Silane compound containing perfluoro(poly)ether group

A perfluoro(poly)ether group containing silane compound of the formula (1a) or the formula (1b):

• A-Rf—X—SiQkY3-k (1a)
• Y3-kQkSi—X—Rf—X—SiQkY3-k (1b)
• wherein A represents a C1-16 alkyl which may be substituted by one or more fluorine atoms;
• Rf represents —(OC4F8)a—(OC3F6)b—(OC2F4)c—(OCF2)d—
• wherein a, b, c and d are each independently an integer of 0 or more and 200 or less, the sum of a, b, c and d is 1 or more and the occurrence order of the respective repeating units in parentheses with the subscript a, b, c or d is not limited in the formula;
• X represents a divalent organic group;
• Y represents, each independently at each occurrence, a hydroxyl group, a hydrolyzable group, or a hydrocarbon group;
• Q represents, each independently at each occurrence, —Z—SiR1nR23-n;
• Z represents, each independently at each occurrence, a divalent organic group:
• with the proviso that Z is not a group which forms a siloxane bond together with a Si atom present in the end of a molecular backbone of the formula (1a) or the formula (1b),
• R1 represents, each independently at each occurrence, a hydroxyl group or a hydrolyzable group;
• R2 represents, each independently at each occurrence, a C1-22 alkyl group or Q′;
• Q′ has the same definition as that of Q;
• n is, each independently in each Q and Q′, an integer selected from 0-3, and the total sum of n one or more;
• in Q, the number of Si atoms which are straightly linked via the Z group is up to five;
• k is an integer each independently selected from 1-3.