Synthesis of Thermotropic Liquid Crystalline Polyimides with Siloxane Linkages

Abstract

Thermotropic liquid crystalline (LC) semi-aliphatic polyimides have been developed from 3,3′,4,4′-tetracarboxybiphenyl dianhydride (BPDA) and diamines containing siloxane spacer units. These polyimides exhibited high thermal stability and lower transition temperature compared to the corresponding polyimides containing alkyl or oxyethylene spacer units.

Characteristic smectic structures of main-chain liquid-crystalline polyimides driven by a microphase separation between aromatic imide mesogen and a siloxane spacer

“…The synthetic route for the BPDA/3SiO4-3F polyimide has been previously reported. [18][19][20] Differential scanning calorimetry (DSC) measurements were carried out with a Perkin-Elmer DSC 7 at a scanning rate of 10 C min À1 under a flow of nitrogen. WAXD patterns were measured using Cu K a radiation generated by a Rigaku-Denki UltraX 18 X-ray generator equipped with a graphite crystal monochromator and a pin-hole collimator.…”

“…17 In this aspect, a series of main-chain liquid-crystalline polyimides, BPDA/nSiOm, which consist of an aromatic imide BPDA mesogen and alkyl and dimethyl siloxane spacers, are interesting because some of them have been found to form both S C and S A phases. [18][19][20] One of the typical materials is the following, and the distinct structural characteristics of the S A and S C phases as examined using the wide-angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectroscopy measurements for the uniaxial fiber and BPDA/3SiO4-3F film.…”

Thermotropic liquid crystalline polyimides toward high heat conducting materials for 3D chip stack

“…Both synthesis of poly(amic acid) (PAA; 2) in N-methylpyrrolidone (NMP) and preparation of film of polyimide 1 by thermal imidization of PAA 2 were reported elsewhere [7]. Thermal imidization of PAA 2 was carried out by heating PAA 2 casted on a glass substrate or a silicon wafer below 200 °C.…”

Cross-Linked Liquid Crystalline Polyimides with Siloxane Units: Their Morphology and Thermal Diffusivity

“…LC polyimides should be more applicable as thermally conductive materials than epoxy resins because the precursors of polyimides, which are poly(amic acid)s (PAAs), have the advantages of solution processability, although most polyimides are generally insoluble. In a previous study, we reported the synthesis of thermotropic LC polyimides from diamines containing dimethylsiloxane spacer units and pyromellitic dianhydride (PMDA) or 3,3′,4,4′-tetracarboxybiphenyl dianhydride (BPDA) − and demonstrated that the BPDA mesogenic group was segregated from the siloxane spacer group to form a layered LC phase (smectic A (SmA) and smectic C (SmC) phases) . The lowest crystal–LC transition temperature was 163 °C during a heating process that originated from long siloxane units and the fluoro substituent on the mesogenic units to reduce the polymer packing interaction.…”

“…In this report, we prepared cross-linked LC polyimides containing siloxane spacer units by the cross-linking reaction of the ethynyl end-groups introduced at the chain end, with controlling the extent of the degree of cross-linking by changing the molar ratio of the ethynyl end-group to the monomer units. The ethynyl group was selected as a thermally cross-linkable moiety around 250 °C, − corresponding to the temperature of LC phase for our reported LC polyimides. − The purpose of this study is to clarify the relationship between the morphology and thermal diffusivity of the LC polyimides maintaining the LC structure at room temperature via cross-linking at elevated temperature. It should be mentioned that there were no reports on the detailed relationship between the LC structures of polyimides and their thermal diffusivity at room temperature.…”