Vinyl polymerization. 416. Polymerization of vinyl monomer initiated by polyethyleneglycol

The polymerization of vinyl monomer initiated by polyethyleneglycol (PEG) in aqueous solution was carried out at 85°C with shaking. Acrylonitrile (AN), methyl methacrylate (MMA), and methacrylic acid were polymerized by PEG–300 (M?_n = 300), whereas styrene was not. The effects of the amounts of monomer and PEG, the molecular weight of PEG, and the hydrophobic group at the end of PEG molecule on the polymerization were studied. The selectivity of vinyl monomer and the effect of the hydrophobic group are discussed according to “the concept of hard and soft hydrophobic areas and monomers.” The kinetics of the polymerization was investigated. The overall activation energy in the polymerization of AN was estimated as 37.9 kJ mol^?1. The polymerization was effected by a radical mechanism.     

Radiation-induced solid-state polymerization of methacrylic acid. II. In-source polymerization

The in-source polymerization of methacrylic acid in the solid state with γ-rays was studied. The conversion rates at various temperatures were obtained as well as the radical concentrations by the measurements of ESR spectrum. The rate of polymerization was found to be proportional to I^0.65 at 0°C. The results could be interpreted on the basis of the assumption that the rate of propagation is proportional to the concentration of the propagating radical, of the monomer, and of the polymer. The addition of water to the monomer seems to accelerate the polymerization reaction. The change of the line shape of the propagating radical during polymerization was interpreted in terms of the change of the matrix which surrounds the propagating radical.     

Emulsion polymerization of vinyl acetate. II

The emulsion polymerization of vinyl acetate was investigated at low ionic strengths and has quite unusual kinetics. The rate of polymerization is dependent on the initiator concentration to the first power and independent of soap concentration. In seeded polymerizations, the rate of polymerization depends on initiator to the 0.8 power, particle concentration to the 0.2 power, and monomer volume to 0.35 power. In all cases the rate of polymerization is almost independent of monomer concentration in the particles until 85–90% conversion. These results were rationalized by the following mechanism: (a) polymerization initiates in the aqueous phase because of the solubility of the monomer and is stabilized there by adsorption of ionic soap on the growing polymer molecule; (b) the growing polymer is swept up by a particle at a degree of polymerization (under our conditions) of about 50–200. Growth continues in the particle. This sweep-up is activation-controlled as both particle and polymer are charged. (c) Chain transfer to the acetyl group of monomer gives a new small radical which cyclizes to the water-soluble butyrolactonyl radical, and reinitiates polymerization in the aqueous phase; (d) the main termination step is reaction of an uncharged butyrolactonyl radical with a growing aqueous polymer radical. A secondary reaction at low ionic strength is sweep-up of an aqueous radical by a particle containing a radical. At high ionic strength, this is the major termination step. The unusual kinetic steps are justified by data from the literature. They are combined with the usual mechanisms operating for vinyl acetate polymerization and kinetic equations are derived and integrated. The integral equations were compared with the experimental data and shown to match it almost completely over the whole range of experimental variables.     

Radiation-induced graft polymerization of metal-containing monomers

Graft polymerization of acrylates and acrylamide complexes of Mn(II), Cr(III), Fe(III), Co(II), Ni(II), and Cu(II) from alcohol solutions onto a polyethylene powder preirradiated in air up to total doses of 10–300 kJ/kg was studied. Graft copolymers with a metal content of as high as 1.7 mass% were obtained. The addition of a σ- or a coordinate-bound metal atom to the monomer molecule (acrylic acid, acrylamide) was shown to decelerate the process of thermal homopolymerization by 4 to 8 times, significantly reduce the reaction order in respect with monomer concentration in solution, and in most cases produce no effect on the polymer chain termination mechanism. The grafting of metal-containing monomers was found not to alter the structure of the monomer unit, valent state, and coordination of the metal atom, either. The graft polymerization of the monomers from solution is distinguished by a weak effect of the radical reaction inhibitors. The effective activation energies for the grafting of the metal-containing monomers lie within 42–60 kJ/mol.     

Solvent effects on free-radical polymerization, 4. Modelling of hompolymerization

A new so-called reactant-solvent complex model is proposed to describe the effect of solvent on chain propagation in homopolymerization. It takes into account complex formation of both monomer and radical with solvent by equilibria. Evaluation methods presented permit to estimate the complex equilibrium constant K which is assumed to be nearly the same for both monomer and radical complexation and the relative reactivity ratio r₁₁, for complexed monomer. Measured reaction rates as function of monomer concentration are needed for calculations.     

Quantitative theory of iniferter polymerization. I. Kinetics

On the basis of a rather general scheme of elementary reactions of radical polymerization conducted in the presence of iniferters, kinetic equations have been derived describing this process over the whole range of monomer conversion. Proceeding from thorough analysis of these equations, different regimes of polymerization have been found that differ in values of order with respect to the iniferter and monomer of the initial rate of polymerization. Conditions for kinetic parameters have been formulated whose fulfillment predetermines that radical polymerization occurs according to the iniferter mechanism. © 1994 John Wiley & Sons. Inc.     

Photoinitiated polymerization of styrene from self‐assembled monolayers on gold. II. Grafting rates and extraction

Ultrathin films of polystyrene (PS) were grown from self‐assembled monolayers by the “grafting‐from” technique. The initiating system consisted of a dithiol azobisisobutyronitrile‐type free‐radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform‐reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water‐jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284–3291, 2002     

Block polymer preparation via both anionic and free radical polymerization

A new method of block polymer preparation using combined anionic and free radical polymerization was investigated. In the method the first monomer was polymerized anionically. The resulting polymeric anions were then reacted with an episulfide to form a polymer with mercaptan end-groups. This mercapto—polymer was mixed with a second monomer(s) in an inert solvent for the free radical polymerization. Conventional free radical initiation methods were used to initiate the polymerization of the second monomer but because of the high chain transfer constant of the mercaptan groups, a large number of the free radical chains would grow from the first polymer to form a block polymer. Block polymers difficult or impossible to make by direct anionic polymerization can thus be prepared. Several block polymers, including the new thermoplastic elastomers, poly[(styrene-co-acrylonitrile)-b-butadiene-b-(styrene-co-acrylonitrile)] and poly(bromostyrene-b-butadiene-b-bromostyrene) were prepared by this method.     

Vinyl polymerization. 413. Polymerization of vinyl monomer initiated by poly(vinylbenzyltrimethyl)-ammonium chloride

The polymerization of vinyl monomer initiated by an aqueous solution of poly(vinylbenzyltrimethyl)ammonium chloride (Q-PVBACI) was carried out at 85°C. Styrene, p-chlorostyrene, methyl methacrylate, and i-butyl methacrylate were polymerized, whereas acrylonitrile and vinyl acetate were not. The effects of the amounts of vinyl monomer, Q-PVBACI, and water on the conversion of vinyl monomer were studied. The overall activation energy in the polymerization of styrene was estimated as 79.1 kJ mol^?1. The polymerization proceeded through a radical mechanism. The selectivity of vinyl monomer was discussed by “a concept of hard and soft hydrophobic areas and monomers.”     

Effects of metal salts on polymerization. Part VII. Radical polymerization and spectra of vinylpyridine in the presence of cobaltous chloride

The radical polymerizability of vinylpyridines in the presence of cobaltous chloride was studied in DMF solution, and the results were correlated with the spectroscopic data obtained for methanol solution. In general, the behavior of vinylpyridine complexed with cobaltous chloride is qualitatively the same as that of zinc complexes reported previously. The rates of polymerization were enhanced by the addition of cobaltous chloride when 4-vinylpyridine(4-VP) or 2-methyl-5-vinylpyridine(MVP) was the monomer, whereas the polymerization of 2-vinylpyridine(2-VP) was retarded by cobaltous chloride. The monomer reactivity of all the vinylpyridines was also enhanced by complex formation as studied by copolymerization with styrene. The enhancement of reactivity of 4-VP complexed with cobaltous chloride is somewhat smaller than that of the corresponding zinc complex.     

Radiation-induced solid-state polymerization of methacrylic acid. III. Post-polymerization

The post-polymerization of methacrylic acid in the solid state was studied. The decay of the trapped radicals was also observed by ESR measurements. The decay of trapped radicals is a first-order reaction below 0°C but a second-order reaction at + 10°C. The results of the post-polymerization were compared with the results of radical decay measurements. A kinetic scheme was proposed for the post-polymerization of methacrylic acid. The effect of conditions of monomer crystallization on the polymer yield was also investigated. Fine crystals gave a greater limiting conversion than large crystals. The addition of water to the monomer increased the polymer yield. The change in the ESR spectrum during post-polymerization was interpreted in terms of the change in the matrix which surrounds the propagating radicals.     

Synthesis of polymers by template polymerization. I. Template polymerization of poly(methacrylic acid) with β‐cyclodextrin

A novel template monomer with multiple methacryloyl groups was synthesized with β‐cyclodextrin by the acetylation of primary hydroxyl groups and the esterification of secondary hydroxyl groups with methacrylic acid anhydride. The average number of methacryloyl groups in the monomer was 11. The radical polymerization of the monomer was carried out with the following initiators: α,α′‐azobisisobutylonitrile, H₂O₂? Fe²⁺ redox initiator, p‐xylyl‐N,N‐dimethyldithiocarbamate (XDC), and α‐bromo‐p‐xylyl‐N,N‐dimethyldithiocarbamate (BXDC). When the concentration of the monomer was less than 4.12 × 10^?3 M, polymerization was limited inside the molecule, and gelation of the system was hindered. For controlled radical photopolymerization with XDC and BXDC, the methacryloyl groups of the monomer were homogeneously polymerized, and poly(methacrylic acid) with a narrow molecular weight distribution was obtained by the hydrolysis of the polymerized products. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3539–3546, 2001     

Radiation-induced polymerization of glass-forming systems. IV. Effect of the homogeneity of polymerization phase and polymer concentration on temperature dependence of initial polymerization rate

The effect of homogeneity of polymerization phase and monomer concentration on the temperature dependence of initial polymerization rate was studied in the radiation-induced radical polymerization of binary systems consisting of glass-forming monomer and solvent. In the polymerization of a completely homogeneous system such as HEMA–propylene glycol, a maximum and a minimum in polymerization rates as a function of temperature, characteristic of the polymerization in glass-forming systems, were observed for all monomer concentrations. However, in the heterogeneous polymerization systems such as HEMA–triacetin and HEMA–isoamyl acetate, maximum and minimum rates were observed in monomer-rich compositions but not at low monomer concentrations. Furthermore, in the HEMA–dioctyl phthalate polymerization system, which is extremely heterogeneous, no maximum and minimum rates were observed at any monomer concentration. The effect of conversion on the temperature dependence of polymerization rate in homogeneous bulk polymerization of HEMA and GMA was investigated. Maximum and minimum rates were observed clearly in conversions less than 10% in the case of HEMA and less than 50% in the case of GMA, but the maximum and minimum changed to a mere inflection in the curve at higher conversions. A similar effect of polymer concentration on the temperature dependence of polymerization rate in the GMA–poly(methyl methacrylate) system were also observed. It is deduced that the change in temperature dependence of polymerization rate is attributed to the decrease in contribution of mutual termination reaction of growing chain radicals to the polymerization rate.     

Synthesis of highly crystalline poly(dimethylbutadiene) (PDMB) by radiation-induced inclusion polymerization: A comparison with PDMBs synthesized by bulk and emulsion polymerization

Poly-2,3-dimethylbutadiene (DMBD) has been synthesized by the radiation-induced inclusion polymerization technique. 2,3-DMBD was included as a clathrate in the channels of thiourea crystals and polymerized with 300 kGy into a crystalline high trans-1,4-polydimethylbutadiene (PDMB) in high yield. For comparison 2,3-DMBD was also polymerized by bulk radiolysis in high vacuum at 150, 300 and 600 kGy. The resulting PDMB was obtained in very low yields and had a microstructure completely different from that observed on PDMB synthesized by inclusion polymerization and more similar to the structure of an emulsion-PDMB prepared by a free radical initiator. Trans-PDMB prepared by inclusion polymerization was characterized by a crystalline melting point at 272 °C.The radiation chemical yield for the PDMB obtained by inclusion polymerization was found G=212 monomer units (in PDMB)/100 eV. This value is 23.5 times higher that measured in PDMB prepared by bulk radiolysis of the monomer.     

A novel synthetic procedure of vinylacetamide and its free radical polymerization

The pyrolysis of N-(α-methoxyethyl) acetamide, which was obtained by one-step reaction of acetamide, acetaldehyde, and methanol, gave N-vinylacetamide (NVA) in a good yield. The polymerizability and copolymerizability of NVA were studied. Free radical polymerization was carried out in the presence of radical initiator or by γ-ray irradiation. The monomer reactivity ratios of NVA were estimated in the copolymerization with acrylamide, vinyl acetate, and methyl methacrylate. The solvents were found to influence the monomer reactivity ratio. NVA showed a typical copolymerizability as nonconjugated vinyl monomer, and Q and e values were obtained in DMF as 0.16 and ?1.57, respectively.     

Radiation-induced emulsion polymerization of ethylene. III. Emulsion polymerization with ammonium perfluorooctanoate as the emulsifier

Radiation-induced emulsion polymerization of ethylene with ammonium perfluoro-octanoate as an emulsifier was studied in order to elucidate the effect of the number of polymer particles. Owing to the stable structure of the emulsifier from a radical attack, no C? F bond was detected in the polyethylene as expected. The polyethylene produced was mostly gel containing a small amount of low molecular weight polyethylene. This may be attributable to chain transfer to the polyethylene. The effects of dose rate and of concentration of the emulsifier were determined without considering the chain-transfer reaction to the emulsifier. By considering the escape of the radical which is produced by chain transfer to the monomer from the polymer particle to the aqueous phase at the steady state, the following equation is derived: The experimental results could be explained by this equation, and the apparent rate constants were obtained.     

Nanoparticle formation by monomer-starved semibatch emulsion polymerization

Latexes with very small particle size are usually manufactured by microemulsion polymerization. This article explains the preparation of nanolatexes by monomer-starved nucleation in a conventional semibatch emulsion polymerization with a low surfactant/monomer ratio and with no need for a cosurfactant. The semibatch emulsion polymerization reactions started with an aqueous solution of a surfactant and a water soluble initiator. Monomer was added at a fixed rate. The size of particles decreased with decreasing rate of monomer addition. High solids content nanolatexes with particles as small as 25 nm in diameter were produced. Several monomers with different water solubilities were compared. The order of the number of particles in terms of the rate of monomer addition was found to depend on the type of monomer. Water soluble monomers produced more particles due to associated chain transfer to monomer and radical exit. The monodispersity of particles at the end of nucleation increased as the rate of monomer addition decreased. The technique seems to be preferable to microemulsion polymerization, which uses a high concentration of surfactant/cosurfactant and is limited to low monomer holdup.     

Kinetics of free radical polymerization—XXXI. Solvent effect on the polymerization rate of ethyl acrylate

The free radical polymerization of ethyl acrylate was investigated in benzene and dimethyl formamide solutions at 50°. The effects of initiator and monomer concentration were studied over a wide range. The overall rate of polymerization was proportional to (initiator concentration)^{$\text{1}\text{2}$} but not to the concentration of the monomer. We attempted to interpret this solvent effect on the basis of (i) the diffusion theory, (ii) the theory of charge transfer complexes and (iii) the theory of hot radicals. Our experimental results could only be explained quantitatively in terms of hot radicals.     

Mechanism of vinyl chloride polymerization

An overall mechanistic scheme for the suspension polymerization of vinyl chloride is presented. The process can be resolved into five discrete stages, each of which presents a unique environment for the interaction of the systems parameters. It is shown that the surface area of the polymer formed during the reaction is not a major factor in autoacceleration and that the increase of kinetic chain length with conversion is due to a radical dilution effect. The latter is a direct result of the difference in rates between polymerization and radical formation, the former being greater. The increase of the initial polymerization rate and the reduction of autoacceleration brought about by chain transfer agents can be explained by the lower diffusion rate and greater bulkiness of the chain transfer agent radical relative to that of the monomer radical. The chaintransfer agent CBr₄ is preferentially absorbed by PVC from solution in vinyl chloride. With lauryl peroxide as initiator it is shown that the “hot spot” is the result of a build-up of initiator in the monomer caused by its exclusion from the polymer phase. Vinyl chloride was found to dissolve 0.03% PVC at ambient temperature and to have no effect on the decomposition rate of lauryl peroxide.     

Modeling stable free-radical polymerization

A kinetic model has been developed for stable free-radical polymerization (SFRP) processes by using the method of moments. This model predicts monomer conversion, number-average molecular weight, and polydispersity of molecular weight distribution. The effects of the concentrations of initiator, stable radical, and monomer, as well as the rate constants of initiation, propagation, termination, transfer, and the equilibrium constant between active and dormant species, are systematically investigated by using this model. It is shown that the ideal living-radical polymerization having a linear relationship between number-average molecular weight and conversion and a polydispersity close to unity is the result of fast initiation, slow propagation, absence of radical termination, and a high level of dormant species. Increasing stable radical concentration helps to reduce polydispersity but also decreases polymerization rate. Thermal initiation significantly broadens molecular weight distribution. Without the formation of dormant species, the model predicts a conventional free-radical polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2692–2704, 1999