reactions under accelerated conditions is explored. This method is based on the preventive grafting of succinic anhydride groups onto selected polyphosphazenes induced by light excitation, followed by the reaction of the functionalized phosphazene substrates with amino-terminated HALS groups. HALS moieties, in fact, are able to strongly inhibit the photooxidation of phosphazene films under accelerated conditions even when randomly attached to the polyphosphazene materials in very low amounts. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:217–231, 1997     

Grafting reactions onto poly(organophosphazenes). VIII. Grafting kinetics, surface properties, thermal and dynamic mechanical characterization of phosphazene grafted copolymers containing poly(vinyl acetate) and poly(vinyl alcohol)

In this paper we report the light-induced grafting kinetics of vinyl acetate onto three poly(organophosphazene) films, i.e., poly[bis(4-methylphenoxy) phosphazene], poly[bis(4-ethylphenoxy)phosphazene], and poly[bis(4-secbutylphenoxy)phosphazene], and the characterization of the poly(organophosphazene)-g-poly-vinylacetate materials and the poly(organophosphazene)-g-poly-vinylalcohol copolymers, derived from hydrolysis of the previous ones. The reactivity of poly(organophosphazenes) was found to be directly dependent on the different crystallinity content. The modification of the surface properties was studied by SEM analysis and DCA measurements. The higher the grafting pereentage, the higher the roughness of surface and the lower the receeding contact angle. DSC analysis revealed that the crystallizability of poly(organophosphazene)-g-poly-vinylacetate decreases as the grafting percentage increases. Finally, DMTA measurements confirmed the presence of polyvinylacetate after grafting and its disappearance and the simultaneous increase in thermomechanical stability after hydrolysis.Presented at the 1st Italian Workshop on Cyclo- and Poly(phosphazene) Materials. February 15–16, 1996, at the CNR Research Area in Padova, Italy.     

Photochemical behavior of poly(organophosphazenes). XI. Photochemistry of poly[bis(4-benzylphenoxy) phosphazene]

In this paper we present results on the photolysis of poly[bis(4-benzylphenoxy)-phosphazene] in solution and in film, both in the presence and in the absence of molecular oxygen. Light irradiation of the polymer in oxygen-saturated CH₂Cl₂ solutions results in a remarkable degradation of the polyphosphazene, while in argon-purged solutions no appreciable variations of the polymer structure could be detected. The photolysis of poly[bis(4-benzylphenoxy)phosphazene] in films induces the cross-linking of the polymer regardless of the presence or the absence of molecular oxygen. The main process observed during the photochemistry both in solution and in the solid state of the polymer is the oxidation of the 4-benzylphenoxy group on the polyphosphazene, without involvement of the inorganic -P=N- backbone. The effect of temperature on the photolysis of the polyphosphazene substrate in film is also reported.     

Grafting reactions onto poly(organophosphazenes). IV. Light-induced graft copolymerization of organic polymers containing free acid or basic functionalities onto poly[bis(4-benzylphenoxy)phosphazene]

The light-induced graft copolymerization of acrylic acid, methacrylic acid, and 4-vinylpyridine onto poly[bis(4-benzylphenoxy)phosphazene] films to prepare new grafted phosphazene copolymers containing acid and basic functionalities is reported. The process was carried out in monomer/methanol mixtures in the presence of benzophenone or benzoin ethyl ether as photosensitizers by selective excitation of these last species. The yield of the grafting processes was evaluated as a function of the monomer concentration in the reaction medium, type of photoinitiator, and characteristics of the grafted organic monomers. The acid functions inserted in poly[bis(4-benzylphenoxy)phosphazene]-g-poly(meth)acrylic acid grafted copolymers, and the basic groups of the poly[bis(4-benzylphenoxy)phosphazene]-g-poly-4-vinylpyridine substrates were allowed to interact with basic and acid dyes, respectively, to form permanently colored polymeric films. The photoactivity of these films as substrates for the photosensitized production of singlet oxygen was tested. © 1995 John Wiley & Sons, Inc.     

Grafting and adsorption of poly(vinyl) alcohol in vinyl acetate emulsion polymerization

Poly(vinyl alcohol) is often used in vinyl acetate emulsion polymerization as a protective colloid, but its role is complex and controversial since it partakes in grafting reactions with the monomer, influencing process mechanisms, and affecting the colloidal properties of the latex. Furthermore, in industrial operations, the wide scatter of macromolecular properties of the commercial types of poly(vinyl alcohol) causes process irreproducibilities. In this work different types of polyvinyl alcohol were used to perform a series of polymerizations, and their kinetics were compared. A selective solubilization procedure was applied to separate the three fractions of poly(vinyl alcohol) in the final latex: free in the water phase, physically adsorbed onto the polymer particles and chemically grafted. These results were compared with those obtained from pure adsorption measurements of polyvinyl alcohol onto ‘emulsifier-free’ polyvinyl acetate dispersions. The rheological behavior of the different latexes was also compared, and the results were used to formulate an hypothesis on the interaction mechanisms acting in these systems.     

Photochemical behaviour of poly(organophosphazenes). 14. Photooxidation of poly[bis(4-isopropylphenoxy) phosphazene] under accelerated conditions

The photooxidation of poly[bis(4-isopropylphenoxy)phosphazene] under accelerated conditions has been followed by FTIR and UV visible spectroscopic techniques. The main photooxidation products are acetophenone and phenol groups. In addition, acetone vapors have been detected by GC MS combined techniques concomitant with the IR spectral changes in the CH stretching region, suggesting a significant decrease in the isopropyl moieties. The presence of polymeric sequences having phenol groups under our conditions gives origin to further oxidation reactions due to electron transfer or radical recombination or to hydrogen abstraction reactions promoted by unhindered phenoxyl radicals. In addition, the absence of UV visible light, i.e., under thermooxidation reaction at 60° C has demonstrated that phenol groups are the main responsible of secondary oxidation products. The complexity of the photooxidation mechanism in the solid state for this polymer makes it difficult to determine a definitive degradation mechanism under both thermo- and photooxidative conditions.Presented at the 1st Italian Workshop on Cyclo- and Poly(phosphazene) Materials, February 15–16, 1996, at the CNR Research Area in Padova, Italy.See Ref. 14.     

Photochemistry and photophysics of poly(organophosphazenes) and related compounds: A review. III. Applicative aspects

In the third part of this review we report some applicative aspects of poly(organophosphazenes) in photochemical fields. In particular, the possible application of phosphazene polymers that contain azobenzene or spiropyran residues as photochromic macromolecules is outlined; the light-induced grafting of organic, carbon-backboned polymers onto polyphosphazene matrices, as a method of modifying both surface and bulk properties of these materials, is highlighted; and the potential application of cyclophosphazenes as photo-stabilizers for commercial organic polymers or as photoinitiators for radical polymerization of vinyl monomers is described.Parts I and II in this series appeared in this journal, Volume 4, Numbers 1 and 2, 1994, respectively.     

Reaction kinetics of graft copolymerization and thermochemical studies of the degradation of poly(vinyl alcohol) graft copolymer

Poly(vinyl alcohol) (PVA) is a water‐soluble and biomedical polymer. 2‐Acrylamido‐2‐methyl‐1‐propanesulfonic acid was grafted onto PVA using ammonium persulfate as radical initiator. The influences of synthesis conditions such as temperature, concentrations of initiator, PVA and monomer were investigated. Both the initial rate of grafting and the final percentage of grafting were increased by an increase in reaction temperature. The reaction kinetics were studied to determine the rate constants of the first‐order reactions. An activation energy of 16.3 kJ mol^?1 was found for the grafting reaction. The graft copolymers were characterized by IR and intrinsic viscosity measurements. A proposed mechanism of the grafting reaction is discussed. Kinetics of the thermal degradation were studied using a thermogravimetric method and the order of thermal stabilities are given. The apparent activation thermodynamic parameters, E_a, ΔH*, ΔS* and ΔG* were determined and correlated to the thermal stabilities of the homo‐ and grafted polymers. © 2001 Society of Chemical Industry     

Melt grafting of poly(ethylene‐vinyl acetate) copolymer with maleic anhydride

Poly(ethylene‐vinyl acetate) (EVA) copolymer was melt grafted with maleic anhydride (MAH) in a twin screw extruder in the presence of peroxide. It is confirmed that MAH has been melt grafted on the backbone of EVA by FTIR using the method of hydrolysis. The NMR analysis suggests that the grafting reaction occurs on the tertiary carbon of main chain of EVA other than the methyl moiety of vinyl acetate (VA) group. The incorporation of VA groups onto the matrix shows a competitive effect on the grafting. The existence of VA groups promotes the extent of MAH graft onto EVA; nevertheless, it also weakens the crystallizability of main chain. When the content of peroxide initiator is 0.1 wt % based on the polymer matrix, the grafting degree increases with increasing the concentration of monomer. When the peroxide content is higher than 0.1 wt %, side reactions such as crosslinking or disproportionation will be introduced into this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 841–846, 2006     

Characterization of poly(vinyl alcohol) grafted with acrylic acid and methylmethacrylate using a Ce(IV) glucose redox system

Poly(vinyl alcohol) (PVA) is a well-known biomedical polymer and is biocompatible. Methylmethacrylate and acrylic acid monomers were grafted onto PVA using a Ce(IV)–glucose redox system at three different temperatures (35, 45, and 55°C) under nitrogen atmosphere. More than 80% grafting could be achieved in the process. The grafted PVA was characterized through infrared spectra, thermal decomposition studies [thermogravimetric analysis (TGA) and decomposition thermal grafting (DTG)], differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The thermal stability and other properties of grafted PVA related to medical applications was found to be better than those of ungrafted PVA. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 677–683, 1999     

Chemical Functionalization of Graphene Oxide by Poly(styrene sulfonate) Using Atom Transfer Radical and Free Radical Polymerization: A Comparative Study

Poly(sodium styrenesulfonate)-functionalized graphene was prepared from graphene oxide, using atom transfer radical polymerization and free radical polymerization. In atom transfer radical polymerization route, the amine-functionalized GO was synthesized through hydroxyl group reaction of GO with 3-amino propyltriethoxysilane. Atom transfer radical polymerization initiator was grafted onto modified GO (GO-NH₂) by reaction of 2-bromo-2-methylpropionyl bromide with amine groups, then styrene sulfonate monomers were polymerized on the surface of GO sheets by in situ atom transfer radical polymerization. In free radical polymerization route, the poly(sodium 4-styrenesulfonate) chains were grafted on GO sheets in presence of Azobis-Isobutyronitrile as an initiator and styrene sulfonate monomer in water medium. The resulting modified GO was characterized using range of techniques. Thermal gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy results indicated the successful graft of polymer chains on GO sheets. Thermogravimetric analysis showed that the amount of grafted polymer was 22.5 and 31?wt% in the free radical polymerization and atom transfer radical polymerization methods, respectively. The thickness of polymer grafted on GO sheets was 2.1?nm (free radical polymerization method) and 6?nm (atom transfer radical polymerization method) that was measured by atomic force microscopy analysis. X-ray diffractometer and transmission electron microscopy indicated that after grafting of poly(sodium 4-styrenesulfonate), the modified GO sheets still retained isolated and exfoliated, and also the dispersibility was enhanced.     

Surface grafting of poly(vinylamine) onto poly(ethylene) film by corona discharge‐induced grafting

Poly(vinylamine) (PVAm) was grafted on a poly(ethylene) (PE) film surface via the surface graft polymerization of N‐vinylformamide (NVF) and N‐vinylacetamide (NVA) and the subsequent hydrolysis of those grafted polymers. The surface was characterized by X‐ray photoelectron spectroscopy (XPS), contact angle, moisture absorption, and the leakage of electrostatic charge from the films. PNVF and PNVA were introduced onto the surface of the PE film successfully, in spite of the fact that the initiator for polymerization was a peroxide group. The grafted amounts of PNVF and PNVA were dependent on the grafting time. A PVAm‐grafted surface was obtained via the hydrolysis of the grafted PNVF. The grafted‐PNVA was not hydrolyzed under mild hydrolysis. The obtained PVAm‐grafted surface appeared to be useful for various applications, such as protein immobilization or chemical modification. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1583–1587, 1999     

Photochemical Behavior of Poly(Organophosphazenes). 15. Light-Induced Cross-Linking of [(4-Benzoylphenoxy)x(Methoxyethoxyethoxy)2 ? x] Phosphazene Copolymers

The synthesis of a new, highly photosensitive, phosphazene copolymer containing an almost-equimolecular quantity of benzophenone and methoxyethoxyethoxy substituents is reported in this paper, together with the photochemical behavior of this material when irradiated in film both in oxygen and in an argon atmosphere. It has been detected that the photoreactivity of the phosphazene material strongly depends on the light absorption process by the benzophenone moieties, whose selective excitation predominantly brings about an intramolecular hydrogen abstraction reaction from the ethylene oxide units, thus producing highly reactive phosphazene macroradicals. The coupling reactions of these species results in the complete cross-linking of the polyphosphazene substrate and in its total insolubilization. Moreover, the influence of molecular oxygen on the overall photochemical process of the benzophenone/ethyleneoxide-substituted phosphazene copolymer is investigated. The implications of the light-induced reticulation process in the controlled insolubilization of poly[ bis (methoxyethoxyethoxy)phosphazene] are also discussed.     

Functionalization of Poly(organophosphazenes). VI. Substituent effect on the grafting reaction of maleic anhydride onto phenoxy-substituted phosphazene polymers

In this paper we describe the solution functionalization reaction of six phenoxysubstituted poly(organophosphazenes) with maleic anhydride and the effect of the phosphazene substituents on the overall grafting yield of anhydride moieties. It was found that the phosphazene polymer substituted with 4-ethylphenoxy groups is the most reactive of the whole series of exploited materials, while that bearing 4-t-butylphenoxy groups is the most inert one. This experimental reactivity trend observed in the grafting process is accounted for on the basis of both thermodynamic and steric factors.     

ESCA spectroscopy of poly(methyl methacrylate) grafted onto wood fibers

The incompatibility of hydrophilic wood fiber and hydrophobic polymers is the main difficulty with wood thermoplastic polymer composites. To overcome this issue, many researchers suggest grafting polymer onto wood fiber for improving the interfacial adhesion during mixing. A systematic ESCA study of chemi-thermo-mechanical pulp (CTMP) grafted fiber has been performed to provide chemical information about surface composition modification. The material analyzed included initial CTMP fiber, the pure polymer i.e., poly(methyl methacrylate) (PMMA) as reference material, and grafted fiber at different polymer loadings. Interest is focused on the carbon and oxygen spectra. Samples at high polymer loading or high grafting level have an O/C, C₁, C₂, C₄, O₁, and O₂ intensities much similar to those of the PMMA but a little different since some wood fiber sites have still not fixed the polymer. ESCA spectra provide information on about 1–5 nm depth. The ESCA technique allows the monitoring of grafting polymer onto wood fiber as a surface phenomenon.     

Graft copolymerization of N‐isopropylacrylamide onto poly(vinyl chloride)

Poly(vinyl chloride) (PVC) was dehydrochlorinated in alkali solution and then grafted with N‐isopropylacrylamide (NIPAM) using benzoyl peroxide as an initiator under a nitrogen atmosphere. The results show that grafting of NIPAM onto dehydrochlorinated PVC (DHPVC) by means of chemical initiation is easily performed. The influence of various reaction conditions such as NIPAM concentration, reaction time, initiator concentration, and PVC content on the grafting copolymerization was investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1234–1241, 1999     

Preparation and kinetic characterization of attapulgite grafted with poly(methyl methacrylate) via R-supported RAFT polymerization

Poly(methyl methacrylate) brushes grafted from attapulgite nanoparticles (ATP@PMMA) were prepared by R-Supported reversible addition-fragmentation chain transfer polymerization (RAFT). ATP was firstly activated, and allowed to react with γ-aminopropyltriethoxysilane (APTES), 4,4′-azobis(4-cyanovaleric acid) (ACVA) and bis(thiobenzoyl) disulfide stepwise to afford 4-cyanopentanoic acid dithiobenzoate functionalized ATP (ATP-CPADB). Then, RAFT polymerizations of MMA mediated by the different systems were conducted and compared systemically. The grafting process was verified by FTIR, XRD, XPS, TGA and TEM data. Kinetic behavior indicated that the anchored CPADB is more effective before diffusing into the bulk phase. The grafting ratio (G _r), while M _n of grafted and free polymer increased linearly with increasing monomer conversion in presence of free CPADB, giving the hybrid particles with more homogeneous distribution of grafted polymer layer.     

Preparation of soapless latexes by sonification of starch-based poly(isoprene–co–acrylonitrile) graft reaction mixtures

Graft copolymerization of isoprene (IP) and acrylonitrile (AN) onto gelatinized starch (S) and cationic starch having quaternary amine functionality through cerium(IV) initiation gave grafted side chains of poly(IP–co–AN). Grafts of various compositions are obtained by controlling the amounts and ratios of monomers added to starch. IP alone does not homograft onto gelatinized starch at 25° or 50°C by cerium(IV) initiation and requires the presence of an “initiator–monomer” such as AN to obtain copolymer side chains. Although cografting of IP and AN onto starch depends on AN to initiate radical chains, the ratio employed of the two monomers is critical for graft polymerization to occur. For example, at a molar ratio of IP to AN of 1 or greater, little polymer was produced; at molar ratios in the range of 0.4 to 0.67, considerable amounts of polymer were produced; and at a molar ratio of 0.13 or less, polymerization of AN was greatly retarded. Concentration of HNO₃ in the cerium(IV) reagent and reaction temperature also influence the grafting reaction. Lower HNO₃ concentrations favor grafting at 50°C, while higher acid concentrations favor grafting at 25°C. Starch graft reaction mixtures were sonified at 20 kHz to form latexes that air dry to clear pliable films. Poly(IP–co–AN) obtained by acid hydrolysis of the starch portion of the grafts failed to dissolve in either dimethylformamide or benzene, thus indicating presence of crosslinks. S–g–poly(IP–co–AN), having about one third starch and grafted side chains averaging about 2 parts polymerized IP per part of polymerized AN, was masticated on steel rolls at 100°C to a tough pliable film which was subsequently vulcanized to a rubber.     

Functionalization of poly(vinyl chloride) through radiation-induced grafting

Poly(vinyl chloride) was irradiated in air with γ-rays. The hydroperoxidized poly(vinyl chloride) when heated with acrylic acid in water was grafted with poly(acrylic acid), thus introducing the elements of glutaric acid on the polymer. Percentage weight gain was investigated as a function of total dose, monomer concentration, and time of reaction. The effect of adding methanol to water as a medium of reaction was studied in terms of percentage weight gain on grafting. © 1995 John Wiley & Sons, Inc.