Improvement of Flex‐Fatigue Life of Carbon‐Black‐Filled Styrene‐Butadiene Rubber by Addition of Nanodispersed Clay

Summary: The flex‐fatigue life of carbon‐black‐filled SBR was dramatically improved by incorporation of 4–5 phr nanodispersed clay. Addition of clay did not decrease the degree of crosslinking of the composite but improved the hysteresis and tearing energy. ESEM observation of the flexing‐fracture morphology indicated that nanodispersed clay layers had the advantage over carbon black in that they could blunt the crack.

Effect of the clay amount on the flex fatigue life of the composites.     

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.     

Fractionation and Analysis of an Impact Poly(propylene) Copolymer by TREF and SEC‐FTIR

TREF fractionation was combined with SEC‐FTIR analysis to measure the compositional heterogeneity within a commercial impact PP copolymer. The chemical composition of all fractions was determined as function of their molecular weight distribution. This approach proved to be highly successful at identifying different constituents within fractions exhibiting bimodal molecular weight distributions. Furthermore, the determination of ethylene and propylene crystallinity distribution across the molecular weight distribution confirmed the morphological nature of each of the components of the bimodal distribution. It is demonstrated that the combination of TREF and SEC‐FTIR provides a simple alternative to more time‐consuming conventional ways of characterising impact PP copolymers of complex heterogeneity.

     

Dynamic Monte Carlo Simulation of Atom‐Transfer Radical Polymerization

Summary: A dynamic Monte Carlo model was developed to simulate atom‐transfer radical polymerization (ATRP). The algorithm used to describe the polymerization includes activation, deactivation, propagation, chain transfer, and termination by combination and disproportionation reactions. Model probabilities are calculated from polymerization kinetic parameters and reactor conditions. The model was used to predict monomer conversion, average molecular weight, polydispersity and the complete molecular weight distribution at any polymerization time or monomer conversion. The model was validated with experimental results for styrene polymerization and compared with simulation results from a mathematical model that uses population balances and the method of moments. The simulations agree well with experimental and theoretical results reported in the literature. We also investigated the control volume size and number of iterations to reduce computation time while keeping an acceptable noise level in the Monte Carlo results.

Comparison of the chain length distribution of polystyrene made with ATRP and conventional free radical (CFR) polymerization at 50% conversion. The initiator to monomer ratios are 1:100 (ATRP left peak), 1:500 (ATRP right peak), and 1:1000 (CFR).     

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.

     

High‐Performance Carbon Nanotube‐Reinforced Bioplastic

The inherent properties of poly(lactide), a biocompatible and biodegradable polymer, are concurrently improved by the incorporation of a small amount of surface functionalized carbon nanotubes. A new method has been used to functionalize the CNTs' outer surface with hexadecylamine. A composite of PLA with functionalized CNTs has been prepared by melt‐extrusion. FT‐IR spectroscopy, Raman spectroscopy, DSC, and optical microscopy are used to investigate the thermal and mechanical property improvement mechanism in f‐CNTs containing PLA composite.

     

Classification of New Melt‐Processable PTFE: Comparison of Emulsion‐ and Suspension‐Polymerized Materials

A new melt‐processable PTFE material is presented and characterized that provides new and economical solutions in polymer technology while bridging the gap between perfluorinated PTFE and fluorothermoplastic materials such as perfluoroalkoxy resins. Thermal transitions, MW and MWD, and microstructures of the melt‐processable PTFE materials are investigated and compared to standard PTFE, modified PTFE, and PFA materials. The influence of the polymerization type used for the preparation of the melt‐processable PTFE (emulsion and suspension polymerization) on the MWD and the comonomer distribution are discussed.

     

Thermal and Mechanical Behavior of Carbon‐Nanotube‐Filled Latex

Summary: Composite films were prepared from a mixture of poly(vinyl acetate) latex and SWNTs. SEM images reveal a segregated SWNT network that grows heavier with increasing concentration. Nanotube segregation is the result of excluded volume created by the much larger polymer particles in the latex. Thermal conductivity exhibits a sharp rise with increasing quantity of nanotubes, although the maximum value is only 10% greater than that of the polymer matrix due to large thermal interface resistance. Storage modulus exhibits a peak and subsequent drop due to pore formation. In the absence of porosity, the Halpin‐Tsai model accurately predicts the composite modulus at 25 °C. The segregated network improves the composite modulus above T_g by nearly an order of magnitude with only 2 wt.‐% SWNT.

Schematic illustration of a segregated network of carbon nanotubes.     

Defined Comonomer Re‐Feeding During the Metallocene‐Catalyzed Copolymerization of 10‐Undecene‐1‐olate with Propene through FTIR In‐Line Monitoring

The consumption of 10‐undecene‐1‐olate (UOA) during its continuous re‐feeding in the metallocene‐catalyzed copolymerization with propene was investigated by ATR‐FTIR spectroscopy in‐line monitoring through evaluation of the integral absorbances of the characteristic IR bands. For the quantitative determination of the comonomer concentration during the copolymerization reaction with and without continuous re‐feeding of UOA, multiple calibration functions based on the chemometric partial least squares method were applied. For the first time, a direct correlation between the consumption of an olefin and the addition of a polar comonomer during a metallocene‐catalyzed copolymerization was demonstrated. By means of this technique, a relatively constant molar stoichiometric ratio of the comonomer and propene over the whole polymerization time was achieved, which is very important in obtaining copolymers with defined random structure and, thus, from the point of view of reaction engineering, constant product quality.

     

CNT Based Elastomer‐Hybrid‐Nanocomposites with Promising Mechanical and Electrical Properties

CNT based elastomer‐hybrid‐nanocomposites prepared by melt mixing have been investigated showing promising results in technologically relevant electrical, mechanical, and fracture‐mechanical properties. It is demonstrated that the incorporation of CNT in silica‐filled natural rubber results in a good dispersion of the CNT. The materials show an enhanced mechanical stiffness and tensile strength, an increased modulus, and a high electrical conductivity with quite low amounts of CNT, though the tear resistance under dynamical loading is slightly reduced. Using DMA and dielectric spectra, a better understanding of the conduction mechanism, the polymer/tube interaction, and the filler networking in CNT nanocomposites is achieved.

     

Preparation and Characterization of Trialkoxysilane‐Containing Acrylic Resin/Alumina Hybrid Materials

Summary: In the present study (3‐methacryloxypropyl)trimethoxysilane (MPMS) containing acrylic resin/alumina hybrid materials with various alumina contents were prepared. The effects of ethylacetoacetate (EAA) content, catalyst type, and water content during sol–gel process for alumina sols on the microstructure and properties of the hybrid materials were investigated by SAXS, AFM, DSC, TGA, and nano‐indentation tester, respectively. It was found that the hybrid materials exhibited a homogeneity and the alumina phase of the hybrids had mass fractal dimension and open structure. The thermal and mechanical properties of the hybrid materials were obviously improved when alumina was incorporated. The EAA contents, catalyst type, and water content during sol–gel process for alumina sols had obvious effects on the microstructure and properties of the hybrid materials.

Typical load–displacement curves of the pure acrylic resin and hybrid materials with increasing alumina content.     

A Completely Biodegradable Poly[(L‐lactide)‐co‐(ε‐caprolactone)] Elastomer Reinforced by in situ Poly(glycolic acid) Fibrillation: Manufacturing and Shape‐Memory Effects

A new completely biodegradable shape‐memory elastomer consisting of PLLCA reinforced by in situ PGA fibrillation is described. The manufacturing processes and shape‐memory effects of the composites are discussed. DMA results reveal a strong interface interaction between in situ PGA fibrillation and PLLCA. Compared with the SMP‐based composites that are commonly used, the shape‐memory test shows that in situ PGA fibrillation can improve the recovery properties of PLLCA; in fact, the shape‐recovery rate increases from 80.5 to 93.2%.

     

Thermosensitive Poly[(2‐(diethylamino)ethyl methacrylate)‐co‐(N,N‐dimethylacrylamide)] Cryogels Prepared by a Two‐Step Polymerization Method

Summary: Temperature‐sensitive P(DEAEMA‐co‐DMAAm) cryogels with five different DMAAm contents were synthesized via a two‐step polymerization method, the initial polymerization being conducted for various times at 22 °C, followed by polymerization at ?26 °C for 24 h. The influence of the first‐step time and the content of DMAAm on the swelling ratio and network parameters such as the polymer/solvent interaction parameter, the average molecular mass between crosslinks, and the mesh size of the cryogels were reported and discussed. The swelling studies indicated that the swelling increased in the following order: 22C45 > 22C30 > 22C15 > 22C0. The cryogels exhibited swelling/deswelling transitions (reentrant phenomena) in water depending on temperature. These properties were attributed to the macroporous and regularly arranged network of the cryogels. Scanning electron microscope graphs reveal that the macroporous network structure of the cryogels can be adjusted by applying a two‐step polymerization.

Chemical structure of the P(DEAEMA‐co‐DMAAm) cryogels.     

One‐Pot Synthesis of Novel Poly(cyclotriphosphazene‐co‐sulfonyldiphenol) Microtubes without External Templates

Summary: Novel poly(cyclotriphosphazene‐co‐sulfonyldiphenol) microtubes were successfully prepared via one‐pot synthesis using special templates generated in situ during the polymerization. The templates could be easily removed by dissolution in water. This approach overcame the multi‐step nature of general template methods. The as‐synthesized microtubes were 1–3 µm in width, about 100 µm in length and contained hexagon‐shaped channels. IR and NMR spectroscopies confirmed the covalently crosslinked chemical structure of the polymer tubes, and the tubes are thus mechanically and thermally stable. The polymer microtubes are of interest for use as chemical or biological sensors, controlled release and delivery of drugs, tissue engineering materials, absorbants and many other microscale investigations.

SEM images of triethylamine hydrochloride crystals produced in situ during formation of the tubes (left) and the polymer microtubes (right).     

Dextrin‐ and Conducting‐Polymer‐Containing Biocomposites: Properties and Behavior as Cellular Matrix

Both α‐cyclodextrin and linear dextrin are used to prepare biocomposites with poly(3,4‐ethylenedioxythiophene). Materials are prepared electrochemically in aqueous solution. Comparison with the pure polymer indicates that the electroactivity and electrostability decrease with the incorporation of the dextrins while the electrical conductivity is retained. The different properties of the two biocomposites suggest that the linear dextrin is mainly located at the surface, whereas the cyclodextrin is homogeneously distributed in the polymeric matrix. Cell adhesion and proliferation assays indicate that the cellular activity is significantly higher in the dextrin‐containing biocomposites.

     

Toughening of Polystyrene with Ethylene‐Propylene‐Diene Terpolymer (EPDM) Compatibilized by Styrene‐Butadiene‐Styrene Block Copolymer (SBS)

Summary: Polystyrene (PS) was toughened with ethylene‐propylene‐diene terpolymer (EPDM) in the presence of styrene‐butadiene‐styrene block copolymer (SBS). Incorporation of SBS into the PS/EPDM blends clearly improved the impact properties. For PS/EPDM/SBS (mass ratio: 69/21/10) blends, the notched Charpy impact strength reached a maximum value of 26.3 kJ/m². Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that SBS was distributed on the interface between PS and EPDM. Butanone extraction and FTIR analysis found that there was a grafting reaction between PS and EPDM phase during melt compounding. Shearing and processing rheological behaviors of blends were evaluated with a Haake capillary rheometer and a torque rheometer, respectively.

     

Characterization of Thiol‐Ene Crosslinked PEG Hydrogels

The properties of synthetic hydrogels can be tuned to address the needs of many tissue‐culture applications. This work characterizes the swelling and mechanical properties of thiol‐ene crosslinked PEG hydrogels made with varying prepolymer formulations, demonstrating that hydrogels with a compressive modulus exceeding 600 kPa can be formed. The amount of peptide incorporated into the hydrogel is shown to be proportional to the amount of peptide in the prepolymer solution. Cell attachment and spreading on the surface of the peptide‐functionalized hydrogels is demonstrated. Additionally, a method for bonding distinct layers of cured hydrogels is used to create a microfluidic channel.

     

Preparation of Nano‐Structured Polyaniline Composite Film via “Carbon Nanotubes Seeding” Approach and its Gas‐Response Studies

Summary: Polyaniline composite film with nano‐structure was prepared through a chemical oxidation method by adding carbon nanotubes (CNTs) as nano‐fiber seeds. Spin‐coating or casting method was employed on the interdigital electrodes of carbon and the composite film was formed with an in‐situ polymerization approach. The gas‐response to trimethylamine was also examined at room temperature. It was found that the difference was not only in the morphology, but also in the value of gas‐sensitivity. Comparing with films without the CNTs, the value of gas‐sensitivity decreased dramatically, while the baseline current of the sensor increased remarkably. This method can be an effective way to adjust the gas‐sensitivity of sensors made from polyaniline composite film by adding a small amount of carbon nanotube. XRD data showed that the degree of orientation of polyaniline was increased greatly with the addition of CNTs.

Morphology and reproducibility (inset) of polyaniline composite film containing carbon nanotubes.     

Copolymers of 3,4‐Ethylenedioxythiophene and 3‐Methylthiophene: Properties,Applications and Morphologies

Copolymers of 3,4‐ethylenedioxythiophene and 3‐methylthiophene have been prepared by recurrent potential pulses using monomer mixtures with various concentration ratios, their properties being compared with those of the corresponding homopolymers. In addition, different technological applications have been tested for the generated copolymers. Results indicate that the properties of the copolymers are closer to those of poly(3,4‐ethylenedioxythiophene) than to those poly(3‐methylthiophene). Furthermore, the ability of the copolymers to store charge and to interact with plasmid DNA suggest that they are very promising materials.

     

Core‐Sheath Structure in Electrospun Nanofibers from Polymer Blends

Summary: Electrospinning of polymer blends offers the potential to prepare functional nanofibers for use in a variety of applications. This work focused on control of the internal morphology of nanofibers prepared by electrospinning polymer blends to obtain core‐sheath structures. Polybutadiene/polystyrene, poly(methylmethacrylate)/polystyrene, polybutadiene/poly(methylmethacrylate), polybutadiene/polycarbonate, polyaniline/polycarbonate, and poly(methylmethacrylate)/polycarbonate blends were electrospun from polymer solutions. It was found that the formation of core‐sheath structures depends on both thermodynamic and kinetic factors. Incompatibility and large solubility parameter difference of the two polymers is helpful for good phase separation, but not sufficient for the formation of core‐sheath structures. Kinetic factors, however, play a much more important role in the development of the nanofiber morphology. During the electrospinning process, the rapid solvent evaporation requires systems with high molecular mobility for the formation of core‐sheath structures. It was found that polymer blends with lower molecular weight tend to form core‐sheath structures rather than co‐continuous structures, as a result of their higher molecular mobility. Rheological factors also affect the internal phase morphology of nanofibers. It was observed the composition with higher viscosity was always located at the center and the composition with lower viscosity located outside.

TEM image of electrospun polybutadiene/polycarbonate nanofibers at 25/75 wt.‐% ratio after staining by osmium tetroxide. The dark regions are polybutadiene and the light region is polycarbonate.