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The evidence that the rates of radicalradical recombination reactions in solution are diffusion-controlled is assessed and the consequences of diffusion-controlled termination reactions in radical polymerisation examined. The cross-termination rate coefficients for two different radicals should be the s u m of the two mutual-termination rate coefficients of these radicals. The frequently used geometric mean relationship is not relevant to diffusion-controlled reactions. The dependence of the diffusion-controlled kt on the size of the macroradicals and its effect on the rate equation for polymerisation is examined. The nature of the mean value, Et, which is measured experimentally, is discussed.The role of diffusion-control a t high conversion is discussed. It is shown that simple diffusion-control of the propagation reaction is incompatible with the observed diffusivities of small molecules in polymer gels. ZUSAMMENFASSUNG:Der Beweis, dafi die Geschwindigkeiten der Kombiinationsreaktionen von Radikalen in Losung durch die Diffusion beschrankt werden, wird erortert und die Folgen der Diffusionsbeschrankungen bei der Abbruchsreaktion der radikalischen Polymerisation untersucht. Wenn die Reaktionen diffusionsbeschrankt sind, sollte die Abbruchsgeschwindigkeitskonstante zwischen zwei verschiedenen Radikalen (R, + R,) der Summe der zwei Abbruchskonstanten der gleichen Radikale (R, + R, nnd R, + R,) gleichen. Das oftmals verwandte geometrische Mittel ist nicht anwendbar. Die Abhiingigkeit des diffusionsbeschrankten kt von der GroBe der Makroradikale und dessen Auswirkung auf die Polymerisationsgeschwindigkeit werden untersucht. Die mittels Versuchen meBbare mittlere Abbruchskonstante Et wird diskutiert.Die Rolle der Diffusionsbeschrdcung bei hohem Umsatz wird erortert, und es wird gezeigt, daS die einfache D i f f u s i o n s b e s c h r l g der Wachstumsreaktion mit den Diffusionsgeschwindigkeiten kleiner Molekiile in makromolekularen Gelen unvereinbar ist.Molecules in the liquid phase, being closely packed, have much lower mobilities than those in the gas phase. This reduced mobility has two effects. Firstly it increases the time taken for two molecules, initially separated, to encounter one another, and secondly it increases the length of the period for which two molecules, having come together, remain in close proximity. The second of these effects is generally known as the 1) E. RABINOWITCE, Trans. Faraday SOC. 33 (1937) 1225.

Dynamic-mechanical and fracture properties and proton-enhanced, magic angle spinning 13C NMR time constants for polymers of the CH2=C(CH3)CO(OCH2CH2)xOCOC(CH3)=CH2 series (x = 1 to i = 22) and poly[tetrakis(ethylene glycol) diacrylate] have been measured. The effects of increasing length of the soft oxyethylene chain, x, undercure (x = 1-4), and oxyethylene crystallization (x = 22) were observed. The results are interpreted in terms of the contributions of components of group motion to the cooperative motion of segments of the network which control the response to a macroscopic deformation.

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Starting from the assumption that a polymer molecule in solution will only degrade under the influence of ultrasonic irradiation if both the resulting fragments are greater than Pe/2 in size, where Pe is the so‐called limiting degree of polymerization, rela tionships are derived giving the rate of degradation in terms of rate of breaking of bonds. If dBi/dt the rate of breakage of bonds in molecules of size Pi, the proposed rate equations are: dBi/dt = k(Pi – Pe)ni for Pi > Pe and dBi/dt = 0 for Pi ⪕ Pe, where k is a constant characteristic of the system and ni is the number of molecules of size Pi. Solutions of this equation are given for three sets of conditions.