Surface free energy analysis of polystrene-poly(beta-hydroxynonanoate) graft copolymers

Polystyrene-poly(beta-hydroxynonanoate) (PS-PHN) graft copolymers having 12, 17, 27, 31, 37, 60, 89, and 94% PS contents were prepared using active PS synthesized from styrene and oligododecandioyl peroxide initiator. Then the copolymer films were cast from chloroform, toluene, cyclohexanone, and butyl acetate. PS and PHN homopolymer blends were also prepared as films having 8, 12, 28, 34, 44, and 64% PS in the same casting solvents. The contact angles of water, glycerol, ethylene glycol, formamide, trans-decaline, and paraffin oil drops were measured on these cast films. The contact angle results were evaluated in terms of surface free energy components using Van Oss-Good methodology. It was determined that the Lifshitz-van der Waals component (gamma(s)(LW)) of the graft copolymers and blend of homopolymers did not differ so much with the copolymer composition. However, the electron donor component of the surface free energy (gamma(s)(-)) decreased with the decrease of PHN content to a considerable extent. It was observed that this decrease is more linear than that of homopolymer blends. The effect of the nature of the casting solvents on the surface properties of the polymers was also investigated in terms of their solubility parameter values and it was found that the more H-bonding solvents resulted in higher (gamma(s)(-)) surfaces. (C) 1996 John Wiley & Sons, Inc.