PREPARATION AND CHARACTERIZATION OF ALKYLATED POLY(VINYL ALCOHOL) HYDROGELS USING ALKYL-HALIDES

A poly(vinyl alcohol) hydrogel coated onto polyethylene was partially alkylated by reaction with an alkylhalide (C-4, C-8 or C-18) in the pr esence of a deprotonating agent (sodium ethoxide or potassium tert-but oxide). Surface coverage determined by X-ray photoelectron spectroscop y (XPS) was respectively similar to 34, 25, and similar to 8% for the C-4, C-8 and C-18 modified surfaces. Statistically significant differe nces were observed in the fraction of C-8 and C-18 grafted alkyl group s as a function of depth (i.e. take-off angle) indicating the presence of a verticle composition gradient. All three surfaces showed maximal surface coverage of alkyl groups after 1 h reaction. At this reaction time, no further coverage was observed beyond a base/PVA ratio twenty times greater than the stoichiometric ratio. The advancing contact an gle data exhibted an increase in hydrophobicity that correlated with t he degree of coverage obtained by XPS: 90 +/- 1, 83 +/- 0.5, and 71 +/ - 1 deg for C-4, C-8 and C-18 alkylated PVA, and 55 +/- 2 deg for PVA respectively. Large contact angle hysteresis was observed on all three surfaces consistent with surface heterogeneity.