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The mechanism of constraint release for an entangled linear chain of polystyrene diffusing by reptation is emphasized, dissolving large N chains in a matrix of shorter N, chains of the same species.Dynamic shear measurements allow us to define an average relaxation time f(NJVt) for the relaxation of the large chains, from which we derive another average relaxation time for the tube modification induced by constraint release. We find that, according to the Klein and Graessley theories, the tube could be considered as a Rouse chain (rmod(1V^VS) AT9*0-1) but constraint release is not directly connected to the reptation of the N, chains (rmod(A''ArB)2'3±0'1)-The process of constraint release included in the diffusion of chains in a binary blend at various component concentrations allows us to specify the idea of "cell" in the Graessley theory and to describe reasonably the variations of the limiting parameters and Je°w ith blend composition.

We have measured the equilibrium forces between two mica surfaces separated by a thin liquid film of a perfluorinated polyether. The observed force law was monotonically repulsive and had a range which was on the order of ten times the radius of gyration of the polymer molecules. The results can be explained by hypothesizing that some of the polymer chains are effectively ‘‘pinned’’ to the surfaces and thus are not free to exchange with chains in the bulk reservoir on the time scale of the experiments. We have also investigated the response of the same polymer melt to both sinusoidal and step perturbations in the distance between the two surfaces as a function of the film thickness. We have developed a simple rheological model for a linear, viscoelastic fluid which relates the experimental data to the effective viscosity of the confined fluid. For surface separations greater than approximately 1500 Å, the effective viscosity of the fluid film was found to be the same as the macroscopically measured value reported for the bulk polymer. For a surface separation of 840 Å, the effective viscosity was found to be greater than the bulk value. The results obtained from the dynamic experiments agreed with those obtained from the transient experiments.

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We report the formation of polyacrylate (molten state polymers: Tg < room temperature) monolayers attached onto silica surfaces using covalently bonded initiators for radical‐chain polymerisation. In a first reaction step, the initiator is self‐assembled on the surface. In a subsequent reaction, the initiator is activated and the polymer formed in situ at the surface of the substrate with high grafting density (‘grafting from’ procedure). Moreover, the use of a living free radical process permits the molecular weight and polydispersity of the polymer chains to be controlled, and thus the polymer monolayer thickness also. We have also made a preliminary qualitative characterisation by X‐ray spectroscopy (XPS) and Fourier transformed infrared (FTIR) measurements. © 2002 Society of Chemical Industry

Considering that the terminal relaxation of every chain in a linear melt is dominated by reptational and constraint release motions, we propose an expression for the relaxation modulus G(t) of entangled polymers as a function of the molecular weight distribution (MWD). The expressions of zero-shear viscosity rj0 and steady-state compliance =/e°d erived from G(t) describe correctly the experimental behavior: 0 scales with average molecular weight as 0 Mw3•4"3•8 for a constant polydispersity P; Je°i ncreases strongly with P and varies widely with the shape of MWD. We also predict a decrease of viscosity with polydispersity; this is a possible explanation of some experimental variations of viscosity, which do not follow the classical power law with Mw. The behavior expected for strictly monodisperse samples shows that it is necessary to consider a relaxation times distribution in the terminal region.

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