Abstract
Summary: The molecular weight distribution (MWD), formed in emulsion polymerization that involves the polymer transfer reaction during Interval II, may approach the power‐law distribution as polymerization proceeds. The power exponent, α, of the weight fraction distribution W(M) = M^−α^ conforms to the relationship, α = 1/P~b~, where P~b~ is the probability that the chain end is connected to a backbone chain. The MWD of emulsion‐polymerized polyethylene reported in literature agrees reasonably well with the relationship, W(M) = M^−α^ with α = 1/P~b~. This simple relationship could be used to estimate the P~b~ value from the MWD data, possibly leading to determining the polymer transfer constant under well‐designed experimental conditions. Because α > 1, the number‐average MW always approaches a finite value, but the weight‐ and higher order‐averages of MWD may continue to increase as the particle grows without limit depending on the magnitude of P~b~. The power‐law distributions are self‐similar, possessing the nature of fractals and lacking a characteristic scale. The i‐th moment of the MWD for the present reaction system continues to increase without limit during Interval II for P~b~ ≥ 1/i.
Molecular weight distribution of the emulsion‐polymerized polyethylene.
magnified imageMolecular weight distribution of the emulsion‐polymerized polyethylene.