Ring opening polymerization of tetrahydrofuran

Currently known initiation methods for ring opening pol)rmerization are reviewed in a systematic way with special emphasis on their influence on the properties of the resulting polymer. The importance of the chemical elements that comprise each group of initiators is demonstrated and it is shown that the behavior of the initiators is related to the position of these chemical elements in the Periodic Chart of the Elements. The ring opening polymerization of tetrahydrofuran is used as a model for the review. 

Scheme 8.17 Mechanism for the /7-chlorobenzenediazonium hexafluorophosphate-initiated living cationic ring-opening polymerization of tetrahydrofuran.

Here, the cationic ring-opening polymerization of tetrahydrofuran (THF) using silver triflate (AgOTf) in the presence of 2-bromopropionylbromide produces a Br-terminated PTHF. Block copolymers can then be prepared using S, MMA, and MA, employing a CuBr/(dNbpy)2 catalyst. 

Ring opening polymerization of tetrahydrofuran and trioxane using 1,l,2-tricyanovinyl 2 trifluoromethansulfonate. 

Scheme 6.1 Cationic ring-opening polymerization of tetrahydrofuran (left) and 2-oxazolines (right).

Scheme 6.8 Living cationic ring-opening polymerization of tetrahydrofuran initiated by the in s/fu-formed adducts of organic halides with Ag(l) hexafluorophosphate.

Figure 6.1 Top Equilibrium between cationic and covalent propagating species for the living cationic ring-opening polymerization of tetrahydrofuran (THE) initiated with methyltriflate. Eower panels H NMR spectra obtained during the methyl triflate-initiated polymerization of THE in different solvents, demonstrating the different equilibria between cationic and covalent species. (Reprinted with permission from Ref [33].)...

Cyclic ether and acetal polymerizations are also important commercially. Polymerization of tetrahydrofuran is used to produce polyether diol, and polyoxymethylene, an excellent engineering plastic, is obtained by the ring-opening polymerization of trioxane with a small amount of cycHc ether or acetal comonomer to prevent depolymerization (see Acetal resins Polyethers, tetrahydrofuran). 

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. 

Another method of producing polyether polyols is the ring-opening polymerization of cyclic ethers, such as tetrahydrofuran, to produce polytetramethylene ether glycols or poly(oxytetramethylene) glycols, (PTMEG), as shown below. 

Figure 2. In situ generation of a calcium alkoxide from bis(tetrahydrofuran)calcium, bis[bis(trimethylsilyl)amide] and an alcohol, for the ring Opening polymerization of cyclic esters...

The absence of linear oligomers is due to rapid reactions of the hydroxy and oxonium ion end groups. This mechanism is quite general for ring-opening polymerizations of cyclic ethers initiated with strong protonic acids. Substituted tetrahydrofurans generally resist polymerizations. 

Also, free-radical ring-opening polymerization of oligomer obtained from complexed 9d with AIBN in tetrahydrofuran at 65°C formed a network. 

Cationic ring-opening polymerization of a bicyclic acetal monomer was a possible method to synthesize cellulose [29]. A polysaccharide of DP 20 was obtained however, a regioselective ring-opening did not take place. The major component was a tetrahydrofuran-ring unit and not a six-membered glucopyranose unit. 

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