Chain copolymerization applications

Copolymerization is also important in step polymerization. Relatively few studies on step copolymerization have been carried out, although there are considerable commercial applications. Unlike the situation in chain copolymerization, the overall composition of the copolymer obtained in a step copolymerization is usually the same as the feed composition since step reactions must be carried out to close to 100% conversion for the synthesis of... 

The copolymerization equation has been experimentally verified in innumerable comonomer systems. The copolymerization equation is equally applicable to radical, cationic, and anionic chain copolymerizations, although the r and r2 values for any particular comonomer pair can be drastically different depending on the mode of initiation. 

The simple copolymer equation [Eq. (7.11)] has been experimentally verified in innumerable comonomer systems. The equation is equally applicable to radical, cationic, and anionic chain copolymerizations, although the and T2 values for any particular monomer pair can be drastically different in the three types of chain copolymerization. For example, for the monomer pair of styrene (Mx) and methyl methacrylate (M2) the ri and T2 values are 0.52 and 0.46 in radical copolymerization, 10 and 0.1 in cationic polymerization, and 0.1 and 6 in anionic copolyraerization. Methyl methacrylate as expected has higher reactivity in anionic copolymerization and lower reactivity in cationic copolymerization, while the opposite is the case for styrene. Thus the copolymer obtained from an equimolar styrene-methyl methacrylate feed is approximately a 1 1 copolymer in the radical case but is essentially a homopolymer of styrene in cationic copolyraerization and a homopolymer of methyl methacrylate in anionic copolymerization. This high selectivity of ionic copolymerization limits its practical use. Since, moreover, only a small number of monomers undergo ionic copolyraerization (see Chapter 8), the range of copolymer products that can be obtained is limited. On the other hand, almost all monomers undergo radical copolymerization and thus a wide range of copolymers can be synthesized. 

Macromolecular chain Synthesis of macromonomers Monomer(s) copolymerized Applications Refs. 

Other examples of peroxy inisurfs can also be found in Russian scientific papers. As for instance in Ref. [41] Voronov et al. describe a polymeric surfactant with peroxy side chains for application as inisurfs in emulsion polymerization. They obtained the polymeric inisurf (Inisurf 2) by copolymerization of a peroxide containing monomer (dimethyl-vinylethinyl-methyl-tm-butyl-peroxide) with acrylic or methacrylic acid or 2-methyl-5-vinyl pyridine with benzoyl peroxide as initiator in the presence of dodecylmercaptan as chain transfer agent. The resulting copolymers are water soluble at appropriate pH-values, surface active, and exhibit a critical micelle concentratioiL... 

For many applications, the homopolymer of styrene is too brittle. To overcome that, many different approaches were originally tried. These included use of high molecular weight polymers, use of plasticizers, fillers (glass fiber, wood flour, etc.), deliberate orientation of the polymeric chains, copolymerization and addition of rubbery substances. Effect of plasticizers is too severe for practical use, and use of high molecular weight polymers exhibits only marginal improvement. Use of fillers. 

The major applications of catalytic chain transfer are in molecular weight control and in synthesis of macromonomcrs based on methacrylate esters. However, they have also been shown effective in polymerizations and copolymerizations of MAA, MAM, MAN, AMS, S and some other monomers. 

Recent progress of basic and application studies in chitin chemistry was reviewed by Kurita (2001) with emphasis on the controlled modification reactions for the preparation of chitin derivatives. The reactions discussed include hydrolysis of main chain, deacetylation, acylation, M-phthaloylation, tosylation, alkylation, Schiff base formation, reductive alkylation, 0-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Among soluble precursors, N-phthaloyl chitosan is particularly useful and made possible a series of regioselective and quantitative substitutions that was otherwise difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone [89]. 

The instantaneous composition of a copolymer X formed at a monomer mixture composition x coincides, provided the ideal model is applicable, with stationary vector ji of matrix Q with the elements (8). The mathematical apparatus of the theory of Markov chains permits immediately one to wright out of the expression for the probability of any sequence P Uk in macromolecules formed at given x. This provides an exhaustive solution to the problem of sequence distribution for copolymers synthesized at initial conversions p l when the monomer mixture composition x has had no time to deviate noticeably from its initial value x°. As for the high-conversion copolymerization products they evidently represent a mixture of Markovian copolymers prepared at different times, i.e. under different concentrations of monomers in the reaction system. Consequently, in order to calculate the probability of a certain sequence Uk, it is necessary to average its instantaneous value P Uk over all conversions p preceding the conversion p up to which the synthesis was conducted. 

In this section, the important concepts related to the formation of hydrogels by free radical copolymerization/cross-linking are examined. Greater depth beyond the scope of this chapter can be obtained from textbooks on polymer chemistry and the papers cited herein. As stated earlier, almost all gels produced from monomers for pharmaceutical applications are synthesized by free radical chain polymerizations. 

The monomers used to make an addition polymer need not be identical. When two or more different monomers are polymerized into the same chain, the product is a copolymer. For instance, we routinely copolymerize ethylene with small percentages of other monomers such as a-olefins (e.g., 1-butene and 1-hexene) and vinyl acetate. We call the products of these reactions linear low density polyethylenes and ethylene-vinyl acetate copolymer, respectively. We encounter these copolymers in such diverse applications as cling film, food storage containers, natural gas distribution pipes, and shoe insoles. 

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