Results with Different Monomers

Styrene is one of the best-behaved of monomers in that it tends to follow most closely classical Ewart and Smith (1948) kinetics. There are many exceptions, however, even with potassium persulfate, the standard chemical initiator. The best agreement was found with potassium persulfate as the initiator and sodium lauryi sulfate as the emulsifier. Until recently (Garreau el aL, 1979), the various studies were mainly conducted with other systems and for reasons other than to check whether there are, indeed, any real differences betwe radiation and chemical initiation in such an ideal system. 

Acres and Dalton (1963a), using the dioctyl ester of sodium sulfosuc-cinate as the emulsifier, found the intensity exponent of the rate to vary with the monomer to water ratio from 0-22 to 0.34 but to reach the classical Smith-Ewart value of 0.4 when extrapolated back to zero monomer concentration. They interpreted this result in terms of the special role of the hydrogen atans arising from the radiolysis of water. 

Araki et al (1967, 1969) conducted some rather straightforward polymerizations of styrene, and the properties of the resulting latiees using y 

Recently, Garreau et al. (1979) reported a careful and rather detailed study of the kinetics of the radiation-induced polymerization of styrene in emulsion with sodium lauryl sulfate under conditions found earlier to lend to close agreement with simple Case 2 Smilh-Ewart kinetics (Smith, 1948). Most of the normal reaction variables were studied, and the rates of polymerization were found to be independent of the luonomer-to-water 

Temperature dependence of the rates and degrees of polymerization for the radiation induced polymerization of styrene. Dose rate OJ093 Mrad/hr (Oarreau er al. 1979 reproduced with permission of Journal of Colloid and Inlerfoct Science.) 

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While sequence distributions are usually subject to more experimental noise than composition data, this is often outweighed by the greater information content. In principle, reactivity ratios can be estimated from a single copolymer sample. The consistency in reactivity ratios estimated with eqs. 45 and 46 for copolymers prepared with different monomer feed compositions and/or obtaining the same result from cqs. 50 and 51 (4 aab—Ai ab) and cqs. 52 and 53 (r aba-Aiba) arc... 

Grazing angle XAS techniques (XANES) can be applied to ultrathin film systems [316]. Selected NEX-AFS, XPS and FUR spectroscopy results were obtained for plasma-polymerised films with different monomers (styrene, acetylene, ethylene and butadiene) [317]. 

The value of these monomers is also emphasised by the observation that OSCI3 with 7-methylNBE gives -50% cis polymer where the cis dyads are syndiotactic and the trans are atactic and the polymers are very blocky. These results confirm the consistency of all the work with different monomers. Furthermore, as expected, (mesitylene)W(CO)3 / EtAlCl2 as catalyst produced a polymer with fully syndiotactic cis dyads and fully isotactic trans dyads. 

The results with benzene, however, deviate considerably from first order. To eliminate viscosity and other problems polymerizations were conducted in benzene solution with differing monomer concentrations using the initial rates only. The values of (C ) were calculated from (Rj /k ) at each concentration and the initial rates corrected for these changes. A log-log plot of Rp/(C" ") values versus the initial monomer concentrations is presented in Figure 5. 

These results do not agree with the predominant effect of the dielectric constant reported previously. To check further, mixtures of monomer, benzene and methylene chloride were prepared, with the same computed overall dielectric constant but with different monomer contents, and the initial rates determined. The values fitted exactly on the same rate versus monomer concentration curve. Further experiments were carried out in benzene with different amounts of methylene chloride but constant initial monomer concentration. A very small amount of methylene chloride reduced the rate of noly-merization to the one determined in pure methylene chloride. The activation energies were also determined and found to be about 7.5 Reals, per mole much less than in bulk or low dielectric constant solvents. 

An alternative way to mne the polymer properties and insert desired functionalities is copolymerization with different monomers. Cyclic carbonates have been copolymerized with various other cyclic monomers, such as lactones or lactides. For example, TMC was copolymerized with 5-methyl-5-benzyloxycar-bonyl-l,3-dioxan-2-one (MBC) using lipase from Pseudomonas flourescens (PF) resulting in a highly amorphous random copolymers (Fig. 8) [74]. In another smdy, 5-benzyloxy-trimethylene carbonate (BTMC) was copolymerized with 5,5-dimethyl-trimethylene carbonate (DTC) using an immobilized hpase on silica particles [79]. In the copolymerization of TMC with a lactone, m-pentadecalactone (PDL), employing Novozyme 435, highly erystalline TMC-PDL eopolymers were obtained, and as opposed to chemical catalysts, enzyme eatalyst (Novozyme 435) polymerized PDL more rapidly than TMC [80]. 

The interpolymers from natural rubber plus monomer vary widely methyl methacrylate and styrene give a soluble product whereas chloroprene, acrylonitrile and methacrylic acid produce a gel containing the polymerized monomer. Extensive investigations were carried out on maleic anhydride [15, 99-101] for the reinforcement of rubber and because of the peculiar reaction. Table 5.15 is a summary of the most important results obtained using natural and synthetic rubbers with different monomers. 

Soum and Fontanillet prepared a living polymer of 2-vin yl pyridine using benzyl picolyl magnesium as the initiator. The values of were measured experimentally for polymers prepared with different concentrations of initiator and different initial concentrations of monomer. The results are given below calculate the theoretical molecular weights expected if polymerization proceeds completely from 100% predissociated initiator and compare the theoretical and experimental values ... 

Crystallinity of polypropylene is usually determined by x-ray diffraction (21). Isotactic polymer consists of heHcal molecules, with three monomer units pet chain unit, resulting in a spacing between units of identical conformation of 0.65 nm (Fig. 2a). These molecules interact with others, or different... 

A copolymer, on the other hand, results from two different monomers hy addition polymerization. For example, a thermoplastic polymer with better properties than an ethylene homopolymer comes from copolymerizing ethylene and propylene ... 

Achieving steady-state operation in a continuous tank reactor system can be difficult. Particle nucleation phenomena and the decrease in termination rate caused by high viscosity within the particles (gel effect) can contribute to significant reactor instabilities. Variation in the level of inhibitors in the feed streams can also cause reactor control problems. Conversion oscillations have been observed with many different monomers. These oscillations often result from a limit cycle behavior of the particle nucleation mechanism. Such oscillations are difficult to tolerate in commercial systems. They can cause uneven heat loads and significant transients in free emulsifier concentration thus potentially causing flocculation and the formation of wall polymer. This problem may be one of the most difficult to handle in the development of commercial continuous processes. 

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