Mixed monolayers of polymerizable liquid crystals and poly(amic acid) alkylamine salt spread at the air-water interface were investigated. The mixed monolayers were polymerized by UV-irradiation and the in situ polymerization was monitored by a multi-channel photodetector. The area changes of the mixed films showed that the UV-irradation induced both the in situ photopolymerization of the liquid crystals causing phase separation and degradation of the monolayer of poly(amic acid) alkylamine salt at the air-water interface. (C) 2001 Published by Elsevier Science B.V.