Simple linear ionic polysiloxane showing unexpected nanostructure and mechanical properties

Mitsuo Hara,Shusaku Nagano,Yuta Iijima,Takahiro Seki

doi:10.1038/s41598-021-97204-8

Abstract

Polysiloxanes are ubiquitous materials in industry and daily life derived from silicates, an abundant resource. They exhibit various properties, which depend on the main-chain network structure. Linear (1D backbone) polysiloxanes provide amorphous materials. They are recognized as fluid materials in the form of grease or oil with a low glass transition temperature. Herein we report that a simple linear polysiloxane, poly(3-aminopropylmethylsiloxane) hydrochloride, shows an elastic modulus comparable to that of stiff resins such as poly(tetrafluoroethylene). By introducing an ammonium salt at all the units of this polysiloxane, inter- and intramolecular ionic aggregates form, immensely enhancing the elastic modulus. This polysiloxane is highly hygroscopic, and its modulus can be altered reversibly 100 million times between moist and dry atmospheres. In addition, it works as a good adhesive for glass substrates with a shear strength of more than 1 MPa in the dry state. Despite its simple structure with a flexible backbone, this polymer unexpectedly self-assembles to form an ordered lamellar nanostructure in dry conditions. Consequently, this work reveals new functions and possibilities for polysiloxanes materials by densely introducing ionic groups.

Highlights

Polysiloxanes are ubiquitous materials in industry and daily life derived from silicates, an abundant resource
We recently introduced an ammonium salt into linear polysiloxanes to construct surfactant-polysiloxane hybrid nanostructures, which show humidity-sensitive phase t ransitions[6,7]
In the course of our explorations, we found that linear polysiloxanes with an ionic group at all siloxane monomer units is vitrified and exhibits a modulus equivalent to that of a typical resin under certain conditions even though it is not chemically crosslinked

Summary

Introduction

Polysiloxanes are ubiquitous materials in industry and daily life derived from silicates, an abundant resource. We report for the first time that a simple linear polysiloxane, poly(3-aminopropylmethylsiloxane) hydrochloride (PSx(NH3+Cl−)), displays the modulus of a typical resin (Fig. 1). PSx(NH3+Cl−) shows a 100 million-fold change in the elastic modulus in response to humidity. The humiditycontrolled IR spectrum of PSx(NH3+Cl−) showed an enhanced vibrational absorption of water molecules as the relative humidity increased (Fig. S4).

Results

Conclusion