The effect of molecular weight on dynamical process of spinodal phase separation of po-lystylene(PS) with carboxylated poly(2

6-dimethyl phenylene oxide) (C-PPO) has been investigated by using time resolved light scattering technique. In the early stage

the effect of molecular weight on dynamical parameters of phase separation

such as the growth rate

R(q) of phase se paration and apparent diffusion coefficient

are distinct

As the molecular weight increasing

the apparent diffusion coefficient

Dapp

decreases. Experimental results obtained from three mixtures tend to support the relationship of q2m/Dapp proportional to the degree of po-lymerization (N)

and the diffusion behaviour coincides the reptation mechanism.