Spatially intermittent polymerization

From this we can see that knowledge of k f and Rf in a conventional polymerization process readily yields a value of the ratio kp fkt. In order to obtain a value for kf wc require further information on kv. Analysis of / , data obtained under non-steady state conditions (when there is no continuous source of initiator radicals) yields the ratio kvlkx. Various non-stcady state methods have been developed including the rotating sector method, spatially intermittent polymerization and pulsed laser polymerization (PLP). The classical approach for deriving the individual values of kp and kt by combining values for kp kx. with kp/k, obtained in separate experiments can, however, be problematical because the values of kx are strongly dependent on the polymerization conditions (Section... 

Fig. 8. Schematic representation and function of a reactor for spatially intermittent polymerization.

Similar in principle to the aforesaid rotating sector method is a method known as spatially intermittent polymerization (O Driscoll and Mahabadi, 1976). It... 

Evidence for kt being chain-length dependent came also from the initial results from Spatially Intermittent Polymerization (SIP) experiments [149]. O Driscoll and Mahabadi found that the termination rate coefficient was a strong function of chain length for both MMA [149] and S [150] up to chain lengths of approximately 1000 for MMA and 2000 for S. For chain lengths exceeding these values, the termination rate coefficient was found to be a... 

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). 

Traditionally, measurement of fep has required determination of the rate of polymerization under steady-state (to give fep/fe, ) and non-steady-state conditions (to give fep/fet). The classical techniques in this context are the rotating sector " and related methods such as spatially intermittent polymerization (SIP). ... 

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