Synthesis and characterization of waterborne polyurethanes with alkoxy silane groups in the side chains for potential application in waterborne ink

• AEAPTMS with two amine groups and three methoxysilane groups is introduced into PU.
• The alkoxy silane group locates on the side chain of PU.
• The incorporation of AEAPTMS increases the adhesion of WPUs on OPP film.
• AEAPTMS is more effective to improve the property of WPUs than APTES.

In this study, a series of waterborne polyurethanes (WPUs) with alkoxy silane groups in the side chains were synthesized by the chain extension with diamine chain extender (3-(2-aminoethyl)aminopropyl)trimethoxysilane (AEAPTMS). The effects of AEAPTMS content on the properties of WPUs were investigated in terms of adhesion strength, mechanical property, crystallinity and thermal stability. FT-IR and 1H NMR spectra demonstrated the successful incorporation of AEAPTMS to polyurethanes. The increase of AEAPTMS content produced a decrease in the surface tension of WPUs as well as the interfacial tension and contact angle between WPUs and oriented polypropylene (OPP) films, implying the improvement of wetting property of WPUs on OPP films. The increase of AEAPTMS content increased the hydrophobicity, tensile strength, glass transition temperature and thermostability of WPU films, and decreased the crystallinity and elongation at break of WPU films. The adhesion strength of WPUs initially increased and then decreased with the increase of AEAPTMS content, and was the highest when the AEAPTMS content was 2.0 wt%. Moreover, compared with 3-aminopropyltriethoxysilane (APTES), AEAPTMS could improve the property of WPUs more greatly. In summary, the synthesized WPU with 2.0 wt% AEAPTMS had low water absorption, high thermal stability, and good adhesion on OPP film, and could be potentially used in waterborne ink for OPP film.

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