The present invention provides a compound having a formula: ##STR00001## where R.sup.1 is selected from the group consisting of alkyl, --CH.sub.2(OC.sub.2H4)OCH.sub.3, and --(OC.sub.2H.sub.4)OCH.sub.3; n is 0-4; Olig is an oligomer having a formula: -L-O-PAGR.sup.2].sub.q where L is a optional linker moiety selected from the group consisting of --CH.sub.2O--, --CH.sub.2OX--, --OX--, --C(O)--, --C(O)X, --NH--, --NHC(O)--, --XNHC(O)--, --NHC(O)X--, --C(O)NH--, --C(O)NHX--, and ##STR00002## where X is alkyl.sub.1-6 or is not present, Y is N or O or is not present, and R.sup.3 is alkyl.sub.1-6; PAG is a linear or branched polyalkylene glycol moiety; R.sup.2 is an alkyl.sub.1-22 capping moiety if X is present or alkyl.sub.2-22 if X is not present; and q is a number from 1 to the maximum number of branches on PAG; and m is 1-5.