In a particularly preferred embodiment herein, in the above structure, --C is selected from the group consisting of --(CH2)n --CH3 and --(CF2)n --CF2 H, where n is an integer in the range of 8 to 20 inclusive, --S-- is selected from the group consisting of --O--, --CH2 --, --(CO)--, --O(CO)-- and --NR-- where R is hydrogen or lower alkyl (1-6C) , and --M-- is --[(CH2)m --CH]-- where m is 0 to 2.