Abstract
We present a field-theoretic renormalization group analysis of a polymer chain immersed in a binary good solvent close to its critical demixing point. We first show that this problem can be mapped on a bicritical field theory, i.e. a (Φ2)2-model with a mass anisotropy. This implies that the end-to-end distance of the polymer is now controlled by a new critical exponent νB related to the quadratic mass anisotropy operator B. To show this, we solve the RG equation and calculate explicitly the exponents and the mean end-to-end length of the chain.