| Polyimine,a new kind of thermosets,are constructed by dynamic covalent imine bonds.Generally,they have stable cross-linked network as traditional thermosets under room temperature,while their cross-linked structure can be changed under certain conditions so that they are able to achieve remolding and degradation.However,according to the reports so far,most reported polyimines are synthesized by aliphatic amine or aliphatic aldehyde,which results in relatively low heat resistance,medium mechanical properties and high sensitivity to moisture.Therefore,we used aromatic aldehydes and aromatic amines as raw materials to prepare aromatic polyimines.Because of aromatic imine bonds which have better stability and aromatic structure,the heat resistance can be greatly improved.The problem of water sensitivity is hopefully dissolved by the use of hydrophobic monomers.Besides,aromatic imine bonds have rigid rod-like structure which would enhance the thermal conductivity of polymer matrix.We did deep research on aromatic polyimine and got the following conclusions:?1?2,2-bis[4-?4-aminophenoxy?phenyl]propane?BAPP?,p-phthalaldehyde?PPHA?and tri[?4-formylphenoxy?methyl]ethane?TFE?were used as the raw materials to prepare four polyimines with different crosslinking degree by controlling the ratio of TFE.The results show that they have outstanding heat resistance.Their 5%weight loss temperature is about440?,and glass transition temperature raises from 217?to 239?with the increase of crosslinking degree.The mechanical properties are tailorable by changing the crosslinking degree,and the tensile strength is 64.3?92.0MPa and the elongation at break is 6.3?12.0%.Furthermore,they exhibit an extremely low water absorption rate as low as about 0.15%so that their mechanical properties are unchanged after being immersed in water.Additionally,these kinds of polyimines are so stable that they did not degrade even in 1M HCl,while by adjusting the solvent parameters to increase the affinity and wetting to the resin,they can be completely and quickly degraded into soluble small molecule in 1M HCl/THF.?2?TFE and different chemical structure of aromatic diamine were used to prepare different polyimines,and we further investigated the relevant between the chemical structure and thermal conductivity.Eventually,polyimine synthesized by p-phenylenediamine and TFE were verified as the better matrix with higher thermal conductivity,and high thermal conductive BN/polyimine composites were further prepared.The results show that this kind of BN/polyimine composites have relatively high thermal resistance with 5%weight loss at over 435?.The composites whose BN contents is 10?60wt%have out-of-plane thermal conductivity of 0.82?3.33 W·m-1·K-1 and in-plane thermal conductivity of 2.51?14.35W·m-1·K-1,which are 1.9?7.7 times and 5.8?33.4 times of the matrix respectively.However,the addition of BN generally leads to decrease in tensile strength and toughness of polyimine,and an increase in tensile modulus.Base on the degradable property of polyimine,we further achieved the recycling of BN from the BN/polyimine composites. |
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