A detailed study of the alkaline modification of poly(vinylidene fluoride) (PVdF) by a phase transfer catalyst (PTC) medium has been carried out by X-ray photoelectron spectroscopy, (XPS), secondary ion mass spectrometry (SIMS) and Raman spectroscopies, to determine the composition of the modified surface layer. The study indicates the formation of a surface layer consisting of conjugated C=C bonds, concomitant with surface defluorination and the inclusion of oxygen functionalities on treatment. A previous investigation studied the affect of alkaline treatment, however without the use of PTCs (Ross GJ, Watts JF, Hill MP, Morrissey P. Surface modification of poly(vinylidene fluoride) by alkaline treatment. 1. The degradation mechanism Polymer 2000;41: 1695-96.), that produced a surface layer with different functionalities. A mechanism for the degradation process in the presence of a PTC is proposed in this paper, which includes the formation of the polyene structure followed by hydroxide attack to yield hydroxyl and carbonyl groups and more complex oxygen functionalities.