Vinyl monomers polymerization kinetics

This monomer polymerizes faster ia 50% water than it does ia bulk (35), an abnormaHty iaconsistent with general polymerization kinetics. This may be due to a complex with water that activates the monomer it may also be related to the impurities ia the monomer (eg, acetaldehyde, 1-methyl pyrroHdone, and 2-pyrroHdone) that are difficult to remove and that would be diluted and partitioned ia a 50% aqueous media (see Vinyl polymers, A/-VINYLAMIDE POLYPffiRS). 

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

For less polar monomers, the most extensively studied homopolymerizations are vinyl esters (e.g. VAc), acrylate and methacrylate esters and S. Most of these studies have focused wholly on the polymerization kinetics and only a few have examined the mierostructures of the polymers formed. Most of the early rate data in this area should be treated with caution because of the difficulties associated in separating effects of solvent on p, k and initiation rate and efficiency. 

In EP of bifunctional vinyl monomers, the reaction rate increases with the emulsifier concentration because the number of particles increases. However, in the crosslinking EP of divinyl monomers, the reaction rate is inversely proportional to the emulsifier concentration. This unusual behavior is due to nucleation taking place in both micelles and monomer droplets. In monomer droplets, the kinetics resembles that of bulk polymerization and therefore the reaction rates... 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

The information available up to 1965 on the polymerization kinetics of vinyl acetate has been reviewed by Lindemann 184% who collected data on the transfer coefficients with monomer and polymer, which may be denoted as Clm and Clp respectively. These are the ratios of rate constants for attack on monomer or polymer (per monomer unit) to the propagation rate constant they are the... 

The emulsion polymerization of vinyl hexanoate has been studied to determine the effect of chain transfer on the polymerization kinetics of a water-insoluble monomer. Both unseeded and seeded runs were made. For unseeded polymerizations, the dependence of particle concentration on soap is much higher than Smith-Ewart predictions, indicating multiple particle formation per radical because of chain transfer. Once the particles have formed, the kinetics are much like those of styrene. The lower water solubility of vinyl hexanoate when compared with styrene apparently negates its increased chain transfer, since the monomer radicals cannot diffuse out of the particles. 

Conix, A., and G. Smets Benzoyl peroxide initiated polymerization kinetics of vinyl monomers in various solvents. J. Polymer. Sci. 10, 525 (1953). 

The subject of the kinetics of vinyl polymerization by radical mechanisms is treated exhaustively in a book by Bamford, et al. (4) and more briefly in many textbooks of polymer chemistry. The polymerization of vinyl monomers is a chain reaction in which the primary reactions are ... 

Several kinetic criteria can be employed to elucidate the nature of the propagating species in vinyl polymerizations. The results of the application of these criteria, as exemplified by styrene, are shown in Table I. This monomer has been chosen in this discussion mainly because... 

In the chain growth free radical polymerization of a vinyl monomer (conventional polymerization), the growth reaction is the repeated reaction of a free radical with numbers of monomer molecules. According to the termination by recombination of growing chains, 2 free radicals and 1000 monomer molecules leads to a polymer with the degree of polymerization of 1000. In contrast to this situation, the growth and deposition mechanisms of plasma polymerization as well as of parylene polymerization could be represented by recombinations of 1000 free radicals (some of them are diradicals) to form the three-dimensional network deposit via 1000 kinetic... 

Detailed analysis of the kinetics of polymerization of cyclic monomers has only relatively recently reached the sophistication of analogous vinyl systems. Despite this an ever increasing volume of relevant data is emerging, and, indeed many reactions are proving to be more amenable to investigation in an absolute manner, than the more extensively studied vinyl polymerizations. This situation has arisen partly as a result of the inherent lower reactivity of these monomers, and also from the fact that, in general, the polymerizations are less susceptible to impurities and side reactions. Even monomer transfer is absent in most of these systems, and a situation approaching that found in anionic vinyl polymerization prevails. 

Termination evidently does not occur as readily in anionic polymerization of thietanes as it does in cationic polymerization. Organo-lithium initiated polymerizations of thietanes lead to living polymers, which have been used to prepare ABA block copolymers of dienes and cyclic sulphides [69, 70]. Since the anionic polymerization of thietanes proceeds via a carbanion, thietEines can initiate vinyl polymerization and their polymerization can be initiated by vinyl monomers. Kinetic parameters of such polymerizations have not yet been reported. 

Aqueous dispersions of poly(vinyl acetate) and vinyl acetate-ethylene copolymers, homo- and copolymers of acrylic monomers, and styrene-butadiene copolymers are the most important types of polymer latexes today. Applications include paints, coatings, adhesives, paper manufacturing, leather manufacturing, textiles and other industries. In addition to emulsion polymerization, other aqueous free-radical polymerizations are applied on a large scale. In suspension polymerization a water-irnrniscible olefinic monomer is also polymerized. However, by contrast to emulsion polymerization a monomer-soluble initiator is employed, and usually no surfactant is added. Polymerization occurs in the monomer droplets, with kinetics similar to bulk polymerization. The particles obtained are much larger (>15 pm) than in emulsion polymerization, and they do not form stable latexes but precipitate during polymerization (Scheme 7.2). 

While the energy transfer model is remtarkably successful in summarizing the polymerization kinetics of vinyl monomer solutions, there may be other explanations w ith certain monomer-... 

This chapter describes the coordination polymerization of acyclic and cyclic vinylic monomers, conjugated dienes, and polar vinylic monomers with the most important catalytic systems known in this area. A chronological classitication for the development of the main coordination catalyst types is outlined, as well as polymerization kinetics and mechanisms and applications of polymers obtained through different metallic complexes. 

Cationic surfactants, in contrast to anionic surfactants, usually reduce both the number of particles involved in the polymerization and the rate of polymerization. The nature of the stabilizing emulsifier has a marked effect on the polymerization kinetics. For example, addition of a non-ionic stabilizer [e.g., poly(vinyl alcohol), a block copolymer of carbowax 6000 and vinyl acetate, or ethylene oxide-alkyl phenol condensates] to a seed polymer stabilized by an anionic surfactant decreased the rate of polymerization to 25% of the original rate. The effect was as if the nonionic stabilizer (or protective colloid) acted as a barrier around the seed particles to alter the over-all kinetics. It may be that the viscosity of the medium in the neighborhood of the nonionic surfactant coating of the polymer particle is sufficiently different from that of an anionic layer to interfere with the diffusion of monomer or free radicals. There may also be a change in the chain-transfer characteristics of the system [156]. 

The emulsion copolymerization of vinyl acetate and butyl acrylate has received considerable attention. The butyl acrylate confers improved film forming characteristics to the polymer. The disparities in their water solubilities and of their individual polymerization rates may help to explain the variations in reactivity ratios that have been reported [170,171]. The variation in reactivity ratios may also by related to the following observations The reaction method has an effect on the morphology of the polymer particles. In a batch emulsion process, a butyl acrylate—rich core is formed which is surrounded by a vinyl acetate-rich shell, in a process in which the monomers are fed into the reactor in a semicontinuous manner, particles form with a more uniform distribution of the monomers [172]. The kinetics for a batch process indicates that the initially formed polymer is indeed high in butyl acrylate. As this monomer is used up, eventually a copolymer high in vinyl acetate develops. It is this latter polymer which forms the final shell around the particles. 

Since the initiator concentration remains fairly unchanged in the course of vinyl polymerization, if the initiator efficiency is independent of monomer concentration, first-order kinetics with respect to the monomer is expected. This is indeed observed over a wide extent of reaction for the polymerization of styrene in toluene solution with benzoyl peroxide as initiator (Figure 7.3). The polymerization of certain monomers, either undiluted or in concentrated solution, shows a marked deviation Irom such first-order kinetics. At a certain stage in the polymerization process, there is a considerable increase in both the reaction rate and the molecular weight. This observation is referred to as autoacceleration or gel effect and is illustrated in Figure 7.4 for polymerization of methyl methacrylate at various concentrations of the monomer in benzene. 

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