Rheological Properties of Anionic Polystyrenes. I. Dynamic Viscoelasticity of Narrow-Distribution Polystyrenes

Abstract

The viscoelastic properties of narrow-distribution polystyrenes have been measured in the molten state by means of a concentric cylinder type rheometer over wide ranges of frequency and temperature. From the frequency dependence of the storage shear modulus G' and the loss modulus G", the characteristic parameters in the so-called terminal zone, such as zero-shear viscosity 0, elasticity coefficient Ac,, and steady-state compliance •8 have been evaluated, and the dependence of these parameters on the molecular weight M has been discussed. 0, Ac, and " for samples having molecular weight higher than the critical molecular weight Me are proportional to 1 23 4•7, M7•5 6, and M°, respectively. For samples having molecular weights lower than Me, 8 is proportional to M, as is predicted by the modified Rouse theory. The quasi-equilibrium modulus Gex8 evaluated from G' in the rubbery region shows a constant value of 2.0 X 10s, independent of M. This value agrees very well with that obtained by integration of the G" vs. log curve. The average molecular weight between entanglement coupling loci, Me, and the average chain length, Ze, have been calculated from Gex°to be 18,000 and 346, respectively. The current molecular theories for entanglement coupling have been discussed on the basis of these experimental results. The temperature and molecular weight dependences of the shift factor aT were also discussed, and a few parameters on the free volume, such as the Vogel temperature T0 and the temperature coefficient of the fractional free volume a¡ have been determined for narrow-distribution polystyrenes.

Extraordinary elevation of the glass transition temperature of thin polymer films grafted to silicon oxide substrates

“…The PS-OH in our samples is likely to be highly entangled since the M W we have used is 100 kg/ mol, well above the molecular weight of entanglement of PS, M e Ϸ17.7 kg/mol. 48,49 For PHS, however, our data indicate that chain entanglement is unlikely to be an important factor in determining the thickness dependence of T g because: ͑1͒ the thickness of the grafted layer after a Soxhlet extraction in THF is within 10% of the thickness after the PGMEA wash, indicating that there is little entangled but ungrafted polymer in the residual layer, and ͑2͒ the molecular weights of the two samples of PHS we have studied are 10 kg/mol and 20 kg/mol, below the M e of PHS. 50,51 In terms of our previous work demonstrating the effect of interfacial energy on the T g of supported films, chains grafted to the substrate could be viewed as constituting a very high-energy interface.…”

Molecular dynamics simulation study of nonconcatenated ring polymers in a melt. II. Dynamics

“…For branched systems strands have to fold back in order to find a new conformation without crossing any other chain, resulting in an exponential growth of the longest relaxation time due to the entropy barrier of O(strand length) between different states [2][3][4] . A number of simulation and experimental results confirm this concept [5][6][7][8][9][10][11][12][13] . For both linear and branched polymer melts, it is the free chain ends that make the known relaxation mechanisms possible.…”

Synthesis of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblocks and their potential as thermoplastic elastomers

“…Since the number of chain entanglements are very limited in the MIM triblocks, the deformation stress is not dissipated by the central block, but directly transferred to the PMMA microdomains. M e for PIOA and for PnBA has been calculated from rheological measurements [27][28][29][30], on the basis of Eq. (3) ( Table 2):…”