| 1. A process for preparing polytetrahydrofuran, polytetrahydrofuran copolymers, and diesters or monoesters of these polymers,
said process comprising:
polymerizing tetrahydrofuran in the presence of at least one telogen and/or comonomer and in the presence of a solid, acid
catalyst,
said catalyst comprising a clay material which comprises at least 20% by weight of SiO2 and at least one further oxide of an element selected from the group consisting of Al, Fe and the elements of groups III A
to VII A of the Periodic Table, and wherein said catalyst further comprises a proportion of alkali-soluble silicon dioxide
of from 20 to 85% by weight, where the catalyst has been calcined at from 150 to 800° C. and has an N2 pore volume of at least 0.35 cm3/g for pore diameters in the range from 2 to 200 nm, with at least 0.2 cm3/g of this N2 pore volume being made up by pores having diameters in the range 5-50 nm and the mean BJH pore diameter (4V/A) of the pores
in the range from 2 to 200 nm being from 2.0 to 10.0 nm, has a BET surface area of at least 160 m2/g and has an acid center density of at least 0.25 mmol/g for pKa values of from 1 to 6.
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