Research On Preparation And Self-healing Properties Of Polyborosiloxane Films

Polyborosiloxane（PBDMS）is a semi-solid and transparent intrinsically self-healing polymer with good ductility and based on boron-oxygen dynamic bonding.As a flexible self-healing optical protective film,PBDMS has great application value in foldable electronic screens,flexible battery substrates,automotive windows and etc.However,current studies on the self-healing properties of PBDMS are mostly based on the bulk materials.Considering PBDMS film has size effect and surface effect,the PBDMS film possess special physical properties.But its related research is rare,and the influencing factors for the self-healing performance of the film are not clear yet.In this research,polydimethylsiloxane（PDMS-OH）and boric acid（H₃BO₃）were used as raw materials to synthesize polyborosiloxane.PBDMS with different polymerization degree and boro-to-silicate ratio were prepared through changing the hydroxyl content of PDMS-OH and the H₃BO₃/PDMS-OH ratio.The chemical structure and rheological properties of the bulk polymers were characterized.Self-healing PBDMS films were prepared by spin-coating and dip-coating methods.The differences in film formation of the two processes were analyzed.The effects of polymerization degree and boron-to-silicon ratio on the surface morphology,surface wettability,self-healing properties and light transmission of the films were investigated.The results are as follows:The hydroxyl content of PDMS-OH and boric acid content in raw materials had an effect on the structure and properties of PBDMS.Infrared spectroscopy analysis showed that the polymerization degree and the number of Si-O-B structure in PBDMS increased with higher hydroxyl content PDMS-OH.Meanwhile with the increase of H₃BO₃ content,the number of B-O-B structure in PBDMS increased leading to the increasing of boro-to-silicon ratio of the polymer.Rheological tests showed that at high shear rates,the shear viscosity increased with the increase of hydroxyl group content and boric acid content of PDMS-OH in the raw material.As number of rigid structure in PBDMS increased,the compliance of the segments and the fluidity of the polymer decreased.Films prepared by spin coating were too thin and had residual stress inside.The healing materials cannot be delivered to the damaged area of the film,lealing to unstability of self-healing effect.The surface of the film prepared by dip-coating method was wrinkled with certain orientations.With the lower the polymer viscosity,the faster the self-healing rate of the film.The self-healing performance of the parallel direction to the pulling direction was better than perpendicular direction.Self-healing rate of the film（PBDMS-D）prepared by the reaction of PDMS-OH with hydroxyl content of 2.4%and H₃BO₃ in a ratio of 1:1 can reach more than 95%just after 15 min.Besides,PBDMS film had good light transmittance under visible light.The light transmittances of all samples were higher than 82%,which meets the requirements of optical film.PBDMS films also have good hydrophobicity,and the surface contact angles are higher than 90°.Silicon dioxide（SiO₂）always is used as a reinforcing agent for silicone materials to enhance the mechanical properties of materials.In this study,Si O₂/PBDMS composite films were prepared by adding nano-Si O₂ to reactants.The influence of silica content on the properties of self-healing films was explored.With the increase of Si O₂ content,the resistance caused by nanoparticles to the movement of molecular segments was greater,leading to decreasment of the self-healing performance of the film.With the increase of Si O₂ content,the surface contact angle increased and then decreased,and the light transmittance of the film decreased.