Optical Probes for Monitoring Intercalation and Exfoliation in Melt‐Processed Polymer Nanocomposites

Summary: Laser‐induced fluorescence spectroscopy of the optical probe Nile Blue A in polymer clay nanocomposites is described. Concentration quenching of the fluorescence dominates the probe behavior until the clay platelets are physically separated by polymer intercalation. Further separation into an exfoliated structure results in an intense increase in probe fluorescence. Preliminary results indicate the ability to discriminate between intercalated and exfoliated structures in nanocomposites formed by melt processing.

Polyamide 6 nanocomposites: Purple, 1 minute processing (left). Red, 7 minute processing (right).     

Controlling the Deintercalation in Hydrogenated Nitrile Rubber (HNBR)/Organo‐Montmorillonite Nanocomposites by Curing with Peroxide

Summary: The effect of peroxide vulcanization on organoclay dispersion in hydrogenated nitrile rubber (HNBR)/organo‐montmorillonite (organo‐MMT) nanocomposites was investigated. Three types of organoclays were tested, one containing a primary amine and two bearing quaternary intercalants. In contrast to sulfur vulcanization, which in combination with primary amine intercalants produced a confined/deintercalated clay structure, the peroxide curing yielded well‐ordered intercalated nanocomposites. The tensile mechanical performance and oxygen permeability of the HNBR nanocomposites were determined.

Oxygen permeability coefficient ratio for the different HNBR films tested at 0 and 60% relative humidity (i.e., dry and wet conditions, respectively).     

High‐Molecular‐Weight Polycarbonates Synthesized by Enzymatic ROP of a Cyclic Carbonate as a Green Process

High‐molecular‐weight PTeMC and PHMC were prepared by the lipase‐catalyzed polymerization of butane‐1,4‐diol or hexane‐1,6‐diol and diphenyl carbonate via the formation of a cyclic dimer by a green process. Cyclic carbonate dimers were prepared by the lipase‐catalyzed condensation of diphenyl carbonate with butane‐1,4‐diol or hexane‐1,6‐diol in dilute toluene solution using an immobilized lipase from Candida antarctica, and was followed by the ring‐opening polymerization of the cyclic dimer in bulk with the same lipase to produce PTeMC with = 119 000 g · mol^?1 and PHMC with = 399 000 g · mol^?1, respectively. Additionally, enzymatic polymerization of cyclic carbonate dimer was analyzed with respect to the K_m and V_max for the lipase.

     

Dynamics of Water Near Oxidized Polystyrene Films

Atomistic MD simulations of water in the vicinity of oxidized amorphous atactic polystyrene are presented. The changes in the orientational and translational dynamics of water near polymer surfaces with different hydrophilicity are studied. Two main orientational relaxation processes of water molecules are distinguished: a process on a fs timescale, associated with the ballistic motion of water molecules, and a process on a ps timescale, associated with the self‐diffusion of water. The fast process is not affected by the presence of the polymeric surface. The second relaxation process differs at the interface from that in the bulk in that the dynamics of water molecules is more heterogeneous in the first. The effect of the representation of polystyrene films on the water dynamics is discussed.

     

Ethylene and Ethylene/Propylene Polymerization Behavior of Bis(phenoxy‐imine) Zr and Hf Complexes with Perfluorophenyl Substituents

The catalytic properties of bis(phenoxy‐imine) Zr and Hf complexes incorporating perfluorophenyl groups with methylaluminoxane were investigated. The fluorinated complexes produced far higher‐molecular‐weight polyethylenes and ethylene/propylene copolymers with increased activities compared with the non‐fluorinated congeners. Moreover, the fluorinated complexes displayed a higher incorporation ability for propylene.

Structures of complexes 1 – 4 .     

High‐Performance Exfoliated Poly(propylene)/Clay Nanocomposites by In Situ Polymerization with a Novel Z–N/Clay Compound Catalyst

Highly exfoliated poly(propylene) (PP)/clay nanocomposites with obvious improvements in both the tensile strength and toughness have been prepared by a novel TiCl₄/MgCl₂/imidazolium‐modified montmorillonite (IOHMMT) compound catalysts. Through this approach, in situ propylene polymerization can actually take place between the silicate layers and lead not only to PP with a high isotacticity and molecular weight, but also to a highly exfoliated structure even at high clay content levels (as high as 19 wt.‐%).

     

Chiral Amplification during Asymmetric‐Induced Copolymerization of Phenylacetylenes with Tight Cis‐Cisoidal Main Chains

A novel phenylacetylene ( 1 ) having two hydroxyl groups and a chiral pinanyl group together with the other three related phenylacetylenes has been synthesized and (co)polymerized by using an achiral catalytic system. Among the four monomers, only 1 is suitable to the asymmetric‐induced polymerization ( AIP ). Chiral amplification phenomenon is only observed in the copolymerization of 1 with an achiral phenylacetylene having two hydroxyl groups ( 3 ). The tight helical cis‐cisoidal main chain formed by making intramolecular hydrogen bonds between the hydroxyl groups in the copoly( 1 / 3 ) enhances the efficiency of chiral induction and as a result chiral amplification phenomenon is observed during the copolymerization.

     

Supramolecular Assembly of Gold Nanoparticles Mediated by Polypseudorotaxane with Thiolated β‐Cyclodextrin

Summary: A water‐soluble gold nanoparticle aggregate 2 was prepared by chloroauric acid and a polypseudorotaxane 1 of mono‐6‐thio‐β‐cyclodextrin with poly(propylene glycol) bis(2‐aminopropyl ether) ( ≈ 2 000) in the presence of sodium borohydride in N,N‐dimethylformamide (DMF) solution. The investigative results indicated that the gold nanoparticle aggregate 2 might act as an efficient DNA‐cleavage reagent.

A typical TEM image of gold nanoparticle aggregate 2 .     

Silica‐Protected Micron and Sub‐Micron Capsules and Particles for Self‐Healing at the Microscale

A generalized silica coating scheme is used to functionalize and protect sub‐micron and micron size dicyclopentadiene monomer‐filled capsules and polymer‐protected Grubbs' catalyst particles. These capsules and particles are used for self‐healing of microscale damage in an epoxy‐based polymer. The silica layer both protects the capsules and particles, and limits their aggregation when added to an epoxy matrix, enabling the capsules and particles to be dispersed at high concentrations with little loss of reactivity.

     

Fabrication of Mussel‐Inspired Highly Adhesive Honeycomb Films Containing Catechol Groups and Their Applications for Substrate‐Independent Porous Templates

Porous surface patterns are used in a wide variety of practical applications. Honeycomb‐patterned porous polymer films are good templates for preparing porous surfaces due to their simple fabrication and the arrangement of pores on the surface. Catechol groups include in adhesive protein of mussels have attracted much attention due to their highly and substrate‐independent adhesive properties. In this paper, highly and substrate‐independent adhesive honeycomb‐patterned porous polymer films are prepared by using amphiphilic copolymer having catechol moieties. Furthermore, porous surface patterns are transferred on various organic or inorganic substrates by wet etching with using adhesive honeycomb films as templates.

     

New Polylactide/Layered Silicate Nanocomposite: Nanoscale Control Over Multiple Properties

The preparation, characterization, materials properties, crystallization behavior and biodegradability of a polylactide (PLA)/organically modified layered silicate nanocomposite is described. Wide‐angle X‐ray diffraction and high‐resolution TEM analyses confirmed that intercalated stacked and disordered/exfoliated mica layers coexist in the nanocomposite. The nanocomposite showed improved materials properties and crystallization behavior with a simultaneous improvement in biodegradability as compared to neat PLA.

Degree of biodegradation (i.e. CO₂ evolution) of neat PLA and PLACN4 under compost conditions.     

Ordered Honeycomb‐Structured Films from Dendronized PMA‐b‐PEO Rod‐Coil Block Copolymers

Summary: Fabrication of honeycomb‐patterned films from amphiphilic dendronized block copolymer (PEO₁₁₃‐b‐PDMA₈₂) by ‘on‐solid surface spreading’ and ‘on‐water spreading’ method is reported. Highly ordered honeycomb films with quasi‐horizontally paralleled double‐layered structure can be fabricated by the on‐solid surface spreading method. This work raises the possibility that such structures can be formed in amphiphilic dendronized block copolymers and extends the family of source materials.

     

Uncharged Water‐Soluble Metal‐Bis‐Porphyrins Like Molecular Tweezers for Amino Acids

Some new water‐soluble bis‐porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI‐TOF mass spectrometry, ¹H NMR and UV‐vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co‐bis‐porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis‐porphyrin behaves like molecular tweezers.

     

Measurement of in situ Monomer Sorption in Poly(propylene)

Summary: An experimental method has been developed to compare the amount of monomer absorbed in freshly produced poly(propylene) with the amount of monomer absorbed in the same material after degassing. It has been found that propylene sorption in freshly produced poly(propylene) is significantly higher than the sorption in the same but degassed polymer. The difference depends on the degree of drying and is time‐dependent. This fact can be an explanation for reduced activity often observed in the transition from liquid‐ to gas‐phase polymerization.

Pressure profile during the pressure‐swing part of the experiment.     

Polymer Brushes with Phototriggered and Phototunable Swelling and pH Response

Photolabile polymer brushes with tailored length containing a photoremovable protecting group (NVOC) are prepared via the SI‐ATRP method. Upon light irradiation, the NVOC group is removed to generate controlled densities of free amine groups (PAMA) randomly distributed along the brush. The presence of the ionizable groups induces a photo‐triggered swelling response. The swelling degree can be tuned by the irradiation dose. A dual (light and pH), tunable response is demonstrated.

     

Decorating Polypyrrole Nanotubes with Au Nanoparticles by an In Situ Reduction Process

Au nanoparticle‐decorated polypyrrole nanotubes (defined as PPy/Au nanocomposites) are prepared by an in situ reduction process. Polypyrrole (PPy) nanotubes are prepared by a self‐degraded template method, and Au nanoparticles are deposited in situ by the reduction of HAuCl₄. The size and uniformity of the Au nanoparticles that decorate the PPy nanotubes can be controlled by adjusting the experimental conditions, such as the stabilizers used and the reaction temperature. The morphologies and optical properties of the nanocomposites have been characterized by scanning electron microscopy, transmission electron microscopy, UV‐vis, and FT‐IR spectroscopy. Conductivity measurements show that the conductivities of the nanocomposites decrease with a decrease of temperature, and the conductivity–temperature relationship obeys the quasi‐one dimensional variable range hopping model.

     

Spontaneous Birefringence in Layer‐by‐Layer Films of Chitosan and Azo Dye Sunset Yellow

Layer‐by‐layer (LBL) films consisting of layers of the azo dye Sunset Yellow alternated with chitosan display spontaneous birefringence, which is attributed to the film anisotropy imparted by the LBL method. This is unusual for azobenzene‐containing materials as they normally form films with randomly oriented molecules, presenting birefringence only due to photoinduced isomerization cycles. Spontaneous birefringence does not appear in cast films, but occurs for LBL films obtained under various experimental conditions.

Chemical structures of (a) Sunset Yellow and (b) chitosan.