Optisch aktive Kohlenwasserstoff-Polymere mit aromatischen Seitenketten. 7. Mitt. Synthese und Eigenschaften der Copolymeren von aromatischen Vinylmonomeren mit Chiral-α-Olefinen

Ohne Zusammenfassung     

Tapping mode AFM evidence for an amorphous reticular phase in a condensation-cured hybrid elastomer: alpha,omega-dihydroxypoly(dimethylsiloxane)/poly(diethoxysiloxane)/fumed silica nanoparticles

A new surface phenomenon is reported for hybrid nanocomposites comprising (1) a low Tg poly(dimethylsiloxane) (PDMS) phase cross-linked by (2) a siliceous phase (SP) generated by in situ hydrolysis/condensation of poly(diethoxysiloxane) (PDES), and (3) fumed silica nanoparticles (FSN). After ambient temperature cure, tapping mode atomic force microscopy (TM-AFM) easily reveals near-surface FSN. For nanocomposites with higher PDES content, FSN surprisingly "disappear" after a further cure at 100 degrees C. The observation is explained by further condensation of extant siliceous fragments creating an amorphous reticular phase, which acts as a mechanical barrier between the FSN and the AFM tip.     

Multiblock copolymers of ε–caprolactone and ethylene glycol containing periodic side‐chain carboxyl groups: Synthesis,characterization, and nanoparticle preparation

Multiblock copolymers containing periodically spaced side‐chain carboxyl groups were obtained by a two‐step synthesis involving the preparation of ABA triblock prepolymers of ε‐caprolactone (A blocks) and ethylene glycol (B block) followed by chain extension to ABA_n multiblock copolymers by reaction with pyromellitic dianhydride (PMDA). NMR analysis demonstrated the incorporation of PMDA in polymer chain and revealed the possibility of PMDA units to exist in two isomers, cisoid and transoid forms. Chain extension resulted in the incorporation of free carboxylic groups in polymer backbone and in an almost twofold increase of molecular weight. Thermal analysis indicated that the presence of PMDA residues interferes with the formation of crystalline phases by the chain‐extended polymers. The polymers were found to slowly degrade in buffer solution at 37 °C. Further, the carboxylated polymers can be processed into nanoparticulates by nanoprecipitation. Depending on the selected organic solvent, the particulate was constituted by either a monodispersed nanoparticles with average size of 150 nm or a bimodal distribution centered at about 100 nm and 7 μm. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3800–3809     

Chiral liquid crystal polymers. VIII Thermotropic poly(ester-β-sulphide)s based on variously spaced twin p-oxybenzoate diads

The synthesis and characterization both in solution (chiroptical properties) and in bulk (thermotropic properties) of a new series of structurally defined chiral liquid-crystalline poly(ester-β-sulphide)s are described. The functional polyesters are constituted by repeating units consisting of two p-oxybenzoate diads interconnected by a linear segment of m methylene groups (m = 6-10, 12), and strictly sequenced by the chiral (R)-3-methyl-1,6-hexanedithiyl spacer. The thermotropic behaviour deviates from the regular profiles generally established in homologous series of mesomorphic polymers and results in peculiar alternations of the liquid-crystalline properties, enantiotropism being exhibited by only a few, mainly odd-numbered, homologues of the series.     

Thermal analysis of soil-buried oxo-biodegradable polyethylene based blends

Low-density polyethylene (LDPE) blended with poly(3-hydroxybutyrate) (PHB) and additivated with pro-oxidant were soil buried for 180 days and characterized using thermogravimetry (TG) and differential scanning calorimetry (DSC). TG data showed that both onset and maximum rate degradation temperatures decreased as a function of biodegradation time. Apparent activation energies (E _a) using the Broido integral method decreased with the burial time increasing. PE crystallinity degree values increased in general up to 2 months of biodegradation. At the end of the soil burial (SB) test these values decreased principally for samples that were previously thermo-oxidized in an oven.     

Synthesis and thermotropic properties of new polyacrylates containing alkanoyl-substituted azobenzene mesogens

The synthesis and characterization of a series of new polyacrylates 1, containing the azobenzene mesogen spaced from the backbone by a hexamethylene segment and substituted in the 4-position by an alkanoyl chain of variable length, together with those of the relevant precursors are reported. Optical and X-ray analyses provided evidence for the presence of a smectic A mesophase in a fairly broad range of temperature in both polymers and low molar mass compounds. In polyacrylates 1, the side-chain substituents were fully interdigitated in a smectic A₁ structure. The comparison of the transition parameters of polymers 1 with those of another series of polyacrylates 7 containing the azobenzene unit substituted in the 4-position by an alkyloxy chain of variable length revealed that the replacement of an oxygen atom by a carbonyl group strongly enhanced the smectogenic character of the azobenzene group.     

One line and n points

We analyze a randomized pivoting process involving one line and n points in the plane. The process models the behavior of the RANDOM ‐EDGE simplex algorithm on simple polytopes with n facets in dimension n ? 2. We obtain a tight O(log² n) bound for the expected number of pivot steps. This is the first nontrivial bound for RANDOM ‐EDGE , which goes beyond bounds for specific polytopes. The process itself can be interpreted as a simple algorithm for certain 2‐variable linear programming problems, and we prove a tight Θ(n) bound for its expected runtime. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2003     

Chiral liquid-crystalline polymers. XI. Thermotropic behavior and chiroptical properties in solution of a new series of optically active poly (ester β-sulfide)s

The synthesis and characterization are described of a series of optically active semiflexible poly(ester β-sulfide)s 6*Sn with repeating units constituted by two p-oxybenzoyl diads spaced in an alternating fashion by a sulfide-containing polymethylene segment of variable length (n = 2-10) and a chiral (R)-3-methylhexanediyl segment of high enantiomeric purity. The polymers were prepared with good yields and relatively high molecular weights and narrow degrees of dispersity by a Michael-type polyaddition reaction of bis-thiols to the same chiral mesogenic bisacrylate monomer. Data are reported on the characterization of their chiroptical properties in dilute solution and thermal-optical properties in the bulk, with attention being devoted to the distinct odd-even alternations of the cholesteric-isotropic melt transition parameters. A comparison of the mesomorphic behavior and relevant thermodynamic quantities is presented between the present series of polymers and the achiral analogues of series 6Sn as well as the chiral, positional isomers of series mS6* . The dependence of the overall properties and their trends on very subtle structural changes is stressed, thus highlighting the critical interconnection between mesogenic cores and spacer segments in semiflexible liquid-crystalline polyesters.