Research On The Crystallization Behavior And Properties Of Semi-crystalline Poly(Arylene Ether Nitrile)

As a novel special engineering polymer,semi-crystalline poly?arylene ether nitrile??PEN?has aroused many attentions due to its brilliant mechanical performance,excellent radiation resistance and high thermal stability,which allow it to show off various applications in automotive,military and aerospace fields.However,the semi-crystalline PEN containing rigid groups possesses slow crystalline rate and low crystallinity,which limits its further practical application.According to research,the crystallization behavior of semi-crystalline polymers mainly depends on the chain structure and the molding process of the polymer material,and the addition of nucleating agent.Therefore,the crystallization behavior and the performance of hydroquinone resorcinol poly?aryl ether nitrile??HQ/RS-PEN?with different molecular weights have been studied by polarizing microscope?POM?,scanning electron microscopy?SEM?,differential scanning calorimetry?DSC?,and X-ray diffraction?XRD?.Moreover,functionalized hexagonal boron nitride?h-BN@?PDA+PEI??and molybdenum disulfide?MoS₂@?PDA+PEI??via mdopamine?DA?and polyethylenimine?PEI?surface co-modified on h-BN and MoS₂ nanoparticles have been used as nucleating agents in the HQ/RS-PEN matrix,respectively.The crystallization behavior and the performance of nanocomposites have been investigated.The specific work is as follows:Firstly,high molecular weight HQ/RS-PEN?HQ/RS-PEN-H?,medium molecular weight HQ/RS-PEN?HQ/RS-PEN-M?and low molecular weight HQ/RS-PEN?HQ/RS-PEN-L?were synthesized via nucleophilic substitution by using hydroquinone?HQ?,resorcinol?RS?and 2,6-dichlorobenzonitrile?DCBN?as monomers.The Avrami non-isothermal kinetics,crystallinity,crystal morphology and performance of HQ/RS-PEN with different molecular weights were studied.The results showed that the crystal forms of HQ/RS-PEN with different molecular weights were spherulites.At the same heating rate,HQ/RS-PEN-H showed higher crystallization temperature.With the increase of the heating rate,the crystallization temperature of HQ/RS-PEN-L,HQ/RS-PEN-M and HQ/RS-PEN-H increased from 199.7 ? to 217.7 ?,230.7 ? to251.6 ?,and 269.4 ? to 278.9 ?,respectively.As the molecular weight of HQ/RS-PEN increases,the crystal activation energy increased from 115.60 KJ/mol to359.91 KJ/mol.Moreover,XRD results showed that the crystallinity of HQ/RS-PEN-L,HQ/RS-PEN-M and HQ/RS-PEN-H was 12.35%,10.50%,and 6.56%,respectively.And the Avrami index n decreased,the thermal,mechanical and dielectric properties of HQ/RS-PEN were enhanced.Secondly,h-BN@?PDA+PEI?via polyethylenimine?PEI?assisted bio-inspired surface functionalization on h-BN were used as a nucleating agent in the HQ/RS-PEN matrix.And?h-BN@?PDA+PEI??/HQ/RS-PEN nanocomposite films was prepared via a solution casting method.The testing results certificated that h-BN@?PDA+PEI?could effectively promote the cold crystallization of HQ/RS-PEN and improve its crystallization rate,2 wt%h-BN@?PDA+PEI?could improve the crystallinity of HQ/RS-PEN from 6.56%to 14.90%,and the spherulite size of HQ/RS-PEN was reduced while the nucleation density of nanocomposites was raised.Furthermore,the non-isothermal crystallization kinetics demonstrated that 2 wt%h-BN@?PDA+PEI?could significantly reduce the cold crystallization temperature of HQ/RS-PEN from273.5 ? to 262.9 ? and the crystallization activation energy from 359.7 KJ/mol to292.8 KJ/mol.In addition,after the introduction of h-BN@?PDA+PEI?,the mechanical tensile strength and dielectric constant of nanocomposite films were enhanced from124.6 MPa to136.1 MPa and increased from 3.54 to 3.91 at 1kHz,respectively,which further broaden the application of semi-crystalline HQ/RS-PEN.Finally,in order to improve the crystallization performance of HQ/RS-PEN and broaden its application in the field of film capacitorsthe.MoS₂ nanosheets prepared by hydrothermal method were modified via mussel inspired co-deposition and crosslinking of polydopamine?PDA?and polyethylenimine?PEI?,followed by incorporating into the PEN matrix to form the MoS₂@?PDA+PEI?/HQ/RS-PEN nanocomposite films.The effect of functionalized MoS₂ mass fraction on the crystallization behavior and performance of HQ/RS-PEN nanocomposites were also detailed investigated.The testing results showed that the MoS₂@?PDA+PEI?can effectively improve the crystallinity?from 6.16%to 17.10%?,and the spherulite size of PEN was reduced form2 um to 0.5 um while the nucleation density of nanocomposites was raised.Besides,the crystal form of HQ/RS-PEN changed after the introduction of MoS₂@?PDA+PEI?.Owing to the well interfacial compatibility between MoS₂ nanosheet and PEN matrix,the resulting PEN nanocomposite film with 20 wt%of MoS₂@?PDA+PEI?exhibited high dielectric constant of 17.0 and quite low dielectric loss of 0.07 at 1 kHz,as well as significant improvement in energy density of 1.29 J/cm³.Besides,the addition of functionalized MoS₂ could also improve effectively the thermal and mechanical properties of PEN composites compared with neat PEN(T_5%>490? and T_s>108MPa).