Kinetics of two‐phase bulk polymerization. II. The influence of dissolved polymer

Abstract

SynopsisThe effect of dissolved polybutadiene on the initial rate of polymerization of styrene was investigated by using high-precision dilatometric techniques. The dissolved polymer reduced the rate of polymerization by amounts greater than can be accounted for by a reduction in monomer concentration. Rate reductions' increased with the amount of dissolved polybutadiene and with its molecular weight and were greater for benzoyl peroxide initiator than for equal concentrations of azobisisobutyronitrile. Surprisingly, analogous rate reductions were observed when polystyrenes were substituted for the polybutadienes, except that at high polystyrene concentrations, the expected autoacceleration was observed. These rate reductions showed no correlation with the viscosity of the reaction mass, nor did the dissolved polymer affect initiator efficiency. At a given level of a particular dissolved polybutadiene, rate reductions were diminished by increasing levels of each initiator, and by adding a chain-transfer agent. Good quantitative agreement was obtained with the number-average length of the growing polymer chains, whether varied by using different initiators, changing initiator level, or adding chain-transfer agent. These results are inconsistent with a chemical mechanism, but they are explained by a proposal originated .by North and Reed whereby the dissolved polymer makes the reaction mass a "poorer" solvent for the growing polymer chains, reducing their overall coil dimensions and enhancing their rate of diffusion together for termination.

Bimolecular Free-Radical Termination at Low Conversion

“…Ludwico and Rosen (79,80) found a similar behavior in the polymerization of styrene in the presence of either polybutadiene or polystyrene. Ludwico and Rosen (79,80) found a similar behavior in the polymerization of styrene in the presence of either polybutadiene or polystyrene.…”

Bulk High‐Impact Polystyrene Process, 1

“…In a typical bulk (or quasi‐bulk) HIPS process, St is polymerized in the presence of 5–10 wt.‐% of PB and a chemical initiator (I) along the following stages: dissolution, prepolymerization, finishing, and devolatilization. The process has been crudely represented by straight lines in ternary St/PS/PB diagrams;2–6 Figure 1 reproduces one of such diagrams by Casís et al,5 where the binodal curve and tie lines were in turn taken from Kruse at 60 °C 4. After dissolving the PB in St, the prepolymerization starts at Point A (Figure 1).…”

“…After dissolving the PB in St, the prepolymerization starts at Point A (Figure 1). Initially, the reaction is homogeneous, but it phase‐separates at a monomer conversion in the range 0.5–2% (Point B) 2–5. Between the phase separation and the phase inversion (Point C), the continuous phase is PB‐rich, and the disperse phase is PS‐rich.…”

Radical Chain Polymerization

“…This occurs because coil size decreases with increasing polymer concentration, but the decrease is steeper in better solvents [Mahabadi and Rudin, 1979]. Many of these predictions for the course of polymerization in stage I have been verified [Abuin et al, 1978;Dionisio and O'Driscoll, 1980;Ludwico andRosen, 1975, 1976].…”