Heterogeneous composites Synthesis

The often used synonym combinatorial catalysis instead of high-throughput catalysis implies that all possible combinations of all parameters that can affect catalyst performance (precursor compounds, chemical composition, synthesis protocol, calcination,. ..) will be screened to find the best suited catalyst for the reaction. Although such strategies are used in combinatorial chemistry, it is almost impossible to adapt them to heterogeneous catalysis. 

In order to correctly approach this research it is necessary to focus (i) the chemical processes which occur during the preparation of a material and that influence their composition (synthesis route, nature of the precursor compounds, processing conditions) (ii) the necessary conditions to produce homogeneous or controlled heterogeneous materials with predictable and reproducible functional properties. 

As a step ahead, researchers have further modified the synthesis process to maximize the consumption of alkalinity in zeolitization and ash dissolution by resorting to fusion method to produce zeolites, in less time and that too with higher yield and better properties. Based on the earlier studies it has been observed that not much has been explored about the need of preparation of homogenous mixtures of synthesis matrix [6]. The matrix connotes to a material which consists of heterogeneous composition of several oxides such as glass in the fly ash, NaOH and water (i.e., the most important parameter) of NaOH and fly ash and its effect on the ingredients of fusion products [10]. There are possibilities of loss of... 

The effect of the initiation and termination processes on compositional heterogeneity can be seen in data presented in Figure 7.3 and Figure 7.4. The data come from a computer simulation of the synthesis of a hydroxy functional oligomer prepared from S, BA, and HEA with a thiol chain transfer agent. The recipe is similar to those used in some coatings applications. 

The synthesis of well defined block copolymers exhibiting controlled molecular weight, low compositional heterogeneity and narrow molecular weight distribution is a major success of anionic polymerization techniques 6,7,14-111,112,113). Blocks of unlike chemical nature have a general tendency to undergo microphase separation, thereby producing mesomorphic phases. Block copolymers therefore exhibit unique properties, that prompted numerous studies and applications (e.g. thermoplastic elastomers). 

A 50% functionalization evokes the interesting question, bearing in mind facile transesterification, of how the fluoroalkyl chains will be distributed over the molecules and how they will be distributed on one particular molecule This question has been examined in detail for dendrimers of the poly(propyleneimine) type functionalized with stearic acid [33]. It was proven that the compositional heterogeneity (distribution of degree of substitution) is random, but the positional heterogeneity (spatial distribution of the substituents over the dendrimer molecule) is not random. However, due to flexibility, no particular effect of the spatial distribution can be observed. Unlike the dendrimers, we expect the hyperbranched polyesteramides to be stiffer, so that spatial distribution could lead to interesting effects if the molecule were composed of a functionalized side and a non-func-tionalized side (Fig. 28), as shown possible for dendrimers via a convergent synthesis [34]. 

We are currently investigating the synthesis and characterization of such molecules for numerous different applications such as surfactants, cosmetics, and toner resins. A point of interest in the preparation and characterization of multifunctional hyperbranched molecules is the compositional heterogeneity (how many and what type of functional groups are on a particular hyperbranched po-lyesteramide molecule) and the positional heterogeneity (spatial distribution of the functional groups on a particular hyperbranched polyesteramide molecule). 

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