Routes to Functionalized Polymers

Click to monomer, then polymerize triazole functionality 

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Iraqi A, Seth S, Vincent C A et al. (1992) Catalytic hydrosilylation of polybutadienes as a route to functional polymers. J Mater Chem 2 1057-1064... 

The advent of late transition metal catalysts for polymerization promises to expand this method as a route to functional polymers. Late transition metals are definitely more tolerant to functionality. The outstanding question is will they have enough activity for traditional non ctional monomers, such as ethylene or propylene. A catalyst that can polymerize both olefins and polars with high activity will be the next breakthrough. 

Chemical reactions on polymers as a synthetic route to new polymers and functionalized polymeric materials... 

Much effort has been invested to use oxazolones as intermediates for the synthesis of polymers. Probably the most important group of oxazolones used for this purpose is the 2-alkenyl-4,4-disubstituted-5(4//)-oxazolones. The reactivity of the exocyclic double bond at C-2 can be exploited to prepare new functionalized oxazolones as well as for copolymerization with other monomers. This possibility, together with the facile ring opening with nucleophiles, has opened very interesting routes to new polymers of industrial interest. 

A special case of controlled initiation is the inifer method. The word inifer (front initiator transfer agentsl describes compounds that function simultaneously as initiators and as chain transfer agents. The inifer technique provided the first carbocationic route toward the synthesis of telechelic ta. to functional) polymers. 

Fig. 7.19 Stepwise and orthogonal routes to functionalization of the universal polymer backbone using DAP-thiamine and pincer-...

The V(acac)3-mediated hompolymerization of ethylene is not living and the polydisper-sity index is quite high (2.0). Nevertheless, ethylene can be successfully copolymerized with propylene while maintaining the livingness of the process. Moreover, the enolate ligated vanadium is a catalyst for the living polymerization of 1,5-hexadiene and copolymerization with propylene. It must be noted that polymerization of 1,5-hexadiene is a route to a polymer that combines constitutive 1,3-cyclopentylenemethylene units (2 ) and vinyltetramethylene units. Therefore, pendant unsaturations are available for further functionalization. 

In order to achieve this goal a synthetic route to functionalized lc polymers was developed (13) (see Scheme II and Table II). Due to the much higher reactivity of hydroxyl groups compared to phenolic groups, it is possible to prepare linear polymers of the structure presented in Scheme II. 

Alditols polyols are readily renewable, inexpensive and harmless to the environment. By incorporation of polyols into aliphatic polyesters, functional linear or hyperbranched polymers can be prepared with specific biological activities and/or that respond to environmental stimuli. Polyesters with carbohydrate or polyol repeat units in chains have been prepared by chemical methods. " In some cases, the reaction conditions led to hyperbranched polymers (HBPs). The highly branched architecture of HBPs leads to unusual mechanical, rheological and compatibility properties. " These distinguishing characteristics have garnered interest for their use in numerous industrial and biomedical fields. Chemical routes to linear polyol-polyesters require elaborate protection-deprotection steps ". Furthermore, condensation routes to hyperbranched polymers generally require harsh reaction conditions such as temperatures above 150 C and highly acidic catalysts ". ... 

The power of column-like reactors for continuous flow processes lies in the possibility to sequentially link them up in order to carry out multistep syntheses in solution in one run (see also Schemes 1 and 2). Lectka and coworkers utilized conventional fritted and jacketed columns for this purpose. These columns were filled with conventional functionalized polymeric beads [47]. The continuous flow was forced by gravity. En route to / -lactams polymer beads functionalized with the Schwesinger base 17, a cinchona alkaloid derivative 18 as a chiral catalyst, and a primary amine 19 were sequentially employed. They first guaranteed the generation of phenyl ketene from phenyl... 

The development of novel titanium carbene complexes by Grubbs has opened up a route to living polymer systems, using coordinating polymerizations as opposed to those derived from ionic initiators, which can be used to form block copolymers or produce chains with a functionalized end group. The initiating species are formed by the reaction of norbomene with a titanocyclobutane derived from 3,3-dimethyl cycloprene... 

FIGURE 7.3 Schematic illustration showing how functional molecules can induce a self-assembly route to conducting polymer nanostructures. 

Synthesis problems remain, however, in providing the complete range of potentially useful polymer substituents and functional groups. One approach to this lies in the development of alternative routes to the polymers. A recent report describes a condensation-polymerization route in which alkyl substituents and, in some circumstances, mixed alkyl substituents can be introduced. 

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