Specific Features of the Obtainment of Imide Forming Copolymers of Acrylonitrile and Methacrylic Acid in Concentrated Solutions of N-Substituted Amides

Achievements and prospects for the synthesis of poly(meth)acrylimide foams. Stage of the thermal imidisation of polymer precursors

“…In recent years, methods have also been proposed for increasing the degree of alternation of nitrile and acid units by introducing additives into monomer mixtures during the synthesis of AN-MAA polymer precursors. 72 PMI foams based on the polymer precursors with a high degree of alternation of AN and MAA units are not inferior in their properties to PMI foams based on the MAN-MAA copolymers. 72,95,96 This opens up opportunities for obtaining high-quality PMI foams based on cheaper monomer raw materials using AN instead of MAN.…”

“…A technique that allows the achievement of such a polymer microstructure was recently proposed. 72 It is well known that at 180°C and above, a cyclisation reaction involving nitrile groups takes place in homo- and copolymers of AN (Figure 5). 73,74 Catalysis by neighbouring carbonyl groups accelerates this reaction, 75 so the thermal imidisation of nitrile-containing polymers is almost always accompanied by the formation of polyene nitrogen-containing structures.…”

“…28,63 In a few recent papers, the effect of the structure and ratio of (meth)acrylonitrile and (meth)acrylic acid units in polymer precursors on thermal imidisation and the properties of PMI foams was also considered. 39,72,84,97 A comparison of the IR spectra of heat-treated copolymers of MAN-MAA (1:1) and AN-AA (1:1) showed 84 that in both cases a similar degree of imidisation was achieved. At the same time, the acrylic precursor, unlike the methacrylic one, is poorly foamed during heat treatment.…”

“…Foaming agents are often used when obtaining PMI foams, for example, urea, methyl urea, formamide, N -methylformamide and others. 30,33,45,66,72,77 -79 They decompose with the release of ammonia or methylamine. In this case, the ammonia or methylamine formed reacts with anhydride units at high temperatures (Figure 6) which leads to the additional formation of imide fragments.…”

“…As the PMI production process improved and many technical problems were being solved, in practice, a ratio of (M)AN and (M)AA units close to equimolar became frequently used, 24,27,69,70,72,95,96 although to obtain PMI with the required properties, the ratio of nitrile and carboxyl units was sometimes significantly different from equimolar according to recent publications. 28,63 In a few recent papers, the effect of the structure and ratio of (meth)acrylonitrile and (meth)acrylic acid units in polymer precursors on thermal imidisation and the properties of PMI foams was also considered.…”