Functionalized polymers with initiator

An alternative to the direct use of peroxides in monomer grafting is to first functionalize the polymer with initiator or transfer agent functionality. 

Copolymers of styrene with 4-vinylpyridine (II) and N-viny1imizado1e (III) were obtained by copolymerization for one day at 60°C in 25 wt% comonomer solutions in toluene, using AIBN as initiator. In all cases the degrees of substitution, a, of the functionalized polymers with ligand groups were derived from the nitrogen contents found by elemental analyses. 

A class of end-functionalized polymers with polymerizable terminal groups are generally called macromonomers. By both functional initiator and terminator methods, a variety of macromonomers have been synthesized in living cationic polymerization of vinyl ethers, styrenes, and isobutene, as summarized in Table 3 [16,31,147,149-151,155,158-171]. Some of these macromonomers are used in the synthesis of graft polymers (Section VI.C). 

End-functionalized polymers with polymerizable groups such as double bonds and heterocycles of course provide macromonomers allyl, vinyl ester, vinyl ether, lactone, and epoxy are examples of such a category whose a-ends are not susceptible or have little susceptibility to metal-catalyzed radical polymerization. As discussed above, for example, allyl chloride and bromide (FI-33 and FI-34) are effective initiators to be used for styrene with CuCl and CuBr catalysts,161 while allyl compounds with remote halogens such as FI-35 and FI-36 allow the polymerization of methacrylates with high initiation effi-... 

The direct synthesis of block copoljmiers by radical polymerization is an alternative to using preformed blocks with functional endgroups. Polymers with initiator end-groups (3a,3b), with end groups accessible to radical activation polyinitiators (6, 7.)... 

The methodology of living anionic polymerization, especially alkyllithium-initiated polymerization, is very useful for the preparation of chain-end functionalized polymers with well-defined structures (9,10). Since these living polymerizations generate stable, anionic polymer chain ends (P Li ) when all of the monomer has been consumed, post-polymerization reactions with a variety of electrophilic species can be used to generate a diverse array of chain-end functional groups as shown in eq. 1,... 

The synthesis and dilnte and hulk solution properties of end-functionalized polymers with zwitterionic end groups have recently been reviewed (187). Reportedly, such polymers with different architectures (linear, block, and star copolymers) can be prepared by means of anionic polymerization. First, dimethylamine groups were introduced by using 3-dimethylaminopropyllithium as functional initiator. This group was then switched to sulfozwitterionic one by reaction with propanesultone. 

Synthetic strategies for the preparation of polymer brushes (A) physisorption, (B) grafting-to approach via reaction of appropriately end-functionalized polymers with complementary functional groups on the substrate surface, (C) grafting-from approach via surface-initiated polymerization. (Reprinted with permission from Barbey et al. 2009. Polymer Brushes via Surface-Initiated Controlled Radical Polymerization Synthesis, Characterization, Properties, and Applications. Chemical Reviews 109 (ll) 5437-5527 copyright (2009) American Chemical Society.)... 

Hexamethylolmelamine can further condense in the presence of an acid catalyst ether linkages can also form (see Urea Eormaldehyde ). A wide variety of resins can be obtained by careful selection of pH, reaction temperature, reactant ratio, amino monomer, and extent of condensation. Eiquid coating resins are prepared by reacting methanol or butanol with the initial methylolated products. These can be used to produce hard, solvent-resistant coatings by heating with a variety of hydroxy, carboxyl, and amide functional polymers to produce a cross-linked film. 

Sonochemistry is also proving to have important applications with polymeric materials. Substantial work has been accomplished in the sonochemical initiation of polymerisation and in the modification of polymers after synthesis (3,5). The use of sonolysis to create radicals which function as radical initiators has been well explored. Similarly the use of sonochemicaHy prepared radicals and other reactive species to modify the surface properties of polymers is being developed, particularly by G. Price. Other effects of ultrasound on long chain polymers tend to be mechanical cleavage, which produces relatively uniform size distributions of shorter chain lengths. 

Hydrosilation silicones or addition cure systems utilize a hydride functional crosslinker with a vinyl functional base polymer and a noble metal catalyst. While the cure can be initiated with UV [48,49], thermal cure versions dominate the commercial market [23,50]. In thermal cure systems, inhibitors are necessary for processing and anchorage additives are common. 

Cationic polymerization in hot melts has been applied to epoxidized polymers [38,39]. No hot melts based on vinyl ether or other cation-sensitive functionalized polymers have been described in the literature. With cationic systems, it is important that the other ingredients in the adhesive be of low basicity to avoid scavenging the initiating acid generated by the photoinitiator. 

The water solubilities of the functional comonomers are reasonably high since they are usually polar compounds. Therefore, the initiation in the water phase may be too rapid when the initiator or the comonomer concentration is high. In such a case, the particle growth stage cannot be suppressed by the diffusion capture mechanism and the solution or dispersion polymerization of the functional comonomer within water phase may accompany the emulsion copolymerization reaction. This leads to the formation of polymeric products in the form of particle, aggregate, or soluble polymer with different compositions and molecular weights. The yield for the incorporation of functional comonomer into the uniform polymeric particles may be low since some of the functional comonomer may polymerize by an undesired mechanism. 

A monomer is a reactive molecule that has at least one functional group (e.g. -OH, -COOH, -NH2, -C=C-). Monomers may add to themselves as in the case of ethylene or may react with other monomers having different functionalities. A monomer initiated or catalyzed with a specific catalyst polymerizes and forms a macromolecule—a polymer. For example, ethylene polymerized in presence of a coordination catalyst produces a linear homopolymer (linear polyethylene) ... 

Functional and end-functional polymers are precursors to block and graft copolymers and, in some cases, polymer networks. Copolymers with in-chain functionality may be simply prepared in copolymerizations by using a functional monomer. However, obtaining a desired distribution requires consideration of the chain statistics and, for low molecular weight polymers, the specificity of the initiation and termination processes, l hese issues are discussed in Section 7.5.6... 

End-functional polymers, including telechelic and other di-end functional polymers, can be produced by conventional radical polymerization with the aid of functional initiators (Section 7,5.1), chain transfer agents (Section 7.5.2), monomers (Section 7.5.4) or inhibitors (Section 7.5.5). Recent advances in our understanding of radical polymerization offer greater control of these reactions and hence of the polymer functionality. Reviews on the synthesis of end-functional polymers include those by Colombani,188 Tezuka,1 9 Ebdon,190 Boutevin,191 Heitz,180 Nguyen and Marechal,192 Brosse et al.rm and French.194... 

Predominantly di-end-functional polymers may be prepared by conducting polymerizations with high concentrations of a functional initiator. Some of the first commercial products of this class, carboxy and hydroxy-terminated polybutadienes, were produced by this route.194... 

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