Azo group-containing polydimethylsiloxanes (PDMS-ACP), macroazoinitiators, were pre pared by polycondensation reaction of 4,4’-azobis-4-cyanopentanoyl chloride (ACPC) with hydroxybutyl-terminated polydimethylsiloxane (PDMS) of varying molecular weights. The activation energy (E(alpha)), activation enthalpy (Delta H-double dagger), and activation entropy (Delta S-double dagger) of the thermodecomposition of PDMS-ACP in toluene increased with increase in poly-dimethyl siloxane chain length (SCL) in PDMS moieties, while the activation free energy (Delta G(double dagger)) was independent on the SCL. The polydimethylsiloxane-poly(methyl methacrylate) block copolymers (PDMS-b-PMMA) were prepared by the use of PDMS-ACP macroazoinitiators, and they were characterized by H-1-, Si-29-, and C-13-nuclear magnetic resonance (NMR) spectroscopies. The microstructure and morphology of copolymers were investigated by proton spin-spin relaxation measurements and scanning electron microscopy (SEM).