Structure of Polyurethane/Acrylic Hybrids Films Studied by SAXS

PERUZZO, P.J.; PARDINI, O.R.; AMALVY, J.I.

Campinas

Congreso; 16ª. RAU Reunión Anual de Usuarios LNLS; 2006

Laboratorio Nacional de Luz Sincrotron - Brasil

Polyurethane-based coating systems have an established place in the coatings industry due to the high loss and good weather stability. Developments in urethane chemistry and e®orts to reduce emissions increased interest in the development of environmentally-friendly water-borne coatings. The incorporation of acrylic monomers lead to cost reduction and properties are a®ected depending on the amount and on the way of incorporation. Film-forming properties of physical blends are not satisfactory. The polymerization of acrylic monomers in the presence of preformed polyurethane chains with polymerizable terminal vinyl groups is a useful synthetic method to achieve better ¯lm-forming properties. Final products are known as polyurethane-acrylate or acrylic-polyurethane hybrids and should produce binders with better technological properties than physical mixtures. In this work the morphology of hybrids acrylic-polyurethane with di®erent acrylic content on cured (60 oC for 48 h) and non-cured ¯lms were studied using SAXS. The scattering intensity I(q) vs. q for pure PU, acrylic and hybrids ¯lms without thermal curing show that a phase separation at 70 wt.% of acrylic content occurs. The SAXS spectra of cured and non-cured samples of pure PU show a broad maximum at ca. 0.1 ºA¡1 due to the typically semi-crystalline nature of the PU polymers, indicating that the morphology does not change after curing. In the pure acrylics sample, however a different behavior is observed after thermal treatment. Two peaks observed at 0.14 and 0.15 ºA¡1 at room temperature are not observed after curing at 60 oC. The absence of peaks in the hybrids samples with acrylics ranging from 10 to 70 wt.% indicates a homogeneous morphology. The presence of acrylic component in°uence the crystallization process. Increasing acrylic content, latex particles of pure acrylic polymer are also formed during polymerization, which in turn segregates during ¯lm-formation. As expected, thermal curing facilitates the phase separation.