The molecular weight distributions were estimated for carbon fiber polymer precursors such as poly(acrylonitrile-

co

- itaconic acid) synthesized by semi batch solution polymerization in mixed solvents media with the azonitrile compounds as initiator under the different ratios of solvent and non solvent from 0.75 to 2.5 in weight. The copolymer was characterized by using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR) analyses. The molecular weight distributions were evaluated by

M

v

/

M

n

ratios estimated from viscosity and osmotic measurements

and

M

w

/

M

n

estimated from size exclusion chromatography. The molecular weight distributions of these polymers as determined from

M

v

/

M

n

and

M

w

/

M

n

are 2.9 to 3.2 and 2.0 to 2.5 respectively. The molecular distributions were close to a narrow distribution of 2.0 when the solvent/non-solvent ratio was varied between 1.4 and 2.0. Intrinsic viscosity [

η

] as a function of molecular weight of poly(acrylonitrile-co-itaconic acid) was evaluated by means of low angle laser light scattering with size exclusion chromatography (SEC-LALLS) and viscometry with SEC (SEC-VISCO). The relationship between [

η

] and

M

w

for poly(acrylonitrile-co-itaconic acid) in DMF at 50℃ was [

η

] = 1.1 × 10

-5

M

w

0.79

where [

η

] is obtained in dL/g.