Monomer disappearance

The three isomeric diallyl phthalates are colorless Hquids of mild, odor, low volatiUty, and relatively slow polymerisation ia the early stages. At ca 25% conversion, the viscous Hquid undergoes gelation and polymerisation accelerates however, the last monomer disappears at a slow rate. 

Polymerization/lsomerization. The polymerization of 5-methyl-1,4-hexadiene (>99% pure) was carried out in n-pentane with a (5-TiCl3/Et2AlCl catalyst at 0°C according to the procedure described previously (14). To assess monomer disappearance and identify isomerization products, samples were withdrawn at specified intervals from the reaction mixture for GLC analysis (14). The final polymer conversion was determined by precipitation in excess methanol. 

Thus, within the approximations on which scheme (1) is based, the yield Y/( 1 + Y) of ring product is solely determined by the value of the initial monomer concentration relative to the kintra/kdim ratio, which Stoll et al. termed the cyclisation constant C. C has units of mol 1 1 and represents the monomer concentration at which intra- and intermolecular processes occur at the same rate. That Stoll et al. disregarded the fact that two monomer units are used up in the intermolecular condensation, as well as that the monomer disappears by reaction with functional groups at the ends of polymer chains was pointed out by Morawetz and Goodman (1970), who proposed an alternative approximate solution to the problem, as based on... 

Monomer disappears by the initiation reaction (Eq. 3-14) as well as by the propagation reactions (Eq. 3-15). The rate of monomer disappearance, which is synonymous with the rate of polymerization, is given by... 

In a homogeneous isothermal liquid polymerization, 20% of the monomer disappears in 34 minutes for initial monomer concentration of 0.04 and also for 0.8 mol/liter. What rate equation represents the disappearance of the monomer ... 

The rate expression for propagation is given by the rate of monomer disappearance ... 

PFS gas as a catalyst in the absence of ECH has given more complex kinetics. Sims (40) found that the rate of monomer disappearance at any given time was higher for higher initial monomer concentrations. There... 

That ethylene oxide can react directly with oxonium ions is shown by its reaction with triethyl oxonium borofluoride but this reaction, because of its complexity, does not shed much light on the polymerization. The sole product is dioxane and the vinyl ether colors appear only after all epoxide has reacted. Initial rates suggest first order in catalyst but the first order plots of monomer disappearance are flat S-curves suggesting a rate which first falls off, then tends towards zero order. The first step in the reaction is most probably a simple bimolecular alkylation of the epoxide by oxonium salt but the subsequent steps are obscure. The simplest path would be... 

When the initiator (I) is very efficient, e.g. kp/k < 0.3, and an excess of monomer (M) is used, the initiator disappears according to a near-first-order law before much monomer has been consumed. Once it is all used up the monomer disappears exactly according to a first-order law since the concentration of living propagating species (P) is now constant and equal to the original concentration of initiator. Hence, provided that both initiator and monomer concentrations can be followed, say by H NMR, both k and kp may be determined60. 

Since every achiral substrate is eventually consumed a(t = oo) = 0 and all the reactions stop asymptotically, Eq. 39 tells us that the product rs should vanish. If there is more R than S initially, S monomer disappears ultimately, for instance. But S molecules do not disappear nor decompose back into achiral substrate. They are only incorporated into the heterodimer RS. The system is not determined solely by monomer concentrations r and s, (or (p and q ) but also depends on heterodimer concentration [.RS]. The flow takes place in a three-dimensional phase space of r, s, [RS], as shown in Fig. 5a. 

Kinetics and Phase Behavior - Table IV represents a simplified picture of the situation however, some polymerizations go through several phase changes in the course of the reaction. For example, in the bulk polymerization of PVC, the reaction medium begins as a low viscosity liquid, progresses to a slurry (the PVC polymer, which is insoluble in the monomer, precipitates), becomes a paste as the monomer disappears and finishes as a solid powder. As might be expected, modelling the kinetics of the reaction in such a situation is not a simple exercise. 

The number average degree of polymerization (Section 1.2), DP, is equal at any instant to the ratio of the rate of monomer disappearance to the rate at which completed polymer molecules are produced. That is,... 

If we now assume that the only significant changes in monomer concentrations result from propagation reactions (i.e., changes in [M,-] from initiation and transfer reactions are negligible), the rates of monomer disappearance according to the reaction schemes of (7-2)-(7-5) are... 

The complex of n-butyllithium with diethylzinc has also been studied as a polymerization initiator [180] for methylmethacrylate. In pure toluene the results obtained with this system were complex and not readily interpretable, but in presence of 1—10% tetrahydrofuran a simpler behaviour was reported. Monomer disappears by a first order process, and the observed first order coefficients can be expressed in terms of initiator, monomer and tetrahydrofuran concentrations in the following way... 

The early work on polymerization from the gas phase was done on what was then thought to be pure formaldehyde. Solid polymer formed on the cold surfaces but the data were very irreproducible. Unknown kinds and unknown amounts of impurities in the monomer and on the glass surfaces made polymerization results erratic. The polymerization of formaldehyde from the gas phase has one advantage over polymerization in solution for kinetic studies. The rate of monomer disappearance can be followed readily manometrically in addition, additives can be added simply and very accurately to gaseous formaldehyde. 

The rate of chloral polymerization was studied by estimating the monomer disappearance by NMR. Figure 26 shows a comparison of the rate of polymerization of chloral initiated by lithium tert-butoxide, a quaternary ammonium chloride and triphenyl phosphine. The rate of chloral polymerization initiated with lithium lert-butoxide was much faster than the chloride initiated polymerization. This may be explained by the much more efficient and essentially quantitative initiation with the butoxide and consequently the greater number of growing polychloral chains. 

Fig. 62 a. Plots of n of concentration of styrene or p-methyl styrene vs. time for a co-polymerization of those two monomers initiated by butyl lithium in benzene. Both monomers disappear in a pseudo-first order fashion. The pseudo-first order constants are A, and X2... 

---