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.     

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.     

Low‐Temperature Polymerization of Olefins in the Presence of Titanium Monoamidinate/MAO Catalyst

This paper reports the predominantly syndiotactic‐specific polymerization of propylene in the presence of titanium monoamidinate/methylaluminoxane (MAO) catalysts. The same catalysts, depending on the reaction conditions, also promote either predominantly 1,4‐cis or 1,4‐trans polymerization of 1,3‐butadiene and polymerization of styrene either to highly syndiotactic or to stereoirregular polymer. Some preliminary information about the features of propylene polyinsertion is also reported.

Expansion of the 20–24 ppm region of the ¹³C NMR spectrum of sample 2. The starred resonance at 21.75 ppm and the shoulders are not assigned.     

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.     

Synthesis and self‐assembly of polymers containing dicarboximide groups by living ring‐opening metathesis polymerization

Polymers with narrow molecular weight distributions and controlled architectures were generated by living ring‐opening metathesis polymerization of exo‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboximide. The dicarboximide units have been previously shown to exhibit biological activity, can selectively bind to the nucleic acid base adenine by hydrogen‐bonding, and are readily functionalizable. Block copolymers containing these moieties were generated, and underwent self‐assembly into nanoscale spherical aggregates, with surface localized molecular recognition motifs.

     

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.

     

Novel Polymerization of Fluorinated 2‐Vinylcyclopropane in Aqueous Solution via Cyclodextrin Complexes

We report on the first examples of the free radical polymerization of a fluorinated 2‐vinylcyclopropane 1 and its copolymerization with an alkyl 2‐vinylcyclopropane 2 in aqueous solution via their host‐guest complexation with a random methylated β‐cyclodextrin (RAMEB) using a water‐soluble initiator (VA50). Upon polymerization, the dethreaded cyclodextrin remained in water solution, whereas the water‐insoluble polymer precipitated out and was isolated. The polymers prepared exhibited mesophase behavior over a wide range of temperature. Both T_g and T_i of the copolymers increased linearly with the amount of fluorinated co‐units.

Complexation of fluorinated vinylcyclopropane 1 with RAMEB and polymerization in water solution.     

An Easy Strategy for the Synthesis of Well‐Defined Aliphatic‐Aromatic Hyperbranched Polyesters

A one‐pot solution polymerization under mild conditions was adapted for the synthesis of well‐defined aliphatic‐aromatic polyesters with different degrees of branching. The esterification was performed at room temperature using 4,4‐bis(4′‐hydroxyphenyl)valeric acid (AB₂) and 3‐(4‐hydroxyphenyl)propionic acid (AB) as monomers. DPTS was used as a catalyst and DCC as a coupling agent. Polyesters with statistical, dendritic topology, controlled degree of branching and > 35 000 g · mol^?1 were obtained. The polymers were characterized by ¹H and ¹³C NMR, SEC, DSC, and TGA. A strong dependence of the degree of branching and the thermal properties of the polymers depending on the AB/AB₂ monomer ratio was observed.

     

Acrylic‐Based Polyurethane/Silica Hybrids Prepared by Acid‐Catalyzed Sol–Gel Process: Structure and Mechanical Properties

Summary: Silica sols were first prepared based on different ratios of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) by an acid‐catalyzed sol–gel process, and then incorporated into acrylic‐based polyurethanes. The structures and morphologies of silicone‐oxo clusters were studied by ²⁹Si NMR, SAXS, and scanning electron microscopy (SEM), whereas the mechanical properties of polyurethane/silica hybrids were characterized by DMA and tensile tests. The silicone‐oxo clusters in both silica sol and polyurethane hybrids became denser and larger at a higher molar ratio of TEOS/MTES and higher silica content, and the silica‐oxo clusters of polyurethane/silica hybrids even became more compact and larger than those of silica sols, increasing the elastic modulus and tensile strength of polyurethane/silica hybrids.

Typical structure of silica sol prepared from the hydrolysis and condensation of TEOS and MTES with acid as the catalyst.     

Polyester Dendrimers Carrying NLO Chromophores: Synthesis and Optical Characterization

Summary: Four dendritic polyesters containing non‐linear optical chromophores on the periphery were synthesized and their material properties were compared for electro‐optic device applications. Thermal and optical parameters of the dendrimer materials were measured along with structural analysis. A high chromophore concentration in the dendritic polyesters produced enhancement of the optical non‐linearity. The second generation dendrimer (G1‐DAIDC) exhibited an electro‐optic coefficient of 43.4 pm · V^?1 at 1.55 µm optical communication wavelength. Aromatic ester backbones elevate the glass transition temperature of the chromophore alignment, representing good thermal stability of the optical films.

     

Synthesis of Vinylphosphonic Acid Anhydrides and their Copolymerization with Vinylphosphonic Acid

We present the synthesis and characterization of the compounds formed in a mixture of vinylphosphonic acid (VPA) and acetic anhydride used for the radical‐initiated VPA polymerization. High‐molecular‐weight PVPA with up to 109 000 g · mol⁻¹ was obtained from the polymerization of a mixture containing VPA, VPAAnh, VPADiAnh and their acetylated derivatives. Relative reactivities of these compounds were estimated. The resulting polymers were characterized by viscosimetry, light scattering and NMR measurements. The complexity of the polymer structure increases with increasing anhydride content in the reaction feed as can be concluded from the ¹H, ¹³C and ³¹P NMR spectra. This finding is in accordance with a cyclopolymerization mechanism resulting in five‐ and six‐membered anhydride rings within the polymer chain.

     

Macromol. Chem. Phys. 24/2009

The behavior of the transmittance self‐oscillation of a polymer chain with a positively charged MAPTAC group is studied. The polymer concentration exerts considerable influence on the behavior and lifetime of the self‐oscillation. The redox potential and transmittance are measured simultaneously showing that the reactivity of the Ru(bpy)₃ moiety is significantly affected by the polymer aggregation state, originating from the solubility of the polymer chain. The behavior and lifetime of the self‐oscillation can be controlled by changing the design of the polymer structure and concentration.

     

Template‐Assisted Fabrication of Highly Ordered Interpenetrating Polymeric Donor/Acceptor Nanostructures for Photovoltaic Applications

The template‐assisted fabrication of well‐ordered interpenetrating donor/acceptor nanostruc‐tures based on polymeric semiconductors on conductive substrates is reported. Arrays of free‐standing crosslinked tetraphenylbenzidine based nanorods are fabricated utilizing sacri?cial AAO templates. TEM con?rms the obtained donor/acceptor nanostructure morphology. The embedded nanorods show no aggregation and collapse of the rods within the ?lm. Photoluminescence measurements reveal a more than three fold improvement in photoluminescence quenching relative to the planar bilayer architecture. The approach offers a versatile all‐solution‐based technique for the fabrication of well‐ordered bulk heterojunction ?lms with a large donor/acceptor interface for the application in polymer/polymer photovoltaic devices.

     

Spectroelectrochemical and Photovoltaic Characterization of a Solution‐Processable n‐and‐p Type Dopable Pyrrole‐Bearing Conjugated Polymer

D‐A‐D‐type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n‐ and p‐type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2 V for oxidation and ?1.4 V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).

     

Investigation of Templated Mesoporous Silicate Thin Films Using High Speed,Solid‐State 1H MAS and Double Quantum NMR Spectroscopy

Two‐dimensional DQ ¹H MAS NMR has been used the investigate the local structure of a surfactant‐templated silicate thin film prepared from adding 4% polyoxyethylene(10) cetyl ether to an acidic TEOS silica sol. A close spatial contact between the surfactant and the silicate present in these materials could be demonstrated, while the high sensitivity of the NMR experiments allowed systems with limited amounts of material to be investigated. The detected inorganic‐organic interactions in these materials provide additional information into the chemical processes occurring during the self‐assembly process and the formation of meso‐structured materials.

Graphical representation of the spatial interactions observed between the silanols, oxomethylene protons of the surfactant and water within the template silicate material.     

Resorcinol‐Formalin Foam Balls Via Gelation of Emulsion Using Phase‐Transfer Catalysts

Summary: Highly spherical (98.5%) low‐density foam balls with 1‐mm diameters were fabricated from a density‐matched emulsion consisting of a resorcinol/formalin aqueous solution and a (mineral oil and carbon tetrachloride) mixture. Phase‐transfer catalysts of carboxylic acid were utilized to induce gelation of the emulsion. The gelation process was monitored by a mechanical test. Gelation forming ball shapes happened within 20–30 min, depending on the catalysts, at room temperature. The gelation time decreased with high‐catalyst concentration. Acids with long alkyl chains did not induce gelation and no balls were obtained. The gelated balls were dried to obtain foam via an exchange of the solvent with 2‐propanol and extraction using the supercritical fluid CO₂. The density obtained from the catalyst was 0.15–0.16 g · cm⁻³. SEM images revealed surface membrane formation, which can be explained by local concentration at the interface of W/O. We observed different bulk foam cell sizes, which may depend on the catalysts and, therefore, on the different gelation rates.

Structure of a highly spherical low‐density foam ball with 1‐mm diameter.     

Anisotropic Dimensional Swelling of Membranes of Ultrafine Hydrogel Fibers

Summary: Interconnecting fibrous membranes were generated by electrospinning an aqueous mixture of poly(acrylic acid) and poly(vinyl alcohol) at a 3.5 COOH/OH molar ratio. The membranes containing 200 to 500 nm diameter fibers were crosslinked by heat‐induced esterification and behaved like anionic hydrogels, i.e., they swelled significantly more at a pH above 4. The dimensional expansion of these fibrous membranes was far greater in their thickness than in their planar areas. The anisotropic dimensional expansion was associated with the spatial arrangement of fibers, i.e., much smaller inter‐fiber spaces along the thickness direction than in the planar directions. Crosslinking under constraint caused further fiber compaction in the thickness direction, leading to anisotropic and accordion‐like dimensional expansion upon swelling.

SEM image of the PAA/PVA membrane (C1) thermally crosslinked under high constraint.     

Novel Poly(butylene succinate)‐Based Ionomers with Sulfonated Succinate Units: Synthesis,Morphology, and the Unique Nucleation Effect on Crystallization

Summary: Poly(butylene succinate) (PBS) and PBS‐based ionomers (PBSi's) with 0.3 and 1.2 mol‐% of sodium sulfonated succinate unit were synthesized. The existence of ionic aggregates in the ionomer matrices was indicated by melt viscosity and glass transition data. It seems that the ionic aggregates have two opposing roles in crystallization: one is the induction of nucleation and the other is the interference with lamellar growth. Because of these two contrary effects, the crystallization behavior of the ionomers exhibited measurably different cooling rate‐dependencies than that of the parent PBS. The rate varied distinctly with ionic content.

Spherulitic morphologies of PBS and PBSi's measured with polarizing optical microscopy.     

Novel diazosulfonate terpolymers for the preparation of structured functionalized surfaces: Synthesis and characterization

We report the synthesis and characterization of novel diazosulfonate copolymers and terpolymers by free‐radical polymerization for the preparation of ultrathin films. Such films were covalently linked to silicon and glass substrates after a spin‐coating and annealing process using 3‐(trimethoxysilyl)propyl methacrylate as the adhesive comonomer. The polymers were characterized by NMR and IR spectroscopy and ellipsometry, and contact‐angle measurements were used to analyze the film properties. The light‐sensitive but thermally stable polymer films can be structured successfully by UV light down to the micrometer scale. The patterns written into the diazosulfonate film were produced by a UV laser without a mask. The photolysis in solution and in film was examined by UV spectroscopy.

UV imaging: area selective representation of the UV transmission between 430 and 450 nm over a 60 × 60 μm² area of a spin coated film of copolymer 2 . Pre‐structuring with a He‐Cd laser (at 325 nm) resulted in a ring‐shaped structure of 30‐μm diameter showing a higher transmissivity (brighter area) resulting from the reduced absorption of the polymer film (decomposition of the diazosulfonate functions).     

Synthesis and Dielectric Study of New Liquid‐crystalline Polysiloxanes Presenting a Thioether Spacer

Three new cyanobiphenyl polysiloxanes presenting long thioether spacers have been carried out. This type of spacer leads to very stable liquid‐crystalline polymers at room temperature and remove the crystallinity phenomenon. Dielectric analysis results show that the thioether spacer brings much more molecular flexibility to the system.

Example of an “interdigitated” structure observed by X‐ray analysis.