Reaction mechanisms, polymers

C. McMeill and A. Ricon, Thermal degradation of polycarbonates reaction conditions and reaction mechanisms, Polym. Degrad. Stab., 39, 13-19 (1993). 

Ford, W. T., and M. Tomoi, Polymer-Supported Phase Transfer Catalysts Reaction Mechanisms, Polym.ScL, 55, 49 (1984). 

Grassie, N., Murray, E.J., Holmes, P.A., The Thermal Degradation of Poly(d-j8-hydroxybutyric acid) part 3—The Reaction Mechanism, Polym. Degr. Stab., 6, 127, 1981. 

Paulussen, H., et al. 2001. New mechanistic aspects on the formation of poly(isothianaphthene) from P4S10 and phthalic anhydride derivatives Carbon-carbon bone formation and cleavage via a cyclic reaction mechanism. Polymer 41 3121. 

Takahashi, M., Satch, T., and Toya, T., Oligoethylenes in high pressure polyethyl-enes. II. Reaction mechanism, Polymer Bull, 2, 643, 1980. 

Of special importance for realization of the controlled gradient formation is an understanding of the reaction mechanism (polymer-analogous transformation /diffusion copolymerization) so that the dmation of the process can be determined in order to control the reaction product. Specifically, the refractive index change with time is investigated, i.e. the function n =J[t) is determined, where n is the refractive index, r is the duration of chemical reaction/diffusion. 

Polymerization Reactions. The polymerization of butadiene with itself and with other monomers represents its largest commercial use. The commercially most important polymers are styrene—butadiene mbber (SBR), polybutadiene (BR), styrene—butadiene latex (SBL), acrylonittile—butadiene—styrene polymer (ABS), and nittile mbber (NR). The reaction mechanisms are free-radical, anionic, cationic, or coordinate, depending on the nature of the initiators or catalysts (194—196). 

This is an exothermic reaction, and both homogeneous (radical or cationic) and heterogeneous (soHd catalyst) initiators are used. The products range in molecular weight from below 1000 to a few million (see Olefin polymers). Reaction mechanisms and reactor designs have been extensively discussed (10-12). 

Bateman, Gee, Barnard, and others at the British Rubber Producers Research Association [6,7] developed a free radical chain reaction mechanism to explain the autoxidation of rubber which was later extended to other polymers and hydrocarbon compounds of technological importance [8,9]. Scheme 1 gives the main steps of the free radical chain reaction process involved in polymer oxidation and highlights the important role of hydroperoxides in the autoinitiation reaction, reaction lb and Ic. For most polymers, reaction le is rate determining and hence at normal oxygen pressures, the concentration of peroxyl radical (ROO ) is maximum and termination is favoured by reactions of ROO reactions If and Ig. 

In general, the reaction mechanism of elastomeric polymers with vulcanisation reagents is slow. Therefore, it is natural to add special accelerators to rubber compounds to speed the reaction. Accelerators are usually organic compounds such as amines, aldehyde-amines, thiazoles, thiurams or dithio-carbamates, either on their own or in various combinations. 

This book will be of major interest to researchers in industry and in academic institutions as a reference source on the factors which control radical polymerization and as an aid in designing polymer syntheses. It is also intended to serve as a text for graduate students in the broad area of polymer chemistry. The book places an emphasis on reaction mechanisms and the organic chemistry of polymerization. It also ties in developments in polymerization kinetics and physical chemistry of the systems to provide a complete picture of this most important subject. 

For any specific BW treatment application, determining the types and concentrations of polymers that are likely to prove the most successful remains a difficult task. There are few design rules, the in-field application and control processes are still more art than dependable science, and the various reaction mechanisms are not... 

Chemistry, reaction mechanisms, and properties have been extensively reviewed.4,5,10-20 Hie present chapter deals witii only one type of fully cyclized aromatic heterocyclic polymers die high-molecular-weight linear polymer witii a special emphasis on die synthesis and structure—property relationships for specific applications. 

Copolymerization is of practical and theoretical interest2,72). The practical interest is a result of the possibility to synthesize polymers with modified properties as opposed to the homopolymers. It is theoretically interesting because the ratios of monomers in the starting mixture are in many cases different from those in the copolymer. This can be helpful for making assertions about reaction mechanisms and relative monomer reactivities. 

Reaction Mechanism. The reaction mechanism of the anionic-solution polymerization of styrene monomer using n-butyllithium initiator has been the subject of considerable experimental and theoretical investigation (1-8). The polymerization process occurs as the alkyllithium attacks monomeric styrene to initiate active species, which, in turn, grow by a stepwise propagation reaction. This polymerization reaction is characterized by the production of straight chain active polymer molecules ("living" polymer) without termination, branching, or transfer reactions. 

Many polymerizations use a low viscosity nonsolvent to suspend the polymer phase. Water is the most common suspending phase. Table 13.6 characterizes a variety of reaction mechanisms in which water is the continuous phase. 

Multi-State Models. In studies of copolymerization kinetics and polymer microstructure, the use of reaction probability models can provide a convenient framework whereby the experimental data can be organized and interpreted, and can also give insight on reaction mechanisms. (1.,2) The models, however, only apply to polymers containing one polymer component. For polymers with mixtures of different components, the one-state simple models cannot be used directly. Generally multi-state models(11) are needed, viz. 

To develop the rate equations suitable for process modeling and reactor design, experimental data have been analyzed on the basis of the postulated reaction mechanism [2] given in Table 1. Here the formation of polymer is excluded because it is not detected under our experimental conditions. All of the reactions are equilibrium-limited and the net rates for the formation of each component with some assumptions [3] are given as follows ... 

In this chapter the topochemical [2+2] photoreactions of diolefin crystals are reviewed from the viewpoints of organic photochemistry, analysis of reaction mechanism, and crystallography as well as in terms of synthetic polymer chemistry and polymer physics. 

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