Polymers, functionalized nucleophilic substitution with

Free radical chlorination of poly(phenylsilane) produces poly(chlorophenylsilane) These chlorinated polymers can be substituted with a variety of nucleophiles such as MeOH or MeMgBr with high selectivities. The spectroscopic properties of these materials are extremely sensitive to the nature of the substituent attached to the polymer backbone. The UV properties of a series of polysilanes containing Si-H, Si-Cl, Si-R and Si-OR functionalities are reported. The absorption maximum of poly(phenylsilane) appears at 294 ran (esi-si = 2489 cm-iM 0 whereas that of poly(methylphenylsilane) appears at 328 nm (esi-si = 4539 cm-iM-i). The absorption spectra of poly(metiioxyphenylsilane) are red shifted considerably relative to the other polymers (X = 348 nm, esi-si = 2710 cm- M-O. These substituent effects are likely due both to conformational as well as electronic perturbations on tfie Si-Si backbone chromophore. 

Polymers of high VDC content are reactive toward strong bases to yield elimination products and toward nucleophiles to yield substitution products. Agents capable of functioning as both a base and a nucleophile react with these polymers to generate a mixture of products (119,133,134). 

The nucleophilic substitution on poly(vinyl chloroformate) with phenol under phase transfer catalysis conditions has been studied. The 13c-NMR spectra of partly modified polymers have been examined in detail in the region of the tertiary carbon atoms of the main chain. The results have shown that the substitution reaction proceeds without degradation of the polymer and selectively with the chloroformate functions belonging to the different triads, isotactic sequences being the most reactive ones. 

Oxidation is the first step for producing molecules with a very wide range of functional groups because oxygenated compounds are precursors to many other products. For example, alcohols may be converted to ethers, esters, alkenes, and, via nucleophilic substitution, to halogenated or amine products. Ketones and aldehydes may be used in condensation reactions to form new C-C double bonds, epoxides may be ring opened to form diols and polymers, and, finally, carboxylic acids are routinely converted to esters, amides, acid chlorides and acid anhydrides. Oxidation reactions are some of the largest scale industrial processes in synthetic chemistry, and the production of alcohols, ketones, aldehydes, epoxides and carboxylic acids is performed on a mammoth scale. For example, world production of ethylene oxide is estimated at 58 million tonnes, 2 million tonnes of adipic acid are made, mainly as a precursor in the synthesis of nylons, and 8 million tonnes of terephthalic acid are produced each year, mainly for the production of polyethylene terephthalate) [1]. 

Grafting on the resin was achieved via a nucleophilic substitution of the benzylic chlorine by the deprotonated OH-linker of 52 (Scheme 29) by using a mixture of KO Bu, 18-crown-6 and CsBr. Determining the nitrogen content of solid phase samples by elemental analyses was accomplished, to verify the functionalization of the polymer. This enables calculation of the degree of functionalization. Usually, an occupancy of more than 20 percent of the theoretical sites was achieved. Saponification of the functionalized Merrifield resin P-52 leads to the monoanionic NJ, 0 functionalized solid phase. Subsequent reaction with [ReBrtCOlsJ afforded the polymer mounted tricarbonyl rhenium complex P-52-Re (Scheme 29). 

Soai et al. [62a] first reported the use of sihca gel or alumina as a heterogeneous support for chiral catalysts in the enantioselective addition of dialkylzincs to aldehydes. Chiral N-alkyhrorephedrines (R = Me, Et, n-Pr) were immobilized covalently on (3-chloropropyl)silyl-functionalized alumina or silica gel via a nucleophilic substitution. However, the catalytic activities and enantioselectivities were only moderate (24—59% ee) in comparison with those of homogeneous and polymer-... 

Spirocyclic [Ijferrocenophanes have also been shown to thermally polymerize and these species function as crosslinking agents that allow access to polyferrocenylsilanes with controlled crosslink densities [67]. Amber, solvent-swellable gels are available by this route (see Section 3.3.6.4). The [l]dichlorosilaferrocenophane 3.23 represents a very useful precursor to [Ijferrocenophanes 3.24 with alkoxy (or amino) substituents, and subsequent ROP allows access to, for example, polyferrocenylalkoxy-silanes 3.25 (Eq. 3.11) [68]. In addition, polymers with Si-H or Si-Cl groups have been prepared, and these provide opportunities for post-polymerization modification by hydrosilylation and nucleophilic substitution, respectively [66]. 

Analogous chemistry (i.e., end functionalization of polymeric organolithiums with l,l-bis(4-tert-butyldimethylsi-loxyphenyl)ethylene) has been utilized for preparation of dendrimacs, a new type of dendritic polymer wherein a key step in the iterative process utilizes the deprotected phenol end groups in polymers as nucleophiles for Williamson ether-type coupling reactions. Hirao and co-workers " have utilized di-monosaccharide-substituted DPEs to prepare well-defined polyisoprenes and polystyrenes labeled at the chain end with monosaccharide residues. 

Nucleophilic substitution of the halogen end group of ATRP-prepared polymers has also been used to synthesize phosphonium-functionalized polymers. ° Model studies of the reaction of triphenylphosphine and tri-n-butylphosphine with alkyl halides revealed that the tri-n-butylphosphine reacted 20 times faster than the triphenylphosphine (eqn [51]). PMMA-Br was reacted with tri-n-butylphosphine (10 molar excess) for 48 h at 30 °C. The resulting polymer was analyzed by MALDI-TOF MS and NMR. It was observed that the bromine end group was completely converted to the phosphonium end group. Similar results were observed for PSBr. 

The functionalization was found to be quantitative and selective formation of the 1,4-addition product (>99%) was obtained when using hexanes/MeCl 60 40 (v/v) at -80 °C and a TiCl4/2,6-di-t rt-butylpyridine initiator system. Quantitative functionalization was also observed with the Mei.sAlBri s initiator system. ° The resulting chloroallyl end-functionalized polymer has become a platform for a wide variety of end-functionalized PIBs, including macromonomers, via postpolymerization nucleophilic substitution at the chain end as shown in Scheme The allyl halide chain end... 

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