Synthesis of polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane via polysiloxane‐based macroinitiator in supercritical CO2

Polydimethylsiloxane‐block‐polystyrene‐block‐polydimethylsiloxane (PDMS‐b‐PS‐b‐PDMS) was synthesized by the radical polymerization of styrene using a polydimethylsiloxane‐based macroazoinitiator (PDMS MAI) in supercritical CO₂. PDMS MAI was synthesized by reacting hydroxy‐terminated PDMS and 4,4′‐azobis(4‐cyanopentanoyl chloride) (ACPC) having a thermodegradable azo‐linkage at room temperature. The polymerization of styrene initiated by PDMS MAI was investigated in a batch system using supercritical CO₂ as the reaction medium. PDMS MAI was found to behave as a polyazoinitiator for radical block copolymerization of styrene, but not as a surfactant. The response surface methodology was used to design the experiments. The parameters used were pressure, temperature, PDMS MAI concentration and reaction time. These parameters were investigated at three levels (?1, 0 and 1). The dependent variable was taken as the polymerization yield of styrene. PDMS MAI and PDMS‐b‐PS‐b‐PDMS copolymers obtained were characterized by proton nuclear magnetic resonance and infrared spectroscopy. The number‐ and weight‐average molecular weights of block copolymers were determined by gel permeation chromatography. Copyright © 2004 Society of Chemical Industry