William W. Graessley

Polymer crosslinking in continuous flow stirred reactors

The effect that tetrafunctional crosslinking of polymers has on molecular weight and molecular weight distribution in a continuous flow stirred reactor (CFSR) is calculated. If all mers have equal likelihood of coupling it is found that steady state operation of the reactor becomes impossible at a degree of crosslinking equal to only 14 that which causes gelation in a batch reactor. In steady state operation the ratio of weight to number average degrees of polymerization in the product cannot exceed 2Dw0/Dn0- 14, the superscripts signifying initial values of degree of polymerization. Unlike in batch reactors, where Dw diverges simultaneously with Dz and higher averages, averages higher than Dw can diverge while Dw remains finite. Thus, significant differences exist when tetrafunctional branching occurs in a CFSR rather than a batch reactor. The relationship of these results to the behavior in polymerizations with branching by polymer transfer is also discussed.

A Simple Method for Estimating Viscosity of Highly Viscous Liquids

Abstract The results indicate that the hanging-strip method provides good values of η0 under favorable circumstances. The value of the method lies in the convenience and simplicity of the experiment. With little more than a meter stick and a clock, one can estimate zero-shear viscosities which are above 0.1 MPa·s. Careful testing is very important to avoid the effects of molding history and clamping, and to assure that the time-dependence of specimen elongation conforms to the Newtonian liquid model.