Obtaining melt viscosity stability of polyoxymethylene compositions

1. A process comprising:

molding a polyoxymethylene composition,

the polyoxymethylene composition comprising:

(a) from 50 to 99.5 weight percent of at least one polyoxymethylene polymer selected from the group consisting of homopolymer, copolymer and mixtures of these;

(b) from 0.5 to 10 weight percent of at least one polymer;

(c) from 0 to 30 weight percent of one or more fillers; and

(d) from 0 to 10 weight percent of additives,

wherein: the total weight percent of (a), (b), (c), and (d) is 100 percent,

wherein the at least one polymer of (b) is selected from the group consisting of:

(I) one or more polymers having a core-link-arm structure such that:

the core comprises one or more carbon atoms, none of which is a carbonate carbon, and is attached to at least three arms comprising diradical repeat units;

(II) one or more polymers having a core-link-arm structure such that:

each arm comprises a diradical repeating unit,

the core has a molecular weight of greater than 45, does not comprise the repeating unit of the arm, and is attached to more than two arms; and

the mass ratio of arms to core in the core-link-arm structure is greater than 3; and

(III) one or more polyols having a core-link-arm structure such that:

the core has a molecular weight from 118 to 1000;

each link is selected from the group consisting of a bond, .O., .CH 2 O., and any combination of these; and

(IV) any combination of (I), (II), and (III), and

wherein number average molecular weight of each arm in the core-link-arm structure of the at least one polymer b) ranges from 500 to 10,000; and

wherein the molded polyoxymethylene composition exhibits at least one of the properties selected from the group consisting of:

(A) a melt viscosity stability, as measured by ASTM D3835 at 220° C. and 100 s −1 shear rate, of greater than −0.005 and a simultaneous increase in notched Izod impact strength, as measured by ASTM D 256-06a, of at least 10 percent when compared to the notched Izod impact strength of a composition consisting of the same polyoxymethylene polymer and the same additives and fillers, measured under the same conditions;

(B) a decrease in relative apparent capillary melt viscosity, as measured by ASTM D-3835 at 220° C. and shear rate 55 sec −1 , of at least 40 percent when compared to the relative apparent capillary melt viscosity of a composition consisting of the same polyoxymethylene polymer and the same additives and fillers, measured under the same conditions;

(C) an increase in flow length, as tested under Flow Length Test Conditions, of at least 5 percent when compared to the flow length of a composition consisting of the same polyoxymethylene polymer and the same additives and fillers, measured under the same conditions; and

(D) when molded into a Type I specimen, an increase in elongation at break, as measured according to ASTM D638-08 at a speed of testing of 50 mm per minute, of least 4 percent when compared to the elongation at break of a composition consisting of the same polyoxymethylene polymer and the same additives and fillers, measured under the same conditions.

2. The process of claim 1 , wherein the polyoxymethylene composition exhibits a melt viscosity stability of greater than −0.002.

3. The process of claim 1 , wherein the increase in flow length is at least 10 percent when compared to the flow length of a composition consisting of the same polyoxymethylene polymer and the same additives and fillers, measured under the same conditions.

4. The process of claim 1 , wherein the polyoxymethylene polymer comprises copolymer.

5. The process of claim 1 , wherein the polyoxymethylene polymer comprises homopolymer.

6. The process of claim 1 , wherein the polyoxymethylene composition has a polymer melt mass flow rate that ranges from 0.1 to 50 grams/10 minutes, as measured by ASTM D1238-04c at Condition 190/2.16.

7. The process claim 1 , wherein the core of the at least one polymer (b) comprises from 4 to 40 carbon atoms.

8. The process of claim 1 , wherein the core of the at least one polymer (b) of (I) or (II) has a molecular weight from 118 to 1000.

9. The process of claim 1 , wherein the core of the at least one polymer (b) comprises one or more units selected from the group consisting of: .CH 2 C(CH 2 O.) 3 , .CH 2 C(CH 2 CH 3 )(CH 2 O.) 2 , .OCH 2 CH(O.)CH 2 ., .CH(O.)CH(O.)., and .CH(O.)CH(O.)CH(O.)..

10. The process of claim 1 , wherein the core of the at least one polymer (b) is free of one or more units selected from the group consisting of: .OC(═O)O., .C(═O)O., .CH 2 CH 2 O., .CH 2 CH 2 OCH 2 CH 2 O., and .CH 2 OCH 2 OCH 2 O..

11. The process of claim 1 , wherein the links of the at least one polymer (b) of (I) or (II) are selected from the group consisting of a bond, .O., .CH 2 O., and any combination of these.

12. The process of claim 11 , wherein the link is .O..

13. The process of claim 1 , wherein at least one arm attached to the core of the at least one polymer (b) has a terminal group selected from .H, .OH, .R, .C(═ 0 )OR, .C(═O)NR 2 , .C(═O)NHR, .C(═O)NH 2 , .OC(═O)R, .C(═O)R, .OR, and .X,

wherein R comprises an optionally substituted alkyl, cyclic, cycloalkyl, or aromatic group of one to twelve carbons, and

X is selected from the group consisting of fluorine, chlorine, bromine, iodine, and any combination of these.

14. The process of claim 1 , wherein the number of arms of the at least one polymer (b) ranges from four to twenty-four.

15. The process claim 14 , wherein the number of arms of the at least one polymer (b) ranges from four to 8.

16. The process of claim 1 , wherein number average molecular weight of each arm attached to the core of the at least one polymer (b) ranges from 800 to 6000.

17. The process of claim 16 , wherein number average molecular weight of each arm attached to the core of the at least one polymer (b) ranges from 1800 to 5000.

18. The process of claim 1 , wherein each arm attached to the core of the at least one polymer (b) is a polyether, and preferably polyethylene oxide.

19. The process of claim 18 , wherein the core-link-arm structure of the at least one polymer (b) was made by covalently attaching a core to arms, or by growing arms out of a core, or by forming a core from arms, or by any combination of these.

20. The process of claim 18 , wherein the link is .O..