Recent advances in synthesis, characterization and rheological properties of polyurethanes and POSS/polyurethane nanocomposites dispersions and films

Aqueous polyurethane dispersions (PUDs) have recently emerged as important alternatives to their solvent-based counterparts for various applications due to increasing health and environmental awareness. There are a number of important variables in the preparation of aqueous PUDs such as carboxylic acid content, solid content, degree of pre-/post-neutralization of the carboxylic acids and chain extension that all impact the dispersion particle sizes and distributions, viscosity, molecular weights, and glass transition temperatures of the PUDs and thin films made from them. This article reviews some new insights into the synthesis, characterization, structure evolution and kinetics, and rheological properties of representative examples of polyurethanes and POSS/polyurethane nanocomposites dispersions and films with prescribed rheological properties, macromolecular structure dynamics and function with the aim of understanding the complex relationships amongst the polymer structure, rheological properties, and performance of the PUDs and nanocomposite films under conditions that they are likely to encounter during use. it will be demonstrated that incorporation of small amounts of POSS into PU films can significantly enhance the thermal stability and mechanical properties, and present a new class of materials for special industrial applications. The unanswered questions are discussed to guide future research directions, and facilitate progress in this area so that the materials can be rationally engineered during synthesis and processing to yield new materials with enhanced properties for a number of applications. Overall, the present review article will provide a quantitative experimental basis for any future theory development of the relatively new waterborne PUDs and hybrid PU/POSS nanocomposites, and their structural dynamics, phase behavior, molecular relaxation, and rheological properties, increasing our level of understanding of the behavior of this important class of polymeric materials and other similar water soluble polymers. Published by Elsevier Ltd.