Sequential reaction control during in situ polymerization and formation processes of reactive polyurethane coatings via adjusting molecular weight and isocyanate content of the prepolymer

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Soft Matter, 2026, Advance ArticleDOI: 10.1039/D6SM00247A, PaperBin Zhao, Huawei Xu, Jie Liu, Junfeng Zhang, Huimin Duan, Peter Müller-Buschbaum, Wenxing Chen, Dongming Qi, Qi ZhongBy regulating molecular weight and free –NCO content of prepolymer, the tuned …

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Sequential reaction control during in situ polymerization and formation processes of reactive polyurethane coatings via adjusting molecular weight and isocyanate content of the prepolymer

* Corresponding authors

a National Base for International Science and Technology Cooperation in Textiles and Consumer-Goods Chemistry & Zhejiang Provincial Engineering Research Center for Green and Low-Carbon Dyeing & Finishing, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China
E-mail: [email protected], [email protected], [email protected]
Fax: +86 571 86843255
Tel: +86 571 86942702

b State Key Laboratory of Bio-based Fiber Materials, Zhejiang Sci-Tech University Hangzhou, P. R. China

c Hexin Kuraray Micro Fiber (Haiyan) Co. Ltd., 383 Haihe Road, 314305 Jiaxing, China

d Zhejiang Provincial Innovation Center of Advanced Textile Technology, Shaoxing 312000, P. R. China

e Chair for Functional Materials, Department of Physics, TUM School of Natural Sciences, Technical University of Munich, James-Franck-Str. 1, Garching, Germany

Abstract

Sequential reaction control during in situ polymerization and formation processes of reactive polyurethane (RPU) coatings is achieved by adjusting the molecular weight and isocyanate content of the prepolymer. Due to the different reactivities between the linear chain extender 1,4-butanediol (1,4-BDO) and star-shaped cross-linker 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (TMP), the cross-linking process can be slower than the chain extension, especially under an atmosphere with high viscosity. Thus, by changing the molecular weight (Mn) of poly(tetrahydrofuran) (PTMEG) during the preparation of the prepolymer, the viscosity as well as the reaction process can be precisely controlled. When the Mn of PTMEG is 2900 g mol−1, the obtained mixture presents high viscosity, which enlarges the reactive difference between 1,4-BDO and TMP. Instead of simultaneous reactions, the chain extension and cross-linking are sequentially set. However, when the Mn of PTMEG is reduced to 1000 g mol−1, the low viscosity causes the difference in reactivity between 1,4-BDO and TMP to be less prominent. The chain extension and cross-linking simultaneously set in, and the three-stage process no longer exists. Similar to the Mn of PTMEG, the isocyanate content of the prepolymer also significantly influences viscosity via the external plasticizer effect during the in situ polymerization and formation processes. Thus, by simply adjusting Mn and the isocyanate content of the prepolymer, not only the reactions, but also the structure of RPU coatings can be fine-tuned. The obtained mechanism can be used as the theoretical guidance for controllable polymerization and formation in the PU industry.