Compounds of the formulae ##STR00001## wherein, provided that at least one of R.sub.1, R.sub.2, and R.sub.3 is not a hydrogen atom, R.sub.1, R.sub.2, and R.sub.3 each, independently of the other, is hydrogen, alkyl, aryl, arylalkyl, or alkylaryl, and wherein R.sub.1 and R.sub.2 can also be alkoxy aryloxy, arylalkyloxy, alkylaryloxy, polyalkyleneoxy, polyaryleneoxy, polyarylalkyleneoxy, polyalkylaryleneoxy, silyl, siloxane, polysilylene, polysiloxane, or a group of the formula ##STR00002## wherein r and s are integers representing a number of repeat --CH.sub.2-- groups, and wherein X is a direct bond, oxygen, sulfur, --NR.sub.40-- wherein R.sub.40 is hydrogen, alkyl, aryl, arylalkyl, or alkylaryl, or --CR.sub.50R.sub.60-- wherein R.sub.50 and R.sub.60 each, independently of the other, is hydrogen, alkyl, aryl, arylalkyl, or alkylaryl, and R.sub.10 and R.sub.11 each, independently of the other, is alkylene, arylene, arylalkylene, or alkylarylene, and wherein R.sub.10 can also be polyalkyleneoxy, polyaryleneoxy, polyarylalkyleneoxy, polyalkylaryleneoxy, silylene, siloxane, polysilylene, or polysiloxane.