Imide polymerization scheme

Furthermore, with this polymerization scheme, end groups can be readily converted to thermo-oxidatively stable imides. For example ... 

A fifth factor is certainly ease of preparation and in this characteristic the melt prepared thermotropic polymers are particularly favored. All of the polymers described thus far may be made in a conventional melt acidolysis process starting with the acetoxy derivatives of the hydroxyl containing monomers used. A typical polymerization scheme is shown in Figure 8, the preparation of the two component polyester derived from the acetylated hydroxybenzoic and hydroxynaphthoic acids. The polymerization may be carried out with or without added catalysts. The poly(ester-amides) commented on here, and the more recently reported aromatic, thermotropic poly(ester-carbonates) and poly(ester-imides), may all be synthesized in a similar manner. 

With this polymerization scheme, end-groups can be readily converted to thermo-oxidatively stable imide moieties anhydrides, by treatment with aniline, and amines, by treatment with phthalic anhydride, give N-phenyl ether-imide and N-aryl phthalimide end-groups, respectively. The presence of small amounts of moisture is of no consequence in these polymerizations since it is simply evolved along with the rest that is formed during the imidization. 

The classical synthetic pathway to prepare polyimides consists of a two-step scheme in which the first step involves polymerization of a soluble and thus processable poly(amic acid) intermediate, followed by a second dehydration step of this prepolymer to yield the final polyimide. This preparative pathway is representative of most of the early aromatic polyimide work and remains the most practical and widely utilized method of polyimide preparation to date. As illustrated in Scheme 4, this approach is based on the reaction of a suitable diamine with a dianhydride in a polar, aprotic solvent such as dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dimethylformamide (DMF), or AT-methylpyrrolidone (NMP), generally at ambient temperature, to yield a poly(amic acid). The poly(amic acid) is then cyclized either thermally or chemically in a subsequent step to produce the desired polyimide. This second step will be discussed in more detail in the imidization characteristics section. More specifically, step 1 in the classical two-step synthesis of polyimides... 

The thermal polymerization of /3-carboxymethyl caprolactam results in a novel polyimide which has been identified as a poly(2,6-dioxo-l, 4-piperidinediyl)trimethylene. The formation of this structure is explained by a mechanism that consists in an initial isomerization of the caprolactam derivative to 3-(3-aminopropyl)glutaranhydride or its linear dimer and subsequent polymerization by condensation involving the terminal amino group and the anhydride moiety. Suggested reaction schemes and corresponding kinetic equations are based upon the premise that the extent of polymerization is represented by the concentration of imide linkages. Results of rate studies carried out at 210°-290°C. support the proposed mechanism. 

Among these, in particular, the acetate [17] and the silyloxyl [31] derivatives are often used as the protecting groups for the hydroxyl (alcohol) function. For example, polymers of 2-acetoxyethyl vinyl ether are readily transformed into a polyalcohol, poly(2-hydroxyethyl vinyl ether), by alkaline hydrolysis [17]. Due to the polar pendant functions, the polymers are of course hydrophilic and often water-soluble, and serve as hydrophilic segments in so-called amphiphilic polymers, as will be discussed later (Sections III.D and VI.B.5). Other important protecting groups include the malonate [23] and the imides [29,30], which lead to polymeric carboxylic acids and amines, respectively (Scheme 1). 

The possibility of applying similar intramolecular hydrogen abstraction reactions to the photoinduced polymerization of methyl methacrylate (MMA), has been tested [1] by using long-chain -alkyl N-substituted imides of 3,3, 4,4 -benzophenone tetracarboxylic dianhydride (BTDA) (Scheme 4). 

The solubility of the polyimide dictates, to a large extent, the synthetic route employed for the copolymerization. The ODPA/FDA and 3FDA/PMDA polyimides are soluble in the fully imidized form and can be prepared via the poly(amic-ac-id) precursor and subsequently imidized either chemically or thermally. The PMDA/ODA and FDA/PMDA polyimides, on the other hand, are not soluble in the imidized form. Consequently, the poly(amic alkyl ester) precursors to these polymers were used followed by thermal imidization [44]. For comparison purposes, 3FDA/PMDA-based copolymers were prepared via both routes. The synthesis of the poly(amic acid) involved the addition of solid PMDA to a solution of the styrene oligomer and diamine to yield the corresponding poly(amic acids) (Scheme 8). The polymerizations were performed in NMP at room temperature for 24 h at a solids content of -10% (w/v). Chemical imidization of the po-ly(amic-acid) solutions was carried out in situ by reaction with excess acetic anhydride and pyridine at 100 °C for 6-8 h. The copolymers were subjected to repeated toluene rinses in order to remove any unreacted styrene homopolymer. 

N-oxide salts (HBTU and TBTU, respectively) [39], or from l-hydroxy-7-azabenzotriazole (HOAt) such as N-[(dimethylamino)-lH-l,2,3-triazolo[4,5-fe] pyridino-l-y]methylene]-N-methy]methanaminium tetrafluoroborate N-oxide (HATU) [40], are well established reagents. They are especially devoted to peptide coupling reactions due to their efficiency and the low degree of undesirable race-mization produced in the final peptide compared to the use of classical carbodi-imide-coupling methods. Therefore, as the polystyrene-supported HOBt is an often used polymeric reagent (Section 7.6.3) [41], its transformation in a supported HOBt and tetramethylurea-derived aminium salt analog to HBTU and TBTU resulted directly. Thus, the reaction of polystyrene-2% divinylbenzene copolymer resin P-HOBt (20) with tetramethylchloroformamidinium tetrafluoroborate (21) (4 equivalents) in the presence of triethylamine gave polymeric N-[(lH-benzotriazol-l-yl)(dimethylamino)methylene]-N-methylmethanaminium tetrafluoroborate N-oxide (P-TBTU, 22) (Scheme 7.6) [42],... 

In the work just described, the formation of a species thought to be the metaphosphon-imidate intermediate was demonstrated by its entrapment with an alcohol, normally MeOH, although Harger and Stephen also used other alcohols and also r rr-butylamine. Other workers, in an examination of the photolytic breakdown of diphenylphosphinic azide, used a variety of agents to trap the intermediate (Scheme 7), but also observed its dimerization to give the l,3,2,4-diazadiphosph(V)etidine 70 accompanied by more extensive polymerization ... 

The synthesis of poly(ether imide)s by condensation of the disodium salt of bisphenol-A with bis(chlorophthalimide)s under microwave irradiation conditions has been described by Zhang et al. (Scheme 14.21) [50]. The polymerization reactions were performed under phase-transfer catalysis (PTC) conditions in o-dichlorobenzene solution. For this purpose a mixture of 16.12 mmol bis(chloro-phthalimide)s and 16.12 mmol disodium salt of bisphenol-A in 60 mL o-dichlorobenzene with 0.56 mmol hexaethylguanidinium bromide was irradiated in a domestic microwave oven for 25 min and the product was precipitated by addition of methanol. The polymerization reactions, in comparison with those under the action of conventional heating, proceeded rapidly (25 min compared with 4 h at 200 °C) and polymers with inherent viscosities in the range 0.55 to 0.90 dL g were obtained. 

Poly(ester imide)s have been synthesized by Mallakpour et al. [53] via a route involving reaction of pyromellitic anhydride with I-leucine, then conversion of the resulting diacid into its diacid chloride, which in turn reacted with several diols (for example phenolphthalein, bisphenol-A, and 4,4 -hydroquinone) under microwave irradiation conditions (Scheme 14.24). The polymerization reactions were conducted in 10 min in a domestic microwave oven in a porcelain dish in which... 

Using a quite different approach, polymeric beads of supported ionic liquid palladium catalysts comprised of polymerized ionic liquid monomers and palladium complexes have been synthesized using traditional suspension polymerization methods [86]. Here, polymeric ionic liquid beads were made from polymerization of l-butyl-3-vinylimidazolium bis(trifluoromethyl sulfonyl)imide and poly(vinylalcohol) by heating with AlBN (2,2 -azobis(2-methylpropionitrile)) in the presence of l,l -bis[l,8-octyl)-3-vinylimidazolium bis(trifluoromethyl sulfonyl)imide as cross-linker (Scheme 5.6-6). The ionic liquid support beads proved to be thermally stable up 250 °C which is significantly higher than conventional vinyl resins. 

Scheme 6,19 Reaction scheme of the preparation of fluorinated block copoly(imide siloxane) where K and L are hard and soft block degrees of polymerization. Taken from Ref. [76].

Polyaddition of organosilicon dihydrides, mainly dihydro(poly)siloxanes to dialkenyl-substituted organic compounds also known as hydrosilylation copolymerization, leads to polycarbosiloxanes with functionalized organic segments (359). Platinum-catalyzed polymerization hydrosilylation of a,allyl-substituted bisphenols, imides, or amides leads to the synthesis of block copolymers that are useful thermoplastic elastomers (Scheme 40). 

On the other hand, a large number of curable and non-curable polymers containing pendant imide rings have been synthesized and studied with the objective of improving the properties of classical addition polymers [234-237]. The synthesis of these polymers fits the general rules to polymerize unsaturated monomers via a chain growth process. Monomers suitable for these purposes are shown in Scheme (45) ... 

Polyethers with pendent nadimide groups have also been synthesized, by ringopening polymerization of nadimide-oxyranes, as depicted in Scheme (49). The polymers could be cured to cross-linked poly(ether imide)s [250]. 

The allylic bromination of cyclohexene was successfully done using co(polyethylene-N-bromomaleimide). When polymeric AT-bromosuccin-imide ( -NBS) was used for bromination of cumene, products other than those of benzylic bromination were also formed (Scheme 12-10) (Yaroslavsky et aL, 1970a,b). The change in mechanism has been attributed to the polar environment provided by neighboring succinimide units in (p)-NBS. Polymeric A/-chloromaleimide, synthesized by Yaroslavsky and Katchalski (1972), on reaction with ethylbenzene, also gave products due to aromatic substitution. 

---