A reactive hydrophobically modified ethoxylated urethane (HEUR) associative polymer bearing benzophenone terminal groups: Synthesis, thickening and photo-initiating reactivity. (12th September 2019)

• Record Type: Journal Article
• Authors: Guan, Tao; Du, Zhukang; Chang, Xueyi; Zhao, Dongli; Yang, Shurui; Sun, Ning; Ren, Biye
• Is Part Of: Polymer. Volume 178(2019)
• Publication Date: 2019-09-12
• Subjects: HEURs -- Reactive thickeners -- Associative network -- Benzophenone -- Photo-initiating reactivity -- Waterborne UV coatings; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2019.121552
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Hydrophobically modified ethoxylated urethanes (HEURs), as a representative class of associative polymers, are widely used as rheology modifiers in waterborne systems such as coatings, emulsions, inks etc. due to their unique associative network structure and finite relaxation behavior in solution. However, conventional HEURs are non-reactive and generally stay free in final cured films, which may induce some damages to the performance of the coatings. To solve the problem, a new concept of reactive HEUR has been proposed. That is, a reactive HEUR should bear reactive hydrophobic end-groups which can chemically crosslink with matrix resins during the curing process of waterborne coatings. In this work, with the help of the hydrogen abstraction photo-initiating reactivity of benzophenone (BP) group, a reactive HEUR (BPC11 HEUR) end-functionalized by a photo-initiator BP moiety has been prepared. In aqueous solution, as demonstrated by steady shear measurement, an exponential increment of solution viscosity along with the increasing of polymer concentration ( C ) was found when C surpassed its critical percolation concentration ( C p ≈ 23.6 g/L). Besides, ultraviolet (UV) light induced photolysis in aqueous solution manifested a typical photochemical reaction behavior of BPC11 HEUR polymer with a final photolysis degree ( D ) of approximate 78% after 300 s of irradiation. In situ 1 H NMR and rheological measurements collectively revealed the efficient photo-initiating reactivity of BPC11 HEUR for waterborne UV monomers or resins. Further, rheological measurements demonstrated that the emulsion zero/low shear viscosity can be greatly enhanced by ca. 50 folds for a commercially available waterborne UV polyurethane acrylate emulsion when the addition amount of BPC11 HEUR varied from 0 to 1.0 wt%. These results shown that the reactive BPC11 HEUR polymer can not only be used to efficiently modify the rheological properties of solutions or emulsions but also can chemically crosslink with waterborne UV acrylic monomers or resins by light irradiation. The work may be of interest for development of reactive HEURs used in waterborne UV coatings, inks, and adhesives, etc. Graphical abstract: Image 1 Highlights: A reactive HEUR polymer bearing benzophenone terminal groups (BPC11 HEUR) was synthesized. The reactive BPC11 HEUR polymer can not only thicken emulsion but also photo initiate radical polymerization of UV resins. The reactive BPC11 HEUR polymer may decrease its migration from cured UV coatings. This work opens a new perspective for developing superior HEUR associative thickeners in waterborne systems.