Perfluoropolyether oligomers and polymers

Perfluoropolyether substance comprising one or a mixture of polyether compounds each consisting essentially of 2 to 20 perfluoropolyether segments bonded together in a chain, each of which segments consist essentially of (1) at least one perfluoroisopropyleneoxy unit, (2) a bis(perfluoromethyleneoxy-terminated) unit of the formula OCF.sub.2 (R.sub.f).sub.x CF.sub.2 O where x is zero or 1 and R.sub.f is a fluoroaliphatic group, and (3) two perfluoroethylidene units terminating the ends of each said segment, the chain being terminated with --COF or a moiety independently selected from the group consisting of H, X, CF.sub.2 H, CF.sub.2 X, CH.sub.2 OH, COX, COR, COOH, COOM, COOR, CF.sub.2 R, CH.sub.2 OC(O)CR'.dbd.CH.sub.2, CON(R")R", CH.sub.2 NH.sub.2, CH.sub.2 NCO, CN, C.sub.3 N.sub.3 (R.sub.f ').sub.2, CH.sub.2 OCOR, where X is F, Cl, or Br, M is an ammonium radical or a monovalent metal atom, R is alkyl, aryl, or a combination thereof, R' is H or CH.sub.3, R" is H, said R, (CH.sub.2).sub.z Si(R'").sub.3 where z is 2 to 11 and R'" is a hydrolyzable group, or the two R" groups can together form an alkylene moiety which together with the amido nitrogen atom form a heterocyclic ring, and R.sub.f ' is a fluoroaliphatic radical.