Kinetic insights into metaphosphoric acid-catalyzed water-crosslinking reactions in silane-grafted polyolefin system

Abstract

Polyphosphoric acid (PPA)-catalyzed water-crosslinking reaction in silane-grafted polyolefin system was investigated. PPA exists as an equilibrium mixture comprising several phosphoric acid oligomers. Distribution of these oligomers depends on the phosphorus pentoxide content (%P₂O₅) of the PPA. Our results revealed that the PPA presented a higher catalytic activity than dibutyltin dilaurate, which is a catalyst most commonly used in polymer industry. The difference in catalytic activities of PPAs was primarily attributed to the distribution of the phosphoric acid oligomers in PPA; as the degree of highly condensed phosphoric acid oligomers increased, the catalytic activities of PPAs were enhanced. From the theoretical results, we concluded that the highly condensed oligomer could form the stable hydrate via hydrogen bond with a water molecule, leading to the enhanced catalytic activity of PPA for the hydrolysis reaction. This finding will add to the understanding in the development of the highly active and eco-friendly catalysts for the crosslinking reaction in polymer systems.

Graphical Abstract

Keywords:

• Water-crosslinking reaction
• alkoxysilane
• polyphosphoric acid
• tin-free
• kinetics

Acknowledgements

The authors thank the Core Clusters for Research Initiatives of Yamaguchi University, “Novel Analytical and Measuring Technology Contributions to Elucidation of Materials aiming at Life-Science Applications.” ¹H-NMR measurements documented in this study were performed at the Center for Instrumental Analysis, Yamaguchi University. All the computations were performed on the high-performance computing systems at the Research Institute for Information Technology at Kyushu University.

Additional information

Funding

This study was supported in part by the Grant-in-Aid for Scientific Research (C) (Grant No. 19K05525) from Japan Society for the Promotion of Science (JSPS), the Adaptable and Seamless Technology transfer Program through Target-driven R&D (A-STEP) (Grant No. JPMJTM20GC) from Japan Science and Technology (JST), and the program of the Chugoku Regional Innovation Research Center, “The New Industrial Innovation Research Workshop.”