In view of both improving properties of waterborne polyurethane (WPU) and sufficient utilization of renewable resources, a series of polydimethylsiloxane (PDMS) and castor oil (C.O.) comodified anionic WPUs with internal cross-linking was prepared through a prepolymer mixing process. The chemical structure of synthesized polymers was characterized by Fourier transforms infrared spectroscopy (FT-IR). In comparison with traditional linear WPU synthesized from petroleum-based polyols, these novel WPU films exhibited superior properties in solvent and water resistance, thermal stability, and mechanical strength, which suggest promising applications of these new environmentally friendly materials, particularly in the area of decorative and protective coatings. In addition, the results showed that with the increase in PDMS content in these co-modified WPUs the average particle size, the water resistance, and the thermal stability increased accordingly while the solvent resistance and the mechanical properties decreased. 1. Introduction Waterborne polyurethane (WPU) dispersions, one of the most rapidly developing and active branches of PU chemistry and technology, have gained great attention in many commercial fields due to their superior properties and environmental advantages relative to conventional solvent-borne polyurethanes [1, 2]. However, some properties of WPU still need to be improved further, such as water and solvent resistance, thermal stability, and mechanical properties. The improvements of these properties have been achieved by copolymerizing or grafting of other polymers, external and internal cross-linking, blending or interpenetrating, polymer network formations, and modifying with nanoparticles [3–7]. Polydimethylsiloxane (PDMS) has many applications due to its unique properties, which arise mainly from its natural structure composed of inorganic Si–O bond and organic graft methyl group. These interesting properties include low surface energy, biocompatibility, high thermal and oxidative stability, good water resistance, chemical inactivity, insulating stability, low glass transition temperature, and great molecular flexibility [8]. Combining the advantages of PDMS with those of WPU has attracted the attention of many researchers for a long time and PDMS has been introduced to WPU through both blending and copolymerization methods [8–16]. Although these linear PDMS-WPU “hybrids” showed much better heat and water resistance than that of WPU, the incorporation of PDMS often has a negative effect on the physical mechanical properties of WPU,
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