Effect of the backbone-chain structure of acrylimide-forming copolymers on the maximum degree of their thermal imidization

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

“…Similar temperature patterns are also observed during the thermolysis of the AN-MAA copolymer. 39,97 Consequently, the precursors of the amide-acid and nitrile-acid types obey similar laws under thermolysis. It was repeatedly noted 20,84 that the patterns of thermal imidisation are sufficiently close for different copolymers of the type (meth)acrylonitrile–(meth)acrylic acid.…”

“…For example, for the AN-MAA copolymer (1:1) obtained by the bulk copolymerisation, the maximum degree of intramolecular imidisation was calculated to be 32% and according to the experimental data (IR spectroscopy) was equal to 30%; for the copolymer containing 31 mol% of nitrile units, the calculated and experimental maximum degrees of imidisation were 13%. According to Dyatlov et al, 97 for AN-MAA copolymers, the intramolecular imidisation proceeds at 120°C and the imidisation degree reaches the maximum values in 0.5 h. Further, imidisation has an interchain nature; it increases the degree of cross linking of polymers and requires a higher temperature (the same as in the preparation of PMI foam). However, from the point of view of optimising the properties of PMI foams, it is necessary to optimise the ratio of intramolecular and interchain imide bonds.…”

“…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.…”

“…39 The glass transition temperature of the non-imidised copolymer of AN-MAK (1:1) is 55°C; for the copolymer with a statistical distribution of units and degree of intramolecular imidisation of 25%, the glass transition temperature is 190°C; for polymers cross linked by intermolecular imide bonds, the flow temperature coincides with the temperature of the beginning of decomposition: 320°C. The maximum degree of imidisation (or maximum mole fraction of imide groups in a copolymer) can be determined based on the results of NMR studies of the microstructure of a polymer precursor by the formula 97…”

“…It was repeatedly noted 20,84 that the patterns of thermal imidisation are sufficiently close for different copolymers of the type (meth)acrylonitrile–(meth)acrylic acid. Therefore, it can be assumed that the revealed patterns 39,40,97 can be extended to the most important industrial thermal imidisation of MAN-MAA copolymers.…”