Homopolymerization high-conversion

One final point should be made. The observation of significant solvent effects on kp in homopolymerization and on reactivity ratios in copolymerization (Section 8.3.1) calls into question the methods for reactivity ratio measurement which rely on evaluation of the polymer composition for various monomer feed ratios (Section 7.3.2). If solvent effects arc significant, it would seem to follow that reactivity ratios in bulk copolymerization should be a function of the feed composition.138 Moreover, since the reaction medium alters with conversion, the reactivity ratios may also vary with conversion. Thus the two most common sources of data used in reactivity ratio determination (i.e. low conversion composition measurements and composition conversion measurements) are potentially flawed. A corollary of this statement also provides one explanation for any failure of reactivity ratios to predict copolymer composition at high conversion. The effect of solvents on radical copolymerization remains an area in need of further research. 

Maleate Surfmers were found to outperform methacrylic and crotonic compounds in the copolymerization of styrene, butyl acrylate and acrylic acid in seeded and nonseeded semicontinuous processes [17]. The maleate Surfmer achieved high conversion without homopolymerization in the aqueous phase which can result in emulsion instability. The methacrylate Surfmer was too reactive as opposed to the crotonate which was not sufficiently reactive. The reported dependence of the maleate Surfmer conversion on the particle diameter is consistent with a reaction at the particle surface. 

Although the resulting highly substituted terminal double bonds are usually nonhomopolymerizable, they can sometimes be reprotonated (reversible transfer) [286]. If co- or homopolymerization is possible, branched polymers of higher molecular weight are produced, primarily at high conversions. 

Although indan formation is significant in styrene polymerizations, j3-proton elimination is much faster than intramolecular alkylation [292]. Unsaturated styrene and a-methylstyrene dimers are prepared quantitatively under high dilution at elevated temperatures without cyclization to indan derivatives [293]. In this case, the carbocations must be quenched before intramolecular cyclization becomes significant at high conversion. However, indan formation competes with depropagation at temperatures above 50° C, which is much too high for unsaturated styrene dimers (D =) to homopolymerize. As outlined in Eq. (95), the unsaturated dimers form indans (Din) in the presence of acid. 

In the past the really well understood particle formation and kinetics involved the single-charge homopolymerization of styrene-like monomers in the presence of micellar surfactants and of water soluble initiators with long half lives. Even for these systems the theory was predictive only at relatively low conversions. Now the kinetics are well imderstood even at high conversions. 

Poly(styrene-c i-t-butyl acrylate). One of the major issues with TEMPO mediated "living free radical polymerizations is the very different reactivities of st5n ene and acrylates. It has been observed that TEMPO mediated styrene homopolymerization achieve high conversion, with low polydispersity and excellent molecular weight control. In contrast acrylate homopolymerizations exhibit considerably lower conversion with much broader polydispersities. Figure 2. However, it has been shown that "living" free radical polymerization permits the synthesis of well defined... 

In contrast to MAH A-substituted maleimides can be homopolymerized with high conversions and up to high molecular weights [1083-1090]. 

In Refs. [15,16], the kinetic models of radical (co)pol5mierization were obtained after the concept of polymerizing system microheterogeneity that considers the process of homopolymerization of polyfimctional monomers till high conversion in two reaction zones and of monofimctional monomers in three reaction zones. 

The kinetics of graft copolymerization substantially correspond to those of styrene homopolymerization except at low rubber concentrations and at high conversions due to cross-linking reactions [34]. Figure 9 illustrates a schematic of a network of polybutadiene and polystyrene [35]. 

Emulsion homopolymerization or copolymerization of MMA is usually carried out in a pressurized batch reactor with a water-soluble initiator and surfactant. The polymerization temperature may be varied from 85 C to 95 C to achieve high conversion. Bacterial attack, common in acrylic polymer... 

Based on the differences in mechanisms of homopolymerization of dimethacrylate and diallyl ethers mentioned above, differences in the processes of gel-matrix formation based on them are quite understandable. It is also noted [72, 84, 85] that, depending on the nature of applied allyl monomers (for example, DAIP, DAP DAC, etc.), a microgel at higher degrees of transformation may be formed due to selection of conditions of homopolymerization performance (the presence of inhibitors, chain transmitters, etc.). Therewith, the proportion of soluble linear and branched products (zole-fraction) increases significantly. It was also found that the zole-fraction output up to high conversion degrees of these monomers is lower than of insoluble polymer. 

RTCP was applicable to acrylonitrile (AN) and various functional monomers, for which NIS (deactivator catalyst) and CHD (precursor catalyst) were particularly effective, as Table 7.3 shows the examples. The compatible functional groups included hydrophobic and hydrophilic groups such as 2-ethylhexyl (EHMA), benzyl (BzMA), phenyl (POMA), epoxy (GMA), hydroxyl (HEMA), poly(ethylene glycol) (PEGMA), dimethylamino (DMAEMA), non-protected amino (ASt), and non-protected carboxylic acid (MAA) groups. In the homopolymerizations and random copolymerizations, Mn well agreed with M , heo. and PDI was small (1.1-1.4) from low to high conversions, with a small amount (1-10 mM) of the catalyst (as in the case of St and MMA) in many cases. 

Equation (31) allows the determination of the ratio of propagation rate constants k3/k2 by correlation of the experimental results obtained in copolymerization using equimolar ratios of monomers with the results obtained at non-equimolar monomer ratio and excess of anhydride (an excess of epoxide should not be used because of homopolymerization of the monomers at high degree of conversion). A value of k3,/k2 equal to 0.2 0.1 was found for the system 2-hydroxy-4-(2,3-epoxypropoxy) benzophenone-phthalic anhydride in nitrobenzene initiated by hexadecyltrimethyl-ammonium bromide 56). 

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