(Wherein R1 is a monovalent hydrocarbon group having 2 or 3 carbon atoms, R2, R3, R4, R5, and R6 are each independently a monovalent hydrocarbon group having 1 to 3 carbon atoms, “a” is a positive number satisfying 0<a<4, and “b” and “c” are each independently a number of 0 to 3, provided that (a+b+c) <4.)
COSMETIC