High-Molecular-Weight Polytetrahydrofuran

Synthesis of high polymers by cationic ring-opening polymerization of heterocycles is hampered by chain transfer which may occur by  

All these reactions proceed to a larger or smaller extent in the cationic polymerization of any heterocycle. In the polymerization of THF the rate of these reactions is reduced and the polymerization becomes a living one. 

The small contribution of macrocyclization in the polymerization of THF is due to two effects The formation of smaller cyclic oligomers like dimer and trimer is thermodynamically unfavorable (in contrast to the formation of e.g. 1,4-dioxane in the polymerization of ethylene oxide) because 10- and 15-membered cyclic ethers are strained. It is also kinetically hampered since the rate of chain transfer to polymer which leads to ring formation is low due to the lower basicity of the polymer units than that of THF. 

Proton transfer in THF polymerization at moderate temperatures is negligible and other sources of termination such as anion instability can be avoided by a proper choice of polymerization conditions. 

The synthesis of high-molecular-weight poly THF became possible after the discovery of the living nature of THF polymerization. This discovery started with the work of Meerwein u and the observations were then formulated in, terms of a living process simultaneously and independently by Rosenberg et al. 1,) Dreyfuss and Drey-fuss 3) and Vofsi and Tobolsky 4) (cf. Adv. Pol. Sci. 37). Further development at DuPont, BASF and other companies led eventually to commercialization of polyTHF 

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Table 1. Typical Properties of High Molecular Weight Polytetrahydrofuran...

Recently in the Sijbesma group, high-molecular-weight linear coordination polymers of diphenylphosphine telechelic polytetrahydrofuran with palladium (II) dichloride were developed [3]. Molecular weights of these polymers could be altered reversibly by ultrasotmd and it has been shown that polytetrahydrofuran chains remain intact during sonication [78]. This implies that only the reversible palladium-phosphorus bonds are broken and coordinatively unsaturated palladium complexes were produced by the application of mechanical forces on these coordination polymers [79]. Furthermore, polymers which include both Pd and Pt were sonicated and it was shown that force selectively breaks the weaker Pd-phosphine bonds which were randomly distributed along the polymer backbone [80]. 

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