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.

A novel process for synthesizing nylon‐6 and poly(ϵ‐caprolactone) by microwave irradiation of the respective monomers, ϵ‐caprolactam and ϵ‐caprolactone, is described. The ring opening of ϵ‐caprolactam to produce nylon‐6 was performed in a microwave oven by the forward power being controlled to about 90–135 W in the presence of an ω‐aminocaproic acid catalyst (10 mol %) and for periods of 1–3 h at temperatures varying from 250 to 280 °C. The ring opening of ϵ‐caprolactone to produce poly(ϵ‐caprolactone) was performed in a microwave oven by the forward power being controlled to about 70–100 W for a period of 2 h in the presence of stannous octoate with and without 1,4‐butanediol over a temperature range of 150–200 °C. The yields, conditions of the reactions, and properties of the products generated relative to the thermal processes are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2264–2275, 2002

The synthesis and characterization of phenylethynyl (PE) end-capped polyimides derived from 4,4‘-(2,2,2-trifluoro-1-phenylethylidene) diphthalic anhydride (3FDA), 4,4‘-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and 3,3‘,4,4‘-biphenylene dianhydride (s-BPDA) are described in this paper, with particular emphasis on the glass transition temperatures and viscosities. The phenylethynyl end-capped 3FDA- and 6FDA-containing oligomides demonstrate much lower minimum complex melt viscosities than s-BPDA-containing oligomides. The PE-3F and PE-6F oligomers also show greater viscosity stability at elevated temperature (310 °C) than s-BPDA oligomides. The lower viscosities can be explained by the presence of the bulky groups CF3 and phenyl on 3FDA and 6FDA relative to the planar configuration of the s-BPDA dianhydride. The greater viscosity stability of the PE-3F and PE-6F oligomers over the s-BPDA oligomers at 310 °C may be explained by the decreased electron density and hence lower reactivity of the ethynyl group in the PE-3F and PE-6F oligomers due to the influence of fluorine in the polymer chain.

Infrared studies of the initial cure and post-cure of RP-46 resin, a nadic end-capped polyimide and a model bisnadimide compound N, N' -(oxydi-3,4 phenylene) di-5,6-norbornene-2,3-dicarboximide (Bis-nadic-3,4'-ODA) were conducted at 316, 325 and 350° C for various time periods. Infrared studies of another model compound, N-phenylnadimide, were conducted at lower temperatures, from 100 to 270° C. N-Phenylnadimide cures at much lower temperatures than Bis-nadic-3,4 -ODA and RP-46. The crosslinking reaction was followed by monitoring the absorption peaks at 841 and 785 cm-1, the endo and exo bands in the 2,3 positions of the nadic end caps and cyclo-aliphatic and cyclo-olefinic peaks on the region 1000 to 600 cm-1 associated with the nadic end-cap curing reaction. Weight losses and changes in the glass transition temperature of the RP-46 resin due to cure and post-cure, were also examined. The infrared changes suggest that complete cross-linking requires a temperature of 325° C or above, and that several new infrared bands are generated in the process. The simple thermally induced reverse Diels–Alder cyclopentadiene N-substituted maleimide recombination reaction or norbornene to norbornene, norbornene to cyclopentadiene or norbornene to substituted maleimide addition reactions may adequately define the cross-linked products derived from the initial cross-linking reaction at 316° C for 1 to 2 h. However, postcure of RP-46 resin or the nadic-3,4 -ODA model compound at 325 or 350° C for several hours generates additional infrared bands in the cyclo-aliphatic and cyclo-olefinic regions (1000–600 cm-1), which are absent in material cured at 316° C for 1 to 2 h. Therefore, completely cured resin consists of simple addition reaction products from the initial cure at 316° C and more complex products from the elevated temperature post-cures. A post-cure at 325° C for about 8 h or at 350° C for 2 h is required for a maximum Tgof 391° C. This is accompanied by a stabilization weight loss of about 2–3%. The weight loss and Tgdata are supporting evidence for the infrared studies.