Anne Buyle Padias

New polymeric material containing the tricyanovinylcarbazole group for photorefractive applications

We report on the synthesis and characterization of a new, completely polymeric material with a large electro‐optic coefficient and photoconductivity. A methacrylic ester polymer containing the tricyanovinylcarbazole group with an alkylene spacer was synthesized. With 49 mW laser power, the photoconductivity of the polymer is 9.8×10−10 Ω−1 cm−1 at an applied electric field of 1.4×106 V/cm. Its electro‐optic coefficient is 6.1 pm/V. The quantum efficiency of photocarrier generation and the photorefractive figure of merit were calculated. This electro‐optic polymer is photoconductive and has photocarrier trap sites without any added sensitizer or photocarrier transport reagent, making it a suitable candidate for photorefractive applications.

Chemical trapping experiments support a cation‐radical mechanism for the oxidative polymerization of aniline

The oxidative polymerization of aniline in aqueous acidic solution was carried out in the presence of a variety of organic compounds as potential traps for postulated intermediates. The polymerization was inhibited by hindered phenols and electron-rich alkenes, traps for cation-radicals. However, polyaniline was still obtained in the presence of electron-rich arenes, such as 1,3-dimethoxybenzene and 1,4-dimethoxybenzene, known as excellent receptors of nitrenium ions. Polymerization of N-phenyl-1,4-phenylenediamine was similarly carried out in the presence of potential traps. Polyaniline containing an N-phenyl group was obtained in the presence of 1,3-dimethoxybenzene and 1,4-dimethoxybenzene. Hindered phenols and 4-methoxystyrene only slightly inhibited polymerization of N-phenyl-1,4-phenylenediamine which most probably proceeded by way of the stable diarylamino radical. Copolymerization of aniline with 10 wt % of N-phenyl-1,4-phenylenediamine in the presence of these traps gave similar results to the polymerization of pure aniline. These results have led to the proposed cation-radical polymerization mechanism of aniline, in which the polymerization is a chain growth reaction through the combination of a polymeric cation-radical and an anilinium cation-radical. Step growth character is also present when a polymeric aminium cation-radical end combines with a diarylaminoended polymer. The copolymerization of N-phenyl-p-phenylenediamine can also occur by reaction of aniline cation-radical with a polyarylamine radical. The nitrenium mechanism was further rejected by the fact that attempted polymerization of N-phenylhydroxylamine, which forms authentic nitrenium ions in acid, failed to give polymer.

Dual-grating formation through photorefractivity and photoisomerization in azo-dye-doped polymers

Gratings formed by photorefractive and photoisomerization processes in an azo-dye-doped polymer, poly(vinyl carbazole):trinitrofluorenone/Disperse Red I, are investigated by polarization- and field-dependent four-wave mixing experiments. High diffraction efficiencies and long storage times are observed for the photorefractive gratings. Both types of grating are erasable, and we can select them by choosing the polarization of the reading beam. The effect of photoisomerization on photorefractivity is discussed. Our results indicate that azo-dye-doped polymers are promising candidates for reversible optical storage applications.

A contemporary survey of covalent connectivity and complexity. The divergent synthesis of poly(thioether) dendrimers. Amplified, genealogically directed synthesis leading to the de gennes dense packed state

A new poly(thioether) dendrimer (d-PTE) family is synthesized using preformed branch cell reagents (BCR) in a “genealogically directed syntheses” (GDS) strategy. Bicyclic orthoester functionality is introduced into a branch cell reagent (BCR) to temporarily mask pentaerythritol derived branch cells which are used to construct the interior of this new dendrimer family. These BCRs with multiplicities =3 (Nb=3), are organized and amplified around an initiator core with multiplicity = 4 (Nc=4). The initiator core, pentaerythritol tetrabromide (Nc=4), is allowed to react with four equivalents of 4-acetothiomethyl-2,6,7-trioxabicyclo[2.2.2]octane (Nb=3) in the presence of base, to form the first generation possessing four bicyclic orthoester groups. After deprotection and transformation to bromide surface groups via tosylate intermediates, the second generation possessing twelve bicyclic orthoester groups is formed. Surprisingly, attempted displacement of all 36 surface groups at the third generation level showed that only one third of the end groups could be substituted. These experimental data suggest that this (Nc=4, Nb=3) type dendrimer family exhibits de Gennes dense packing properties at the third generation level. Elemental analysis, FTIR, H/C13 nmr spectroscopy and mass spectroscopy were used to confirm the structures. Molecular simulation data suggest that this dendrimer family should not undergo de Gennes dense-packing until the fourth generation. Steric requirements of the bulky mercaptomethyl anion used in the SN2 displacement of terminal bromides on this congested surface are proposed as the reason for incomplete formation of the third generation. This observation illustrates another example of “sterically induced stoichiometry” (SIS).

Photorefractive effect in a poled polymer containing the tricyanovinylcarbazole group

The photorefractive properties of a poled polymer containing the tricyanovinylcarbazole group with an alkylene spacer are investigated by four‐wave mixing experiments and Mach–Zehnder type electro‐optic measurements. The photorefractive effect is demonstrated in a polymer that shows both the photoconductivity and the electro‐optic effect intrinsically.

The hydrolytic polymerization of ε-caprolactone by triphenyltin acetate

The polymerization of ε-caprolactone (CL) using triphenyltin acetate has been investigated. Polymers with broad MWD were obtained in almost quantitative yield. After an initial induction period, the polymerization showed zero order kinetics with respect to monomer and nearly first order with respect to catalyst. The mechanism of the propagation reaction is proposed to proceed via an ester alcoholysis, with initiation by traces of water. The zero order kinetics are explained as follows: the tin catalyst is coordinated by the cyclic lactone, monomer addition to the polymer chain in the rate-determining step results in formation of an acyclic ester link, which is no longer a strong donor, and leads to a coordinatively unsaturated tin species.

Computational Investigation of the Competition between the Concerted Diels–Alder Reaction and Formation of Diradicals in Reactions of Acrylonitrile with Nonpolar Dienes

The energetics of the Diels-Alder cycloaddition reactions of several 1,3-dienes with acrylonitrile, and the energetics of formation of diradicals, were investigated with density functional theory (B3LYP and M06-2X) and compared to experimental data (Hall et al., J. Org. Chem.1993, 58, 7049-7058). For the reaction of 2,3-dimethyl-1,3-butadiene with acrylonitrile, the concerted reaction is favored over the diradical pathway by 2.5 kcal/mol using B3LYP/6-31G(d); experimentally, this reaction gives both cycloadduct and copolymer. The concerted cycloaddition of cyclopentadiene with acrylonitrile is preferred computationally over the stepwise pathway by 5.9 kcal/mol; experimentally, only the Diels-Alder adduct is formed. For the reactions of (E)-1,3-pentadiene and acrylonitrile, both cycloaddition and copolymerization were observed experimentally; these trends were mimicked by the computational results, which showed only a 1.2 kcal/mol preference for the concerted pathway. For the reactions of (Z)-1,3-pentadiene and acrylonitrile, the stepwise pathway is preferred by 3.9 kcal/mol, in agreement with previous experimental findings that only polymerization occurs. M06-2X is known to give more accurate activation and reaction energetics (Pieniazek, et al., Angew. Chem. Int.2008, 47, 7746-7749), but the energies of diradicals are too high.

Syntheses of polyarylates by alcoholysis and esterolysis

The synthesis of polyarylates containing dimethyl 2,6-naphthalenedicarboxylate (DMNDC), an industrially available, readily purified, and tractable monomer, was investigated by using two synthesis routes, namely alcoholysis and esterolysis in the presence of tin catalyst. Diphenyl ether was used as solvent to keep the co-reactants in solution and to ensure stoichiometric balance. The polyarylates from dimethyl isophthalate (DMI)/dimethyl terephthalate (DMT)/bisphenol-A (BPA) or DMI/DMNDC/ BPA were synthesized by alcoholysis in a two step process. A two step esterolysis process was used to synthesize high molecular weight polyarylate starting from DMI/ DMT/bisphenol-A diacetate (BPAOAc) or DMI/DMNDC/BPAOAc ([η] inh = 0.48 dL g -1 ). Simplification to a one step esterolysis reaction led to a high molecular weight polyarylate ([η] inh = 0.48 dL g -1 ) starting from the mixture DMI/DMNDC/BPAOAc.

Captodative olefins in polymer chemistry

The radical polymerization behavior of captodative olefins such as acrylonitriles, acrylates, and acrylamides α-substituted by an electron-donating substituent is reviewed, including the initiated and spontaneous radical homo- and copolymerizations and the radical polymerizations in the presence of Lewis acids. The formation of low-molecular weight products under some experimental conditions is also reviewed. The reactivity of these olefins is analyzed in the context of the captodative theory. In spite of the unusual stabilization of the captodative radical, the reactivity pattern of these olefins in polymerization does not differ significantly from the pattern observed for other 1,1-disubstituted olefins. Classical explanations such as steric effects and aggregation of monomers are sufficient to rationalize the observations described in the literature. The spontaneous polymerization of acrylates α-substituted by an ether, a thioether, or an acylamido group can be rationalized by the Bond-Forming Initiation theory.

Cycloaddition Reactions of Ketene Diethyl Acetal toward the Synthesis of Cyclobutene Monomers

Abstract The [2+2]-cycloaddition reactions of ketene diethyl acetal with methyl acrylate and acrylonitrile were optimized. Highly efficient ketal cleavage to either 2-cyano-1-cyclobutanone or 2-methoxycarbonyl-1-cyclobutanone was achieved using formic acid. Among the numerous reduction methods attempted, only sodium cyanoborohydride in acidic medium led successfully to the corresponding alcohols, but isolation of the desired products was not achievable. We show that the anomalous cyclobutanone chemistry is due to the acidic α-proton and the electron-withdrawing substituent in the α-position. Substitution of the α-proton by a methyl group results in a turnaround back to textbook chemistry.