Photochemically reactive polymers; the synthesis and photochemistry of amide polymers and model compounds containing metal–metal bonds and internal radical traps

Nieckarz, Gregory F.; Litty, John J.; Tyler, David R.

doi:10.1016/s0022-328x(97)00598-6

Cited by 19 publications

(13 citation statements)

References 27 publications

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“…urethanes and polyureas containing Mo 2 (CO) 6 (η-C 5 H 4 R) 2 units along the polymer backbone. [30][31][32][33][34][35][36] This flexible methodology employing functionalized cyclopentadienyl rings was utilized to prepare photochemically reactive polymers; in the solid state, light and oxygen combine to cleave the Mo-Mo linkage and destroy the polymer, affording a visible light photodegradable polymer. Replacement of the photoactive Mo 2 (CO) 6 (η-C 5 H 4 R) 2 group with photostable cluster units is a logical procedure.…”

Section: Introductionmentioning

confidence: 99%

“…Replacing the P- or N-ligands with substituted cyclopentadienyl ligands, which are significantly more strongly bound to clusters, is expected to remedy this problem. Tyler and co-workers have prepared polyamides, polyurethanes and polyureas containing Mo 2 (CO) 6 ( η -C 5 H 4 R) 2 units along the polymer backbone. − This flexible methodology employing functionalized cyclopentadienyl rings was utilized to prepare photochemically reactive polymers; in the solid state, light and oxygen combine to cleave the Mo−Mo linkage and destroy the polymer, affording a visible light photodegradable polymer. Replacement of the photoactive Mo 2 (CO) 6 ( η -C 5 H 4 R) 2 group with photostable cluster units is a logical procedure.…”

Section: Introductionmentioning

confidence: 99%

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Mixed-Metal Cluster Chemistry. 16. Syntheses of Oligourethanes Containing Clusters in the Backbone

2001

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Bis(hydroxyalkylcyclopentadienyl)-containing mixed molybdenum-iridium clusters Mo2Ir2-(CO)10{η-C5H4(CH2)xOH}2 [x ) 2 (1), 10] react with alkyl or aryl 1,ω-diisocyanates OCNRNCO [R ) (CH2)y (y ) 4, 6, 12), trans-1,4-cyclohexyl, or 4-C6H4CH2-4-C6H4] to form oligourethanes with transition metal clusters in the oligomer backbone. Characterization of the cluster-containing oligourethanes is aided by spectral comparison with model cluster diurethanes Mo2Ir2 6), 6, 12], trans-1,4-cyclohexyl] prepared from reaction between the cluster diol 1 and alkyl isocyanates HRNCO. The precursor diol cluster 1 and cluster diurethane 6 have been characterized by single-crystal X-ray diffraction studies. The extent of polymerization has been assessed by gel permeation chromatography, with little dependence on diisocyanate precursor linker R but strong dependence on alkylcyclopentadienyl linker length (CH 2)x, suggesting that the steric influence of the bulky dimolybdenum-diiridium cluster core and co-ligands is the most important factor governing extent of polymerization. Supporting this assessment, the considerably more sterically hindered precursor 2-butyn-1,4-diolsubstituted cluster Mo2Ir2{µ4-η 2 -C2(CH2OH)2}(CO)8(η-C5H5)2 fails to react to any significant extent with 1,6-diisocyanatohexane.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mixed-Metal Cluster Chemistry. 16. Syntheses of Oligourethanes Containing Clusters in the Backbone

2001

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“…[11][12][13] Iron centers are also frequently utilized as templates in supramolecular and dendrimer chemistry, 14 and often these systems exhibit multiple reversible redox transformations. Metal-containing polymers that fragment in response to light 15,16 or display heat-sensitive ligand dissociation 17 have also been reported.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Thermochromic Iron(II) Tris(bipyridine)-Centered Star-Shaped Polyoxazolines and Their Bipyridine-Centered Macroligand Counterparts

2000

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Iron tris(bipyridine) complexes [Fe{4,4′-bis(chloromethyl)-2,2′-bipyridine}3], 1a, and the corresponding iodide analogue generated in situ using NaI, 1b, were explored as initiators for the polymerization of a series of 2-R-2-oxazoline monomers (R ) ethyl, EtOX; methyl, MeOX; phenyl, PhOX; and undecyl, UnOX). The resulting labile core, red-violet Fe-centered star polymers fragment during molecular weight analysis by gel permeation chromatography (GPC). Thus, samples were subjected to chemical cleavage in aqueous K2CO3 to generate metal-free bipyridine-centered polyoxazolines, bpyPROX2. When combined with ferrous ammonium sulfate, these bpyPROX2 macroligands chelate to Fe(II), regenerating the [Fe(bipyridine)3] 2+ chromophores. Both preparative and analytical kinetics experiments generally produce polymers with reasonably narrow molecular weight distributions (∼1.1-1.5). Molecular weight vs % monomer conversion plots with either the iodide or chloride initiating system were nearly linear for all monomers ; however, only PEOX and PUOX products show good correlation with Mn(calcd) based on monomer/initiator loading. For most monomers, reactions with iodide initiators are faster than the chlorides, and linear first-order kinetics plots were observed. Polymerization of oxazolines with 4,4′bis(halomethyl)-2,2′-bipyridines produced polymers with very narrow molecular weight distributions but with molecular weights higher than targeted based on monomer loading. 1 H NMR data illustrates that termination with dipropylamine is efficient for EtOX polymerizations. Thermal analysis by DSC and TGA reveal few differences between Fe-centered stars and their bpy-centered PROX macroligand counterparts. Variable-temperature UV/vis data is provided for an Fe-centered PEOX thin film sample.

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“…All of the following manipulations were performed under nitrogen. Cyclopentadienylethylamine (CpCH2CH2NH2) was prepared as described in the literature 50 from the reaction of NaCp with 2 equiv of 2-bromoethylamine hydrobromide and purified by distillation under reduced pressure. A solution of CpCH2CH2NH2 (9.01 g, 82.6 mmol) in THF was prepared by degassing CpCH2CH2NH2 by one freeze-pump-thaw cycle and adding freshly distilled THF (100 mL).…”

Section: Methodsmentioning

confidence: 99%

Radical Cage Effects in the Photochemical Degradation of Polymers: In-Cage Trapping of Photochemically Generated Radical Cage Pairs in Polymer Model Compounds

et al. 1999

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This study explored the origins of the observation that the overall quantum yields for polymer photodegradation depend on the polymer chain length. The (CH3(CH2) n C(O)NHCH2CH2Cp)2Mo2(CO)6 (n = 3, 8, 13, 18) complexes (1 − 1 − 4 − 4) were synthesized and used as model complexes for the study. As is common for metal−metal bonded complexes of this type, irradiation of these molecules cleaved the metal−metal bonds and formed free radicals via the intermediate formation of a radical cage pair. Studies on previous model complexes showed that the quantum yields for degradation decreased as the chain length of the complex increased. The decrease in quantum efficiency was partially attributed to an increase in the radical cage effect as the chain length increased. Surprisingly, however, the overall quantum yields and cage effects for complexes 1 − 1 − 4 − 4 did not vary significantly with chain length. The similarity in the quantum yields and in the cage effects for these molecules is attributed to an internal trapping reaction of the metal radicals in the solvent cage by the H atom of the amide group. The resulting Mo···(H)−N agostic interaction forms a six-membered ring. The trapping reaction takes place by segmental rotation of the metal-containing end of the radical chain; the rate of this motion is independent of the chain length, and thus differences in the cage effects and the overall quantum yields will be diminished for the four molecules. The X-ray crystal structure of the (CH3(CH2)3C(O)NHCH2CH2Cp)2Mo2(CO)6 molecule is also reported.

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Photochemically reactive polymers; the synthesis and photochemistry of amide polymers and model compounds containing metal–metal bonds and internal radical traps

Cited by 19 publications

References 27 publications

Mixed-Metal Cluster Chemistry. 16. Syntheses of Oligourethanes Containing Clusters in the Backbone

Mixed-Metal Cluster Chemistry. 16. Syntheses of Oligourethanes Containing Clusters in the Backbone

Synthesis of Thermochromic Iron(II) Tris(bipyridine)-Centered Star-Shaped Polyoxazolines and Their Bipyridine-Centered Macroligand Counterparts

Radical Cage Effects in the Photochemical Degradation of Polymers: In-Cage Trapping of Photochemically Generated Radical Cage Pairs in Polymer Model Compounds

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