PURPOSE: To obtain a compatible polymer composition exhibiting LCST(low critical solution temperature) behavior which meets technical requirements in various points particularly well by mixing two specified polymers with each other.

CONSTITUTION: This is a polymer composition comprising two different polymer components, exhibiting an LCST behavior and provided for use in a technique requiring temperature-dependent light transmittance. This composition P is formed by mixing a polymer component P1 being a poly-α-methylstyrol with a polymer component P2 being a polyvinyl methyl ether in a weight ratio of 98:2 to 2:98. Composition P may also contain 0.1-1,000 pts.wt., per total weight of P1 and P2, low-molecular component W (e.g. softener or solvent). In this way, the separation temperature (usually 60-100°C) of the composition can be further lowered.