The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Steven K. Pollack - One of the best experts on this subject based on the ideXlab platform.
-
The structure and attempted topochemical polymerization of single crystalline 1,1,4,4-bis(pentamethylene)-1,2,3-Butatriene
Journal of Chemical Crystallography, 1999Co-Authors: Robert E. Bachman, Ashebir Fiseha, Steven K. PollackAbstract:The photo-initiated solid-state topochemical polymerization of 1,1,4,4-bis(pentamethylene)-1,2,3-Butatriene ( 1 ) was attempted unsuccessfully. Since 1 readily polymerizes in the liquid state, a structural study was undertaken to better understand its inertness in the solid-state. 1 crystallizes in the monoclinic space group P 2_1/ n with a = 6.4597(6), b = 10.8914 (10), c = 8.4396(8) Å, β = 100.168(2)°, V = 584.44(9) Å^3, and Z = 2. The crystal structure reveals that while the alignment of the π-systems in the solid-state is acceptable for supporting the targeted polymerization reaction, the reaction centers are located too far apart to allow the reaction to take place. Additionally, comparison of the molecular structure of 1 with the limited number of other structurally characterized Butatrienes has provided insight into the steric and electronic influences played by the substituents attached to the cumulene moiety.
-
singlet triplet gap in 1 2 3 Butatriene and its consequences on the mechanism of its spontaneous polymerization
Journal of Physical Chemistry B, 1998Co-Authors: Vernon R Morris, Steven K. PollackAbstract:The reactivity of 1,2,3 Butatriene, C4H4, has been postulated to be due to the presence of low-lying triplet states. However, there have been no experimental or theoretical determinations of the energy separations or geometries of these states. We have examined the structures, energetics, and possible mechanisms involved in the self-polymerization of the title compound using single-determinant ab initio molecular orbital theory. We find that the magnitude of the singlet−triplet gap for the monomer and its relatively high positive heat of formation does not allow for a mechanism involving the direct formation of an isolated triplet species. We speculate on an alternative mechanism and show its relationship to recent work on related reactive monomers.
-
Butatriene based polymer chemistry 2 synthesis and characterization of poly 1 1 4 4 bis pentamethylene 1 2 3 Butatriene 1
Macromolecules, 1997Co-Authors: Steven K. Pollack, Ashebir Fiseha, Babu NarayanswamyAbstract:The cumulene 1,1,4,4-bis(pentamethylene)Butatriene has been shown to undergo a thermally induced 1,4 free-radical polymerization to yield a crystalline polymer with a unique nonconjugated acetylene containing backbone. This polymerization occurs in both the melt and in solution. Typical free-radical inhibitors prevent the thermally induced polymerization. The reaction occurs in the presence or absence of free-radical initiators. The polymer is crystalline with a triclinic unit cell (a = 9.87 A, b = 6.10 A, c = 4.97 A, α = 113.7°, β = 85.2°, γ = 100.6°). No melting or glass transition is observed via differential calorimetry, but an irreversible exothermic transition is observed from both solution and melt polymerized material. This is interpreted as a cold crystallization process. Trapping of the polymerizing monomer with TEMPO leads to soluble oligomers.
-
free radical polymerization of bis pentamethylene Butatriene a novel monomer for the preparation of poly 2 butyne 1 4 diyl s
Macromolecules, 1993Co-Authors: Steven K. Pollack, Babu Narayanswamy, Roger S Macomber, Daniel E Rardon, Ioannis Constantine ConstantinidesAbstract:Free radical or thermal polymerization of bis(pentamethylene)Butatriene yields a polymer with the postulated structure [C(C 5 H 10 )-C≡C-C(C 5 H 10 )] n . Copolymerization of BPB with maleic anhydride yields the soluble corresponding alternating copolymer
Babu Narayanswamy - One of the best experts on this subject based on the ideXlab platform.
-
Butatriene based polymer chemistry 2 synthesis and characterization of poly 1 1 4 4 bis pentamethylene 1 2 3 Butatriene 1
Macromolecules, 1997Co-Authors: Steven K. Pollack, Ashebir Fiseha, Babu NarayanswamyAbstract:The cumulene 1,1,4,4-bis(pentamethylene)Butatriene has been shown to undergo a thermally induced 1,4 free-radical polymerization to yield a crystalline polymer with a unique nonconjugated acetylene containing backbone. This polymerization occurs in both the melt and in solution. Typical free-radical inhibitors prevent the thermally induced polymerization. The reaction occurs in the presence or absence of free-radical initiators. The polymer is crystalline with a triclinic unit cell (a = 9.87 A, b = 6.10 A, c = 4.97 A, α = 113.7°, β = 85.2°, γ = 100.6°). No melting or glass transition is observed via differential calorimetry, but an irreversible exothermic transition is observed from both solution and melt polymerized material. This is interpreted as a cold crystallization process. Trapping of the polymerizing monomer with TEMPO leads to soluble oligomers.
-
free radical polymerization of bis pentamethylene Butatriene a novel monomer for the preparation of poly 2 butyne 1 4 diyl s
Macromolecules, 1993Co-Authors: Steven K. Pollack, Babu Narayanswamy, Roger S Macomber, Daniel E Rardon, Ioannis Constantine ConstantinidesAbstract:Free radical or thermal polymerization of bis(pentamethylene)Butatriene yields a polymer with the postulated structure [C(C 5 H 10 )-C≡C-C(C 5 H 10 )] n . Copolymerization of BPB with maleic anhydride yields the soluble corresponding alternating copolymer
Magnus Pfaffenbach - One of the best experts on this subject based on the ideXlab platform.
-
Structural Complexity Through Multicomponent Cycloaddition Cascades Enabled by Dual-Purpose, Reactivity Regenerating 1,2,3-Triene Equivalents
2016Co-Authors: Fuyuhiko Inagaki, Magnus PfaffenbachAbstract:Multicomponent reactions allow for more bond-forming events per synthetic operation, enabling more step and time economical conversion of simple starting materials to complex and thus value-added targets. These processes invariably require that reactivity be relayed from intermediate to intermediate over several mechanistic steps until a termination event produces the final product. Here we report a multicomponent process in which a novel 1,2,3-Butatriene equivalent (TMSBO: TMSCH2C≡CCH2OH) engages chemospecifically as a two-carbon alkyne component in a metal-catalyzed [5+2] cycloaddition with a vinylcyclopropane to produce an intermediate cycloadduct. Under the reaction conditions, this intermediate undergoes a remarkably rapid 1,4-Peterson elimination, producing a reactive four-carbon diene intermediate that is readily intercepted in either a metal-catalyzed or thermal [4+2] cycloaddition. TMSBO thus serves as an yne-to-diene transmissive reagent coupling two powerful and convergent cycloadditions- the homologous Diels-Alder and Diels-Alder cycloadditions- through a vinylogous Peterson elimination, and enabling flexible access to diverse polycycles. A pre-eminent goal of synthesis is to produce targeted structural complexity and thu
-
structural complexity through multicomponent cycloaddition cascades enabled by dual purpose reactivity regenerating 1 2 3 triene equivalents
Nature Chemistry, 2014Co-Authors: Paul A Wender, Dennis N Fournogerakis, Ryan V Quiroz, Fuyuhiko Inagaki, Matthew S Jeffreys, Magnus PfaffenbachAbstract:Cascade reactions allow step-economical generation of molecular complexity. Now, a Butatriene equivalent, TMSCH2C ≡ CCH2OH, is used to couple two powerful and convergent cycloadditions — the homologous Diels–Alder ([5 + 2]) and the Diels–Alder ([4 + 2]) reactions –– through a vinylogous Peterson elimination, en route to a series of kinase inhibitors inspired by staurosporine.
-
structural complexity through multicomponent cycloaddition cascades enabled by dual purpose reactivity regenerating
2014Co-Authors: Paul A Wender, Dennis N Fournogerakis, Ryan V Quiroz, Fuyuhiko Inagaki, Matthew S Jeffreys, Magnus PfaffenbachAbstract:Multicomponent reactions allow for more bond-forming events per synthetic operation, enabling more step and time economical conversion of simple starting materials to complex and thus valueadded targets. These processes invariably require that reactivity be relayed from intermediate to intermediate over several mechanistic steps until a termination event produces the final product. Here we report a multicomponent process in which a novel 1,2,3-Butatriene equivalent (TMSBO: TMSCH2C≡CCH2OH) engages chemospecifically as a two-carbon alkyne component in a metalcatalyzed [5+2] cycloaddition with a vinylcyclopropane to produce an intermediate cycloadduct. Under the reaction conditions, this intermediate undergoes a remarkably rapid 1,4-Peterson elimination, producing a reactive four-carbon diene intermediate that is readily intercepted in either a metal-catalyzed or thermal [4+2] cycloaddition. TMSBO thus serves as an yne-to-diene transmissive reagent coupling two powerful and convergent cycloadditions - the homologous Diels-Alder and Diels-Alder cycloadditions - through a vinylogous Peterson elimination, and enabling flexible access to diverse polycycles.
Ashebir Fiseha - One of the best experts on this subject based on the ideXlab platform.
-
The structure and attempted topochemical polymerization of single crystalline 1,1,4,4-bis(pentamethylene)-1,2,3-Butatriene
Journal of Chemical Crystallography, 1999Co-Authors: Robert E. Bachman, Ashebir Fiseha, Steven K. PollackAbstract:The photo-initiated solid-state topochemical polymerization of 1,1,4,4-bis(pentamethylene)-1,2,3-Butatriene ( 1 ) was attempted unsuccessfully. Since 1 readily polymerizes in the liquid state, a structural study was undertaken to better understand its inertness in the solid-state. 1 crystallizes in the monoclinic space group P 2_1/ n with a = 6.4597(6), b = 10.8914 (10), c = 8.4396(8) Å, β = 100.168(2)°, V = 584.44(9) Å^3, and Z = 2. The crystal structure reveals that while the alignment of the π-systems in the solid-state is acceptable for supporting the targeted polymerization reaction, the reaction centers are located too far apart to allow the reaction to take place. Additionally, comparison of the molecular structure of 1 with the limited number of other structurally characterized Butatrienes has provided insight into the steric and electronic influences played by the substituents attached to the cumulene moiety.
-
Butatriene based polymer chemistry 2 synthesis and characterization of poly 1 1 4 4 bis pentamethylene 1 2 3 Butatriene 1
Macromolecules, 1997Co-Authors: Steven K. Pollack, Ashebir Fiseha, Babu NarayanswamyAbstract:The cumulene 1,1,4,4-bis(pentamethylene)Butatriene has been shown to undergo a thermally induced 1,4 free-radical polymerization to yield a crystalline polymer with a unique nonconjugated acetylene containing backbone. This polymerization occurs in both the melt and in solution. Typical free-radical inhibitors prevent the thermally induced polymerization. The reaction occurs in the presence or absence of free-radical initiators. The polymer is crystalline with a triclinic unit cell (a = 9.87 A, b = 6.10 A, c = 4.97 A, α = 113.7°, β = 85.2°, γ = 100.6°). No melting or glass transition is observed via differential calorimetry, but an irreversible exothermic transition is observed from both solution and melt polymerized material. This is interpreted as a cold crystallization process. Trapping of the polymerizing monomer with TEMPO leads to soluble oligomers.
H Shirakawa - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of a soluble conjugated cumulene polymer poly biphenyl 4 4 diyl 1 4 bis 4 dodecyloxyphenyl buta 1 2 3 triene 1 4 diyl
Macromolecular Rapid Communications, 2000Co-Authors: Ikuo Kinoshita, Masashi Kijima, H ShirakawaAbstract:A conjugated polymer with a Butatriene segment in the main chain, poly(biphenyl-4,4'-diyl-1,4 bis(4-dodecyloxyphenyl)buta-1,2,3-triene-1,4-diyl), was synthesized from 1,4-bis(4-bromophenyl)-1,4-bis(4-dodecyloxyphenyl)buta-1,2,3-triene by dehalogenative poly-condensation using Ni(cod) 2 . The polymer was well soluble in usual organic solvents such as CHCl 3 and THF. Structural analyses and characterizations were carried out by IR, NMR, UV-Vis, PL, and Raman spectroscopy, as well as electrical conductivity. It is suggested that π-conjugation is extended to some degree through biphenylyl ene and butatrienylene linkages.
