Monomers, polymerization rates various

Data illustrating the relationship of the initial rate to the concentration of monomer at fixed initiator concentration are given in Table X for styrene in benzene and for methyl methacrylate polymerized at various concentrations in the same solvent. If the efficiency / of utilization of primary radicals is independent of the monomer concentration, the quantity given in the last column should be... 

Some of the vinyl monomers polymerized by transition metal benzyl compounds are listed in Table IX. In this table R represents the rate of polymerization in moles per liter per second M sec-1), [M]0 the initial monomer concentration in moles per liter (M) and [C]0 the initial concentration of catalyst in the same units. The ratio i2/[M]0[C]0 gives a measure of the reactivity of the system which is approximately independent of the concentration of catalyst and monomer. It will be observed that the substitution in the benzyl group is able to affect the polymerization rate significantly, but the groups that increase the polymerization rate toward ethylene have the opposite effect where styrene is concerned. It would also appear that titanium complexes are more active than zirconium. The results with styrene and p-bromostyrene suggests that substituents in the monomer, which increase the electronegative character of the double bond, reduces the polymerization rate. The order of reactivity of various olefinically unsaturated compounds is approximately as follows ... 

Relatively few attempts have been made to demonstrate the presence of ions in the polymerization of styrene, the most extensively studied of all monomers. Pepper [11] made conductivity studies on stannic chloride solutions in various solvents with and without monomer and added water, using open systems. He concluded that his results shed little light on the question of whether chain-carrying cations were present (which, indeed, he presumed) or on their concentration. Brown and Mathieson [12] found that for the polymerization of styrene by chloroacetic acids in nitromethane, the conductivity was indistinguishable from zero when no water was added, although the reaction rate was appreciable, and with increasing amounts of added water the conductivity increased, but the polymerization rate decreased. Therefore their results gave no useful information on the question of the participation of carbonium ions. 

For most practical photopolymerizations there is appreciable attenuation of light intensity with penetration and the dependence of polymerization rate on monomer, photoinitiator, and light intensity is more complex (see Eqs. 3-54 and 3-55 for exact definitions). Equation 3-54 is especially useful for analyzing the practical aspects of a photopolymerization. When polymerizing any specific thickness of reaction system it is important to know Rp at various depths (e.g., front, middle, and rear surfaces) than to know only the total Rp for that system thickness. If the thickness is too large, the polymerization rate in the rear (deeper) layers will be too low, and those layers will be only partially polymerized—the result would be detrimental because the product s properties (especially the physical properties) would be... 

These results show that the big differences in the polymerization rate in the various solvents are caused mainly by the position of the equilibria, and only to a small extent by the direct interaction of the solvent. Figure 11 shows the equilibria as functions of temperature, calculated with the parameters of Table II and the corresponding rate constants for monomer addition. 

The frequency of the transfer reactions (4 a) and (4 b) depends on the competition between substrate (polymer) and monomer for the radicals present in the solution, i.e. on the competition between growth and transfer. This competition is usually characterized by a transfer constant which is equal to the ratio of the transfer rate constant to the propagation rate constant, and which can be determined by measurements of the degree of polymerization at various concentration ratios of transfer agent... 

Figure 8. Rate of particle formation (dNp/dt) vs. polymerization rate at 20% conversion for various amounts of SDS (-%-) or monomer/water ratio ( X )...

The kinetics of polycondensation hy nucleophilic aromatic substitution in highly polar solvents and solvent mixtures to yield linear, high molecular weight aromatic polyethers were measured. The basic reaction studied was between a di-phenoxide salt and a dihaloaromatic compound. The role of steric and inductive effects was elucidated on the basis of the kinetics determined for model compounds. The polymerization rate of the dipotassium salt of various bis-phenols with 4,4 -dichlorodiphenylsulfone in methyl sulfoxide solvent follows second-order kinetics. The rate constant at the monomer stage was found to be greater than the rate constant at the dimer and subsequent polymerization stages. 

Henrici-Olive and Olive were the first to put forward the hypothesis that complexes are sometimes formed between the active centre and the monomer and or/solvent [45], As only the complex with monomer is capable of propagation, part of the centres is inhibited and the polymerization rate is reduced. This theory was found to be valid with styrene [46], but not with MMA [47]. Burnett called attention to the important circumstance that radicals solvated in various ways may react differently, or at least at different rates [47]. His conclusions were based on kinetic studies of MMA polymerization in various halogenated aromatics. In the copolymerization of butyl vinyl ether with methacrylates, complex formation between the active centre and condensed aromatics prior to monomer addition was observed by Shaik-hudinov et al. [48], The growing polymer forms a stable donor-acceptor complex with naphthalene, described by the formula. 

The pH dependence of the polymerization rate of acrylic acid [54] in the presence of various neutralizing agents does not exhibit a course. Between pH 2 and 6, the rate drops abruptly afterwards it grows, depending on the degree of neutralization and the kind of neutralizing agent. The rate increase is connected with the presence of a cation which restricts the repulsion between the anions of the active centre and the monomer... 

Cationic polymerization of 2-methylpropene at temperatures about 170 K may be almost flash-like the transformation of tetrahydrofuran to an equilibrium polymer-monomer mixture may last tens to hundreds of hours at 260 K. Evidently the overall polymerization rate is a function of many factors which may be interconnected or may act separately. The aim of kinetic measurements is to describe the polymerization, and to find conditions under which it would proceed in the desired manner. This is usually only possible after the various factors and their consequences have been isolated and investigated. The rate of monomer consumption during polymerization mostly depends on the generation rate of active centres, and on their concentration and reactivity. 

The yield of the catalyst, 0, was measured at various ethylene concentrations (see Fig. 10). According to the results, initiation is rapid and the catalytic system maintains full capacity for a long time, for at least 1 h. In this interval, the polymeric particles increase their size 5-10 fold. Thus the monomer supply into the pores of the particles by diffusion cannot be hindered. In the subsequent phase, activity already decreases. Either the conditions for monomer transport to the centres by diffusion are deteriorating, and/or the centres are slowly decaying. The polymerization rate, i>pol, can be determined from the slopes of the curves in Fig. 10. The determined values of the initial rates are directly proportional to monomer concentration (except for the lowest values of [M]), as shown in Fig. 11. 

In emulsion polymerization the situation is entirely different in that the increase in rate due to gel-effect depends on experimental conditions such as initiator concentration, particle size and particle number. Therefore, accounting for gel-effect in emulsion polymerization is considerably more complex than in bulk polymerization. However, we have recently shown that the increase in rate due to gel-effect in emulsion polymerization of various monomers can be accounted for quantitatively by means of data from bulk polymerization U, ). 

In LCVD, the simplest parameter that can be correlated with the flow rate of monomer is the polymer deposition rate, which is generally and most logically expressed by (mass)/(area)(time). As long as the dependence of polymer deposition rate on monomer flow rate is sought for a given monomer only, the monomer flow rate given by seem can be used without difficulty when such a correlation is extended to different monomers and the polymer deposition characteristics are compared, however, the flow rate based on cubic centimeters per minute cannot be used because the mass of a mole of gas depends on the molecular weight of the monomer. The polymer deposition rates of various monomers should be compared on the basis of the mass flow rate otherwise, polymer deposition rates are not directly proportional to the polymerization rates. 

TaWe 13. Photoinitiated polymerization rate (Rp) of various monomers in the presence of high- and low-molecular-weight aliphatic ketone initiators [83]... 

Frequently, the order of rates of polymerization of various lactams is different from that of the thermodynamic parameters for polymerization. For example, the initial rates of hydrolytic polymerization were practically the same for capro-, enantho- and capryllactam [25—27], whereas the corresponding heats of polymerization differed significantly for these monomers [27] —AH = 3.3, 5.3 and 7.8 kcal mole", respectively). Similarly, for substituted caprolactams the sequence of free energies of polymerization is just opposite to the order of rates of anionic polymerization (Fig. 1). 

Many factors affect the progress of the interfacial polymerization reaction, including choice of solvent, the use of detergents as emulsifiers, temperature, rate of addition of one monomer, and rate of stirring [6]. However, no major study has yet been made of reaction rates, the extent of formation of unreactive cyclic oligomers, and the nature and extent of various possible side reactions in this class of polycondensation. 

Reactivity of itaconic add in copolymerization is dependent upon pH and degrees of ionization of the add. Acid reactivity has been studied most carefully in acrylonitrile copolymerization 33, 37). Under acidic conditions an increase in itaconic concentration greatly decreases the polymerization rate, while at pH s of 7—9.8 moderate increases of itaconate do not reduce the rates so strongly. Monomer reactivity ratios and Q and e values have been calculated for the various states of ionization of the acid as reported in Table 5. As the pH rises, drops from 1.57 to 0.1 suggesting, as stated earlier, that the dianion undergoes little homopolymerization. The change in is less than 2-fold which indicates appreciable copolymerization of the dianion. The much greater decrease... 

Table II. Polymerization Rates of Various Monomer Batches...

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