# Influence of Monomer Sequence on the Cyclization Behavior of Poly(acrylonitrile-_co_-acrylamide)
## 3 Results and Discussion  
### CopolymerSynthesis  
The copolymerization of AN with low amounts of AAM should proceed with similar rate as the homopolymerization of AN. Indeed, in the batch process the content of AAM in the monomer feed in the range of 2-7 mol. % has negligible effect on the copolymerization kinetics (Figure 1a). Simultaneously, the kinetic plots are described by first-order kinetics (Figure 1b), which is typical for RAFT polymerization [41; 42; 43; 44]. In continuous and semi-continuous process, the total amount of AAM introduced into reaction is higher (10-15 mol. %, Table 1). However, due to the slow addition of AAM to the monomer mixture it has no visible effect on the copolymerization rate (Figure 1c). Similarly to the batch reaction, the copolymerization kinetics is first-order with respect to monomer concentration in the wide range of the polymerization time (Figure 1d). The changes of the copolymer composition throughout copolymerization were studied by ATR FTIR spectroscopy. Figure 2 presents the dependences of the molar part of AAM units in the copolymers formed in batch, continuous, and semi-continuous processes on the monomer conversion. AAM is a more active monomer than AN in solution polymerization in DMSO; the relative monomer activities are \(\mathrm{r_{AN}}=0.65\) and \(\mathrm{r_{AAM}}=1.98\)[31]. In batch copolymerization, the molar part of AAM units in the copolymer remains constant throughout reaction and the experimental values of copolymer composition (points) are in a good accordance with theoretical values (lines) calculated on the basis of \(\mathrm{r_{AN}}\) and \(\mathrm{r_{AAM}}\) values (Figure 2a). Continuous and semi-continuous processes give an opportunity to control the introduction of AAM in the copolymer chain (Figure 2b, curves 2-4). The lower the rate of AAM addition to the reaction mixture, the lower the AAM content in the copolymer. The average AAM molar fraction increases with the progress of the monomer conversion. In conditions of the conventional free radical copolymerization, the change of the average copolymer composition is accompanied by the growth of the composition dispersity. It can be illustrated by the following example. Let us suppose that the experiment 7 is conducted in the absence of BTC. In this case, before starting the addition of AAM, the polymer formed should be pure PAN due to the presence of AN in the polymerization mixture only. After AAM is added to the polymerization system, a copolymer should form. As a result, the copolymer formed at the end of the reaction will consist of the macromolecules of different composition. In RAFT copolymerization, the compositional  
Figure 1: (**a**,**c**) Time-conversion dependences for AN-AAM copolymerization in 60 wt% DMSO solution at 80 \({}^{\circ}\)C, [AIBN] = [BTC] = 1 mmol/L (**a**) and [AIBN] = [BTC] = 2 mmol/L (**c**); (**b**,**d**) corresponding semi-logarithmic dependences of the monomer concentration on the polymerization time. Numbering of the curves corresponds to the numbering of the samples from Table 1.  
heterogeneity of macromolecules is replaced by the composition heterogeneity along the macromolecule, but all macromolecules have similar composition. So, the copolymer is compositionally homogeneous. Thus, in experiment 7 performed in the presence of BTC, the polymer formed during a period below 0.5 h is also pure PAN, while later it is transferred to block-gradient copolymer due to chain-extension. Thus, combination of batch/continuous/semi-continuous process with RAFT mechanism allows synthesis of the copolymers with various monomer sequence distributions. Being active in cyclization reaction, the AAM unit distribution along the chain should affect the thermal behavior of AN/AAM copolymers.