Monomer loss, rate

The monomer recovery process may vary ia commercial practice. A less desirable sequence is to filter or centrifuge the slurry to recover the polymer and then pass the filtrate through a conventional distillation tower to recover the unreacted monomer. The need for monomer recovery may be minimized by usiag two-stage filtration with filtrate recycle after the first stage. Nonvolatile monomers, such as sodium styrene sulfonate, can be partially recovered ia this manner. This often makes process control more difficult because some reaction by-products can affect the rate of polymerization and often the composition may vary. When recycle is used it is often done to control discharges iato the environment rather than to reduce monomer losses. 

Since propagation is the stage that involves the major consumption of monomer (otherwise polymer would not form), the rate of monomer loss can be expressed in terms of propagation only ... 

Thus, 0 = Rate of monomer loss through reaction + Rate of polymer accumulation... 

General conclusions about relative rates of monomer loss are probably valid at low conversion (<20%) before true network conditions are established. 

Figure 3 compares the experimental rate of monomer loss in Gardon s batch reactor, the tubular reactor,and... 

The possibility of a radical leaving a particle has furthermore been mentioned by Edelhauser (20) and Breitenbach (22), who also point out that small monomeric radicals are being formed during polymerization by transfer reaction to monomer. Loss of radicals by diffusion out of the particles in a system which obeys the Smith-Ewart rate theory does not influence the kinetics, provided that there is no appreciable termination in the aqueous phase. For each particle losing one radical in a random process, another particle gains this radical in an equally random manner. 

The loss rate of fc-mers due to the addition of a monomer and subsequent growth will then be... 

The Rp curves of miniemulsion and conventional emulsion polymerization obtained by calorimetry show the same general behavior [219]. In contrast to conventional emulsion polymerization, in miniemulsion polymerization, the monomer concentration in polymer particles diminishes throughout the polymerization. At the beginning, the nucleation rate overcompensates the decrease of monomer concentration leading to the first rise in the Rp. The number of droplets decreases and the remaining droplets shrink in size due to monomer loss by molecular diffusion to the polymer particles. As a consequence, the nucleation rate diminishes and eventually it may not be fast enough to compensate the decrease of the monomer concentration. Thus, Rp may reach a maximum and decrease before the end of the nucleation period [219], In conventional emulsion polymerization, the nucleation period ends before the first maximum in Rp, which is ascribed to the disappearance of monomer droplets [125]. 

Rate of monomer loss due to reaction within the reactor... 

Care also has to be taken not to overcool the reaction. If so, a slowdown in the polymerization rate may occur, with excess free monomer, leading to an exotherm followed by foaming or an overloading of the condenser. A reduction in the monomer feed rate at this time is essential, but again care has to be exercised, as a sudden loss of cooling from the incoming monomer stream coupled with a drop-off in the reflux rate can give an uncontrollable exotherm. 

The rate of monomer loss during the n-butyllithium-initiated anionic polymerisation of styrene in ethylbenzene was measured using Raman spectroscopy. GPC measurements on the reaction products were used as an... 

The rate of monomer loss from solution (R, molal/sec) tends to be proportional to the fourth power of monomer concentration (Icopini et al., 2005 Rothbaum and Rohde, 1979). Icopini et al. (2005) explain this by assuming that the ratedetermining step is a reaction converting the trimer, formed by reaction (9.7), into a cyclical tetramer. 

The main technique used to look at exchange processes in equilibrium systems employs labeled surfactants, particularly with ESR spectroscopy. Fox s ESR study [92] of a paramagnetic surfactant in micellar solution was the first of its kind, and yielded a solution-micelle monomer exchange rate of 10 s" at room tanperature for 2,2,6,6-tetramethylpiperidine-oxidedodecyldimethylammonium bromide. These techniques, along with time-resolved luminescence quenching, have shown that the entry of surfactant molecules into micelles is near-diffusion controlled, whereas loss from micelles is rate limiting, and hence kinetically controlled [93]. A decade later (1981), Bolt and Turro [94] were able to find the separate exit and reentry rate constants for 10-(4-bromo-l-naphthoyl)decyltrimethylammonium bromide as 3.2 x 10 s and 5.7 x 10 mok s", respectively. 

In the propagation step, the rate of monomer loss can be equated to the rate of propagation (Rp) which is represented by the Eq. (1.9) ... 

Pure dry reactants are needed to prevent catalyst deactivation effective inhibitor systems are also desirable as weU as high reaction rates, since many of the specialty monomers are less stable than the lower alkyl acrylates. The alcohol—ester azeotrope (8) should be removed rapidly from the reaction mixture and an efficient column used to minimize reactant loss to the distillate. After the reaction is completed, the catalyst may be removed and the mixture distilled to obtain the ester. The method is particularly useful for the preparation of functional monomers which caimot be prepared by direct esterification. 

The second context is the process reac tor. There is a potential for a runaway if the net heat gain of the system exceeds its total heat loss capabihty. A self-heating rate of 3°C/day is not unusual for a monomer storage tank in the early stages of a runaway. This corresponds to 0.00208°C/min, 10 percent of the ARC s detection limit. ARC data for the stored chemical would not show an exotherm until the self-heating rate was 0.02°C/min. Therefore, onset temperature information from ARC testing must be used with considerable caution. 

Dialkyl peroxydicarbonates have been reported as low temperature sources of alkoxy radicals (Scheme 3.30)lfMJfb and these radicals may be formed in relatively inert media. However, it is established, for primary and secondary peroxydicarbonates, that the rate of loss of carbon dioxide is slow compared to the rate of addition to most monomers or reaction with other substrates.186,187 Thus, in polymerizations carried out with diisopropyl peroxydicarbonate (47), chains will be initiated by isopropoxycarbonyloxy (48) rather than isopropoxy radicals (49) (see 3.4.2.2).188... 

Aliphatic acyloxy radicals undergo facile fragmentation with loss of carbon dioxide (Scheme 3,69) and, with few exceptions,428 do not have sufficient lifetime to enable direct reaction with monomers or other substrates. The rate constants for decarboxylation of aliphatic acyloxy radicals are in the range l 10xl09 M 1 s at 20 °C.429 lister end groups in polymers produced with aliphatic diacyl peroxides as initiators most likely arise by transfer to initiator (see 3.3.2.1,4). The chemistry of the carbon-centered radicals formed by (3-scission of acyloxy radicals is discussed above (see 3.4.1). 

There will be a gradual loss of stable radical with these systems as the di- or triarylmethyl radicals produced from the macroinitiator can add monomer, albeit slowly.99 100 This side reaction provides a mechanism for mopping up the excess stable radical formed as a consequence of termination between propagating radicals and may be essential to maintaining polymerization rates. 

Concentrations of the monomer, solvent, polymer, and initiator Solution viscosity Number average polymer mol. wt. Weight average polymer mol. wt. Polymerization Rate Reaction time Heat generated Heat losses Solution Temperature Partial pressures of the monomer, solvent, and nitrogen Total pressure... 

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