Intermittent illumination method

Combination rate constants for difluorochloromethyl radicals (1. 2 x 10 1 mol s ) (28) and chlorodecafluorocyclo-hexyl radicals (3 x 10 1 mol s" ) (29) are the only others which have been measured for fluoroalkyl radicals. Since these were determined by the intermittent illumination method they obviously need checking by independent techniques. 

In the ripple method a series of ripples is caused to travel over the surface of the liquid, the ripples being formed by means of an an electrically driven tuning fork dipping into the liquid. If viewed by means of intermittent illumination conveniently arranged by periodic interception of the light by interposition of a screen attached to one limb of the fork, apparently stationary waves may be observed and the mean wave length readily determined. 

The data on kp and kt as reported in the literature differ considerably. Therefore, we conducted new studies on methyl methacrylate (MMA), benzyl methacrylate (BMA), and styrene (St) as monomers. The constants were obtained by applying the method of intermittent illumination (rotating sector) combined with stationary state methods. The viscosity of the solvents varied between 0.5 and 100 cP. No mixed solvents composed of low- and high-molecular components were used but pure solvents only, the molecules of which did not deviate very much from a spherical form (methyl formate, diethyl phthalate, diethyl malonate, dimethyl glycol phthalate, etc.). 

The ratio kjkp can also be obtained, from relation (55). This is a somewhat difficult, but relatively accurate method [34]. Reliable determination of the instantaneous rate during polymerization decay is not simple. The measurements are much easier when the pre- and post-effects are alternated in close order. An elegant way of producing such conditions is illumination of photo-initiated polymerization either with intermittent switching or by the motion of the polymerizing mixture in bands of light and darkness. 

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