by 1-3 members from the group consisting of methyl and ethyl, especially methyl and ethyl and most especially methyl; and [0040] (5) each of R1-R4 is independently selected from the group consisting of methyl, ethyl, propyl, isopropyl, a siloxane chain, and phenyl, wherein the phenyl may optionally be substituted by 1-3 members from the group consisting of methyl and ethyl (with more particular v