Self‐Immobilizing Precatalysts: Norbornene‐Bridged Zirconium ansa‐Metallocenes

We report here the synthesis of new tethered biscyclopentadienyl and bisindenyl zirconocenes, bearing one unsaturation on the interannular bridge, and their use as self‐immobilizing catalysts. They proved to be active catalysts towards ethylene polymerization in solution, with activities comparable to those displayed by commercial rac‐Et(Ind)₂ZrCl₂. When tested as self‐polymerization catalysts under suitable experimental conditions, they gave colored precipitates that, once reactivated with MAO, were significantly active in ethylene polymerization, although lower than those of the corresponding catalytic systems in solution. The molecular weights of the produced polymers were similar to those obtained with the same catalysts in solution, but their distribution resulted to be broader, with values typical of heterogeneous catalytic systems. From ¹³C NMR studies we had the first spectroscopic evidence of the actual incorporation of a metallocene of this type into a polymeric chain.     

Ganzzell‐ISPR‐Prozessentwicklung: Chancen und Risiken

Whole Cell ISPR Process Development: Chances and Pifalls The contribution intends to elucidate chances and pitfalls of in situ product removal (ISPR) approaches by focusing on microbial processes for the production of low molecular products. With the aid of illustrative examples of industry‐like and industrial processes, common characteristics are outlined which are hold to be important for successful commercialization. Finally, the attempt of a future prognosis for ISPR processes is given.     

Soybean‐ and castor‐oil‐based thermosetting polymers: Mechanical properties

Maleic anhydride modified soybean‐ and castor‐oil‐based monomers, prepared via the malination of the alcoholysis products of the oils with various polyols, such as pentaerythritol, glycerol, and bisphenol A propoxylate, were copolymerized with styrene to give hard rigid plastics. These triglyceride‐based polymers exhibited a wide range of properties depending on their chemical structure. They exhibited flexural moduli in the 0.8–2.5 GPa range, flexural strength in the 32–112 MPa range, glass transition temperatures (T_g) ranging from 72 to 152°C, and surface hardness values in the 77–90 D range. The polymers prepared from castor oil exhibited significantly improved modulus, strength, and T_g values when compared with soybean‐oil‐based polymers. These novel castor and soybean‐oil‐based polymers show comparable properties to those of the high‐performance unsaturated polyester (UP) resins and show promise as an alternative to replace these petroleum‐based materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1497–1504, 2006     

Camptothecin‐7‐yl‐methanthiole: Semisynthesis and Biological Evaluation

The introduction of a methylenthiol group at position 7 of camptothecin was carried out in four steps. This preparation also yielded the corresponding disulfide, which behaves as a prodrug due to its reactivity with glutathione. Assessment of their antiproliferative activities, investigations of their mechanism of action, and molecular modeling analysis indicated that the 7‐modified camptothecin derivatives described herein maintain the biological activity and drug–target interactions of the parent compound.     

Zeo‐Click Synthesis: Copper‐Zeolite‐Catalyzed Synthesis of Ynamides

Copper(I)‐zeolites, especially copper(I)‐ultra stable Y zeolite (USY), are very efficient heterogeneous catalysts for the coupling of functionalized 1‐bromoalkynes and various nitrogen derivatives. Under these conditions, sulfonylated alkyl‐ or arylamines and various N‐heterocycles, such as oxazolidinones or indoles, could be efficiently transformed into the corresponding N‐alkynyl derivatives. However, imidazoles gave addition products rather than coupling products. The reaction conditions proved compatible with a variety of functional and protecting groups. Such zeolitic catalysts can be recycled and reused at least five times without significant deactivation. Low catalyst loading could be used (4 mol%) and as low as 0.8 mol% of this heterogeneous copper catalyst still gave good conversion and yields.

     

Flax‐fabric‐reinforced arylated soy protein composites: Brittle‐matrix behavior

Biocomposites were successfully prepared by the reinforcement of soy protein isolate (SPI) with different weight fractions of woven flax fabric. The flax‐fabric‐reinforced SPI‐based composites were then arylated with 2,2‐diphenyl‐2‐hydroxyethanoic acid (DPHEAc) for 4 h to obtain arylated biocomposites. A new method was proposed to determine the amount of carbon dioxide evolved during the arylation of the soy protein in the presence of DPHEAc. Characterizations of the arylated and nonarylated biocomposites were done by Fourier transform infrared spectroscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis. The results indicate that the arylated soy‐protein‐based composites exhibited mechanical behavior like brittle‐matrix composites, which differentiated them from nonarylated soy‐protein‐based composites, which showed mechanical behavior similar to polymer–matrix composites. In the arylated composites, there was clear evidence of a stick–slip mechanism, which perhaps dominated and, therefore, prevented easy deformation of the reinforced film. Scanning electron microscopy studies revealed cracks in the arylated soy protein composites when they were subjected to tensile tests. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermo‐ and pH‐ responsive copolymers: Poly(n‐Isopropylacrylamide‐co‐IAM) copolymers

Poly(N‐isopropylacrylamide) (NIPAAm) is well known as a smart material with good thermal sensitivity and favorable biocompatibility. A series of new smart hydrogels, NIPAAm copolymerized with IAM (itaconamic acid; 4‐amino‐2‐methylene‐4‐oxobutanoic acid), were synthesized through radical solution polymerization in this work. Poly(NIPAAm‐co‐IAM) can respond to the changes of temperature as well as pH value. Such a characteristic is due to the fact that IAM contains not only a hydrophilic acrylic acid moiety but also an acrylamide moiety to be thermal and pH sensitive. The experimental results show that the lower critical solution temperature (LCST) of the copolymer increases as the molar fraction of IAM increases. Moreover, based on the current experimental data, 3 wt % of Poly(NIPAAm‐co‐IAM) aqueous solution in this study exhibits a phase transition temperature (37.8°C) close to the human body temperature in the buffer solution of pH 7 possibly to be useful in drug delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42367.     

Wood‐fiber/high‐density‐polyethylene composites: Compounding process

The compounding process directly influenced the compounding quality of wood–polymer blends and finally affected the interfacial bonding strength and flexural modulus of the resultant composites. With 50 wt % wood fiber, the optimum compounding parameters for the wood‐fiber/high‐density‐polyethylene blends at 60 rpm were a temperature of 180°C and a mixing time of 10 min for the one‐step process with a rotor mixer. The optimum compounding conditions at 90 rpm were a temperature of 165°C and a mixing time of 10 min. Therefore, a short compounding time, appropriate mixing temperatures, and a moderate rotation speed improved the compounding quality of the modified blends and the dynamic mechanical properties of the resultant composites. The melt torque and blend temperature followed a polynomial relationship with the loading ratio of the wood fiber. The highest melt torque and blend temperature were obtained with 50% wood fiber. The coupling treatment was effective for improving the compatibility and adhesion at the interface. The two‐step process was better than the one‐step process because the coupling agents were more evenly distributed at the interface with the two‐step process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2570–2578, 2004     

Bio‐inspired cationic polymerization of isoprene and analogues: state‐of‐the‐art

Natural rubber (NR), which is polyisoprene about 100% 1,4‐cis of high molar mass, > 10⁶ g mol^?1, is mainly produced in southeast Asia and represents around 40%–45% of total worldwide elastomer consumption. Whereas more than 2500 plant species are able to produce polyisoprenoids, the only established commercial source of NR is Hevea braziliensis. NR presents high performance properties that are so far not matched by synthetic rubbers. As a consequence, NR is irreplaceable in many applications (aircraft tires, surgery gloves etc.). Nature and synthetic polymer chemists start from different substrates to synthesize polyisoprenes, i.e. isopentenyl pyrophosphate (IPP), which is a universal building brick utilized by plants and animals, and isoprene monomer, respectively. Nevertheless, we proposed that the elementary processes involved in the biosynthesis of NR are very similar to those of cationic polymerization. In the course of a study on bio‐inspired cationic polymerization of isoprene and IPP analogues, it appeared that cationic polymerization of isoprene proceeds readily and leads mainly to its 1,4‐trans addition; such a process nevertheless remains difficult to control due to the occurrence of many side reactions (transfer, protic initiation, branching, cyclization). The present paper describes our understanding of the cationic polymerization of isoprene and its analogues catalyzed by different Lewis acids, in solution and aqueous dispersions. Copyright © 2011 Society of Chemical Industry     

The High‐Pressure Characterization of Energetic Materials: 2‐Methyl‐5‐Nitramino‐2H‐Tetrazole

The isothermal structural properties, equation of state, and vibrational dynamics of 2MNT were studied under high‐pressure using synchrotron XRD and optical Raman and IR microspectroscopy. Analysis of the XRD patterns revealed no indication of a phase transition to near 15 GPa and the pressure‐volume isotherm remained smooth to 15 GPa. Near 15 GPa, significant sample damage was observed from the X‐ray beam which precluded the acquisition of patterns above this pressure. XRD and Raman spectroscopic measurements showed the monoclinic ambient condition phase of 2MNT remains the dominant phase to near 20 GPa, although a shift of the NO₂ IR active vibrational modes to lower frequencies suggested a subtle geometry modification not reflected in the XRD data.     

Chemorheological time‐temperature‐transformation‐viscosity diagram: Foamed EPDM rubber compound

Thermal analysis, rheometry, and kinetic modeling are used to generate a comprehensive processability diagram for thermosetting and elastomeric resins. A chemorheological “time‐temperature‐transformation‐viscosity” diagram is proposed to fully characterize curing reactions toward process' on‐line control, optimization, and material design. Differential scanning calorimetry and thermogravimetric techniques are used to measure total reaction heat, degree of vulcanization, and cure kinetics. The viscosity, as a function of temperature and cure degree, is obtained from parallel plate rheometry. The auto‐catalytic Kamal–Sourour model, including a diffusion‐control mechanism, is used to model cure kinetics, while the Castro–Macosko model serves to model the rheological behavior. Non‐linear least‐squares regression and numerical integration are used to find models' parameters and to construct the chemorheological diagram. The usefulness of the proposed methodology is illustrated in the context of an industrial‐like Ethylene Propylene Diene Termononer rubber compound that includes a chemical blowing agent. Even though the rubber formulation contains crosslinking agents, primary and secondary accelerators, promoters, activators, and processing aids, the chemorheological diagram is obtained consistently, validating the proposed methodology to any thermosetting or elastomeric resin. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43966.     

Polyhydroxybutyrate/acrylonitrile‐g‐(ethylene‐co‐ propylene‐co‐diene)‐g‐styrene blends: Their morphology and thermal and mechanical behavior

Polyhydroxybutyrate (PHB) is a biodegradable bacterial polyester emerging as a viable substitute for synthetic, semicrystalline, nonbiodegradable polymers. An elastomer terpolymer of acrylonitrile‐g‐(ethylene‐co‐propylene‐co‐diene)‐g‐styrene (AES) was blended with PHB in a batch mixer and in a twin‐screw extruder to improve the mechanical properties of PHB. The blends were characterized with differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy, and impact resistance measurements. Despite the narrow processing window of PHB, blends with AES could be prepared via the melting of the mixture without significant degradation of PHB. The blends were immiscible and composed of four phases: poly(ethylene‐co‐propylene‐co‐diene), poly(styrene‐co‐acrylonitrile), amorphous PHB, and crystalline PHB. The crystallization of PHB in the blends was influenced by the AES content in different ways, depending on the processing conditions. A blend containing 30 wt % AES presented impact resistance comparable to that of high‐impact polystyrene, and the value was about 190% higher than that of pure PHB. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008