Some Aspects of the Cure of RP-46, a Nadic End-capped Polyimide, and Phenyl Nadimide and Bis-Nadic-3,4'-ODA Model Compounds

Abstract

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.

Effects of dianhydrides on the thermal behavior of linear and crosslinked polyimides

“…Therefore, crosslinked parts or remained uncrosslinked single ends of polyimides can be decomposed at relatively lower temperatures than the main chains; the initial decomposition temperature was lower than that observed for the linear polyimide . However, during the curing process, almost chains were connected to each other and the motion of the chains was highly limited by crosslinking until decomposition.…”

“…Peaks of crosslinking corresponding to CC bonds of the nadic ring at 843 cm −1 and CH bonds at 810–790 cm −1 (Refs. 11 and 12) were weak and broad …”

Synthesis and properties of modified PMR-matrix resin type polyimide and composite with non-carcinogenic diamine

“…The band at 843 cm À1 becomes very weak and disappears and that at 832 cm À1 becomes stronger and sharper when heated at 275 and 300 C for 1 h at each temperature. The above changes in the FTIR spectra and other changes shown in Table 1 indicate that norbornene undergoes cross linking by a combination of the following reactions: (i) retro-Diels-Alder reaction of the norbornene to form cyclopentadiene and maleimide and latter two subsequently recombined to form new cross-linked product 17 and (ii) homo polymerization of norbornene. 17 The above reactions are completed when the modified PMR prepolymer was post cured at 325 C for 1 h as indicated by the FTIR spectrum (Table 1).…”

“…Weight losses exceeding these values can be due to moisture, solvent (methanol), unreacted monomers and decomposition products. 17 Table 3 shows that after 250 C for 1 h, where there was complete conversion to PAA, a weight loss of 12.21% was noted. This sample was further heated at 325 C for 1 h when it underwent an additional 4.62% weight loss to yield a total weight loss of 16.83%.…”

Synthesis and Properties of Novel Meltable Fluorinated Aromatic Oligoimides Endcapped with 4-Phenylethynylphthalic Anhydride

“…The representative latent reactive endcapping agents used in polyimide matrix resins include maleic anhydride, nadic anhydride as well as ethynyl-or phenylethynyl-containing organic compounds [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Recently, phenylethynyl-endcapped aromatic polyimides have received considerable attention because the phenylethynyl groups in the polymer backbone showed appropriate chain crosslinkability and extendibility after thermal curing, resulting in both strong and tough materials [13][14][15][16][17][18][19][20][21].…”