Chemical space networks

A network polymer [Fig. 1.3(d)], on the other hand, can be described as an interconnected branched polymer. For example, a three-dimensional or space network structure will develop, instead of the branched structure (XI), if styrene is copolymerized with higher concentrations of divinyl benzene. In a network structure, all polymer chains are linked to form one giant molecule. Thus, instead of being composed of discrete molecules, a piece of network polymer constitutes, essentially just one molecule. With the formation of network structure polymers acquire greater rigidity, dimensional stability, and resistance to heat and chemicals. Because of their network structure such polymers cannot be dissolved in solvents and cannot be melted by heat strong heating only causes decomposition. 

Equation (9) is predicated on the assuraiptions that both networks are continuous in space, network II swells network I, and that the swelling agent then swells both networks. The several PS/PS IPN s under consideration constitute an excellent model system with which to examine.fundamental polymer parameters. Questions of interest in the field of IPN s relate to the relative continuity of networks I and II and their consequent relative contribution to physical properties and the extent of formation of physical crosslinks or actual chemical bonds between the two networks. The reader will note that if equation (9) is obeyed exactly, the implicit assumptions require that both networks be mutually dissolved in one another and yet remain chemically independent. Then the only features of importance are the crosslink densities and the proportions of each network. 

Krein MP, SukumarN (2011) Exploration ofthe topology of chemical spaces with network measures. J Phys Chem A 115 12905-12918... 

Ripphausen P, Nisius B, Wawer M, Bajorath J (2011) Rationalizing the role of SAR tolerance for ligand-based virtual sereening. J Chem Inf Model 51 837-842 Stumpfe D, Dimova D, Bajorath J (2014) Composition and topology of chemical spaces with network measures. J Chem InfModel 54 451-461... 

In paper [126] it was shown that universality of the critical indices of the percolation system was connected directly to its fractal dimension. The self-similarity of the percolation system supposes the availability of the number of subsets having order n (n = 1, 2, 4,. ..), which in the case of the structure of amorphous polymers are identified as follows [125]. The first subset (n = 1) is a percolation cluster frame or, as was shown above, a polymer cluster network. The cluster network is immersed into the second loosely packed matrix. The third (n = 4) topological structure is defined for crosslinked polymers as a chemical bonds network. In such a treatment the critical indices P, V and t are given as follows (in three-dimensional Euclidean space) [126] ... 

In Figure 9.1 the comparison of dimensions and for the studied EP is adduced. Their good correspondence indicates unequivocally that their loosely packed matrix, which serves simultaneously as a natural nanocomposite matrix, is the fractal space where the nanocluster structure of epoxy polymers is formed. Since for linear amorphous polymers = 3 [9], i.e., their nanostructure formation is realised in three-dimensional Euclidean space, then the conclusion that chemical crosslinking network availability in the considered EP serves as the indicated distinction cause is obvious enough. In Figure 9.2 the dependence of on crosslinking density is... 

The recurrent patterns of specific stuff properties allow the building of the ontological category of stuff kinds, which we use when we claim that two objects consist of the same stuff. The building blocks are the pure substances that retain their identity during phase transition and purification. Two objects are chemically identical if and only if they are found at the same place in chemical space. Chemical space contains all possible substances. Seen as a (nonlinear) network, chemical space consists of pure substances at the nodes the relationships between the nodes are chemical reactions correlated to experimental practice (including reactions with as yet non-existing substances). This forms the chemical core of experimental chemistry [1998, 135]. ... 

As a first approximation, when developing a modeling formalism for a reacting system, the state space associated with chemical reaction networks can be partitioned into regions that depend on the nature of the system. Doing so is valuable since it allows one to evaluate which approximations are reasonable, and provides a comprehensive picture for the segue between the regions where models must be solved with stochastic methods and where ordinary differential equations can be used. 

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