Viscoelastic properties of branched polyacrylate melts

The viscoelastic properties of poly(n-butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate) melts have been studied using samples that varied in both molar mass and the mol% branched repeat units, these properties having been previously determined by gel permeation chromatography and C-13 NMR spectroscopy, respectively. Poly(n-butyl acrylate) was studied most extensively using seven samples; one sample of poly(n-butyl acrylate), two samples of poly(ethyl acrylate) and one sample of poly(methyl acrylate) were used to study the effect of side-group size. Storage and loss moduli were measured over a range of frequency (1x10(-3) to 1x10(2)rads(-1)) at temperatures from T-g + 20 degreesC to T-g + 155 degreesC and then shifted to form master curves at T-g + 74 degreesC through use of standard superposition procedures. The plateau regions were not distinct due to the broad molar mass distributions of the polyacrylates. Hence, the upper and lower limits of shear storage modulus from the nominal 'plateau' region of the curves for the seven poly(n-butyl acrylate) samples were used to calculate the chain molar mass between entanglements, M-e, which gave the range 13.0kg mol(-1) <M-e< 65.0kg mol(-1) The Graessley-Edwards dimensionless interaction density and dimensionless contour length concentration were calculated for poly(n-butyl acrylate) using the mean value of plateau modulus (1.2 x 10(5) Pa) and three different methods for estimation of the Kuhn length; the data fitted closely to the Graessley-Edwards universal plot. The Williams-Landel-Ferry C-1 and C-2 parameters were determined for each of the polyacrylates; the data for the poly(n-butyl acrylate) samples indicate an overall reduction in C-1 and C-2 as the degree of branching increases. Although the values of C-1 and C-2 were different for poly(n-butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate), there is no trend for variation with structure. Thus the viscoelastic properties of the polyacrylate melts are similar to those for other polymer melts and, for the samples investigated, the effect of molar mass appears to dominate the effect of branching. (C) 2001 Society of Chemical Industry.