Among them, more preferable examples of the R are alkylene and alkenylene groups having 1 to 6 carbon atoms, and the most preferable examples of them are: alkylenes having 1 to 3 carbon atoms such as methylene, methylmethylene (ethylidene), ethylene, ethylmethylene (propylidene), dimethylmethylene (isopropylidene), methylethylene (propylene) and trimethylene; alkenylenes having 2 to 3 carbon atoms