Molecular simulation of physical properties of hindered-amine light stabilizers in polyethylene

Novel Monte Carlo methods are used to simulate the excess chemical potentia l of commercial hindered-amine light stabilizers (HALS) in polyethylene. Th e solubility change incurred by increasing the size of the pendant tail of HALS molecules by a single methylene segment is estimated using simulations . Our results indicate that HALS molecules undergo a conformational transit ion at intermediate pendant-tail chain lengths. Our results also indicate t hat, above the boiling temperature of a particular stabilizer HALS, a segme ntal chain length increase raises its solubility in polyethylene. Similar p henomena are observed for small alkanes in polyethylene both theoretically and experimentally. The relative solubility of HALS of different lengths ap pears to increase with decreasing temperature. Results of molecular dynamic s simulations yield diffusion coefficients that are consistent with availab le experimental data.