Transient decays of triplet-triplet (TT) absorption of excited triplet benzophenone (BP) chromophore in poly(4-methacryloylbenzophenone-co-methyl methacrylate) (BPX, X is the mol % of BP, X = 1-100) films were studied by laser photolysis with a kinetic scheme involving a TT annihilation in a wide temperature range (20-240 K). The rate constant of the TT annihilation was analyzed by a diffusion model of the BP triplet state. The calculated diffusion coefficient (D) increased greatly with the increase of temperature and BP concentration in the BPX sample from 1 x 10(-11) cm(2) s(-1) (20 K, X = 1) to 5 x 10(-7) cm(2) s(-1) (240 K, X = 100). The steep increase in D was observed at the average BP distance less than 1.2 nm and above ca. 150 K. This temperature corresponds to T-gamma of poly(methyl methacrylate), alpha-methyl rotation.