Synthesis and comparative studies of carbosilane liquid crystalline dendrimers with chiral terminal mesogenic groups

A new series of carbosilane liquid crystalline (LC) dendrimers from the first to the third generations with 8, 16 and 32 chiral terminal mesogenic groups, respectively, has been synthesized. The molecular structures and purity of all new compounds were confirmed by ¹H NMR spectroscopy and GPC analysis. Data of polarization microscopy and SAX analysis demonstrated that all LC dendrimers synthesized form a chiral smectic SmC* phase at temperatures below 50 °C. It has been found that bistable electrooptical switching is observed for all dendrimers. The influence of chiral mesogenic fragment length on phase behavior and ferroelectric properties of carbosilane LC dendrimers is discussed.     

Synthesis of dendrimers with terminal formyl groups

A method for preparation of dendrons and dendrimers with formyl groups at the terminal aromatic rings, ether bonds in the branching blocks, and ester bonds in the core of the macromolecules is proposed. A way for the selective synthesis of p-hydroxymethylbenzaldehyde is described.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1995–1999, September, 2004.     

Synthesis,structure, and phase behavior of carbosilane LC dendrimers with terminal butoxyphenylbenzoate mesogenic groups

Two series of carbosilane LC dendrimers with terminal protonated and deuterated butoxyphenylbenzoate mesogenic groups linked to carbosilane dendritic matrices of the first to fifth generations via an undecylene spacer have been synthesized. The chemical structure of new dendrimers has been studied by ¹H NMR spectroscopy and gel-permeation chromatography. The dendrimers of first-fourth generations are characterized by formation of the smectic C mesophase in a wide temperature range, whereas much more complex columnar supramolecular structures are formed in dendrimers of the fifth generation. Structural studied of mesophases by X-ray diffraction and small-angle neutron scattering show that segregation takes place in mixtures of deuterated and protonated LC dendrimers; as a result, huge aggregates composed of hundreds of chemically unbound molecules develop and the sizes of these aggregates reversibly change with temperature.     

Liquid-Crystalline copolymers and polymer blends containing electron donor and acceptor groups: Effects of mesogenic structures on the smectic phase and the miscibility

Side-chain liquid-crystalline copolymers and polymer blends containing an electron-donating (carbazolylmethylene)aniline group and electron-accepting nitrophenyl groups with various central linking groups between aromatic groups in the mesogenic units, i.e., N?CH, CH?CH, N?N, and COO, were prepared to examine effects of the mesogenic structure on thermal behaviours. The most remarkable effects of the central linking group on the thermal properties and the miscibility were observed for the polymer blends. The 1:1 miscible polymer blends were prepared from the electron-donating polymer containing (carbazolylmethylene)aniline group (PM6C_z) and the electron-accepting polymers with similar central linking groups, i.e., N?CH, CH?CH, and N?N. For example, the 1: 1 polymer blend of PM6C_z and the electron-accepting polymer containing the nitrostilbene group induced a smectic phase from 73 to 207°C. This isotropic temperature was 46°C higher than the calculated value (161°C) based on the composition without the electron donor-acceptor interaction. On the other hand, the 1: 1 polymer blend of PM6C_z and the electron-accepting polymer containing the nitrophenylbenzoate group showed phase separation. Thus, the remarkable thermal stability and the miscibility of the polymer blends containing the electron donor and acceptor groups might be caused by planar structures between the mesogenic side groups which have similar central linking groups through the electron donor-acceptor interaction. A similar tendency was seen for copolymers and binary mixtures of both low-molecular-weight compounds containing the same mesogenic groups. © 1995 John Wiley & Sons, Inc.     

Thermodynamic properties of the first to fifth generations of carbosilane dendrimers with allyl terminal groups

Temperature dependences of the specific heats, characteristic temperatures, and enthalpies of physical transformations of the first to fifth generations of carbosilane dendrimers with allyl terminal groups were studied using an adiabatic vacuum calorimeter in the temperature range 6—340 K. The error of measurements was, as a rule, about 0.2%. Thermodynamic characteristics of physical transformations of the dendrimers were determined and their thermodynamic functions C _p°(T), H°(T)—H°(0), S°(T)—S°(0), and G°(T)—H°(0) were calculated for the temperature range 0—340 K. The thermodynamic functions of the dendrimers are linearly related to their molecular weights, the number of allyl groups on their outer spheres, and the number of moles of diallylmethylsilane per mole of the dendrimers formed. Additive dependence of the properties of the dendrimers on their chemical composition and structure indicates that the energy of interaction between structural fragments of the dendrimers is independent of the dendrimer generation number. The fractal dimensions, D, of all dendrimers studied in this work are 1.2—1.3 in the temperature range 30—50 K, thus indicating a chain-layered structure of the dendrimer glasses.     

Effect of smectogenicity of the ionic groups on the thermotropic liquid crystalline behavior of pyridinium and poly(4-vinylpyridinium) salts quaternized with mesogenic groups

In order to demonstrate the important smectic power of the ionic functions present in mesogenic molecules, a series of N-alkylpyridinium bromides ω-substituted with (4-cyanobiphenylyl)oxy or [4-(2-methyl-1-butoxy)biphenylyl]oxy mesogenic group and their analogous 4-vinylpyridinium polymers were synthesized and characterized. The liquid crystalline behavior was studied by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Smectic mesophases, namely A, B, and E, were identified for the low molecular weight compounds, whereas smectic A and E mesophases were identified for the analogous polymers. Both structures were found to be very similar. They consist of single layers of upright molecules laterally arranged head-to-tail; the polymer backbone is inserted in between the layers. The monolayer smectic ordering observed in spite of the presence of the interacting cyano and chiral groups demonstrates the prevailing effect of the electrical interactions upon the structural organization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2569–2577, 1997     

Synthesis and characterization of 2,2‐bis(methylol)propionic acid dendrimers with different cores and terminal groups

Three sets of aliphatic polyester dendrimers based on 2,2‐bis(methylol)propionic acid (bis‐MPA) were synthesized. Two of the sets had benzylidene terminal groups and either a trimethylolpropane or triphenolic core moiety. The last set had acetonide terminal groups and a triphenolic core moiety. Benzylidene‐[G#1]‐anhydride and acetonide‐[G#1]‐anhydride were used as the reactive building blocks in the construction of all dendrimers. The large excess of building blocks used in the coupling reactions initially resulted in considerable material loss. This waste was eliminated through the development of a recycling method. ¹H and ¹³C NMR and matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) analysis were used to verify the purity of all compounds. Size exclusion chromatography (SEC) was used, as well as MALDI‐TOF, for molecular weight determinations. The SEC measurements were conducted with a universal calibration method and an online right‐angle laser light scattering detector. Measured dendrimer molecular weights were close to their theoretical molar masses. Observations were also made of the hydrodynamic radius and intrinsic viscosity for the different dendrimers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1758–1767, 2004     

Thermodynamic properties of carbosilane dendrimers of the seventh and ninth generations with terminal butyl groups in the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 600 K

Temperature dependences of the heat capacity of carbosilane dendrimers with butyl terminal groups of the seventh and ninth generations were determined in the temperature range from 6 to 600 K by precision adiabatic vacuum calorimetry and differential scanning (dynamic) calorimetry. The physical transitions were revealed and their thermodynamic characteristics were analyzed. The experimental data obtained were used to calculate the standard thermodynamic functions C _p (T), H°(T) − H°(0), S°(T), and G°(T) − H°(0) for the temperature range from T → 0 to 600 K. The thermodynamic function-molar weight isotherms for the dendrimers of the third–ninth generations with terminal butyl groups in the glassy and highly elastic state are linear. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1924–1928, October, 2007.