A Liquid‐Crystalline Co‐Polysiloxane with Asymmetric Bent Side Chains

A co‐polysiloxane has been prepared with an asymmetric bent side group based on a liquid‐crystalline monomer showing a B₂ (SmCP) phase. In order to dilute the side chain mesogens along the polymer backbone, octyl side chains were also incorporated. X‐ray studies confirmed that the resulting co‐polysiloxane exhibits a liquid‐crystalline layered phase, the siloxane polymer chains being microphase segregated from the incompatible side chain mesogens. The mesophase of polymer exhibits a homeotropic structure that can be successfully aligned by unidirectional shear. This phase does not exhibit polar switching under an applied electric field unlike the bent‐core monomer used as the side chains of this polymer. This can be caused by the homeotropic alignment of the polymer samples.

     

Microstructure-Driven Self-Sorting of Chemically Indistinguishable Side Chains in Pre-Programmed Alkyl Siloxanes Leading to Amplification of Mechanical Properties

A unique microstructure-driven self-sorting of chemically indistinguishable side chains in alkyl siloxanes is reported for the first time. The difference in cooperativity among the side alkyl chains caused by the variation in backbone microstructure is the key to drive this self-sorting. The study also reveals that while alkyl chains of random and fully blocked siloxane discriminate each other, the alkyl chains of partially blocked siloxane can form crystals with both polymers resulting in reinforcement of the mechanical property of the blends.     

Dynamic Homogeneity by Architectural Design – Bottlebrush Polymers

The self‐organization and dynamics of bottlebrush polymers consisting of poly(2‐bromoisobutyryloxyethyl methacrylate) (PBiBEM) backbone and grafted n‐butyl acrylate (PBA) chains are studied as a function of the side‐chain length by X‐ray scattering, dielectric spectroscopy, and rheology in relation to the respective homopolymers. All short‐range correlations are dominated by the PBA side chains, whereas long‐range correlations reflect the screening of the backbones by the side chains. Such correlations show up also in the segmental dynamics. The PBA segmental dynamics are slowed‐down, whereas the backbone dynamics are plasticized by the side chains. Overall the bottle‐brush architecture imparts dynamic homogeneity to the backbone and side‐chain dynamics.     

Direct Insertion Mass Spectrometric Analysis of Thermal Degradation of Poly(2‐alkyl‐2‐oxazoline)

Direct pyrolysis mass spectrometry is applied to investigate the thermal behavior of poly(2‐isopropyl‐2‐oxazoline) (PIPOX, a thermoresponsive polymer) and poly[2‐(3‐butenyl)‐2‐oxazoline] (PBOX, a “clickable” polymer). It is found that the thermal degradation of PIPOX is started by a loss of side chains. At slightly higher temperatures the degradation of the polymer backbone occurs by random chain scission processes. In the case of PBOX, vinyl polymerization of the side chains produces chains with variable thermal stabilities. The number of repeating units of the polymer has almost no effect on the thermal behavior of PIPOX, but significantly affects both thermal stability and degradation product distribution of PBOX.     

Frustrated Behavior of a Side‐Chain Liquid Crystalline Polyacrylate

Polyacrylate with phenyl benzoate mesogenic side groups was synthesized and fractionated into narrow fractions. Structure and phase behavior of the narrow‐molecular‐weight samples have been studied by X‐ray diffraction. Depending on the degree of polymerization the polymer shows nematic, smectic A_d, re‐entrant nematic and new phase with two‐dimensional (2D) periodicity. Such behaviour is implicit to so‐called frustrated systems. However, the mesogenic side chains are nonpolar and thus the origin of frustration is different from that in conventional polar liquid crystals. We found that this phenomenon is steric (entropic) in nature and depends on the length of the polymer backbone. The phase transformations of mesogen side chain polyacrylates are discussed in terms of coupling between the smectic ordering of the side groups and the polymer backbone conformations.     

Optical anisotropy of comb-like macromolecules of lateral and semilateral structure

Maxwell effect and Kerr effect techniques were used to study the intramoleculare axial ordering of anisotropic side groups of an isolated macromolecule in solution. Three comb-like polymers with a methacrylic main chain were investigated. The side chains contain aliphatic spacers separating the mesogenic fragments R from the backbone. R contains two or three phenylene rings with ester linking groups and cyano end groups. Fragments R are attached to the side chains, by the end or middle-point, through the para- or ortho-phenylene ring. The main-chain conformation in solution was identified to assess the hydrodynamic data using the Gaussian coil approximation. The optical anisotropy of the macromolecule segment was determined and related to the monomer unit structure. The specific Kerr constant obtained in diluted benzene solution of polymer was compared with those of low molecular weight analogues of the polymer mesogenic groups. The mobility and intramolecular ordering of the mesogenic groups in the isolated macromolecules are discussed. These properties are compared with those of comb-like polymers with another type of attachment of mesogenic groups, and with another (siloxane) chemical structure of the backbone chain. The differences in restrictions of side-chain mobility due to the backbone linkage in different types of comb-like polymers are also discussed.     

Chain Microstructure,Crystallization, and Morphology of Olefinic Blocky Copolymers

The chain microstructure, crystallization, and morphology of three olefinic blocky copolymers (OBCs) are compared. The weight percentage of the hard block and the octene content in it are calculated from the ¹³C NMR spectra with a two‐site first‐order Markovian model. The lengths of the hard blocks are compared from the melting and crystallization behaviors. The remarkable difference between the crystallinity measured by DSC, and wide‐angle X‐ray diffraction (WAXD) indicates the presence of partially ordered phases. Small angle X‐ray scattering (SAXS) shows that the partially ordered phases in OBC‐A are mainly located at the interface between the crystalline and amorphous phases, but exist as separated microdomains in OBC‐B. As the hard block becomes shorter, there are also more, separated partially ordered phases in OBC‐C. Spherulites are observed in all OBCs by POM and the size of the spherulites decreases in the order: OBC‐A > OBC‐B > OBC‐C. TEM shows that spherulites are poorly developed in a thin film of OBC‐B.     

Thermoresponsive Poly(2‐Oxazoline) Molecular Brushes by Living Ionic Polymerization: Modulation of the Cloud Point by Random and Block Copolymer Pendant Chains

Molecular brushes (MBs) of poly(2‐oxazoline)s were prepared by living anionic polymerization of 2‐isopropenyl‐2‐oxazoline to form the backbone and living cationic ring‐opening polymerization of 2‐n‐propyl‐2‐oxazoline and 2‐methyl‐2‐oxazoline to form random and block copolymers. Their aqueous solutions displayed a distinct thermoresponsive behavior as a function of the side‐chain composition and sequence. The cloud point (CP) of MBs with random copolymer side chains is a linear function of the hydrophilic monomer content and can be modulated in a wide range. For MBs with block copolymer side chains, it was found that the block sequence had a strong and surprising effect on the CP. While MBs with a distal hydrophobic block had a CP at 70 °C, MBs with hydrophilic outer blocks already precipitated at 32 °C.     

Effect of Tacticity on the Structure of Poly(1‐octadecene)

Summary: A sample of poly(1‐octadecene), synthesized with a highly active heterogeneous Ziegler‐Natta catalyst, has been fractioned with heptane, giving soluble and insoluble fractions. Both fractions and the original polymer have been characterized by size exclusion chromatography, solution and solid‐state ¹³C NMR, DSC and X‐ray diffraction. The results show that the fractionation occurs on the basis of both molecular mass and tacticity differences, with the atactic content concentrated in the lower molecular mass chains. Thus, the soluble fraction, having a lower average molecular mass than the original sample, consists predominantly of atactic chains, whereas the insoluble fraction is mainly isotactic. The analysis of the solid‐state structure reveals that both atactic and isotactic fractions are able to crystallize, although their crystalline structures are different. The NMR and X‐ray data together support the “most probable” structure for the isotactic polymer advanced by Turner‐Jones. That structure is characterized by an orthorhombic crystal form, where a) the backbone crystallizes in a quaternary helical conformation, b) the sidechains are packed in a way analogous to orthorhombic polyethylene, and c) successive sidechains are conformationally inequivalent. Support for points b) and c) are respectively found in the chemical shift of the sidechains and in the splittings observed for backbone carbons and for some sidechain carbons located near the points of attachment. In addition, there is evidence that the mobility of sidechain sites at points near both the bonded and free ends are not uniform from chain to chain. On the other hand, the crystal form for the atactic polymer shows only sidechain order with some support for the notion that this order approximates the disordered hexagonal rotator phase of the alkanes.

X‐ray diffractograms of the three poly(1‐octadecene) samples.     

Ordered Nanostructures of Carbon Nanotube–Polymer Composites from Lyotropic Liquid Crystal Templating

A series of polymer nanocomposites containing single‐walled carbon nanotubes (SWNTs) are prepared from polymerizable quaternary ammonium surfactants using photo‐polymerization and investigated by means of polarized optical microscopy, small‐angle X‐ray scattering, and rheological measurements. The surfactant monomers with various alkyl chains of nonpolar tails form lyotropic liquid crystalline (LLC) mesophases in aqueous medium with hexagonal packing of cylindrical micelles. The physical adsorption of nonpolar tails of surfactants on the surface of SWNTs results in de‐bundled nanotubes. The LLC phase diagram is investigated as functions of alkyl chain length, concentration, temperature, and SWNTs. As such, addition of SWNTs does not change the hexagonal mesophases but enhances the order–disorder transition temperatures and alters the rheological behaviors. After photo‐polymerization, the microstructures of hexagonal packing are changed while addition of SWNTs does not disrupt the resulting microstructures. The polymerized composites are consistent with both lamellar and gyroid nanostructures and a possible model is proposed to interpret the observed phenomenon. Under the shear flow, the defect‐free monodomain structures are obtained in the LLC phase and subsequently locked in the solid film after polymerization.     

Structure of Poly(amino‐s‐triazine)s with Long Methylene Segments

Linear poly(amino‐s‐triazine)s with segments of ten and twelve methylene groups have been synthesized and characterized. Their structure has been studied by means of X‐ray and electron diffraction, and molecular simulation. The polymers are found to crystallize in a unit cell very similar in chain axis projection to that of polyethylene. Furthermore, molecular simulation indicates that the polymethylene segments of the polymer chains are placed with a setting angle very close to that found in the polyethylene structure. The packing of the new polymers appears to be further stabilized by intermolecular hydrogen bonds that involve all nitrogen atoms of the amino‐triazine units.     

New Thermo‐Sensitive Graft Copolymers Based on a Poly(N‐isopropylacrylamide) Backbone and Functional Polyoxazoline Grafts with Random and Diblock Structure

New thermo‐sensitive functionalized graft copolymers characterized by a poly(N‐isopropylacrylamide) backbone and grafts containing 2‐ethyl‐2‐oxazoline and 2‐(2‐methoxycarbonylethyl)‐2‐oxazoline units were synthesized. The conformation transition temperatures of the graft copolymers could be modified by variation of the molar composition in the side chain, by different side chain structure (random distribution of both oxazolines vs. diblock structure) and by hydrolysis of the methylester to the acid form. Graft copolymers with long functional oxazoline side chains allowed the stabilization of aggregates above the phase transition temperature of the backbone until the LCST of the side chain. The temperature window allowing for the formation of stable aggregates was widened with acid functions in the corona.

     

Synchrotron X‐Ray Study of Liquid Crystalline Polyoxetanes Containing Two Mesogenic Groups Connected by a Flexible Spacer in the Side Chain

The study of the mesophase behaviour of a family of new side chain liquid crystalline polymers by means of synchrotron X‐ray diffraction is reported. These systems contain two bibenzoate rigid units in the side chain that are interconnected through a flexible spacer. A polymerisable oxetane unit is linked to one end of the dimer structure, and a flexible terminal chain is linked to the other end. All the polymers form phases with variable degree of order (from low ordered smectic to crystalline) depending on the chemical constitution of the different segments. The influence of the length, parity, and lateral substitution of the spacers on the transitional parameters and the symmetry of the mesophases that are formed is analysed. Close similarities were found between the phase behaviour of the monomer precursors and the derived polyoxetanes. The arrangement of the mesogens, the flexible groups and the polymeric backbone in the layered structure is discussed with respect to the L/d ratio. Different values were obtained depending on the parity of the central spacer and on the degree of order of the mesophase. Interpenetrated structures, where the flexible groups of different lengths are mixed, seem to be compatible with low ordered smectic phases, but sterically disfavoured when building up highly ordered mesophases.

     

An In Situ Investigation into the Formation of the Solvent‐Induced Crystalline Phase of Poly(9,9‐Dioctylfluorene) in Solvent Vapor Annealing

A new metastable solvent‐induced clathrate liquid crystalline phase of β phase (named β' here) in crystalline poly(9,9‐dioctylfluorene) (PFO) thin film induced by solvent annealing is found by a combination of in situ ultraviolet and visible spectrophotometry (UV‐vis), photoluminescence spectroscopy (PL), and grazing incidence wide‐angle X‐ray scattering (GIWAXS). The solvent annealing process consists of three processes: diffusion of solvent molecules into the film; saturation of solvent in the film; and drying of the film under nitrogen. The formation of β' phase with ordered packing of side chains and disordered packing of backbones occurs during the diffusion process of solvent molecules into the film. When the solvent molecules penetrate the film, the disordered side chains start to align themselves to form an ordered structure, and the ordering would gradually in the saturationprocess. Furthermore, the ordering of side chains drives an ordered rearrangement of the backbones during the drying process; however, the crystallinity of the side chains decreases with the orderly rearrangement of backbones due to the helical conformation of PFO.

     

On the Phase B of Comb‐Like Poly(α‐alkyl‐β‐L‐aspartate)s: A Simulation of the Solubility of Small Penetrants

The structure and thermal properties of the phase B of poly(α‐alkyl‐β‐L ‐aspartate)s, abbreviated PAALA‐n (n being the number of carbon atoms in the linear alkyl side chain), with n = 14 and 16 were determined using X‐ray diffraction and DSC methods, respectively. These data together with those previously reported by us for the dodecyl derivative were used to perform Monte Carlo simulations of these comb‐like polymers. The results allowed to predict the solubility of different gases in the phase B of PAALA‐n. The variation of both the unoccupied space and the excess chemical potential with the size of the penetrant were computed. An attractive interaction between the polymer matrix and the penetrants was found when small gases were considered. The results have been compared with those recently obtained for crystalline poly(α‐alkyl‐β‐L ‐aspartate)s bearing short linear alkyl side chains.     

Orientation of the Main Chain in Liquid‐Crystalline Side‐Chain Polyesters with Variation of Main‐Chain Spacer Length

Previous X‐ray investigations on liquid‐crystalline side chain polyesters with variable spacer length in the side chain as well as in the main chain led to the assumption that the structure will change qualitatively if the main chain spacer length exceeds a certain value. We obtained indications supporting this assumption by applying two‐dimensional ¹³C NMR. It was shown that for a sample with main chain spacer shorter than the critical length, the main chain segments align perpendicular to the side chains (〈P₂〉 = ?0.46), and for spacer length larger than critical length, the main chain segments preferentially orient themselves parallel to the side chain (〈P₂〉 = 0.28).

Visualization of the main‐chain order as revealed by the values of Table 2 . The opening angle of the cones corresponds to the average angle of deviation as defined in the text.     

Preparation of Hierarchically Structured Amorphous Carbon Monoliths with Closed Spherical Mesopores via the Lower Critical Solution Temperature Phase Transition

Some polymer mixture systems become immiscible above a specific temperature, the so‐called lower critical solution temperature (LCST). In this work, the LCST behavior of a mixture of poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) triblock copolymers and phenolic resin oligomers is observed, and the corresponding phase transition is exploited to develop a facile route to hierarchically structured carbon monoliths. Whereas evaporation‐induced self‐assembly generates hexagonal channels in the monoliths, an additional phase transition at the LCST leads to an ordered arrangement of isolated pores. The fabrication method involves annealing the gel‐phased mixture with polymeric microbeads in a 3D‐structured mold at the LCST, followed by thermosetting and a carbonization process. The LCST phase transition behavior is observed experimentally by in situ small‐angle X‐ray scattering, optical transparency measurements, differential scanning calorimetry, and infrared spectroscopy. The fundamental mechanism of the LCST phase transition is further investigated by atomistic molecular dynamics simulations.     

Surface Properties of Mesophase‐Forming Fluorinated Bicycloacrylate/Polysiloxane Methacrylate Copolymers

Novel random copolymers were synthesized by free‐radical polymerization of a bicycloacrylate monomer carrying a fluorocarbon chain side group (BAF10) with a methacrylate monomer having a polysiloxane side graft (SiMA). The copolymers with higher contents of BAF10 gave rise to a well‐ordered smectic bilayer mesophase. The surface structure of the derived polymer films was investigated by measurements of the contact angle with several interrogating liquids and X‐ray photoelectron spectroscopy (XPS) at different photoemission angles. The values of the contact angles were used to evaluate the film surface tension, following different additive‐component and equation‐of‐state methods. The low surface energies found were attributed to the pronounced hydrophobicity and oleophobicity of the outermost surface caused by the preferential segregation of the fluorocarbon chains to the polymer–air interface.

     

Fluorophobic Effect Driven Self‐Organization of Semifluorinated Alkyl Chain Substituted Conjugated Polymer

This paper reports on the effect of a semifluorinated alkyl side chain for achieving a self‐organized nanostructure to facilitate the efficient charge carrier transport. So far, semifluorinated alkyl side chains have rarely been introduced into semiconducting polymers, despite their interesting properties such as hydrophobicity, thermal stability, and solvent resistance, as well as self‐organization. Herein, this study synthesizes the semifluorinated alkyl chain introduced poly(3‐dodecylthiophene), SFA‐P3DT, and demonstrates that self‐organization of SFA‐P3DT is intensely induced in nonfluorous solvent by the so‐called fluorophobic effect, resulting in the formation of nanofibrillar structure. In presence of the semifluorinated alkyl side chain, organic thin film transistor (OTFT) devices exhibit the improved charge carrier mobility than that of poly(3‐dodecylthiophene) with hydrocarbon alkyl chain. Moreover, higher charge carrier mobility can be obtained from the nonfluorous solvent, in comparison to the fluorous solvent, confirming the crucial role of fluorophobic effect. These observations suggest that the introduction of semifluorinated alkyl chains into a conjugated polymer may enhance the performance of OTFTs through the development of a well‐ordered nanostructure via self‐organization by fluorophobic effect, which, in turn, facilitates the efficient charge carrier transport.

     

Liquid‐Crystalline Complexes of Polyurethane Containing an Isonicotinamide Moiety with 4‐Dodecyloxybenzoic Acid

A series of supramolecular side‐chain liquid crystalline polyurethanes (SCLCPUs) was prepared by utilizing the selective hydrogen bonding interaction between polyurethane containing pyridine moieties ( 1 ) and 4‐dodecyloxybenzoic acid ( 2 ). Hydrogen bonding was confirmed by FTIR spectroscopy and supported by medium high level ab‐initio MO calculations. The components are miscible up to 0.7 mole of 2 versus the polyurethane repeat unit and the resulting complexes behave as uniform liquid‐crystalline polymers, which exhibit stable, reversible mesophases. The liquid crystalline behavior of these supramolecular polymeric complexes was established by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X‐ray diffractometry (XRD). The complexes show a highly ordered smectic phase, which does not appear for either of components 1 and 2 separately , and a nematic phase. Above the concentration limit of 0.7 mole of the acid 2 , the excess low molar mass molecules emerge to form a two phase system consisting of a polyurethane supramolecular complex and 4‐dodecyloxybenzoic acid ( 2 ). For complexes derived from polyurethane 1 and 4‐octyloxybenzoic acid ( 3 ) or 4‐butyloxybenzoic acid ( 4 ) with alkyl tails shorter than 2 , the phase separation occurs at lower molar ratios of 3 and 4 versus 1 . This means that the length of the alkyl tail in 4‐(alkoxy)benzoic acids plays an important role in the stabilization of supramolecular polyurethane complexes.