A Solid-State ¹³C NMR Study of the Cure of ¹³C-Labeled Phenylethynyl End-Capped Polyimides

Abstract

The cure reactions of phenylethynyl end-capped polyimides were investigated using solid-state 13C magic-angle spinning (MAS) nuclear magnetic resonance (NMR). A 13C-labeled model compound (13C-PEPA-3,4‘-ODA) and an imide oligomer (13C-PETI-5) were synthesized and characterized. The thermal cure process for 13C-PEPA-3,4‘-ODA was followed over the temperature range 318−380 °C and for13C-PETI-5 over the temperature range from 350 to 400 °C. Our NMR results showed that, for the model compound, as curing proceeded, the percentage of polymeric structures containing double-bonded and single-bonded carbon increased while the percentage of triple-bonded carbon gradually decreased and finally disappeared at the elevated temperatures. The PETI-5 cure process was very similar to the PEPA-3,4‘-ODA cure process, and the percentage of double-bonded carbon structure of PETI-5 increased during the cure process as the percentage of triple-bonded carbon decreased. Moreover, for the PETI-5 resin system, a weak broad 13C signal due to a single-bonded structure was observed after cure. The carbonyl groups remained relatively constant during the curing reactions for both the model compound and PETI-5 resin. The appearance of single-bonded structures in the cure of the model compound and PETI-5 can be derived from polyene structures by a further intra- or intermolecular Diels−Alder reaction to form cycloolefinic ring or branched structures. On the basis of the chemical shift data of several low molecular weight compounds with aromatic ring structures and polyene structures, we cannot exclude the formation of substituted aromatic ring structures from PEPA-3,4‘-ODA or from PETI-5.

Synthesis of Thermally Cross-Linkable Fluorine-containing Poly(aryl ether ketone)s I. Phenylethynyl Terminated Poly(aryl ether ketone)s

“…Previous study has reported that phenylethynyl moiety turns thermally into chain extension, branching and cross-linking through the formation of C=C double bond and that the structure of cross- links were polyene, aromatic ring and so on. 11 The carbonyl stretching vibration is observed at 1680 cm −1 in both spectrum of the uncured and cured compound. This peak has a shoulder at ca.…”

“…[6][7][8][9][10][11][12][13][14][15] It is of importance to design the cross-linkable moiety that crosslinking reaction should occur without the evolution of small volatile compounds to form the clear film and coating. Cross-linkable moieties that meet the required condition are phenylethynyl, cyanate, benzocyclobutane and so on.…”

“…7 Various oligomers, such as imide, sulfone and so on, terminated by phenylethynyl moiety have been reported. [8][9][10][11][12][13][14] Upon thermal curing, they undergo a complex reaction involving chain extension, branching and cross-linking to afford materials with attractive properties such as solvent resistance and thermal stability. The phenylethynyl group offers certain distinct advantages over other reactive groups.…”

Synthesis and Characteristic of Novel Soluble Triazoleimide Oligomers with Terminated Arylacetylene

“…[23][24][25][26][27][28] Solid-state 13 C-NMR, FT-IR and ESR analyses have brought some insight into the cure mechanism of arylacetylene group. The results demonstrated that the arylacetylene group underwent cyclotrimerization, hydrogen addition, DielsAlder cycloaddition, etc., and formed a complex crosslinked structure like condensed polycyclic aromatic structure during the cross-linking process.…”

Synthesis and characterization of a novel silicon‐containing polytriazole resin

“…The following wide exothermic peak (II) occurred in the range from 175 to 275 C. The third exothermic peak (III) appeared at above 300 C. Combined with the FTIR analysis results, the first exothermal peak was attributed to 1,3-dipolar cycloaddition between azide groups and ethynyl or ethynylene groups to form the polymer with 1,4-disubmitted and 1,5-disubmitted 1,2,3-triazoles. The second peak related to the polymerization of ethynyl of ethynylene to form polyene, benzene ring, and naphthalene ring, 18 and the third peak attributed to polymerization of ethynylene, as well as decomposition of cured resin successively, as shown in Scheme 1. Figure 4 shows the 13 C CP/MAS spectra of the PDMSEPE-DAMBP samples cured at 80 C for 12 h or then postcured at 250 C. The peaks at 74.18 and 79.10 ppm were attributed to the ethynyl group and 90.19, 103.08 ppm were assigned to the ethynylene group.…”