Photo-optical properties of new combined chiral photochromic liquid crystalline copolymers

For the first time, a series of cholesteric copolymers containing combined chiral photochromic side groups has been synthesized and the phase behaviour and optical properties of the copolymers have been characterized. Specific features of the photochemical and photo-optical behaviour of such systems were studied, and the quantum yields of the photo-induced process in solution and in the condensed state of the cholesteric copolymers were calculated. The selective light reflection wavelength was found to be controlled by the UV radiation. The synthesized polymers were shown to be promising candidates for colour data recording.     

New benzopyranocarbazoles: synthesis and photochromic behaviour

The synthesis of three new benzopyranocarbazoles (=[indole]naphthopyrans) from hydroxybenzo[a]carbazoles is described. The photochromic properties of these novel compounds were investigated under flash photolysis and continuous irradiation. Compared to known [indole]benzopyrans these new compounds showed a significant bathochromic shift in the spectra of the open forms, an increase in colourabilities and slower ring closure kinetics. The photochromic behaviour of compound 4 has been further investigated. Continuous near-UV irradiation led to the formation of one photoisomer (TC) that was subsequently partially converted, to the other (TT). Thermal reversion of the preirradiated system to the original form was only partial and followed a monoexponential decay involving the back-conversion of the TC-isomer to the uncoloured closed form (CF). The thermally stable TT-isomer could only be photobleached with visible light. This process was shown to proceed through a fast photoconversion TT→TC followed by the thermal path TC→CF. Thermal relaxation of the activated system was also studied at various temperatures.     

Photosensitive cholesteric copolymers with spiropyran-containing side groups I. Phase behaviour and photo-optical properties

A number of terpolymers were synthesized by copolymerization of nematogenic, chiral and photochromic monomers with different contents of spiropyran photosensitive side groups. The synthesized copolymers possess selective light reflection in the visible region of the spectrum. Action of UV light on planarly-oriented films of the copolymers leads to the formation of the merocyanine form of the dye with a maximum of absorbance coinciding with the selective light reflection peak. The 'degeneration' of the selective light reflection is observed during this process. It was shown that such types of material can be used for reversible information storage; the principal scheme for the processes of optical data recording and reading is suggested.     

Photosensitive cholesteric copolymers with spiropyran-containing side groups I. Phase behaviour and photo-optical properties

A number of terpolymers were synthesized by copolymerization of nematogenic, chiral and photochromic monomers with different contents of spiropyran photosensitive side groups. The synthesized copolymers possess selective light reflection in the visible region of the spectrum. Action of UV light on planarly-oriented films of the copolymers leads to the formation of the merocyanine form of the dye with a maximum of absorbance coinciding with the selective light reflection peak. The 'degeneration' of the selective light reflection is observed during this process. It was shown that such types of material can be used for reversible information storage; the principal scheme for the processes of optical data recording and reading is suggested.     

A comparative study of photo-optical behaviour of photosensitive chiral copolymers with cholesteric mesophases induced in nematogenic and smectogenic matrices

The photo-optical behaviour of two series of chiral photochromic acrylic copolymers with a chiral nematic phase has been studied. These copolymers contain identical chiral photochromic units, but have different structures of the phenyl benzoate mesogenic side groups which are responsible for the development of LC phases. This approach allowed us to examine specific features of the photo-optical behaviour of the copolymers as a function of the nature of the LC 'matrix' in which the cholesteric phase was induced. The action of UV irradiation was shown to lead to the E-Z isomerization of the chiral side groups and, as a consequence, to untwisting of the cholesteric helix of the copolymers. For copolymers of both series, the effective quantum yields of this photochemical process were calculated. In the case of copolymers in which the cholesteric mesophase is induced in a smectogenic matrix, the corresponding values of the quantum yield are lower and depend slightly on temperature. A plausible explanation of the above phenomena is suggested.     

A comparative study of photo-optical behaviour of photosensitive chiral copolymers with cholesteric mesophases induced in nematogenic and smectogenic matrices

The photo-optical behaviour of two series of chiral photochromic acrylic copolymers with a chiral nematic phase has been studied. These copolymers contain identical chiral photochromic units, but have different structures of the phenyl benzoate mesogenic side groups which are responsible for the development of LC phases. This approach allowed us to examine specific features of the photo-optical behaviour of the copolymers as a function of the nature of the LC 'matrix' in which the cholesteric phase was induced. The action of UV irradiation was shown to lead to the E-Z isomerization of the chiral side groups and, as a consequence, to untwisting of the cholesteric helix of the copolymers. For copolymers of both series, the effective quantum yields of this photochemical process were calculated. In the case of copolymers in which the cholesteric mesophase is induced in a smectogenic matrix, the corresponding values of the quantum yield are lower and depend slightly on temperature. A plausible explanation of the above phenomena is suggested.     

Dendritic homopolymers and block copolymers: Tuning the morphology and properties

The synthesis and characterization of dendritic homopolymers and block copolymers of ?‐caprolactone and lactide (L ‐lactide and racemic lactide) were performed with multifunctional initiators in combination with living polymerization and the selective placement of branching junctures in a divergent growth strategy. A hexahydroxy‐functional 2,2‐bis(hydroxymethyl) propionic acid derivative was used as an initiator for the stannous‐2‐ethylhexanoate‐catalyzed living ring‐opening polymerization of ?‐caprolactone, L ‐lactide, and racemic L ,D ‐lactide. Branching junctions at the chain ends were introduced with benzylidene‐protected 2,2‐bis(hydroxymethyl) propionic acid. Subsequent generations were then polymerized, after deprotection, from these star‐shaped macroinitiators. Successive chain end capping and initiation produced three generations of polymers with molecular weights in excess of 130,000 g/mol and narrow polydispersities (<1.20). It was possible to prepare diblock and triblock copolymers with phase‐separated morphologies, and with L ‐lactide or D ,L ‐lactide, semicrystalline and amorphous morphologies were demonstrated. The polymers were characterized by ¹H NMR, ¹³C NMR, size exclusion chromatography, and differential scanning calorimetry. The compositions of the block copolymers and the conformational structures of the optically active polymers were also confirmed by optical rotation measurements. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1174–1188, 2004     

Non-ionic amphiphilic homopolymers: synthesis, solution properties, and biochemical validation

A novel type of nonionic amphipols for handling membrane proteins in detergent-free aqueous solutions has been obtained through free-radical homo-telomerization of an acrylamide-based monomer comprising a C(11) alkyl chain and two glucose moieties, using a thiol as transfer reagent. By controlling the thiol/monomer ratio, the number-average molecular weight of the polymers was varied from 8 to 63 kDa. Homopolymeric nonionic amphipols were found to be highly soluble in water and to self-organize, within a large concentration range, into small, compact particles of ~6 nm diameter with a narrow size distribution, regardless of the molecular weight of the polymer. They proved able to trap and stabilize two test membrane proteins, bacteriorhodopsin from Halobium salinarum and the outer membrane protein X of Escherichia coli, under the form of small and well-defined complexes, whose size, composition, and shape were studied by aqueous size-exclusion chromatography, analytical ultracentrifugation, and small-angle neutron scattering. As shown in a companion paper, nonionic amphipols can be used for membrane protein folding, cell-free synthesis, and solution NMR studies (Bazzacco et al. 2012, Biochemistry, DOI: 10.1021/bi201862v).     

Dynamic scattering properties of mixtures of cyclic and linear homopolymers and copolymers

The dynamic scattering properties of mixtures of cyclic copolymers and homopolymers are discussed. These properties are compared with those characterizing linear chain mixtures in similar conditions. The differences between cyclic and linear chains are introduced through the form factors only. The interaction parameter between different monomer species are assumed to be the same whether they belong to cyclic or linear chains. The dynamical model is based upon a generalization of the random phase approximation neglecting hydrodynamic interaction and mode coupling effects. Despite these simplifications, substantial differences are found in the dynamics of mixtures containing cyclic copolymers and homopolymers when compared to those of linear chain systems in similar conditions of temperature, concentration, and molecular weight. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1191–1200, 1997     

Synthesis, crystal structures and photochromic properties of novel chiral Schiff base macrocycles

Enantiomerically pure and racemic forms of calixsalen-type macrocycles 1 and 2 were synthesized and their crystal structures were determined. The enantiomerically pure crystals of (S,S,S,S,S,S)-1 exhibited thermally reversible photochromism from yellow to orange-red upon photoirradiation in the solid state, while rac-crystals of 2 with the guest CH₃CN did not show any photocolouration.     

Three-dimensionally packed nanohelical phase in chiral block copolymers

Chirality-driven microphase-separated morphology, poly(l-lactide) (PLLA) left-handed nanohelices hexagonally packed in PS matrix, was obtained from chiral diblock copolymers, poly(styrene)-b-poly(l-lactide). This is perhaps for the first time; the helical superstructures of chiral block copolymers were generated in the bulk and self-assembled to a two-dimensionally (2D) packed lattice. Now, the analyses of block copolymer thermodynamics should be complicated by the chiral entities of constituted components. Orderly packed nanohelical channels can be obtained after hydrolysis, and this provides new opportunities for block copolymer applications in the fields of nanosciences.     

Non-symmetric chiral isoflavone dimers: synthesis,characterisation and mesomorphic behaviour

A new series of non-symmetric chiral isoflavone-based liquid crystalline dimers, α-(2-methylbutyl-4′-(4″-phenyloxy)benzoate)-ω-(3-(4′-decyloxyphenyl)-4H-1-benzopyran-4-one-7-oxy)alkanes, with 3–12 carbon atoms in the alkyloxy spacer, have been synthesised. A pronounced odd–even effect for the phase transition temperatures upon varying the spacer length was observed. The short dimers exhibited monolayer smectic A (SmA) and smectic C (SmC*) phases while for longer homologues a chiral nematic (N*) phase was found. The temperature range of the nematic phase was broadened with elongation of the alkyl spacer. Stabilisation of the nematic phase resulted from competition between the monolayer and intercalated smectic structures. The SmA–SmC* phase transition was second order for all studied compounds with a cross over to the de Vries type behaviour for the shortest homologue.     

Controlled synthesis of homopolymers and block copolymers based on 2-(acetoacetoxy)ethyl methacrylate via RAFT radical polymerisation

Reversible addition-fragmentation chain transfer (RAFT) radical polymerisation enables to synthesise well-defined homopolymers and block copolymers based on 2-(acetoacetoxy)ethyl methacrylate, which are capable to strongly coordinate to metals and metal ions.     

Synthesis and study of photochromic properties of copolymers based on functionalized chromenes

Chromenes functionalized with methacryl groups were synthesized and involved into the radical polymerization to obtain copolymers with ethyl acrylate. Comparison of spectral kinetic characteristics of poly(methyl methacrylate) glasses containing chromenes and photochromic copolymers as additives led to a conclusion that incorporation of a photochromic compound as a part of a copolymer into the polymeric glass increases efficiency of photocoloration of photochromic compounds in the polymeric layer.     

Novel fluoroacrylated copolymers: synthesis, characterization and properties

The development of polymer waveguides leads to synthesis of fluorinated amorphous polymers with high transmission capacity, potential to tune their optical properties by tailoring the molecular structure, together with good processability, easy handling, good flexibility and low cost.In this work we have investigated new thermoplastic fluoroacrylated copolymers, synthesized by radical copolymerization of fluoroalkene(s) with five-membered cyclic carbonate and a third monomer or transfer agent, both containing OH group susceptible to be used for grafting of photocrosslinkable groups. The reaction of hydroxy functionalized copolymers with different acrylating agents results in fluoroacrylated resins with molecular weight in the range of 2000-3000 g mol⁻¹, yield >75% and good solubility in reactive diluents. In the presence of photoinitiator(s), they were crosslinked under UV-radiation in order to obtain optical waveguides.The copolymers synthesized were characterized by ¹H, ¹⁹F and ¹³C NMR as well as FT-IR spectroscopies and have good thermal stability (T_d > 200 °C). The refractive indeces of hydroxy functionalized fluorooligomers and acrylated resins were found to range from 1.44 to 1.45 at 23 °C and the T_gs (by DSC) varied from 40 to 110 °C depending on the content of the cyclic monomer. The optical characteristics of these thermoplastic fluoroacrylated copolymers are under progress.     

Shear induced mixing/demixing: blends of homopolymers,of homopolymers plus copolymers,and blends in solution

Shear may shift the phase boundary towards the homogeneous state (shear induced mixing, SIM), or in the opposite direction (shear induced demixing, SID). SIM is the typical behavior of mixtures of components of low molar mass and polymer solutions, SID can be observed with solutions of high molar mass polymers and polymer blends at higher shear rates. The typical sequence with increasing shear rate is SIM, then occurrence of an isolated additional immiscible area (SID), melting of this island into the main miscibility gap, and finally SIM again. A three phase line originates and ends in two critical end points. Raising pressure increases the shear effects. For copolymer containing systems SID is sometimes observed at very low shear rates, preceding the just mentioned sequence of shear influences.     

Styrene-methyl acrylate copolymers and acrylate homopolymers in solution

Molecular weight determinations by light scattering and osmometry and intrinsic viscosity measurements were made in various solvents on fractions of styrene–methyl acrylate copolymers with different compositions and on acrylate homopolymers prepared by free-radical reaction. Relations between intrinsic viscosity [η] and molecular weight M thus established are compared with those reported by other authors. 2-Methylcyclohexanol was found to be a theta solvent for the copolymers and both parent homopolymers, and isoamyl acetate was a theta solvent for poly(methyl acrylate). From theta point viscosity data obtained with these solvents, unperturbed chain dimensions were estimated. The results are compared with the unperturbed dimensions estimated from the [η]–M relations obtained in good solvents. On the basis of the experimental data it was found that the unperturbed dimension depends linearly on the copolymer composition, in contrast to the case of styrene–methyl methacrylate copolymers. Composition dependences of the theta temperature and of the parameter describing the long-range interactions between nonadjacent segments in polymer chains were investigated. The result implies that long-range interactions between monomeric units never disappear even when those between the same monomeric units vanish. The Huggins constant for copolymer is discussed in terms of the excluded volume variable.     

Synthesis and characterization of modular polyphosphonate homopolymers and copolymers

Linear polyphosphonates with the generic formula –[P(Ph)(X)OR′O]_n– (X = S or Se) have been synthesized by polycondensations of P(Ph)(NEt₂)₂ and a diol (HOR′OH = 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, tetraethylene glycol, or 1,12-dodecanediol) followed by reaction with a chalcogen. Random copolymers have been synthesized by polycondensations of P(Ph)(NEt₂)₂ and mixture of two of the diols in a 2:1:1 mol ratio followed by reaction with a chalcogen. Block copolymers with the generic formula –[P(Ph)(X)OR′O]_{(x + 2)} –[P(Ph)(X)OR′O]_{(x + 3)}– (X = S or Se) have been synthesized by the polycondensations of Et₂N[P(Ph)(X)OR′O]_{(x + 2)}P(Ph)NEt₂ oligomers with HOR′O[P(Ph)(X)OR′O]_{(x + 3)}H oligomers followed by reaction with a chalcogen. The Et₂N[P(Ph)(X)OR′O]_{(x + 2)}P(Ph)NEt₂ oligomers are prepared by the reaction of an excess of P(Ph)(NEt₂)₂ with a diol while the HOR′O[P(Ph)(X)OR′O]_{(x + 3)}H oligomers are prepared by the reaction of P(Ph)(NEt₂)₂ with an excess of the diol. In each case the excess, x is the same and determines the average block sizes. All of the polymers were characterized using ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, TGA, DSC, and SEC. ³¹P{¹H} NMR spectroscopy demonstrates that the random and block copolymers have the expected arrangements of monomers and, in the case of block copolymers, verifies the block sizes. All polymers are thermally stable up to ~300°C, and the arrangements of monomers in the copolymers (block vs. random) affect their degradation temperatures and T_g profiles. The polymers have weight average MWs of up to 3.8 × 10⁴ Da.     

Inherently chiral molecular clips: synthesis, chiroptical properties, and application to chiral discrimination

Inherently chiral molecular clips (MCs), pseudoenantiomeric anti-1 and anti-2, as well as mesoid syn-3, were synthesized by diastereodifferentiating repetitive Diels-Alder reactions of the achiral bisdienophile 6 with chiral diene 5 generated in situ from (-)-menthyl 3,4-bis(dibromomethyl)benzoate 4. These MCs were successfully separated by chiral HPLC to give optically active anti-1 and anti-2 and almost optically inactive syn-3. The structures of anti-1, anti-2, and syn-3 were assigned by high-resolution NMR and the absolute configurations of anti-1 and anti-2 were determined by the exciton-chirality method. Optically active anti-2 can serve as a chiral host. It binds the HCl adduct of D-tryptophan methyl ester (D-TrpOMeHCl) 3.5 times stronger than the L-enantiomer (KD/KL=3.5).     

Design,synthesis and mesomorphic properties of chiral benzoates and fluorobenzoates with direct SmCA*-Iso phase transition

Novel chiral (S)-(+)-4?-(1-methylalkoxycarbonyl)biphenyl-4-yl 4-[ω-(2,2,3,3,4,4,4-hepta?uoro-butoxy)alkoxy]benzoates and 4-[ω-(2,2,3,3,4,4,4-hepta?uorobutoxy)alkoxy]-2-fluorobenzoates were prepared using different optically active alcohols: (S)-(+)-2-hexanol, (S)-(+)-2-heptanol, (S)-(+)-2-nonanol, (S)-(+)-2-decanol, (S)-(+)-2-undecanol and (S)-(+)-5-methylhexan-2-ol. Properties, such as the sequence of phases, transition temperatures and enthalpies, were tested by polarising optical microscopy and differential scanning calorimetry. Extremely low melting compounds were found (below 10°C) for derivatives of (S)-(+)-2-hexanol. The antiferroelectric smectic phase (SmC_A*) with a direct transition from the antiferroelectric to isotropic phase (SmC_A*-Iso) was observed, usually for propoxy-(CH₂)₃- spacing group. Initially, multicomponent mixtures with broad temperature ranges of antiferroelectric phase and direct SmC_A*-Iso transition were formulated.