Synthesis and Characterization of Novel Processable and Flexible Polyimides Containing 3,6-Di(4-carboxyphenyl)pyromellitic Dianhydride

Table 2

Solubility and inherent viscosity of polyimides (PI-1–PI-6).

Polyimide	DMSO	DMAc	DMF	THF	m-cresol	H2SO4	ηinn (dL/g)
PI-1	++	+	+	−	+	+++	0.68
PI-2	++	+	−	−	++	+++	0.98
PI-3	+++	−	++	+	++	+++	1.01
PI-4	++	+	+	−	++	+++	0.72
PI-5	++	+	+	+	++	+++	0.94
PI-6	+++	+	−	+	++	+++	1.04

+++ = soluble at room temperature, ++ = soluble on heating, + = slightly soluble on heating, − = insoluble.