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POSTER PRESENTATION
Tuesday, 15:40, Panel No. 4
Structure and dynamics of polyethylene melts bearing short chain branches frequently spaced along their backbone as revealed from atomistic simulations
V. Dimitriadis1, N. Karayiannis1, V.G. Mavrantzas1, E. Chiotellis2, D. Mouratides2, C.D. Kiparissides2
1 Department of Chemical Engineering, University of Patras & FORTH-ICE/HT, Patras GR 26504, Greece
2 Department of Chemical Engineering, Aristotle University of Thessaloniki & CPERI-CERTH, Thessaloniki 54124, Greece
Based on the molecular architecture of the constituent chains polyethylene (PE) is usually classified as HDPE (High Density PE), LLDPE (Linear Low Density PE), and LDPE (Low Density PE). HDPE consists of linear chains resulting from the catalytic reaction of pure ethylene monomers, LLDPE consists of chains bearing short branches sparsely distributed along their main backbone and LDPE consists of chains with densely packed branches of variable length that may carry additional arms thus creating a complex, dendritic-like structure. LDPE and other well-defined polymers with several kinds of molecular architecture are nowadays synthesized by metallocene and other single-site catalysts through anionic living polymerization techniques by employing organolithium initiators. Also, dangling branches are considered in general as ''long'' or ''short'' if their length longer or shorter, respectively, than the characteristic molecular length between entanglements, Ne, which for PE is around C70. In this work, we will present results for the effect of short chain branching (SCB) on the volumetric, structure, conformational and dynamic properties of PE obtained from detailed atomistic MC and MD simulations with two families of PE microstructures: the first corresponded to a total of 142 carbon atoms per chain (MW = 1990 g/mol) and the second to a total of 320 carbon atoms per chain (MW = 4482 g/mol). We will show that short-chain branched (SCB) PE melts are characterized by significantly smaller dimensions than linear PE melts of the same total chain length under the same temperature and pressure conditions, due to the more symmetric arrangement of their material around the chain center-of-mass. In contrast, SCB and linear PE melts of the same chain length exhibit practically identical volumetric properties, suggesting that the differences recorded at temperatures below their melting point in the densities of the ''LLDPE'' and ''HDPE'' end-products of PE are due to their totally different degrees of crystallinity. We will also show that short-chain branching causes a decrease in the chain self diffusion coefficient compared to the value exhibited by the linear melt of the same total chain length by a factor which can range from 10 up to 40% depending on the molecular characteristics of the simulated system (branch length, branching frequency, and total chain length). © IWNET 2006
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and Kleanthi for IWNET 2006