Effect of Acetate Distribution on Surface Segregation in Poly(vinyl alcohol-co-vinyl acetate) Copolymer Films

Abstract

The level of acetate-group surface segregation in poly(vinyl alcohol-co-vinyl acetate) (PVA−PVAc) films was found to depend markedly on the functional group distribution along the backbone (blockiness). PVA−PVAc polymers with both random and blocky distributions were prepared at levels between 2 and 12 mol % acetate and cast into films from aqueous solution. Films from polymers with blocky distributions showed significantly higher levels of acetate at the surface than in the bulk, while polymers with random distributions of acetate functionality exhibited little or no surface segregation. The level of acetate surface segregation was determined by both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Blocky PVA−PVAc films containing 4 mol % were seen to have approximately 40 mol % PVAc at the outermost surface by XPS at low take-off angle. Bulk acetate levels and acetate group distributions were determined by NMR. Variations in the weight average molecular weight (M w) between 40k and 155k, modifying the casting solvent, or annealing the films above T g did not effect the level of surface segregation, suggesting that the segregation is not simply a kinetic phenomenon.

Estimation of the Surface Properties of Styrene-Acrylonitrile Random Copolymers from Contact Angle Measurements

“…Kulmer et al (4) characterized a series of acrylonitrile-co-methylmethacrylate statistical copolymers by XPS and their results indicate that the surface composition of the statistical copolymers is the same as that of the bulk. Similar studies performed by Helfand et al (5) involving the comparison between block and random copolymers of poly(vinyl alcohol-co-vinyl acetate) using XPS also suggest that the random copolymer surface compositions closely match their respective bulk values. The same behavior was observed by T. Teraya et al (6) in random copolymers of polystyrene and poly(methoxy poly(ethylene glycol) methacrylate), using dynamic contact angle (DCA) measurements and XPS.…”

“…An alternative to the above equation, [5] was proposed by Wu (14), which uses a harmonic, rather than a geometric, mean for estimating both ␥ i d and ␥ i p .…”

Surface Segregation Assessment In Poly(ε‐caprolactone)‐poly(ethylene glycol) Multiblock Copolymer Films

“…In particular, XPS represents a valuable tool for probing surface segregation in common multi-phase amphiphilic polymer systems. [22][23][24][25][26] It is widely accepted that the polymer surface is indeed stable and the results of the analysis obtained under high vacuum conditions can also be applied to non-vacuum environments. Since conventional XPS probes the top 10 nm, whereas cells only probe the outermost molecular layer, angle-resolved XPS (AR-XPS) has been utilized in order to investigate more surface layers.…”

Influence of the linkage type between the polymer backbone and side groups on the surface segregation of methyl groups during film formation

“…67 The results from the annealing experiments indicate that the observed surface structure formation at the PVAc film cast by dilute solution is dominated by thermodynamic requirements. These observations are in agreement with Helfand's speculations regarding the results from the studies of the poly(vinyl alcohol-co-vinyl acetate) copolymer by XPS and Tof-SIMS.…”