Refrigerating machine oil, and working fluid composition for refrigerating machines

1. A working fluid composition for a refrigerating machine comprising:

a refrigerating machine oil comprising, as a base oil, a polymer having a structural unit represented by the following formula (1):

wherein R 1 , R 2 and R 3 , which may be the same as or different from each other, represent a hydrogen atom or a hydrocarbon group; and R 4 represents a hydrocarbon group or an organic group containing an oxygen atom, and

having a number average molecular weight Mn of 300 or more and 3000 or less and a ratio of a weight-average molecular weight Mw to a number average molecular weight Mn (Mw/Mn) of 1.10 or more and 2.00 or less; and

a refrigerant selected from the group consisting of difluoromethane, a mixture of difluoromethane and pentafluoroethane, a mixture of difluoromethane, pentafluoroethane and 1,1,1,2-tetrafluoroethane, a mixture of pentafluoroethane, 1,1,1,2-tetrafluoroethane and 1,1,1-trifluoroethane, unsaturated hydrofluorocarbons, hydrocarbons and carbon dioxide.

2. The working fluid composition for a refrigerating machine according to claim 1 , wherein —OR 4 in the formula (1) is represented by the following formula (2):

—O(R 5 O) m R 6   (2)

wherein R 5 represents a divalent hydrocarbon group or a divalent hydrocarbon group containing an ether-bond oxygen atom; R 6 represents a hydrocarbon group; and m represents an integer of 0 or more; with the proviso that if m is 2 or more, a plurality of R 5 may be the same as or different from each other.

3. The working fluid composition for a refrigerating machine according to claim 1 , wherein the polymer has the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is 2-methylpropyl group.

4. The working fluid composition for a refrigerating machine according to claim 3 , wherein the refrigerant is selected from the group consisting of difluoromethane, a mixture of difluoromethane and pentafluoroethane, unsaturated hydrofluorocarbons, and hydrocarbons.

5. The working fluid composition for a refrigerating machine according to claim 1 , wherein the polymer has

the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is ethyl group,

the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is n-butyl group, or

the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is 2-methylpropyl group.

6. The working fluid composition for a refrigerating machine according to claim 5 , wherein the refrigerant is selected from the group consisting of difluoromethane, a mixture of difluoromethane and pentafluoroethane, unsaturated hydrofluorocarbons, and hydrocarbons.

7. The working fluid composition for a refrigerating machine according to claim 1 , wherein the polymer has

the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is ethyl group, or

the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is propyl group.

8. The working fluid composition for a refrigerating machine according to claim 7 , wherein the refrigerant is selected from the group consisting of difluoromethane, a mixture of difluoromethane and pentafluoroethane, unsaturated hydrofluorocarbons, and hydrocarbons.

9. The working fluid composition for a refrigerating machine according to claim 1 , wherein the polymer has the structural unit wherein R 1 to R 3 are each a hydrogen atom and R 4 is ethoxymethyl group.

10. The working fluid composition for a refrigerating machine according to claim 9 , wherein the refrigerant is selected from the group consisting of difluoromethane, a mixture of difluoromethane and pentafluoroethane, unsaturated hydrofluorocarbons, and hydrocarbons.