# Influence of Monomer Sequence on the Cyclization Behavior of Poly(acrylonitrile-_co_-acrylamide)
## 4 Conclusions  
In the present study we have synthesized first a number of copolymers of AN and AAM with desired MW, narrow MWD, and various monomer sequences (random, gradient, and block-gradient). These RAFT-based copolymers were used to clarify the influence of chain microstructure on the cyclization behavior of the copolymers in inert and air atmosphere.  
We have demonstrated that cyclization reaction dominated in argon atmosphere. The ionic mechanism of cyclization prevailed over radical one if the molar part of AAM units in copolymer exceeded \(\sim\)3 mol. % for random copolymer and \(\sim\)6 mol. % for block-gradient copolymer. It was demonstrated first that the activation energy of ionic cyclization was not influenced by both copolymer composition and chain microstructure. Besides, we have found that the ratio of homo- and hetero-triads affects the rate of the cyclization reaction. In particular, the decrease in the molar part of AN-AAM-AN and AAM-AN-AAM triads is followed by the decrease in the cyclization rate.  
On the contrary, the oxidation reactions dominated in air atmosphere. In this case, the formation of conjugated C=C bonds developed along with conjugated C=N bonds resulting in the lower values of the conversion of nitrile groups. It was shown first that the oxidative reactions were found to be less sensitive for copolymer composition and chain microstructure.  
Thus, it may be proposed that the low content of AAM units (\(\sim\)3 mol. %) randomly distributed along the chain is enough to perform successful thermo-oxidative stabilization of AN copolymer.  
**Supplementary Materials: The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13063734/s1](https://www.mdpi.com/article/10.3390/app13063734/s1)]([https://www.mdpi.com/article/10.3390/app13063734/s1](https://www.mdpi.com/article/10.3390/app13063734/s1)), Figure S1: Calibration curve for determination copolymer composition; Figure S2: SEC traces of the copolymers formed in the experiments 4-7 (Table 1) at various conversions; Figure S3: \({}^{1}\)H NMR spectra of copolymers 5 (a), 6 (b), 7 (c), and \({}^{12}\)C NMR spectrum of copolymer 7 (d); Figure S4: DCS thermograms of samples 1, 2, 4-6 registered in argon at different heating rates; Figure S5: FTIR spectra of AN and AAM copolymers subjected to thermal treatment in Ar atmosphere at 200 \({}^{\circ}\)C for 0 (1), 5 (2), 10 (3) 20 (4), 60 (5), and 120 min (6); Figure S6: FTIR spectra of AN and AAM copolymers subjected to thermal treatment in Ar atmosphere at 225 \({}^{\circ}\)C for 0 (1), 7 (2), 30 (3) 60 (4), and 120 min (5); Table S1: Formulations of the RAFT copolymerization of AN and AAM.**  
**Author Contributions: Conceptualization, E.V.C.; methodology, R.V.T. and A.Y.G.; investigation, R.V.T., M.S.B. and A.V.P.; writing--original draft, E.V.C., writing--editing, N.I.P. All authors have read and agreed to the published version of the manuscript.**  
**Funding: This research received no external funding.**  
**Data Availability Statement: Not applicable.**  
**Conflicts of Interest: The authors declare no conflict of interest.**