Elastomeric polymeric networks

The SANS experiment is applicable to polymeric networks containing some deuterium labeled chains. The chain geometry can be probed not only in the unperturbed network, but changes in chain shape and size can be measured as a function of strain or swelling. This enhances the applicability of SANS experiments for elastomeric systems. 

Although both polymeric networks in IPN s may be visualized as continuous, their milky appearance hints at a more complex morphology. In order to characterize the morphology, the elastomeric portion of the IPN s was stained selectively using osmium tetroxide (see Section 2.4) to facilitate staining, about 1% of butadiene was incorporated as a comonomer in the PEA. This special product was designated PEAB. 

C (Figure 15.20). The elastomeric polymeric networks from 14 and 17 were found to have degradation temperatures ranging from 500 to 550 °C. 

Mark, J. E., Some Topological Issues in the Area of Elastomeric Polymeric Networks. NewJ. Chem. 1993,17, 703-709. 

In the following sections a recipe for calculating a statistical mechanical partition junction of an elastomeric polymeric network is proposed. It was formulated with the above-mentioned anomalies in mind. 

Distribution functions for the end-to-end separation of polymeric sulfur and selenium are obtained from Monte-Carlo simulations which take into account the chains geometric characteristics and conformational preferences. Comparisons with the corresponding information on PE demonstrate the remarkable equilibrium flexibility or compactness of these two molecules. Use of the S and Se distribution functions in the three-chain model for rubberlike elasticity in the affine limit gives elastomeric properties very close to those of non-Gaussian networks, even though their distribution functions appear to be significantly non-Gaussian. 

In any case, if this polymerized form of elemental sulfur is quenched (cooled rapidly), it becomes a solid. This solid is glassy at very low temperatures, but becomes highly elastomeric above its glass-transition temperature of approximately -30 °c.6 8 14 30 The situation is complicated by the presence of unpolymerized S8 molecules which would certainly act as plasticizers. So far, attempts to cross-link the elastomeric form into a network structure suitable for stress-strain measurements have not been successful. The polymer is unstable at room temperature, gradually crystallizing, and eventually reverting entirely to the S8 cyclics. 

Ti has also been incorporated into elastomeric Si-containing networks. These are prepared by Sn-catalyzed polymerization of tetraethoxysilane (TEOS) and oligomeric dimethyl silanols, containing 5 or 10 Si atoms. Part of the TEOS can be replaced by Ti(OiPr)4 or Ti tetrakis(2-ethylhexyloxide) ... 

In our laboratory, much attention has been devoted to the investigation of in situ sequential polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (SEQ PUR/PAc IPNs) (2- ) in which the elastomeric polyurethane network is completely formed in the presence of the methacrylic monomers before the onset of the radical copolymerization which leads to the second network. To each polymerization process corresponds a typical kinetics, which however is not completely independent from each other ( -8). The results obtained with such SEQ IPNs show that the properties do in... 

A number of variations of the above-mentioned full IPNs have also been stated in the literature. One of them involves having either Polymer I or II as linear (not crosslinked) polymer, in which case it is called semi-IPN. The other variation involves the formation of Polymer I and II simultaneously through two noninterfering polymerization processes (such as stepwise and chain polymerizations) in which case it is called simultaneous IPN (SIN). If a linear polymer is formed simultaneously with a crosslinked polymer, then we have a semisimultaneous IPN (semi-SINS). Still another type is taking a mixture of two linear polymers, and crosslinking both components simultaneously, in which case it is called interpenetrating elastomeric network (lEN). The common feature of... 

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