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Abstract
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Poly(methyl-methacrylate), PMMA, is a disubstituted vinyl polymer whose properties depend significantly
on its tacticity. Here we present a detailed study of the structure, conformation, and dynamics of
syndiotactic, atactic, and isotactic PMMA melts at various temperatures (580, 550, 520, and 490 K) via
all-atom molecular dynamics simulations. The calculated volumetric properties are close to
experimental data. The Tg and chain dimensions of PMMA model systems are found to depend
strongly on tacticity in agreement with experimental findings. The backbone bonds in trans (t), diads in
tt, and inter-diads in t|t torsional states are the most populated for all PMMA stereo-chemistries and
their fractions increase with the number of syndiotactic sequences. Also, the effective torsional barrier
heights for the backbone, ester side group, and a-methyl group are larger for syndiotactic PMMA
compared to the isotactic one. The structure of the PMMA chains is studied by computing the intraand
inter-chain static structure factors, S(q), and the radial pair distribution functions. In the first peak
of S(q), both intra- and inter-chain components contribute, whereas the second and third peaks
mainly come from inter- and intra-chain parts, respectively. For all PMMA stereo-isomers a clear
tendency of ester-methyl groups to aggregate is observed. The local dynamics are studied by
analyzing torsional autocorrelation functions for various dihedral angles.
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