Anhydride hydrolysis polyimides

Amine-anhydride reactions, equilibrium, 115 Anhydride-amine reaction, equilibrium, 115 Anhydride hydrolysis, polyimides, 58,60r,61/62 Aqueous ion extraction, kinetic model, 438-440 Aromatic polyimides applications, 67 properties, 26 structures, 27,28/ use as dielectric materials, 26... 

In comparison, no structural modification of model B was seen before 120 h of aging (80 °C). However, after 120 h two small doublets appeared in the NMR spectrum and several additional peaks became noticeable in the NMR spectrum. It was determined by NMR and IR spectroscopy that the hydrolysis products were an imide/carboxylic acid and an imide/anhydride. Model B was then aged for 1200 h at 80 °C to quantitatively determine the amount of hydrolysis products as a function of time. The relative intensity of the peaks due to carboxylic acid is constant after some time. The authors suggest that an equilibrium occurs between model B and the products formed during hydrolysis, and therefore, the conversion to hydrolysis products is limited to about 12%. This critical fraction is probably enough to cause some degradation of polymeric materials, but research on six-membered polyimides has remained active. 

IR spectroscopy may be used to follow two reactions occurring in polyimides exposed to high temperatures and humidities hydrolysis of the imide linkages and hydrolysis of residual anhydride end groups. The hydrolytic susceptibilities of several polyimides were measured at 90°C/95% R.H. Polymers based on benzophenone tetracarboxylic acid dianhydride (with either oxydianiline or m-phenylene diamine) appeared to undergo rather rapid hydrolysis initially, but the reaction had essentially halted by the time the measured imide content had decreased by 5-6%. Polymers based on 3,3 ,4,4 -biphenyl tetracarboxylic acid dianhydride (with p-phenylene diamine) and pyromellitic dianhydride (with oxydianiline) showed no significant imide hydrolysis. In all the polymers, the anhydride was hydrolyzed quite readily. 

Measurements of the changes in both the imide (4) and the anhydride (1, 2) concentrations by IR spectroscopy have already been reported. This paper will demonstrate another approach to using IR to measure anhydride contents and will then present results obtained during hydrolysis of thin films of five polyimides. The structures of the polyimides are shown in Table I. The effects of changes in the curing conditions will also be discussed. 

Arylene-bis-(pyrrole dicarboxylic acid anhydrides) were prepared by the condensation of two moles of diethyl diacetyl succinate with one mole of aromatic diamine, followed by hydrolysis and dehydration. Condensation of these novel dianhydrides with various aromatic diamines resulted in the formation of poly (amic acids) which were further condensed to polyimides. If the diethyl diacetyl succinate and aromatic diamine were reacted in equimolar quantities an N-(amino aryl) pyrrole diester was formed which can be further condensed to give polyimide directly. 

Polyimides have been the topic of investigation for fuel cells for many years [180-184]. By poly condensation of sulfonated amines and phthalic or naphthalen-ic anhydride it is possible to tailor statistic or block copolymers with good proton conductivity. Polyimides have some susceptibility to hydrolysis, better stability being achieved with naphthalenic structures [185]. Sulfonimide membranes [186, 187] have been investigated due their strong superacidity, water uptake and retention above 80 °C. However, although they are thermally quite stable, the hydrolytic stability is not high. 

P(NB/MA) proved to be surprisingly resistant to hydrolysis, both in solution and as a thin film(2. Moreover, the diacid prepared by hydrolysis in concentrated TMAH reverts to the anhydride upon heating(2ri). Similarly, alcoholysis with methanol is difficult and the methyl half-ester reverts to the anhydride on heating(2ri). Reactions with amines to yield poly(amic acids) and poly(imides) proceed more readily. However polyimides are too strongly absoibing at 193 nm to make suitable resist matrices. Also, because primaiy amines are potent imidization catalysts for amic adds(P), amidization of P(1 /MA) with these also causes strong absoibance at 193 nm. Selective amidization can be achieved with buU secondary amines which yield stable poly(amic add) with aqueous base solubility and acceptable transparency (absorbance = ca 0.5 AU/pm at 193 nm). These materials... 

Spectroscopic evidence of the seven-membered rings has been found in the preparation of polyimides from pyromellitic dianhydride and methylenediphenyl-diisocyanate (MDI) [105]. The reaction is conducted in solution of aprotic solvents, with reagents addition at low temperature and a maximum reaction temperature of about 130 °C. On the other hand, polyimides of very high molecular weight have not been reported by this method. The mechanism is different when the reaction is accelerated by the action of catalysts. Catalytic quantities of water or alcohols facilitate imide formation, and intermediate ureas and carbamates seem to be formed, which then react with anhydrides to yield polyimides [106]. Water as catalyst has been used to exemplify the mechanism of reaction of phthalic anhydride and phenyl isocyanates, with the conclusion that the addition of water, until a molecular equivalent, markedly increases the formation of phthalimide [107] (Scheme 13). The first step is actually the hydrolysis of the isocyanates, and it has been claimed that ureas are present in high concentration during the intermediate steps of the reaction [107]. Other conventional catalysts have been widely used to accelerate this reaction. Thus, tertiary amines, alkali metal alcoholates, metal lactames, and even mercury organic salts have been attempted [108]. 

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