Polymers with pendant azide

Macromolecules with carbodiimide linkages in their repeat units are obtained from aliphatic and aromatic diisocyanates using a phospholene oxide catalyst. However, instead of linear polymers, only crossUnked thermosets are obtained in this manner. In contrast, linear polymers with pendant carbodiimide units are obtained from poly(vinyl azide) by subsequent reaction with triphenylphosphine to formpoly(phosphine imines) followed by reaction with monoisocyanates to generate the Unear poly(carbodiimides). 

The aza-Wittig reaction is also used to form polymers with pendant carbodiimide groups. For example, reaction of the polymeric azide 31 with benzyl isothiocyanate and triphenylphosphine gives the corresponding carbodiimide 32, a precursor for oligomeric guanidines." ... 

Finally, Lecomte and coworkers reported the synthesis of mikto-arm star-shaped aliphatic polyesters by implementing a strategy based on click chemistry (Fig. 36) [162]. Firstly, the polymerization of sCL was initiated by a diol bearing an alkyne function. The chain-ends were protected from any further undesired reaction by the esterification reaction with acetyl chloride. The alkyne was then reacted with 3-azidopropan-l-ol. The hydroxyl function located at the middle of the chain was then used to initiate the ROP of sCL and y-bromo-s-caprolactone. Finally, pendant bromides were reacted successfully with sodium azide and then with N, N-dimethylprop-2-yn-l-amine to obtain pendant amines. Under acidic conditions, pendant amines were protonated and the polymer turned out to exhibit amphiphilic properties. 

The preparations and properties of many polymers containing pendant aryl azide groups were described by Delzenne and London. There were attempts made to combine azide groups with cinnamoyl groups in one pendant substituent on polymers" ... 

Figure 12.8 Schematic representation of (a) step-growth coupling of bivalent azide and bivalent acetylene telechelic polymers (b) polymer modi cation by CuAAC of pendant alkyne groups of polymers, e.g., poly(vinyl acetylene), with an azide-bearing substrate and (c) functionalization of polymer by CuAAC of pendant azide with alkyne-bearing functional moiety. Azide terminated dendrimers are similarly subjected to CuAAC with alkyne-derivatized functional moieties to achieve desired functionalization of dendritic macromolecules.

A copolymer bearing proline and permethylated p-CD was used as catalyst in aldol condensation [23]. The linear copolymer bearing both pendant permethylated p-CD and proline groups was designed on the basis that the hydrophobic cavity of the CDs could approach the substrates close to the proline that acted as catalyst through host-guest interactions. The synthesis of the CD monomer was carried out by a copper-catalyzed azide-alkyne cycloaddition. The CD monomer was then polymerized with a protected hydroxyproline methacrylate to give the linear polymer with a monomer ratio proline/CD of 4.The Me-p-CD-Pro polymer was subsequently obtained after acid deprotection of proline (Scheme 2.9). 

SCHEME 8.4 Schematic illustration of the processes involved in the graft copolymerization of DMAEMA from PVDF main chains via AGET-ATRP, preparation of PVDF-g-PDMAEMA membrane by phase inversion, and quaternization of PVDF-g-PDMAEMA membrane by propargyl bromide to produce PVDF-g-PQDMAEMA membrane with pendant aUcyne groups, covalent immobilization of hyperbranched polymer HPG-Nj or PEI-Nj onto the PVDF-g-PQDMAEMA membrane surface via surface alkyne-azide click reaction. PVDF, poly(vinylidene fluoride) DMAEMA, 2-(V, V-dimethylamino)ethyl methacrylate VC = L-ascorbic acid PMDETA = V,V,M,V, A"-pentamethyl diethylene triamine HPG-N3 = az/hyperbranched polyglycerols PEI-N3 = azirfo-polyethylenimine. Reprinted with permission from Reference 114. Copyright 2013 American Chemical Society. 

Other methods for modifying polymers with carbohydrates via the postpolymerization technique include the photo-grafting of poly(ethylene terephthal-ate) (PET) fibers with glycosyl azides [218] and the use of carbohydrates bearing isocyanate [219] or aldehyde [220] groups, which react efficiently with polymers bearing pendant amino residues. 

Several studies have demonstrated the successful incoriDoration of [60]fullerene into polymeric stmctures by following two general concepts (i) in-chain addition, so called pearl necklace type polymers or (ii) on-chain addition pendant polymers. Pendant copolymers emerge predominantly from the controlled mono- and multiple functionalization of the fullerene core with different amine-, azide-, ethylene propylene terjDolymer, polystyrene, poly(oxyethylene) and poly(oxypropylene) precursors [63,64,65,66,62 and 66]. On the other hand, (-CggPd-) polymers of the pearl necklace type were fonned via the periodic linkage of [60]fullerene and Pd monomer units after their initial reaction with thep-xy y ene diradical [69,70 and 71]. 

Tsarevsky has found that hypervalent iodine compounds can be used for the direct azidation of polystyrene and consecutive click-type functionalization [49]. In particular, polystyrene can be directly azidated in 1,2-dichloroethane or chlorobenzene using a combination of trimethylsilyl azide and (diacetoxyiodo)benzene. 2D NMR HMBC spectra indicate that the azido groups are attached to the polymer backbone and also possibly to the aryl pendant groups. Approximately one in every 11 styrene units can be modified by using a ratio of PhI(OAc)2 to trimethylsilyl azide to styrene units of 1 2.1 1 at 0 °C for 4 h followed by heating to 50 °C for 2 h in chlorobenzene. The azidated polymers have been further used as backbone precursors in the synthesis of polymeric brushes with hydrophilic side chains via a copper-catalyzed click reaction with poly(ethylene oxide) monomethyl ether 4-pentynoate [49],... 

Tunca et al. [27, 28,38] reported in a series of papers on a multi-click approach for the preparation of brush copolymers. The backbone consisted of homopolymers, statistical polymers, or block copolymers from ONBEs with orthogonal side groups for Diels-Alder click reaction [27,28,38], azide/alkyne click reaction, [27, 28, 38] and nitroxide coupling [27]. In a grafting-to approach, maleimide-or ONBE-functionalized polymers (PEG, P BA, PMMA (56)) were attached by Diels-Alder click reaction with the anthracene groups pendant at the polymer backbone (55) (Scheme 9.8b). PCL chains were attached by an azide/alkyne click reaction, while a combination of Diels-Alder and azide/alkyne click reaction allowed the synthesis of graft copolymers with PS-/ -PEG-, PS-h-PMMA-, or PS-/ -P BA side chains. 

The azide-alkyne click reactions are useful to attach a number of polar FGs including various azobenzene moieties to the pendants of poly(l-phenyl-5-chloro-l-pentyne), (Eq. (7)) [90]. Nucleophilic substitutions of the same starting polymer result in the formation of an imidazole-functionalized, disubstituted acetylene polymer, (Eq. (8)) [91]. The degree of incorporation of the imidazole moiety is about 65%, and the product polymer exhibits good solubility in ethanol. Hydrolysis reaction of poly[l-(/w-methoxycarbonylphenyl)-l-octyne] yields a carboxy-functionalized disubstituted acetylene polymer poly[l-(/w-carboxyphenyl)-l-octyne], (Eq. 9) [92]. Hydrazine-catalyzed deprotection of poly[l-phenyl-ll-Af-benzimide-l-undecyne] affords the corresponding polyamine, which can be further ionized with hydrobromic acid to give a polyelectrolyte ammonium salt, (Eq. (10)) [93]. 

There are also reports that mixing of DNA with polymers leads to formation of hydrogel by crossUnking. When photo-crosslinkable polyvinyl alcohol (azide-unit pendant water-soluble photopolymer AWP) was mixed with DNA and the resulting mixture irradiated with ultraviolet light, a hydrogel film was formed, due to photo-crosslinking of DNA and AWP, that shows expansion and contraction in response to the media in which it is soaked. It expands in pure water whereas it... 

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