Polymer reaction block copolymer

Another consequence of living polymerization systems is that they can be used to synthesize block copolymers. Under these conditions, once the initial quantity of monomer in a given reaction is consumed, the resultant polymer chains are terminated with metal carbene end groups that are still active for aUcene metathesis. As long as these carbenes do not react rapidly with the acyclic aUcenes in the polymer chain, addition of a second monomer will result in the synthesis of a block copolymer. This reaction is illustrated in equation (13) for the synthesis of a polymer that consists of block of x repeat units of monomer A followed by a block of y repeat units of monomer B. 

One of the most important uses of end-functionalized polymers is the preparation of block copolymers. ° The reactions are identical to the chain extensions already mentioned, except that the sequences being joined are chemically different. In the case of the—OSiR R Y chain end R is typically and Y can be NH, OH, COOH, CH = CH, and so on. 

Yang B, Zhao Y, Fu C, Zhu C, Zhang Y, Wang S, Wei Y, Tao L (2014) Introducing the Ugi reaction into polymer chemistry as a green click reaction to prepare middle-functional block copolymers. Polym Chem 5(8) 2704-2708... 

When traditional sequential monomer addition is employed in the preparation of star-block copolymers, the reaction is usually stopped before complete conversion of the first monomer to circumvent excessive terminations. The A block is usually isolated by precipitation, and used as macroinitiator for the polymerization of monomer B. If the second monomer is added before complete conversion of the first monomer, a gradient copolymer is formed with characteristics similar to those of the block [156]. The synthesis of gradient copolymers simplifies the process with some loss of control over the polymer structure. 

It has been shown that transformation reactions could be carried out on anionic living polymers to generate polymeric cations which were then able to propagate with a second monomer to form block copolymers. These reactions involved the formation of an intermediate bromide, by reaction either with excess bromine... 

In addition to being used for block copolymers, the reaction of Mn2(CO)io with halogen groups attached to polymer backbones has been utilized for the synthesis of graft copolymers [268-273]. A drawback of this method is that in many cases, combination of macroradicals is observed giving rise to cross-linking rather than grafting. Network formation versus... 

Amide interchange reactions of the type represented by reaction 3 in Table 5.4 are known to occur more slowly than direct amidation nevertheless, reactions between high and low molecular weight polyamides result in a polymer of intermediate molecular weight. The polymer is initially a block copolymer of the two starting materials, but randomization is eventually produced. 

Polymerization of methacrylates is also possible via what is known as group-transfer polymerization. Although only limited commercial use has been made of this technique, it does provide a route to block copolymers that is not available from ordinary free-radical polymerizations. In a prototypical group-transfer polymerization the fluoride-ion-catalyzed reaction of a methacrylate (or acrylate) in the presence of a silyl ketene acetal gives a high molecular weight polymer (45—50). 

Copolymers. There are two forms of copolymers, block and random. A nylon block copolymer can be made by combining two or more homopolymers in the melt, by reaction of a preformed polymer with diacid or diamine monomer by reaction of a complex molecule, eg, a bisoxazolone, with a diamine to produce a wide range of multiple amide sequences along the chain and by reaction of a diisocyanate and a dicarboxybc acid (193). In all routes, the composition of the melt is a function of temperature and more so of time. Two homopolyamides in a moisture-equiUbrated molten state undergo amide interchange where amine ends react with the amide groups. 

Phenolic Resins. At elevated temperatures, phenoHc resins are cured with polysulfide resins through a condensation reaction. The product may be considered a block copolymer of the rigid phenoHc resin and the flexible polysulfide. Thus, the polysulfide acts to flexibiHze the resulting polymer. 

R. P. Quirk, D. J. Kiniiing, and L. J. Fetters, in G. AHen, ed.. Block Copolymers, in Comprehensive Polymer Science The Synthesis, Characterisation, Reactions... 

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