The object of the invention are compounds of the formula wherein R1 is H, methyl or ethyl, R2 is C1- to C4 alkyl, A is a C2- to C4 alkylene group, m is number from 10 to 400, n is 1, 2, 3, 4, or 5, a method for their production and their use in the production of polyurethane prepolymers. The game controller is arranged to play a game wherein one or more random events are caused to be displayed on and, if a predefined winning event results, the machine awards a prize. The pixel exposure source is then de-energized at the end of a second predetermined time interval to terminate exposure at the trailing edge of the pixel, whereby spatial dimensions of each pixel are maintained at variable transport speed or density of pixel.