Post-polymerization addition method

Currently, graft post-polymerization of monomers in the gaseous phase (2) is the more widely used process because it has at least two basic advantages. First, side processes of homopolymerization are minimized which reduces the consumption of monomers and makes unnecessary additional treatment of the modified materials with solvents. Second, this method is universal and allows the grafting to the surfaces (such as silica) to be carried out with low radiation yields of active sites as compared to the monomers. 

Post-polymerization functionalization has also been applied to the synthesis of terpyridine-modified polymers [ 126]. In a recent approach, Schubert and colleagues employed this method to prepare poly(pentafluorostyrene) with terpyridines in the side chains [127]. First, poly(pentafluorostyrene) with a narrow polydispersity index of just 1.08 was synthesized by nitroxide-mediated polymerization. In a second step, this polymer was converted with amine-functionalized terpyridine under microwave heating, selectively substituting the para-fluorines. Addition of iron(II) sulfate to a solution of the terpyridine-functionalized polymer in a mixture of chloroform and methanol leads to gelation at a polymer concentration of 33 g In another work, Schubert and coworkers prepared metal-cross-Iinked polymer networks from linear and tri-arm PEG precursors, both functionalized with terpyridine at their OH-termini [128]. Quantitative functionalization of these precursors was achieved by conversion of the hydroxy-functionalized PEG derivatives with 4-chloro-2,2 6, 2"-terpyridine under basic conditions. However, quantitative cross-linking with iron(II) chloride was not observed in methanol solutions, neither at room temperature nor at elevated temperature, but only a small quantity of cross-linked material precipitated from the solution. This observation was attributed to a strong tendency of the tri-arm PEG to form intramolecular complexes, acting as a chain stopper rather than as a cross-linker. 

The first method, which provides quantitative and reliable information on the extent of cure, is a time-consuming technique. In addition, there is certain error included in the measurement owing to the post-polymerization reaction, which occurs during the lapse of time between the end of exposure and the measurements... 

The properties of polymers are determined by the nature and composition of the structural units, as well as the molecular architecture. Polymers are most often made from the corresponding monomers. In comparison with developing new monomers and polymerization methods, a less expensive route to tailor-making of polymers is through blending, copolymerization, architecture control during polymerization, post-polymerization chemical modification, and additives. Detailed discussions on such possibilities are available in several reviews [37-42]. Here we will briefly highlight two recent developments in the areas of block copolymers and polymeric nanocomposites. 

Hydrophobically modified hydroxyethyl cellulose (HEC) has also been synthesized by post-polymerization reaction. HEC is reacted with low levels of certain reactive hydrophobes e.g. long chain alkyl epoxides, alkyl halides, acyl halides, isocyanates or anhydrides [1, 2, 25]. (Scheme 1.1 [3]). To handle the incompatibility of the hydrophobic reagent and hydrophilic polymer, the reaction is run in solution with a common solvent or in slurry ipedia. Slurry methods are preferred because of their lower reactor viscosities. A typical slurry process involves swelling HEC with isopropanol, adding NaOH in H2O, followed by addition of a long chain epoxide such as 1,2-epoxydecane, 1,2-epoxydodecane. 

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