Terminal Hydrophilicity-Induced Dispersion of Cationic Waterborne Polyurethane from CO₂-Based Polyol

Abstract

Cationic waterborne polyurethane (CWPU) was initially developed as a specific adhesive for anionic surface but now is ubiquitous in innovative material systems such as poly­(ionic liquid)­s, polyelectrolytes, antibacterial coatings, and drug carriers. However, state-of-the-art CWPU faces imperative challenges like easy degradation and poor water resistance, which is caused by excessive incorporation of internal emulsifiers with tertiary amines into the backbone than necessary, since emulsification performance of cationic internal emulsifier is much less efficient compared with the anionic analogue. Here, a terminal internal emulsifier-induced efficient dispersion strategy was developed. Taking oligo­(carbonate ether) diol (a CO2-polyol from telomerization of CO2 and propylene oxide) as example, stable CWPU with only 1.00 wt % internal emulsifier was prepared. An emulsifying capacity parameter was introduced to quantitatively evaluate the emulsification performance of internal emulsifier according to its steric hindrance and mobility, and the terminal internal emulsifier was proven to show the highest emulsification performance. The terminal hydrophilicity-induced dispersion strategy exhibits excellent universality for a broad range of oligomer diols, effective not only for CO2-polyols but also for widely used polyether polyols and polyester polyols, affording CWPU with excellent water resistance. Therefore, the chemistry disclosed here paves a way for a vast number of water- and oxidation-resistant CWPUs which were hardly available until now.

Carbon dioxide copolymers: Emerging sustainable materials for versatile applications

“…53 Moreover, for application in adhesives, more advanced and comprehensive properties are endowed by the use of CO 2 -derived polyols with the coexistence of carbonate and ether, in terms of both anionic and cationic waterborne Pus (WPUs). 54,55 Delightfully, there are a library of synthetic polymers using CO 2 as feedstock in a direct and indirect pathway, and the scale is still enlarging by continuous breakthroughs. Several recent reviews have comprehensively summarized the state-of-the-art technology toward catalyst development, 56 new synthetic protocols, 57 more diverse architecture and functionality.…”

“…53 Copyright 2014 The Royal Society of Chemistry F I G U R E 1 2 Enhanced material properties of CO 2 -WPU compared with oligoesterol and oligoetherol derived WPU. 54,55 (A) Outstanding water resistance of anionic CO 2 -WPU compared with PBA-WPU (polybutylene adipate polyol based WPU). (B) Superior oxidation resistance of anionic CO 2 -WPU against PPG-WPU(polypropylene glycol based WPU).…”

“…154 Very recently, the stable dispersion of cationic CO 2 -WPUs was prepared by terminal hydrophilicity-induced dispersion strategy, where the internal emulsifier was reduced as low as 1.0 wt%, resulting in unprecedented water resistance as well as integrated hydrolysis/oxidation resistance. 55 Polycarbonate polyols synthesized by Co salen catalyst also find applications in PU production. For example, using organophosphorus CTA, such as phenylphosphonic acid, nonflammable CO 2 -polyols were synthesized and further used as synthon to prepare flame-retarding thermoplastic PU.…”

“…In addition to anionic CO 2 ‐WPUs, cationic WPU were also necessary for some special use, for example, adhesive for anionic surface, but it faces long‐term dilemma of trade‐off among internal emulsifier dosage, stable dispersion, and water resistance 154 . Very recently, the stable dispersion of cationic CO 2 ‐WPUs was prepared by terminal hydrophilicity‐induced dispersion strategy, where the internal emulsifier was reduced as low as 1.0 wt%, resulting in unprecedented water resistance as well as integrated hydrolysis/oxidation resistance 55 …”

“…For example, CO 2 ‐polyol‐derived PU foams exhibit similar tensile strength compared with conventional polyether derived ones 53 . Moreover, for application in adhesives, more advanced and comprehensive properties are endowed by the use of CO 2 ‐derived polyols with the coexistence of carbonate and ether, in terms of both anionic and cationic waterborne Pus (WPUs) 54,55 …”