Monomer friction effects

Figure 9.8 Dependence of (a) D on and (b) on M/Mcd for a wide variety of polymer and solvent systems. Note that in (a) the monomer friction effect has been removed and the data follow a universal curve. In (b) is taken from an equivalent concentration and is shown plotted in arbitrary units. Mqd corresponds to the intersection of the and M" asymptotes. (From A.I. Maklakov et al. [105] and reproduced by permission of the Gulf Publishing...

We present here the results of such a systematic investigation on the dependence of the self-diffusion coefficient of flexible polymer chains as a function of P and N, conducted on polydimethylsiloxane (PDMS). This model polymer is well above its glass temperature at room temperature (Ta = - 120°C), so that one can expect that spurious effects associated with the variation of the free volume and of the local monomer-monomer friction coefficient with the molecular weights of the chains are minimised. 

An important question is to decide how far one can believe that a self-diffusion coefficient varying like N is characteristic of reptation. It has been argued that additional molecular weight dependences could exist and compensate for departures from the N 2 law [48 to 52]. Such an effect can come from the local monomer-monomer friction coefficient w hich appears as a prefactor in equation 8, hidden in the diffusion coefficient D. Several processes can combine and lead to a local friction which is molecular weight dependent, and W hich decreases when the polymer molecular weight is decreased. This is, for example, the... 

The purpose of our study was a rheological evaluation of the effect of composition on the properties of ABS resins in the molten state. Steady-state viscosity was determined over a wide range of temperatures and shear rates. The shear modulus in the molten state was determined by measurement of the diameter of the extrudate. ABS resins in the molten state behaved as an amorphous homophase polymer. The effect of the elastomer phase on the viscoelastic properties which characterize the behavior of the continuous matrix, i.e. monomer friction coefficient and molecular weight between entanglements (Me), was calculated by the application of the molecular theories. The significance of these properties in heterophase systems is discussed. 

In very dilute solutions we have considered mainly single chain motions, and we have studied dynamic quantities in the limit of zero concentration. When the concentration is non-zero, one must take into account interactions between different chains, both static interactions and hydrodynamic interactions. If the concentration is smaller than the overlap concentration c, in the so-called virial regime, these effects are small and can be treated as perturbations. This is not the case, however, in a semi-dilute regime, where the motions become collective and thus renormalize the local monomer friction C which becomes concentration dependent. 

This equation relates the screening length of the hydrodynamic interactions A to the effective monomer friction ... 

The effective monomer friction constant is obtained by dividing the blob friction Cb by the number of monomers per blob g = c ... 

Rouse behavior observed on PI homopolymer melts has to be modified if the labelled (protonated) PI species are replaced by diblock copolymers of proto-nated PI and deuterated polystyrene (PS) [46]. The characteristic frequency Q(Q) is slowed down considerably due to the presence of the non-vanishing X-parameter. Thus, the reduction is stronger at smaller Q-values or at larger length scales than in the opposite case. In addition, as a minor effect, Q(Q) becomes dependent on both friction coefficients per mean square monomer length, //2, valid for PI and for PS. 

J 2 mw 178.14, O 53.89% It-yel ndls (from alc), mp 86-87° dec, darkens on exposure to light explodes violently on heating in a flame, or on impact or friction sol in eth, acet methanol, chlf, CCl4 benz insol in w or petr eth can be prepd by reacting aq Na peroxide furoyl chloride at 0°(Refs 1, 2 3). Cooper (Ref 4) studied the effect of structure of diacyl peroxydes on their radical-induced decompn in vinyl monomers... 

Comparison of Eqs (8.16) and (8.25) reveals that the Zimm time is shorter than the Rouse time in dilute solution. In principle, a chain in dilute solution could move a distance of order of its size by Rouse motion, by Zimm motion, or some combination of the two. The chain could simply move its monomers by Rouse motion through the solvent without dragging any of the solvent molecules with it, or it could drag all of the solvent in its pervaded volume with it, thereby moving by Zimm motion. In dilute solution, Zimm motion has less frictional resistance than Rouse motion, and therefore, the faster process is Zimm motion. The chain effectively moves as though it were a solid particle with volume of order of its per-... 

---