Grafting of vinyl polymers onto VGCF surface and the electric properties of the polymer-grafted VGCF

The graft polymerization of vinyl monomers onto vapor grown carbon fibers (VGCF) initiated by the system consisting of molybdenum hexacarbonyl (Mo(CO)₆) and trichloroacetyl (COCCl₃) groups introduced onto the surface was investigated. The introduction of trichloroacetyl groups onto VGCF surface was successfully achieved by the reaction of carboxyl groups on VGCF surface with trichloroacetyl isocyanate. It was found that the radical graft polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and glycidyl methacrylate (GMA) is successfully initiated by the system consisting of Mo(CO)₆ and COCCl₃ groups introduced onto the surfaces. In the polymerization, the corresponding vinyl polymers were effectively grafted onto the VGCF surface, based on the propagation of polymer from surface radicals formed by the interaction of trichloroacetyl groups and Mo(CO)₆: the percentage of PMMA grafting reached 40%. Polymer-grafted VGCF gave a stable colloidal dispersion in good solvents for grafted polymer. The electric resistance of composite prepared from the polymer-grafted VGCF suddenly increased in organic solvent vapor over 10³ times, and returned to initial resistance when it was transferred into dry air. These results indicate that such composites can be used as novel gas sensors.     

Surface grafting of polymers onto glass plate: Polymerization of vinyl monomers initiated by initiating groups introduced onto the surface

The surface grafting of polymers onto a glass plate surface was achieved by the polymerization of vinyl monomers initiated by initiating groups introduced onto the surface. Azo groups were introduced onto the glass plate surface by the reaction of 4,4′-azobis(4-cyanopentanoic acid) with isocyanate groups, which were introduced by the treatment with tolylene-2,4-diisocyanate. The radical polymerization of various vinyl monomers was initiated by azo groups introduced onto the glass plate surface and the corresponding polymers were grafted from the surface: The surface grafting of polymers was confirmed by IR spectra, and the contact angle of surface, with water. The contact angle of the glass plate increased by the grafting of hydrophobic polymers, but decreased by the grafting of hydrophilic polymers. The radical postpolymerization was successfully initiated by the pendant peroxycarbonate groups of grafted polymer on the surface to give branched polymer-grafted glass plate. The cationic polymerization of vinyl monomers was also successfully initiated by benzylium perchlorate groups introduced onto the glass plate surface and the corresponding polymers were grafted onto the surface. The contact angle of the glass plate surface obtained from the cationic polymerization of styrene was larger than that obtained from the radical polymerization. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2165–2172, 1997     

Grafting of polymers onto vapor grown carbon fiber surface by ligand-exchange reaction of ferrocene moieties of polymer with polycondensed aromatic rings of the wall-surface

To improve the dispersibility of vapor grown carbon fiber (VGCF) in solvents, the grafting of copolymer containing vinyl ferrocene (VFE) onto the surface by ligand-exchange reaction between ferrocene moieties of the copolymer and polycondensed aromatic rings of VGCF was investigated. The copolymer containing VFE was prepared by the radical copolymerization of VFE with methyl methacrylate (MMA) using 2, 2′-azobisisobutyronitrole as an initiator. It was found that by heating of VGCF with poly(VFE-co-MMA) in the presence of AlCl₃ and Al powder, the copolymer was grafted onto the wall-surface: the percentage of grafting reached to 57.5%. It is considered that the copolymer was grafted onto VGCF surface by ligand-exchange reaction between ferrocene moieties of the copolymer and polycondensed aromatic rings of VGCF. In addition, carboxyl groups were successfully introduced onto VGCF wall-surface by the ligand-exchange reaction of 1,1′-dicarboxyferrocene with VGCF in the presence of AlCl₃ and Al powder. The carboxyl groups on VGCF were reacted with hydroxyl-terminated polymers to give the corresponding polymer-grafted VGCF. The polymer-grafted VGCF gave a stable colloidal dispersion in solvents for grafted polymer. The electric properties of composite prepared from polymer-grafted VGCF in solvent vapor were investigated.     

Graft polymerization of vinyl monomers from initiating groups introduced onto polymethylsiloxane-coated titanium dioxide modified with alcoholic hydroxyl groups

The grafting of vinyl polymers onto the surface of polymethylsiloxane-coated titanium dioxide modified with alcoholic hydroxyl groups (Ti/Si–R–OH) were investigated. The introduction of azo and trichloroacetyl groups onto the surface of Ti/Si–R–OH was achieved by the reaction of the surface alcoholic hydroxyl groups with 4,4′-azobis(4-cyanopentanoic acid) and trichloroacetyl isocyanate, respectively. The radical polymerizations of vinyl monomers were successfully initiated by the azo groups introduced onto the surface and by the system consisting of Mo(CO)₆ and Ti/Si–R–COCCl₃. During the polymerization, the corresponding polymers were effectively grafted onto the titanium dioxide surface through propagation from surface radicals formed by the decomposition of azo groups and by the reaction of Mo(CO)₆ with trichloroacetyl groups on the surface. The percentage of grafting and grafting efficiency in the graft polymerization initiated by the system consisting of Ti/Si–R–COCCl₃ and Mo(CO)₆ were much larger than those initiated by azo groups. The polymer-grafted titanium dioxide was found to produce a stable colloidal dispersion in good solvents for the grafted polymer. The dispersibility of poly(N,N-diethylacrylamide)-grafted titanium dioxide in water was controlled by temperature. In addition, the wettability of the surface of titanium dioxide to water was readily controlled by grafting of hydrophilic or hydrophobic polymers.     

Postgrafting of vinyl polymers onto hyperbranched poly(amidoamine)-grafted nano-sized silica surface

To prepare polymer-grafted nano-sized silica with hydrophilic core and hydrophobic shell and with higher percentage of grafting, the postgraft polymerization of vinyl polymers onto hyperbranched poly(amidoamine)-grafted (PAMAM-grafted) nano-sized silica initiated by the system consisting of Mo(CO)₆ and terminal trichloroacetyl groups of PAMAM-grafted silica was investigated. The introduction of trichloroacetyl groups onto PAMAM-grafted silica surfaces was readily achieved by the reaction of trichloroacetyl isocyanate with terminal amino groups of PAMAM-grafted silica. It was found that the polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and glycidyl methacrylate (GMA) was successfully initiated by the system consisting of Mo(CO)₆ and terminal trichloroacetyl groups of PAMAM-grafted silica. In the polymerization, the corresponding vinyl polymers were effectively postgrafted onto PAMAM-grafted silica, based on the propagation of polymer from surface radicals formed by the reaction of terminal trichloroacetyl groups with Mo(CO)₆: the percentage of PMMA postgrafting onto PAMAM-grafted silica reached to 400% after 30 min, but the formation of gel was observed after 35 min. The formation of gel tends to decrease by use of hyperbranched PAMAM-grafted silica with higher percentage of grafting. The vinyl polymer-postgrafted nano-sized silica gave a stable colloidal dispersion in various organic solvents.     

Grafting of branched polymers onto nano-sized silica surface: Postgrafting of polymers with pendant isocyanate groups of polymer chain grafted onto nano-sized silica surface

To control the surface wettability of nano-sized silica surface, the postgrafting of hydrophilic and hydrophobic polymers to grafted polymer chains on the surface was investigated. Polymers having blocked isocyanate groups were successfully grafted onto nano-sized silica surface by the graft copolymerization of methyl methacrylate (MMA) with 2-(O-[1′-methylpropylideneamino]caboxyamino)ethyl methacrylate (MOIB) initiated by azo groups previously introduced onto the surface. The blocked isocyanate groups of poly(MMA-co-MOIB)-grafted silica were stable in a desiccator, but isocyanate groups were readily regenerated by heating at 150 °C. The hydrophilic polymers, such as poly(ethylene glycol) (PEG) and poly(ethyleneimine) (PEI), were postgrafted onto the poly(MMA-co-MOIB)-grafted silica by the reaction of functional groups of PEG and PEI with pendant isocyanate groups of poly(MMA-co-MOI)-grafted silica to give branched polymer-grafted silica. The percentage of grafting increased with increasing molecular weight of PEG, but the number of postgrafted chain decreased, because of steric hindrance. The hydrophobic polymers, such as poly(dimethylsiloxane) were also postgrafted onto poly(MMA-co-MOI)-grafted silica. It was found that the grafting of hydrophobic polymer and the postgrafting of hydrophilic polymer branches readily controls the wettability of silica surface to water.     

Surface grafting of polymer onto carbon thin film

The surface grafting of polymers onto carbon thin film deposited on a glass plate was achieved by two methods: the graft polymerization initiated by initiating groups introduced onto the surface; and the trapping of polymer radicals by surface aromatic rings of the thin film. It was found that the radical and cationic graft polymerization of vinyl monomers are initiated by azo and acylium perchlorate groups introduced onto the surface, respectively, and the corresponding polymers are grafted onto the surface: the surface grafting of polymers were confirmed by the contact angle of the surface with water. In addition, the anionic ring-opening alternating copolymerization of epoxides with cyclic acid anhydrides was found to be initiated by potassium carboxylate groups on the carbon thin film to give the corresponding polyester-grafted carbon thin film. On the other hand, polymer radicals formed by the decomposition of azo polymer, such as poly(polydimethylsiloxane-azobiscyanopentanoate) and poly(polyoxyethylene-azobiscyanopentanoate), were successfully trapped by the surface aromatic rings of carbon thin film and polydimethylsiloxane and polyoxyethylene were grafted onto the surface. © 1995 John Wiley & Sons, Inc.     

Graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto silica surface by Michael addition

The introduction of peroxycarbonate groups onto a silica surface and the graft polymerization of vinyl monomers initiated by peroxycarbonate groups introduced onto a silica surface were investigated. The introduction of peroxycarbonate groups onto a silica surface was achieved by Michael addition of amino groups introduced onto the silica surface to t‐butylperoxy‐2‐methacryloyloxyethylcarbonate (HEPO). The amount of peroxycarbonate groups was determined to be 0.17 mmol/g. The graft polymerization of various vinyl monomers such as styrene (St), N‐vinyl‐2‐pyrrolidinone (NVPD), and 2‐hydroxyethyl methacrylate (HEMA) was initiated by peroxycarbonate groups introduced onto the silica surface to give the corresponding polymer‐grafted silicas. The percentage of poly(St)‐grafting reached about 120% after 5 h. This means that 1.20 g of poly(St) is grafted onto 1.0 g of silica. The surface of poly(St)‐grafted silica shows a hydrophobic nature, but the surfaces of poly(NVPD) and poly(HEMA)‐grafted silica show a hydrophilic nature. Furthermore, the poly(St)‐grafted silica was found to give a stable colloidal dispersion in a good solvent for the grafted polymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1491–1497, 1999     

Surface grafting of polymers onto aramid powder: graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface of aramid powder

The radical graft polymerization of vinyl monomers onto the surface of aramid powder, i.e., poly(p-phenylene terephthalamide) powder, initiated by azo groups introduced onto the surface was investigated. The introduction of azo groups onto the aramid surface was achieved by the reaction of surface acyl chloride groups, which were introduced by the treatment of aramid powder with adipoyl dichloride, with 2,2′-azobis[2-(2-imidazolyn-2-yl)propane] in the presence of pyridine: the amount of azo groups thus introduced onto the surface was determined to be 0.57 mmol/g by elemental analysis. It was found that the polymerizations of methyl methacrylate (MMA) and styrene were successfully initiated by the azo groups on the surface and that the corresponding polymers were grafted onto the surface. The percentage of surface grafting of polystyrene and poly(methyl methacrylate) (PMMA) increased up to 37.6 and 26.5%, respectively. Thermogravimetric analysis of polymer surface-grafted aramid powder confirmed that the grafting of polymers is limited on the surface. The polymerization rate was found to bear a first-order dependence on the concentration of aramid powder having azo groups. This suggests that in graft polymerization, unimolecular termination preferentially proceeds.     

Responsiveness of electric resistance of polymer-grafted carbon black/alumina gel composite against solvent vapor and solute in solution

The carbon black/alumina gel composites were prepared by sol-gel reaction of aluminum isopropoxide in the presence of polymer-grafted carbon black. The electric resistance of the alumina gel composite from polymer-grafted carbon black was very sensitive to vapor of good solvent for grafted polymer on carbon black: the electric resistance of the alumina gel composite suddenly decreased in solvent vapor and returned to initial resistance when it was transferred into dry air. The effect of surface area and particle size of carbon black on the responsiveness was also investigated. In addition, the electric resistance of the alumina gel composite was found to respond to water and methanol in n-hexane and diethyl ether.     

Suface grafting of polymers onto nanodiamond by ligand-exchange reaction of ferrocene moieties of polymers with polycondensed aromatic rings of the surface

To improve the dispersibility of nanodiamond (ND) in solvents and polymer matrices, the grafting of copolymers containing vinyl ferrocene (Vf) onto the surface by a ligand-exchange reaction with ferrocene moieties of the copolymer and polycondensed aromatic rings of ND surface was investigated. The copolymer containing Vf was prepared by the radical copolymerization of Vf with vinyl monomers, such as methyl methacrylate (MMA), styrene (St), and N-isopropylacrylamide (NIPAM), using 2, 2′-azobisisobutyronitrile as an initiator. It was found that by heating of ND with poly(Vf-co-MMA), poly(Vf-co-St), and poly(Vf-co-NIPAN) in the presence of AlCl₃ and Al powder as catalysts, the corresponding copolymer was successfully grafted onto the surface. On the contrary, in the absence of AlCl₃, no grafting of these copolymers was observed. The grafting of polymers onto the ND surface was confirmed by FT-IR. These polymer-grafted NDs were found to give stable dispersions in solvents for the grafted polymer. In addition, the dispersibility of poly(Vf-co-NIPAM)-grafted ND uniformly dispersed in water below 32 °C but precipitated above the temperature. Therefore, it was concluded that the dispersibility of ND in water could be controlled by the temperature of water.     

Synthesis of vinylferrocene and the ligand-exchange reaction between its copolymer and carbon nanotubes

To improve the dispersibility of carbon nanotubes (CNTs), poly(vinylferrocene-co-styrene) (poly (Vf-co-St)), was grafted onto the surface of CNTs by a ligand-exchange reaction. Poly(Vf-co-St) was obtained by a radical copolymerization reaction using styrene and vinylferrocene as the monomers. The vinylferrocene was synthesized from ferrocene via a Friedel-Crafts acylation. The molecular weight, molecular weight distribution, and amount of Vf in the poly(Vf-co-St) were 1.32 × 10⁴, 1.69 and 17.6% respectively. The degree of grafting of the copolymer onto the CNTs surface was calculated from thermogravimetric analysis and varied from 27.1% to 79.7%. The addition of the poly(Vf-co-St) greatly promoted the dispersibility of the modified CNTs in anhydrous alcohol. The electrical conductivity of composites prepared from the polymer-grafted CNTs and copolymer (acrylonitrile, 1,3-butadiene and styrene, ABS) strongly depended on the degree of grafting. These results show that the amount of polymer grafted onto the surface of CNTs can be controlled and that the electrical properties of composites prepared with these grafted polymers can be tuned.     

An example of free radical graft polymerization where the mechanism from-to applies

Free-radical grafting on natural and synthetic polymers is a method widely used to modify these polymers chemically. A number of these chemical systems show an unexpected behaviour of the polymerization rate when the monomer concentration is sufficiently high: it decreases and sometimes it increases afterwards. Here, the effect of varying the monomer concentration on the graft yield when grafting methyl acrylate, vinyl acetate and a mixture of both monomers onto cellulose initiated by ceric ions is discussed, considering a three-component mechanism of grafting (mechanisms from, onto and from-to). It is suggested that the unexpected behaviour indicated above is accounted for by the presence of the grafting mechanism from-to. Some knowledge about the copolymer structure can be reached by using this mechanistic approach.     

The free radical polymerization of vinyl monomers in the presence of carbon black

The polymerization of vinyl monomers has been carried out in the presence of furnace blacks using initiators such as 2,2′-azobisisobutyronitrile (AIBN) and benzoyl peroxide (Bz₂O₂) in nitrogen or oxygen atmosphere. The results indicate that free radicals form by the decomposition of initiators reacting with carbon blacks to give active sites on their surface which then capture either the free radicals or the growing polymer radicals. Using the monomers with negative e values, such as styrene and vinyl acetate, a marked retardation was observed in Bz₂O₂-initiated polymerization in the presence of furnace blacks, while a moderate inhibition was found in the polymerization initiated by AIBN. The polymerization reaction using Bz₂O₂ was found to be very sensitive to oxygen in the presence of furnace blacks and the involvement of oxygen was found to promote grafting onto the surface of carbon black by the growing polymer radicals, consequently giving polymer-grafted particles while hindering the formation of homopolymers. Furthermore, the reaction of Bz₂O₂ with the surface of furnace blacks in oxygen atmosphere has been studied in carbon tetrachloride at 45°C. The resulting carbon blacks show an increase in the number of surface quinone groups with an increase in reaction time.     

Reactive carbon black having acyl imidazole or acid anhydride groups: Preparation and reaction with functional polymers having hydroxyl or amino groups

The introduction of acyl imidazole groups onto a carbon black surface was achieved by the reaction of the carboxyl groups on the surface with N N′-carbonyldiimidazole, the loading of acyl imidazole groups introduced was determined to be 0.28 mmol/g. In addition, reactive carbon black having acid anhydride groups was prepared by the reaction of phenolic hydroxyl groups with trimellitic anhydride chloride; the amount of acid anhydride groups introduced onto the surface was determined to be 0.20 mmol/g. The reaction of acyl imidazole groups on carbon black with commercially available polymers having hydroxyl or amino groups such resulted in polymers that were found to be grafted onto the surface via ester or amide bonds. The percentage of grafting of diol-type poly(propylene glycol) and diamine-type polydimethylsiloxane was increased to 27.2 % and 42.5 %, respectively. Furthermore, acid anhydride groups on carbon black also reacted with functional polymers having hydroxyl or amino groups to give polymer-grafted carbon blacks. The grafting reaction was accelerated by the addition of tertiary amines. These polymer-grafted carbon blacks produced a stable colloidal dispersion in good solvents for the grafted polymer, but readily precipitated in poor solvents.     

Synthesis of polymer‐grafted natural rubbers by radical photopolymerization of vinyl monomers initiated from the rubber chains

The synthesis of polymer‐grafted natural rubbers (NRs) was considered through photopolymerization of vinyl monomers initiated from N,N‐diethyldithiocarbamate groups previously introduced onto cis 1,4‐polyisoprene units of NR chains. The development of the procedure was made with methyl methacrylate (MMA) as monomer. First, initiation of MMA photopolymerization was tested using a model molecule of the N,N‐diethyldithiocarbamate‐functionalized 1,4‐polyisoprene unit to verify the feasibility of the procedure considered. Then, MMA polymerization was successfully initiated from N,N‐diethyldithiocarbamate‐functionalized NR backbone used as macroinitiator, and the conditions of grafting were optimized. It was shown that MMA grafting could occur either in monomer medium, in solution in toluene, and in latex medium, and that the quantities of homopolymer formed were still low. Thereafter, grafting studies were performed with other vinyl monomers (styrene, methacrylonitrile, acrylamide, acrylic acid) showing that grafting efficiency depends essentially on the nature of the monomer. The method developed here was shown particularly well adapted for the synthesis of polymer‐grafted NR with monomers of low polarity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel gas sensor from crystalline polymer-grafted carbon black: responsibility of electric resistance of composite from crystalline polymer-grafted carbon black against solvent vapor

Summary Crystalline polymers, such as poly(ɛ-caprolactone) (PCL), poly(ethylene adipate) (PEA), and polyethylene (PE), were successfully grafted onto carbon black surface by direct condensation of terminal groups of these polymers with carboxyl groups on the surface using N,N'-dicyclohexylcarbodiimide as a condensing agent. The electric resistance of a composite prepared from these crystalline polymer-grafted carbon black drastically increased to 10⁴–10⁵ times of initial resistance in good solvent vapor of grafted polymer and returned to initial resistance when it was transferred into dry air. However, the change of electric resistance of the composite hardly observed in poor solvent vapor. These results suggest that these composite can be applied as a novel gas sensor. Received: 18 February 1999/Accepted: 25 March 1999     

Preparation of amphiphilic carbon black by postgrafting of polyethyleneimine to grafted polymer chains on the surface

Summary To prepare amphiphilic carbon black, we investigated the postgrafting reaction of polyethyleneimine (PEI) with pendant glycidyl groups of grafted polymer on carbon black surface. The grafting of polymers having pendant glycidyl groups onto carbon black surface was achieved by the copolymerization of glycidyl methacrylate (GMA) with methyl methacrylate (MMA) initiated by azo groups introduced onto the surface. Pendant glycidyl groups of poly(GMA-co-MMA)-grafted carbon black was found to react with PEI, and the corresponding polymers postgrafted to the grafted copolymer chains on carbon black surface: the percentage of PEI-postgrafting was readily controlled by the reaction conditions. PEI-postgrafted to poly(GMA-co-MMA)-grafted carbon black, whose PEI postgrafting is 3.9% showed amphiphilic nature and acted as an emulsifier. Received: 13 April 1998/Revised version: 20 May 1998/Accepted: 22 May 1998     

Functionalization of multi-walled carbon nanotubes by free radical graft polymerization initiated from photoinduced surface groups

An easy method for preparing polymer-grafted multi-walled carbon nanotubes (MWCNTs) with high graft yields was developed by using free radical graft polymerization (FRGP) from photoinduced surface initiating groups on MWCNTs. The surface initiating groups were first formed by UV irradiation of MWCNTs previously modified with 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (VA-086) (MWCNTs-OH) in the presence of benzophenone in benzene, and the subsequent FRGP of vinyl monomers was carried out consecutively at 80 °C. The surface initiating groups were homolytically cleaved to surface radicals and semipinacol radicals by thermal activation, and the surface radicals initiated FRGP. Polystyrene, poly(butyl acrylate), poly(methyl methacrylate), and poly(2-hydroxyethyl methacrylate) were successfully grafted onto the surface of MWCNTs with graft yields of 46, 26, 37, and 53 wt.%, respectively, after 15 h of FRGP.     

Peroxide‐catalyzed swell grafting of maleic anhydride onto polypropylene

A new grafting method was developed to incorporate maleic anhydride directly onto solid‐state polypropylene powders. Maleic anhydride grafts altered the nonpolar characteristics of polypropylene so that much better mixing was achieved in blends and composites of polypropylene with many other polymers and fillers. Maleic anhydride was grafted onto polypropylene by the peroxide‐catalyzed swell grafting method, with a maximum extent of grafting of 4.60%. Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, tensile testing, and impact testing were used to characterize the isotactic polypropylene (iPP), maleic anhydride grafted polypropylene (MAH‐g‐iPP), and (isotactic polypropylene)/(calcium carbonate) composites (iPP/CaCO₃). The crystallinity and heat of fusion of the MAH‐g‐iPP decreased as the extent of grafting increased. The mechanical properties of the CaCO₃ filled polypropylene were improved by adding MAH‐g‐iPP as a compatibilizing agent. The dispersion of the fillers in the polymer matrix and the adhesion between the CaCO₃ particles and the polymer matrix were improved by adding the compatibilizer.