Determination of free-radical propagation rate coefficients of butyl, 2-ethylhexyl, and dodecyl acrylates by pulsed-laser polymerization

Analysis of the molecular weight distributions (MWDs) of polymer produced by pulsed-laser polymerization (PLP) is an effective method for the determination of free-radical propagation rate coefficients (k(p)). The PLP technique has been successfully applied to many slowly propagating monomers, but k(p) determination by PLP for faster propagating systems such as the acrylates is more difficult. Experimental conditions for the polymerization must be selected so that laser pulses are the dominant chain-starting and chain-stopping events. Interference from excessive chain-transfer reactions, or from termination reactions which are either too fast or too slow, results in MWDs which are not suitable for k(p) determination. Guidelines for design of successful experiments are outlined using an extensive n-butyl acrylate data set, from which k(p) has been determined over the temperature range 5-30 degrees C; limited data for n-dodecyl acrylate and 2-ethylhexyl acrylate are also presented.