An organosiloxane block copolymer comprising: 40 to 90 mole percent disiloxy units of the formula [R 1 2 SiO 2/2], 10 to 60 mole percent trisiloxy units of the formula [R 2 SiO 3/2], 0.5 to 35 mole percent silanol groups [≡SiOH]; wherein: each R 1, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond, each R 2, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond; wherein: the disiloxy units [R 1 2 SiO 2/2] are arranged in linear blocks having an average of from 100 to 300 disiloxy units [R 1 2 SiO 2/21] per linear block; the trisiloxy units [R 1 2 SiO 3/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, at least 30% of the non-linear blocks are crosslinked with each other; each linear block is linked to at least one non-linear block via -Si-O-Si- linkages; the organosiloxane block copolymer has a weight average molecular weight of at least 20,000 g/mole, wherein the average molecular weight is determined by gel permeation chromatography; and the organosiloxane block copolymer comprises from 0.5 to 5 mole % C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond. 40 to 90 mole percent disiloxy units of the formula [R 1 2 SiO 2/2], 10 to 60 mole percent trisiloxy units of the formula [R 2 SiO 3/2], 0.5 to 35 mole percent silanol groups [≡SiOH]; wherein: each R 1, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond, each R 2, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond; wherein: the disiloxy units [R 1 2 SiO 2/2] are arranged in linear blocks having an average of from 100 to 300 disiloxy units [R 1 2 SiO 2/21] per linear block; the trisiloxy units [R 1 2 SiO 3/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, at least 30% of the non-linear blocks are crosslinked with each other; each linear block is linked to at least one non-linear block via -Si-O-Si- linkages; the organosiloxane block copolymer has a weight average molecular weight of at least 20,000 g/mole, wherein the average molecular weight is determined by gel permeation chromatography; and the organosiloxane block copolymer comprises from 0.5 to 5 mole % C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond. wherein: each R 1, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond, each R 2, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond; each R 1, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond, each R 2, at each occurrence, is independently a C 1 to C 30 hydrocarbyl or a C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond; wherein: the disiloxy units [R 1 2 SiO 2/2] are arranged in linear blocks having an average of from 100 to 300 disiloxy units [R 1 2 SiO 2/21] per linear block; the trisiloxy units [R 1 2 SiO 3/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, at least 30% of the non-linear blocks are crosslinked with each other; each linear block is linked to at least one non-linear block via -Si-O-Si- linkages; the organosiloxane block copolymer has a weight average molecular weight of at least 20,000 g/mole, wherein the average molecular weight is determined by gel permeation chromatography; and the organosiloxane block copolymer comprises from 0.5 to 5 mole % C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond. the disiloxy units [R 1 2 SiO 2/2] are arranged in linear blocks having an average of from 100 to 300 disiloxy units [R 1 2 SiO 2/21] per linear block; the trisiloxy units [R 1 2 SiO 3/2] are arranged in non-linear blocks having a molecular weight of at least 500 g/mole, at least 30% of the non-linear blocks are crosslinked with each other; each linear block is linked to at least one non-linear block via -Si-O-Si- linkages; the organosiloxane block copolymer has a weight average molecular weight of at least 20,000 g/mole, wherein the average molecular weight is determined by gel permeation chromatography; and the organosiloxane block copolymer comprises from 0.5 to 5 mole % C 1 to C 30 hydrocarbyl group comprising at least one aliphatic unsaturated bond.