For the first time, stabilizer-free vinylidene fluoride (VDF) hornopolymerizations were carried out in homogenous phase with supercritical CO2 using the conventional initiator di-tert butyl peroxide (DTBP). In-line FT-NIR spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography and polymer endgroup analysis by H-1-NMR spectroscopy. The number average molecular weights were below 10(4) g mol(-1) and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. For allowing isothermal reaction, high CO2 contents ranging from 61 to 83 wt % were used. The high-temperature and high-pressure conditions required for homogeneous polymerization did not alter the amount of defects in VDF chaining. Scanning electron microscopy indicated that regular stack-type particles are obtained upon expansion of the homogeneous polymerization mixture. (c) 2007 Wiley Periodicals, Inc.