Addition reaction polyimide

Covers material and process requirements for fabrication sandwich radomes with hot-melt, addition-reaction polyimide-resin-i-mpregnated quartz cloth shells and polyimide-resin syntactic foam cores. Application is primarily as a radar-transparent structure for use as an electromagnetic window up to 230°C (450°F). 

AIAA American Institute of Aeronautics and API addition reaction polyimide... 

An interesting approach to thermosetting acetylene-terminated polyimides via the Michael addition reaction has appeared (38). Acetylene-terminated aspartimides are readily prepared ia high yield via two routes, shown ia Figure 7. 

Thus, N-pyrimidine phthalimide reacted with hexylamine at room temperature to form an amide-amide. The initial amide-amide formation proceeded more rapidly in chloroform as compared to dimethylsulfoxide (DM SO). However, the ring closure reaction to the imide was favored by the more polar, aprotic DMSO solvent, yielding the imide in nearly quantitative yield after 3 hours at 75 °C. The authors were able to utilize this synthetic approach to prepare well-defined segmented poly(imide-siloxane) block copolymers. It appears that transimidi-zation reactions are a viable approach to preparing polyimides, given that the final polyimide has a Tg sufficiently low to allow extended excursions above the Tg to facilitate reaction without thermal decomposition. Additionally, soluble polyimides can be readily prepared by this approach. Ultimately, high Tg, insoluble polyimides are still only accessable via traditional soluble precursor routes. 

The term "condensation polymers" was introduced by W. H. Carothers in his early work on the preparation of polyesters and polyamides to distinguish this class of polymers from vinyl polymers made by addition reactions. Condensation polymers were defined as polymeric molecules that may be converted by hydrolysis, or its equivalent, into monomers that differ from the structural units by one molecule of H2O, HCl, NHj, etc. This broad definition includes many polymers made by ring-opening or addition reactions, for example, lactone and lactam polymers, polyurethanes, polyureas, polyimides, and polyhydrazides, as well as polymers made by true condensation reactions. 

HR-602 - This system represents a different resin chemistry through use of acetylene-terminated polyimide structure. The cure mechanism consists of an addition reaction with no release of volatiles during cure. The intermediate acetylene-terminated polyimide structure is shown below. Reaction to the final cured structure is proposed as a trimerization of the acetylene groups to form an aromatic structure. 

The norbornene concept was further developed by NASA Lewis Research Center and culminated in the so-called PMR-concept, a novel class Of addition-type polyimides formed by in situ polymerization of monomeric reactants. 5 jhe reaction sequence36-37 involves aromatic diamine, S-norbornene-2,3-dicarboxy1ic acid monoalkyl ester and dialkyl ester of an aromatic tetracarboxylic acid which produces methanol, water, and the following intermediates [6]. 

Radiation-induced cyclo-addition reactions of JV-ethyl maleimide with benzene and isopropylbenzene have also been studied and polyimides curable by intramolecular cycloaddition with dibenzoanthracene formation have also been... 

The reaction has been described for pyromellitic dithioanhydride and aromatic diamines [138]. It is a two-step reaction that involves the formation of a soluble poly(amic thioacid), which is converted into polyimide by cyclocondensation (Scheme 24). The hydrogen sulphide that separates can be neutralized by an addition reaction with acrylonitrile. This latter works as an effective acceptor against SH2. Polyimides with inh higher than 0.3 dL/g have not been attained by this method. 

Thermosetting polyimides are low molecular weight systems with imide functions in their backbone and reactive terminations capable to react by an addition reaction to give a cross-linked system. These materials were developed in the 1970s in order to fulfil the requirements of the aerospace industry in the domain of high performance adhesives and matrices based on glass, carbon and aramide fibers. 

Polyimides are the highest-temperature polymer in general advanced composite use, with a long-term upper temperature limit of 232°C (450°F) or 316°C (600°F). Two general types are condensation polyimides, which release water during the curing reaction, and addition type polyimides, with somewhat easier process requirements. 

Chen H, Yin J (2003) Preparatirai of auto-photosensitive hyperbranched co-polyimide by the condensation of 4,4 -(hexafluoroisopropylidene)diphthalic anhydride and 3,3, 4,4 -benzophenonetetracarboxylic dianhydride with l,3,5-tris(4-aminophenoxy)benzene through a stage addition reaction method. Polym Bull 50 303—310... 

Additive Polyimides. Rhc ne-Poulenc s Kin el molding compound and Kerimid impregnating resin (115), Mitsubishi s BT Resins (116), and Toshiba s Imidaloy Resin (117) are based on bismaleimide (4) technology. Maleic anhydride reacts with a diamine to produce a diimide oligomer (7). Eurther reaction with additional diamine (Michael addition) yields polyaminohismaleimide prepolymer with terminal maleic anhydride double bonds. Cure is achieved by free-radical polymerization through the terminal double bonds. 

Tan et al. investigated polymers made from bis-benzocyclobutenes [13-15]. As the benzocyclobutane is analogous to tbe dien, tbe Diels-Alder addition takes place. This reaction is applied to the preparation of polyimides. The advantage of this system is that the resultant polymer is oxidized to form thermally stable aromatic polyimides (Fig. 7). 

The kinetics of PAA, synthesized from 4,4 -oxydianiline and pyromellitic dianhydride, solid-state imidization both in filler absence and with addition of 2 phr Na+-montmorillonite was studied [1], The nanofiller was treated by solution of P-phenylenediamine in HC1 and then washed by de-ionized water to ensure a complete removal of chloride ions. The conversion (imidization) degree Q was determined as a function of reaction duration t with the aid of Fourier transformation of IR-spectra bands 726 and 1014 cm 1. The samples for FTIR study were obtained by spin-coating of PAA/Na+-montmorillonite mixture solution in N,N-dimethylacetamide on KBr disks, which then were dried in vacuum for 48 h at 303 K. It was shown, that the used in paper [1] method gives exfoliated nanocomposites. The other details of nanocomposites polyimid/Na+-montmorillonite synthesis and study in paper [1] were adduced. The solid-state imidization process was made at four temperatures 7) 423, 473, 503 and 523 K. 

Imides - Polyimides (PI) have been conventionally prepared by the chemical or thermal cyclodehydration of polyamic acids formed from the solution reaction of aromatic tetracarboxylic dianhydrides and aromatic diamines. The early PI were insoluble and relatively intractable. The polyamic acid was the processable intermediate. However, the polyamic acid precursor has two major shortcomings, hydrolytic instability and the evolution of volatiles during the thermal conversion to PI. In addition, residual solvent was left in adhesive tapes and prepregs to obtain tack, drape and flow. During the fabrication of components, the evolution of volatiles caused processing problems and led to porosity in the part. As work progressed on PI, other synthetic routes were investigated (e.g. reaction of esters of aromatic tetracarboxylic acids with diamines... 

BMI or aminobismaleimides or addition polyimides from the reaction of a diamine and a bismaleimide to make a prepolymer that is then cured by an excess of diamine. This type is particularly convenient for the manufacture of thick parts. 

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