Dynamic viscoelasticity of a series of poly(4-n-alkylstyrene)s and their alkyl chain length dependence

Abstract

Dynamic viscoelastic measurements were performed for a series of poly(4-n-alkylstyrene)s with six different n-alkyl side chains, that is, methyl, ethyl, propyl, butyl, hexyl and octyl groups. Based on the time-temperature superposition principle, storage modulus G′, loss modulus G″ and loss tangent tan δ were shifted with horizontal shift factor aT and vertical shift factor bT, giving well superposed master curves for all the polymers. With increase of the number of carbon atoms, plateau modulus GN0, which corresponds to G′ value at minimum tan δ, decreases, while entanglement molecular weight Me(=ρRT/GN0) increases, where ρ is the polymer density, R is the gas constant and T is the absolute temperature. Degree of polymerization at onset of entanglement, Ne, which defined as Me/M0, where M0 denotes the molecular weight of each monomer, also increases with increase of n-alkyl side chain length. Packing length estimated from the empirical equation by Fetters also increases with increase of n-alkyl lengths. These results are presumably due to large polymer chain thickness caused directly by substituents on phenyl rings of styrene units.