Free radical solution polymerization of acrylonitrile in dimethyl sulfoxide (DMSO) solvent using 2,2’-azobisisobutyronitrile (AIBN) initiator was carried out to prepare polyacrylonitrile (PAN) solution for spinning acrylic precursor fiber for carbon fiber. The polymerization reaction was conducted in a batch reactor at constant temperature, whereas, initiator concentration was varied to achieve desired molecular weight and polymer conversion. The polymer prepared in these reactions yielded narrow molecular weight distribution (1.71-1.84)