Preparation Of Low Dielectric Constant Polyimide/Crown Ether Host-Guest Inclusion Films

Polyimide(PI) is a kind of high performance engineering plastics with wide applications range and in great demand, which has good thermal resistance(the onset temperature for thermal decomposition over 500oC),excellent mechanical properties(tensile strength over 100MPa) and low dielectric constant(?=2.8-3.6). It is very suitable to use in electric circuits as insulating substrates and electronic packaging materials. However, with the rapid development of ultra large scale integrated circuits, the size of electronic components is smaller and smaller, which requires polyimide to possess the better dielectric property to reduce the resistance capacitance delay effect and energy loss,that is to say,to get lower dielectric constant.This paper prepared a series of PI/crwon ether(CE) composite films by using different kinds of CE, diamine and dianhydride as reactants through complexation between CE and diamine monomer, in which the CE acted as host molecules and PI backbone acted as guest molecules.The structure and properties were studied by nuclear magnetic resonance spectroscopy, infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, dielectric spectroscopy,tensile testing machine and so on.1. After 15-crown-5(15-CE) or 18-crown-6(18-CE) formed host guest inclusion complexes with 4,4’-oxidianiline(ODA) monomer, pyromellitic dianhydride(PMDA) was added to polymerize into two kinds of precursors polyamic acid(PAA), PAA-1/15-CE and PAA-1/18-CE by in-situ polycondensation.PI-1/15-CE and PI-1/18-CE composite films with different contents of CE were preparedfollowing spin coating and thermal imidization.NMR and IR results demonstrated the complexation between crown ether and ODA monomer, and thenecklace-like host guest inclusion structure. Thermal gravimetric results illustrated the inclusion rate was 50%.Positron annihilation lifetime test showed that the crown ether increasedthe molecular free volume ofcomposite films. When the molar ratioof 18-crown-6to ODA amount was 0.4, the dielectric constant of the composite film could be reduced to 2.99, while Young’s modulus, tensile strength and elongation at break could be enhanced to 4.86 GPa, 130 MPa and 51.8%, respectively.2. Three kinds of composite films with different fluoride content were prepared through polycondensation of4,4’-(Hexafluoroisopropylidene)diphthalic anhydride(6FDA) or PMDA and complex between18-crown-6 and ODA or 2,2’-bis(trifluoromethyl)benzidine(TFDB), named as non-fluorinated PI-1/18-CE,semi-fluorinatedPI-2/18-CE and perfluorinated PI-3/18-CE.The supramolecular structure between 18-CE and several different PI backbones was analyzed in detail.The introduction of F atoms increased molecular free volume, reduced molecular polarizability,and enhanced hydrophobicity, which decreased the film dielectric constant, and the mechanical properties. But with the increasement of amount of 18-CE, the mechanical properties of fluorinatedcomposite films wereimproved, and the dielectric constant of PI-3/18-CE composite films continued to reduce to 2.72 whenthe molar ratioof 18-crown-6 to TFDB amount was 0.4.3. Two kinds of crown ether ACE and 11-ACE with different length of side chain were prepared through the dehydrating cyclization between allyloxy triethylene glycol and triethylene glycol ditosylate for ACE and between triethylene glycol ditosylate and α-undecylene oxymethyltriethylene glycol for 11-ACE.Then PI-1/ACE and PI-1/11-ACE supramolecularcomposite films were synthesized byin-situ polymerization, in whichACE or 11-ACE acted as host molecules and PI-1 backbone acted as guest molecules. The result showed that the host-guest inclusion rate was 50%, and the introduction of side chain containing allyloxy orα-undecylene oxymethylimproved the thermal stability of 18-CE.These modifiedcrown ethers not only increased the molecular free volume, but also introduced air holes in the thermal imidization process by volatilizing the decomposed crown ether. When the molar ratio oflong alkyl side chain 11-ACE to ODA was 0.4, the dielectric constant of PI-1/11-ACE composite films could be reduced to 2.17.4. Two kinds of crown etherwith different side chain length terminated by tri-(trimethylsilyloxy)were synthesized through the silicon hydrogen addition reaction and as host molecules to fabricate two kinds of host-guest composite films PI-1/SiCE and PI-1/11-SiCE with different content of crown ether.The results suggested that the siloxane group in crown ether molecules decreased the polarization rate and hydrophilicity. Furthermore,the siloxane group with dendrimers structure could increase the molecular free volume, introduce more air holes, and reduce the waterabsorption and dielectric constant of composite films.When the molar ratio of 11-SiCE to ODA dosage was 0.4,Young’s modulus of the composite filmenhancedmore than 50%,while the tensile strength and elongation at break maintained a considerable level, compared to PI-1. The dielectric constant of PI-1/11-SiCE composite films could be reduced to 1.94 and meet the requirement of the application in modern ultra large scale integrated circuit.