Chain Dynamics of Poly(oxyethylene) in Nanotubes of α‐Cyclodextrin by Solid‐State 2H NMR

Summary: Solid‐state ²H NMR spectroscopy was used to examine the chain dynamics of perdeuterated poly(oxyethylene) (d‐POE) inside α‐cyclodextrin (α‐CD) nanotubes. The nanotubes were prepared by aqueous self‐assembly of α‐CD onto either low‐molecular‐weight (1.5 kg/mol) or high‐molecular‐weight (25.8 kg/mol) monodisperse d‐POE. At a given temperature, POE chain segments exhibit faster dynamics when included inside the CD nanotubes as compared to the bulk. Even at 150 K, when no large‐angle dynamics are detected in bulk POE, evidence for chain motions in the nanotube‐confined POE is observed. The ²H line shapes representing this motion were modeled by a discrete 3‐site jump using a ln‐Gaussian distribution of correlation times. An activation energy of 15 ± 1 kJ/mol was determined and the motion envisioned as gauche defects propagating along the primarily trans chains included within CD nanotubes. As the nanotube length decreased, the jump angle became much less defined and more isotropic motions were observed for POE segments at elevated temperatures (>270 K).

     

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.     

α,ωn‐Heterotelechelic Hyperbranched Polyethers Solubilize Carbon Nanotubes

The synthesis of novel linear‐hyperbranched (linhb) polyether block copolymers based on poly(ethylene oxide) and branched poly(glycerol), bearing a single pyrene or myristyl moiety at the α‐position of the linear chain is described. The polymers exhibit low polydispersity ( < 1.3) and controlled molecular weights ( = 5 000 g · mol^?1). The mainly hydrophilic block copolymers with multiple hydroxyl end groups readily dissolve multiwalled carbon nanotubes (MWCNTs) in water by mixing and subsequent sonification, resulting in noncovalent attachment of the linhb hybrid structure to the carbon nanotubes (CNTs). Transmission electron microscopy (TEM) was employed to visualize the solubilized nanotubes; after sulfation of the multiple hydroxyl groups the polymer layer was detected in the TEM images.

     

Cyclodextrins in polymer synthesis: Steric retardation of the free‐radical polymerization in aqueous medium of 4‐vinylbenzaldehyde/methylated β‐cyclodextrin complex

4‐Vinylbenzaldehyde ( 3 ) was complexed with methylated β‐cyclodextrin ( 4 ) (me‐β‐CD) yielding the water soluble host‐guest complex ( 5 ). Radical polymerization was initiated with K₂S₂O₈/Na₂S₂O₅ in water at room temperature and also at 70 °C. The polymerization tendency of this complex ( 5 ) is lower compared to the styrene/me‐β‐CD‐complex ( 7 ). Also copolymerizations of 5 and complexed styrene ( 6 ) at these two temperatures were carried out and the results are discussed in respect to the behavior of the homopolymerization. The resulting polymers ( 8a‐k , 9a , 9b ) were characterized by SEC‐measurements and ¹H NMR spectroscopy. TEM‐measurements of the homopolymers 8f and 8k show differences in the particle size depending on the amount of me‐β‐CD.

TEM recordings of the polymers 8f (left) and 8k (right).     

Synthesis and Properties of Hydrophilic Networks Based on Poly(ethylene glycol) and β‐Cyclodextrin

New hydrophilic networks combining poly(ethylene glycol) (PEG) and β‐cyclodextrin (β‐CD) have been prepared. Both components are linked by reacting PEG chains previously end‐capped with isocyanate groups and β‐CD, forming urethane links. Networks of molar compositions (β‐CD/PEG) ranging from 1/4 to 1/14, and with four different molar masses (400, 600, 900, and 1 350 g · mol^?1) of the end‐capped PEG precursor have been synthesized. The networks have good thermal stability and low glass transition temperatures. Crystallinity has only been detected for the two higher molar mass PEG precursors. The swelling properties of these hydrogels depend on the chain lengths of the PEG precursor and also on the temperatures.

     

Synthesis of Poly(ester amide)s Derived from Glycolic Acid and the Amino Acids: β‐Alanine or 4‐Aminobutyric Acid

The polymerization of metal salts of N‐chloroacetyl‐β‐alanine and N‐chloroacetyl‐4‐aminobutyric acid was investigated. The former gives a mixture of polymer and a seven‐membered cyclic compound constituted of glycolic and β‐alanine units, and its reaction proceeds in the solid state. However, liquefaction is observed in the second case giving rise to a polymer with a moderate molecular weight. Condensation kinetics of both sodium and silver salts of N‐chloroacetyl‐β‐alanine have been studied by differential scanning calorimetry. Copolymers of glycolic acid and β‐alanine with a molar ratio of glycolic acid/β‐alanine varying from 0.5 to 1.0 have been synthesized by thermal reaction of co‐precipitated crystals of the sodium salts of chloroacetic acid and N‐chloroacetyl‐β‐alanine. NMR spectroscopy indicates that copolymers tend to have a random distribution. The resulting new poly(ester amide)s have been characterized by spectroscopy and thermal analysis.

DSC heating runs corresponding to different mixtures of the sodium salts of chloroacetic acid and chloroacetyl‐β‐alanine.     

Induced Circular Dichroism to Optically Active Poly{[methyl(1‐naphthyl)silylene](o‐phenylene)methylene}s Assisted by Supramolecular Complexation with β‐Cyclodextrin

Summary: Optically active poly{methyl(1‐naphthyl)silylene](o‐phenylene)methylene}s with different molecular weights and configurations were prepared, and their supramolecular complexes with β‐cyclodextrin were investigated in a water–tetrahydrofuran mixture (1:1 v/v) at the temperatures between 25 and 68 °C. Complexation was very sensitive to sample preparation, molecular weight of the polymer as well as the configuration of the chiral silicon center. Supramolecular complexation, followed by changes in the circular dichroism, took place enantioselectively and the complex of the high‐molecular weight (+)‐polycarbosilane with β‐cyclodextrin exhibited a dramatic change in its induced circular dichroism. The mechanism of this unique complexation was investigated by SEC, ¹H NMR spectroscopy, UV, fluorescence, and circular dichroism.

Supramolecular complexation of β‐cyclodextrin with the optically active and isotactic polymer.     

Polyrotaxanes of Pyrene–Triazole Conjugated Azomethine and α‐Cyclodextrin with High Fluorescence Properties

The paper reports on the preparation of a new 2‐rotaxane monomer through an acid coupling reaction between 1‐pyrenecarboxaldehyde and α‐CD/3,5‐diamino‐1,2,4‐triazole inclusion complex. Pyrenyl groups are large enough to provide a blocking effect toward cyclodextrin de‐threading. The oxidative C? C coupling of 2‐rotaxane in the presence of RuCl₃ catalyst afforded conjugated azomethine polyrotaxanes. The expected modifications of the solubility, morphology, film forming ability for rotaxane polymer were proved. As shown by fluorescence and UV‐vis spectroscopy, a material with optical properties appropriate for use in photonics was obtained.

     

Proton‐Conducting Properties of Acid‐Doped Poly(glycidyl methacrylate)‐1,2,4‐Triazole Systems

1,2,4‐triazole‐functional PGMA polymers have been synthesized and their anhydrous proton‐conducting properties were investigated after doping with phosphoric acid and triflic acid. PGMA was prepared by solution polymerization and then modified with 1H‐1,2,4‐triazole (Tri) and 3‐amino‐1,2,4‐triazole (ATri). FT‐IR, ¹³C NMR and elemental analysis verify the high immobilization of the triazoles in the polymer chain. Phosphoric‐acid‐doped polymers showed lower T_g and higher proton conductivities. PGMA‐Tri 4 H₃PO₄ showed a maximum water‐free proton conductivity of approximately 10^?2 S · cm^?1 while that of PGMA‐ATri 2 H₃PO₄ was 10^?3 S · cm^?1. The structure and dynamics of the polymers were explored by ¹H MAS and ¹³C CP‐MAS solid‐state NMR.

     

Characterization of Carbon Monoxide Centered Triads in Poly[ethylene‐co‐(butyl acrylate)‐co‐(13C‐carbon monoxide)] by Isotopic Labeling and Two‐Dimensional NMR

Summary: Poly[ethylene‐co‐(butyl acrylate)‐co‐(carbon monoxide)] (polyEBC) samples, prepared from ¹³C‐labeled carbon monoxide, were characterized using two dimensional (2D) pulsed field gradient (PFG) 750 MHz NMR spectroscopy. To elucidate the complex mixture of structures present in this terpolymer, 2D ¹H/¹³C‐heteronuclear multiple bond correlation (HMBC) experiments were conducted by selectively exciting the enhanced peaks resulting from ¹³C‐labeling. High resolution 2D NMR combined with ¹³C‐labeling of the polymer greatly simplifies the 2D NMR spectra, selectively enhances the weak peaks from low occurrence C‐centered triad structures and aids in their resonance assignments.

     

Aromatic Polyethers with a 4‐Chloro‐3‐trifluoromethylphenyl Group

Summary: A novel bisphenol, (4‐chloro‐3‐trifluoromethyl)phenylhydroquinone (3FC‐PH), was synthesized via a three‐step synthetic procedure. Four aromatic polyethers based on 3FC‐PH were prepared via a nucleophilic aromatic substitution polycondensation. These polymers had a high thermal stability, and the temperatures at a 5% weight loss were above 516 °C in air. The solubility of the polyethers was improved by the introduction of bulky pendant groups. The average refractive indices of the polymer films at 1 320 nm were in the range 1.5381–1.6145. The dielectric constants of the polyether films estimated from the refractive indices were 2.69–2.98. Highly fluorinated 3FC‐PAE exhibited lower light absorption in the near‐IR region.

Part of the ¹H NMR spectra of 3FC‐PAE.     

Degradation of Poly(butyl acrylate) and Poly(2‐hydroxyethyl methacrylate) Model Compounds Under Extreme Environmental Conditions

The degradation of low‐MW ( = 1 500 g · mol^?1) model compounds of pBA and pHEMA were studied under conditions corresponding to the worst‐case temperatures and irradiation intensities likely to be experienced by a surface coating exposed to the harsh Australian environment. Vinyl‐terminated polymers were compared to their saturated analogues; the terminal vinyl bond was found to be a source of instability which rendered the polymers more susceptible to degradation. The cyclic degradation mechanism derived from degradation of pMMA in our previous publication is also relevant to pBA and pHEMA. In addition, pBA and pHEMA are susceptible to other degradation and crosslinking reactions; crosslinking is particularly rapid in pHEMA exposed to UV radiation.

     

Synthesis,Characterization and Field‐Effect Transistor Performance of Poly[2,6‐bis(3‐alkylthiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]diselenophene]s

Benzo[1,2‐b:4,5‐b′]diselenophene (BDS) has been incorporated for the first time in a polymer. bis(Stannyl)‐functionalized BDS was copolymerized with 3,3′‐bis(alkyl)‐5,5′‐bithiophenes (dodecyl and tetradecyl side chains) through Stille copolymerization, to yield p‐type polymer semiconductors for organic field‐effect transistor application. The electronic and structural effect of the selenium atoms, compared to sulphur atoms in analogous copolymers, is described. The molecular weight has a decisive influence on the photophysical properties and supramolecular ordering, expressed in field‐effect transistor measurements. Saturation mobilities around 10^?2 cm² · V^?1s^?1 are obtained on standard silicon substrates.

     

Stereocomplex Crystallization Behavior and Physical Properties of Linear 1‐Arm, 2‐Arm,and Branched 4‐Arm Poly(L‐lactide)/Poly(D‐lactide) Blends: Effects of Chain Directional Change and Branching

For number‐average molecular weight (M _n) below 1 × 10⁴ g mol^?1, the comparison of cold crystallization temperature and spherulite growth rate and crystallinity of linear 1‐arm, 2‐arm, and branched 4‐arm poly(L ‐lactide)/poly(D ‐lactide) blends exhibits that the effects of chain directional change and branching significantly disturb stereocomplex crystallization. In contrast, the comparison of glass transition and melting temperatures of linear 1‐arm, 2‐arm, and branched 4‐arm poly(L ‐lactide)/poly(D ‐lactide) blends indicates that the effects of chain directional change and branching insignificantly alter and largely increase the segmental mobility of the blends, respectively, and the crystalline thickness of the blends is determined by M _n per one arm not by M _n and is not affected by the molecular architecture.

     

Synthesis and Characterization of Block Copolymers of ε‐Caprolactone and DL‐Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)

Biodegradable copolymers were prepared by ring‐opening polymerization of sequentially added ε‐caprolactone and DL ‐lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by ¹H NMR, SEC, IR, DSC, TGA, and X‐ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA‐containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering.

Block copolymerization of ε‐caprolactone and DL ‐lactide initiated by dihydroxyl PEG.     

Polymerisation of Norbornene Catalysed by Highly Active Tetradentate Chelated α‐Diimine Nickel Complexes

A series of three recently synthesised tetradentate chelated α‐diimine nickel complexes of the type [NiBr₂(Ar‐BIAN)] (where Ar = 2‐(1‐R‐1H‐1,2,3‐triazol‐4‐yl)phenyl; R = benzyl 1 , 1‐phenylethyl 2 , phenyl 3 ) are used as precatalysts for the polymerisation of norbornene. When activated with MAO, 1 – 3 are highly active catalysts for the production of high molecular weight polynorbornene (e.g., 1.39 × 10⁷ g PNB mol Ni^?1 · h^?1). The catalytic activity and polymer molecular weight increase markedly with the initial concentration of norbornene, but both parameters decrease with the reaction time. The characterisation of the polynorbornenes by NMR, GPC/SEC, X‐ray diffraction, and DSC/TGA leads to the assignment of a structure typical of a polynorbornene originated by a coordination vinyl addition mechanism.

     

Cyclodextrins in Polymer Synthesis: Free Radical Polymerization of β‐Cyclodextrin Complexes of Photosensitive Mesoionic 6‐Oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olates in Aqueous Medium

Solid mesoionic 2‐[2‐(isopropenylcarbonyloxy)ethylthio]‐1‐methyl‐6‐oxo‐3‐phenyl‐5‐propyl‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate was complexed in water using β‐cyclodextrin (β‐CD) and randomly methylated β‐CD, which resulted in polymerizable complexes with 2:1 stoichiometry. The β‐CD complex was characterized using ¹H NMR, ROESY NMR and UV spectroscopy. Polymerization of the complex prepared from methylated β‐CD led to a photosensitive polymer, which precipitated during polymerization and was nearly free of CD. Polymerization was carried out with a water‐soluble redox initiator. In addition, a copolymer with methyl methacrylate was prepared from the complexes, which showed a different mass‐dependent distribution in the incorporation in comparison to a copolymer prepared without CD in organic solvents.

     

Water‐Soluble Conjugated Polyelectrolyte‐Based Fluorescence Enzyme Coupling Protocol for Continuous and Sensitive β‐Galactosidase Detection

A simple, rapid, continuous and homogeneous fluorescent assay for β‐galactosidase was developed, combining an enzyme‐coupled reaction and signal amplification property of conjugated polyelectrolytes (CPs). The procedure is based on a sequence of two coupled biocatalytic steps in which the β‐galactosidase hydrolyzes its substrate to a phenol derivative followed by conversion to quinone (secondary product) with fluorescence quenching ability by the tyrosinase. The fluorescence of PFP?SO is efficiently quenched by the quinone via an electron transfer process. The limit of detection (LOD) of this assay is less than 0.0005 U · mL^?1, which is better than that of electrochemical method and is comparable to that of most sensitive chemiluminescent techniques. In principle, this sensor mechanism will extend the application window of CPs for wide‐spectrum enzyme detections. This “mix‐and‐detect” approach could be expanded to a high‐throughput manner.

     

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.

     

Selective Dimerization of γ‐Branched α‐Olefins in the Presence of C2v Group‐4 Metallocene‐Based Catalysts

Summary: The oligomerization of γ‐branched α‐olefins in the presence of catalytic systems based on group‐4 metallocenes with C_2v symmetry has been investigated. The highest reactivity was obtained by using dimethylsilyl‐bis(cyclopentadienyl)zirconium‐dichloride activated by methylaluminoxane. Highly regioregular dimers were selectively obtained for hindered γ‐branched monomers, while the less hindered ones produced higher molecular weight oligomers. A molecular modeling approach was used to rationalize the experimental results. In fact, a decrease in the β‐hydrogen elimination barrier and an increase in the insertion barrier with the monomer bulkiness were calculated.

General structure of the obtained dimers.