The new complex 25,27‐dipropyloxy‐26,28‐dioxocalix[4]arene titanium (IV) dichloride ( 1 ) was evaluated as an ethylene polymerization catalyst. Activation with methylalumoxane resulted in an active system producing ultrahigh‐molecular‐weight polyethylene. As expected for a Ziegler‐Natta catalyst, the polymerization reaction follows first‐order kinetics. The most striking feature of the catalytic system ( 1 /MAO) is its remarkably high thermal stability. This peculiarity probably relies on the electronic stabilization of the metal center by the two coordinating propoxy groups.
The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH2 and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, 1H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.
Kinetic investigations on the cationic ring‐opening polymerization of 2‐ethyl‐2‐oxazoline were conducted using acetyl chloride, acetyl bromide, and acetyl iodide as initiators. Various polymerization temperatures ranging from 80 to 220 °C were applied under microwave irradiation. The resulting polymerization mixtures were characterized with GC and GPC for the determination of monomer conversion and molecular weight distribution, respectively. Well defined polymers with narrow molecular weight distributions ( = 6 000 Dalton, PDI ≈ 1.10) were obtained with all three initiators.
A novel approach to amphiphilic polymeric Janus micelles based on the protonation/deprotonation process of poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (P2VP‐b‐PEO) diblock copolymers in THF is presented. It is found that addition of HCl to the micelles solution of P2VP‐b‐PEO copolymers leads to the formation of vesicles. Subsequently mixing a small amount of hydrazine monohydrate with the vesicle solution can induce the dissociation and reorganization of the vesicles into Janus micelles. When HCl is replaced by HAuCl4 precursors, composite Janus particles containing gold in P2VP blocks are obtained.
The PLP technique in combination with MALDI‐ToF‐MS was used to determine the Arrhenius plots for the propagation rate coefficients of THFA and ADBL, which polymerize much faster than alkyl acrylates. It is demonstrated that this is not due to higher propagation rate coefficients. It is shown that the temperature at which the PLP experiment brakes down increases in the order ADBL > THFA > alkyl acrylates, indicating a high extent of transfer to polymer for these monomers. Although kp decreases in the same order, the decrease of the corresponding overall polymerization rate is much larger. Therefore, the high polymerization rates of ADBL and THFA cannot be accounted for by fast propagation rates but more likely are linked to a low rate of termination.
εCL was polymerized using the triflates of lanthanum, samarium, magnesium, aluminum, scandium, and bismuth as catalysts. Bismuth triflate proved to be extraordinarily reactive, and catalyzed polymerizations of εCL even at 20 °C. Adding DTBMP reduced the polymerization rate only slightly. Furthermore, no evidence of a cationic mechanism was found by end‐group analyses. Polymerization at 20 °C either in bulk or in solution only yielded polyesters of low or medium molecular weights ($\overline {M} _{{\rm n}} $ up to 30 000 Da). Yet addition of alcohols allowed for a proper control of molecular weight and end‐groups. Additionally, low catalyst concentrations and low temperature resulted in narrow molecular weight distributions and polylactones almost free of cyclic compounds.
Alkynyldextrans with a DS in the range 0.1–1.67 have been prepared as reactive intermediates for further polymer‐analogous functionalisation. DS and substituent distribution were determined by GLC and GLCMS after hydrolysis and acetylation, or methanolysis and trimethylsilylation. Reactivity was in the order O‐2 > O‐4 ≥ O‐3 with pronounced differences in the distinct patterns for propargyl ethers and its higher homologous. A large deviation from a random substituent distribution was observed. Propargyldextrans were not stable during long‐time storage in the solid state, while terminal pentynyl and hexynyl ethers are. Pentynyldextrans showed structure formation of various geometries. They bound silver efficiently, yielding silver nanoparticles by reduction.
The bis(acetylacetonato)platinum(II) is a common thermal catalyst for the hydrosilation reaction, and it is reported to serve also as a photoactivated catalyst for hydrosilation addition of silanes to alkenes and alkynes. In this paper, it is demonstrated that the UV‐activation of hydrosilation reaction proceeds via a thermal‐frontal mechanism. UV light activates the polymerization on the surface of the sample and, subsequently, the heat released by hydrosilation generates a thermal front, converting the UV‐generated homogeneous catalyst to a Pt0 heterogeneous catalyst. The UV‐induced frontal polymerization mechanism can exhaustively explain the dark‐curing process observed in the UV‐activated hydrosilation reaction.
The synthesis of two new monomers based on 4‐hydroxythiazoles, with a non‐classical chromophore structure similar to the luciferin dye of glowworms, is presented. These dyes are functionalized with methacrylates and copolymerized with methyl methacrylate using a RAFT polymerization process. The obtained polymers reveal PDI values below 1.2 and are characterized by NMR spectroscopy, SEC including a diode‐array detector, UV‐vis and fluorescence spectroscopy. In addition, thin films of the polymers are prepared by spin‐coating and investigated regarding their optical properties.
Self‐assembly has emerged as a powerful approach to control nanostructure in materials containing globular proteins, both through templated self‐assembly and direct self‐assembly of globular protein‐polymer conjugates or fusion proteins. The folded structures of globular proteins that are critical to their function introduce complex shapes and interactions into block copolymers that significantly alter the physics of self‐assembly. This article discusses the different methods for controlling the nanostructure of globular proteins using block copolymers, highlighting efforts at understanding the physics of self‐assembly in concentrated solution and solid‐state bioconjugate copolymers.
New polyhydrazides and poly(amidehydrazide)s bearing redox‐active carbazole and triphenylamine units were prepared. The resulting poly(1,3,4‐oxdiazole)s and poly(amide‐1,3,4‐oxadiazole)s had high glass‐transition temperatures (288–330 °C) and high thermal stability. The dilute solutions of all the hydrazide and oxadiazole polymers showed a weak–medium photoluminescence with emission maxima around 474–506 nm. The polymer films revealed two well‐defined and reversible redox couples upon electrochemical oxidation, together with interesting electrochromic behaviors. They showed enhanced redox‐stability and electrochromic performance. CV of the oxadiazole polymers also showed reduction processes due to the formation of radical anions of the oxadiazole units.
A series of layer‐structured zinc‐containing metallopolymers were prepared through a solvothermal reaction of zinc acetate with 1,4‐benzene dicarboxylic acid derivatives bearing various nonpolar n‐alkyl groups as side chains. The resulting metallopolymers were investigated. The reaction time and the length of the alkyl substituents on the backbone have a marked effect on the mesophase structure and thermal behaviors of the metallopolymers. The metallopolymer with tetradecyloxy side chains prepared by solid‐to‐solid transformations within solvothermal synthesis exhibits a unique mesophasic behavior with melt tractability.
New thiols for efficient thiol‐ene polymerization reactions are presented. They do not exhibit any unpleasant odor, are characterized by quite good light‐absorption properties at λ > 300 nm, and generate thiyl radicals upon UV‐light exposure. Due to these interesting properties and contrary to many previously reported methodologies, the present thiol‐acrylate polymerizations can be efficiently carried out without the presence of any additional photoinitiator. The chemical mechanisms are investigated by steady‐state photolysis and electron spion resonance (ESR) experiments. Important parameters can also be extracted from molecular orbital calculations.
A one‐step synthesis of heterobifunctional hyperbranched polyethylenes covalently tethered with dual acryloyl and 2‐bromoisobutyryl functionalities at controllable contents is reported. It is achieved in one pot by chain‐walking terpolymerization of ethylene with two functional acrylate comonomers, 1,6‐hexanediol diacrylate and 2‐(2‐bromoisobutyryloxy) ethyl acrylate. The unique chain‐walking mechanism renders the hyperbranched polymer chain topology and its remarkable capability in incorporating acrylate comonomers enables the incorporation of both comonomers to give two valuable functionalities. The two comonomers exhibit nearly equal vinyl reactivity and are incorporated independently in the terpolymerization with their molar contents controlled by adjusting the comonomer feed concentrations.
PLLA/PDLA blends were crystallized between 120 and 195 °C. The stereocomplex spherulites acquired in equimolar and non‐equimolar blends were compared using POM, WAXD, DSC, and AFM. For equimolar blends, stereocomplex crystals show spherulites with positive birefringence, which is ascribed to the existence of domains made up of tangentially oriented lamellae. For PLLA‐rich (or PDLA‐rich) blends, the signs of the birefringence changed from a positive spherulite to a mixed spherulite and then to a negative spherulite. In negative spherulites, most lamellae orient radially. Radial and tangential cracks were observed in equimolar blends when crystallization took place above 175 °C whereas no cracks formed for non‐equimolar blends.
The self‐assembled monolayer formation of a series of thiophene dendron thiols with different generations and alkyl chain lengths onto gold surfaces is studied. Average film thicknesses and dielectric constants were calculated from SPR using a two‐subphase differential method. The in situ adsorption of the thiophene dendron thiols was monitored by SPR kinetics measurements and fitted using an empirical three‐step model. Electrochemical redox molecular probing experiments provided additional insight into surface coverage, which showed different abilities to block electron transfer at the monolayer/electrode interfaces. The surface coverage of the films was also estimated by QCM measurements and supported by static WCA measurements.
Amphiphilic copolymers have been synthesised by free radical copolymerisation of 2‐hydroxyethyl acrylate with butyl acrylate, the reactivity ratios of which indicate practically equal reactivity. The copolymers containing less than 30 mol‐% of BA were soluble in water and exhibited a LCST in aqueous solutions. It was found that the interaction between these copolymers and poly(acrylic acid) in aqueous solutions resulted in the formation of interpolymer complexes stabilised by hydrogen bonds and hydrophobic interactions. This interaction was significantly affected by solution pH and led to modification of the temperature‐responsive behaviour of the copolymers.
A simple and economical approach to the preparation of superhydrophilic and water‐capturing surfaces is reported. In this method, a common polymer aqueous blend is drop‐cast onto a substrate, and the natural drying of the aqueous drop allows for the formation of phase‐segregated nanosegregants between the bulk film and substrate surface. The nanosegregant is then exposed by dissolving the bulk film using water. The nanosegregant is stable, water‐insoluble and optically transparent, and exhibits superhydrophilicity with a minimum contact angle below 10°. It also displays strong water‐attracting ability. The mechanism of superwettability and water‐capturing behavior is discussed in terms of the self‐organization and functional group of the nanosegregant.
The controlled integration of sequence‐defined oligopeptides into synthetic polymers leads to peptide‐polymer conjugates with precisely defined, multifunctional peptide segments. These bioconjugates allow for the direct realization of bio‐inspired polymer science. Peptides combine self‐assembly properties with the potential to actively interact with biological systems. Hence conjugates can be exploited to program microstructure formation processes in polymeric materials by controlling secondary interactions between the peptide segments. Moreover, the programmable functionalities of the peptides can be used to tune specific interactions, e.g., between drugs and polymeric drug carriers or between inorganic crystal surfaces and polymeric crystal‐growth modifiers.
Thermally stable copolymers with an alternating repeating structure, poly(RMI‐alt‐IB)s, were synthesized by radical copolymerization of N‐substituted maleimides containing a polar group with isobutene. The onset temperature of decomposition was higher than 300 °C and the glass‐transition temperature increased by the introduction of hydroxy and carboxy groups. IR spectroscopic analysis revealed the role of intermolecular hydrogen bonding on the thermal stability of the copolymers. It was also revealed that the amount of water absorbed into poly(RMI‐alt‐IB)s with a hydroxymethyl substituent was as high as 270% of the weight of the used polymer, while the introduction of a carboxy group resulted in lower water absorption properties.
