Analysis of Crosslinked Styrene‐Butadiene Rubbers by Liquid Chromatography and FT‐IR Spectroscopy, 1

Crosslinked styrene‐butadiene and butadiene rubbers can efficiently be analyzed by liquid chromatography and FT‐IR spectroscopy. In a first step the vulcanizate is pyrolyzed under mild conditions. The resulting high molar mass fragments are extracted from the bulk material and analyzed by size exclusion chromatography. The molar masses of the extractables are in the range of 3 000 to 25 000 g/mol. The chemical composition as a function of molar mass is visualized by coupled SEC‐FT‐IR spectroscopy. By quantitative analysis of the FT‐IR spectra the concentrations of the different structural units, including styrene, 1,4‐trans‐butadiene, 1,2‐vinylbutadiene, and 1,4‐cis‐butadiene, are determined. It is shown that the chemical composition of the original non‐crosslinked rubbers and the chemical composition of the extractables are rather identical. Therefore, this technique can be used to obtain structural information on rubber formulations even in the case when the material is already vulcanized.

SEC chromatograms of SBR 1712 and the extractables after pyrolysis, stationary phase: SDV linear, mobile phase: THF, detector: ELSD.     

Kinetics of Cationic Photopolymerizations of UV‐Curable Epoxy‐Based SU8‐Negative Photoresists With and Without Silica Nanoparticles

Summary: This paper reports on the photocuring kinetics of protonic‐acid‐initiated cationic polymerizations of UV‐curable epoxy‐based SU8‐negative photoresist systems with and without silica nanoparticles, as assessed using photo‐DSC, FTIR spectroscopy, UV‐vis spectroscopy, and SEM. Photo‐DSC analysis using an autocatalytic kinetic model demonstrated that the cross‐link density and cure rate increased as the concentration of silica nanoparticles with surface silanol groups increased to 2.5 wt.‐%. This result was confirmed by FTIR spectroscopy, and suggests that the presence of silica nanoparticles of up to 2.5 wt.‐% promoted the cure conversion and cure rate of the UV‐curable hybrid organic/inorganic negative photoresists due to the synergistic effect of silica nanoparticles acting both as an effective flow or diffusion‐aid agent and as a proton‐donor cocatalyst during the cationic photopolymerization process. The decrease in the cross‐link density that occurred when the silica content was higher than 2.5 wt.‐% was attributed to aggregation between silica nanoparticles due to their high surface energy.

SEM photograph at the film‐air interface of the UV‐cured hybrid organic/inorganic photoresist containing 10 wt.‐% silica nanoparticles.     

A Novel Impact Modifier for Nylon 6

A new carboxylated styrene‐butadiene rubber (CSBR) in ultrafine powder form was used to modify the properties of nylon 6. The nylon 6/CSBR blends possessed higher toughness than nylon 6/maleic anhydride‐grafted polyethylene‐octene elastomer (POE‐g‐MAH) system. TEM micrographs revealed the fine dispersion of CSBR particles with a diameter of 150 nm. The effective toughening of nylon 6 with CSBR was attributed to the good interface, fine dispersion, and shear yielding.

TEM photograph of undeformed Nylon 6/CSBR (80/20) blend (×40 000).     

Production of Narrow‐Size‐Distribution Polymer‐Pigment‐Nanoparticle Composites via Electrohydrodynamic Atomization

Near‐monodisperse, size‐controllable, poly(methyl methacrylate)‐pigment nanoparticle composites were produced using electrohydrodynamic atomization (EHDA). The geometric mean diameters of the composite particles were in the 0.91 to 1.90 µm‐diameter range with geometric standard deviations of approximately 1.05 to 1.12. Increasing the polymer volume fraction and liquid flow‐rate resulted in an increase in the diameter of the composite particles, which agreed well with droplet scaling relations for EHDA. The results here demonstrate that EHDA can be used for polymer‐nanoparticle‐composite production and as an alternative to conventional inkjet printing.

     

Effect of Silicone Carbide on the Elastic Properties of Starch‐Based Composites: A Three‐Phase Model

The effect of a rigid filler on the elastic properties of starch‐based composites is investigated. Thermomolding of the targeted composite is conducted using a starch matrix with varying silicone carbide content. Mechanical testing reveals that the composite's Young modulus cannot be rationalized using two‐phase analytical models. The effect of a weak interphase region is highlighted using a finite‐element model that assumes the generation of virtual microstructures. Numerical results are discussed by describing the influence of the structural and interphase parameters on the composite's elastic modulus. Identification of optimal interphase parameters quantitatively demonstrates the weak adhesion between intrinsic phases for all studied filler fractions.

     

Effect of Silica‐Coated Poly(butyl methacrylate)‐block‐poly(methyl methacrylate) Double‐Shell Particles on the Mechanical Properties of PMMA Composites

Silica nanoparticles with an average diameter of 12 nm are grafted with PBMA‐b‐PMMA double shells through typical sequential ATRP from bromoisobutyrate initiators anchored at the silica surface using an epoxysilane. A commercially available PMMA homopolymer is used for the preparation of composites with unmodified, silane‐modified and double‐shell‐modified silica particles. Good mechanical properties are obtained for silica double shell containing systems. The silica content in double shell particle systems is varied from 0 to 2.5 wt%. A significant improvement in impact properties is observed. The surface‐modified silica particles are characterized by ATR‐FTIR, NMR, GPC, and thermal analyses. TEM analysis is used to analyze the nature of dispersion of particles in the composites.

     

Improving the Thermal Behavior of Poly(propylene) by Addition of Spherical Silica Nanoparticles

Spherical silica nanoparticles were mixed with a PP matrix and the thermal behavior of the nanocomposites was studied. The nanocomposites presented drastic improvements in the degradation behavior under thermo‐oxidative conditions, showing complex multistep processes. Under inert conditions the improvements were lower. Our results indicate that mechanisms based on the labyrinth effect, nanoconfinement or trapping model, are not able to explain the whole enhanced thermal stability in these nanocomposites. Moreover, the high specific area of the nanoparticles (≈70 m² · g^?1) indicates that processes based on the adsorption of volatile polar products coming from the oxidative degradation mechanism are plausible.

     

Electrospun Silica—Polybenzimidazole Nanocomposite Fibers

A new route for the manufacturing of silica/poly(benzimidazole) (PBI) nanocomposites fibers is described. PBI was synthesized via melt polycondensation and polycondensation in poly(phosphoric acid). Solutions of PBI and silica nanoparticles in N,N‐dimethylacetamide (DMAc) were electrospun to fibers and non‐wovens. The resulting materials were analyzed by ATR‐IR spectroscopy, small‐angle X‐ray scattering (SAXS) and nitrogen sorption measurements. The non‐wovens could be processed towards dense, cross‐linked membranes by hot pressing and treatment with p‐xylylene dichloride.

     

Artificial Opals as Effect Pigments in Clear‐Coatings

Summary: In this paper, we describe the use of artificial opals from polymer beads as effect pigments in transparent industrial and automotive coatings. For this purpose, we synthesized monodisperse colloids from fluorinated methacrylates by surfactant‐free emulsion polymerization. The fluorinated monomers, in combination with crosslinking, lead to a refractive index contrast, thermal stability, and solvent resistivity necessary for use as effect pigments. After crystallization of the monodisperse polymer beads, crystal flakes with iridescent colors can be obtained. The crystal flakes can act as effect pigments in various transparent industrial and automotive coatings. Due to photonic crystal behavior of effect pigments, color flops up to 100 nm are observed.

Crystal flakes of CS ‐7 as effect pigments in a transparent coating. The diameter of the tube is 5 mm.     

Role of Interface Rheology in Altering the Onset of Co‐Continuity in Nanoparticle‐Filled Polymer Blends

Developing co‐continuity in a polymer blend determines a multiphase system with enhanced properties which originate from the synergism of its constituents. Filling a blend with nanoparticles is a promising route to guide its morphology and eventually affect the co‐continuity transition. We add different kinds of nanoparticles to an HDPE/PEO blend to study how they affect the morphology of the blend as function of their surface properties and form factor. We find that PEO drop size is drastically reduced by particles adsorbed at the HDPE/PEO interface. However, we show that a drastic shifting of the co‐continuity threshold may only be achieved when particles affect the rheology of the interface.

     

An Application of Silica‐Based Monolithic Membrane Emulsification Technique for Easy and Efficient Preparation of Uniformly Sized Polymer Particles

Summary: Uniformly sized polymer particles were prepared by an emulsification and polymerization technique utilizing a silica monolithic membrane, namely the “silica monolithic membrane emulsification technique”. In this paper, we utilized silica monolithic membrane as a device for the preparation of uniformly sized polymer particles. A mixture of monomers, diluents and oil‐soluble initiator was emulsified into a continuous medium through the silica monolithic membrane and polymerized. The particles obtained had a higher size uniformity than that of particles prepared by previously reported membrane emulsification techniques, such as the Shirasu Porous Glass (SPG) emulsification technique. Through the silica monolithic membrane emulsification technique, we could prepare particles having availability as a possible packing material for solid‐phase extraction (SPE) and high performance liquid chromatography (HPLC).

SEM photograph of silica particles prepared through capillary plate membrane.     

One‐Step Immobilization of Protein‐Encapsulated Core/Shell Particles onto Nanofibers

A novel method is described to functionalize nanofibers to form a nanocomposite with core/shell particles in order to control protein release. The nanocomposite is produced by electrically neutralizing negatively charged poly(lactic acid) nanofibers with positively charged poly[(lactic acid)‐co‐(glycolic acid)] particles via a one‐step electrohydrodynamic jetting process. The protein‐encapsulated core/shell particles exhibited no significant initial burst release or denaturation. The protein release profile was controlled by porosity and protein/polymer interactions. The method may be promising to engineer intelligent scaffolds that can fulfill the needs of biomimetic materials.

     

Bio‐Based Rubbers by Concurrent Cationic and Ring‐Opening Metathesis Polymerization of a Modified Linseed Oil

Bio‐based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl‐modified linseed oil, Dilulin?, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio‐based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio‐based rubbers have maximum decomposition temperatures of over 450 °C with their thermal stability decreasing with increasing loadings of NBDC.

     

A Novel Route to Multiphase Polymer Systems Containing Nano‐Droplets: Radical Polymerization of Vinylic Monomers in Gelled Water‐in‐Oil Miniemulsions

Summary: A new strategy for the synthesis of composite polymers with larger volume fraction of aqueous inclusions less than 1 µm in diameter is presented. A water‐in‐oil miniemulsion of aqueous droplets in a continuous, cross‐linkable monomer phase is prepared. The addition of an organo‐gelator allows the immobilization of the droplets in a solid gel, thus avoiding the usual demixing upon polymerization of the continuous phase. This pregelled system is then converted into a composite polymer by photoinitiated free radical polymerization. Such coatings may be used for an improved climate control of buildings or as a deposit for the controlled release of actives from polar nano‐droplets.

SEM image of a cross‐linked composite polymer showing controlled droplet inclusions with a maximal diameter of 500 nm.     

Layered Silicate‐Induced Enhancement of Fracture Toughness of Epoxy Molding Compounds over a Wide Temperature Range

Summary: The fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro‐silica particles. Layered silicate‐EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o‐cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above T_g of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 °C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.

     

Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

Core‐Shell Nanoblends from Soy Protein/Polystyrene by Emulsion Polymerization

Novel soy protein/polystyrene nanoblends with core‐shell structures were successfully prepared by introducing nano‐sized PS into soy protein through emulsion polymerization. The nanoblends showed core‐shell structures, with the core being of PS and the shell of sodium dodecane sulfonate and soy protein polypeptides, when investigated by electron microscopy. Nanoblends containing high levels of PS (>30%) exhibited characteristic infrared spectrum bands, X‐ray diffraction peak, and glass transition, since PS microsphere aggregated to form independent PS domains. Mechanical strength and water resistance were effectively improved by introducing PS. An effective structure‐performance relationship was thereby established to describe the nanoblends.

     

Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

Effect of the Addition of Toluene on the Structure and Properties of Styrene‐Isoprene‐Butadiene Rubber/Montmorillonite Nanocomposites

Summary: Styrene‐isoprene‐butadiene rubber/montmorillonite nanocomposites were synthesized by the addition of toluene into clay and living anionic polymerization. These silicate layers (B‐M) were exfoliated within 30 min after polymerization initiation, whereas the layers in the nanocomposites prepared without using toluene (A‐M) were only partially exfoliated and not well‐dispersed in the matrix. The results of TEM and X‐ray diffraction revealed disperse silicates and a strong interaction between the terpolymer matrix and clay in the B‐M nanocomposites. The B‐M‐exfoliated nanocomposites exhibited higher decomposition and glass transition temperatures, storage moduli, tensile strengths and elongations at the break than those of the pure terpolymer and A‐M. With an organophilic montmorillonite (OMMT) content of 3 wt.‐%, the exfoliated nanocomposite exhibited the best thermal stability and mechanical properties. In addition, GPC and ¹H NMR results showed that the introduction of OMMT caused a slight increase in the of terpolymer, but hardly affected the microstructure of the terpolymer independent of the preparation method. Thus, the addition of toluene plays an important role in enhancing the dispersion of OMMT, which leads to the improvement of the structure and properties of the B‐M nanocomposites.

TEM image of the SIBR/MMT nanocomposite.     

Structure and Mechanical Properties of Poly(lactic acid) Filled with (Starch nanocrystal)‐graft‐poly(ε‐caprolactone)

Poly(ε‐caprolactone) (PCL) was grafted to the surface of starch nanocrystals (StN) via microwave‐assisted ROP. The resultant nanoparticles were then incorporated into a poly(lactic acid) matrix to produce fully‐biodegradable nanocomposites with good mechanical properties. A loading level of 5 wt.‐% StN‐g‐PCL resulted in simultaneous enhancements of strength and elongation. The StN‐g‐PCL self‐aggregated as rubbery microparticles to enhance the elongation by ca. 10‐fold over that of neat PLA. Meanwhile, the grafted PCL chains were miscible with PLA and formed a stress‐transferring interface to the StN, providing a reinforcing function.