Friday, January 2, 2015

Polymer chemists are constantly offered new and effective tools available. Within the last two deca

"Click" in polymers 1
Polymer chemists are constantly offered new and effective tools available. Within the last two decades, the controlled radical polymerization "atom transfer radical polymerization" (ATRP) and "reversible addition fragmentation transfer" (RAFT) achieved widespread use. During the last decade, we have also been able to exploit the efficient and robust "click" reactions in the work to produce new polymers in ways that were not possible before. This describes the how.
What is "click" "click" chemistry is a common name for a number of effective, irreversible coupling reactions caused sulfide by reactants with favorable thermodynamic driving forces. The original, now classic "click" reaction sulfide is based on Huisgens almost 50 year old high temperature (> 250oC) 1,3-cycloaddition between azide and alkyne [1]. Here we can hoist the Dannebrog, since we believe that it was a contribution by Meldal and Tornøe from Carlsberg Laboratory [2], who were the first in 2001 showed that Cu (I) catalysis at low temperature has almost "miraculous" influence the cycloaddition. Meldals [3] and Sharpless' [4] groups cemented in 2002, that Cu (I) capable of catalyzing the reaction at room temperature to a stereo specific product (1,4-disubstituted-1,2,3-triazole) in very high yields (Figure 1), which we will subsequently designate CuAAC by Sharpless. A number of other reactions have subsequently received the predicate "click" [5]. The most commonly used, thiol-ene reactions are illustrated in Figure 2.
"Click" in polymers Polymer chemists were quick to spot the potential. They took advantage of the new opportunities of macromolecular carpentry for producing such. block copolymers [6-9], dendrimers [10] and not least biopolymer [11,12]. The possibilities are almost legion, but here we concentrate on our use of "click" chemistry to produce a range of very different, new functional polymer materials. When designing polymers with chemical functionality, we can in principle use two different methods. We can polymerize functional monomer, or we can post derivatise template polymers. An illustrative and particularly useful example of the latter is poly (hydroxystyrene) (PHS). When the template polymer often preferred over direct polymerization of functional monomers is due to two main factors. In the first place the desired functionality may not be a monomer that can be polymerized in a controlled manner. Second, the polymer characteristics including molecular weights and molecular weight distributions are difficult to reproduce, whereas a template polymer will not alter the polymer characteristics reaches the next derivatisation takes place optimally. PHS is an interesting precursor polymer for the manufacture of functional polystyrenes as phenolfunktionen invites to the classic Williamson ether synthesis. Unfortunately, there hydroxystyrene not as monomer why a protected form, for example. tert butoxystyren may be used, which after polymerization can easily be deprotected. We have prepared copolymers with polystyrene (PS) and PHS both as random copolymers sulfide by conventional radical polymerization, [13], or as block copolymers by living anionic polymerization. As copolymerisationsforholdene sulfide is favorable, we can also predetermine the relationship between the building blocks of the statistical PS-state-PHS. sulfide Hydroxystyrene function sulfide can now be easily converted for example. propargyl-one function by Williamson's synthesis of propargyl bromide (PS-state-PAS), as illustrated in Figure 3 [13,14]. This is subsequently used CuAAC to "clicking" a number sulfide of mono- and divalent aliphatic as well as aromatic sulfide carboxylic acids with azide functionality of the PS backbone [13,14] in order to produce highly karboxylsyreholdige and water-insoluble polymeric materials for micro-osmotic pumps .
Electrolyte membranes for fuel cells polymer electrolyte membranes (PEM) for low temperature fuel cells using hydrogen or methanol as a propellant, is challenging materials. The industry standard is a perfluorinated sulphonic acid polyether eg., Nafion, which only operates in highly hydrated state. Furthermore falls proton conductivity significantly by operations over 90oC, where an actual degradation of the polyether begins. In our attempts sulfide to develop new PEM materials we have used "click" chemistry to link sulfonic acid groups on the PS state-PAS [15]. Here, the short azidterminerede sulfonic acid salts or carbamates clicked on the PS state-PAS for the preparation of sulfonic acid and base-containing copolymers (Figure 4). It should be noted that equivalent materials may be prepared by conventional Williamson ether synthesis, of course, with other precursor few. As the film-forming properties of these stoichiometric acid-base balanced copolymerpar are not optimal, it seems that route is not viable [15]. Far more promising is a new concept where the proton wire is based on phosphorous acid, which by

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