Molecular Modeling of Novel Graft Copolymers
Bobby G. Sumpter1, Donald W. Noid1, Jimmy W. Mays1,2, Samuel P. Gido3, Roland Weidisch4
1Computer and Mathematics Division, ORNL
Recently the tensile properties of tetra-functional multigraft copolymers was shown to have surprising high strain at break (~2100%), about double that of commercial thermoplastic elastomers such as Kraton! Multigraft copolymers can be synthesized with a variety of branches (single, bi, tri-, tetra and with different lengths) at each branch point and there can be a large number of branch points per molecule that are regularly, randomly, or heterogeneously spaced, each of which can have effects on mechanical properties. Unfortunately experimental synthesis and characterization of these novel polymer systems is quite time consuming. This is where molecular modeling and simulation are critical for mapping out the fundamental mechanisms responsible for the observed behavior and to optimize/focus the experimental efforts. We have recently used extensive molecular dynamics, molecular mechanics, Monte Carlo, and normal mode analysis to examine the properties tri- and tetra-functional, multi branch point copolymers consisting of a polyisoprene backbone and polystyrene branches. These simulations combined with experimental characterization have revealed a number of novel structural and dynamical properties. In particular, the effect of adding tetra-functional branch points on a polyisoprene backbone leads to complete nanophase separation of the two polymer components, with the polystyrene branches self-organizing into nano-domains uniformly distributed along the backbone. A large number of branch points per molecule allow the elastic polyisoprene backbone to more effectively couple to the larger number of reinforcing polystyrene domains which effectively communicate structural and mechanical rigidity among their neighboring domains. Compared to tri-functional branch points, an enhanced performance in mechanical properties seems to result from the increased density of molecular interactions between the polystyrene nano-domains. The new molecular-based insight has allowed us, to a priori predict qualitative mechanical performance properties of newly synthesized multifunctional graft copolymers.
Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy
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Updated:Friday, 07-Jan-2005 10:06:46 EST