Elastomer kinetics

Olander, B. Wirsen, A. Alhertsson, A.-C., Oxygen Microwave Plasma Treatment Silicone Elastomer Kinetic Behavior and Surface Composition. J. Appl. Polym. Sci. 2003, 91,4098-4104. 

Chloro 1 3 butadiene (chloroprene) is the monomer from which the elastomer neoprene IS prepared 2 Chloro 1 3 butadiene is the thermodynamically controlled product formed by addi tion of hydrogen chloride to vinylacetylene (H2C=CHC=CH) The principal product under conditions of kinetic control is the allenic chlonde 4 chloro 1 2 butadiene Suggest a mechanism to account for the formation of each product... 

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

Elastomers are used for their flexibility in seals, gaskets and hoses and to resist abrasion (through absorption of the kinetic energy of the impinging particles). The range of materials includes natural and synthetic rubbers and modem elastomers with chemical resistance. 

Methyl-l,10-undecadiene, ADMET polymerization of, 442 Michaelis-Menten enzymatic kinetics, 84 Microbial hydrolysis, 43 Microcellular elastomers, 204-205 Microphase-separated block copolymers, 6-7... 

Structurally, plastomers straddle the property range between elastomers and plastics. Plastomers inherently contain some level of crystallinity due to the predominant monomer in a crystalline sequence within the polymer chains. The most common type of this residual crystallinity is ethylene (for ethylene-predominant plastomers or E-plastomers) or isotactic propylene in meso (or m) sequences (for propylene-predominant plastomers or P-plastomers). Uninterrupted sequences of these monomers crystallize into periodic strucmres, which form crystalline lamellae. Plastomers contain in addition at least one monomer, which interrupts this sequencing of crystalline mers. This may be a monomer too large to fit into the crystal lattice. An example is the incorporation of 1-octene into a polyethylene chain. The residual hexyl side chain provides a site for the dislocation of the periodic structure required for crystals to be formed. Another example would be the incorporation of a stereo error in the insertion of propylene. Thus, a propylene insertion with an r dyad leads similarly to a dislocation in the periodic structure required for the formation of an iPP crystal. In uniformly back-mixed polymerization processes, with a single discrete polymerization catalyst, the incorporation of these intermptions is statistical and controlled by the kinetics of the polymerization process. These statistics are known as reactivity ratios. 

The flocculation results presented in Figure 22.2 give strong evidence that kinetically aggregated filler clusters or networks are formed in elastomer composites, as shown in Figure 22.5. 

If two immiscible liquids A and B (i.e., possessing very different 8 values) form two layers when brought together, and an elastomer of similar 6 to A is completely immersed in the (denser) B layer (schematically in Eigure 23.5), nevertheless, the elastomer will evenmaUy swell as if immersed completely in A. This arises because each liquid of an immiscible mixture stiU dissolves a minute amount of the other. At equilibrium, the chemical potential p of A will be the same, whether as pure liquid, dissolved in B, or dissolved in the elastomer. At the same temperature, the same p would apply for the elastomer immersed directly in A. However, the kinetics of absorption will be different, being much slower than... 

Figure 6 presents the variation of the contact angle, 6(0, on the same rubber, but this time the elastomer had not been preswollen by TCP. In comparison with the spreading kinetics on rigid solids (Teflon PFA, fused silica), we observe the same qualitative behavior as before, i.e., a relatively slower variation of the contact angle 6(t) on the elastomer. However, after the main variation of the contact angle occurring within the first 30 minutes, we observe a very slow, yet continuous, decrease of 6(t) over a period of several hours before a stable value for Go is obtained. 

In each case, the polymer is obtained as a white elastomer of high molecular weight (>106 in some experiments). Each of these polymers is soluble in benzene, in chlorinated hydrocarbons and in dipolar aprotic solvents. Figure 1 shows the kinetics of chloride substitution by tetra-n-butylammonium benzoate in N,N-dimethylacetamide at 50°C, for PECH and for the polymers of 2a-c. Under these conditions, each of the higher homologues is about equally reactive, and all are converted to the benzoate more rapidly than PECH. Each... 

G Rossi, KA Mazich. Kinetics of swelling for a cross-linked elastomer or gel in the presence of a good solvent. Phys Rev A 44 r4793-r4796, 1991. 

The synthesis and phase behavior of the model polydiethylsiloxane networks have also been studied. The networks were made by hydrosilylation of well-defined vinyl and allyl telechelic siloxanes obtained by kinetically controlled polymerization of cyclic trisiloxane.314 The effects of molecular weight between the cross-linkings on segment orientation in polydiethylsiloxane elastomers were studied.315... 

Table 1. Dependence of the kinetic parameters of the reaction, the structural parameters of the network and the physico-mechanical properties of polyurethane elastomers on the molar fraction of OH groups in the monofunctional reagent21...

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