Moiety, imide

The thermal polymerization of reactive polyimide oligomers is a critical part of a number of currently important polymers. Both the system in which we are interested, PMR-15, and others like it (LARC-13, HR-600), are useful high temperature resins. They also share the feature that, while the basic structure and chemistry of their imide portions is well defined, the mode of reaction and ultimately the structures that result from their thermally activated end-groups is not clear. Since an understanding of this thermal cure would be an important step towards the improvement of both the cure process and the properties of such systems, we have approached our study of PMR-15 with a focus only on this higher temperature thermal curing process. To this end, we have used small molecule model compounds with pre-formed imide moieties and have concentrated on the chemistry of the norbornenyl end-cap (1). 

In a different sequence of reactions, N-acetylation of 274 and exposure of the intermediate imide 275 to ethanolic KOH gave a mixture (about 2 1) of the desired carboxylic acid 276 together with the starting lactam 274 via the non-selective hydrolysis of the imide moiety of 275 (148a,c). When 276 was treated with /V-bromosuccinimide (NBS), an intermediate bromolactone was produced which was heated at reflux in pyridine in the presence of DBU to give 277. The conversion of the lactone 277 to the lactam 278 was effected by heating 277 in aqueous NaOH followed by protection of the resulting allylic alcohol function as a tetrahydropyranyl ether. 

The polyimide-base PR system [79,80] was designed on the premise that porphyrin-electron acceptor (quinones or imide moieties) systems are well-known model compounds for photosynthetic processes and exhibit very interesting charge transfer properties [81], A high quantum yield of charge separation can be achieved in these systems. Polyimides are found to be photoconductive and allow charge transport [82], Furthermore, polyimides possess high Tg and therefore, the electric field-induced dipole orientation can be fixed after imidization [83],... 

Sakamoto et al. reported an intramolecular [2+2] thietane formation in the solid state (Scheme 7). [26] Achiral A-(thiobenzoyl)methacrylamide 39 formed (E,Z)-conformation of the imide moiety, crystallized in a chiral space group Phhh, and the photolysis of single homochiral crystals at room temperature resulted in the formation of an optically active thietane-fused 3-lactam (40,75%) with 10% ee. The solid-state photoreaction proceeded even at -45°C to give higher ee value, 40% ee (conv. 30%, yield 70%). 

In the first case, achiral IV-methacryloylthiobenzanilide 39 formed (E,Z)-conformation of the imide moiety and crystallized in a chiral fashion. The solid-state photoreaction gave optically active 3-lactam 40. The dynamic molecular rearrangement for cyclization was elucidated on the basis of direct comparison of the absolute configuration of both the starting material and the photoproduct (Scheme 11).[25][38]... 

Isonitriles 592 undergo a palladium mediated insertion into aryl bromides 593 followed by intramolecular cycliza-tion upon reaction with the pendant alcohol to afford isochromans that feature a C-l imidate moiety 594 (Equation 245) <2004TL6995>. 

Benzylation with benzyl trichloroacetimidate and a catalytic amount of triflic acid (TfOH) is a mild and efficient procedure (Scheme 2.1c).5 The acid protonates the nitrogen of the imidate moiety converting it into a very good leaving group. Nucleophilic attack by an alcohol introduces a benzyl ether. The procedure is often compatible with base- and acid-sensitive functionalities with esters, (7-isopropylidene and (7-benzylidene acetals. Benzyl trichloroacetimidate is commercially available but can easily be prepared by reaction of benzyl alcohol with trichloroacetonitrile in the presence of a mild base. 

Macrocycle 177 in which the 2,6-pyridino and the 1,4-piperazino moieties were incorporated into the macrocyclic framework has been reported. The synthesis of 177 (10%) was accomplished by treatment of 2,6-dichloropyridine with the dianion of Ar,Ar -W. (2-hydroxyethyl)piperazine in refluxing xylene. Attempts to prepare the cobalt(II) complex of 177 resulted in diprotonation of the macrocycle. The X-ray crystal structure determination analysis has been performed for both 177 and 178. According to the crystal structure analysis of 178, the piperazine rings are in the chair conformation in the solid state and the molecule is fairly rigid due to the imposed steric constraints of the imidate moieties l39). 

NH(CHO)2, reproduces the valence electronic properties of the nitrogen-carbonyl part of pim, we compare the partial DOVS spectrum for the imide part of these two molecules (see Figure 5, the spectra are normalized in such a way that the maximum peak has the same height in both cases). Indeed, the two spectra are remarkably similar. In particular, we calculate the relative difference in LCAO coefficients for the nitrogen lone pair orbital in peak A of the two systems to be less than 3%. The only major difference between the two spectra is a stabilization of the D peak in going to the pim molecule. This behavior is understood from the fact that in pim, the orbitals of peak D are delocalized over both the imide- and the benzene moieties, whereas in NH(CHO)2 they are forced to be localized to the imide moiety. 

These results in Table I can be explained by reactions in Scheme 2. As shown in Figures 2b and 2c, peaks at 1270 cm due to C-O stretching band in conjugated ester disappeared, while peaks at 1730 cm due to ester C=0 groups remained. These results indicate that the transesterification proceeded in the presence of alcohols and diols. In case of diol, the transesterification at both ends would afford re-crosslinking. A similar trend was observed for other difunctional additives such as diamine and amino acid. When amino compounds were added, recovered polymers had a peak at 1700 cm as shown in Figures 2d and 2e due to cyclic imide moieties. 

C-P-Im triad 49 was prepared in order to further investigate this phenomenon [184]. An electron acceptor moiety based on the 4,5-dinitro-l,8-naphthalenedicar-boximide system was used in this triad, as this imide is more easily reduced that pyromellitimide (—0.88 V versus ferrocene/ferrocenium as an internal reference, compared to —1.24 V for the imide moiety of 48), and can therefore serve as an acceptor for a wider variety of donors. Excitation of the porphyrin moiety of 49... 

A similar approach towards norbornane carboxylic acid derivatives was developed using pseudoenantiomeric A-acyl-D-galactosyl and D-arabinosyl-oxazolidinones 96 and 97. Reaction with cyclopentadiene under promotion of Me2AlCl, and subsequent hydrogenolysis of the double bond and basic hydrolysis of the imide moiety, furnished the 3-methyl-norbornane-2-carboxylic acids 98 and 99, respectively, in high enantiomeric purity [74,75] (Scheme 10.32). 

The reaction of sulfenyl chlorides with imides, e.g. maleimide, succinimide or phthalimide (66), provides a useful route for the preparation of disulfides (67) (Scheme 40) (see p. 57). The intermediate sulfenylimide (68) is quite stable but reacts with a thiol with expulsion of the imide moiety, which is a good leaving... 

Porous polystyrene cross-linked with l,l -(methylene-4,4 -phenylene)bismaleimide (72) shows good recoveries for aniline (la), 1,2- (lj) and 1,3-phenylenediamine (lk) in water solution, probably due to adsorption on the imide moieties. Other cross-linked porous aromatic polymers show poor results with these PAA analytes even if they adsorb efficiently similarly substituted nitroaromatic analytes. Recovery of the analytes from the SPE cartridges can be done with MeOH end analysis was by HPLC-DA-UVD132. 

The inability of control molecule (22) to catalyze the reaction allowed us to exclude the Kemp s imide moiety of (6) as a source of direct chemical catalysis (Table 1, entry 8). 

The smallest symmetrical imide moiety which might play the role of a mesogen is the pyromellit imide group (PMDI, see structures 49-54 and 56-60). Its mes-ogenic potential has been a matter of controversial reports. A first short comment on PEIs of structure 49a-gwas published by the author in the introduction of a paper dealing with benzophenone-tetracarboxylic imide (BTCI) [63]. The formation of a LC-phase was assumed only for the PEIs of hydroquinone (49a) and 4,4- dihydroxydiphenyl ether (49g). Furthermore, Aducci et al. mentioned a thermotropic character of the PEIs 52a-d and 53a-e in two reviews [8,64]. Yet... 

More recently, two research groups reported [122,124] on the properties of polyimides derived from biphenyltetracarboxylic anhydride (173a-c). Despite the higher length/diameter ratio of the imide moiety even these polyimides were not thermotropic. Also the polyimides derived from diphenylether-3,3, 4,4 -tet-racarboxylic anhydride (174a), benzophenone-3,3, 4,4 -tetracarboxylic anhydride (174b) or diphenylsulfone-3,3, 4,4 -tetracarboxylic anhydride (174c) were... 

Finally, it should be emphasized that the existence of a smectic solid state does not necessarily entail the formation of a smectic LC-phase above the melting temperature. As outlined in Sects. 4 and 5, numerous poly imides have been synthesized forming smectic layers in the solid state and yielding an isotropic, nematic or cholesteric phase upon melting. Poly(ester-imide)s containing highly symmetrical imide moieties, such as PMDI units, are typical examples of poly-imides combining a smectic solid state with an isotropic melt. 

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