The ultrasonic velocity in semidilute polymer solution near the theta temperature

Polymer solution are fallen into three region as function of concentration C:dilute,semidilute and concentrated (0<C-dil.<C*<C-semidil.<C**<C-conc). The concentration of tri- or multi-critical point in PS-trans-decalin solution has been determined in ultrasonic method as a function of cross over line C* and C**. Chain crossover concentration C*' from neutron scattering method differs from C* that's viscosity and ultrasonic method by an order of magnitude. New suggestion was made in this work that the polymer solutions in dilute zone were appeared new additional tri- or multi-critical phenomena under anisotropic stress of polymer expansion in end-end direction. The new multi-critical phenomena have been shown by ultrasonic method.