Study on radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. I. Radiation-induced polymerization of styrene adsorbed on several inorganic substances

The radiation-induced polymerization of styrene adsorbed on silica gel, white carbon, silicic acid anhydride, zeolite, and activated alumina was carried out to elucidate the effect of properties of inorganic substances on the polymerization. The rate of adsorbed state polymerization on these inorganic substances was very fast in comparison with that of bulk-state polymerization. The amount of unextractable polymer depends on the specific surface area and chemical compositions of these inorganic substances. Inorganic substances which contain aluminum as a component element are more likely to be grafted than those which consist of SiO₂ alone. The molecular weight and molecular weight distribution of unextractable polymer and extractable polymer differ from one another in each inorganic substance. In case of silicic acid anhydride, unextractable polymer has smaller molecular weight than extractable polymer. These results suggest that unextractable polymer cannot be extracted due to chemical bonds with the inorganic surface.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VIII. Polymerization of styrene and methyl methacrylate adsorbed on aerosil

Aerosil is silica having a purity which is very high compared with that of silica gel and having, unlike silica gel, no micropores. To investigate the effects of impurities and micropores on the radiation-induced polymerization of styrene and methyl methacrylate adsorbed on silica gel, the radiation-induced polymerization of styrene and methyl methacrylate adsorbed on Aerosil was carried out. The results of both the styrene–Aerosil 300 system and the methyl methacrylate–Aerosil 300 system were similar to those of the styrene–silica gel and methyl methacrylate–silica gel systems, respectively. This suggests that in the radiation-induced polymerization of both styrene–silica gel and methyl methacrylate–silica gel systems the impurity and the presence of micropores have almost no effects on the reaction mechanism. The effect of aluminum as an impurity was investigated on the styrene–Aerosil MOX 170 system. It was found that aluminum accelerated the cationic polymerization.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VII. Effect of pretreatment temperature of silica gel on styrene–silica gel system

To investigate the reaction mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effect of pretreatment temperature of silica gel was studied. Preheating of silica gel was carried out at 200, 500, and 800°C. The number of silanol groups of silica gel surface decreased as preheating temperature increased. The rate of polymerization on the silica gel preheated at 500°C was faster than that at 200°C, but the polymerization rate on the silica gel preheated at 800°C was the lowest. These results suggest that rate of polymerization on the silica gel is affected by the conditions of silica gel surface such as the number of silanol groups and the pore size. At the same monomer conversion, percent grafting decreased as preheating temperature of silica gel increased. The GPC spectra of both graft polymers and homopolymers have two peaks at all preheating temperatures. The monomer conversion of low molecular weight peaks of graft polymers decreased as preheating temperature of silica gel increased. This result suggests that there is a probability that the grafting sites of low molecular weight peaks of graft polymers somehow interact with silanol groups.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. X. Influence of H2O on the styrene–silica gel system

To elucidate the reaction mechanism of radiation-induced polymerization of the styrene—silica gel system, the influence of H₂O as adsorbed water and inhibitor of cationic polymerization was investigated by two methods. Monomer conversion decreased as H₂O increased. In general, percent grafting decreased as H₂O increased, but the presence of a small amount of H₂O increased the percent grafting. Grafting at 16 Mrad has a maximum value at a water content of about 0.2%. This seems to be due to two effects of H₂O: percent grafting increases due to restraint of cationic polymerization by H₂O, but the percent grafting decreases due to adsorption water which interrupts the contact of styrene with silica gel. In GPC spectra, the low molecular weight peaks of both graft polymers and homopolymers decreased when H₂O was added. The GPC results suggest that the number of positive holes which initiate cationic polymerization is very large.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. III. Effect of p-benzoquinone and ammonia on radiation-induced polymerization of styrene adsorbed on silica gel

In order to elucidate the mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effect of p-benzoquinone and ammonia was investigated. The high molecular weight GPC peaks of both graft polymers and homopolymers decreased with increasing p-benzoquinone concentration, while the low molecular weight peaks of both graft copolymers and homopolymers decreased with increasing ammonia concentration. The results indicate that the high molecular weight peaks of both graft and homopolymers are formed as a result of a radical mechanism and that the low molecular weight peaks of both types of polymers are formed by a cationic mechanism. In formation of both graft polymers and homopolymers both radical and cationic polymerization take place at the same time.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. IX. Preirradiation polymerization of styrene–silica gel system

Preirradiation polymerization of the styrene–silica gel system was studied in detail. Both graft polymers and homopolymers have bimodal GPC spectra. High molecular weight peaks were formed in a radical mechanism and the low molecular weight peaks were formed in a cationic mechanism as same as those in the simultaneous irradiation polymerization. The rate of formation of the low molecular weight peaks was very high compared with that of the high molecular weight peaks. Monomer conversion and percent grafting leveled off at about 1–2 Mrad. Radiation dose dependence of the four peaks were different from each other. Monomer conversion and percent grafting decreased as the preheating temperature of silica gel increased. The amount of the low molecular weight peaks of graft polymers depended on the number of silanol groups, as in the case of the simultaneous irradiation polymerization. A reaction mechanism for the preirradiation polymerization is proposed based on the results obtained.     

Radiation effect on polystyrene deposited and grafted on silica gel

The effect of radiation on polystyrene was studied in the presence and absence of silica gel by molecular weight measurement with GPC. Polystyrene crosslinked under vacuum in the absence of silica gel, but it either crosslinked or degraded by radiation, depending on the molecular weight of the polymer in the presence of silica gel. Part of the deposited polymer bonded to silica gel by radiation; the G value for graft-chain formation is in the range of 0.01–0.1. Irradiation of polystyrene grafted on silica gel resulted in degradation of the graft chain because of the transfer of energy from silica gel. The G value for main chain scission was about 2 when graft polymer was irradiated in the absence of homopolymer. The degradation of graft polymer was suppressed when the polymer was irradiated in the presence of homopolymer, and the amount of unextractable polymer from silica gel increased with increasing irradiation. This adds evidence to the estimation that an increase in grafting percent coupled with a slight decrease in molecular weight at a later stage of radiation-induced polymerization of styrene adsorbed on silica gel is due to a secondary effect of radiation on the polymer.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. IV. Dose rate and temperature dependences in the styrene–silica gel system

In order to elucidate the mechanism of radiation-induced polymerization of styrene adsorbed on silica gel, the effects of dose rate and irradiation temperature were studied in detail. Monomer conversion increased with increasing dose rate and temperature. At the same conversion, the percent grafting increased with decreasing dose rate and also with increasing temperature. In general, GPC spectra of graft polymers and homopolymers showed two peaks; the ratio of the two peaks changed with dose rate and irradiation temperature. The dose-rate exponents of the polymerization rate of four peaks were different from each other. The activation energies of radical polymerization and cationic polymerization were about 2.6 kcal/mole and 0 kcal/mole, respectively. Based on the results obtained, a reaction mechansim is proposed.     

Effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel was investigated with the monomer amounting from less than monolayer adsorption to more than the equilibrium adsorption. The rate of graft polymerization and the molecular weight of the polymer changed with the amount of monomer adsorbed on silica gel. Maximum grafting efficiency was obtained at monolayer adsorption. The molecular weight of graft polymer was higher than that of homopolymer in both radical and cationic polymerizations, and the ratio in molecular weight of graft polymer to that of homopolymer tends to be unity with increasing amount of adsorbed monomer. These results can mainly be explained in terms of the number of initiating species (radical and cation) that change in relation to the amount of adsorbed monomer. Propagation and termination change with amount of adsorbed monomer in relation to the molecular mobility of adsorbed monomer. A very high-molecular-weight graft polymer is formed only with a small amount of adsorbed monomer in the initial stage. The grafting percent with a large amount of adsorbed monomer increased after most of the monomer has been polymerized. Secondary effect of radiation on the graft and homopolymers due to energy transfer from silica gel is suggested from the complicated phenomena in the later stage of the reaction.     

Radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. VI. Temperature dependence and effects of additives on methyl methacrylate–silica gel system

To elucidate the reaction mechanism of radiation-induced polymerization of methyl methacrylate adsorbed on silica gel, the temperature dependence and effects of acetone and pyridine were investigated. It was found that even at ?78°C the polymerization rate was quite fast. The amounts of high molecular weight GPC peaks of both graft polymers and homopolymers increased with increasing irradiation temperature. The activation energy of the adsorbed state polymerization was low compared with that of bulk polymerization. The low molecular weight peaks of homopolymers decreased with acetone addition but were almost unaffected by pyridine. The low molecular weight peaks of homopolymers were thus polymerized by an anionic mechanism. In the methyl methacrylate–silica gel system both radical and anionic polymerization take place at the same time in formation of graft polymers and homopolymers. A reaction mechanism for the methyl methacrylate–silica gel system was proposed based on the results obtained to date.     

Immobilization of RAFT agents on silica nanoparticles utilizing an alternative functional group and subsequent surface‐initiated RAFT polymerization

Silica–polystyrene core‐shell particles were successfully prepared by surface‐mediated reversible addition fragmentation chain transfer (RAFT) polymerization of styrene monomer from the surfaces of the silica‐supported RAFT agents. Initially, macro‐RAFT agents were synthesized by RAFT polymerization of γ‐methacryloxypropyltrimethoxysilane (MPS) in the presence of chain transfer agents (CTAs). Immobilization of CTAs onto the silica surfaces was then performed by reacting silica with macro‐RAFT agents via a silane coupling. Grafting of polymer onto silica forms core‐shell nanostructures and shows a sharp contrast between silica core and polymer shell in the phase composition. The thickness of grafted‐polymer shell and the diameter of core‐shell particles increase with the increasing ratio of monomer to silica. A control experiment was carried out by conventional free radical emulsion copolymerization of MPS‐grafted silica and styrene under comparable conditions. The resulting data provide further insight into the chemical composition of grafted‐polymers that are grown from the silica surface through RAFT process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 467–484, 2009     

In situ radical transfer addition polymerization of styrene from silica nanoparticles

The in situ radical transfer addition polymerization of styrene from silica nanoparticles was carried out by the free radical polymerized of styrene in the presence of mercaptopropyl-modified silica nanoparticles as chain-transfer agent. The effects of the amount of the initiator, polymerizing temperature and polymerizing time on the convention of styrene (C) and the percentage of grafting were investigated. Results of elemental analysis, IR, X-ray photoelectron spectrometer and transmission electron microscope demonstrated that the desired polymer chains have been covalently bonded to the surface of the silica nanoparticles. A C of 42.56% and a PG of 38.10% could be achieved with the optimal condition. The polystyrene grafted silica nanoparticles could be separated and used as nanofiller for polymers.     

Effect of inorganic salt on the dose sensitivity of polymer gel dosimeter

The effect of inorganic salts, non-transition metal chlorides, on the dose sensitivity of methacrylic-acid-based polymer gel dosimeter is investigated. Dose-R₂ responses are obtained from magnetic resonance imaging data. Temperature increase due to exothermic polymerization reaction in the gel is also measured directly during irradiation. As a result, substantial increases in R₂ response are observed in the polymer gel dosimeter containing inorganic salt, especially with MgCl₂. The sensitivity of the gel with 1.0 M MgCl₂ is approximately 2.8 times higher than that of without MgCl₂. As the salt concentration increases, an increase of polymerization rate is also observed via the temperature measurements. These results indicate that inorganic salt acts as an accelerator for radiation-induced free-radical polymerization in methacrylic-acid-based gel.     

Effect of dose rate on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of dose rate on the rate of polymerization and molecular weight distribution of radiation-induced polymerization of styrene adsorbed on silica gel was studied in a wide dose rate range of 4.4 × 10⁴ to 3 × 10⁸ rad/hr by γ rays of ⁶⁰Co and electron beams with a Cockcroft-Walton-type accelerator. Dose rate dependence on the initial rate of polymerization was about 1 below 3 × 10⁷ rad/hr, and it decreased gradually at high dose rates. Throughout the dose rate range, graft polymerizations and homopolymerizations by cationic and radical mechanisms proceeded simultaneously. Dose rate dependence of the cationic polymerization was 1 below 3 × 10⁷ rad/hr, while dose rate dependence of the radical polymerization was 0.65 below 3 × 10⁷ rad/hr. At high dose rates, molecular weight and fraction of graft polymer decreased, and fraction of cationic polymerization increased. A very high-molecular-weight graft polymer was formed above 4.4 × 10⁵ rad/hr at the initial stage of the polymerization. The dose rate dependence of this polymerization was larger than 1 and decreased with increase in dose rate. The polymerization seems to be related to an excitation of monomer or growing chain.     

Graft polymerization of styrene initiated by covalently bonded peroxide groups on silica

The graft polymerization of styrene initiated by immobilized peroxide groups was investigated. Three different types of modification reactions were used to introduce peroxide groups which are directly attached onto the surface of two different silica supports. Silanol groups were chlorinated using thionyl chloride or tetrachlorosilane. In another reaction pathway 1,3,5-benzenetricarbonyl chloride enabled the introduction of free acid chloride residues bonded onto the surface of silica. tert-Butyl hydroperoxide (TBHP) was used to transform the chlorosilyl and the acid chloride groups into peroxide residues. In a further reaction step the covalently bonded peroxides initiated the polymerization of styrene to form grafted polystyrene directly attached onto the silica support. Solid-state 13C CP/MAS NMR spectroscopy, and thermogravimetric and scanning electron microscope measurements enabled a clear structure and property elucidation of the different bonded phases. The highest amount of grafted polystyrene was achieved employing the acid chloride synthesis pathway with silica-gel, whereas modification of spherical silica only led to minor amounts of grafted polymer. The results contribute to the evolving need to understand particle surface modifications and may have positive impact on development of new HPLC stationary phases for improved elutant resolution.     

无机物表面引发聚合反应制备端接枝聚合物膜*

无机物表面引发聚合反应是聚合物合成化学的又一新领域。分子自组装技术的发展使得各种类型的聚合反应都有转移到固体表面进行的可能。本文综述了无机物表面引发聚合反应用于制备高键合密度端接枝聚合物膜的研究进展,并对其今后的发展提出了见解。     

Synthesis of hydrophilic polymer-grafted ultrafine inorganic oxide particles in protic media at ambient temperature via atom transfer radical polymerization: use of an electrostatically adsorbed polyelectrolytic macroinitiator

A new approach for the surface grafting of polymer chains to colloidal substrates is described. A cationic macroinitiator has been designed for the surface polymerization of a wide range ofhydrophilic methacrylates from ultrafine inorganic oxide sols by atom transfer radical polymerization in protic media at ambient temperature. One advantage of this approach is that it allows one-pot syntheses: the macroinitiator is adsorbed onto the sol, followed by an in situ polymerization. Nonionic, cationic, and betaine monomers can be polymerized directly by this protocol, with reasonably high conversions being obtained, as judged by 1H NMR spectroscopy. Anionic monomers such as sodium 4-styrenesulfonate cannot be polymerized directly due to incompatibility problems with the cationic macroinitiator-coated sol. However, hydroxylated monomers such as glycerol monomethacrylate can be surface-polymerized and then converted to anionic polyelectrolytes by reaction with succinic anhydride under mild conditions. This derivatization was confirmed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic analysis. Thermogravimetry was used to assess the degree of polymer grafting. Higher target degrees of polymerization led to increased grafted polymer loadings, as expected. Particle morphologies and relative degrees of dispersion in aqueous solution were assessed by transmission electron microscopy and dynamic light scattering, respectively. Surface characterization of the polymer-grafted sols was achieved by X-ray photoelectron spectroscopy and aqueous electrophoresis measurements. Most of the data reported in this study concern surface polymerizations from ultrafine silica sols, but some preliminary data for ultrafine tin(IV) oxide sols are also presented. Since most surfaces are negatively charged, this cationic macroinitiator approach can, in principle, be extended to include a wide range of sols, latexes, and planar substrates without requiring a separate surface functionalization step.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. V. Effects of p-benzoquinone and dose rate on methyl methacrylate–silica gel system

In order to elucidate the mechanism of radiation-induced polymerization of methyl methacrylate adsorbed on silica gel, the effects of p-benzoquinone addition and dose rate were studied in detail. Most of the polymerization is inhibited by p-benzoquinone at levels above 10^-2 mole/l. The GPC spectra of both graft polymers and homopolymers show two peaks. The high molecular weight material appears to have been formed by polymerization by a radical mechanism, because these peaks decrease as p-benzoquinone concentration increases; on the other hand, their low molecular weight polymers seem to be products of an ionic polymerization mechanism because those peaks are almost not affected by p-benzoquinone. The four GPC peaks differ in dose rate dependences of their polymerization rate. The dose-rate exponents of polymerization rate were obtained for the four GPC peaks. The behavior of the low molecular weight peaks of graft polymers and homopolymers were quite different, suggesting that the polymers differ considerably in formation mechanism.     

Surface grafting of polymers onto inorganic ultrafine particles: Reaction of functional polymers with acid anhydride groups introduced onto inorganic ultrafine particles

The surface grafting onto inorganic ultrafine particles, such as silica, titanium oxide, and ferrite, by the reaction of acid anhydride groups on the surfaces with functional polymers having hydroxyl and amino groups was examined. The introduction of acid anhydride groups onto inorganic ultrafine particle was achieved by the reaction of hydroxyl groups on these surfaces with 4-trimethoxysilyltetrahydrophthalic anhydride in toluene. The amount of acid anhydride groups introduced onto the surface of ultrafine silica, titanium oxide, and ferrite was determined to be 0.96, 0.47, and 0.31 mmol/g, respectively, by elemental analysis. Functional polymers having terminal hydroxyl or amino groups, such as diol-type poly(propylene glycol) (PPG), and diamine-type polydimethylsiloxane (SDA), reacted with acid anhydride groups on these ultrafine particles to give polymer-grafted ultrafine particles: PPG and SDA were considered to be grafted onto these surfaces with ester and amide bond, respectively. The percentage of grafting increased with increasing acid anhydride group content of the surface: the percentage of grafting of SDA (M_n = 3.9 × 10³) onto silica, titanium oxide, and ferrite reaching 64.7, 33.7, and 24.1%, respectively. These polymer-grafted ultrafine particles gave a stable colloidal dispersion in organic solvents.     

Effect of surfactant adsorbed on encapsulation of fine inorganic powder with soapless emulsion polymerization

The encapsulation of fine inorganic powder was carried out with the soapless emulsion polymerization of methyl methacrylate in water in the presence of the powder, a layer of surfactant being adsorbed. The powder used was titanium dioxide. Surfactants added prior to the polymerization were sodium dodecyl sulfate, dodecyltrimethyl ammonium bromide, and polyoxyethylene sorbitan mono-oleate. The encapsulation state of the powder with polymer was closely related to the amount of surfactant adsorbed on the powder; and an amount of adsorption above a certain value was necessary for uniform encapsulation. Ionic surfactants were more useful than nonionic in the surfactants used, and could be adsorbed utilizing the electrostatic interaction between powder and the ionic end group. The combination of electric charges between the ionic end groups of surfactant and initiator was found to influence the molecular weight of capsulating polymer.