as defined above, and the plural R2 may be the same or different and each are an amino group-containing alkyl group having 1 to 10 carbon atoms, ##STR19## wherein the plural R1 may be the same or different and each are as defined above, and n is an integer of 1 or 2, ##STR20## wherein the plural R1 may be the same or different and each are as defined above, n is also as defined above, and X is an