groups include acetyl propionyl butyryl and pentanoyl the term u201c acyloxy u201d represents a unit consisting of an acyl group that is bonded to an oxygen atom examples of preferred acyloxy groups include ch 3 c o o c 2 h 5 c o o n c 3 h 7 c o o and n c 4 h 9 c o o the term u201c alkyl u201d includes straight or branched chain aliphatic hydrocarbon groups that are saturated and have 1 to 15 carbon atoms the alkyl groups may be substituted with other groups such as halogen hydroxyl or alkoxy preferred straight or branched alkyl groups include methyl ethyl propyl isopropyl butyl and t butyl the term u201c cycloalkyl u201d includes straight or branched chain saturated or unsaturated aliphatic hydrocarbon groups which connect to form one or more rings which can be fused or isolated the rings may be substituted with other groups such as halogen hydroxyl alkoxy or lower alkyl preferred cycloalkyl groups include cyclopropyl cyclobutyl cyclopentyl and cyclohexyl the term u201c alkoxy u201d represents an alkyl group attached through an oxygen linkage the term u201c carbonyl group u201d represents a carbon atom double bonded to an oxygen atom wherein the carbon atom has two free.