Thursday, January 1, 2015

Polymers with complex structures and built-in functionality A major advantage of ATRP is the fact t

Controlled free radical nacl polymerization - a world of new opportunities
A variety of commercially available plastics based on polymers made by free radical initiated polymerization. This process does not give good control of chain length and structure, since the growing polymer chains are constantly undergoing various non-controllable termination or transfer reactions. Wanted polymers with well-controlled chain lengths, and in particular chemical functionality nacl such. the chain ends or in well-defined nacl blocks, has so far been used anionic or cationic living polymerization techniques. The living polymerisationskoncept means that the polymeric structure can be extremely well controlled by well-defined, rapid initiation, propagation and termination without the conservation of the active, ionic chain end, when all the monomer has reacted. Subsequently, block copolymers can be prepared by the addition of a new monomer. Technically, it is very difficult, and only a very limited number of monomers can be used in this way.
Atom Transfer Radical Polymerization Within the last eight years a number of controlled free-radical techniques, however, have been developed. The main innovation is that they are usually unavoidable transfer and termination reactions occur by free radical polymerization, can be suppressed almost completely. The reason is that the growing chains in the vast majority of the polymerization process is in a quiescent state for only a moment to be activated to a polymer chain radical, adding one or more monomers and then return to the off state. For Atom Transfer Radical Polymerization nacl (ATRP) [1] of the styrene, this is illustrated in Figure 1. The reversible redox process in which polymer radicals formed, catalysed by a copper complex, which undergoes a one-electron oxidation, while the halogen (here bromide) at the same time is transferred from the the dormant polymer chain end. Deaktiveringshastighedskonstanten, kd, however, is 108 times greater than aktiveringskonstanten, ka, so the rest state is restored after a few monomeradditioner. Polymer Radical concentration during polymerization is very small, nacl so termination reactions occur only to a small extent, nacl as these are second-order terms. Polymer radical concentration. The technique is experimentally simple and can be conducted under bulk conditions or in solution. It usually demands only that the polymerization is carried out under oxygen-free conditions. ATRP has been successfully applied to a wide variety of vinyl monomers, for example substituted styrenes, acrylates nacl and methacrylates, acrylonitrile, (meth) acrylamides and (meth) acrylic acids.
Polymers with complex structures and built-in functionality A major advantage of ATRP is the fact that the chain ends of the activity is retained when the polymerization is stopped and the polymer was isolated. Block copolymers are prepared by using the isolated polymer as an initiator, so-called macroinitiator for the polymerization of a new monomer. This can be repeated and the number nacl of linear nacl block copolymers with blocks or block copolymers having long side chains regular, popularly referred to as polymer brushes, are prepared. Also very regular star-shaped or super branched polymers can be synthesized. Functionalized colloids, surface-treated fibers and modified nacl surfaces nacl has been generated by the same time to initiate polymerization of multiple activated sites on the respective objects. As monomers with very different structure, functionality and affinity nacl for example. water can sampolymeriseres in this way, the design of a variety of new polymer materials with very specific uses, inter alia, for medical nacl use notice. Special nacl chemical or physical functionality can be built through special monomers or initiator, which starts the growing polymer chain. Since a wide range of different functional groups, for example. of the initiator (for example, allyl, hydroxy, carboxylic acid, cyano), at the same time has been found not to inhibit the polymerization, the polymers of different chemical end group functionality are prepared. Further, the halogen nacl atom at the opposite nacl end of the polymer chain through simple reactions transformed quantitatively into other functional groups, for example. amino, hydroxy, or epoxy. Thus, it is also possible to produce a number of different, very well-controlled linear polymers of different chemical functionality in the two end groups.
Activities in the Danish Polymer Centre Around the World is controlled free radical polymerization, especially ATRP, now the fastest growing area in polymer chemistry. The Danish Polymer Centre at DTU has controlled free radical polymerization was a large and active research and education field since its inception in the mid 90s. Two current project concepts in design of new polymer materials using ATRP to illustrate the technique span and potential. Water-soluble polymers with pH and concentration dependent morphology Amphiphilic block copolymers containing both hydrophilic (good character

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