Aurica Farcas

Synthesis and Characterization of a Fully Aromatic Polyazomethine with Main Chain Rotaxane Architecture

A new aromatic polyazomethine with rotaxane architecture containing a blocking group in every structural unit has been synthesized by polycondensation of 3,6-diformyl-9-butyl carbazole with p,p′-diaminobiphenyl (benzidine)/β-cyclodextrin adduct. As compared with polymers obtained in the absence of β-cyclodextrin, this polymer is more hygroscopic and soluble in polar solvents such as DMF and DMSO. The IR, 1H-NMR, GPC and DSC data support the presence of β-cyclodextrin in the polymer chain. Measurements made by gel permeation chromatography of the DMF soluble main-chain polyrotaxane show high molecular weight. This polymer is a light-yellow coloured product and its electrical conductivity is as high as 10−9 S cm−1. Doping with iodine markedly increased the conductivity of the orange-brown coloured semiconductive polyazomethine with a maximum conductivity of 10−6 S cm−1.

Synthesis and characterization of poly(azomethine)s with rotaxane architecture

Poly(azomethine)s with rotaxane architecture were synthesized by means of solution polycondensation of terephthalaldehyde with 1,6 -hexamethylenediamine/a- and β-cyclodextrin adducts, and blocking of the chain ends with a bulky aromatic amine, i.e., p-aminophenyltriphenylmethane. As compared with the polymer obtained in the absence of cyclodextrin, these polymers are more hygroscopic and soluble in polar solvents while their IR, NMR and DSC data support the presence of cyclodextrins in the polymer chain.

Anionic ring-opening polymerization of ethylene oxide in DMF with cyclodextrin derivatives as new initiators

Anionic polymerization initiated by cyclodextrins suffers from a poor solubility of those derivatives in standard polymerization solvents. The possibility to perform ethylene oxide polymerization initiated by monofunctional initiators (allyl alcohol, 2-methoxyethanol) by living ring opening polymerization in DMF, a good solvent for any CD derivative, was demonstrated by SEC, (1)H and (13)C NMR analyses. The study was extended to the use of native CD as initiator, leading to the synthesis of ill-defined structures, explained by the reactivity scale of the various hydroxyl functions. Two selectively modified CD derivatives are then used to synthesize a new family of star-shaped poly(ethylene oxide) polymers with CD core, having 14 or 21 arms. The polymerization was found to be living and DOSY experiments confirmed the well-defined structures for the synthesized star-polymers.

Poly(Azomethine)s with Rotaxane Architecture Containing a Blocking Group in Every Structural Unit: Synthesis and Characterization

Poly(azomethine)s with rotaxane architecture containing a blocking group in every structural unit of the polymer chain have been synthesized by polycondensation of 3,6-diformyl-9-butyl carbazole with 1,6-hexamethylenediamine/α-or β-cyclodextrin adducts. As compared with the polymers obtained in the absence of cyclodextrins, these polymers are more hygroscopic and soluble in polar solvents such as dimethylformamide and dimethyl sulfoxide. The infrared, proton nuclear magnetic resonance, gel permeation chromatography and differential scanning calorimetry data support the presence of cyclodextrins in every structural unit of the polymer chain.

Polyrotaxanes composed of β-cyclodextrin and polydimethylsiloxanes: synthesis, morphology and thermal behavior

Epoxy-terminated polydimethylsiloxanes (E-PDMSs) of different molecular weight M n were proved to undergo inclusion complexation into the inner cavity of β-cyclodextrin (β-CD), resulting in polyrotaxanes (PRots). The dethreading of the macrocycle was prevented by blocking the siloxane chain with a bulky substituent derived from 4-aminophenyltriphenyl methane (APhTPhM). As revealed by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy (SEM), wide-angle X-ray diffraction and statistical analysis of SEM images, the thermal properties and the morphology of polyrotoxanes are dependent upon M n, β-CD/E-PDMS molar ratio and the presence of free β-CD in the complexes.

Synthesis and Characterization of Polyrotaxanes based on Cyclodextrins and Viologen-modified Polydimethylsiloxanes

β-Cyclodextrin (1 -CD) and 2 -cyclodextrin (2 -CD) (hosts) formed inclusion complexes with 4,41-bipyridinium dication derivatives with long chains (guests), in which the substituents on the bipyridinium nitrogen atoms are 1,3-bis(chloromethylphenethyl)-1,1,3,3-tetramethyldisiloxane. The number of 2 -CD molecules threaded onto the polymer chain increases with the length of the guest chain. In contrast, the number of β-CD molecules threaded onto the polymer is approximately 4 corresponding to each molecular chain, due to the repulsive interaction between β-CD and the quaternary bipyridinium units. The complexes were isolated in high yield and characterized by 1H NMR, 13C NMR, X-ray diffraction, thermal and scanning electron micrographs studies. As proven by X-ray analysis, the synthesized polyrotaxanes are crystalline materials with crystalline patterns significantly different from that of native cyclic oligosaccharide. The thermal stabilities of polyrotaxanes are higher than that of the physical mixture between cyclodextrin and the alternating copolymer, denoting the formation of the inclusion complexes. Scanning electron micrographs of polyrotaxanes reveal cubic and linear shapes without a well formed shape. Shape regularity and geometrical regularities in the agglomerating forms can be observed.

Synthesis and photophysical characteristics of polyfluorene polyrotaxanes

Summary Two alternating polyfluorene polyrotaxanes (3·TM-βCD and 3·TM-γCD) have been synthesized by the coupling of 2,7-dibromofluorene encapsulated into 2,3,6-tri-O-methyl-β- or γ-cyclodextrin (TM-βCD, TM-γCD) cavities with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propanediol) ester. Their optical, electrochemical and morphological properties have been evaluated and compared to those of the non-rotaxane counterpart 3. The influence of TM-βCD or TM-γCD encapsulation on the thermal stability, solubility in common organic solvents, film forming ability was also investigated. Polyrotaxane 3·TM-βCD exhibits a hypsochromic shift, while 3·TM-γCD displays a bathochromic with respect to the non-rotaxane 3 counterpart. For the diluted CHCl3 solutions the fluorescence lifetimes of all compounds follow a mono-exponential decay with a time constant of ≈0.6 ns. At higher concentration the fluorescence decay remains mono-exponential for 3·TM-βCD and polymers 3, with a lifetime τ = 0.7 ns and 0.8 ns, whereas the 3·TM-γCD polyrotaxane shows a bi-exponential decay consisting of a main component (with a weight of 98% of the total luminescence) with a relatively short decay constant of τ1 = 0.7 ns and a minor component with a longer lifetime of τ2 = 5.4 ns (2%). The electrochemical band gap (ΔE g ) of 3·TM-βCD polyrotaxane is smaller than that of 3·TM-γCD and 3, respectively. The lower ΔE g value for 3·TM-βCD suggests that the encapsulation has a greater effect on the reduction process, which affects the LUMO energy level value. Based on AFM analysis, 3·TM-βCD and 3·TM-γCD polyrotaxane compounds exhibit a granular morphology with lower dispersity and smaller roughness exponent of the film surfaces in comparison with those of the neat copolymer 3.

The effect of permodified cyclodextrins encapsulation on the photophysical properties of a polyfluorene with randomly distributed electron-donor and rotaxane electron-acceptor units

Summary We report on the synthesis as well as the optical, electrochemical and morphological properties of two polyrotaxanes (4a and 4b), which consist of electron-accepting 9,9-dicyanomethylenefluorene 1 as an inclusion complex in persilylated β- or γ-cyclodextrin (TMS-β-CD, TMS-γ-CD) (1a, 1b) and methyltriphenylamine as an electron-donating molecule. They are statistically distributed into the conjugated chains of 9,9-dioctylfluorene 3 and compared with those of the corresponding non-rotaxane 4 counterpart. Rotaxane formation results in improvements of the solubility, the thermal stability, and the photophysical properties. Polyrotaxanes 4a and 4b exhibited slightly red-shifted absorption bands with respect to the non-rotaxane 4 counterpart. The fluorescence lifetimes of polyrotaxanes follow a mono-exponential decay with a value of τ = 1.14 ns compared with the non-rotaxane, where a bi-exponential decay composed of a main component with a relative short time of τ1 = 0.88 (57.08%) and a minor component with a longer lifetime of τ2 = 1.56 ns (42.92%) were determined. The optical and electrochemical band gaps (ΔE g) as well as the ionization potential and electronic affinity characterized by smaller values compared to the values of any of the constituents. AFM reveals that the film surface of 4a and 4b displays a granular morphology with a lower dispersity supported by a smaller roughness exponent compared with the non-rotaxane counterpart.

Synthesis and characterization of new phenanthrolinetriether copolymers with rotaxane architecture

Abstract This paper is devoted to the preparation and characterization of new phenanthroline-triether copolymers with rotaxane architecture by reaction of complexes of α- or β- cyclodextrin and tri(ethylene glycol) ditosylate with 2,9-di(4-hydroxyphenyl)-1,10- phenanthroline, which is large enough to prevent dethreading of cyclodextrin molecules. Comparative 1H-NMR analysis of tri(ethylene glycol) ditosylate complexes and of rotaxane copolymers evidenced the lower cyclodextrin content in rotaxane copolymers as compared to the calculated values. The rotaxane copolymers present bimodal molecular weight distributions attributed to the separation of the fractions with different content of cyclodextrin threaded on the copolymer chain. As evidenced by thermogravimetric analysis, the rotaxane copolymers show higher thermal stability than its non-complexed homologue.