Poly Methyl Methacrylate Radical Research Articles

DFT Study of the Interaction between Chloroiron(III) Porphyrin and Poly(methyl Methacrylate) Macroradicals

The heats of possible reactions between the model poly(methyl methacrylate) radical (PMMA) and the molecule of iron chloroporphyrin (FeClP) were calculated by density functional theory methods. It was shown that the interaction of iron atom of FeClP and PMMA radical energetically is more favourable via the carbonyl group of the latter. The chlorine atom transfer reaction between PMMA radical and FeClP containing Fe atom in the spin state 3/2 is the most probable process among the studied reactions.

Substituent Effects in the Reaction between Acetophenones and Polymethyl Methacrylate Radicals

Abstract The substituent effects in the reaction between acetophenones and the polymethyl methacrylate radical have been correlated with Swain and Lupton's Field (F) and Resonance (R) parameters including Williams and Norrington's unique positional weighting factors (SLWN) and also in terms of a conventional Hammett type equation with σ+. Excellent correlations have been obtained with both models. Attempts have also been made to ascertain the nature and characteristics of the transition state from the sign and magnitude of the reaction parameters.

Rate parameters for transfer reactions of some polymer radicals: in terms of Swain and Lupton's f and r and the unique positional weighting factors of Williams and Norrington

Rate parameters of the reaction of phenols, deuterated phenols and nitrobenzenes with polyvinylacetate radicals and of aromatic thiols with polymethylmethacrylate radicals have been correlated with Swain and Lupton's substituent constants ( F k and R k ) and Williams and Norrington's unique positional weighting factors ( f j and r j ) by the following equation: P i = α iƒ jF k + β ir jR k + e i + P 0 i where P i 's are the rate parameters, P 0 i being that for a standard reference state. The correlations were found to be quite satisfactory. The sign and magnitude, and the ratio of the reaction dependent parameters α i and β i throw light on the nature of the transition state and the relative contributions of the mesomeric and inductive effects. The present studies also show that the mesomeric effect of meta-substituents is significantly greater than reported by earlier workers.

Study of the reactivity of polymethyl methacrylate radicals combined in a complex in chain transfer to CBr 4

A study was made of the effect of ZnCl 2 on chain transfer to CBr 4 in radical polymerization of methyl methacrylate (MMA). It was found that the chain transfer constant C t and the rate constant for chain transfer k t decrease in the presence of ZnCl 2. These effects are caused by a reduction in the reactivity of radicals combined in a complex in extension of PMMA as a result of a change of polarization and conjugation. The dependence of k t on the content of ZnCl 2 in the reaction system enabled us to evaluate the equilibrium constant ▪. The value of K>1 proves a greater affinity of ZnCl 2 complexes with radicals than with the monomer. The value of K determined in this study agrees with that obtained previously from results of copolymerization in the MMA-vinylidene chloride-ZnCl 2 system. Study of the effect of ZnCl 2 on C t in copolymerization of MMA with styrene indicates that active centres responsible for chain extension in alternating copolymerization in the presence of ZnCl 2 are radicals, of which the activity does not markedly differ from that of free radicals responsible for statistical copolymerization of MMA with styrene in the absence of ZnCl 2.

Determination of Chain Transfer Constant for Solvent When the Viscosity of the Polymerizing System Is Considered Important

Abstract The chain transfer constant of the polymethyl methacrylate radical for N,N-dimethylaniline was determined in two solvents, benzene and dimethyl phthalate. Plots were made using1/Pn=kt°Rp/kp 2[M]2η + CS1 [S1]/[M] + CS2 [S2]/[M] +CM where η=viscosity of monomer-solvents mixture, kt°=rate coefficient of termination when η=1 cP, S1=benzene or dimethyl phthalate, S2=N,N-dimethylaniline, and other symbols have their usual meanings. The plots agreed well for the two solvents. If the plots were made without considering the viscosity term, two separate lines resulted for the two solvents. Thus it is essential to consider the viscosity of the polymerizing system in the analysis of chain transfer reactions when the termination reaction is diffusion-controlled and the viscosities of the monomer and solvent differ markedly.

Electron spin resonance studies of photo-oxidation by metal ions in rigid media at low temperatures. Part 3.—Ce(IV) photo-oxidations of aldehydes, ketones, esters and amides

A survey is presented of the primary processes in the photo-oxidation by Ce(IV) ions at 77 K of a variety of organic molecules classified by functional group; these processes have been determined by characterization of the resulting organic free radical by electron spin resonance spectroscopy. Aldehydes RCHO and aldehyde hydrates RCH(OH)2 are oxidized to RĊO and RĊC(OH)2 respectively, although C2H5ĊO disappears at 120 K, producing instead CH3ĊHCHO. Ketones produce either the alkyl radical R from RCOR′ or the radical derived by abstraction of a hydrogen atom from the methylene or methine groups adjacent to the carbonyl group; in some cases both types of radical are discernible. Esters also undergo C—H or C—C fission processes depending on the degree of substitution of the R fragment of RCO2R′, whilst formamide yields a spectrum of ·CONH2. Methyl methacrylate yields a vinylic monomer radical at 77 K which induces polymerization at 175 K to give the polymethyl methacrylate radical.

ESR Measurement and Irradiation at Variable Temperatures below 77°K

Abstract An apparatus for irradiation and subsequent ESR measurements at variable temperatures below 77°K was constracted by combining an ESR spectrometer, and an X-ray irradiator, and a laboratory scale low temperature refrigerator operating at the temperature region between 77 and 4.2°K. A device for rotating the single crystal specimen was made to measure the angular dependence of the ESR spectra. The lowest specimen temperature achieved was estimated to be 6°K and the precision of the temperature control was less than ±0.5°K for a period of several hours. The apparatus makes it possible to irradiate samples and to measure ESR spectra at any temperature in the range between 77 and 6°K. Some applications for irradiation and ESR measurements at low temperatures are also described. An unstable radical which disappears at about 60°K was found in an irradiated single crystal of l-cystine dihydrochloride. Experimental evidence for the quantum tunnelling of the methyl group in polymethylmethacrylate radical was also found by the temperature dependence of the spectra observed at temperatures lower than 77°K.

ESR Study of Quantum Tunneling of a Methyl Group in Polymethyl-methacrylate Radical

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Effects of Substituents of the Chain-transfer Reactivities of Nuclear-substituted Acetophenones toward the Polymethyl Methacrylate Radical

Effects of Substituents of the Chain-transfer Reactivities of Nuclear-substituted Acetophenones toward the Polymethyl Methacrylate Radical

A contribution to the ESR spectrum of polymethylmethacrylate radicals

A contribution to the ESR spectrum of polymethylmethacrylate radicals

Effects of salts of metals on vinyl polymerization. Part 1.—Polymerization of methyl methacrylate in presence of cupric chloride

The polymerization of methyl methacrylate initiated with AIBN and inhibited with cupric bromide in DMF has been studied at from 40–70°C. Rate constants for the initiation reaction, obtained by the inhibition period method, were 6.2 × 10–7, 3.7 × 10–6, 1.42 × 10–5 and 8 × 10–5 s–1 at 40, 50, 60 and 70°C respectively, yielding an activation energy of 137.5 kJ mol–1. The acceleration period following complete inhibition was rapid and became distributed due to self-heating effects when ordinary dilatometers were used. Disc-bulb dilatometers helped to removed this distortion. Values of the ratio where kx/kp, where kx is the rate constant from the reaction between polymethyl-methacrylate radicals and the cupric salts, were greater than those obtained using cupric chloride as an inhibitor.

The chain transfer mechanism of substituted diphenyl disulfides

AbstractChain transfer constants of substituted diphenyl disulfides in radical bulk polymerization of methyl methacrylate were determined. The effect of the substituent on the reactivity of the disulfide bond toward a polymethyl methacrylate radical was dependent on the electron density of the substituent. The chain transfer constant to substituted diphenyl disulfides increased negative e‐value of the polymerizing monomer.

Grafting of methyl methacrylate to polypropylene and polyethylene

AbstractIn a study of chemical modification of hydrocarbon polymers an investigation was made of the grafting of methyl methacrylate onto polypropylene and polyethylene. The grafting process was carried out both through preliminary polymer hydroperoxide formation and through chain transfer reactions. Polymer hydroperoxide‐induced grafting proceeds via direct free radical initiation of side chain growth and via hydrogen atom transfer from the hydrocarbon polymer to the polymethyl methacrylate radical. Here the contributions to the chain transfer from the initiator and the methyl methacrylate radical were determined for the separate polymers. Since the grafting was carried out in swollen polymers the effect of viscosity of the medium on the course of the grafting of methyl methacrylate was examined. During the grafting of methyl methacrylate to polyethylene and polypropylene the possibility of crosslinking of these polymers arises. Of particular interest is crosslinking of polypropylene, in view of the fact that the direct reaction induced by ionizing radiation or by hydroperoxide decomposition is connected with certain complications brought about by degradation of the polymer backbone. In the case in question, the formation of a crosslinked structure is due to recombination of the growing methyl methacrylate chains. The crosslinking of the graft polymer is hindered by the chain transfer reaction and by disproportionation during chain termination. In the case of methyl methacrylate, the ratio between recombination and disproportionation is favorable to crosslinkage of the graft polymers, a fact which has been confirmed experimentally. Based on the data concerning the chain transfer reactions and the conditions of formation and decomposition of polymer hydroperoxides a discussion has been presented of the most favorable procedures for grafting methyl methacrylate onto polypropylene and polyethylene and for the formation of crosslinked graft polymers.

The polymerization of acrylonitrile in aqueous solution. Part I. The reaction catalyzed by Fenton's reagent at 25°C.

AbstractAn apparatus is described for following dilatometrically the polymerization of acrylonitrile in aqueous solution initiated by ferrous salts and hydrogen peroxide. A steady rate (Rp) is rapidly established which ultimately decreases rapidly but does not fall to zero after the initiator is consumed. From measurements of the concentration of the ferrous ion surviving the reaction, the effect of cupric, fluoride, and ferric ions on this, on Rp, on the final phases of this reaction, and on the corresponding reaction with methyl methacrylate, it is concluded that polyacrylonitrile radicals are oxidatively terminated by cupric and ferric ions, but polymethyl methacrylate radicals are not. When this linear termination is suppressed, Rp is proportional to [m1]2 at low monomer concentrations and linearly dependent on [m1] at high concentrations. The transition from one state of affairs to the other occurs at a monomer concentration which first decreases and then increases as the initiation rate (Ri) increases. These results are believed to be general for all modes of initiation and include all previous data, reconciling conflicting information. A qualitative interpretation of these results is given in terms of the fairly rapid attainment of a constant number of polymer particles on which monomer is weakly adsorbed, a proportion of which are at any given moment inert, the remainder growing by consuming adsorbed monomer. Initiation, propagation, and mutual termination in the aqueous phase all play a significant part.

Radiochemical studies of free‐radical vinyl polymerizations. Part I. The nature of the initiation and termination processes in methyl methacrylate and styrene polymerizations using C14‐labeled initiators

AbstractC14‐Labeled initiators, viz., di‐(ar‐C14)‐benzoyl peroxide, di‐(carboxyl‐C14)‐benzoyl peroxide, and C14‐azobisisobutyronitrile (AZBN), have been used to initiate the polymerization of methyl methaerylate at 60°C. in benzene. Determination of the rates of polymerization, and the molecular weights (M̄n) and C14‐contents of the resultant polymers permits the following conclusions to be made. (1) Rates of initiation by benzoyl peroxide and AZBN are given by the equations, Ri = 5.15 × 10−6 [Bz2O2] mole l.−1 sec.−1 and Ri = 1.17 × 10−5[AZBN] mole l.−1 sec.−1, respectively. (2) The initiator efficiency, f, for AZBN is 0.50; f for benzoyl peroxide cannot be evaluated in the absence of a reliable kd value for this compound in the present system. (3) Initiation is solely by addition of initiator radicals, R·, to the monomer; in the case of benzoyl peroxide, 43% of the radicals R· are phenyl and 57% are benzoyloxy under the reaction conditions used. (4) The average number of C14‐initiator fragments per polymer molecule, n, is 1.27, indicating that bimolecular termination of polymethyl methacrylate radicals is 57.5% by disproportionation and 42.5% by combination.

Radiochemical studies of free‐radical vinyl polymerizations. Part II. The polymerization of vinyl monomers in the presence of polyisoprenes: Use of C14‐labeled initiators to determine the mechanism of graft‐interpolymer formation

AbstractPolymerization of methyl methacrylate at 60°C. by benzoyl peroxide in benzene solutions of polyisoprenes (e.g., natural rubber and gutta‐percha) yields polymethyl methacrylate and a graft interpolymer having polymethyl methacrylate side chains attached to the polyisoprene backbone. Use of azobisisobutyronitrile (AZBN) as initiator in comparable systems gives free polymethyl methacrylate, but no graft interpolymer. The cause of this specific initiator effect, and the mechanism of graft polymerization have been determined by using C14‐labeled initiators. Benzoyl peroxide initiates graft polymerization by prior reaction of the derived phenyl and benzoyloxy radicals with the polyisoprene by addition to the double bond, and by abstracting α‐methylenic hydrogen atoms to give polyisoprenic alkyl and alkenyl radicals, respectively, which act as loci for methyl methacrylate polymerization. In the system gutta‐percha‐methyl methacrylate, at 60°C., 35–45% of the grafted vinyl polymer side chains are initiated by hydrogen abstraction, and about 90% of the initiator radicals undergoing addition to the double bond are benzoyloxy. The modes of termination of the grafted and free polymethyl methacrylate radicals have been evaluated semiquantitatively, and it is found that, in the graft interpolymer, 13–27% of the polymethyl methacrylate chains have both ends attached to gutta‐percha chains (i.e., have an “I” structure), while 73–87% are attached at one end only to gutta‐percha chains (i.e., are “T” structures). The reliability of the separatory procedure previously devised8 to resolve the bulk polymer obtained in the graft‐polymerization system has now been verified by use of the isotopedilution technique. The inability of AZBN to initiate graft polymerization is attributed to the markedly inferior capacity of the resonance‐stabilized Me2Ċ(CN) radicals, relative to C6H5· and C6H5COO·, to engage in double bond addition and hydrogen abstraction reactions.

The termination reaction in radical polymerizations. II. Polymerizations of styrene at 60° and of methyl methacrylate at 0 and 60°, and the copolymerization of these monomers at 60°

AbstractStyrene has been polymerized at 60° and methyl methacrylate at 0 and 60° using 2,2′‐azo‐bis‐isobutyronitrile labeled with C14 as initiator. The average number of labeled end groups per molecule has been determined for the various polymers and so the relative importances of combination and disproportionation have been assessed. It has been found that polystyrene radicals undergo combination at 60°. In the case of methyl methacrylate, disproportionation occurs about 6 times as frequently as combination at 60° and about 1.5 times as frequently at 0° the activation energy for disproportionation is about 4 kcal. per mole greater than that for combination. The copolymerization of styrene and methyl methacrylate at 60° has been studied by this technique. It is found that when polystyrene radicals interact with polymethyl methacrylate radicals at this temperature combination occurs. The rates of initiation in the copolymerizations have been determined by a new method; the rate of this step is found to be virtually independent of the composition of the monomer mixture.

The termination reaction in radical polymerizations. Polymerizations of methyl methacrylate and styrene at 25°

AbstractStyrene and methyl methacrylate have been polymerized at 25° using α,α′‐azo‐bis‐isobutyronitrile labeled with C14 as initiator. The numbers of initiator fragments per polymer molecule have been determined by measurements of the average molecular weights of the polymers by osmometry and the specific activities of the polymers and the initiator by gas counting. It is found that polystyrene radicals combine at 25° and that for polymethyl methacrylate radicals at this temperature disproportionation occurs about twice as frequently as combination.