The monomeric and polymeric glycerides present in thermally polymerized linseed oils can be separated quantitatively by molecular distillation. Analysis of the fatty acids of monomeric and polymeric glycerides indicate the occurence of intra-and intermolecular condensations respectively. Whereas in the former reaction, leading to the formation of bicyclic, dimeric fatty acid groups within the orginal glycerides, no increase in the molecular weight of the oil takes place, in the latter one, characterized by an increase in the molecular weight, fatty acids of different glyceride molecules are involved. It is shown, however, that the overall increase in molecular weight is due to the dimeric glycerides which are formed by interesterification reactions between glyceride monomers containing dimeric fatty acid groups, the latter resulting from intramolecular condensation.
Uber den Mechanismus der thermischen Polymerisation des Lein-6les Die monomeren und polymeren Glyceride in thermisch behandelten Leinolen konnen mit Hilfe der Molekulardestillation quantitativ getrennt werden. Analysen der Fettsauren der monomeren bzw. polymeren Glyceride lassen auf intra-bzw. intermolekulare Addition scfilie0en. Bei der erstgenannten Reaktion, die ohne Zunahme des Molekulargewichtes des Oles erfolgt, entstehen bicyclische, dimere Fettsauregruppen innerhalb der urspriinglichen Glyceride, wahrend bei der letztgenannten Reaktion, begleitet von einer Zunahme des Molekulargewichtes, Fettsauren verschiedener Glyceridmolekiile beteiligt sind. Es wird festgestellt, daD die gesamte Zunahme des Molekulargewichtes in betrachtlichem MaDe durch die Anwesenheit dimerer Glyceride verursacht wird, die durch Umesterung zwiscfien den durcfi intramolekulare Addition gebildeten dimeren Fettsauregruppen-haltigen monomeren Glyceriden entstehen.
It is well known that the basic reaction occurring in the thermal polymerization of linseed oil is a Diels-Alder addition of two fatty acid groups. This mecha- nism was first proposed by C. P. A. Kappelmeier' and subsequently proved by H. I. Watermane*3. The addition may take place between two fatty acid groups that belong to two separate glycerides. This intermolecular reaction causes a dimerization of the triglycerides concerned. On the other hand, Diels-Alder addition may also occur between two fatty acid groups that are part of the same triglyceride molecule. This second, intramolecular, reaction does not increase the molecular weight of the stand oil.
C . van Loon, T. P . Hilditch and other workers have
pointed out that interesterification may take place between two triglycerides, in one of which two fatty acid groups have been joined together (as for instance through a Diels-Alder addition). However, it had not so far been shown that T . P. Hilditch's contention is correct. It is diffi-