synopsisThe bulk polymerization of vinyl chloride initiated by AIBN at temperature levels of 30", 50°, and 70°C has been studied. Molecular weight averages and distribution (MWD) were measured by gel permeation chromatography. A model has been proposed which accurately predicts conversion to high levels and MWD. Molecular weight measurements show that transfer to monomer plays the important role in controlling molecular weight averages. Disproportionation is probably the dominant mode of termination.

SynopsisThis manuscript reports an experimental investigation of the mechanical degradation of polyacrylamide in aqueous solution using a high-shear couette viscometer. Equilibrium molecular weight distributions (MWD) at various shear stresses were measured by gel permeation chromatography. Degradation data indicate that the MWD becomes narrower at higher shear stresses, in general agreement with Bueche's midpoint break theory. An empirical correlation of the critical molecular weight and degrading shear stress is presented. It has the form 3.59 x 108 = where M, is the critical molecular weight and T is the degrading shear stress in dynes/cm*.

Numerical solutions of the Navier-Stokes equations have been obtained for steady flow around circulating liquid spheres in liquid media in the Reynolds number range 1-50. The results are given in the form of surface vorticity and pressure distributions and drag coefficients. The computed total drag coefficients are in excellent agreement with experimental values for a number of liquid-liquid systems.

synopsisThis manuscript reports on the development of a high-shear Couette viscometer. The main design considerations for a high-shear concentric cylinder viscometer are reviewed and discussed. I n principle, the instrument is identical to those used by other investigators. However, some modifications were found necessary. Attention is drawn to the importance of the concentricity problem. The instrument was first tested and calibrated using Newtonian standard oils. Then non-Newtonian runs were performed using narrow polystyrene standards of molecular weights 97,200, 411,000, and 860,000. Solutions of the polymer in n-butylbenzene ranged in concentration from 0.08 g/cc up to 0.5 g/cc. The shear rates applied ranged from 10' sec-1 up to 106 sec-1. The results obtained were compared to the molecular entanglement theory, and excellent agreement was observed.

SynopsisThe applicability of a model after Talamini for the bulk polymerization of vinyl chloride with several commercial initiators has been examined. The model agrees well with experimental rate data for the initiators: diisopropyl peroxydicarbonate, disecbutyl peroxydicarbonate, t-butyl peroxypivalate, lauroyl peroxide and benzoyl peroxide.Bulk polymerization of vinyl chloride is a typical example of what is known as "heterogeneous polymerization." The polymer being insoluble in its own monomer precipitates during the course of reaction giving rise to a two-phase polymerizing system.Many workers have studied the bulk polymerization of vinyl chloride experimentally, and a common observation was autocatalysis from the onset of the reaction. Many models have been proposed to describe the kinetics of the reaction. A review of these is given by Talamini and Peggion.' Most of the models proposed to date fit experimental rates up to relatively small conversions and involve parameters which have not been measured over a useful temperature range.In a previous publication12 we proposed a model which accurately predicts the molecular weight distribution as \d as the conversion to high levels. The model assumes a two-phase polymerization, in a monomerrich and polymer-rich phase. The composition of each phase remains constant, but as reaction proceeds, the mass of polymer-rich phase grows while the monomer-rich phase diminishes. Since the reaction rate per unit volume is higher in the polymer-rich phase, due to gel effect, there is an acceleration in the overall reaction rate.Under these heterogeneous conditions, the polymer molecules aggregate, forming monomer-swollen particles insoluble in the monomer. These aggregates are roughly spherical in shape; their size depends on the conversion in the early stages since they grow a little after precipitation from about 0.2 to about 1 micron in d i a m e t~r .~ The size distribution, solubility, and stability depend on the polymerization temperature. An average