A novel poly(amideimide siloxane) block copolymer was prepared from oligo(dimethylsiloxane), trimellitic anhydride chloride and oxylene diamine using trimethylsilyl chloride as the reaction activator. Trimethylsilyl chloride enhanced the reactivity of oligo(dimethylsiloxane), resulting in a higher yield and viscosity of the product. The high reactivity of N-trimethylsilylated siloxane diamine stems from the silicon sigma-pi effect, and a nucleophilic addition-elimination reaction is proposed. The addition of a small amount of N-methylpyrrolidone in tetrahydrofuran led to a higher yield. The temperature of 10% weight loss for the product exceeded 355 degrees C according to thermogravimetric analysis data. A transient change in the contact angle of water on the sample surface was observed, suggesting surface segregation of the hydrophobic component in the polymer.