Syndiotactic Polystyrene Films: Orientation and Structural Changes Upon Biaxial Drawing

The orientation developed in biaxially stretched sPS (BoSPS) films before and after crystallization is studied using XRD and FT‐IR. On BoSPS films, thermal treatment induces crystallization into the trans‐planar α‐crystalline phase and a “planar” crystalline phase orientation is observed. In contrast, solvent treatments on BoSPS films induce crystallization into the helical δ‐crystalline phase, representing the first example of a polymeric framework that is able to absorb low‐molecular‐mass guest molecules from water and air at low activities and that is promising for applications in chemical separation or water purification applications; in this case a high degree of a_//c_// “uniplanar” crystalline phase orientation is observed.

     

Evidence of Intramolecular Cyclization in Copolymerization of Ethylene with 1,3‐Butadiene: Thermal Properties of the Resulting Copolymers

Summary: Ethylene and butadiene were copolymerized with a silylene‐bridged bis(fluorenyl) complex {[Me₂Si(C₁₃H₈)₂]NdCl} ( 1 ) in combination with various alkylating agents (BuLi/AlH(iBu)₂, (Bu)MgCl, Mg(Bu)(Oct)). Copolymers have a unique microstructure since they contain 1,2‐cyclohexane rings and unsaturations along the polymer chain. An intramolecular mechanism was proposed for the formation of six‐membered rings. The influence of these cyclic structures on thermal properties of the copolymers has been investigated.

Proposed mechanism for formation of 1,2‐cyclohexane rings.     

On the Lamellar Crystal Structure of Nylons 6,8 and 8,10: A Study Combining Electron Microscopy and Energy Analysis

Lamellar crystals of nylon 6,8 and nylon 8,10 with chains in a fully extended conformation were obtained by crystallization in solution, and examined by electron and X‐ray diffraction. The same crystal structure appeared to be shared by both nylons crystallized in glycerin. This structure consisted of a mixture of α‐ and β‐forms with features similar to that previously described for lamellar crystals of nylon 4,6 grown in the same solvent. Crystallization of nylon 8,10 in hexane‐2,5‐diol afforded lamellar crystals with sheets stacked in the β‐form. A comparative energy evaluation of the different models that are feasible for the crystal structure of these nylons with fully extended chains indicated very small energy differences among them. The presence of different chain arrangements in the same lamellar crystal, as well as the crystallization of the same nylon in different crystal forms upon slight modification of the crystallization conditions, are fully consistent, therefore, with the results obtained in the energy analysis.

Nylon 8,10 crystals grown in hexane‐2,5‐diol at 150 °C. Inset: The respective electron diffraction patterns.     

Biotransformation of pinenes XVII. Transformation of α-and β-pinenes by means of Armillariella mellea (honey fungus), a parasite of woodlands

A culture of Armillariella mellea species was adapted to carry out microbial transformations of (+), (-), and (±)-α-pinene and (-)-β-pinene . The composition of products obtained indicated that allylic hydroxylation of all substrates was the most characteristic reaction for Armillariella mellea species. The hydroxylation occurred either directly in unchanged pinane skeleton yielding among other compounds verbenol ( ) and verbenone ( ) or was preceded by a cleavage of four-membered rings in substrates to form a menthane skeleton. The latter reaction leads to allylic alcohols and diols, mainly trans-sobrerol ( ) and 7-hydroxy-α-terpineol ( ).     

Anionic synthesis of secondary amine functionalized polymers by reaction of polymeric organolithiums with N‐benzylidenemethylamine

Functionalization of poly(styryl)lithium and poly(butadienyl)lithiums (PBDLi) with N‐benzylidenemethylamine was investigated in hydrocarbon solvents at room temperature. The resulting secondary amine functionalized polymers were characterized by size exclusion chromatography, titration, ¹H NMR, ¹³C NMR, and thin‐layer chromatography. No dimeric side‐products were observed by SEC. The secondary amine functionalized polystyrene was obtained in high yields (96%) in benzene solvent. The functionalization reactions of PBDLi in the absence or presence of 12 vol.‐% triethylamine gave high yields (≥ 96%), whereas the same reaction in the presence of 12 vol.‐% diethyl ether was less efficient (yield = 61%). The low functionalization yields in the presence of diethyl ether were attributed to the increased reactivity of PBDLi in the presence of diethyl ether, which promotes side reactions such as metalation between PBDLi and N‐benzylidenemethylamine.

     

Photodeformable Polymers: A New Kind of Promising Smart Material for Micro‐ and Nano‐Applications

Summary: Starting in the 1960s, several kinds of photodeformable polymers have been developed, such as monolayers, polymer gels, solid films and liquid‐crystalline elastomers with different photodeformation mechanisms. This field evolved slowly until recently when significant achievements have been made. Most recently, Lendlein and co‐workers have put forward another new concept – using photo‐crosslinking to prepare deformable polymers with various pre‐determined shapes (Nature 2005 , 434, 879). This highlight gives a general introduction into photodeformable polymers and brings forth future challenges.

A polymer film doped with SCAA molecules where (a) is the permanent shape, (b) is the temporary shape and (c) is the recovered shape.     

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.     

Gold Nanoparticle/Carbazole Dendron Hybrids

The synthesis, spectral properties, and electropolymerization of hybrid gold nanoparticle core/carbazole dendron shells are reported. Ligand exchange of short‐chain alkane thiol stabilized Au‐NP is compared with direct synthesis using peripheral carbazole dendron ligands. Optical spectra, light scattering, TEM, and electron diffraction data confirm size, polydispersity, and composition. The direct synthesis route yields higher carbazole surface functionality. Higher dendron generation yields larger carbazole species on the surface. The advantage of a larger Au‐NP core is highlighted in terms of conformational mobility and electropolymerizability to form π‐conjugated polycarbazole species. Absorption and fluorescence shift is observed with the electropolymerized film.

     

The evaluation of the size and the structure of the interphase in composite particles containing a macromonomer studied by solid‐state NMR

The degree of coverage and the structure and thickness of interphases in composite latex particles consisting of a poly(butyl acrylate) (PBA) core incorporated with poly(methyl methacrylate) (PMMA) macromonomer of different molecular weight and a PMMA shell was analyzed by using solid‐state NMR spin‐diffusion measurements. By changing the temperature at a given filter strength or by adjusting the filter strength at a given temperature, the spin‐diffusion experiment could be performed in such a way that the overall structure could be detected. At filter strengths softer than necessary for the detection of the overall structure, information regarding larger structures can be obtained, whereas for stronger filters detailed information about small structures in the interphase region can be extracted. The data obtained by NMR were related to previous TEM and dynamic mechanical studies on these particles.

     

Supramolecular Branching and Crosslinking of Terpyridine‐Modified Copolymers: Complexation and Decomplexation Studies in Diluted Solution

A series of poly(methyl methacrylate) copolymers with terpyridine units in the side chains was obtained by free radical polymerization. The free terpyridine units were complexed by iron(II ) and zinc(II ) ions, and the complexation behavior was studied in detail, utilizing UV‐vis and viscosity titration experiments. Complexation of the polymer chains could be observed, which resulted in characteristic UV‐vis absorption bands and an increase in the solution viscosity. Addition of a strong competitive ligand (hydroxyethyl ethylenediaminetriacetic acid, HEEDTA) resulted in an efficient decomplexation.

UV‐vis spectra and photos of uncomplexed copolymer 2b before and after complexation with iron(II ) ions (in chloroform) and after decomplexation with HEEDTA.     

A New Dithienylbenzotriazole‐Based Poly(2,7‐carbazole) for Efficient Photovoltaics

A new dithienyl benzotriazole‐based conjugated polymer was synthesized by Suzuki coupling reaction. The polymer was found to be soluble in common organic solvents, such as chloroform, tetrahydrofuran and chlorobenzene, with excellent film‐forming properties. The structure of the polymer was confirmed by ¹H NMR, the molecular weights determined by GPC and the thermal properties investigated by TGA and DSC. The polymer films exhibited an absorption band in the wavelength range 300 to 610 nm. Preliminary photovoltaic cells based on the composite structure of indium tin oxide (ITO)/PEDOT:PSS/ PCDTBTz:PC ₆₀ BM (1:2 w/w)/Al showed an open‐circuit voltage of 0.92 V, a power conversion efficiency of 2.2% and a short circuit current of 5.33 mA cm^?2.

     

Synchrotron X‐ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p′‐bibenzoate)

Time‐resolved synchrotron X‐ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p′‐bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110 °C. Moreover, the annealing of PDEB at temperatures above T_g for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained.

Scattering profiles corresponding to sample PDEB85 in a melting experiment.     

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.     

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.

     

Are Electrografted Polymers Chemisorbed or Physisorbed onto their Substrate?

Summary: AFM‐based single‐molecule force spectroscopy was used to evaluate the mechanical strength of the link between a polymer and the substrate onto which the polymer is electrografted. Poly(N‐succinimidyl acrylate) was electrografted onto gold substrates and brought into contact with an aminothiol‐functionalized AFM tip. Bridging of single polymer chains resulting from the strong coupling between the activated esters on the polymer and amine groups on the tip was investigated. We found that the link between the polymer and the gold substrate can withstand a force far beyond the force characteristic for physisorption on gold.

     

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.

     

Synthesis and Surface Attachment of ABC Triblock Copolymers Containing Glassy and Rubbery Segments

Summary: The synthesis of an ABC triblock copolymer containing glassy and rubbery segments was conducted using a combination of living anionic and atom transfer radical polymerizations (ATRP). A poly(dimethylsiloxane) (pDMS) macroinitiator ( = 6 200; = 1.19) was prepared by living anionic ring‐opening polymerization, followed by hydrosilation reactions to incorporate 2‐bromoisobutyrate end groups for initiation of ATRP. The ATRP of styrene (S) using the pDMS macroinitiator yielded a diblock copolymer ( = 66 730; = 1.38). Chain extension of the pDMS‐b‐pS macroinitiator with 3‐(dimethoxymethylsilyl)propyl acrylate (DMSA) by ATRP yielded an ABC triblock copolymer. The latter reactive segment was covalently attached to silanol groups on a silicon wafer. The presentation of either glassy pS or flexible pDMS segments of the brushes attached to the surface was reversibly controlled by treatment with selective solvents for each segment.

Surface immobilization of pDMS‐b‐pS‐b‐pDMSA triblock copolymer to Si wafer. Treatment of brush with toluene, methanol, or annealing yields brush with hard pS surface. Treatment with hexane selectively solvates pDMS, and the soft layer is presented to the brush surface.     

High‐Content Pendant Photochromic Copolymer with Dithienylethene/Fluorene 2:1 Mole Ratio

Summary: Two photochromic dithienylethene units were incorporated into one fluorene unit as a monomer and the mole ratio of photochromic unit/repeat unit reached to 2:1 using this monomer. The content of dithienylethene component in the polymer could be improved effectively by polymerization of this monomer, which contains more than one dithienylethene units. All the starting materials concerned in the synthesis are commercially available and so the synthesis could be performed on a large scale. The polymer obtained by typical palladium‐catalyzed Suzuki coupling reaction is photochromic both in solution and in solid state and possesses good solubility. The photochromic and photomodulation luminescence properties of the polymer are also presented.

Structure of the photochromic polymer based on dithienylethene.     

Enhanced,Perpendicular Liquid‐Crystal Alignment on Rubbed Films of a Coumarin‐Containing Polystyrene

We synthesized a series of polystyrene derivatives containing coumarin side groups using polymer analogous reactions. The liquid‐crystal (LC) alignment director for these polymer films was found to be perpendicular to the rubbing direction. The contrast ratio and anchoring‐energy values of these polystyrene derivatives were found to be much greater than those of polystyrene and poly(chloromethylstyrene), indicating that the coumarin side groups increase the aligning ability. For example, the anchoring energy of a polymer with 82 mol‐% of coumarin‐containing monomeric units, compared to polystyrene, is about 7 × 10^?5 J · m^?2 and 1 × 10^?7 J · m^?2, respectively.

     

Semicontinuous Emulsion Polymerization of Butyl Methacrylate and 1, 3‐Butadiene in the Presence of Cyclodextrins and Cytocompatibility of Dicarboxylic Acid Telechelic Oligo(butyl Methacrylate)s Derived from Ozonolysis of the Latexes

Ozonolysis of unsaturated polymers produced useful telechelic oligomers that can form building blocks for networks and block copolymers. The unsaturated polymers can be prepared by semicontinuous emulsion polymerization with dienes, and here it is shown that the addition of cyclodextrins enhanced the incorporation of these comonomers. Both α‐ and β‐cyclodextrin provide copolymers with higher fractions of butadiene (BD) incorporated into the chain but α‐cyclodextrin had the highest levels of incorporation. Oxidative work up after ozonolysis produced latexes of carboxylic acid oligomers of different molar masses. A clear effect of polymer size on toxicity was observed with the oligomers with < 2 700 g · mol.^?1 proving to have similar cytotoxic effects to lactic acid. However, oligomers with above 2 700 g · mol.^?1 were cytocompatible and gave similar results to a polylactide control material.