Control of In‐Plane and Out‐Of‐Plane Reorientation in Photo‐Cross‐Linkable Copolymer Liquid‐Crystal Films by Irradiation with Linearly Polarized Ultraviolet Light and Annealing

This paper describes thermally enhanced in‐plane and out‐of‐plane reorientation of mesogenic groups in copolymer liquid‐crystal (CPLC) films that have a photo‐cross‐linkable 4‐(4′‐methoxycinnamoyl)biphenyl (MCB) side group and a 4‐methoxybiphenyl (4MB) side group. The side groups are cross‐linked by irradiation with linearly polarized ultraviolet (LPUV) light and subsequent annealing. Due to axis‐selective photo‐cross‐linking, a small negative optical anisotropy is observed for all CPLCs after exposure to LPUV light. When the composition of the 4MB comonomer is less than 45 mol‐%, thermal treatment in the liquid‐crystalline temperature range causes in‐plane reorientation of the film and results in an in‐plane order parameter of 0.71. In contrast, when the composition of the 4MB is increased, out‐of‐plane reorientation is generated. Three‐dimensional molecular reorientation and inclined out‐of‐plane reorientation are achieved by adjusting the exposure angle.

Angular dependence of UV absorption spectrum of film 3 . The inset shows a conoscope observation of the film. The film was annealed at 130 °C for 10 min.     

Metallocenic Copolymers of Isotactic Propylene and 1‐Octadecene: Crystalline Structure and Mechanical Behavior

Summary: A set of copolymers of isotactic propylene and 1‐octadecene (CiPOD) and the corresponding isotactic poly(propylene) homopolymer (iPP) have been synthesized using a metallocene catalyst. The influence of the incorporation of this long chain comonomer on the structure and final properties exhibited by iPP has been examined. Wide‐angle X ray diffraction and optical microscopy have been used to analyze the effect of introducing 1‐octadecene comonomer within the iPP backbone. The initial monoclinic crystal lattice with a well‐developed lamellar morphology is transformed into a mesomorphic modification showing very small entities. All these structural changes significantly influence the mechanical behavior of these copolymers. Thus, stiffness and microhardness are diminished and the brittle‐ductile transition can be observed by simply varying composition when deformation takes place at room temperature. On the other hand, the intensity of the process associated with cooperative movements within the amorphous phase (β relaxation) significantly goes up with the incorporation of 1‐octadecene and its location is shifted to lower temperature because of the decrease in the crystallinity content.

X‐ray diffraction patterns at room temperature, with increasing comonomer content.     

Thermally Reversible Cross‐Linked Polyamides with High Toughness and Self‐Repairing Ability from Maleimide‐ and Furan‐Functionalized Aromatic Polyamides

Polyamides having various amounts of maleimide (PA‐MI) and furan (PA‐F) pendent groups, respectively, as well as their cross‐linked polymers (PA‐MI/PA‐F) were prepared. PA‐MI/PA‐F cross‐linked polymers showed thermally reversible cross‐linking behavior via Diels‐Alder (DA) and retro‐DA reactions. Cross‐linked PA‐MI/PA‐F films exhibited enhanced toughness and mechanical properties compared to PA‐MI and PA‐F precursors. Moreover, PA‐MI/PA‐F films also showed thermal self‐repairing behavior, which was observed in the micrographs and instron tests.

     

Increased Electrical Conductivity in Poly(3,4‐ethylenedioxythiophene) upon Cross‐Linking

Cross‐linked poly(3,4‐ethylenedioxythiophene) (PEDOT) films were synthesized by the oxidative polymerization of 3,4‐ethylenedioxythiophene in the presence of five different conjugated and non‐conjugated cross‐linkers. The concentration and structure of the cross‐linker was systematically varied to explore the influence on the electrical conductivity. Optimized compositions displayed an electrical conductivity of up to ≈800 S · cm^?1; this corresponds to a conductivity increase of up to 36% compared to linear PEDOT prepared under identical conditions. An increase in the conductivity was only observed for the conjugated cross‐linkers that were incorporated in low concentrations, typically at a level of less than 2 mol‐%. Attempts to incorporate higher concentrations of cross‐linker led to phase separation and crystallization of the cross‐linker and afforded materials in which a significant reduction of the electrical conductivity was observed. The optical properties of the polymer were only marginally affected upon cross‐linking, even at high cross‐linker concentrations.

     

Formation of Thermoresponsive Gold Nanoparticle/PNIPAAm Hybrids by Surface‐Initiated,Atom Transfer Radical Polymerization in Aqueous Media

Summary: We investigated the formation of thermoresponsive gold nanoparticle/poly(N‐isopropylacrylamide) (AuNP/PNIPAAm) core/shell hybrid structures by surface‐initiated, atom transfer radical polymerization (SI‐ATRP) in aqueous media and the effect of cross‐linking on the thermoresponsiveness of the AuNP/PNIPAAm hybrids. The disulfide containing an ATRP initiator was attached onto AuNPs and the monomer, NIPAAm, was polymerized from the surface of AuNPs in the absence or presence of a cross‐linker, ethylene diacrylate, in aqueous media at room temperature. The resulting brush‐type and cross‐linked AuNP/PNIPAAm hybrids were characterized by Fourier‐transform infrared spectroscopy, transmission electron microscopy, and variable temperature dynamic light scattering.

     

Determination of the Crystal Structure of Syndiotactic 3,4‐Poly(2‐methyl‐1,3‐butadiene) by Molecular Mechanics and X‐Ray Diffraction

Summary: The crystal structure of syndiotactic 3,4‐poly(2‐methyl‐1,3‐butadiene) has been determined by the joint use of molecular mechanics and X‐ray diffraction. Molecular mechanics calculations have been performed both on the isolated chain and on the crystal by the use of various force fields. The energy minimizations predict a model of the crystal structure. The calculated X‐ray powder diffraction pattern is in good agreement with the experimental one. This model has been refined in order to obtain the best agreement with all the experimental data. The space group is Pbcm and the parameters of the unit cell are a = 6.6 Å, b = 13.2 Å, c = 5.27 Å. The presence of defects in the crystal has been taken into account. Analogies and differences with the crystal structure of syndiotactic 1,2‐poly(1,3‐butadiene) are discussed.

X‐ray fiber diffraction pattern of syndiotactic 3,4‐poly(2‐methyl‐1,3‐butadiene).     

Fractionation and Characterisation of Propylene‐Ethylene Random Copolymers: Effect of the Comonomer on Crystallisation of Poly(propylene) in the γ‐Phase

Summary: Three propylene‐ethylene random copolymers, of varying ethylene content, were fractionated using preparative TREF. The TREF fractions were subsequently analysed offline by CRYSTAF, DSC, ¹³C NMR spectroscopy, HT‐GPC, and WAXD. The effect of the ethylene comonomer on the crystallisability of the propylene was investigated, along with the effect of the comonomer on the type of crystal phase formed during the crystallisation. The results show that the comonomer inhibits the crystallisation of the copolymer and that as the ethylene content increases, the crystallisation and melting points decrease. It was also shown that the higher the ethylene content, the more of the γ‐phase crystal type is formed. The inter‐molecular distribution of the ethylene comonomer and stereo errors vary between the samples analysed, and this accounts for the relative differences in crystallisation behaviour of the samples.

¹³C NMR of propylene‐ethylene random copolymer.     

Multicyclic Poly(ether ketone)s by Polycondensation of 1,3,5‐Tris(4‐fluorobenzoyl)benzene with Various Diphenols

Summary: 1,3,5‐Tris(4‐fluorobenzoyl)benzene (TFBB) was polycondensed with silylated 4,4′‐dihydroxybiphenyl, bisphenol‐A or 4‐tert‐butylcatechol in N‐methylpyrrolidine with K₂CO₃ as a promoter. The TFBB/diphenol feed ratio was varied from 1.0:1.0 to 1:0:1.5. Partial cross‐linking was observed with the stiff 4,4′‐dihydroxybiphenyl, even at the 1.0:1.0 ratio. With bisphenol‐A, no gelation took place up to a feed ratio of 1.0:1.3, indicating a high cyclization tendency. With 4‐tert‐butylcatechol, no cross‐linking occurred up to the 1.0:1.5 ratio, proving an even higher cyclization tendency. The formation of cyclic, bicyclic and multicyclic oligo‐ and polyethers was detected by means of MALDI‐TOF mass spectrometry for all reaction products. These results demonstrate that increasing chain stiffness reduces the influence of cyclization. Cyclization proved unavoidable, however, and a high cyclization tendency prevents the formation of hyperbranched and networked structures.

     

Benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐terthiophene Copolymers Containing Styryl‐Triphenylamine Side Chains: Synthesis and Photovoltaic Performance Optimization with Fullerene Acceptors

A new two‐dimensional‐conjugated polymer (PBDTT3‐TPA) containing benzodithiophene (BDT) and a side chain isolation comonomer is designed and synthesized. Interestingly, PBDTT3‐TPA is compatible with higher lowest unoccupied molecular level (LUMO) acceptors of indene‐C₆₀ bisadduct (ICBA), and polymer solar cells based on PBDTT3‐TPA/ ICBA show an open‐circuit voltage (V_OC) of ca. 0.80 V and a power conversion efficiency of 2.48% under AM1.5G illumination of at 100 mW cm^?2. Furthermore, the energy loss in the corresponding fullerene acceptor devices is discussed, and the increase in the observed V_OC is explained quantitatively by the up‐shifted LUMO energy of ICBA (0.17 eV) and the reduced saturation current (J_SO) in the blends.

     

Synthesis of 12,12‐Ammonium Ionenes with Functionality for Chain Extension and Cross‐Linking via UV Irradiation

A novel synthetic methodology for preparing chain‐extended and cross‐linked ionenes using UV irradiation is described. 12,12‐Ammonium ionenes were functionalized with either cinnamate or styrenic functionality at the chain ends and were subsequently exposed to UV irradiation. In addition, a novel copolymer (poly(cinDMPC‐co‐bocDMPC)) was mixed with the cinnamate‐functionalized 12,12‐ammonium ionene to prepare photo‐cross‐linked networks. The UV irradiation process was monitored via UV–Vis spectroscopy after each exposure. The chain‐extended 12,12‐ammonium ionene possessed superior tensile properties compared to the original 12,12‐ammonium ionene. Successful cross‐linking was confirmed with solubility testing of the thin films in methanol. The results indicated that photo‐cross‐linked 12,12‐ammonium ionenes offer potential in membrane technology applications.

     

Characterisation of the Chemical Composition Distribution of LLDPE Using Interactive Liquid Chromatography

It is demonstrated that copolymers of ethylene with higher 1‐olefins can be separated using bare silica gel as the stationary phase and a gradient of ethylene glycol monobutyl ether and 1,2,4‐trichlorobenzene as the mobile phase at 160 °C. The separation of ethylene 1‐hexene copolymers according to their composition is confirmed by linking the chromatographic separation to infrared spectroscopy. Using well‐characterised model fractions from temperature rising elution fractionation or solvent/non‐solvent fractionation (“Holtrup”), it can be shown that both the content and type of the comonomer mainly govern the elution in two peaks which differ in their comonomer content. The molar mass only plays a subordinate rule.

     

Metallocenic Isotactic Poly(propylene) and its Copolymers with 1‐Hexene and Ethylene

A comprehensive study of the structure and properties has been performed for copolymers of propylene‐1‐hexene, CiPH, and propylene‐ethylene, CiPE, synthesized by an isotactic metallocene catalyst system. The comonomer content constitutes the most important factor affecting the structure and properties of these CiPH and CiPE copolymers, although the length of the comonomer is also very important. Thus, a considerable decrease in crystallinity is observed in the two kinds of copolymers as the comonomer content increases. The structure in the CiPH copolymers evolves, however, from the typical, monoclinic crystal lattice to mesomorphic‐like, ordered entities for the highest 1‐hexene molar fraction, whereas in the CiPE copolymers the structural evolution with molar fraction goes from a monoclinic lattice to an almost amorphous material. All of these variations in crystal structure significantly influence the viscoelastic and mechanical behavior of these CiPH and CiPE copolymers. Consequently, the location and intensity of the different relaxation mechanisms, as well as the rigidity parameters (storage and Young's moduli and microhardness) and deformation mechanism are strongly dependent upon composition.

     

Synthesis of π‐Conjugated Organometallic Polymer Networks

The present paper reports the synthesis of π‐conjugated organometallic polymer networks based on poly[2,5‐dioctyloxy‐1,4‐diethynyl‐phenylene‐alt‐2,5,‐bis(2′‐ethylhexyloxy)‐1,4‐phenylene] (EHO‐OPPE), a soluble poly(p‐phenylene ethynylene) (PPE) derivative. The ethynylene moieties of the polymer coordinate to Pt⁰ centers, which act as conjugated cross‐links. These materials are readily accessible through ligand‐exchange reactions between the linear PPE and Pt(styrene)₃. The in‐situ NMR investigation of model reactions of Pt(styrene)₃ with diphenylacetylene (DPA) has shown that the ethynylene moieties comprised in the PPE readily coordinate to Pt⁰ centers under release of the relatively weakly‐bound styrene ligands. Spin‐coating has resulted in cross‐linked films of good optical quality. We also have been able to produce PPE‐Pt‐gels with high solvent content (> 95 wt.‐%). As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift.

Ligand‐exchange reaction between EHO‐OPPE and [Pt(PhCH?CH₂)₃] leading to the target EHO‐OPPE‐Pt⁰ networks.     

Polymethacrylate Copolymers Containing 4,5‐Dicyanoimidazole‐Based Chromophores and their Nonlinear Optical Behavior

Summary: Two series of methacrylate copolymers were prepared, based on two new nonlinear optically (NLO) active chromophores 2‐[4‐(N‐methacryloyloxyethyl‐N‐methylamino)phenylazo]‐4,5‐dicyanoimidazole (chromophore A ) and 1‐ethyl‐2‐[4‐(N‐methacryloyloxyethyl‐N‐methylamino)phenylazo]‐4,5‐dicyanoimidazole (chromophore B ). Second order NLO properties of the two series of copolymers ( A or B as monomer and methyl methacrylate as the comonomer) were investigated by SHG procedures at the fundamental wavelength 1368 nm; d₃₃ values in the range 0.2–3.3 pm · V⁻¹ were obtained, depending on the chromophore and on its molar content. The dependence of d₃₃ on the molar content of chromophore was investigated in the two cases.

     

Amphiphilic Block Copolymers Containing Regioregular Poly(3‐hexylthiophene) and Poly(2‐ethyl‐2‐oxazoline)

Poly(3‐hexylthiophene)‐block‐poly(2‐ethyl‐2‐oxazoline) amphiphilic rod–coil diblock copolymers have been synthesized by a combination of Grignard metathesis (GRIM) and ring‐opening cationic polymerization. Diblock copolymers containing 5, 15, and 30 mol‐% poly(2‐ethyl‐2‐oxazoline) have been synthesized and characterized. The synthesized rod–coil block copolymers display nanofibrillar morphology where the density of the nanofibrills is dependent on the concentration of the poly(2‐ethyl‐2‐oxazoline) coil segment. The conductivity of the diblock copolymers was lowered from 200 to 35 S · cm^?1 with an increase in the content of the insulating poly(2‐ethyl‐2‐oxazoline) block. By contrast, the field‐effect mobility decreased by 2–3 orders of magnitude upon the incorporation of the poly(2‐ethyl‐2‐oxazoline) insulating segment.

     

Crystallization and Ring‐Banded Spherulite Morphology of Poly(ethylene oxide)‐block‐Poly(ε‐caprolactone) Diblock Copolymer

Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.

DSC heating curve for the PEO‐b‐PCL block copolymer.     

Physically and Chemically Cross‐Linked Poly{[(maleic anhydride)‐alt‐styrene]‐co‐(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)}/Poly(ethylene glycol) Proton‐Exchange Membranes

Novel proton exchange membranes were solvent‐cast from DMF solutions of the terpolymers poly[(MA‐alt‐S)‐co‐AMPS], containing hydrophobic phenyl and reactive hydrophilic carboxylic and organo‐sulfonic acid fragments with different compositions, and PEGs with different molecular weights and amounts. These membranes were formed as a result of physical (via H‐bonding) and chemical (via PEG) cross‐linking. The structures of membranes were confirmed by FT‐IR and ¹H‐ and ¹³C NMR spectroscopy. Mechanical and thermal properties, swellability, and proton conductivity of these membranes were significantly affected both by the chemical composition of the terpolymers (mainly the AMPS content) and also the cross‐linker (PEG) molecular weight and content in the final form of the membranes. It was concluded that the membranes prepared by using the terpolymer with an AMPS content of 36.84 mol‐% and PEG with a molecular weight of 1 450 and with an initial PEG content of 30 wt.‐% are the most suitable ones for fuel cell applications.

     

Synthesis,Characterization, and Intramolecular End‐to‐End Ring Closure of α‐Isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal Polystyrene‐block‐polyisoprene Block Copolymers

Cyclic polystyrene‐block‐polyisoprenes of controlled dimensions have been synthesized for the first time by the direct coupling of α‐isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal‐heterodifunctional linear polystyrene‐block‐polyisoprene precursors previously prepared by living anionic polymerization. Cyclization is achieved under high dilution by intramolecular coupling of the polymer ends under acid catalyst conditions. Using this strategy polystyrene‐block‐polyisoprene macrocycles of controlled chain dimensions are prepared in high yield (> 90%). Pure cycles were finally recovered by flash chromatography. The synthesis and characterization of both the linear α,ω‐heterodifunctional polystyrene‐block‐polyisoprenes block copolymers precursors and of the corresponding cyclized chain architectures are reported.

200 MHz ¹H NMR spectrum (CDCl₃) of cyclized polystyrene‐block‐polyisoprene copolymer (M _n = 12 000).     

Photocurable Shape‐Memory Copolymers of ε‐Caprolactone and L‐Lactide

Biodegradable and photocurable block copolymers of ε‐caprolactone and L ‐lactide were synthesized by polycondensation of PLLA diol ( = 10 000 g · mol^?1), PCL diol ( = 10 000 g · mol^?1), and a chain extender bearing a coumarin group. The effect of copolymer composition on the thermal and mechanical properties of the photocured copolymers was studied by means of DSC and cyclic tensile tests. An increase in Young's modulus and a decrease in the tensile strain with increasing PLLA content was observed for the block copolymers. Block copolymers with high PCL content showed good to excellent shape‐memory properties. Random copolymers exhibited R_f and R_r values above 90% at 45 °C for an extremely large tensile strain of 1 000%.