Synthesis And Properties Of Silicone Materials Via Imine Chemistry

Polysiloxanes are a valuable class of hybrid organic/inorganic polymers with excellent properties and broad applications,which are composed by repeating silicon-oxygen units with variable side groups along the polymeric backbone.In general,conventional polysiloxanes are synthesized by the polycondensation of chlorosilanes/alkoxysilanes and the ring-opening polymerization of cyclic siloxane monomers.Such synthetic processes have poor tolerance of functional groups,which limits the varieties of functional groups to a few ones including amine,hydride,mercapto,and vinyl groups.The lack of structural diversity has made traditional polysiloxanes inadequate to meet the increasing demand for high performance and diversified functional materials.Therefore,several reactions including michael addition,thiol-ene,copper-catalyzed 1,3-dipolar cycloaddition,and hydrosilylation,have been explored for derivatizing silicones via post-polymerization modification.Considering the limited range of suitable substrates in every reaction,there is a great need for new general synthetic strategies to produce new polysiloxanes with multiple functional groups and improved properties.Imine compounds are generally synthesized via the condensation between primary amines and aldehydes,which proceeds under ambient conditions without catalysts and involves only water as a byproduct.As the most explored dynamic covalent reactions,imine formation and exchange exhibit error-checking and proof-reading capabilities.Imine compounds possess excellent coordination ability due to the presence of lone pair electrons on the nitrogen atom of the imine group.It is not surprising that imine ligands are widely used in the preparation of metal complexes due to their synthetic easiness and diverse structures.Over the past decade,imine chemistry have attracted significant interest in both chemistry and material science thanks to the synthetic flexibility,dynamic covalent chemistry and excellent coordination capacity.Considering the great importance of imine chemistry and the availability of polysiloxanes containing amino groups,it's of great worth to investigate the imine-functionalization of polysiloxanes and also their silicone elastomers.In this paper,we designed and synthesized functionalized polysiloxanes and silicone elastomers based on imine chemistry,and explored their properties.The main content divided into the following aspects:1.A series of imine-functionalization of polysiloxanes was synthesized by the condensation reaction between poly[(aminopropyl)methylsiloxane-co-dimethylsiloxane]with various aromatic aldehydes.Their structures were characterized by IR,NMR and UV spectra.The properties of the polymers were investigated by TGA and DSC,the results show that the synthesized imine-polymers possess excellent thermostability and low glass transition temperature.Fluorescence analysis indicates that the prepared imine-polysiloxanes emit blue light at 376 nm,which was caused by the presence of N?Si coordination bonds in polymers structure.This work will provide a simple and effective way to synthesize functional polysiloxanes.2.Based on the metal coordination of imine-polysiloxanes,a series of silicone elastomers were prepared with tunable mechanical properties adjusted by changing the imine content,metal ion type,metal ion content and substituent electron effect.IR and UV analysis proved that the successful coordination between polymers and metal ions.By tensile test,we found that the tensile strength of elastomers decrease with the increase of electron-withdrawing ability of substitute groups.Due to the dynamic reversibility of coordination bonds,elastomers exhibit reusability.Moreover,the tensile strength of the elastomers was improved by double crosslinking.This work provides a new scheme to change the mechanical properties of elastomers.3.Based on the schiff base reaction and trimerization of phenylboric acid,we prepared silicone elastomers with dynamic covalent bonds(imine bond,boroxine bond)and hydrogen bond.Compared with coordination elastomer prepared in the previous chapter,the mechanical properties of elastomers are improved.Without any filler,the tensile strength of the elastomers can reach 4.23 MPa and Young's modulus can reach 77.94 MPa.Due to the synergistic effect of multiple dynamic bonds,the elastomers are reprocessable.This study lays a foundation for the preparation of new silicone elastomer with excellent mechanical properties.