Cholesteric Liquid‐Crystalline Side‐on Polysiloxanes: Effects of Biaxiality on the Cholesteric Structure

Summary: Biaxial side‐on cholesteric copolysiloxanes with laterally attached mesogenic groups were investigated in mixtures with a low molar mass liquid crystal. While mixtures with a low concentration of the polymer exhibit the conventional fingerprint texture, for concentrations above about 60 mol‐% characteristic irregularities appear in the cholesteric structure that are obviously due to phase biaxiality. Besides the absence of pseudo‐isotropic lines, irregular patterns perpendicular to the helix axis emerge and the periodic distance of regions with similar optical properties along the helix axis is strongly disturbed. This suggests that the photonic band gap width of a uniaxial cholesteric phase becomes strongly affected when a phase transformation into a biaxial cholesteric phase occurs.

Cholesteric fingerprint texture of a mixture of uniaxial nematic monomer and biaxial cholesteric polymer.     

Complexes based on alkylboranes and α,β‐unsaturated carbonyl compounds as bicomponent transfer agents for free‐radical polymerisation

The free‐radical polymerisation of several monomers (styrene, ethyl acrylate, methyl methacrylate) was carried out in the presence of complexes based on alkylboranes and α,β‐unsaturated carbonyl compounds with a view of determining whether such complexes could function as transfer agents. Methyl vinyl ketone 1 or acrolein used in combination with triethylborane 2 exhibited transfer coefficients in the range of 0.25–1.24 in the polymerisation of the three monomers mentioned above. Conversely, associating 2 with cyclohex‐2‐one, and 3‐methyl but‐3‐en‐2‐one was found inefficient, the 3‐methyl but‐3‐en‐2‐one/ 2 complex being useful only with styrene. Attempts involving methyl vinyl ketone associated with either butyldichloroborane or diethylmethoxyborane failed to produce transfer in free‐radical polymerisation.

Mechanism of the reaction of organoboranes with α,β‐unsaturated carbonyl compounds. 5     

Chemical Binding of Unsaturated Fluorenes to Poly(2‐chloroxylylene) Thin Films

A series of substituted fluorenes with vinyl groups as reactive sites were synthesized and characterized. Fluorene‐based polymers with vinyl groups as end chains and side chains functionalities were also prepared. In both cases, successful preparation of functionalized Parylene C films (modylayers) was achieved. The set of spectral methods used has allowed us to conclude that such functionalization is based on the chemical reaction of double bonds with xylylene radicals during deposition process. Parylene C films chemically modified with specially synthesized polyfluorenes showed PL quantum efficiency comparable with neat polyfluorenes.

     

Nitroxide‐Mediated Radical Polymerization of N‐tert‐Butylacrylamide

The nitroxide‐mediated polymerization of N‐tert‐butylacrylamide (TBAM) in DMF at 120 °C using SG1/DEPN and AIBN has been investigated. Linear growth in number‐average molecular weight ( ) versus conversion and narrow molecular weight distributions (MWDs) with high livingness were obtained up to ≈8 000 g · mol^?1. For higher molecular weights, the MWDs gradually became broader with low molecular weight tailing, and deviated downwards from theoretical values. Quantitative analyses of MWDs, along with specifically designed conventional radical polymerizations at 120 °C, were consistent with chain transfer to monomer limiting the attainable . This finding can be equally applied to existing literature polymerizations of TBAM.

     

Active Poly(4‐chloromethyl styrene)‐Functionalized Multiwalled Carbon Nanotubes

Concentrated nitric acid‐treated multiwalled carbon nanotubes (MWCNTs) are functionalized with active poly(4‐chloromethyl styrene) (PCMS) through the esterification reaction of the carboxyl groups of the former and the p‐benzyl chloride groups of the latter in the presence of a phase‐transfer catalyst. Characterization using Raman spectroscopy, Fourier transform infrared spectroscopy, and hydrogen nuclear magnetic resonance spectroscopy demonstrates that the active PCMS chains are chemically tethered onto the side walls (or surfaces) of the MWCNTs. The core‐shell nanostructure of active PCMS‐modified MWCNTs (MWCNT‐PCMS) can be observed by high resolution transmission electron microscopy, and the amount of PCMS present is 31.3 wt% by thermogravimetric analysis. Solubility testing shows that MWCNT‐PCMS dissolves well in tetrahydrofuran, chloroform, toluene, and N,N‐dimethylformamide, and the maximum nanotube concentration in toluene is 413 mg L^?1.

     

Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous‐Flow Microreactor

The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol^?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.

     

Effect of Molecular Structure and Thermal Treatment on Photo‐optical Properties of Photochromic Azobenzene‐containing Polymer Films

Three novel photochromic azobenzene‐containing comb‐shaped polyacrylates are synthesized and their phase behavior and photo‐optical properties are studied. The influence of the side photochromic group structure, thermal treatment, and light irradiation on aggregation of azobenzene chromophores in thin spin‐coated films of the polymers is investigated in detail. Special attention is paid to studying the photo‐orientation processes in polymers films induced by polarized blue light (473 nm). The relationship between the photochromic group architecture, phase behavior, thermal treatment of films, and kinetics of chromophore photo‐orientation is established and discussed. It is found that the position of the N?N bond in chromophores plays an important role in the kinetics of the process, but does not affect the maximum value of dichroism.

     

Synthesis of Norbornene Derivatives by Diels‐Alder Cycloaddition and Subsequent Copolymerization with Maleic Anhydride

Summary: Several norbornene (Nb) derivatives were synthesized by facile Diels‐Alder cycloaddition reactions of cyclopentadiene with α‐olefins containing electron‐withdrawing groups such as nitrile (CN), phosphonate, and ester. The Diels‐Alder adducts were subsequently copolymerized with maleic anhydride (MAH) using free radical polymerization conditions previously determined for MAH/Nb copolymerizations. Further functionality was introduced into the copolymers through acid‐catalyzed hydrolysis of poly(Nb‐alt‐MAH) and poly(NbCN‐alt‐MAH) copolymers. FTIR confirmed hydrolysis of the anhydrides to carboxylic acid‐functionalities and indicated no appreciable hydrolysis of the nitrile functionality. Observed copolymerization rates (k_obs) were measured using in situ FTIR. A dramatic decrease in the rate of copolymerization was observed for the Nb derivatives that contained a strong electron‐withdrawing functionality. This observation suggested a significant electronic influence on the free radical copolymerization rate with maleic anhydride due to the electron‐withdrawing nature of the Nb substituents.

Vinylene region of in situ FTIR “waterfall” plot for 50/50 Nb/MAH alternating copolymerization.     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Preparation and Characterization of Acetoacetoxyethyl Methacrylate‐Based Gels

Novel polymeric gels have been prepared by radical copolymerization of acetoacetoxyethyl methacrylate (AAEM) and hydroxyethyl methacrylate (HEMA) in water‐ethanol medium. The influence of the HEMA:AAEM ratio and crosslinker concentration on properties of gels was studied. Independently on gel composition the maximum swelling was detected in chloroform. It was found that PAAEM gels possess phase transition temperature or upper critical solution temperature (UCST) in alcohol‐water solutions. UCST decreases in linear order from 75 to 10 °C when HEMA content in gel structure increases. The minimal UCST of AAEM/HEMA gels in binary alcohol‐water mixtures is shifted toward lower temperatures and lower alcohol concentrations when the alkyl chain of alcohol increases.

AAEM/HEMA gels prepared at different BIS concentrations (1:1 mol‐%, 2:2.5 mol‐%, 3:5 mol‐%).     

Poly(carbazole)‐Based Copolymers Containing Deep‐Blue Chromophore for Polymer Light‐Emitting Diode Applications

A new series of two poly(carbazole)‐based copolymers (poly(9‐hexyl‐carbazole‐co‐9‐(6‐(3‐(4‐phenylquinolin‐2‐yl)carbazol‐9‐yl)hexyl)carbazole) (PCVz) and poly(9,9‐dioctylfluorene‐co‐9‐(6‐(3‐(4‐phenylquinolin‐2‐yl)carbazol‐9‐yl)hexyl)carbazole) (PFCVz)) containing carbazoylphenylquinoline pendant groups were synthesized via the Suzuki coupling reaction for polymer light‐emitting diode applications. The electro‐optical properties of ITO/PEDOT/Polymer/PBD/LiF/Al devices based on these copolymers were investigated using UV‐visible, photoluminescence, and electroluminescence spectroscopy. The turn‐on voltages of the copolymer devices were found to be 6.0–8.0 V. The maximum brightness and luminescence efficiency of the copolymers device were found to be 230 cd · m^?2 and 0.28 cd · A^?1 at 11 V, respectively.

     

Fluorene‐Based Single‐Chain Copolymers for Color‐Stable White Light‐Emitting Diodes

Fluorene‐based single‐chain copolymers with a white light emitter consisting of a blue and an orange chromophore have been synthesized and their photophysical and electroluminescent properties are investigated. The experimental results suggest that only a relatively small fraction of the orange‐emitting units incorporated into the fluorene is needed to achieve efficient white light emission by controlled incomplete energy transfer. A device from a copolymer with 0.02% DDQ content showed the highest external quantum efficiency of 2.64% with a luminance efficiency of 4.06 cd · A^?1 with CIE coordinates (0.28, 0.24). The EL emissions are extremely stable over a wide range of current densities.

     

A Facile One‐Pot Synthesis to Dextran‐Based Nanoparticles with Carboxy Functional Groups

Summary: Stabilized nanoparticles functionalized with carboxy groups were synthesized directly from dextran and acrylic acid (AA), without using any organic solvent and surfactant. The composition and morphology of these dextran‐based nanoparticles, as well as the mechanism of this one‐pot synthesis, were also investigated in this paper. This approach is anticipated to be applicable to various water‐soluble polysaccharides to fabricate nanoparticles facilely.

Facile synthesis of stabilized nanoparticles functionalized with carboxy groups from dextran and AA.     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

Synthesis and Properties of a New Poly(arylene ethynylene) Containing 1,3,5‐Triazine Units

Summary: A new photoluminescent poly(arylene ethynylene) containing 1,3,5‐triazine units was prepared by polycondensation between 2,4‐diphenyl‐6‐N,N‐bis(4‐bromophenyl)amino‐1,3,5‐triazine and 1,4‐didodecyloxy‐2,5‐diethynylbenzene using Pd(PPh₃)₄ and CuI as the catalysts in the presence of triethylamine. The polymer showed good solubility in common organic solvents and had a number average molecular weight, , of 3 400, and a weight average molecular weight, , of 8 100. In toluene the polymer exhibited an intrinsic viscosity [η] of 0.11 dL · g^?1 at 30 °C. The polymer showed photoluminescence (PL) with emission peaks at 479 nm in CHCl₃ and at 509 nm in the solid state; quantum yield of the PL in CHCl₃ was 21%. Electrochemical reduction (or n‐doping) of the polymer started at about ?2.05 V versus Ag/AgNO₃ and gave a peak at ?2.30 V versus Ag/AgNO₃.

The 1,2,3‐triazine unit‐containing poly(arylene ethynylene) (PATZ) polymer synthesized and investigated here.     

Synthesis and ATRP Activity of New TREN‐Based Ligands

Summary: Ligands suitable for atom transfer radical polymerization (ATRP) were prepared by the Michael addition of several acrylates (allyl, benzyl, butyl, 2‐ethylhexyl, and 3‐(dimethoxymethylsilyl)propyl acrylates) with tris(2‐aminoethyl)amine (TREN). These ligands, readily prepared from inexpensive precursors, were used for the preparation of catalyst complexes suitable for polymerization of (meth)acrylates and styrene, providing activity comparable to catalysts currently used for these monomers. Catalysts containing ligands with a dimethoxymethylsilyl substituent were examined for copper removal after the reaction mixture was contacted with silica gel.

     

Cationic Copolymerization Behavior of Glycidyl Phenyl Ether with Seven‐Membered Cyclic Carbonate

Summary: To clarify the cationic copolymerization behavior of epoxide and cyclic carbonate, the copolymerization behavior of glycidyl phenyl ether (GPE) with seven‐membered cyclic carbonate (7CC) was carried out using methyl trifluoromethanesulfonate (MeOTf) as a cationic initiator. The addition of 7CC accelerated the consumption rate of GPE, and the resulting copolymers were richer in 7CC‐derived unit compared to the feed ratio of 7CC. During the copolymerization, a large amount of five‐membered cyclic carbonate having a phenoxymethyl group (PM‐5CC) was produced as a by‐product, which suggests the corresponding spiroorthocarbonate was formed as an intermediate and that residual oxytetramethylene (OTM) unit was incorporated into the copolymer sequence. From ¹H NMR analysis, it was found that the copolymers had a statistically random sequence consisting of GPE, 7CC, and OTM units.

     

Design and Synthesis of Phosphorescent Iridium Containing Dendrimers for Potential Applications in Organic Light‐Emitting Diodes

Three phosphorescent dendrimers ( IrC1 , IrC3 , and IrF2 ) with an iridium complex core and oligocarbazole or oligofluorene substituted ligands were synthesized and characterized. The structures of the oligocarbazole were designed to maintain high triplet energy of the ligands so that phosphorescence quenching in the resulting dendrimers can be prevented, while the oligofluorene in IrF2 resulted in undesired phosphorescence quenching. Best performance was obtained from an IrC3 based electrophosphorescent light‐emitting device with a maximum luminance of 13 060 cd · m^?2 at a driving voltage of 11.5 V and a peak current‐efficiency of 4.3 cd · A^?1 at a luminance of 3 400 cd · m^?2, owing to its high PL efficiency, and efficient energy transfer between the iridium complex core and the ligands.

     

A Study of Copolymerization of 1‐Hexene with 2,5‐Norbornadiene Using Metallocene Catalysts

Summary: Copolymerization of 1‐hexene with a symmetrical diene, namely 2,5‐norbornadiene was studied using four different metallocene catalysts. Copolymerization was found to occur exclusively through one of the two equally reactive endocyclic double bonds with all the four catalysts. Copolymerization results in low molecular weight oligomers with the number average molecular weight ( ) varying from 1 000–3 000. End group analysis of the co‐oligomers revealed that the β‐hydrogen transfer after 2,1 insertion also occurs in the presence of highly regiospecific catalysts. The regio errors were also found to depend on various reaction parameters such as polymerization time, Al/Zr mol ratio, metallocene concentration and polymerization temperature.

Plots of variation in end groups and NBD incorporation with time.     

Synthesis and Characterization of Red‐Emitting Poly(aryleneethynylene)s Based on 2,5‐Bis(2‐ethylhexyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione (DPP)

Synthesis and characterization of a series of PAEs containing DPP units in the main chain are described. of the polymers was in the range 10 800–111 900. The polymers formed a deep blue solution in chloroform with absorption maxima between 589 and 645 nm and optical band gaps ranging from 1.61 to 1.74 eV. When excited at the absorption maxima, the polymer solutions showed red fluorescence with emission maxima between 656 and 676 nm. The polymers exhibited quasi‐reversible oxidation process with HOMO energy levels between ?5.60 and ?6.17 eV. EL properties of three polymers were investigated with device configuration ITO/PEDOT:PSS/Polymer/LiF/Al. When appropriate bias voltage was applied, a red EL with a maximum brightness of 17.5–24 cd · m^?2 could observe from the devices.