What is described is a compound of formula IwhereinR1 is a linear alkyl, alkenyl, or alkynyl of 2 to 12 carbons, or a branched alkyl with 12 to 20 carbons,R2 is a branched alkyl with 12 to 20 carbons,L1 and L2 are independently a linear alkylene with 1-18 carbons or alkenylene with 2-18 carbons,X is S or O,L3 is a bond or an alkylene with 1 to 6 carbons,R3 is an alkylene with 1 to 6 carbons, andR4 and R5 are the same or different, each a linear or branched alkyl with 1 to 6 carbons.
