Formation of SBS triblock copolymers using waste soybean oil as coupling agent

Triglyceride in the waste soybean oil (WSO) was used as coupling agent to synthesize a linear styrene‐butadiene‐styrene (SBS) triblock copolymer. The reaction occurred via a living anionic polymerization of styrene‐butadiene block copolymer (SB) using n‐butyllithium as initiator and cyclohexane as solvent and followed by the coupling reaction with the added WSO. Gel permeation chromatography (GPC) showed that for all SB‐Li precursors except the one with the M_n of 1000 g/mol, the resultant products consisted of two different sizes, one with the nearly comparable size with the precursor, the other with a M_n two‐fold higher than the precursor. On the other hand, the reaction of the SB‐Li precursor with the M_n of 1000 g/mol and the WSO only resulted in forming the molecule with a M_n two‐fold higher than the precursor. The results from the GPC and spectral analysis supported that upon the nucleophilic attack the ester group of the triglyceride in the WSO was broken, giving the SB‐C(O)‐fatty acid susceptible to the second the nucleophilic attack, thus forming the coupled product. The size of the SB‐Li precursor, the SB‐Li : WSO molar ratio, the S:B weight ratio and the coupling time were found to influence on the coupling efficiency. However, the size of the SB‐Li precursor showed highest impact on the coupling efficiency at which the larger the SB‐Li precursor, the lower the coupling efficiency. Regardless of the low coupling efficiency of the WSO, the WSO was found to be a potential coupling agent for the formation of the linear triblock copolymer. This was because the SBS triblock copolymer containing high SB diblock copolymers and prepared by the WSO showed slightly higher tensile strength than the one with less SB diblock copolymers prepared by a traditional coupling agent. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40684.     

Preparation,structure, and properties of end‐functionalized miktoarms star‐shaped polybutadiene–sn–poly(styrene–butadiene) rubber

Two miktoarm star‐shaped rubbers with large‐volume functional groups of 1,1‐diphenylhexyl at the ends of arms (DMS–PB–SBR) and one miktoarm star‐shaped rubber with n‐butyl groups at the ends of arms (BMS–PB–SBR) were prepared by 1,1‐diphenylhexyllithium (DPHLi) and n‐butyl lithium as initiators, respectively. The molecular structures and morphological properties of the three rubbers (MS–PB–SBR) were studied and compared with those acquired from the blend consisting of star‐shaped solution‐polymerized butadiene styrene rubber (S‐SSBR) and butadiene rubber (PBR) prepared by ourselves. The results showed that MS–PB–SBR exhibited a more uniform distribution of PBR phase and a smaller phase size of PBR than that of S‐SSBR/PBR blend. It is found that MS–PB–SBR composites filled with CB showed the lower Payne effect than that of S‐SSBR/PBR/CB composite, suggesting that the MS–PB–SBR/CB composite (particularly the DMS–PB–SBR/CB composites) would possess excellent mechanical properties, high wet‐skid resistance, and low rolling resistance. For the studied MS–PB–SBR systems, the contribution of large‐volume functional groups at the end of PBR molecular chains to decrease the rolling resistance was larger than that of Sn coupling effect. It is envisioned that the miktoarm star‐shaped rubbers with 1,1‐diphenylhexyl groups at the molecular ends would be useful for making treads of green tires. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40002.     

无机纳米复合技术在热塑性弹性体研究中的应用

综述了热塑性弹性性/无机物纳米复合的研究进展,并展望其技术发展趋势。     

Patterning of worm-like soft polydimethylsiloxane structures using a TiO2 nanotubular array

Patterned polydimethylsiloxane (PDMS) is an important structure for soft lithography. Various materials have been deployed as mold for patterning PDMS. Anodized nanotubular array has been sought after as cost-effective alternative for textured silicon. An array of TiO₂ nanotubes with characteristic diameter ≈140 nm and the length of ≈1.5 microns, created by anodic oxidation of a titanium substrate, was used here as a template for soft PDMS molding. The optimal molding process was developed by a combination of silanization, use of solvent, application of a vacuum, and hydraulic pressing. The silanization was confirmed by Fourier transform infrared spectroscopy and contact angle measurements while the PDMS structure was examined by scanning electron microscope and energy dispersive X-ray spectroscopy. Hydraulic pressing significantly improved the infiltration of PDMS into the pores of nanotubular array resulting in formation of PDMS nanobumps after separation of the polymer from the template. Complete infiltration of PDMS precursor into the cavity of nanotubes was observed on the hydraulic-pressed sample without toluene impurities. The hydraulic-pressed samples exhibited higher adhesion strength than nonpressed ones. The adhesive strength was measured by a simple experimental arrangement, in which the PDMS layer was stuck on a vertical glass surface followed by pulling it downwards.     

Electro-thermal and -mechanical model of thermal breakdown in multilayered dielectric elastomers

Multiple breakdown phenomena may take place when operating dielectric elastomers. Thermal breakdown, which occurs due to Joule heating, becomes of special importance when using multilayered stacks of dielectric elastomers, due to the large volume-to-surface-area-ratio. In this article, a 2D axisymmetric finite-element model of a multilayered stack of dielectric elastomers is set up in COMSOL Multiphysics®. Both the electro-thermal and electro-mechanical couplings are considered, allowing for determination of the onset of thermal breakdown. Simulation results show that an entrapped particle in the dielectric elastomer drastically reduces the possible number of layers in the stack. Furthermore, the possible number of layers is greatly affected by the ambient temperature and the applied voltage. The performance of three hyperelastic material models for modeling the elastomer deformation are compared, and it is established that the Gent model yields the most restrictive prediction of breakdown point, while the Ogden model yields the least restrictive estimation.     

The influence of MWCNT and hybrid (MWCNT/nanoclay) fillers on performance of EPDM-CIIR blends in nuclear applications: Mechanical,hydrocarbon transport,and gamma-radiation aging characteristics

Blends of EPDM and chlorobutyl (CIIR) rubbers are used in nuclear plants where they have to withstand the combined effect of radiation and hydrocarbon aging. To improve their mechanical properties as well as hydrocarbon and gamma radiation resistance, the blends are reinforced with 0.5, 1, 1.5, and 2 phr of MWCNT. The increase in mechanical properties was highest for 1.5 phr MWCNT with 69% increase in tensile strength. The improvement in properties was correlated to MWCNT dispersion and filler–polymer interactions, which were confirmed by TEM and FTIR analysis. Hydrocarbon transport coefficients decreased on addition of MWCNT. The nanocomposites were exposed to 0.5, 1, and 2 MGy cumulative doses of gamma radiation. Depending on the radiation dose, crosslinking and/or chain scission occurred causes changes in physical properties. MWCNT reinforcement reduced the magnitude of changes in mechanical and transport properties after γ-irradiation. ESR and FTIR spectra provided qualitative information on free radical formation and chemical changes due to γ-rays exposure. To further enhance the properties, hybrid nanocomposites with 1.5 phr MWCNT and varying nanoclay contents (0.5, 1, 1.5, 2, and 5 phr) were prepared. Due to synergism between MWCNT and nanoclay, the hybrid composites had superior properties with hybrid containing 5 phr nanoclay giving 98% increase in tensile strength.     

Thermoplastic polyurethane–urea elastomers with superior mechanical and thermal properties prepared from alicyclic diisocyanate and diamine

High-performance thermoplastic polyurethane (TPU) elastomers have long been the objective of numerous studies. In this work, thermoplastic polyurethane–urea (TPUU) elastomers with balanced superior mechanical and thermal properties, in comparison with the rare cases of high-performance TPU/TPUU elastomers with super-high tensile strength, were synthesized by the reaction of polycarbonate diols with excess alicyclic isophorone diisocyanate, followed by the chain extension of alicyclic isophorone diamine. When the content of hard segment was around 47%, the TPUU elastomer had super-high tensile strength of 51.7 MPa, initial elastic modulus of 698 MPa and elongation at break of 480%. The temperature range of this TPUU elastomer's rubbery state was up to 120°C with storage modulus above 200 MPa, and its rubbery flow state reached 200°C where the storage modulus was still as high as 100 MPa. Fourier transform infrared spectroscopy analysis indicated the presence of strongly hydrogen bonded urethane and urea groups in these TPUU elastomers. Atomic force microscopy and differential scanning calorimetry studies demonstrated significant and nearly perfect microphase separation in these TPUU elastomers when the hard segment content was around or below 47%. These noncrystalline TPUU elastomers could be thermally processed or processed in the form of a solution.     

Foaming of EPDM with water as blowing agent in injection molding

Chemical foaming of elastomers is state of the art and preferred to the more complex systems engineering of physical foaming, yet, many commonly used chemical blowing agents often are hazardous. In current investigations, we introduced water bound to carrying substances (silica, carbon black) into elastomer compounds. A stable, reproducible foaming process can be implemented using water as physical blowing agent. In first tests, the average cell diameters in injection molded elastomer parts exceed the average cell diameters of chemically foamed parts. Yet, varied amounts of blowing agent can reduce the cell diameters. Furthermore, nucleating agents and water carriers are being examined to reduce cell diameters and reach cellular structures and mechanical properties of chemically foamed parts. In conclusion, foaming of elastomers with water is a promising. Yet, further examinations have to cover the effect mechanism of foaming and vulcanization as well as continuous processing and compounding. Rear end of an EPDM part foamed with water carried on silica in injection molding process (mold temperature 195 °C, breathing mold opening 2 mm) © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43613.     

Poly1‐hexene: New impact modifier in HIPS technology

Poly1‐hexene was prepared using a conventional heterogeneous Ziegler–Natta catalyst and its stereoregularity was characterized using ¹³C‐NMR analysis. New kind of high impact polystyrene (HIPS) was prepared by radical polymerization of styrene in the presence of different amounts of synthesized poly1‐hexene (PH) as impact modifier (HIPS/PH) and compared with conventional high impact polystyrene with polybutadiene (HIPS/PB) as rubber phase. Scanning electron microscopy (SEM) revealed that the dispersion of poly1‐hexene in polystyrene matrix was more uniform compared with it in HIPS/PB. The impact strength of HIPS/PH was 29–79% and 80–289% higher than that in HIPS/PB and neat polystyrene, respectively. FTIR was used to confirm more durability of HIPS/PH samples toward ozonation. To study the effect of rubber type and amount on the T_gs of polystyrene, differential scanning calorimetry was employed. Results obtained from TGA demonstrated higher thermal stability of HIPS/PH sample in comparison with conventional HIPS/PB one. Our obtained results suggest new high impact polystyrene that in all studied aspects has better performance than the conventional HIPS. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43882.