Polymeric networks bimodal

This atom-abstraction route was also used for the preparation of polymeric networks from alkylated [3,3 ]bis-(trithia)ferrocenophanes. A bimodal molecular weight distribution, with maxima at 4/n 5,000 and 5 x 10, was obtained by GPC for the material from which a polymer fraction was isolated (4/ = 8.5 x 10 ). Low molecular weight poly(ferrocenylene perselenides) have also been prepared from the selenium analog of 114. These materials also undergo photodegradation upon exposure to UV light in air. ... 

FIGURE 1.7 Influence of the polymerization time on the porosity of monolithic MS/BVPE polymer networks, determined by MIP. Reduction of the polymerization time converts a narrow monomodal pore distribution into a broad bimodal distribution, comprising mesopores. 

Stress-strain isotherms have also been calculated with this approach. Examples are unimodal networks of polyethylene and POMS, " polymeric sulfur and seleniirm, short n-alkane chains, natural rubber, several polyoxides, and elastin, and bimodal networks of PDMS. It is possible to include excluded volume effects, in such simulations. In the case of the partially helical polymer polyoxymethylene, the simulations were used to resolve the overall distributions into contributions from imbroken rods, once-broken rods, twice-broken rods, and so on. It was also shown how applying stresses to the ends of chains of this typ>e can be used to bias the distributions in the direction of increased helical content and increased average end-to-end distances. In this sense, imposition of a stress has the same effect on the helix-coil equilibriirm as a decrease in temperature. ... 

Data on NMR-speetra recorded during homopolymerization of bifunctional (diallyl) monomers (for example, DIAP, DEGBAC) have been published. It is found [26] that the H-NMR-speetrum of the system (in the case of DAIP homopolymerization, initiator [BP] = 3.81%, Treact = 80°C) is bimodal, in which the presence of a wide component in the spectrum is confirmed by formation of a network fraction, and a narrow component is confirmed by a quasi-linear structure. Intensity of the narrow component decreases during polymerization, but that of the wide one increases. Comparison of the correlation of wide and narrow components at different stages of polymerization allows determination of the ratio of fiactions in samples. 

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