A compound which is a perfluoro(poly)ether group containing silane compound of any of the formulae,,, and: (Rf-PFPE) β' -X 5 -(SiR 1 n R 2 3-n) β ··· (Rf-PFPE) γ -X 7 -(SiR a k R b l R c m) γ ··· (C1 (R c m R b l R a k Si) γ -X 7 -PFPE-X 7 -(SiR a k R b l R c m) γ ··· wherein, each independently at each occurrence, PFPE is - (OC 4 F 8) a -(OC 3 F 6) b -(OC 2 F 4) c -(OCF 2) d -, wherein a is an integer of 0-30, b is an integer of 0-30, c is an integer of 1-200 d is an integer of 1-200, with (a+b+c+d) ≥ 3, in the above formulae the c/d ratio is 0.2-0.85, and the occurrence order of the units in parentheses with subscript a, b, c or d is not limited; Rf is C 1-16 -alkyl optionally substituted by one or more F; R 1 is H or C 1-22 -alkyl; R 2 is OH or a hydrolyzable group; R 11 is H or halogen; R 12 is H or C 1-20 -alkyl; X 1 is a single bond or a 2-10 valent organic group; X 2 is a single bond or a divalent organic group; t is an integer of 1-10; α is an integer of 1-9; α' is an integer of 1-9; X 5 is a single bond or a 2-10 valent organic group; β is an integer of 1-9; β' is an integer of 1-9; X 7 is a single bond or a 2-10 valent organic group; γ is an integer of 1-9; γ' is an integer of 1-9; R a is -Z-SiR 71 p R 72 q R 73 r wherein, each independently at each occurrence, Z is O or a divalent organic group; R 71 is R a'; which is defined as R a; and in R a the number of Si atoms which are straightly linked via Z is ≤ 5; R 72 is OH or a hydrolyzable group; R 73 is H or C 1-20 -alkyl; p is an integer of 0-3; q is an integer of 0-3; r is an integer of 0-3; in one R a (p+q+r) = 3, and there is at least one R 72 in formula and; R b is OH or a hydrolyzable group; R c is H or C 1-20 -alkyl; k is an integer of 1-3; l is an integer of 0-2; m is an integer of 0-2; and (k+l+m) = 3 in each unit in parentheses with the subscript γ; and further n is, independently per a unit (-SiR 1 n R 2 3-n), an integer of 0-3, with the proviso that there is at least one R 2 in the formulae, and. PFPE is - (OC 4 F 8) a -(OC 3 F 6) b -(OC 2 F 4) c -(OCF 2) d -, wherein a is an integer of 0-30, b is an integer of 0-30, c is an integer of 1-200 d is an integer of 1-200, with (a+b+c+d) ≥ 3, in the above formulae the c/d ratio is 0.2-0.85, and the occurrence order of the units in parentheses with subscript a, b, c or d is not limited; a is an integer of 0-30, b is an integer of 0-30, c is an integer of 1-200 d is an integer of 1-200, Rf is C 1-16 -alkyl optionally substituted by one or more F; R 1 is H or C 1-22 -alkyl; R 2 is OH or a hydrolyzable group; R 11 is H or halogen; R 12 is H or C 1-20 -alkyl; X 1 is a single bond or a 2-10 valent organic group; X 2 is a single bond or a divalent organic group; t is an integer of 1-10; α is an integer of 1-9; α' is an integer of 1-9; X 5 is a single bond or a 2-10 valent organic group; β is an integer of 1-9; β' is an integer of 1-9; X 7 is a single bond or a 2-10 valent organic group; γ is an integer of 1-9; γ' is an integer of 1-9; R a is -Z-SiR 71 p R 72 q R 73 r wherein, each independently at each occurrence, Z is O or a divalent organic group; R 71 is R a'; which is defined as R a; and in R a the number of Si atoms which are straightly linked via Z is ≤ 5; R 72 is OH or a hydrolyzable group; R 73 is H or C 1-20 -alkyl; p is an integer of 0-3; q is an integer of 0-3; r is an integer of 0-3; in one R a (p+q+r) = 3, and there is at least one R 72 in formula and; Z is O or a divalent organic group; R 71 is R a'; which is defined as R a; and in R a the number of Si atoms which are straightly linked via Z is ≤ 5; R 72 is OH or a hydrolyzable group; R 73 is H or C 1-20 -alkyl; p is an integer of 0-3; q is an integer of 0-3; r is an integer of 0-3; in one R a (p+q+r) = 3, and there is at least one R 72 in formula and; R b is OH or a hydrolyzable group; R c is H or C 1-20 -alkyl; k is an integer of 1-3; l is an integer of 0-2; m is an integer of 0-2; and (k+l+m) = 3 in each unit in parentheses with the subscript γ; n is, independently per a unit (-SiR 1 n R 2 3-n), an integer of 0-3, with the proviso that there is at least one R 2 in the formulae, and.