A polyorganosiloxane polyoxyalkylene block copolymer having one or more polyorganosiloxane blocks and one or more polyoxyalkylene blocks linked to each other via divalent radicals which comprises at least two silicon-bonded alkoxy groups, preferably of the form PS (A PO)m (A PS)n, wherein PO is a polyoxyalkylene block, PS represents a polyorganosiloxane block, A is a divalent radical, m and n have independently a value of at least 1, comprising at least one alkoxy-substituted siloxane unit of the formula (R′)q(OR)—SiO3−q/2 ′, wherein R represents an alkyl group having 1 to 4 carbon atoms and each R′ represents an alkyl group having 1 to 6 carbon atoms, a phenyl group, or an alkoxy group of the formula —OR and q has a value of 0, 1 or 2, provided at least two silicon-bonded groups OR are present in the block copolymer. Also provided is a curable composition of the above which may comprise a condensation catalyst and a hydrophilic polymer network made from curing the composition in the presence of moisture, which exhibit interesting reversible hydrophilic properties.