An organosiloxane block copolymer includes 65 to 90 mol % of diorganosiloxane units having the formula R12-SiO2/2 (I). These diorganosiloxane units are arranged in linear blocks which have an average of from 10 to 400 diorganosiloxane units per linear block. The organosiloxane block copolymer also includes 10 to 35 mol % of siloxane units that have the average formula R2x(OR3)ySiO(4-x-y)/2 (II). The siloxane units are arranged in nonlinear blocks having at least 2 siloxane units per nonlinear block wherein 0.5≦x≦1.5 and 0≦y≦1. In addition, each R1 is independently a C1 to C10 hydrocarbyl, each R2 is independently an aryl or C4 to C10 hydrocarbyl, at least 50 mol % of R2 are aryl, and each R3 is independently R1 or H. Moreover, the organosiloxane block copolymer has a light transmittance of at least 95%.