Poly imide s

In 1951, Flory reported the condensation reaction of diacid chlorides, e.g. with potassium salts of imides, e.g. the condensation of sebacyl chloride with potassium phthalimide. In this way, A -acyl diimides are formed. Flory pointed out the possibility of forming polymers, when components with higher functionality are used. Poly(imide)s (PI)s from pyromeUitic acid were reported in 1955 by Edwards and Maxwell at DuPont. Tbe diamines used were of aliphatic nature. Later, in addition, aromatic diamines were used. The two major types of Pis are  

Poly(ether imidejs (PEI)s are a particular class of PI which combine the high-temperature characteristics of PI but still have sufficient melt processability to be easily formed by conventional molding techniques such as compression molding, gas assist molding, profile extrusion, thermoforming and injection molding.  

To the thermoset type belong bismaleimides and bisnadimides as well as oligomeric end capped imides. End capping occurs with reactive phen-ylethyl groups. These types are used for reactive injection molding and related techiuques. The chemistry of formation of the imide moiety is quite similar for both the thermoset type and the thermoplastic type. There are several monographs on PIs. Bismaleimides are a separate subclass 

In all important dianhydride compovmds, the anhydride groups are attached to aromatic moieties. 

Pyromellitic dianhydride (PMDA) is prepared by the oxidation of durene, which is 1,2,4,5-tetramethylbenzene. The synthesis is eompletely analogous to the synthesis of phthalic anhydride. 

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Postsulfonation of polymers to form PEMs can lead to undesirable side reactions and may be hard to control on a repeatable basis. Synthesis of sulfonated macromolecules for use in PEMs by the direct reaction of sulfonated comonomers has gained attention as a rigorous method of controlling the chemical structure, acid content, and even molecular weight of these materials. While more challenging synthetically than postsulfonation, the control of the chemical nature of the polymer afforded by direct copolymerization of sulfonated monomers and the repeatability of the reactions allows researchers to gain a more systematic understanding of these materials properties. Sulfonated poly(arylene ether)s, sulfonated poly-(imide)s, and sulfonated poly(styrene) derivatives have been the most prevalent of the directly copolymerized materials. 

Bisimide 301, derived from compound 288, was used to ptepare an alternating (as opposed to block) poly(estet-imide) by teaction with bisphenol A. Such polymets have better solubility properties than pure poly(imide)s <2000PSA1090>. 

Poly(vinyl alcohol) (different cross-linkers) Poly(aayclic acid) (different cross-linkers) Various poly(amide)s (different substituents) Various poly(imide)s (different substituents) Nafion... 

Poly(imide)s as a class of polymer exhibit a range of properties, such as high Tg, excellent thermal stability, high chemical resistance, low dielectric constant and ease of fabrication, which have lead to important uses in the semiconductor and advance composite industries. In addition, the high aromatic content of many of these polymers and consequent high stability to ionizing radiation, leads to usage of poly(imide) films and composites in the nuclear and aerospace industries. 

Many poly(imide)s are insoluble in their processed form, either because of interchain charge-transfer interactions, or because of the presence of crosslinks in cured poly(imide) resins. The range of analytical techniques available to characterize processed poly(imide)s is therefore limited. NMR spectroscopy, and in particular solid-state NMR [1-3], has an important role to play in the determination of structure, conformation, morphology and molecular motion in poly(imide) materials. The aim of this chapter is first, to briefly summarize the various classes of poly(imide)s, second, to review the current literature on NMR of these materials and finally, to hopefully indicate where NMR spectroscopy will make further additions to the knowledge of the properties of poly(imide)s. 

Poly(imide)s first became commercially important with the development of the condensation poly(imide) Kapton [4, 5] in 1965. The two-step reaction of a dianhydride (pyromellitic dianhydride) with a diamine (p-phenylene diamine) to initially form a poly(amic acid), and subsequent thermal cycliz-ation to form the poly(imide), is a common route to the formation of poly-(imide)s, as well as being exploited for the synthesis of oligomeric precursors for addition poly(imide)s. Usually, such condensation polymers are insoluble... 

An alternative route to the formation of poly(imide)s is the nitro-displace-ment reaction to form the Ultem series of polymers, first exploited by White et al. [11] at General Electric. These, and similar materials, have application in composite materials and as specialty thermoplastics. Compared to the amic acid route described above, the nitro-displacement reaction is highly controlled, and materials of high chemical regularity produced, as demonstrated by White et al. [11] in their solution-state NMR study of Ultem poly(imide)s. 

In the early 1960s, a new class of addition polymer and addition poly(imide)s was developed by the Rhone Poulenc company. The most important of these were /jw-maleimides (BMI) [12, 13], which could be crosslinked or copolymerized to form thermosets with outstanding thermal and chemical resistance. These materials cure without volatile by-products, thereby, minimizing the formation of voids, and have high glass transition temperatures and low moisture absorption. The major uses of this class of resin is in advanced composites and printed circuit boards. 

Characterization of poly imide)s and studies of curing of poly imide)s by and NMR... 

Studies of conversion of poly amic acid)s to poly imide)s As mentioned above, IR spectroscopy has often been used to study the conversion of amic acids to imides. Despite the popularity of this technique, important questions have been raised concerning the quantitative aspects of the results, especially at high conversion [38]. NMR spectroscopy, in particular solution-state NMR, has the advantage of greater chemical information, and when care is taken, provides quantitative measurements of the extent of conversion of amic acid to imide. The situation is less clear with insoluble poly(imide)s, since increased linewidth [39] in solid-state NMR spectro-... 

Yang et al. [53] prepared a novel series of metal-containing poly(imide)s. Polymers of pyromellitic dianhydride with the zinc, strontium, lead, calcium and nickel salts of p-aniline sulfonic acid, were prepared and examined by C CPMAS NMR. There was little difference in the chemical shifts of the dianhydride carbons, compared with the chemical shifts of the poly(imide) with diaminodiphenyl methane. 

Finally, Marek and coworkers [54] characterized a series of poly(imide)s... 

There is much interest in the formation of blends of poly(imide)s with other polymers, so as to improve properties such as toughness and processability [14-19, 58, 59]. The subject of measurement of interactions and miscibility of blends by NMR spectroscopy has been discussed by Takagoshi and Asano in Chapter 10 of this book, and will not be referred to in detail here. The use of NMR to study miscibility in blends containing poly(imide)s is somewhat restricted because most poly(imide)s contain a high proportion of aromatic groups, and consequently form blends with other highly aromatic polymers. The CPMAS spectra, which as discussed above are broad and... 

MacKnight and coworkers found that several poly(imide)s, such as Ultem poly(ether imide) and XU218 poly(imide), formed miscible blends with poly (benzimidazole) (FBI) [58, 59]. The miscibility of these blends is believed to result from specific interactions between the benzimide ring of the poly(im-ide) and benzimidazole ring of FBI. In a later study, Grobelny et al. [60] reported the CFMAS spectra of several of these blends. Slight changes in the lineshape were observed in the intimate blends, and seen as evidence of the specific interactions between the polymers. In particular, the peak in the spectra, due to the imide carbonyl carbon, was seen to broaden towards... 

A large number of linear aromatic poly(imide)s are highly intractable and cannot be processed due to the inherent stiffness of the chains and, more importantly, due to strong interactions between aromatic rings on adjacent polymer chains. An approach to improve the processability of such stiff macromolecules is to attach flexible alkoxy chains to the aromatic rings (see, for example. Refs. [63-65]). 

In a later study. Swanson and coworkers [81] studied the cure of acetylene-terminated poly(imide)s selectively labelled at various positions with nuclei. Curing of the sample, labelled at the imide carbonyl group, confirmed the completion of the imidization reaction on heating. The product of addition onto the carboxyl group was not observed. Four new peaks were identified in the spectrum of the cured sample labelled at the Ci-acetylene group, while a similar result was obtained for the sample labelled at the C2-acetylene position. Analysis of these results rules out the participation of coupling reactions and the biradical mechanism, which would produce triple-bond structures, but confirms the presence of the product of cyclotrimerization and Friedel-Crafts reactions. The latter mechanism is confirmed from the presence of small peaks due to aliphatic carbons in the spectra of the materials labelled at the acetylene groups. 

Wong and coworkers. [82, 83] used solution and solid-state NMR to study the cure of the norbornene end-capped poly(imide)s 2NE/DDM and PMR-15. At lower cure temperatures, exo-endo isomerization was observed to be a major product [84]. Loss of cyclopentadiene was suggested to result in initiation of the partner maleimide, as well as Diels-Alder addition of cyclopentadiene with norbornene. There was no evidence of internal double bonds formed by incorporation of the cyclopentadiene into the polymer backbone. The solid-state spectra were very poorly resolved, but did allow confirmation of the mechanism of reaction [83]. Spectra obtained at higher fields did not show improved resolution, indicating that the dominant mechanism for line-broadening in these materials is the dispersion of isotropic chemical shifts resulting from frozen conformations. In later work, Milhourat-Hammadi and coworkers [84, 85] reported solution-state and NMR studies of PMR-15 prepolymers. 

NMR spectroscopy and in particular solid-state NMR spectroscopy proved to be a powerful method for studying the mechanism and extent of reaction in complex poly(imide) materials. In particular, during the cure of BMI resins, careful use of C CPMAS NMR indicated that measurements of the extent of cure by DSC were significantly overestimated [86, 87]. This article demonstrates that NMR spectroscopy has been able to characterize the structure of condensation poly(imide)s and, more successfully, the cure of BMI, PMR and acetylene-terminated resins. 

Solid-state NMR has been applied successfully in a few cases for the study of poly(imide) blends. It can be said, however, that the techniques arising from recent advances in the analysis of polymer blends, such as selection techniques based on multipulse methods, and improvements in the modelling methods of spin diffusion, have yet to be applied to the study of blends containing poly(imide)s. It is suggested that these techniques will have an important role to play in future studies of poly(imide) blends, particularly for blends such as impact-modified BMI resins. 

The great power of NMR compared with other spectroscopic techniques is the ability to study both the frequency and geometry of molecular rearrangements in the solid state. It is true to say that there have been few studies of molecular motion in poly(imide)s using NMR spectroscopy. The main reason for this has been the previously limited temperature range of commercial CPMAS probes. Therefore, future work in poly(imide)s is expected to exploit the ground-breaking efforts of other workers in the field of multidimensional NMR spectroscopy in the solid state [3]. 

Poly(iV-epoxypropyl)carbazoIe (PEPC) films are photosensitive only in a near UV range. However, composites from the poly(imide)s with PEPC and its dichloro derivatives and dibromo derivatives exhibit an appreciable photoelectric sensitivity in the near UV and visible range. ... 

Poly(imide)s with the dithiathianthrene group are accessible from the reaction of thianthrene-2,3,7,8-tetracarboxylic dianhydride aromatic diam-ines. Thianthrene-2,3,7,8-tetracarboxylic dianhydride can be synthesized via a nucleophilic aromatic substitution of A-phenyl-4,5-dichloro-phthalimide with thiobenzamide, thioacetamide, and sodium sulfide. The polymers obtained have a good thermal stability in air and nitrogen. The polymers are amorphous and have been found to be soluble only in H2SO4. 

Blends of poly(aryl ether ketone)s and certain poly(amide imide)s and poly(imide)s (PI)s are highly compatible. They tend to form one phase in the amorphous state, and thus are miscible systems. As a result, such blends significantly improve the processability of the poly(amide imide) or the PI material. Further, by increasing its Tg, the ultimate use temperature of the poly(aryl ether ketone) is significantly increased. ... 

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