Vinyl monomers, living polymerization

Examples of vinyl monomers for addition polymerization include acrylates, methacrylates, vinyl ethers and styrene derivatives. Radical, ionic, and group-transfer polymerizations are possible according to polymerizabil-ity of the monomers. Living polymerization is difficult because mesogenic monomers often contain bonds such as benzoate ester, which are easily attacked by growing ends. Cyclic and condensation monomers are less... 

Organoaluminum porphyrins with axial alkyl groups (la, lb) are effective for the living polymerization of unsaturated monomers such as acrylates (20)- and methacrylates (21),-2 whereas chloride, alcoholate, phenolate and carbox-ylate complexes (Ic-f) are totally inert for the polymerization of these monomers. In contrast to the polymerization of polar vinyl monomers, controlled polymerization of nonpolar vinyl monomers such as styrene with aluminum porphyrins has been unsuccessful. 

Block copolymers have also been produced by the addition of vinyl monomers to occluded or long lived macroradicals. These "pseudo" living macroradicals are produced when vinyl monomers are polymerized in poor solvents (16-18) or in viscous medium (19). 

For carbon-based vinyl monomers, controlled polymerization has been traditionally achieved by ionic mechanisms [174]. The living anionic polymerizations of styrene and methyl methacrylate are quite common, resulting in preservation of the polymer functionality. However, alike the inorganic analogues the ionic polymerization mechanism is limited to a rather narrow class of monomers, under conditions of the most stringent purity. Therefore, the aim to develop a controlled free radical... 

VEs do not readily enter into copolymerization by simple cationic polymerization techniques instead, they can be mixed randomly or in blocks with the aid of living polymerization methods. This is on account of the differences in reactivity, resulting in significant rate differentials. Consequendy, reactivity ratios must be taken into account if random copolymers, instead of mixtures of homopolymers, are to be obtained by standard cationic polymeriza tion (50,51). Table 5 illustrates this situation for butyl vinyl ether (BVE) copolymerized with other VEs. The rate constants of polymerization (kp) can differ by one or two orders of magnitude, resulting in homopolymerization of each monomer or incorporation of the faster monomer, followed by the slower (assuming no chain transfer). 

To be eligible to living anionic polymerization a vinylic monomer should carry an electron attracting substituent to induce polarization of the unsaturation. But it should contain neither acidic hydrogen, nor strongly electrophilic function which could induce deactivation or side reactions. Typical examples of such monomers are p-aminostyrene, acrylic esters, chloroprene, hydroxyethyl methacrylate (HEMA), phenylacetylene, and many others. 

Vinyl copolymers contain mers from two or more vinyl monomers. Most common are random copolymers that are formed when the monomers polymerize simultaneously. They can be made by most polymerization mechanisms. Block copolymers are formed by reacting one monomer to completion and then replacing it with a different monomer that continues to add to the same polymer chain. The polymerization of a diblock copolymer stops at this point. Triblock and multiblock polymers continue the polymerization with additional monomer depletion and replenishment steps. The polymer chain must retain its ability to grow throughout the process. This is possible for a few polymerization mechanisms that give living polymers. 

As the first, and perhaps the most well-studied form of living polymerizations, anionic procedures have attracted considerable attention both academically and industrially [2, 3], While numerous examples of living procedures have been developed, they can be classified into two main families carbanionic polymerization of vinyl monomers and anionic ring opening polymerizations. 

A fluorous biphasic system has been used to reduce the metal contamination arising in the copper-catalysed living radical polymerization of vinyl monomers. 

Siloxane containing block or segmented copolymers can be synthesized either by living anionic polymerization of the cyclic organosiloxane trimers with appropriate vinyl monomer(, 4 ) or by step-growth or condensation copolymerization of preformed a,w-difunctional siloxane oligomers with conventional difunctional... 

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