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Influence of molecular weight distribution on the linear viscoelastic properties of polymer blends
Author(s) -
Han Chang Dae
Publication year - 1988
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1988.070350115
Subject(s) - dispersity , materials science , polymer , molar mass distribution , polymer chemistry , polymer blend , methyl methacrylate , viscoelasticity , styrene , acrylonitrile , copolymer , molecular mass , dynamic mechanical analysis , dynamic modulus , composite material , chemistry , organic chemistry , enzyme
Literature data for the dynamic viscoelastic properties of binary blends of nearly monodisperse polybutadienes, polystyrenes, and poly(methyl methacrylate)s was analyzed using logarithmic plots of dynamic storage modulus G ′ versus loss modulus G ″, based on a recent theoretical study by Han and John. 28 It has been found that for binary blends of monodisperse polymers with molecular weights M much greater than the entanglement molecular weight M e , the value of G ′ in log G ′ − log G ″ plots becomes independent of molecular weight, increases sharply as small amounts of a high‐molecular‐weight component are added to a low‐molecular‐weight component, and passes through a maximum G′ max at a critical blend composition (ϕ 2 ) max , and that G′ max becomes larger and (ϕ 2 ) max becomes smaller as the ratio of component molecular weights increases. However, as the molecular weight distribution of the constituent components becomes broader, the effect of blend composition on G ′ in log G ′ − log G ″ plots becomes less pronounced. This observation has enabled us to explain why log G ′ − log G ″ plots of binary blends of commercial polymers, namely, blends of two low‐density polyethylenes, blends of poly(ϵ‐caprolactone) and poly(styrene‐ co ‐acrylonitrile), and blends of poly(methyl methacrylate) and poly(vinylidene fluoride), all having broad molecular weight distributions, give rise to values of G ′ between those of the constituent components. When one of the constituent components has molecular weight smaller than M e , while the other has molecular weight larger, and as small amounts of the high‐molecular‐weight component are added to the low‐molecular‐weight component, log G ′ − log G ″ plots of binary blends give rise to values of G ′ larger than those of the constituent components at low values of G ″, but approaches the value of G ′ for the low‐molecular‐weight component as the value of G ″ is increased. However as the amount of the high‐molecular‐weight component is increased above a certain critical composition, binary blends give rise to values of G ′ close to that of the high‐molecular‐weight component at all values of G ″. The experimentally observed dependence of G ′ on blend composition in log G ′ − log G ″ plots is favorably compared to the theoretical prediction of a blending law proposed by Montfort and co‐workers. 14,15