Synthesis of Polyphenylene Ether Derivatives: Estimation of Their Dielectric Constants

A series of poly(2‐alkyl‐6‐phenylphenylene ether)s were prepared by the oxidative polymerization of 2‐alkyl‐6‐phenylphenols. Their dielectric constants were approximately 2.5, whereas it was found that the phenyl group at the 6‐position clearly increased the Q factor of the polymer compared with poly(2,6‐dimethylphenylene ether), PPE. These values were qualitatively predicted from the polarizability and the molar volume calculated by the theoretical analysis of the unit structure at the HF/6‐31G* level.

     

Dendronized Polymers: Recent Progress in Synthesis

This article divides the synthetic routes leading to dendronized polymers into two main categories (attach‐to and macromonomer) and compares their respective advantages and disadvantages. It gives a comprehensive overview on the kind of structures presently available and also spans the bridge between both polymers and molecular objects, decorated with only a few dendrons, and the structurally related, but less well defined polymers with hyperbranched side chains.

A coiled polymer backbone's stretching through the attachment of increasingly sterically demanding dendrons: a) no dendrons; b) dendrons of the first generation; c) second generation; d) third generation.     

Structural Reasons for Restricted Backbone Motion in Poly(n‐alkyl methacrylates): Degree of Polymerization,Tacticity and Side‐Chain Length

Summary: The complex dynamics of poly(n‐alkyl methacrylates) is studied by advanced ¹³C NMR spectroscopy as well as mechanical and dielectric relaxation. Extended backbone conformations are identified as the molecular units involved in structural relaxation. From the variation in the degree of polymerization and a comparison with the presence of stereoregular sequences in the sample, the length of the extended units is determined to involve about five, at most ten monomeric units. Syndiotactic and isotactic sequences behave similarly. These findings are indicative of locally structured polymer melts.

     

Morphology and Phase Characteristics of High‐Density Polyethylene Probed by NMR Spin Diffusion and Second Moment Analysis

Summary: A dipolar filter pulse sequence combined with cross‐polarization‐MAS is applied to characterize the phase distribution, morphology, and spin diffusion within a high‐density polyethylene sample. A new method to obtain quantitative ¹³C NMR by combining cross‐polarization‐MAS and spin diffusion NMR is presented. The derived crystallinity is consistent with the corresponding crystallinity obtained by ¹H NMR.

Illustration of the pulse sequence(s) applied in the present work.     

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.

     

Chain Extension of Carboxy‐Terminated Aliphatic Polyamides and Polyesters by Arylene and Pyridylene Bisoxazolines

Summary: The bulk reactions between carboxy‐terminated polyamide‐12 ( PA12 ) or carboxy‐terminated poly(butane‐1,4‐diyl adipate) ( PBDA ) and 2,2′‐(1,3‐phenylene)bis(2‐oxazoline) ( mbox ), 2,2′‐(1,4‐phenylene)bis(2‐oxazoline) ( pbox ), 2,2′‐(2,6‐pyridylene)bis(2‐oxazoline) ( pybox ) as chain‐coupling agents were studied by size exclusion chromatography, carboxy end‐group titration, and NMR spectroscopy. The chain‐coupling reaction yielded high‐molar mass polymers within 20 to 180 min, depending on reaction temperature, starting oligomer molar mass, bisoxazoline/oligomer molar ratio, and the nature of bisoxazoline. No side‐reactions were observed. Bisoxazoline pybox , used for the first time in the bulk chain extension of carboxy‐terminated polymers, exhibited the highest reaction rates. The thermal properties of the resulting polymers, studied by differential scanning calorimetry and thermogravimetric analysis, are also discussed.

The reaction of PBDA and PA12 with mbox , pbox , and pybox to give rise to the polymers studied here.     

Effects of the Reaction Conditions on the Syndiospecific Polymerization of Propene Promoted by Bis(phenoxyimine) Titanium Catalysts

Summary: The propene polymerization behavior of two typical bis(phenoxyimine) titanium catalysts has been investigated by varying reaction conditions, such as the monomer concentration, the solvent, and the cocatalyst. The experimental results indicate that the stereoregularity and regioregularity of the obtained poly(propylene)s are significantly affected by the reaction conditions. Fractionation of some poly(propylene) samples indicates the formation of macromolecules of different stereoregularity in the same run, suggesting that different active complexes can be generated in situ from these bis(phenoxyimine) titanium precatalysts.

     

Synthesis and Optical Properties of a New Series of Side‐Chain Poly(amic acid)s With p‐π Conjugation

Summary: After the condensation polymerization of benzoguanamine (BGA) and pyromellitic dianhydride (PMDA) under microwave irradiation, the resulting p‐π conjugate poly(amic acid) was grafted via the azo coupling reaction. The obtained side‐chain polymers were further grafted with TDI‐aliphatic alcohol derivatives and TDI‐aniline derivatives. The third‐order NLO coefficient and response time of PAA and graft polymers were measured by degenerated four wave mixing (DFWM) technique and their fluorescent properties were also investigated. All of the graft polymers have larger NLO coefficients and film‐formability than PAA. Their fluorescent properties were also changed by the different electronic effect of the side‐chains. The influences of the introduction of side‐chains, the side‐chain length and the electronic effect of the substituting groups on the azobenzol side‐chain to both optical properties of the polymers by varying the conjugation degree were investigated.

     

Solid‐State Olefin Metathesis: ADMET of Rigid‐Rod Polymers and Ring‐Closing Metathesis

Summary: Solid‐state olefin metathesis of rigid‐rod acyclic diene metathesis (ADMET) polymers and ring‐closing metathesis (RCM) have been investigated. 1,4‐Dipropoxy‐2,5‐divinylbenzene ( 4 ) was synthesized and used in a bulk ADMET polymerization to produce oligomers of dialkoxy poly(phenylene vinylene). The reaction was continued in the solid state, effectively doubling the molecular weight. Solid‐state RCM was investigated with a variety of solid dienes and metathesis catalysts, and demonstrated in low conversions using amide diene 5 with catalysts 9 , 13 , and 14 .

     

Spreading and Dewetting of Single Bottle‐Brush Macromolecules on Nanofacetted SrTiO3 Substrate as Induced by Different Vapours

Responsive bottle‐brush macromolecules undergo vapour‐induced spreading and dewetting cycles on facetted SrTiO₃ surfaces with a saw‐toothed topography. The macromolecular transformations are followed by environmental scanning force microscopy in real time. A set of the wafers with different groove periods are tested as the substrates for the transforming macromolecules. In order to estimate the orienting influence of the anisotropic patterned substrate, an asymmetry factor is measured for the dewetting macromolecules at different groove periods. The most evident template influence of the substrate occurs when the period is in range of 20–40 nm. This range is commensurable with the typical lateral dimension of the adsorbed bottle‐brush macromolecules with a dense flat corona of extended side chains.

     

Saccharide Polymers 6

Summary: The 2,4,6‐tri‐O‐acetyl‐3‐deoxy‐D ‐erythro‐hex‐2‐enono‐1,5‐lactone, briefly Ac‐Gluc‐enlactone (GEL) ( 1 ), is easily synthesized in an one‐step reaction from glucono‐δ‐lactone with good yields. Free radical polymerizations of GEL with vinyl esters with side chain of different length including fatty acids esters were carried out in substance or in solution under various conditions. The structures and chemical compositions of the polymers were established by elemental analysis, FT‐IR‐, ¹H‐, and ¹³C NMR spectroscopy. Copolymerization kinetics were investigated. Characteristic properties of polymers, e.g. molecular weight, optical rotation, and thermal properties are reported. The products are of interest as components in commodities with binding and adhesive properties.

     

UV‐Induced Modification of Conjugated Polymers Using Gaseous Organosilanes

Summary: This paper describes the use of trialkylsilanes for photoinduced patterning of electroluminescent polymers as a new field of application for this type of organosilicon compounds. Under UV irradiation, trialkylsilanes selectively saturate the vinylene groups in poly(p‐phenylenevinylene) (PPV)‐type polymers, while leaving aromatic units virtually unaffected (selective photobleaching). Spin cast films of polymer blends consisting of two or three different conjugated polymers were UV irradiated in the presence of gaseous trialkylsilane reagents (trimethylsilane and ethyldimethylsilane) to achieve multicolor patterning. Exploiting the host‐guest concept with polyfluorene (PF) derivatives as totally aromatic host matrix and PPV derivatives as guest polymers, dual‐color displays and, with constraints, three‐color LED displays were realized. Compared to previously reported reagents such as hydrazine and thiols, trialkylsilanes enable photochemical patterning under non‐toxic and odorless conditions. Possible mechanisms for the photoreaction with trialkylsilanes as well as perspectives for applications are discussed.

Electroluminescence spectra of LEDs based on the host‐guest system.     

Polyurea With L‐Lysinyl Residues as Components: Application to Membrane Separation of Enantiomers

Novel polyureas are synthesized from lysinyl residues. The polyurea thus prepared yields a durable self‐standing membrane that can be converted into a molecular recognition material by using Z‐D ‐Glu or Z‐L ‐Glu as a print molecule. The Z‐D ‐Glu molecularly imprinted membrane adsorbes the D ‐isomer of Glu in preference to the corresponding L ‐Glu and vice versa. Even though the polyurea consists of L ‐lysinyl residues, both Z‐D ‐Glu and Z‐L ‐Glu work as print molecules to construct molecular (chiral) recognition sites in the membrane. Those molecularly imprinted membranes show chiral separation abilities when a concentration gradient or an applied potential difference is applied as a driving force for membrane transport.

     

Computer Simulations of the “Hairy Rod” Model

Summary: Using extensive Molecular Dynamics simulations we study the behavior of very rigid polyelectrolytes with hydrophobic side chains that are known to form cylindrical micelles in aqueous solution. We investigate the stability of such micelles with respect to hydrophobicity, Coulomb interaction, and micellar size. We show that for the parameter range relevant for poly(p‐phenylene sulfonate)s (PPP) one finds a stable finite micellar size close to the experimental parameter region. We also point out that our model has some similarities to DNA solutions with added condensing agents, hinting to the possibility that the size of DNA aggregates is under certain circumstances thermodynamically limited.

DNA‐like morphologies of the polyelectrolytes.     

Nuclear Magnetic Resonance Spectroscopy in Macromolecular Science

A historical overview of the role of NMR spectroscopy in macromolecular science in general and its coverage in “Macromolecular Chemistry and Physics” in particular is given. In the early days physics‐application to study molecular dynamics, partial alignment of macromolecules and phase separation prevailed, deduced from broad‐line solid‐state NMR. Only somewhat later, high‐resolution NMR in solution was established as an important tool for elucidating the chain microstructure. In the future, these two aspects are expected to merge.

Side group liquid crystalline polymers: ²H NMR has elucidated alignment and dynamics of these complex materials.     

New Star‐Branched Poly(acrylonitrile) Architectures: ATRP Synthesis and Solution Properties

Summary: Atom transfer radical polymerization (ATRP) has been chosen as “living”/controlled free radical polymerization system to synthesize a number of novel poly(acrylonitrile) (PAN) architectures. The reaction conditions for the synthesis of linear samples with control over molar mass and molar mass distribution have been investigated together with the possibility of obtaining copolymers of acrylonitrile with small quantities of methyl acrylate (max. 5 mol‐%). Well‐defined star polymers with 3, 4 and 6 arms have been successfully synthesized together with linear chains initiated by a bifunctional initiator and star‐branched polymers with a hyperbranched poly(ester amide) as core. Molar masses were determined by NMR and GPC with the latter leading to a significant over estimation. Solution viscosity studies indicated that the stiff structure of the PAN chains is still maintained in the homopolymer star architectures and that the incorporation of small quantities of methyl acrylate as comonomer has a stronger effect on chain flexibility than the incorporation of star‐branch points.

     

Synthesis of Silica‐Supported Metallocene Catalysts for Olefin Polymerization

Four supported metallocene catalysts were synthesized directly on silica [Si(CpZrCp), Si(CpZrInd), Si(IndZrCp), and Si(IndZrInd)]. The first ligand was chemically tethered to silica (internal ligand) while the second was free from silica (external ligand). The polymerization of ethylene and the copolymerization of ethylene with hexene were investigated. The activity of the catalysts and the molecular weights of the polymers were found to depend on the position of the ligands. In all cases, high‐molecular‐weight polyethylene with moderate polydispersity was obtained. Moreover, the copolymerization of ethylene with hexene provided a homogeneous polymer.

Reaction of ZrCl₄(OC₄H₈)₂ with modified silica (SiCp).     

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.

     

Site Specific Proton and Deuteron NMR Relaxation Dispersion in Selectively Deuterated Polyisoprene Melts

Summary: The frequency dependence of proton and deuteron NMR relaxation times was determined in selectively deuterated and undeuterated polyisoprene melts and compared to polybutadiene melts. Master curves were generated by the Williams‐Landel‐Ferry (WLF) formalism which resulted in very similar dispersions for all samples with a high and a low frequency branch following characteristic power laws. The results show a consistently weaker frequency dependence than any reported so far for other polymer melts. The reason for this finding is identified in the distribution of intramolecular motion modes, while intermolecular contributions are ruled out.

Master curves for ¹H relaxation dispersions obtained from measurements between 223 K and 348 K shifted relative to a reference temperature of 296 K.     

ADMET Polymerization as a Route to Functionalized Polycarbosilanes

It is now evident that ADMET chemistry can be employed to prepare a family of unsaturated carbosilane polymers containing a common backbone decorated with different alkoxysilane pendant groups, demonstrating the generality and potential utility of this chemistry. Four functionalized silicon containing dienes have been synthesized by nucleophilic substitution of the same parent diene monomer containing two reactive silicon‐chlorine bonds. These new α,ω‐diene monomers have been polymerized under ADMET conditions using the 2^nd generation Grubbs's ruthenium catalyst, producing polymers with useful molecular weights. Variation of the pendant group results in differing chemical and physical properties of the resulting polymers. We believe this chemistry offers much to broaden the synthetic pathways to new organosilicon polymers.