The mechanism of the initiation reaction for the polymerization of cyclic ethers and lactones by triethyloxonium-, acetyl-and dioxolenium-salts was studied.Triethyloxonium salts initiate the polymerization of cyclic ethers simply by the alkyl exchange reaction. Cyclic esters react with triethyloxoninm salts at both ether and carbonyl oxygens but the polymerization proceeds by the acyl-oxygen fission. The k, value of the polymerization of THF by triethyloxonium salts is almost constant independent of gegenanion. Acetyl cation initiates the polymerization of THF partly by bonding mechanism, bul dioxolenium salt initiates completely by bonding. ZUSAMMENFASSUNG:Der Mechanismus der Initiierungsreaktion bei der Polymerisation von cyclischen Athern und von Laktonen mit Triathyloxonium-, Acetyl-und Dioxoleninm-Salzen wurde untersucht.Triathyloxonium-Salze initiieren die Polymerisation cyclischer Ather iiber eine Umalkylierung. Mit cyclischen Estern tritt eine Reaktion sowohl am Ather-als auch am Carbonyl-SauerstoE ein ; die Polymerisation verlauft aber ausschliefilich iiber eine Acyl-Spaltung.Bei der Polymerisation von T H F mit Triathyloxonium-Salzen ist die Geschwindigkeitskonstante der Wachstumsreaktion k, nahezu unabhangig vom Gegen-Anion. Acetyl-Kationen starten die THF-Polymerisation nur teilweise unter Ausbildung von gebundenen Oxonium-Ionen mit den Monomeren ; Dioxolenium-Salze starten dagegen ausschliel3lich nach diesem Mechanismus.

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Copolymerization of 1,3-dioxolane (DOL) with tetrahydrofuran (THF) was attempted with triethyl oxonium tetrafluoroborat+ (Et30BF4) as initiator. The gas chromatographic determination of the unreacted monomers during the reaction indicated that preferential polymerization of THF occurred in the initial stage of the reaction, and that once DOL began to polymerize after an induction period, the polymerization of T H F declined gradually and ceased. However, it was resumed, although very slowly, after the polymerization of DOL reached the equilibrium conversion. Two-step polymerizations of THF and DOL by utilizing the living nature of the polymerization by Et30BF4 yielded a mixture of the homopolymers. The mechanism of this unusual polymerization is discussed. The addition of THF t o the cationic chain ends with DOL as the terminal unit does not occur but proton transfer takes place. ZUSAMMENFASSUNG:Die Copolymerisation von 1.3-Dioxolan (DOL) mit Tetrahydrofuran (THF) wurde mit Triathyloxoniumtetrafluoroborat ((CzH&OBF4) als Initiator versucht. Es ergab sich aus der gaschromatographischen Bestimmung der Monomerkonzentrationen im Verlauf der Reaktion, dafi das THF vorzugsweise im Anfangsstadium der Reaktion polymerisiert und dafi die Polymerisation des T H F stufenweise abnimmt und schliefilich aufhort, sobald das DOL nach einer Induktionsperiode einmal begonnen hat zu polymerisieren. Jedoch beginnt die Polymerisation des THFwenn auch sehr langsamvon neuem, nachdem die Polymerisation des DOL das Gleichgewicht erreicht hat. Zweistufenpolymerisationen von THF und DOL, die mit (CzH5)30BF4 als Jebende" Polymerisation durchgefuhrt wurden, ergaben ein Gemiscb der Homopolymeren. Der Mechanismus dieser ungewohnlichen Polymerisation wird diskutiert : die Addition von THF an kationische Kettenenden niit endstandigem DOL-Baustein erfolgt nicht ; statt dessen tritt Hydridubertragung ein.

ABSTRACT:Copolymerization of 1,3-dioxolane(DOL) and isoprene(Ip) by BFa·Et2O has been studied, particularly laying stress on the microstructure of the products. The diad fractions determined by NMR analysis have indicated that both monomer units are distributed randomly in the copolymer chain. The loss of unsaturation (the fraction of saturated Ip units to total Ip units), which was generally observed in cationically prepared Ip homopolymers, diminished with increasing DOL fraction and became practically negligible in the copolymers rich in DOL units. The structure of Ip units in the copolymer was also found to depend on the composition, namely, the fraction of the 1,4-structure, which was prevailing in Ip homopolymers prepared by the cationic initiator, decreased markedly with increasing DOL fraction in the copolymer.

Cationic polymerization of tetrahydrofuran (THF) with 2-methyl-1,3dioxoleum perchlorate proceeded as a living system without chain transfer and termination, and the initiation reaction was shown to be the bonding mechanism. Poly-THF with terminal dioxolenium perchlorate group was synthesized from poly(tetramethylene glycol) by stepwise reaction with adipoyl chloride, ethylene bromohydrin, and silver perchlorate. The quantitative formation of macromolecular dioxolenium salt was proved from the polymerization behavior of the THF. Polymerization of 3,3-bischloromethyloxetane by the initiator yielded block copolymer, and no chain-transfer reaction except the termination reaction was observed. Polymerization of 7-oxabicyclo[2.2.l]heptane by the initiator yielded homopolymer as well as block copolymer, and a significant amount of chain transfer reaction was observed. Polymerizatian of dioxolane and tetraoxane by the initiator yielded little block copolymer, demonstrating the different mechanism of the initiation reaction in the case of cyclic formals.