The random polycondensation of telechelic linear chains cured with triand tetrafunctional cross-linkers has been simulated. Calculations are done for both bulk and solution reactions; critical points are located by different methods, with results in good agreement with experiment. Critical exponents ß and 7 vary from system to system, with average values ß = 0.300 ± 0.024 and 7 = 1.77 ± 0.16. The average value C_/C+ = 13.58 ± 3.50 is slightly larger than that from standard percolation.

Simultaneous cross-linking and chain scission reactions that are induced by ionizing radiation have been simulated with a computer. These studies were performed for both bulk-and solution-cured poly(dimethylsi1oxane) (PDMS) systems. Variations of network structures and mechanical properties that depend on the degree of cross-linking are presented. It is shown that radiation-cured networks are barely connected and contain large amounts of defect structures. More than 90% of the defects are found to be dangling ends, and isolated ends are dominant in this population. The weight fraction of loops is quite small, but they deplete a large fraction of the cross-links. These results are in good agreement with experiment and with other calculations. Potential correlations between network structures and the Mooney-Rivlin coefficients 2C1 and 2C2 are also discussed.ABSTRACT Partial sulfonation of poly(2-vinylnaphthalene) (P2VN) yields water-soluble copolymers (SP2VN) that appear to exhibit hypercoiling in aqueous media. Luminescence emission studies show that excimer emission

Computer simulations of the formation of trifunctional and tetrafunctional polydimethylsiloxane networks that are crosslinked by condensation of telechelic chains with multifunctional crosslinking agents have been carried out on systems containing up to 1.05 X 10 6 chains. Eigenvalue spectra of Kirchhoff matrices for these networks have been evaluated at two levels of approximation: (1) inclusion of all midchain modes, and (2) suppression of mid chain modes. By use of the recursion method of Haydock and Nex, we have been able to effectively diagonalize matrices with 730 498 rows and columns without actually constructing matrices of this size. The small eigenvalues have been computed by use of the Lanczos algorithm. We demonstrate the following results: (1) The smallest eigenvalues (with chain modes suppressed) vary as JL-2/3 for sufficiently large JL, where JL is the number of junctions in the network; (2) the eigenvalue spectra of the Kirchhoff matrices are well described by McKay's theory for random regular graphs in the range of the larger eigenvalues, but there are significant departures in the region of small eigenvalues where computed spectra have many more small eigenvalues than random regular graphs; (3) the smallest eigenvalues vary as n 1.78 where n is the number of Rouse beads in the chains that comprise the network. Computations are done for both monodisperse and polydisperse chain length distributions. Large eigenvalues associated with localized motion of the junctions are found as predicted by theory. The relationship between the small eigenvalues and the equilibrium modulus of elasticity is discussed, as is the relationship between viscoelasticity and the band edge of the spectrum.

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Computer model calculations have been used to simulate the reaction of polyoxypropylene triol with hexamethylene diisocyanate. Various molecular weight distributions and degrees of polymerisation are used in the calculation. The effect of side reactions is investigated and compared with experiment. Good agreement for both cyclisation and gel points is found for bulk and concentrated solutions. The model can be used to simulate random polycondensation reactions with a reliability approaching that of experiments, and it gives crucial results that cannot be obtained in any other way.