Macromolecular chain reactivity

Quite recently, Plate and Noah — have critically discussed all the theoretical aspects of macromolecular chain reactivity, and we summarize below the main conclusions related to the processes of interest in our studies kinetically controlled irreversible reaction of a low molecular weight compound R on an homopolymer An, involving a single monomeric unit A. 

On the other hand, two important factors of macromolecular chain reactivity in solution deserve more attention,namely the nature of the reaction medium and the polymer concentration. 

The quantitative bulk conversion of unsaturated functional groups in PHAs to epoxides has been achieved by reaction with m-chloroperbenzoic acid as the chemical reagent [107]. No chain scission of the macromolecular chain was observed. Epoxy-modified PHAs are chemically even more reactive than unsaturated PHAs and therefore could be useful in further chemical reactions (e.g. grafting of therapeutic important substances) [108]. 

Chemical modification of polymers (J.) still remains a field of continuously increasing importance in macromolecular chemistry. In spite of its high diversification, it may be divided into 2 distinct but complementary main research lines a) the fundamental study of the chemical reactivity of macromolecular chains b) the synthesis of new homopolymers and copolymers, and the functionalization of linear or crosslinked polymers. Some of these facets have been reviewed in the last years (2-6), and the purpose of this presentation is to illustrate a number of characteristic topics both from fundamental and applied points of view, through some literature data and through our own studies on nucleophilic substitution of polymethylmethacrylate (PMMA). 

Theoretical framework of the analysis of the chemical reactivity of macromolecular chains... 

Mechanistic and theoretical aspects of the reactivity of macromolecular chains in solution... 

Though a macromolecular chain is composed of an accumulation of certain repeating units, its characteristics and reactivity are not considered to be simply the sum of the repeating units. Rather, the characteristics and reactivities are attributable to interactions between repeating units. Therefore, one cannot discuss polymer effects without taking into account inter- and intrachain interactions. However, only few data on these types of interactions between polymers have been reported. The polymer effects are characterized as follows ... 

The aim of this review is to summarize the developments concerning the synthesis of hydroxyl-terminated polymers by a radical process. Hydroxytelechelic , a term also used for denominating this type of polymers, means the presence of one OH group at each end of the macromolecular chain. These reactive ends can be further used for chain extension or network build-up if a multifunctional reagent is used, but these must be distinguished from macromonomers as pointed out by Rempp and Franta 1). 

Both physical and technological properties of copolymers are influenced by the sequence distribution in the macromolecular chains. The mathematical relationships governing the distribution, first developed by Alfrey and Goldfinger (7), are based upon kinetic and statistical considerations implying three fundamental assumptions a) steady state copolymerization, b) terminal effect only (i.e. influence of the last, but not of the penultimate unit of a growing chain on the addition of the next monomeric unit), and c) constant monomer feed. Under these assumptions, which may be defined as a first order approximation, the copolymers are described by two quantities, the ratio / of the molar fractions of the two monomers and the product of reactivity ratios... 

A strategy that is based on the use of reactive antioxidants can also be explored to achieve stabilization of polymers suitable for human-contact applications. Reactive antioxidants that become an integral part of the macromolecular chain can result in nonmigratory stabilizer systems that would be unaffected by extractive hostile contact media. 

Most macromonomers are made from the macromolecular chain linked to a reactive double bond for further radical polymerizations. 

As already mentioned, the vinyl group is not the only kind of reactive function found for the macromonomers. A macromonomer can be constituted of two condensable functions at the same chain end. The synthesis of this kind of macromonomer is quite recent, explaining the low number of publications. However, this new category of macromonomers is of great interest because the condensable functions are numerous (hydroxyl, carboxyl, amine, etc.). Table 22 gives some macromonomer structures, i.e., two condensable functions bearing a macromolecular chain. 

This review introduces the method of active ester mtheris, and discusses its application to the preparation of a variety erf specialty polymers, including amphiphilic gels, graft copolymers, and side chain reactive and liquid crystalline polymers. The polymerization and copolymerization of activated acrylates by solution and suspension techniques are discussed, and polymer properties such as comonomer distribution, molecular weights, C-NMR spectra and gel morphology are reviewed. Potential applications of these polymers are also highlighted, and the versatility of active ester synthesis as a new dimension of creativity in macromolecular chemistry is emphasized. 

Influence of the structure on the reactivity of fluorine-containing methacrylates in the bulk radical copolymerisation with vinyl monomers, as well as the dependence of structure of macromolecular chain of copolymers obtained on these factors is not well-studied [3]. 

Determining the composition and sequence of comonomer units is essential in the case of copolymers, since both parameters influence the physical and chemical properties of these materials. Furthermore, comonomer sequence is related to the mechanism of copolymerization, and to the reactivity ratios of the comonomers. Among the techniques developed for polymer characterization. Mass Spectrometry (MS) is one of the most powerful. The mass spectrum of a polymer contains plenty of information on polymer properties such as the structure, the repeat units which constitute the mac-romolecular backbone, the length of macromolecular chains, the end groups which terminate the chains, the chemical heterogeneity, the sequence of copolymers and their composition heterogeneity. 

If there is only a small number of reactive groups per macromolecule, the environment of these groups is not changed as the reaction proceeds. The macromolecular chain simply acts as a diluent. Of course, neighboring group effects can also play a role, especially if five- and six-membered cyclic transition states can be formed. An example of this is the partial imidization of poly(methacrylamide) at temperatures above 65°C ... 

It is well known that the heterogeneous nature of Ziegler-Natta catalysts, combined with the use of cocatalysts and electron donors as activating agents will lead to the presence of multiple types of active sites on the catalyst. Each type of site will have its own steric environment and reactivity toward (co)monomer and hydrogen. The consequence is that the polyolefin will be a mixture of macromolecular chains with various molecular weights and structure (isotacticity and/or comonomer incorporation). 

The way in which ethylene and propylene distribute themselves along the macromolecular chain is expressed by the product of the reactivity ratios r and C2 (Figure 12.7). In particular, if the comonomer insertion ... 

An analysis of the published data suggests that phosphorus flame retardants or products of their transformation serve as agents and catalysts for the substituent detachment reactions in the macromolecular chain, for cyclization reactions and for other reactions ofpolymers. As has already been mentioned, such reactions favor the formation of the carbon skeleton. Pyrolytic dehydrogenation reactions and dehydrohalogenation reactions of organic compounds are aided by the presence of phosphorus compounds. In this case, one of the most important factors to be considered is the relationship between the chemical structure of phosphorus-containing compounds and their reactivity, which determines the specific interaction with a polymer substrate under the conditions of its preliminary treatment and combustion. 

Several techniques have been examined for determining the anhydride content and structural effects of the macromolecular chain on the reactivity of the anhydride moiety for the acrylate - MA and methacrylate-MA... 

The kinetic tteatinent developed in Section 7.4 for divalent monomers applies to systems with w > 2. In the latter case, macromolecular chains grow simultaneously in many directions and each one carries a growing number of reactive functional groups. A three-dimensional network is eventually formed after the conversion reaches a critical value called the gel point. In such a tridimensional sample, only a small fraction of polymer, which decreases with conversion, is soluble and the insoluble part is considered to have infinite molar mass. 

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