Polymeric-analogous reaction

Polymer identification starts with a series of preliminary tests. In contrast to low molecular weight organic compounds, which are frequently satisfactorily identified simply by their melting or boiling point, molecular weight and elementary composition, precise identification of polymers is difficult by the presence of copolymers, the statistical character of the composition, macromolecular properties and, by potential polymeric-analogous reactions. Exact classification of polymers is not usually possible from a few preliminary tests. Further physical data must be measured and specific reactions must be carried out in order to make a reliable classification. The efficiency of physical methods such as IR spectroscopy and NMR spectroscopy as well as pyrolysis gas chromatography makes them particularly important. 

The attachment of mesogenic units to a polymer backbone via polymer analogous reactions is not a new concept, although they are much less frequently used than the polymerization of mesogen containing monomers. Liquid crystalline polyacrylates,... 

In contrast to the substituted PPO s, It Is theoretically possible to obtain the same substituted PECH s by homopolymerization of the corresponding mesogenic oxirane, or by its copolymerization with epichlorohydrin. We have attempted these polymerizations in order to better interpret the thermal behavior of the more complicated copolymers that we have obtained by polymer analogous reactions. Homopolymerization would be instructive because the incorporation of nonmesogenic units into liquid crystalline homopolymers doesn t as a rule change the type of mesophase obtained (5). 

Results obtained with germanes also provide models for the kinds of reactions that may be occurring in the silane polymerization reaction as well. For example, we have succeeded in carrying out the reaction shown in Equation 4 (26). The analogous reactions with triphenylsilane, or triphenylstannane, were not... 

A number of groups have attempted to develop the analogous reaction for cyclotri- and cyclotetrasilazanes. Ring opening polymerization represents an alternative to direct ammonolysis even though the cyclomer precursors are normally made by ammonolysis or aminolysis. 

Many other compounds have been shown to act as co-catalysts in various systems, and their activity is interpreted by analogous reactions [30-33]. However, the confidence with which one previously generalised this simple picture has been shaken by some extremely important papers from Eastham s group [34], These authors have studied the isomerization of cis- and Zraws-but-2-ene and of but-l-ene and the polymerization of propene and of the butenes by boron fluoride with either methanol or acetic acid as cocatalyst. Their complicated kinetic results indicate that more than one complex may be involved in the reaction mechanism, and the authors have discussed the implications of their findings in some detail. 

Of particular interest was the reaction of two equivalents of potassium phthalimide with PFB using 18-crown-6 in refluxing acetonitrile. This reaction with either small molecules or the polymeric analogs represents a novel approach to arylimide synthesis via PTC. After 4 hr. under nonoptimized PTC reaction conditions, disubstitution afforded the bisimide 6 in ca. 50% yield. This shows that phthalimide anion, a considerably poorer nucleophile than either the phenoxide or thiophenoxide, is a strong enough nucleophile in the presence of 18-crown-6 to displace aryl fluoride with facility, and demonstrates that the synthesis of polyimides, an important class of thermally stable polymers, is feasible by this PTC polycondensation route. 

The third possibility for synthesizing polymeric substances is the modification of existant natural or synthetic macromolecules (see Chap. 5). These processes can either be chemical or physical. Chemical modifications are reactions on macromolecules without degradation of the main chain (macromolecular substitution routes, polymer-analogous reactions ) like, for example, hydrolysis. 

This is as a rule not possible as these data are not available for high-molecular-weight samples. In order to be able to exclude the influence of the distribution of degree of polymerization for various polymer structures, polymer analogous reactions may be carried out, where polymers of differing chemical structures and molecular weights, but with the same distribution of degree of polymerization are obtained (e.g., Kulicke, Horl 1985). Of particular interest in this report are polyelectrolytes. 

Bryant has calculated the changes in free energy for various reaction steps of the polymerization of tetrafluoroethylene. He concluded (1) that the initiation and propagation are about twice as favorable for tetrafluoroethylene as the analogous reactions for ethylene, (2) that termination by combination is more favorable than disproportionation, and (3) that chain-transfer to monomer and to polymer are less likely than the combination of radicals. 

Because of their high refractive index, these materials possess desirable optical and thermal properties, in addition to being impervious to a variety of chemicals [5]. Analogous reactions involving carbon disulfide and epoxides have provided extremely interesting examples of atom-exchange polymerization processes. 

Pyrolysis of these trimeric aminoboranes generally leads to dissociation into the starting materials. Some B-mono and B-dichloroborazine was also identified amongst the reaction products also, polymeric materials were observed which resulted from B-haloborazine condensation. B-trihaloborazines were not obtained. Analogous reactions were observed with borazanaphtalene, B5N5H8 149) 10, which forms an adduct with 5 HX. 

This article surveys the research work on the synthesis and modification reactions of poly(ethyleneimine) as well as its applications to metal complexation processes. Poly-(ethyleneimine), one of the most simple heterochain polymers exists in the form of two different chemical structures one of them is branched, which is a commercially available and the other one linear which is synthesized by cationic polymerization of oxazoline monomers and subsequent hydrolysis of polyf(/V acylimino)cthylcne]. The most salient feature of poly(ethyleneimine) is the simultaneous presence of primary, secondary, and tertiary amino groups in the polymer chain which explains its basic properties and gives access to various modification reactions. A great number of synthetic routes to branched and linear poly(ethyleneimine)s and polymer-analogous reactions are described. In addition, the complexation of polyfethyleneimine) and its derivatives with metal ions is investigated. Homogeneous and heterogeneous metal separation and enrichment processes are reviewed. 

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