Epichlorohydrin, polymerization tetrahydrofuran

Lamot (117) prepared novel, non-nitrogen-containing compounds from calcium and diphenylethylene, (Ar) 2Ca, and then complexed the compounds with various amounts of epichlorohydrin, ECl, with tetrahydrofuran, or with a 1 0.7 mole ratio of epichlorohydrin to tetrahydrofuran. After preliminary testing of the complexes as initiators for polymerization of epichlorohy-... 

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 cationic ring-opening polymerization of epichlorohydrin in conjunction with a glycol or water as a modifier produced hydroxyl-terminated epichlorohydrin (HTE) liquid polymers (1-2). Hydroxyl-terminated polyethers of other alkylene oxides (3 4), oxetane and its derivatives (5 6), and copolymers of tetrahydrofuran (7-15) have also been reported. These hydroxyl-terminated polyethers are theoretically difunctional and used as reactive prepolymers. 

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 ... 

The initiation of tetrahydrofuran polymerization by direct addition of oxonium salts is of interest because it reveals a good deal about the mechanism, but for practical purposes the salts may be formed in the reaction mixture. The obvious method is, of course, to add a little epichlorohydrin to the mixture of monomer and Friedel Crafts reagent for only antimony pentachloride is sufficiently active to start the reaction with monomer alone, but other reactions which accomplish the same purpose are ... 

The scope of applications of cationic oxetane polymerization is rather limited, with one exception [3,3-bis(chloromethyl)oxetane, BCMO] polyoxetanes have not found any practical application. BCMO, is not as easily available as some of the 3-or 5-membered cyclic ethers (ethylene oxide, propylene oxide, epichlorohydrin, tetrahydrofuran) which are made from simple petrochemical products. 

Other initiators for tetrahydrofuran polymerizations also include Lewis acids in combinations with promoters. These are complexes of Lewis acids, like BF3, SnCU, or C2H5AICI2 with epirane compounds like epichlorohydrin. The small-ring compounds are more reactive toward many Lewis acids, or protonic acids, than tetrahydrofuran and act as promoters of the initiation reactions. The initiations in the presence of small quantities of oxirane compounds can be illustrated as follows ... 

Oxepanes are polymerized by various cationic initiators like (C2H5)3C BF4 , (C2H5)3C -SbCl6 , BF3-epichlorohydrin, and SbCl6-epichlorohydrin. The reactions take place in chlorinated solvents, like piethylene chloride. The rates of these reactions, however, are quite slow. In addition, these polymerizations are reversible. The rates of propagation of the three cyclic ethers, oxetane, tetrahydrofuran, and oxepane, at 0 °C fall in the following oider ... 

A living cationic polymerization of tetrahydrofuran, using BH3 as the initiator in the presence of epichlorohydrin and 3,3-bis(chloromethyl)oxacyclobutane, results in the formation of block copolymers. Two types form. One is an A------type. It consists of polytetrahydrofiiran blocks attached to... 

---