M. Laus

Hybrid nanocomposites based on polystyrene and a reactive organophilic clay

The preparation of new hybrid nanocomposites, by emulsion polymerization of styrene in the presence of a reactive organophilic clay, and their characterization are described. The reactive organophilic clay is synthesized by exchanging the inorganic cations in the interlayer structure of a natural clay with the quaternary salt of the aminomethylstyrene. This salt is prepared by a Gabriel reaction starting from the (chloromethyl)styrene. The polymeric matrix of the resulting materials was found to be constituted by polystyrene homopolymer and by a blocky copolymer of styrene and quaternary salt of the (aminomethyl)styrene units. The glass transition temperature of the nanocomposites increase as the percentage of organophilic clay increases, although the average molar masses of the polymeric matrix decrease, because of termination and/or chain-transfer reactions caused by the organophilic clay during the polymerization. Accordingly, the inherent reinforcing action due to the presence of the reactive organophilic clay is higher than the observed one.

Linear viscoelasticity of side chain liquid crystal polymer

Abstract Small amplitude oscillatory shear has been used to study thermotropic liquid-crystalline polymers that have mesogenic groups pendant to flexible backbones. The polymers studied form nematic and smectic glasses, enabling viscoelastic response to be studied over a wide range of frequencies using time-temperature superposition. In contrast to main chain liquid-crystalline polymers, the nematic side chain polymers exhibit linear viscoelastic response over a wide range of strain amplitudes that is independent of thermal and shear histories. Viscoelastic response is very sensitive to smectic-nematic and smectic-isotropic transitions, but insensitive to the nematic-isotropic transition, as time-temperature superposition applies across this transition. We compare viscoelastic data with diffusion data by calculating the time τ that it takes a polymer to diffuse a distance equal to its coil size R (τ=R2/D). At frequencies lower than 1/τ side chain polymers in their nematic show the terminal response charac...

Phase and orientational behaviors in liquid crystalline main‐chain/side‐group block copolymers

The phase and orientational behaviors of a series of liquid crystalline (LC) AB-type diblock copolymers comprising thermotropic main-chain (MC) polyester and side-group (SG) polymethacrylate blocks were investigated by X-ray diffraction. The MC and SG blocks were phase separated and gave rise to their individual mesophases that coexisted at equilibrium. The samples were oriented by using either a magnetic field or a mechanical field. In magnetically aligned samples both the MC and SG microphases were oriented with their smectic planes orthogonal to the magnetic field direction, independent of the copolymer composition. Mechanically aligned, fiber samples showed different orientations of the MC and SG smectic planes for different sample compositions. In this case the disposition of the smectic planes of the MC and SG blocks was driven by the relative length of the two blocks. Some features of the X-ray patterns of the copolymers were compared to those of the MC and SG homopolymers. In addition, the MC smectic domains crystallized on annealing without affecting the orientation that had been achieved by applying a magnetic field.

Diblock and triblock functional copolymers by controlled radical polymerization

Controlled polystyrenes with different molar mass values were synthesized starting from benzoyl peroxide and TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy). The polystyrene homopolymers served as initiators for the block copolymerization of phthalimide methylstyrene (PIMS) to synthesize polystyrene-b-poly(PIMS) diblock copolymers. Diblock copolymers with well defined structures as well as controlled and narrow molar mass distribution were obtained from the lower-mass polystyrene homopolymers. The lower-mass copolymers were found to be active as initiators in the synthesis of the polystyrene-b-poly(PIMS)-b-polystyrene triblock copolymers. In each reaction step, the effects of conversion and reaction time on the molar mass characteristics of the prepared block copolymers were investigated. The diblock and triblock copolymers were modified using hydrazine as the reagent in order to obtain the corresponding functional amino block copolymers.

Core-shell functional microspheres by dispersion polymerization: 2. Synthesis and characterization

Abstract Polystyrene microspheres ranging in diameter from 3 to 10 μm were prepared in alcoholic media by dispersion polymerization of styrene in the presence of a methacrylic acid/ethyl acrylate 1:1 statistical copolymer (Eudragit) as the stabilizer precursor. The effects of the initial Eudragit and free radical initiator concentrations on the microsphere dimensions, the microsphere size distribution and surface functionality were investigated. The particle dimensions were found to increase with increasing initiator concentration and decrease with increasing steric stabilizer precursor concentration. The percentage Eudragit in the microspheres was found to increase with the stabilizer precursor concentration and decrease with the initiator concentration. The resulting double-shell microspheres, with specific surface functionalities, are promising as tailor-made supports for biocatalysts.

Hybrid Liquid-Crystalline Block Copolymers with Polystyrene and Polyester Blocks

SummaryThe synthesis and some thermal and dynamic-mechanical properties of a novel class of hybrid block copolymers comprised of polystyrene and liquid-crystalline polyester blocks are reported. The two blocks appear to be incompatible in the solid and melt phases and undergo distinct thermal transitions. The mesophase transition temperatures of the block copolymers are constant within all the composition range. The mesophase transition enthalpies are directly proportional to the weight fraction of the liquid-crystalline polyester block.

Isothermal crystallisation kinetics of liquid crystal semiflexible polyesters

Abstract The isothermal crystallisation from the nematic phase of five thermotropic liquid crystalline TR m polyesters formed from two mesogenic p -oxybenzoyl diads alternately flanked by a trioxyethylene segment and a polymethylene spacer of variable length ( m = 6–10) was investigated. The melting behaviours, thermodynamic melting temperatures and crystallisation kinetic parameters are discussed in terms of the polymer structure. The activation energy for the formation of critical nuclei proved to be dependent on the inherent flexibility and parity of the spacer.

Thermotropic liquid crystalline poly(β-thioester)s containing azoxybenzene mesogenic units

Abstract A new homologous series of thermotropic liquid crystalline poly(β-thioester)s was prepared by a Michael-type polyaddition of various α,ω- polymethylenedithiols to a diacrylate containing the mesogenic azoxybenzene unit. The mesomorphic properties were studied as a function of the dithiol spacer length. Analyses by DSC and optical microscopy demonstrated the occurrence of enantiotropic behaviour in the polymer containing the ethanedithiol residue, and of monotropic behaviour in the polymers containing the dithiol spacers with 3/6 methylene segments. The systems based on longer dithiol segments did not show mesomorphism. The poly(β-thioester)s were characterized by greater thermal stability than the corresponding poly(β-aminoester)s previously investigated. In the case of the poly(β-thioester) incorporating the pentanedithiol spacer, nematic schlieren textures with quite unusual high strength singularities S = 3 2 and S = 2 were detected.

Monotropic liquid crystalline poly(β-thioester)s containing bis (p-oxybenzoate) mesogenic units

SummaryA new series of thermotropic liquid crystalline poly(β-thioester)s was prepared by a Michael-type polyaddition of α,ω-polymethylenedithiols of different length to a mesogenic diacrylate containing two bis(p-oxybenzoate) units symmetrically connected through a dodecamethylene segment. The thermotropic behaviour was studied by combined DSC and thermal-optical analyses. All the poly(β-thioester)s investigated exhibited quite unusual monotropic mesomorphism.

Core-shell functional nanospheres for oligonucleotide delivery. II

Two polymethylmethacrylate functional nanosphere series, specifically designed for the reversible adsorption of oligonucleotides, were prepared by emulsion polymerization in the presence of two structurally different ionic comonomers, namely two quaternary ammonium salts of 2-(dimethylamino)ethyl methacrylate. The nanosphere size is substantially affected by the ionic comonomer structure and amount. The width of the size distribution tends to decrease with increasing the comonomer amount in solution, and monosized nanosphere samples are obtained at a high comonomer amount. The ionic comonomer weight percentage on the nanospheres increases monotonically in both sample series as the comonomer concentration increases. In contrast, the trend of the quaternary ammonium group surface density is different in the two sample series displaying a regular increase or a maximum value as the ionic comonomer concentration increases.