Synthesis and Characterization of Long-Chain Branched Poly(ether imide)s with A₃ Comonomers

The synthesis of an aromatic trisamine enabled the generation of long-chain branched poly­(ether imide)­s (LCB-PEIs). The nucleophilic aromatic substitution of 1-chloro-4-nitrobenzene with 1,1,1-tris­(4-hydroxy­phenyl)­ethane resulted in tris­((p-nitrophenoxy)­phenyl)­ethane, and a subsequent reduction afforded tris­((p-amino­phenoxy)­phenyl)­ethane (TAPE) in high yields (>90%). Introducing TAPE at low percentages with m-phenylene­diamine and bisphenol A dianhydride enabled synthesis of high molecular weight, branched poly­(ether imide)­s with varied branch lengths. The stoichiometric imbalance and phthalic anhydride end-capping controlled molecular weights. Complementary ¹H NMR spectroscopy and size exclusion chromatography (SEC) identified average branch length as a function of TAPE incorporation and provided comparisons in molecular weights and distributions. The melt viscosity and thermal stability at elevated temperatures (∼340 °C) probed the feasibility of melt processing of LCB-PEIs in comparison to linear analogues. At equivalent molecular weight and below 1.5 mol % TAPE, melt viscosities increased at low shear rates. However, increasing TAPE above 1.5 mol % decreased melt viscosities at low shear rates, suggesting a correlation of branch length and polydispersity with melt viscosity. Mechanical testing of injection-molded samples demonstrated minimal changes in tensile and impact properties with branching. The LCB-PEIs herein establish their potential role in molding processes such as blow molding that requires high melt strength and advantageous shear thinning.