Process for the production of polyoxymethylene block copolymers

1. A process for preparing polyoxymethylene block copolymers comprising catalytically adding one or more alkylene oxides and optionally additional comonomers onto at least one polymeric formaldehyde starter compound having at least one terminal hydroxyl group, in the presence of a double metal cyanide (DMC) catalyst, which comprises

(i) activating the DMC catalyst in the presence of the polymeric formaldehyde starter compound, in which activation of the DMC catalyst is accomplished by adding a portion, based on the totality of the amount of alkylene oxides used in the activation and polymerization, of one or more alkylene oxides,

and

(ii) adding one or more alkylene oxides and optionally additional comonomers to the mixture resulting from (i), in which the alkylene oxides used in (ii) may be the same as or different than the alkylene oxides used in (i),

wherein the activation of the DMC catalyst in (i) is effected at an activation temperature (T act ) of 20 to 120° C.

2. The process as claimed in claim 1 , wherein said at least one polymeric formaldehyde starter compound comprises at least one open-chain polymeric formaldehyde starter compound having n repeat oxymethylene units and a functionality F of 1 to 10, wherein n is an integer of from 2 to 400, and wherein the starter compound may be present in the form of a mixture of polymeric formaldehyde starter compounds each having different values of n.

3. The process as claimed in claim 1 , wherein said polymeric formaldehyde starter compound comprises paraformaldehyde.

4. The process as claimed in claim 1 , wherein the amount of one or more alkylene oxides used in (i) is 2 to 100 molar equivalents based on the amount of polymeric formaldehyde starter compound present.

5. The process as claimed in claim 1 , wherein carbon dioxide is added as comonomer in (ii).

6. The process as claimed in claim 1 , wherein the first step (i) comprises

(α) initially charging a suspension medium or the polymeric formaldehyde starter compound and, optionally, removing water and/or other volatile compounds by means of elevated temperature and/or reduced pressure, with the DMC catalyst being added to the polymeric formaldehyde starter compound or to the suspension medium before or after the drying,

(β) activating the DMC catalyst in the presence of the polymeric formaldehyde starter compound is accomplished by adding a portion, based on the entirety of the amount of alkylene oxides used in the activation and polymerization, of one or more alkylene oxides to the mixture resulting from (α), where this portion of alkylene oxide may optionally be added in the presence of additional comonomers and where the temperature spike which occurs due to the exothermic chemical reaction that follows and/or a pressure drop in the reactor is then awaited in each case, and where (β) for activation may also be repeated,

and the second step (ii) comprises:

(γ) adding one or more alkylene oxides and optionally further comonomers, especially carbon dioxide, to the mixture resulting from step (β), where the alkylene oxides used in step (γ) may be the same as or different than the alkylene oxides used in step (β),

wherein at least one polymeric formaldehyde starter compound is added at least in one of ( 60 ) and (β).

7. The process as claimed in claim 6 , wherein the polymerization in (y) is conducted at a temperature of 70 to 140° C.

8. The process as claimed in claim 6 , wherein the suspension medium used in (α) comprises at least one compound selected from the group consisting of 4-methyl-2-oxo-1,3-dioxolane, 1,3-dioxolan-2-one, acetone, methyl ethyl ketone, acetonitrile, nitromethane, dimethyl sulfoxide, sulfolane, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dioxane, diethyl ether, methyl tert-butyl ether, tetrahydrofuran, ethyl acetate, butyl acetate, pentane, n-hexane, benzene, toluene, xylene, ethylbenzene, chloroform, chlorobenzene, dichlorobenzene and carbon tetrachloride.

9. The process as claimed in claim 6 , wherein

(α) comprises

(α1) initially charging a suspension medium and the DMC catalyst and removing water and/or other volatile compounds, at a temperature of 90 to 150° C., by injecting an inert gas at 1 bar to 100 bar (absolute) at least once subsequently reducing the elevated pressure to about 1 bar to 20 bar (absolute) after each injection of an inert gas,

and, subsequently,

(α2) adding the formaldehyde starter compound to the mixture from (α1).

10. The process as claimed in claim 2 , wherein said polymeric formaldehyde starter compound has a functionality F of 2 to 3.