METHOD FOR PRELIMINARY DETERMINATION OF THE COMPOSITION OF COPOLYMERS FOR THE SYNTHESIS OF ELECTROLYTES BASED ON ACRYLIC POLYMERS

ABSTRACT

In this work, the theoretical basis of the synthesis of acrylonitrile and methyl acrylate - based copolymer for polymer electrolytes, which is the basis for the preparation of metal-ion batteries, is shown. This method makes it possible to pre-calculate the proportion of monomers in the copolymer.

АННОТАЦИЯ

В данной работе показаны теоретические основы синтеза сополимера акрилонитрила и метилакрилата для полимерных электролитов, который является основой для получения металлоионных батарей. Этот метод позволяет предварительно рассчитать долю мономеров в сополимере.

Keywords: copolymerization, acrylonitrile, methyl acrylate, copolymerization constant, resonance parameter, polarity factor.

Ключевые слова: сополимеризация, акрилонитрил, метилакрилат, константа сополимеризации, параметр резонанса, фактор полярности.

Introduction

Polymer electrolytes have many advantages over liquid electrolytes for metal-ion batteries. They can play an important role in improving the performance and safety of metal-ion batteries by reducing or eliminating the need for flammable organic solvents, reducing dendrite formation at negative electrodes, improving electrolyte stability and electrochemical window, and other factors. Dissolved salts may be contained in the polymer phase, but no solvent or other small organic molecules are present. They usually have a semi-crystalline structure and have a relatively low temperature conductivity, falling to or below their glass transition temperature. For practical use, ionic conductivities of about 10^-3 S∙cm^-1 are required, which is difficult to achieve with solid polymer electrolytes, but can be easily achieved with gel polymer electrolytes [1-5].

Acrylic polymers have a wide range applications in industry [6-10]. In this work, copolymerization constants are calculated and a mode of sequential loading of monomers into the reaction medium is developed to carry out the copolymerization process. According to the last link model, during the copolymerization of two monomers M₁ and M₂, propagation reactions of four elementary chains are considered, in which these monomers and two growing active centers ~m₁* (the last part of the monomer 'chain with link M₁) and ~m₂* (chain with last link M₂) are involved. The symbol * can mean an unpaired electron, a positive or a negative charge [6, 11].

Methods

Purification of monomers. It is known that an inhibitor is added to prevent polymerization of monomers during storage. Before polymerization, the monomers are distilled using a vacuum distillating laboratory assembly as shown in the figure 1 below.

Figure 1. Fractionation assembly: 1-oil bath, 2-fine ceramics, 3- flask, 4-deflegmator, 5- laboratory distillation head, 6-thermometer, 7-Libikh cooler, 8- allonge, 9-chlorcalcium tube, 10-collector

Study of copolymerization process based on acrylonitrile and methylacrylate. In this scientific research work, copolymerization constants are calculated and a mode of sequential loading of monomers into the reaction medium is developed to carry out the copolymerization process. According to the last link model, during the copolymerization of two monomers M₁ and M₂, propagation reactions of four elementary chains are considered, in which these monomers and two growing active centers ~m₁* (chain with a terminal link of the monomer M₁) and ~m2* (chain with end link M₂) are involved. The symbol * can mean an unpaired electron, a positive or a negative charge.

It is known that any chemical reaction has its own kinetics, i.e. speed. It is required to determine the rates of mutual copolymerization for these selected monomers. For this we сan use the following:

where k₁₁, k₁₂, k₂₁, k₂₂ are the rate constants of reactions of addition of monomers to growing active centers (the first number of the index refers to the active center, the second to the monomer); [m₁*], [m₂*], [M₁], [M₂] are molar concentrations of reagents.

Now we present the equation of dependence of these rate constants on binary copolymerization constants:

The Q and ε values represent the binding of the reactant to the reaction center, respectively, and reflect the resonance parameter of acrylonitrile and methyl acrylates, and the polarity factor resulting from polarization.

Results and discussions

Using the above equations, binary copolymerization constants are calculated according to the Q-e scheme (see Table 1).

Table 1.

Binary copolymerization constants according to the Q-e scheme

Also, the dependence of the composition of the copolymer on the composition of the monomer mixture is presented in the form of a composition diagram in the coordinates M₂ (mol. share of the M₂ monomer in the initial mixture) - m₂ (mol. share of the M₂ monomer chain in the copolymer). The curve of this dependency is called the copolymer composition curve, and this curve is constructed according to the following equation if the copolymerization constants r₁ and r₂ are known:

By putting the initial percentage of M₂ monomer on the abscissa axis, and the corresponding value found on the ordinate axis, we find a curve representing the composition of the copolymer formed at different initial proportions of monomers (See Figure 2).

Figure 2. Dependence of the composition of the copolymer (m₂) on the composition of the mixture of monomers (M₂)

Conclusion

With the help of this method, based on the copolymerization constants of the monomers in the copolymers, it is possible to determine how much of the monomers were included in the copolymer or how much remained uncopolymerized when taken in certain proportions. Using this method, it is possible to determine the composition of the copolymer in advance. It will be possible to proof the composition after being purified and performing elemental analysis.

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