ABSOLUTE PROPAGATION RATE COEFFICIENTS IN RADICAL POLYMERIZATION FROMGEL-PERMEATION CHROMATOGRAPHY OF POLYMERS PRODUCED BY INTERMITTENT INITIATION

The pulsed laser polymerization technique is now a well accepted metho d to determine propagation rate coefficients for radical polymerizatio n from molar mass distributions resulting from intermittent initiation . A simplified apparatus for the periodic photoinitiation is used whic h is much less expensive than the laser equipment. The usefulness of t he simplified equipment was proved by the determination of k(p) for st yrene at technically relevant temperatures up to 130 degrees C for the first time. Furthermore, careful inspection of the molar mass distrib ution (mmd) reveals that depending on the reaction conditions, inflect ion points (L(i)) can not only be found at integer multiples of k(p) . t(0) .[M] but also at 0.5(i) . k(p) . t(0) .[M], i = 1, 2, 3,.... A r ule to find the inflection points leading to correct values for k(p) i s proposed. It is shown that the shape of the mmd inter alia depends o n the amount of primary radical termination compared to the terminatio n reaction between growing chains. With dominant primary termination, the maxima of the distribution will give the correct k(p), whereas in the absence of primary termination the inflection points should be use d. Experimental conditions like initiator concentration, light intensi ty etc. may influence the position of the L(i) at least to some extent , and so may give a small but principal error or uncertainty in k(p). A new mathematical method for the time-dependent simulation of the res ulting mmd is presented which allows the calculations being performed on a PC within an acceptable time.