Principle of computer synthesis of network polymers possessing a specified interval of glass temperatures

For the first time, the model and the principle of constructing a corresponding computer program for the electronic synthesis of polymer networks with a given glass transition temperature range have been proposed. A repeating network fragment is synthesized from the smallest basic fragments that are connected to each other using a steering matrix of interactions. As an example, 10 cross-linked points, 16 basic fragments for constructing inter cross-linked chains and 5 repeating fragments of polymer networks are presented, the glass transition temperatures of which are within the specified range from 450 to 480K.


Introduction
The problem of predicting the glass transition temperature Tg of cross-linked polymers based on their chemical structure was considered in detail in monographs [1][2][3][4][5][6][7]. In monographs [8][9], such an approach is absent, and they only make corrections to the methods for calculating linear polymers, which make it possible to estimate the Tg values of cross-linked polymers.
In the works [1][2][3][4][5][6][7], a model and a computer program have been developed that allow the computer synthesis of linear polymers. The synthesis is carried out on the basis of the smallest basic fragments that cannot be "cut" along the axis of the macromolecule. As an example, Table 1 shows a number of such fragments. Markers determine the possibility of chemical attachment of atoms to the structure of the basic fragment. Among the atoms are carbon C, hydrogen H, oxygen O, nitrogen N, sulfur S, etc. The left marker means that this atom is attached to the left side of the basic fragment, and the right marker means that this atom is attached to the right side of the basic fragment. In this case, the attached atoms can be different; for example, oxygen is attached to the left and carbon is attached to the right.
In the proposed work devoted to the computer synthesis of cross-linked polymers, linear chains are the structural elements of a repeating fragment of the network connecting the cross-linked points. In works [1][2][3][4], 96 basic fragments were used, some of which are presented in Table 1. The possibility of attaching one or another atom to the basic fragment in the process of computer synthesis is determined by the so-called connectivity matrix, presented below ( Table 2): Table 2. Matrix of markers, which controls the computer synthesis of polymers.

Network polymers
Earlier, in [2,4,11], the model and calculation scheme were described for a quantitative assessment of the glass transition temperature T g of cross-linked polymers. The T g value is calculated using the equation (1) . . From the point of view of chemical structure, a network node consists of an atom, from which chain branching begins, and neighboring atoms chemically bonded to it. The latter contain chemical substituents, which are also included in the cross-linked point Table 3 lists a number of atoms and atomic structures from which chain branching occurs. In total, in this work, there are 78 such structures that form cross-linked points of polymer networks. As an example, let us choose the range of glass transition temperatures of cross-linked polymers from 450 K to 480 K. The program synthesizes many repeating fragments of polymer networks, of which, for example, select only 5 structures (Table 4):

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All T g values fall within the specified glass transition temperature range. Thus, the fundamental possibility of carrying out electronic synthesis of not only linear polymers, which was developed by us earlier [1][2][3][4], but also of network polymers has been shown. Further work in this direction is related to taking into account the networks topology. Indeed, with the same chemical structure of the basic fragments and their amount, as well as with the same cross-linked points, polymer networks can possess different chemical structures. It depends on where the chain links are located, not to mention structural defects (the formation of cycles, the presence of branching chains, at one end of which they do not join the network structure, etc.). Let's give an example of this influence. For radiation-cross-linked polymer chains of polyethylene, the following structure is possible: