Preformed polymers synthesis

The chemical adjustment of charge density is another potentially rewarding technique. It does, however, require either the synthesis of new polymers or the chemical modification of preformed polymers (e.g., supersulfation of hyaluronic acid [16]). This procedure has not been evaluated in our screening. 

In earlier times, polymer networks were generally prepared by reactions between small monomers and by vulcanization of primary chains. Successively, the notion of a precursor developed for a preformed polymer molecule carrying functional groups, or a distribution of them. Synthesis of precursors and their use in network build-up have been motivated by the following needs ... 

Previous work on the synthesis of TTF (tetrathiafulvalene) containing polymers has been reported by at least seven groups of researchers. Most of this work concerns condensation 6,7,8,9 polymers or polymers made from vinyl substituted TTF molecules . Without exception, the polymers produced by these methods have been largely unacceptable for subsequent physical study because of their brittle,intractable, highly insoluble nature. Only by reaction of a suitably monofunctionalized TTF derivative with the preformed polymer poly(vinylbenzylchloride) has it been found possible — to prepare soluble TTF homopolymers with more manageable physical properties. 

Because the opportunities for controlled chain growth are more restricted in inorganic than in organic systems, an alternative approach to polymer synthesis becomes appealing. This involves the use of substitution processes carried out on a preformed reactive polymeric intermediate. In this way molecular diversity can be introduced by different substitution reactions rather than by a diversification of the polymerization process. 

A line of research that has aroused much interest in recent years is the study of head-to-head, tail-to-tail polymers (96-98). Their direct synthesis has little likelihood of being successffil as head-to-tail sequences usually predominate in vinyl polymerization. One possibility for their preparation is through the chemical modification of suitable preformed polymers. In the case of the head-to-head, tail-to-tail polypropylene, different stereoisomeric forms have been isolated, depending on the method of preparation. In the general scheme, the precursor is an unsaturated polymer obtained by polymerization of the disubsti-tuted butadiene (2,3-dimethylbutadiene or 2,4-hexadiene) then, by chemical or catalytic reduction, this polymer is converted into the desired polypropylene, whose stmcture can then be examined by NMR spectra. Head-to-head, tail-to-... 

Template or matrix polymerization can be defined as a method of polymer synthesis in which specific interactions between preformed macromolecule (template) and a growing chain are utilized. These interactions affect structure of the polymerization product (daughter polymer) and the kinetics of the process. The term template polymerization usually refers to one phase systems in which monomer, template, and the reaction product are soluble in the same solvent. 

For reasons which have already been described (Sect. 3.2.1) the synthesis of azo functions onto preformed polymers generally give poor results and are thus not common in the literature 22 -27). However, in a few cases it has proved possible to successfully introduce azo functions in this way. For example polymers having alcohol side groups have been esterified with azo compounds also containing an acid chloride function and the products used for grafting reactions 26) ... 

In the present paper we will review principally the different methods of synthesis which proceed through a radical or ionic mechanism. Condensation reactions will only be considered when they unite preformed polymer molecules into a graft or a block copolymer. 

In addition to block copolymer synthesis by subsequent polymer growth along one polymer chain, Eq. (21), and the reaction sequence of Eqs. (19, 22—24), preformed polymer blocks can be linked via reactive end groups. Polynorbomene with one titanacyclobutane end group was reacted in a Wittig-type reaction with... 

Recently, highly efficient catalysts have been developed that are one component systems and contain a preformed alkylidene or metallacycle as the catalyst initiatorSome of these complexes have shown excellent utility in the synthesis of organic molecules and will be the major topic of Ae last part of this chapter. These complexes will not only change many of the approaches in simple alkene metathesis but will also have a major influence on the future applications in organic and polymer synthesis. 

It is worth repeating that one of the real advantages of preparing interfaces by simple adsorption of a preformed polymer is ease of fabrication. Another is chemical versatility which is limited only by the synthesis of new polymers. One recent synthetic development is reductive loss of Cl" followed by re-oxidation and pyridyl incorporation, all of which can be made to occur within a preformed electrode-polymer interface, as shown on the next page. The work is described in another paper in this volume (34). Another development is the preparation of an extended series of related PVP polymers based on Ru-bpy chemistry, -(py)Ru(bpy)2X2+... 

Reactive antioxidants may either be copolymerized with monomers during polymer synthesis or grafted on preformed polymers they are therefore linked to the polymer. Although the copolymerization route has been successfully exploited, " it has not received greater attention because of cost incurred in the synthesis and production of tailor-made speciality materials for low-volume specific applications. On the... 

This type of polymerization method has the potential to give more complex polymer structures with less defects than the normal practice of carrying out reactions on preformed polymers. Therefore we have continued with the synthesis and cyclopolymerization of new complex monomers. Most of the previously synthesized monomers were made by a one-step Mannich reaction using a diallylamine and either a phenol or an aromatic amine. This chapter describes the synthesis and attempted polymerization of a much wider variety of monomer structures. 

Chain transfer to a second polymer can be exploited as a possible avenue for block copolymer synthesis. The homopolymerization of a given monomer A in the presence of a preformed polymer B or the Interaction between two homopolymers in the presence of a cationic initiator (J, 153. 154) produce in the first step of the reaction block copolymers. Synthesis of other block copolymers was... 

The synthesis of comb-type polymers with randoni hydrophobe placement, via addition of the hydrophobes to the isocyanate functions of preformed polymer, is illustrated in Scheme III. This type of polymer geometry... 

This ch ter surveys the synthesis of functional polymers by direct anionic, cationic, free radical and coordination polymerization, as well as the bulk and surface modification of preformed polymer backbones. Moreover, an introduction to typical applications of functional polymers is presented. 

Synthesis by Adding Antimicrobial Agents to Preformed Polymers... 

The methods used for synthesis of ionic polymers can be divided mainly into three types (1) direct synthesis, (2) post-functionalization of a standard preformed polymer, and (3) post-functionalization of a special preformed polymer. 

Synthesis of Iron Oxide Nanoparticles in the Presence of Preformed Polymer Particles... 

All the studies detailed in the previous section rely on the use of preformed iron oxide nanoparticles, in the presence of which emulsion polymerization has been carried out. By contrast, this section focuses on the synthesis of iron oxide nanoparticles inside or onto the surface of preformed polymer particles. The studies using this strategy are by far less numerous and are detailed below. 

Another field of enzymatic polymer synthesis is the enzyme-catalyzed modification of preformed polymers by esterification or transesterification. Thereby, it is possible to either introduce functional side groups into an existing polymer with a stable backbone (no polyester) to synthesize functional homopolymers as well as random copolymers or to generate multiblock copolymers by enzymatic transesterification between two different homopolymers. 

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