Laser-induced polymerization advantages

The attractiveness and major advantage of using pulsed lasers in kinetic studies is a result of the short duration of the laser pulse (typically 10 to 20 ns). Opposed to more conventional methods such as rotating sector and spatially intermittent polymerization, the initiation period can now be considered to be instantaneous on the time scale of propagation. As a consequence, all radicals formed in one laser pulse are of approximately the same chain length at any moment in time, which greatly simplifies the kinetic scheme. It is this quality of laser-induced experiments that leads to the reliability of the PLP method to determine kp values (in conjunction with an accurate MWD determination). 

This technique proved particularly well suited to follow ultra-fast polymerizations induced by laser beams and Aus to obtain directly the kinedc profile of the reaction, as shown by Figure 10. One of the unique advantages of this method is that it now becomes possible, based on these kinetic curves, to determine instantly and at any moment, both the true rate of polymerization and the amount of residual unsaturation in the cured polymer, i.e., its crosslink density. 

The TR-SP-PLP technique enables the time-resolved measurement of the rate of polymerization by spectroscopically monitoring the decrease of the monomer concentration induced by one single laser pulse. Only when the conversion per laser pulse is reasonably high, time-resolved measurements are possible. The method is therefore limited to monomers with a reasonable high kp value (or a low kt value), including ethylene [3-5, 16-18], methyl acrylate [19], butyl acrylate [20-23] and dodecyl acrylate [19]. Recently, however, it has been extended to the methacrylates [24]. The relatively low conversion per pulse is actually also an advantage as it enables a high conversion resolution for the determination of kinetic parameters in these kinds of experiments. 

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