Poly(ethyl-n-butylsilylene): Structural, thermal, and flow properties of a liquid crystalline polysilane

Poly(ethyl-n-butylsilylene) (PEBS) was synthesized by sodium coupling of ethyl-n-butyldichorosilane and separated into fractions with differing molecular weights,M _w=1.4×10⁶ and 2.0×10⁴. Both fractions were studied by differential scanning calorimetry and by X-ray diffraction, UV spectroscopy, polarizing optical microscopy, and capillary rheometry, all as a function of temperature. Both samples adopt a hexagonal columnar liquid crystalline structure at room temperature and below. They undergo a weak endothermic transition at –20°C and a first-order phase transition to a nematic liquid crystalline form at 90°C for the low and 170°C for the highM _w fraction. Melting to an isotropic liquid takes place at 106°C for the low and 185°C for the highM _w polymer. Both samples undergo two successive thermochromic transitions in the UV, one near the first-order exothermic transition and one near the –20°C transition; the reasons underlying these thermochromic transitions are discussed. Flow properties of PEBS were investigated as a function of molecular weight.Presented at the xxvith Silicon Symposium, Indiana University—Purdue University at Indianapolis, March 26–27, 1993.     

Structure and liquid crystalline phases of amphiphilic side chain polymers in aqueous solution

Functional amphiphilic molecules which form liquid crystalline (l.c.) phases in aqueous solutions, can be polymerized to amphiphilic side chain polymers. Depending on the formation of the polymer backbone via the hydrophobic (type A) or hydrophilic part (type B) of the monomer, it can be differentiated between two polymers. For both types of polymers a model is proposed which explains their micellar association in solution. In aqueous solutions polymers of type A should form normal spherical, rodlike and disc-like micelles, while polymers of type B should form the corresponding reversed micelles. The phase behavior in aqueous solutions is investigated with two model systems of monomer/side chain polymer of type A. It is shown that the polymers exhibit l.c. phases, which are stable within a broader concentration range, as well as to higher temperatures compared to the corresponding monomers. The structures of the l.c. phases are in accordance with the model considerations.     

Synthesis of a novel comb-like poly(vinyl ether) with isopropylnaphthoxy pendant by cationic polymerization

Summary A novel comb-like polymer having isopropylnaphthoxy pendant with the controlled molecular structure was synthesized by the cationic polymerization of 2-(6-isopropyl-2-naphthoxy)ethyl vinyl ether with AlEtCl₂ catalyst. Although the polymer's molecular weight (Mn: 4,000–17,000) could be controlled by the reaction conditions (sovent polarity, temperature and initial monomer concentration), the steric structure was not affected by them at all, giving almost the same amount of the meso and racemic diads irrespective of the conditions. The polymer showed only an amorphous character (Tg: 22–45 °C) but not any liquid crystalline phase.     

Transformations in the cellulose nitrate structure in the process of solvent vapor sorption

Summary A technique permitting to record structure transformations in a polymer film by X-ray analysis directly in the process of low molecular weight solvent vapor sorption is developed. Applying it to cellulose nitrate (CN) — ethyl acetate (EA) system evidences the formation of a set of crystalline reflections in the initially amorphous film at a definite EA vapor activity (p/p_s 0.6), the reflections disappearing after the removal of EA. The ordering of structure is associated with molecular complexes (MC) formation, MC being thermodynamically stable within a certain p/p_s range. It proves the validity of a qualitative phase diagram offered for CN — EA system (6). The peculiarities of MC formation and destruction are bound to assist in interpretation of sorption and diffusion properties of the system in question.     

Characterization and free radical polymerization of liquid crystalline acrylic acid/cellulose diacetate and N-vinyl-2-pyrrolidinone/cellulose diacetate solutions

Polymerizations of liquid crystalline solutions of cellulose diacetate (CDA) in acrylic acid (AA) and N-vinyl-2-pyrrolidinone (NVP) were conducted in an attempt to prepare molecular composites (polymer blends) processing a rigid rod polymer with liquid crystalline orientation. CDA was found to form liquid crystalline solutions in both AA and NVP at concentrations avove 40 wt% CDA. Polymerization of anisotropic 50 wt% CDA-AA and CDA-NVP solutions occurred with considerable retention of the starting solution anisotropy and yielded homogeneous blends (1 T_g) when the rate of polymerization was fast relative to the phase separation of the free radically polymerizing AA or NVP with CDA. Slow polymerizations lead to phase separated blends (2 T_g).     

Facile preparation of magnetic nanocrystals using amphiphilic hyperbranched polymers as unimolecular nanoreactors and magnetofection in vitro

A new strategy for the preparation of Fe₃O₄ nanocrystals (NCs) and FePt bimetal NCs with amphiphilic hyperbranched polymers as unimolecular nanoreactors has been described. The amphiphilic hyperbranched polymers were synthesized by grafting methyl acrylate to hyperbranched poly(ethylenimine)s (HPEI) with the help of Michael addition reaction. The hydrophilic HPEI core was used to stabilize the magnetic NCs, whereas the hydrophobic methyl ester terminals can prevent the aggregation of polymers and NCs, thus magnetic NCs with a narrow size distribution were prepared. The resulting Fe₃O₄ NC/amphiphilic hyperbranched polymer nanocomposites also showed slightly better magnetofection property than HPEI transfection and their luciferase expression level in maximum was 1.3‐fold greater than that for HPEI transfection. POLYM. COMPOS., 37:429–434, 2016. © 2014 Society of Plastics Engineers     

Mesomorphic properties of cholesteric side‐chain liquid crystalline polysiloxanes and elastomers

A series of crosslinked liquid crystalline polymers and corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization. Their liquid crystalline properties were characterized by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The results showed that the crosslinking obtained in the isotropic state and the introduction of nonmesogenic crosslinking units into a polymeric structure could cause additional reduction of the clearing point (T_i) of the crosslinked polymers, compared with the corresponding uncrosslinked polymers. The crosslinked polymers (P‐2–P‐4) with a low crosslinking density exhibited cholesteric phases as did the uncrosslinked polymers. In contrast, a high crosslinking density made the crosslinked polymer P‐5 lose its thermotropic liquid crystalline property. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 773–778, 2004     

Supramolecular structures of an amphiphilic hairy-rod conjugated copolymer bearing poly(ethylene oxide) side chain

The structures of an amphiphilic conjugated graft copolymer, poly(2,3-diphenyl-5-(trimethylene-heptadeca(oxyethylene)-methoxy-phenylene vinylene) (denoted as PVEO₁₇) composing of a conjugated DP-PPV backbone and PEO side chains, in bulk and solutions with tetrahydrofuran (THF) and water have been investigated by small-angle X-ray scattering (SAXS). In bulk state, the DP-PPV main chains in PVEO₁₇ stacked to form flat disk microdomains dispersed in the PEO side-chain matrix. The corresponding wide angle X-ray scattering pattern revealed the existence of crystallinity of the PEO side chains. The structure of the polymer in solution was affected by the solvent quality and the polymer concentration. PVEO₁₇ chains were relatively well dispersed in THF. In aqueous solutions, however, the amphiphilic PVEO₁₇ chains aggregated significantly over the concentration range of 1–8 wt%, where the polymer was found to self-organize to form cylindrical micelles with the aggregation number increasing with the increase of concentration. The photophysical properties characterized by UV–Vis and photoluminescence spectroscopy were strongly affected by the aggregation state of the polymer.     

Determination of the molecular orientation in the polymeric liquid crystalline systems by low frequency Raman spectroscopy

Anisotropic polymer composites with fixed, oriented liquid crystalline organisation prepared by in situ photopolymerisation of acrylic or methacrylic acids in several cellulose derivatives were investigated by low frequency Raman scattering. The results were interpreted basing on a model of non-continuous structure of polymer glasses. The Raman investigations have shown that the macromolecules of the non-mesogenic (acrylic) component are oriented in the anisotropic composites, and that the orientation of the polyacrylic chains is more pronounced in the composites with higher concentration of the liquid crystalline cellulose derivative. It was found, that the interactions between the components play a crucial role in the formation of the composites (template-like photopolymerisation) and they determine their supramolecular structure. The liquid crystalline cellulose derivatives able to form hydrogen bonds play a role of specific cross-linking agents, while the cellulose derivatives with aliphatic side chains work as plasticisers.     

Approximate Method for Optimization of the Geometric Structure of Polyatomic Systems

A compact method of calculation for solving a fundamental problem in structural chemistry — the problem of optimizing the geometric structure of molecular systems — is proposed. Solution of this problem will allow predicting a number of properties of polymer systems based on the existence of a structure—property correlation. It should be noted that the proposed method allows performing all calculations in analytical form.     

Synthesis and characterization of optically active liquid crystalline polyacrylates containing mesogenic phenylbenzoate groups

A series of novel side chain liquid crystalline polyacrylates with pendant chiral groups were synthesized. It was found that monomers with electron releasing -OC₄H₉ terminal groups seem beneficial for the formation of liquid crystalline phases. Copolymerization of the monomers was carried out and the physical properties of the copolymers were investigated. All synthesized polymers revealed liquid crystalline phases and appeared highly thermally stable with decomposition temperatures (T_d) at 10% weight loss greater than 384 °C and about 50% weight loss occurred beyond 442 °C under nitrogen atmosphere. Two miscible chiral compounds were also synthesized and used as chiral dopants to induce cholesteric liquid crystalline phases of polymers. Liquid crystalline phases of the polymers were investigated using DSC and XRD, and confirmed with POM technique. The optical properties of the induced cholesteric liquid crystalline polymers were investigated using UV-vis spectrometer. The appearance and the color variation of the polymer films before and after UV irradiation were also investigated. Typical helical morphology of the cholesteric liquid crystalline film was analyzed by SEM technique.     

Crystalline transformation of isotactic polybutene-1 in supercritical CO2 studied by in-situ fourier transform infrared spectroscopy

The solid-solid crystalline transformation of isotactic polybutene-1 (iPB-1) from tetragonal form II to hexagonal form I could be accelerated by supercritical carbon dioxide (scCO₂). In this study, in-situ Fourier transform infrared spectroscopy (FTIR) and two dimensional correlation spectroscopy (2DIR) is used to observe and investigate the crystallization behaviour of iPB in scCO₂ and compressed CO₂. Based on the transform sequence given by 2DIR analysis, this transformation of helical chain structures is found to be initiated with the motion of side chains and followed by the movement of main chains. It is speculated that the motion of polymer chains was enhanced with the diffusion of CO₂. Also this crystalline transition is observed even in compressed CO₂, suggesting that CO₂ could also diffused into polymer under high pressure near the critical pressure. This diffusion of CO₂ is indicated by the growth of IR bands being assigned to the stretching vibration of C–O. A further investigation on the mechanically heating and freely cooling of iPB provides more evidences on the process of structure transition. The result implies that the nucleus of tetragonal form II formed in the melt is not affected by the existence of scCO₂, but the crystallization temperature become obviously lower.     

Effect of a compatibilizer on the structural development of a thermotropic liquid crystalline polymer/polystyrene blend

A fine fibril structure of a thermotropic liquid crystalline polymer (TLCP, a poly(ester amide)) can be developed in a shear flow field of a thermoplastic matrix (polystyrene, PS). Addition of a third component, a poly(styrene‐co‐maleic anhydride) (SMA), that interacts with the thermotropic liquid crystalline polymer facilitates the structural development of the TLCP phase by acting at the interface. Moreover, it brings about good adhesion at the interface and enables the dispersed liquid crystalline polymer phase to be deformed in shear flow without strong elongation even though the viscosity of the matrix is much lower than that of the liquid crystalline polymer. The mechanical properties were substantially improved because of both the good adhesion at the interface and fibril generation, which were ascribed to the SMA interaction. These results have important implications in that they provide a means to produce strong and tough in‐situ composites when the viscosity of the matrix polymer is lower than that of the dispersed liquid crystalline polymer which is immiscible with the matrix polymer. Morphological observations determined the significance of the third component (SMA) in immiscible polymer blends, and an optimum amount of SMA exists for best mechanical performance.     

Liquid crystallization of poly(styrene‐co‐maleic anhydride) induced by intermolecular hydrogen bonds

The liquid crystallization of general polymer (GP) with maleic anhydride in the main chain has been realized through molecular recognition and self‐assembly based on intermolecular hydrogen bonds. Poly[styrene‐co‐(N‐4‐carboxylphenyl)maleimide] (SMIBA) was synthesized by imidization and dehydration of Poly(styrene‐co‐maleic anhydride) (SMA) with p‐aminobenzoic acid (ABA) for use as an H‐bonded donor polymer. 4‐Methoxy‐4′‐stilbazole (MSZ) and 4‐nitro‐4′‐stilbazole (SZNO₂) were prepared as an H‐bonded acceptor. SMIBA was complexed with MSZ or SZNO₂ by slow evaporation from pyridine solution to form a self‐assembly, which exhibits the mesophase, while neither of the individual components is mesogenic. The phase diagrams of a variety of mixtures between of SMIBA and stilbazoles have been established using DSC and POM. They show complete miscibility and high thermal stability of the liquid crystalline phase over the whole composition range. The tuning of liquid crystalline properties was achieved by changing the composition of the mixture and involving it with a mixture of SZNO₂ and MSZ. IR measurements strongly support the existence of an H‐bonded complex between the carboxylic acid of SMIBA and the pyridine group of stibazoles. Unlike conventional side‐chain liquid crystalline polymer (SLCP), supramolecular SLCP with a lower molecular weigh polymeric donor has higher thermal stability of the liquid crystalline phase due to the microphase separated in the hydrogen bonding case. Liquid crystallization of GP, such as SMA, induced by hydrogen bonds, offers a new route to prepare functional material with controlled molecular architecture from readily accessible and simpler precursors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 97–105, 1999     

Synthesis and Characterization of Novel AB and ABA Rod–Coil Block Copolymers

Two series of novel rod–coil block copolymers, poly(ɛ-caprolactone)-b-poly{2,5-bis[(4-methoxyphenyl) oxycarbonyl] styrene} (PCL-b-PMPCS) and poly{2,5-bis[(4-methoxyphenyl) oxycarbonyl] styrene}-b-poly(ɛ-caprolactone)-b-poly{2,5-bis[(4-methoxyphenyl) oxycarbonyl] styrene} (PMPCS-b-PCL-b-PMPCS), were successfully synthesized via atom transfer radical polymerization in chlorobenzene solution using macro-initiator and CuBr/Sparteine complex as catalyst. The results show that the number average molecular weight M_n increased versus the monomer conversion and that the polydispersity M_w/M_n was quite narrow (<1.35), which were the character of controlled polymerization. The structure of the block copolymers was experimentally confirmed by ¹H NMR. And the liquid crystalline behavior of them was studied using DSC and POM. The data obtained implied that the block copolymers with low molar percentage of PMPCS block could show T_m of PCL. While only the copolymers with long rigid segment PMPCS could form liquid crystalline phase, which was quite stable with a high clearing point.     

Preparation of hydrophilic polysulfone porous membrane by use of amphiphilic cellulose

A cellulose‐based amphiphilic co‐polymer with grafted myristyl groups was synthesized and used as an additive to modify polysulfone (PSf) membranes. Fourier transform infrared (FTIR) spectroscopy and Solid‐state cross polarization magic angle spinning carbon‐13 nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy were used to characterize the structure of the synthesized amphiphilic cellulose. The good compatibility between amphiphilic co‐polymer and PSf was confirmed by differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) was conducted to inspect morphology of the membrane. Furthermore, Thermal performance was indicated by thermogravimetric analysis (TGA). Contact angle, flux and retention behavior were also measured in this work. The structural similarity enhanced compatibility among components by introducing flexible alkyl groups. According to the findings obtained from characterization, better compatibility of cellulose with PSf was achieved after amphiphilic treatment. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41664.     

Phenomenological and Thermodynamic Aspects of Melting and Formation of Polymer Crystals in the Presence of Liquids

Based on the results of a phenomenological and thermodynamic analysis of melting and crystal formation in polymers in the presence of liquids, it was hypothesized that crystalline equilibrium in amorphous crystalline polymer—liquid systems does not obey the phase rule. A new interpretation of the phase diagram of such a system was given within the framework of this concept.     

Synthesis and characterization of four-armed star mesogen-jacketed liquid crystal polymer

The synthesis of four-armed star mesogen-jacketed liquid crystal polymer was achieved by atom transfer radical polymerization in chlorobenzene solution using pentaerythritol terakis(2-bromoisobutyrate) (PT-Br) as an initiator and CuBr/sparteine complex as a catalyst. The results show that the number average molecular weigh is creased linearly vs. monomer conversion, and that the polydispersities were quite narrow (<1.19), which is the character of controlled polymerization. The structure was experimentally confirmed by ¹H NMR. The liquid-crystalline behavior of the four-armed star polymer was studied using DSC and POM. Only the polymer with a M_n,GPC beyond 3.68×10⁴ g/mol formed a liquid crystalline phase which was quite stable with a high clearing point.     

Adhesion aspects of levulinic-acid-modified furan polymers to crystalline zinc phosphate metal surfaces

The nature of the interfacial interactions between functional levulinic-acid-modified furan resin coatings and crystalline zinc phosphate hydrate films deposited on carbon steel surfaces has been systematically investigated. The typical surface topography of the highly crystallized zinc phosphate films was found to be characterized by the presence of a dendritic microstructure array of interlocking triclinic crystals. This structure acts significantly to develop mechanical interlocking bonds with the functional blend polymer which penetrates into the open surface structure of the films. Both the thickness of deposition film and the polar H₂O molecules of hydrate at the outermost film surface sites play essential roles in wetting by the functional liquid resin. When the polarized furan polymers spread on the oxide film surfaces, the carboxylate groups derived from the levulinic ester and acid molecules react to form strong hydrogen bonds with the crystallized H₂O molecules on the hopeite film. This formation of hydrogen bonding was shown to be a major factor affecting the chemical intermolecular attractions. A formulation consisting of 95 parts furan to 5 parts levulinic acid was found to yield the optimum protective coating. More than 5 parts levulinic acid resulted in the transformation of the characteristics of the polymer film from hydrophobic to hydrophilic.     

Novel amphiphilic polymer gel electrolytes based on (PEG‐b‐GMA)‐co‐MMA

Amphiphilic conetwork–structured copolymers containing different lengths of ethylene oxide (EO) chains as ionophilic units and methyl methacrylate (MMA) chains as ionophobic units were prepared by free radical copolymerization and characterized by FTIR and thermal analysis. Polymer gel electrolytes based on the copolymers complexed with liquid lithium electrolytes (dimethyl carbonate (DMC) : diethyl carbonate (DEC) : ethylene carbonate (EC) = 1 : 1 : 1 (W/W/W), LiPF₆ 1.0M) were characterized by differential scanning calorimetry and impedance spectroscopy. A maximum ion conductivity of 4.27 × 10^?4 S/cm at 25^oC was found for the polymer electrolyte based on (PEG2000‐b‐GMA)‐co‐MMA with long EO groups. Moreover, the effect of temperature on conductivity of the amphiphilic polymer electrolytes obeys the Arrhenius equation. The good room temperature conductivity of the polymer electrolytes is proposed to relate to the enhancement in the amorphous domain of the copolymers due to their amphiphilic conetwork structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010