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     

Thermal‐ and Photo‐Induced Isomerization of All‐E‐ and Z‐Isomer‐Rich Xanthophylls: Astaxanthin and Its Structurally‐Related Xanthophylls,Adonirubin, and Adonixanthin

The effects of heating and photo‐irradiation on the stability of all‐E‐isomer‐rich and Z‐isomer‐rich xanthophylls, astaxanthin and its structurally related xanthophylls, adonirubin, and adonixanthin, are investigated. The xanthophylls with high Z‐isomer content are prepared from their high‐purity all‐E‐isomers by thermal isomerization and filtering techniques, that is, total Z‐isomer ratios of adonirubin, astaxanthin, and adonixanthin are 80.9%, 89.5%, and 72.5%, respectively. The all‐E‐ and Z‐isomer‐rich xanthophylls dissolved in ethanol are stored at 4, 30, and 50 °C in the dark and at 30 °C under photo‐irradiation using a fluorescent light for 21 days. In the all‐E‐isomer‐rich xanthophylls, as the storage temperature increases, the total Z‐isomer ratio becomes higher, whereas in the Z‐isomer‐rich xanthophylls, the all‐E‐isomer ratio becomes higher. Photo‐irradiation slightly promotes Z‐isomerization in (all‐E)‐xanthophylls, but highly promotes all‐E‐isomerization in Z‐isomer‐rich xanthophylls. In addition, photo‐irradiation prevents thermal Z‐isomerization of (all‐E)‐xanthophylls. Moreover, it is found that some xanthophyll Z‐isomers such as (9Z)‐astaxanthin are more stable than that of the other Z‐isomers against heating and photo‐irradiation. These findings can contribute not only to establishing suitable storage conditions for Z‐isomer‐rich xanthophylls, but also to developing control techniques for the E/Z‐isomer ratio of the xanthophylls. Practical Applications: The fundamental data on the stability of xanthophyll isomers against heating and photo‐irradiation and finding stable xanthophyll Z‐isomers are very important to develop xanthophyll materials rich in the Z‐isomers. Moreover, this study clearly shows that the heat treatment enhances the Z‐isomerization of xanthophylls, whereas the photo‐irradiation enhances the all‐E‐isomerization and prevents thermal Z‐isomerization of them. This information can be utilized in technology for arbitrarily controlling E/Z‐isomerization of xanthophylls.     

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.     

Hydrogel‐forming agar‐graft‐PVP and κ‐carrageenan‐graft‐PVP blends: Rapid synthesis and characterization

Grafting of agar and κ‐carrageenan with polyvinylpyrrolidone (PVP, average molecular weight 10,000 D) in an aqueous medium at a pH of about 7 produced agar‐graft‐PVP and κ‐carrageenan‐graft‐PVP blends capable of forming hydrogels. The reaction was carried out with microwave irradiation in the presence of a water‐soluble initiator, potassium persulfate. Optimum microwave irradiation conditions for obtaining hydrogels of the grafted products were achieved. The structural characteristics and thermal stability of the grafted blends were studied by Fourier transform infrared, ¹³C‐NMR, and thermogravimetric analyses. Appearance of new IR bands at 1661, 1465, and 1426 cm^?1 in the grafted products indicated the insertion of PVP into the polysaccharide structure. Powder X‐ray diffraction studies revealed the enhanced crystallinity in the products compared to in the control polysaccharides as well as PVP. Agar and κ‐carrageenan were grafted to a considerable degree, with 62.5 E % and 125 G % for agar‐graft‐PVP and 65.5 E % and 131 G % for κ‐carrageenan‐graft‐PVP. Optical micrographs of the grafted blends indicated considerable changes in the morphology of the agar and the κ‐carrageenan, substantiating the X‐ray diffraction data. A plausible mechanism for the crosslinking of PVP to agar and κ‐carrageenan is proposed. These hydrogels exhibited enhanced water‐holding capacity despite weaker gel strength than that in the respective control polysaccharides. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3654–3663, 2006     

Composition‐ and Pressure‐Induced Relaxor Ferroelectrics: First‐Principles Calculations and Landau‐Devonshire Theory

We report calculations with first‐principles density‐functional theory and Landau–Devonshire theory that provide an atomic‐scale mechanism for the composition‐ and pressure‐induced relaxor ferroelectrics. A multiphase with coexisted cubic structures (MPCCS) is found to correspond to any of the composition‐ and pressure‐induced relaxor ferroelectrics. On the other hand, a normal ferroelectric without relaxor behavior is structurally characterized by a single phase. Furthermore, the presence of the MPCCS in a composition‐ and pressure‐induced relaxor increases the degrees of freedom of relaxors and no energy barriers are involved for the rotations of the polarization direction, leading to high electromechanical coefficients.     

Calixarene‐Derived Mono‐Iminophosphoranes: Highly Efficient Ligands for Palladium‐ and Nickel‐Catalysed Cross‐Coupling

The first mono‐iminophosphoranes based on a calix[4]arene skeleton have been synthesised and tested in the arylation of aryl bromides and aryl chlorides. Combining these ligands with [Pd(OAc)₂] or [Ni(cod)₂] resulted in highly active Suzuki–Miyaura and Kumada–Tamao–Corriu cross‐coupling catalysts, respectively. TOFs up to ca. 4×10⁵ mol(ArBr)⋅mol(M)⁻¹⋅h⁻¹ were obtained in each case. The remarkable activities observed probably arise from the ligands’ ability to form complexes with cavity‐entrapped “MArX” moieties (endo‐complexes), their highly crowded metal environment favouring formation of mono‐ligated intermediates over that of less reactive bis‐ligated ones. Possible supramolecular interactions within the cavity involving the receptor wall and the aromatic substrate may also significantly influence the reaction rates, notably by increasing the proportion of endo‐complexes.     

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.     

Genipin‐cross‐linked chitosan‐based hydrogels: Reaction kinetics and structure‐related characteristics

The main aim of this work is the synthesis and characterization of cross‐linked chitosan systems. Chitosan hydrogels can be prepared by physical or chemical cross‐linking of polymer chains. Chemical cross‐linking, leading to the creation of hydrogel networks possessing improved mechanical properties and chemical stability, can be achieved using either synthetic agents or natural‐based agents. In this work, the cross‐linker Genipin, a naturally derived compound, was selected because of the lower acute toxicity compared to many other commonly used synthetic cross‐linking reagents. In particular, the chemical stabilization of chitosan through genipin cross‐linking molecules was performed and characterized by calorimetric analyses (differential scanning calorimetry), swelling measurements in different pHs, and ionic strength. The reaction kinetics was carried out by means of rheological measurements, and both the activation energy (E_a) and the reaction order (m) were calculated. The hydrogel analyses were carried out at different concentrations of genipin (GN1 and GN2). The results were used to evaluate the possibility to use the chemical cross‐linked chitosan–genipin hydrogel for biomedical applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42256.     

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     

Novel polyethylene‐b‐polyurethane‐b‐polyethylene triblock copolymers: Facile synthesis and application

A series of novel polyethylene‐b‐polyurethane‐b‐polyethylene (EUE) triblock copolymers is successfully prepared through a facile route combining the thiol‐ene chemistry, addition polymerization, and coupling reaction. The resulting EUE triblock copolymers are characterized by Nuclear magnetic resonance (¹H NMR), Fourier transform‐infrared spectra (FT‐IR), High temperature gel permeation chromatography (HT‐GPC), Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA), and Transmission electron microscopy (TEM). In addition, the EUE triblock copolymers have been evaluated as compatibilizers in the polymer blends of thermoplastic polyurethane elastomer (TPU) and high‐density polyethylene (HDPE). The SEM results show that the compatibility of immiscible blends is enhanced greatly after the addition of EUE triblock copolymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42967.     

Rubber‐toughened polypropylene/acrylonitrile‐co‐butadiene‐co‐styrene blends: Morphology and mechanical properties

The RTPP/ABS (rubber toughened polypropylene/poly (acrylonitrile‐co‐butadiene‐co‐styrene) blends, both noncompatibilized and compatibilized with polypropylene‐g‐polystyrene, were prepared by melt mixing in a Brabender Plasti‐Corder. As the torque ratio of RTPP and ABS was about 2, phase cocontinuity in the blends was achieved at ABS volume fractions around 0.16, which was evidenced by both microscopic analysis and mechanical testing. A new microscopic and image analysis technique was introduced, whose combination provides two semiquantitative parameters: structure roughness and structure cocontinuity. The latter parameter is closely associated with the predictive scheme based on the equivalent box model and percolation theory, which was used in this study. The predicted mechanical properties were confronted with the experimental data for tensile modulus, yield strength, and tensile impact strength. While the modulus of noncompatibilized blends is reasonably fitted by the model, the compatibilizer accounts for a positive deviation attributed to a strong interaction between the compatibilizer and the matrix. The yield strength of noncompatibilized blends indicates poor interfacial adhesion, which is so enhanced by the compatibilizer that no phase debonding occurs before yielding. Tensile impact strength, in contrast to modulus and yield strength, passes through a deep minimum for both types of blends; two tentative explanations of this detrimental behavior were suggested. POLYM. ENG. SCI., 47:582–592, 2007. © 2007 Society of Plastics Engineers.     

Solid‐State Conversion of Single Crystals: The Principle and the State‐of‐the‐Art

Solid‐state conversion of single crystals from polycrystalline materials has the advantages of cost‐effectiveness, chemical homogeneity, and versatility over the conventional melt growth and solution growth methods, particularly for systems with high melting points, incongruent melting, high reactivity (volatility), and phase transformations at high temperature. Nevertheless, for commercial production, this technique has only been successful in a few limited systems, in particular ferroelectric systems. This is mostly because of the difficulty in controlling the microstructure, particularly suppressing grain growth in the polycrystal during its conversion. This article describes the principle and the current status of the solid‐state conversion of single crystals. We first introduce the recently developed principle of microstructural evolution to explain the basis of the microstructure control in polycrystals for solid‐state conversion. We then report recent technical developments in fabricating single crystals by the solid‐state single crystal growth (SSCG) method and their physical properties. The SSCG method is expected to be studied and utilized more widely in fabricating single crystals with complex compositions as a strong alternative to the melt growth and solution growth methods.     

Polyamide‐6‐b‐polybutadiene block copolymers: Synthesis and properties

Polyamide‐6 (PA6)/polybutadiene (PB) block copolymers were synthesized with macroactivators (MAs) based on hydroxyl‐terminated polybutadiene functionalized with diisocyanates and having three N‐acyllactam chain‐growing centers per molecule. Two different diisocyanates, hexamethylene diisocyanate and isophorone diisocyanate, were applied as precursors for the MAs. The sodium salt of ε‐caprolactam was chosen as an initiator. The influence of the MA type and concentration on the anionic ring‐opening polymerization of ε‐caprolactam at 180°C was studied. A large percentage of the gel fraction in the copolymers was estimated, indicating crosslinked macromolecules. The structure and phase behavior of the copolymers were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, thermogravimetric analysis, and dynamic mechanical thermal analysis. In the copolymers, only the PA6 chains crystallized, and the crystallinity depended on the PB content. Different glass‐transition temperatures for the PB blocks and PA6 blocks were observed, indicating microphase separation in the copolymers. The mechanical properties of the copolymers were studied by notched impact testing and hardness measurements. The impact strength increased linearly with the soft component concentration up to 10 wt % and reached values six times higher than those of the PA6 homopolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 711–717, 2003     

1,2,3,4‐Tetrachloro‐5,5‐dimethoxy‐cyclopenta‐1,3‐diene: Diels Alder Reactions and Applications of the Products Formed

Readily available 1,2,3,4‐tetrachloro‐5,5‐dimethoxy‐ cyclopenta‐1,3‐diene ( 2 ) is an excellent cyclic diene for Diels—Alder reaction with a vast variety of dienophiles. The products so formed (norbornene derivatives) constitute important building blocks for the synthesis of diverse complex natural as well as non‐natural products. Apart from very high endo selectivity associated with Diels—Alder reactions, there are several other fascinating features associated with these bicyclic products which make them convenient entities in the synthesis of complex molecules. The most important is the rigid framework that act as a powerful template to provide high degree of selectivity and directional nature to various substituents. The proposed article is intended to focus on Diels‐Alder reactions of 2 and the applications of norbornene derivatives in organic synthesis.     

1‐amino‐4,5‐8‐naphthalenetricarboxylic acid‐1,8‐lactam‐4,5‐imide‐containing macrocycles: synthesis,molecular modelling and polymerization

Novel macrocycles containing 1‐amino‐4,5‐8‐naphthalenetricarboxylic acid‐1,8‐lactam‐4,5‐imide and 1,4,5‐8‐naphthalenetetracarboxylic bisimide fragments were synthesized by the high‐temperature pseudo‐high‐dilution acylation of the corresponding diols with isophthaloyl chloride, 4,4′‐ and 2,2′‐dichlorocarbonyl biphenyls with up to 60% yield. An important side‐reaction that impedes cyclization was found to be the reaction of diol OH groups with HCl during the acetylation. The ring strain in synthesized macrocyles and model cycles was estimated using the isodesmic reaction approach at the B3LYP/6–311 + G(d,p)//HF/3–21G level of theory. Lactamimide‐containing macrocycles were found to be more strained than bisimide‐containing macrocycles. The ring‐opening polymerization (ROP) of synthesized macrocycles in the molten state shows that the driving force of this process is the strain release on ring‐opening. The ROP of lactamimide‐containing macrocycles was found to be an efficient way to obtain lactamimide‐containing polymers, which are otherwise difficult to synthesize. Copyright © 2003 Society of Chemical Industry     

Durable and regenerable antimicrobial textiles: Synthesis and applications of 3‐methylol‐2,2,5,5‐tetramethyl‐imidazolidin‐4‐one (MTMIO)

A new precursor of halamine compounds, 3‐methylol‐2,2,5,5‐tetramethylimidazolidin‐4‐one (MTMIO), was synthesized by methylolation of 2,2,5,5‐tetramethylimidazolidin‐4‐one (TMIO) and characterized by ¹H‐NMR and FTIR. By chemically reacting MTMIO with cellulose, TMIO rings were successfully grafted onto cellulose‐containing fabrics. After a subsequent chlorination, the treated fabrics were converted to halamine structures, which then demonstrated effective antibacterial efficacy. As expected, the halamine structure generated from TMIO is much more stable, and therefore, the biocidal functions of the finished materials are more durable. The results indicated that this halamine structure could survive repeated home laundering and would require less frequent chlorine recharging to maintain the biocidal properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2418–2425, 2003     

Cationic Gold‐ and Silver‐Catalyzed Cycloisomerizations of Propargylic Ureas: A Selective Entry to Oxazolidin‐2‐imines and Imidazolidin‐2‐ones

A comparative study on transition metal‐catalyzed cycloisomerizations of propargylic ureas derived in situ from secondary propargylic amines and tosyl isocyanate was performed. The influence of catalytic system on the reaction outcome was thoroughly studied on two model examples resulting in the establishment of two selective protocols for both O‐ and N‐cyclizations. The application of cationic gold(I) catalysis generally resulted in a formation of oxazolidin‐2‐imines as major products while the application of silver(I) triflate selectively provided the corresponding imidazolidin‐2‐ones. An attempt to rationalize the observed chemoselectivity is described. The scope of both processes was demonstrated through the use of variously substituted secondary propargylic amines.