Non-ideal kinetics in vinyl polymerization: Note on primary radical termination in benzoyl peroxide initiated polymerization of vinyl chloride in dichloroethane

The kinetics of vinyl chloride polymerization initiated by benzoyl peroxide doubly labelled with ¹⁴C and 'H were studied in 1,2-dichloroethane solution at 60°. The importance of primary radical termination in the polymerization is examined by kinetic analysis and by analysis of polymers for combined initiator fragments.     

Suspension polymerization of vinyl chloride and the processibility of poly(vinyl chloride)

The most important technological procedure in the production of PVC is the suspension polymerization of vinyl chloride, as processibility of the polymer may be influenced to a considerable extent by the choice of polymerization conditions. Structure heterogeneities in PVC powders manifest themselves in plasticized PVC by the occurrence of “fish eye” particles. This review concerns the formation and properties of these particles and discusses the causes of their difficult processibility. Also, the relation between polymerization process and PVC dehydrochlorination is discussed and a new mechanism of its initiation based on the reactivity of cisoid enone structures is proposed. These structures catalyze elimination of hydrogen chloride from regular units of PVC by an interchain enzyme-like mechanism giving rise to chloroallyl structures.     

Non-ideality in vinyl polymerization—VI: Polymerization of methyl methacrylate initiated by benzoyl peroxide

The polymerization of methyl methacrylate in benzene was initiated by benzoyl peroxide and examined by kinetic analysis particularly from the point of view of primary radical termination. It is concluded that the velocity constant for dissociation of the benzoyloxy radical to give the phenyl radical is affected by the nature of the medium.     

Kinetic study of early stages of heterophase polymerization of vinyl chloride initiated by radiation

The kinetics of the radiation-induced bulk polymerization of vinyl chloride in the early stages was determined in the temperature range of ?30 to 50°C and dose rates varying from 0.6 to 17 rad/sec by the dilatometric method. Some runs of polymerization of vinyl chloride added with different percentages of tetrahydrofuran were also carried out. The results were found to agree with those previously obtained with polymerizations carried out to high conversions. The results are discussed on the assumption of a decrease in the extent of swelling of the polymer by monomer with decreasing polymerization temperature. By comparison with the data of other precipitating polymerization systems the possibility of a generalized interpretation for the heterophase polymerization is examined.     

Kinetics of polymerization initiated by peroxides containing heterocyclic groups. I. Kinetics of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide

The rate and degree of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide and, for comparison, by dilauroyl and dibenzoyl peroxides were measured at several temperatures as a function of the initiator concentration. Also the rates of initiation were determined by the inhibition method with Banfield's radicals. The rate of polymerization initiated by difuroyl peroxide appears to be lower than could be expected from the rate of initiation determined by the inhibition method and from the decomposition of difuroyl peroxide. In the case of polymerization of vinyl acetate there are significant deviations from the proportionality between R_p and the square root of the initiator concentration, which follows from the conventional kinetic scheme. The degrees of polymerization are also low, and the plots of P _n^?1 versus R_p are not linear. These deviations can be accounted for by postulating a retardation effect of the furan cycle and chain transfer to difuroyl peroxide.     

Polymerization initiation by in situ initiator formation. II. in situ formation of several peroxydicarbonates and diisobutyryl peroxide

The rate of formation of a number of dialkyl peroxydicarbonates and one acylperoxide under in situ conditions were followed by using a simulated suspension polymerization system. Results confirm previous findings based on polymer conversions and indicate that for dialkyl peroxydicarbonates, the in situ mode is suitable only for the lower alkyl derivatives.     

Nitroxide-mediated styrene polymerization initiated by an oxoaminium chloride

An oxoaminium chloride that is prepared by reacting 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) with chlorine in carbon tetrachloride initiates radical polymerization of styrene at 120°C. In the early stages of polymerization, a monomeric adduct, 2,2,6,6-tetramethyl-1-(2-chloro-1-phenylethoxy)piperidine, is formed. Thereafter, styrene polymerization exhibiting the characteristics of living polymerization proceeds. High molecular weight polymers with relatively narrow molecular weight distributions are obtained by this polymerization. ¹H-NMR spectra of the polymers reveal that a chlorine atom and a TEMPO group are present at the α- and ω-termini, respectively. The monomeric adduct was prepared by heating the oxoaminium chloride and styrene in carbon tetrachloride at 65–70°C, and was characterized by ¹H- and ¹³C-NMR spectroscopy. It was found to be suitable as an initiator for nitroxide-mediated radical polymerization of styrene to make polymers with chlorine on the chain end. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2555–2561, 1998     

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.”     

Anionic polymerization of vinyl chloride

Anionic polymerization of vinyl chloride has been studied. Of the organometallic compounds tested as initiators, only butyllithium was found to initiate polymerization. Polymerization in bulk at 0°C and with tert-butyllithium as initiator gave poly(vinyl chloride) in a yield of 38% with M _n = 55,000. Tacticity of the anionic PVC was similar to that of conventional PVC prepared at similar temperatures. Anionic PVC was found to be less branched and more heat-stable than the conventional polymer.     

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.     

High-pressure polymerization of vinyl chloride

The radical polymerization of vinyl chloride was investigated at 60°C under high pressure up to 5000 bar in benzaldehyde, benzonitrile, toluene, heptane, cyclohexane, and dioxane as solvent. In benzaldehyde and benzonitrile, the polymerizations were depressed by increased pressure. This unusual behavior was explained by the solvent participation and the effect of pressure on the propagating radicals. The crystallinities of polymer obtained in all solvents decreased with increasing pressure, as judged by the absorbance ratio of the infrared spectra. However the effects of pressure on the absorbance ratio of the polymer obtained in benzaldehyde and benzonitrile were not identical with those in the other solvents. These facts also suggest that both solvents play a special role for the solvent participation in the propagating step.     

Kinetics of polymerization of vinyl monomers initiated by lead tetraacetate

A systematic study of the thermal polymerization of α-chloroacrylic acid and α-bromoacrylic acid in aqueous nitric acid was carried out. The effect of variation of monomer concentration lead tetraacetate concentration, hydrogen ion concentration, ionic strength, and temperature on the rate of monomer disappearance was carried out. Based on the experimental observations, suitable reaction schemes were proposed for the polymerization of the above monomers. The rate constants and the thermodynamic parameters were evaluated.     

Introduction of peroxide groups onto carbon black surface by radical trapping and radical graft polymerization of vinyl monomers initiated by the surface peroxide groups

The introduction of peroxide groups onto carbon black surface was achieved through the trapping of the peroxide radicals formed by the decomposition of polymeric peroxide, such as poly(tetraethylene glycol peroxyadipate) (ATPPO), and bis-peroxide, such as 1,1′-bis (t-butyldioxy)cyclohexane (Perhexa-C), by the surface: the amount of peroxide groups introduced onto carbon black surface by the treatment with ATPPO and Perhexa-C were determined to be 0.07 mmol/g and 0.12 mmol/g, respectively. The polymerization of vinyl monomers with positive e-value, such as methyl methacrylate and 2-hydroxyethy methacrylate, was successfully initiated by the peroxide groups introduced onto carbon black surface. During the polymerization, the corresponding polymers were effectively grafted onto the surface as a result of the propagation of polymer from the surface radicals formed by decomposition of the peroxide groups. The polymerization of vinyl monomers with negative e-value, such as styrene and vinyl acetate, however, was scarcely initiated by the peroxide groups on carbon black. This may be due to the fact that surface active radicals, which were formed by the hydrogen abstraction from carbon black by fragment radicals, inhibit the polymerization of vinyl monomers with negative e-value. © 1996 John Wiley & Sons, Inc.     

Methyl methacrylate polymerization initiated by triethylborane–peroxide mixtures

The polymerization of methyl methacrylate initiated by triethylborane or triethylborane–peroxide mixtures was studied. The rate of initiation by a mixture of triethylborane and tert-butyl peroxide was found to be first-order in peroxide. The order in triethylborane changes from one at low triethylborane/peroxide to nearly zero at high triethylborane/peroxide. The possibility of a mechanism involving a fast reaction followed by a slow reaction that would initiate the polymerization is discussed.     

Cationic polymerization of vinyl monomers initiated by phosphorus compounds containing halogens

Polymerization of vinyl monomers having large negative e values in the presence of phosphorus compounds containing halogens was studied in order to examine the cationic initiation ability of phosphorus compounds. N-Vinylcarbazole was effectively polymerized by phosphorus compounds such as PCI₃, PBr₃, PCI₂C₆H₅, PCI(C₆H₅)₂, POCI₃, and POCI₂C₆H₅ even in benzene. The initiation ability of phosphorus compounds decreased in the order; PCI₂ ? PBr₃ > PCI₂C₆H₅ > PCI(C₆H₅)₂, and also POCI₃ > POCI₂₆₅. On the other hand, PCI₃ and PBr₃, which were less effective than POCI₃, showed initiation ability for the polymerizations of styrene and α-methylstyrene in nitrobenzene as a solvent. The results of the copolymerization of styrene with methyl methacrylate by PCI₃ in nitrobenzene, the result of solvent dielectric constant effect, and the effect of additives such as water, tert-butyl chloride, triethylamine, and hydroquinone, indicate the polymerization of styrene by PCI₃ to proceed by a cationic mechanism.     

Atom transfer radical polymerization of styrene initiated by triphenylmethyl chloride

Triphenylmethyl chloride (TPMCl) was employed for the first time as the initiator of atom transfer radical polymerization (ATRP) of styrene in the presence of CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst and cyclohexanone as solvent. The kinetic plot was first-order with respect to monomer. A linear increase of number average molecular weight (M_n) vs. monomer conversion was observed, and the molecular weight distribution (MWD) was relatively narrow (M_w/M_n = 1.2-1.5). ¹H NMR spectra revealed the ω-Cl group at the chain end. Another two initiators, benzyl chloride (BzCl) and diphenylmethyl chloride (DPMCl), were also employed in contrast with triphenylmethyl chloride to investigate the influence of phenyl numbers on the polymerization.     

Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals

A small quantity of 10-methylphenothiazine cation radical (MPT^.+), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. ¹H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D₂O indicated that electron transfer from the monomer to MPT^.+ was involved in the initiation step. ¹H- and ¹³C-NMR and MO calculation implied that monomers with higher electron densities on the vinyl groups and with lower ionization potentials were more susceptible to the initiation of MPT^.+. © 1994 John Wiley & Sons, Inc.