SURFACE-PROPERTIES AND ABHESION OF UNDECYL OXAZOLINE BLOCK AND HOMOPOLYMERS

The surface properties of three undecyl oxazoline homopolymers and two phenyl/undecyl oxazoline block copolymers (as comparison) were studied. After coating on glass slides and annealing, all films had a low critical surface energy of 21 dynes/cm. Water contact angles were higher than 107-degrees for the most hydrophobic films. The deduction that the polymer surfaces contained close-packed methyl groups was further confirmed by electron spectroscopy chemical analysis (ESCA) angle profiling on an annealed undecyl oxazoline homopolymer film. A model was developed for the variation of elemental ratios as a function of photoelectron take-off angle. This verified that the polymer films had the polymer back-bones parallel to the surface with the undecyl tails oriented toward the surface. When these block and homopolymers were coated on copy paper and glass slides, the peel strengths of pressure-sensitive adhesives with these surfaces were very low for short dwell times at room temperature. At long dwell times or at elevated temperatures, the peel strengths remained low for the homopolymers but increased greatly for the block copolymers to values higher than those in the tape on glass. After 24 h at 70-degrees-C, ESCA analysis showed that the adhesive diffused into the phenyl block domains of the diblock copolymer, generating high peel strength and cohesive failure. However, under the same annealing conditions, the triblock copolymer showed adhesive failure while peel strength increased. ESCA analysis showed very little diffusion of the adhesive into the triblock copolymer. The homopolymers were stable toward vinyl acetate type adhesives even at elevated temperature; they were abhesive up to 100-degrees-C with no interdiffusion.