Synthesis and comparative study on polyetherimides from isomeric 4,4′-isopropylidenediphenoxy bis(phthalic anhydride)s

Two isomers of commercial 4,4 '-(4,4 '-isopropylidenediphenoxy) bis(phthalic anhydride) (4,4 '-BPADA), that is, 3,4 '-(4,4 '-isopropylidenediphenoxy) bis(phthalic anhydride) (3,4 '-BPADA) and 3,3 '-(4,4 '-isopropylidenediphenoxy) bis(phthalic anhydride) (3,3 '-BPADA), were synthesized through aromatic nucleophilic substitution from nitrophthalonitrile and bisphenol A. 3,4 '-BPADA was first synthesized from two intermediates, that is, 3-(4-[4-hydroxyphenylisopropylidene] phenoxy) phthalonitrile (3-BPADN) and 3,4 '-(4,4 '-isopropylidenediphenoxy) bis(phthalonitrile) (3,4 '-BPATN). The corresponding three series of polyetherimides (PEIs) were prepared with two representative aromatic diamines (4,4 '-oxydianiline and m-phenylenediamine (m-PDA)) via two-step procedure and chemical imidization. Isomeric polyimides showed T(g)s from 206 to 256 degrees C in nitrogen and T(d5%)s from 488 to 511 degrees C in argon, good mechanical properties (tensile moduli of 2.3-3.3 GPa, tensile strengths of 70-96 MPa, and elongations at break of 3.2%-5.1%), and good solubility. With the introduction of 3-substituted phthalimide unit, PEIs displayed higher T-g values, lower strengths and elongations, better solubility and larger d-spacings. The rheological properties of thermoplastic polyimide resins based on the BPADA isomers were investigated, which showed that polyetherimide PEI-3b derived from 3,3 '-BPADA and m-PDA had the lowest melt viscosity among the isomers, indicating that the melt processibility had been greatly improved.