Novel lubricant additives

A compound of the formula I ##STR30## wherein one of R.sub.1 and R.sub.3 is hydrogen and the other is OH, each of R.sub.2, R.sub.4 and R.sub.5 independently is C.sub.1 -C.sub.12 alkyl, C.sub.5 -C.sub.7 cycloalkyl, C.sub.6 -C.sub.10 aryl or C.sub.7 -C.sub.9 aralkyl, and R.sub.4 and R.sub.5 are also hydrogen, R.sub.6 is C.sub.1 -C.sub.18 alkyl, each of m and n independently is an integer from 0 to 6, X is the direct bond, --O--, --S--, --N(R.sub.7)--, --Q--R.sub.8 -- or ##STR31## wherein R.sub.7 represents hydrogen, C.sub.1 -C.sub.12 alkyl, phenyl or a group of the formula II ##STR32## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and m are as defined above, Q is --O-- or --NH--, R.sub.8 represents a group of the formula III

• --CH.sub.2 --CH(OR.sub.10)--CH.sub.2 --O-- (III)
• wherein R.sub.10 is hydrogen, C.sub.1 -C.sub.12 alkyl or a group of the formula IV ##STR33## wherein r is an integer from 0 to 6, R.sub.11 is hydrogen, C.sub.1 -C.sub.12 alkyl, C.sub.5 -C.sub.7 cycloalkyl, C.sub.6 -C.sub.10 aryl or C.sub.7 -C.sub.9 aralkyl, and R.sub.9 is --O--, --NH--, --CH.H.sub.2 N--, --O--CH.sub.2 CH.sub.2 --S--, ##STR34## --O--R.sub.8 --, or a group of the formula V ##STR35## wherein R.sub.8, R.sub.11 and r are as defined above, and R.sub.12 is C.sub.1 -C.sub.18 alkyl, C.sub.5 -C.sub.7 cycloalkyl, C.sub.6 -C.sub.10 aryl, C.sub.7 -C.sub.9 aralkyl or a group of the formulae VI or VII
• --(C.sub.u H.sub.2u)--COOR.sub.10 (VI)
• or ##STR36## wherein u is an integer from 1 to 6 and R.sub.10, R.sub.11 and r are as defined above.