Tunable colorless and transparent copoly(ester imide)s and nanocomposites derived from an optimized composition

A series of colorless and transparent copoly(ester imide)s (Co-CPEIs) were synthesized by reacting diamine p-xylylenediamine (p-XDA) with two types of dianhydrides of various molar contents, namely 2,7-dihydroxynaphthalene bis(trimellitate anhydride) (NATA) and hydroquinone bis(trimellitate anhydride) (HQTA) in N,N'-dimethylacetamide (DMAc). All the Co-CPEI films synthesized by changing the molar ratio of the two dianhydrides from 0 to 1.0, were colorless, transparent, flexible, and tough. The thermomechanical properties and optical transparencies of the Co-CPEI films were investigated according to the molar compositions of the different dianhydrides. Among the synthesized Co-CPEIs, hybrid films were created by dispersing various concentrations of organoclay into Co-CPEI with a p-XDA: NATA: HQTA molar ratio of 1.0:0.50:0.50. These hybrids were synthesized by a solution intercalation method. STN, the organoclay used for hybridization, was obtained through the organo-modification of hectorite. Various amounts of STN (5-40 w%) were incorporated into the matrix Co-CPEI to obtain Co-CPEI hybrid films. The thermomechanical properties, optical transparency, and clay dispersion morphology of the Co-CPEI hybrid films with various STN contents were investigated and compared. A TEM analysis showed that the clay was uniformly dispersed at a nanoscale until the clay content reached 10 wt%; however, when the clay content exceeded 10 wt%, most of the clay agglomerated. The physical properties of the hybrid containing a specific critical clay content exhibited the highest values, and the physical properties deteriorated when the clay content exceed the critical limit.