Thermal Cloud Point Fractionation of Poly(vinyl alcohol-co-vinyl acetate): Partition of Nanogels in the Fractions

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 degrees C. This fractionation was carried out in order to get an insight in the partition of the initially present nanogels in the different fractions. All the fractions were characterized by size exclusion chromatography (SEC), NMR and dynamic light scattering (DLS) giving access to average degree of polymerization (DPw) over bar, average degree of hydrolysis (DH) over bar, average sequence lengths of vinyl acetate n(0)((VAc) over bar), volume fraction and average size diameter (Dv) of nanogels and "free PVA chains". The polydispersity of the samples in (DPw) over bar, (DH) over bar and n(0)((VAc) over bar) could be confirmed. The nanogels characterized by the highest values of volume fraction and Dv, in the range of 40-43 nm, were separated in the first coacervate fraction, whereas the most soluble fraction with low VAc content does not contain nanogels but only "free chains" of a Dv value of around 7-8 nm. The nanogels in the various fractions could further be disaggregated into "free chains" by complex formation with sodium dodecyl sulfate (SDS).