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Second virial coefficients and radii of gyration for an off-lattice model of linear and star polymer chains in a good solvent (or excluded volume conditions) have been obtained by means of a Monte Carlo method. The results are discussed in terms of the dimensionless interpenetration factor, which combines these two quantities. Comparisons with theoretical prediction from the renormalization group theory and with existing simulation and experimental data are performed for the different types of chains.

We have performed Monte Carlo simulations to reproduce the intrinsic viscosity corresponding to different generation of several types of dendrite molecules: polyamidoamine dendrimers with an ethylendiamine core, polypropylene-imine with a diaminobutane core, and monodendrons and tridendrons of polybenzylether. With this end, we have employed coarse-grained idealizations of the molecules constituted by only two beads in each repeat unit (one in a branching or end unit and one intermediate along the repeat unit) and a simple hard-sphere potential between non-neighboring beads. Our goal is to investigate if this simple model is able to provide a reasonable description of some differences between these systems that have been observed experimentally, in particular, the location of the maximum in the intrinsic viscosity as a function of the generation number. Experimental radii of gyration in a given solvent are reproduced by a fit of the hard-sphere potential diameter. Subsequently, intrinsic viscosities are calculated by the variational approach of Fixman, which yields an accurate lower-bound value with an additional hydrodynamic interaction parameter (the friction radius of the beads). The results show a pronounced variation of the maximum location with the value of the friction radius and the structural details that cannot be mimicked with simpler models. The initial conformations for the Monte Carlo procedure are taken from atomistic configurations thermalized by means of a molecular dynamics.

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High even moments and distribution functions of the end-to-end distance of short poly(dimethylsiloxane) (PDMS) and poly(oxyethylene) (POE) chains, described by means of the rotational isomeric state model, are evaluated according to a method recently proposed by Fixman et al. The application of the method to these heterogeneous chains includes a slight modification of the iterative procedure previously used for calculations of polymethylene (PM) moments. The distribution functions obtained this way are in good agreement with Monte Carlo calculations. The distribution functions of PDMS chains have been employed to derive an elastic equation that describes the non-Gaussian behavior of networks at high elongations. The method has been applied to model bimodal PDMS networks yielding a fair description of the experimental data. A semiquantitative estimation of the distribution of strains within the network chains indicates the expected high degree of nonaffineness in the deformation of these bimodal networks.

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