Abstract. In the preparation of a thermo-responsive, poly(N-isopropylacrylamide) (PNIPAAm)-grafted polydimethylsiloxane (PDMS) surface by means of benzophenone-initiated photopolymerization, we observed that thick (>1 mm) PDMS substrates were much more difficult to be grafted with PNIPAAm than thin ones. Investigations revealed that the shortage of diffused benzophenone molecules in the sur…