Composite foams result from one-shot integration of unmodified lignin into a silicone pre-elastomer, where it performs as both crosslinker and reinforcing agent.

The polymerisation of vinyl acetate at various temperatures between+l8 "C. and -50°C. to various conversions has been carried out to obtain polymers with different degrees of branching. All polymer samples showed a fall in intrinsic viscosity after hydrolysis and reacetylation. This change is related to the amount of branching in the original polymer. but the relationship did not become clear for unfractionated material. One sample was fractionated, and the fractions studied by following the changes in intrinsic viscosity and osmotic molecular weight occurring on hydrolysis and reacetylation. The fractionated sample was made from radio-active initiator, which enabled the number of catalyst-fragments per molecule to be counted, An intramolecular branching mechanism is proposed to explain the incidence of branch points in molecules which are in effect linear. ZUSAMMENFASSUNG: Um Polymere mit verschiedenem Verzweigungsgrad zu erhalten, wurde die Polymerisation des Vinylacetats bei verschiedenen Temperaturen zwischen + 18°C und -50°C und mit verschieden groBen Umsatzen dnrchgefiiit. Alle diese Polymeren zeigten nach ihrer Hydrolyse und Reacetylierung einen Viskositatsabfall. Der Abfall hiingt vom Grad der Verzweigung im urspriinglichen Polymeren ab, doch lieB sich fiir unfraktionierte Produkte keine klare Beziehung erkennen. Daher wurden an den Fraktionen einer Probe die dnderungen der Viskositat und des osmotischen Molekulargewichts bei der Hydrolyse und Reacetylierung verfolgt. Da die fraktionierte Probe mit radioaktivem Initiator hergestellt worden war, konnte die Zahl der Initiator-Bruchstiicke pro Molekiil ausgezlihlt werden. Urn das Auftreten von Verzweigungspunkten in wirklich linearen Molekiilen zu deuten, wird ein intramolekularer Verzweigungsmechanismus vorgeschlagen.

The rates of polymerization of monomers in rubber in aqueous dispersion are higher than in the corresponding bulk polymerizations. The higher rates, which are independent of latex concentration over the range of concentration studied, have been attributed to the ingress of free radicals from a certain volume of the aqueous phase surrounding each particle. The γ‐radiation‐initiated graft polymerization of styrene with rubber is similar to that with methyl methacrylate, though the fraction of grafted polymer is lower. In the photoinitiated systems, styrene behaves differently from methyl methacrylate in that the rate of polymerization diminishes at higher monomer concentrations.

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