All-Aromatic (AB) n ‑Multiblock Copolymers via Simple One-Step Melt Condensation Chemistry

We have prepared (AB) n -multiblock copolymers based on N-(3′-hydroxyphenyl)­trimellitimide (IM), 4-hydroxybenzoic acid (HBA), and 6-hydroxy-2-naphthoic acid (HNA) via a simple one-pot melt condensation method. The blocky nature is the result of phase separation taking place in the early stages of the melt polymerization process. The liquid crystal HBA/HNA fraction phase separates from the isotropic HBA/IM fraction and this phase separation effectively shuts down transesterification reactions, preventing randomization of the polymer backbone. The (AB) n -multiblock copoly­(esterimide)­s exhibit two distinct glass transition temperatures (T gs). The first T g at ∼120 °C can be assigned to the HBA/HNA rich A-block and the second T g at ∼220 °C can be assigned to the HBA/IM rich B-block. When introducing imide-based phenylethynyl end-groups, these reactive functionalities end-up exclusively at the termini of the HBA/IM rich B-blocks, effectively forming a phenylethynyl-terminated B­(AB) n -reactive oligomer. Upon thermal treatment, cross-linking via the phenylethynyl end-groups results in a thermoset where the T g of the B-block increases by as much as ∼106 °C. The T g of the HBA/HNA A-block remains unchanged. Scanning electron microscopy experiments show a gradual change in morphology, from a typical fibrous LCP texture for the HBA/HNA rich polymers to a more consolidated morphology for the HBA/IM rich polymers. Atomic force microscopy images confirm the presence of two distinct domains when 44 mol % of HBA was replaced by IM. The “hard” imide rich B-blocks form domains of ∼100–200 nm that are embedded in the imide poor or “soft” A-blocks.