Polymers with pendant alkyne

While a large majority of the photoerosslinkable polymers that were investigated over the years erosslink by free-radieal meehanism, utilization of ionie meehanism has reeeived some attention. This ineludes polymers with pendant eyelie ethers and alkyne groups. 

Employing a molar excess of the alkyne over the active hydrogen of only 12 percent the selectivity (determined by proton NMR after work-up) may be expressed as the ratio of Si-C=CH- to Si-CH2-CH2-CO-, which is about 100 1 [16]. The same reaction, carried out with silicone polymers with 10 or more pendant silicon-bonded hydrogen atoms, proceeds similarly cleanly without noticeable crosslinking by acrylic hydrosilylation. A slight excess of triple bond over Si-H groups is mandatory to suppress this side reaction as well as hydrosilylation of the olefinic group of the 2-silylalkene isomer product (see Table 2.). 

Combining two different hydrosilylation catalysts in sequence with chlorodimethylsilane has allowed the construction of complex dye assemblies and conducting polymers. In the example shown (Scheme 8), Karstedt s catalyst was chosen after a brief screen for the hydrosilylation of an aromatic diyne with chlorodimethylsilane. After reduction of the chlorosilane, an equimolar mixture of disilane B and diyne A was treated with a catalytic amount of Wilkinson s catalyst, resulting in the formation of polymer C.42 Hydrosilylation of alkynes has also been studied as a means of synthesizing oligo(phenylenevinylene) units with pendant alkoxysilanes to create curable, hole-transporting films.43,43 ... 

Another example of self-assembly of porphyrin-containing polymer was illustrated by Li et al.73 Polyacetylene functionalized with fullerene and zinc porphyrin pendant groups were synthesized by polymerizing the corresponding fullerene/porphyrin substituted alkyne monomers with rhodium(I) norbomadiene catalyst (Scheme 5.5).74 Polymers with different ratio of C60 and porphyrin were synthesized. The polymers showed photocurrent response when the thin films were irradiated with white light, which was due to the electron transfer from the photo-excited porphyrin to the C60 units. In addition, the copolymers aggregated into ellipse-shaped nanorod structures with a diameter of approximately 100 nm and a length of... 

Nurmi et have attached a functional thiol by Michael addition TEC at a polymer chain end, followed by CuAAC reaction of the pendant alkynes from the monomer units, further demonstrating orthogonality between CuAAC and TEC. Yu etal have synthesized alkene- and alkyne-terminated PNIPAAm for reaction by thiol-ene, or the closely related thiol-yne, chemistry. These polymers were then functionalized with commercially available thiols, and NMR spectroscopy showed complete consumption of the allyl or propargyl protons with concomitant appearance of unique resonances for the added thiols. Integration of these peaks demonstrated that thiol-yne chemistry provided full double functionalization, while thiol-ene provided full stoichiometric conversion. 

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. 

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. 

Other functional groups that can be used to form photocrosslinkable polymers are alkyne, male-imides, stilbene, styrene, 1,2,3-thiadiazole, thymine, and anthracene. Pendant groups with anthracene moiety, however, are believed to crosslink by a 47t + An type of cycloaddition ... 

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]. 

Finally, Fukase and coworkers have used the Sonogashira reaction to anchor glycoside moieties with a pendant acetylenic side chain to polymer-bound aryl iodides, forming a novel alkyne linker system [100]. 

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