Tetrahydrofuran polymerization halide

Conqparlson of the rates of silver halide formation with rates of tetrahydrofuran polymerizations using model hhlldes and different silver salts. 

It has been shown for many metal halides and monomers that binary mixtures of these can be prepared (usually in a solvent) without any polymerization taking place. Such a quiescent mixture can be made to react by the addition of a suitable third compound, which is called the co-catalyst. This term is preferable to the word promoter , because in certain contexts a substance is called promoter which enhances the rate or yield of a reaction that will also go in the absence of the promoter herein lies the true distinction between promoter and co-catalyst [28]. (For example, small quantities of epoxides or epichlorohydrin act as promoters in the cationic polymerization of tetrahydrofuran.) I will take it that in the above quotation the word promoter was inadvertently used in place of co-catalyst , for only thus does it become really meaningful. 

The current work on Friedel-Crafts polymerization of cyclic ethers may be considered to date from about 1940 when Meerwein and his associates prepared a series of tertiary oxonium salts and applied them to the polymerization of tetrahydrofuran. These salts, of the general form R30+... M X4i, are easily prepared from the corresponding metal halide in a reaction with an epoxide (preferably epichlorohydrin) in ether solution. According to Meerwein et al. (3) this reaction takes place in the following steps ... 

Scheme 8.18 Mechanism for the living cationic ring-opening polymerization of tetrahydrofuran initiated by the addition of both an organic halide and silver(I) hexafluorophosphate.

Several alkyl, allyl, and benzyl halides were found to be ef dent initiators for tetrahydrofuran (THF) polymerization when allowed to react with AgPF, or AgC10 . The time required for reaction (2) to occur was measured and the... 

Diverse combinations of metal halides and Lewis bases also allowed living/controlled polymerization of monomers with high and poor reactivities. For example, polymerization of NVC was controlled under conditions milder than those of the previous report. The combination of ZnCU with a rdatively strong Lewis base, tetrahydrofuran (THF), produced polymers with a narrow MWD (Mw/A n[Pg.534]

Details of the manufacture of polytetrahydrofuran have not been disclosed. Polymerization of tetrahydrofuran can be effected only by cationic initiators. Combinations of metal halides with water are not effective but protic acids (e.g. HCIO4) and oxonium salts (e.g. ( 2115)30 ) are efficient initiators. 

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