Accelerated Curing of Aryl−Ethynyl End-Capped Polyimide Oligomers and Model Compounds:  A Kinetic Study Probing Substituent Effects

Abstract

phthalimide (1), N-phenyl-4-(4-methoxy-1-naphthylethynyl)phthalimide (2), and N-phenyl-4-(4-benzonitrileethynyl)phthalimide (3) were synthesized to probe the effect(s) of electronic subsituents on the thermal curing of aryl-ethynyl end-capped oligomers using end-cap model compounds. The curing kinetics were analyzed using SEC and NMR techniques and Arrhenius parameters were determined and compared to the anthracenyl, naphthyl, and phenyl analogues, 4, 5, and 6, respectively. A thermal curing rate acceleration was attributed to the electron-donating methoxy functionality. This acceleration is independent from the previously observed rate acceleration (phenyl < naphthyl < anthracenyl). Analyses of product distribution of 95% cured model compounds via SEC reveal slight differences between 1 and 4 but no discernible differences between 2 and 5. The incorporation of the electron-withdrawing group has no effect on the thermal cure rates, as the curing kinetics of 3 are nearly identical to those of 6. A new end-capping reagent, 4-(4methoxy-1-naphthylethynyl)phthalic anhydride ( 7) was synthesized and further used in the synthesis of 4-methoxynaphthylethynyl end-capped oligomer (4-MeO-NETI-5). By comparison to NETI-5, no significant changes are introduced by the methoxy-functionality except a reduction in thermal stability via SEC, DSC, and TGA. The curing kinetics of 4-MeO-NETI-5 were determined by monitoring the change in T g and analysis using the DiBenedetto equation. Unlike all analogous oligomers and model compounds including 2, a second-order rate law describes the curing kinetics of 4-MeO-NETI-5 better than a firstorder rate law. Arrhenius analysis of 4-MeO-NETI-5 using either a first-or second-order rate law results in indistinguishable Arrhenius parameters, and 4-MeO-NETI-5 cures with a lower Ea than NETI-5.

Resin Transfer Moldable Fluorinated Phenylethynyl-Terminated Imide Oligomers with High Tg: Structure–Melt Stability Relationship

“…However, more researchers have demonstrated the cure of ethynyl of PEPA would be promoted by electron-withdrawing groups attached to phenylethynyl or ethynyl moiety. By replacing the phenyl group attached to ethynyl moiety of PEPA with naphthyl or anthracenyl group could decrease the cure temperature by 30–80 °C [ 31 , 32 , 33 ]. Harris et al [ 34 ] reported that end groups derived from PEPA with electron-withdrawing attached to phenylethynyl moiety exhibited higher reactivity.…”

Rheological behaviour and cure kinetic studies of a trifunctional phenylethynyl-terminated imide oligomer

“…Depending on the cross-linking units, imide oligomers include phenylethynyl unit-based oligomers, ethynyl-based oligomers and nadic anhydrideterminated oligomers. Compared to the other thermosetting polyimides, phenylethynyl-terminated imide oligomers (PETIs) have received more attention, [6][7][8][9][10] because PETIs could undergo thermal curing without the evolution of volatile by-products, and the cured resins display high glass transition temperatures (T g s), excellent chemical resistance and better thermal oxidative stability. [11][12][13] Hence, PETIs have been employed as matrices to fabricate carbon fibrereinforced composites for high temperature applications.…”

Use of a self‐expanding super‐elastic all‐metal endoprosthesis; To treat degenerated SVG lesions: The SESAME first in man trial

“…The thermal‐curing kinetic analysis of the oligomeric systems OI‐5 and OI‐6 were also carried out via DSC by monitoring the change in T g as a function of time at the various temperatures 350, 360, 370, and 380 °C. The extent of curing (x) was calculated by DiBenedetto equation modified for highly crosslinked networks according to the literatures 38–41, 45, 46. Applying first‐order data analysis (−ln(1 − x) = K t ), the rate constant ( K ) at certain temperature was obtained from the very good line fit.…”

“…Among them, PETI‐5 was selected as the adhesive and composite matrix for the excellent mechanical properties and good processability 37. In recent years, Wright found that the curing rate increased in the order of phenylethynyl < naphthylethynyl < anthracenylethynyl in phthalimide model compound as well as the corresponding imide segment in PETI‐5 at the same temperature 38–41. Hergenrother prepared 4‐(2‐phenylethynyl)‐1, 8‐naphthalic anhydride (PENA) and 4‐(1‐naphthylethynyl)‐1, 8‐naphthalic anhydride (NENA), then studied the thermal and mechanical properties of imide oligomers terminated with these aryl ethynyls 36…”