Methanol-Assisted ADMET Polymerization of Semiaromatic Amides.

A method for the acyclic diene metathesis polymerization of semiaromatic amides is described. The procedure uses second-generation Grubbs' catalyst and N-cyclohexyl-2-pyrrolidone (CHP), a high boiling, polar solvent capable of solubilizing both monomer and polymer. The addition of methanol to the reaction was found to significantly increase polymer molar mass although the role of the alcohol is currently not understood. Hydrogenation with hydrogen gas and Wilkinson's catalyst resulted in near-quantitative saturation. All polymers synthesized here exhibit a hierarchical semicrystalline morphology driven by ordering of aromatic amide groups via strong nonbonded interactions. Furthermore, the melting points can be tuned over a >100 °C range by precise substitution at just one of the backbone positions on each mer (<5% of the total).

Alternating 5,5-Dimethylcyclopentadiene and Diketopyrrolopyrrole Copolymer Prepared at Room Temperature for High Performance Organic Thin-Film Transistors.

We report that the inclusion of nonaromatic 5,5-dimethylcyclopentadiene monomer into a conjugated backbone is an attractive strategy to high performance semiconducting polymers. The use of this monomer enables a room temperature Suzuki copolymerization with a diketopyrrolopyrrole comonomer to afford a highly soluble, high molecular weight material. The resulting low band gap polymer exhibits excellent photo and thermal stability, and despite a large π-π stacking distance of 4.26 Å, it demonstrates excellent performance in thin-film transistor devices.

Poly(cyclopentadienylene ethynylene)s: Breaking Conventional Polyenyne Motifs.

Conjugated polyenynes comprising dienyne constituents have been synthesized for the first time, expanding the architectural scope of this unique polymer class. The poly(cyclopentadienylene ethynylene)s (PCE)s are soluble in common organic solvents, a rare feature among polyenynes, and possess physicochemical properties that are influenced by the structure of their solubilizing groups. A comparative analysis between the PCEs and other soluble polyenynes, poly(arylene ethynylene)s, and a hybrid of both polymer classes show among other characteristics that the inclusion of cyclopentadienes into the conjugated backbone significantly reduces electronic transition energies while completely suppressing photoluminescence.

Decreasing aromaticity in π-conjugated materials: efficient synthesis and electronic structure identification of cyclopentadiene-containing systems.

An efficient route to cyclopentadiene-containing π-conjugated molecules is reported. A comparative analysis between the aryl/dienyl hybrids and their aromatic congeners shows a propensity of the diene moiety to reduce the optical band gap of a π-conjugated system without compromising a planar structural topology. Moreover, a novel poly(fluorene) derivative bearing alternating cyclopentadiene repeat units was synthesized to demonstrate the applicability of this method in polymer synthesis.

Tunable thermoresponsive pyrrolidone-based polymers from pyroglutamic acid, a bio-derived resource.

A series of pyrrolidone-based polymers is prepared from pyroglutamic acid, a bio-derived resource. Polymers bearing simple alkoxy substituents (e.g., methoxy, ethoxy, and butoxy) are soluble in common organic solvents and possess glass transition temperatures that are dependent on the length of the alkoxy residue. Replacing these substituents with an ether moiety (CH3 OCH2 CH2 O-) affords a highly sensitive and reversible thermoresponsive polymer with a lower critical solution temperature (LCST) of 42 °C in water. Copolymers composed of repeat units bearing both the ether and simple alkoxy residues are found to exhibit LCSTs that are highly dependent on the nature of the hydrophobic alkoxy residue suggesting that the LCSTs of these polymers can be successfully tuned by simply tailoring the copolymer structure.

Mechanistic study of the stereoselective polymerization of D,L-lactide using indium(III) halides.

We report the results of a comprehensive investigation of the recently discovered stereoselective and controlled polymerization of racemic lactide (D,L-LA) using an initiator prepared in situ from indium(III) chloride (InCl(3)), benzyl alcohol (BnOH), and triethylamine (NEt(3)). Linear relationships between number-average molecular weight (M(n)) and both monomer to alcohol concentration ratio and monomer conversion are consistent with a well-controlled polymerization. Studies on polymerization kinetics show the process to be first-order in [InCl(3)](0) and zero-order in both [BnOH](0) and [NEt(3)](0). The rate of D,L-LA conversion is also dependent on the indium(III) halide (i.e., t(1/2)(InCl(3)) approximately = 43 min versus t(1/2)(InBr(3)) approximately = 7.5 h, 21 degrees C, CD(2)Cl(2), [D,L-LA](0)/[BnOH](0) approximately = 100, [D,L-LA](0) = 0.84 M, [InX(3)](0)/[BnOH](0) = 1) and lactide stereoisomer (i.e., k(obs)(D,L-LA) approximately = k(obs)(meso-LA) > k(obs)(L-LA)). A model system that polymerizes D,L-LA with the same high degree of stereoselectivity was developed using 3-diethylamino-1-propanol (deapH) in lieu of BnOH and NEt(3). The product of the reaction of deapH with InCl(3) was identified as [InCl(3)(deapH)(H(2)O)](2) by elemental analysis, X-ray crystallography, and NMR and FTIR spectroscopies. An anhydrous version of the complex was also isolated when care was taken to avoid adventitious water, and was shown by pulsed gradient spin-echo (PGSE) NMR experiments to adopt a dinuclear structure in CD(2)Cl(2) solution under conditions identical to those used in its stereoselective polymerization of D,L-LA. The combined data suggest that the initiating species for the InCl(3)/BnOH/NEt(3) system is similar to [InCl(3)(deapH)(H(2)O)](2) and of the type [InCl((3-n))(OBn)(n)](m). With this information we propose a mechanism that rationalizes the observed stereocontrol in D,L-LA polymerizations. Finally, in an exploration of the scope of the InCl(3)/BnOH/NEt(3) system, we found this system to be effective for the polymerization of other cyclic esters, including epsilon-caprolactone and several substituted derivatives.

Stereoselective and controlled polymerization of D,L-lactide using indium(III) trichloride.

Indium trichloride, benzyl alcohol, and triethylamine (without an added 'directing' multidentate ligand) generate a catalyst in situ for the room temperature polymerization of D,L-lactide affording highly heterotactic polylactide of controlled molecular weight and narrow molecular weight distribution.

Conjugated thiophene-containing oligoacenes through photocyclization: bent acenedithiophenes and a thiahelicene.

The preparation of bent anthradithiophenes (BADTs) using an oxidative photocyclization-based synthetic strategy is reported. The optical properties of the new compounds were characterized by UV-vis and fluorescence spectroscopies, and the redox properties were probed by cyclic voltammetry. Structural studies using single crystal X-ray crystallography show that the unsubstituted BADT adopts a slipped cofacial stacking arrangement in the solid state with pi-pi interactions along the intermolecular stacking axis. The dialkylated derivatives adopt similar packing motifs with varying degrees of slipping along their long and short molecular axes while the diphenyl derivative packs into an edge-to-face herringbone arrangement. Powder diffraction data show that in thin films prepared by vacuum evaporation, molecules of the unsubstituted BADT are oriented nearly perpendicular to the substrate surface whereas the dialkylated derivatives adopt either multiple phases or new polymorphs. A thiahelicene prepared from the oxidative photocyclization of two isomers of 2,5-dithienyl-1,4-distyrylbenzene is described and the crystal structure reported.

Synthesis and structures of novel luminescent bent acenedithiophenes.

1,4-dithienyl-2,5-divinylbenzenes are readily available compounds that undergo oxidative photocyclization to afford bent anthradithiophenes (BADTs). The new parent and didodecyl-functionalized derivatives have been structurally characterized, and their absorption and emission spectra are reported.