Synthesis and characterization of semiaromatic polyamides with dicyclohexane units

Abstract

Two new difluorobenzamide monomers, N,N′-bis(4-fluorobenzamide)dicyclohexyl methane and N,N′-bis(4-fluorobenzamide)-3,3′-dimethyl dicyclohexyl methane were synthesized from 4,4′-diamino dicyclohexyl methane and bis-(3-methyl-4-aminocyclohexyl)-methane with 4-fluorobenzoyl chloride through a facile interfacial reaction. Both of the monomers were used to prepare semiaromatic polyamides by a nucleophilic polycondensation reaction with 1,1-bis(4-hydroxyphenyl)-1-phenylethane (BHPPE). The resultant semiaromatic polyamides were characterization by FT-IR, differential scanning calorimetry, thermogravimetric analysis, dynamic thermomechanical analysis etc. These semiaromatic polyamides were found to have excellent thermal properties: the glass transition temperature (T_g) of Ph-DCM and Ph-MCM was 217.2 °C and 236.9 °C, and the 5% weight-loss temperature (T_5%) was 442.3 °C and 429.8 °C, respectively. The tensile test and dynamic thermo-mechanical analysis indicates that the resultant polyamides have good mechanical properties. The rheological testing showed that when the temperature increased from 290 °C to 350 °C, the complex viscosities of Ph-DCM decreased from 8.7 to 2.9 kPa s and the complex viscosities of Ph-MCM dropped from 20.8 to 0.9 kPa s. The results indicate that these semiaromatic polyamides have good melt flowability and are suitable for the melting processing. In particular, the polyamide with pendent methyl groups was found to have lower complex viscosities than that with no pendent methyl groups.