We found a thermally-induced threshold reorientation of the nematic liquid crystal from homeotropical alignment to planar one. The fenomenon was observed in a symmetric cell with inner surfaces covered with fluoro polyvinyl-cinnamate. This threshold reorientation is an anchoring transition of the second order. We suggest that a competition of aligning abilities of flexible polymer fragments and main polymer chains is the basic reason for this phenomenon.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.