pH- and Thermoresponsive Self-Assembly of Cationic Triblock Copolymers with Controlled Dynamics

Transient hydrogels formed by cationic BAB triblock copolymers consisting of a hydrophilic poly­(dimethyl­amino­ethyl methacrylate) (P­(DMAEMA)) A block and amphiphilic B blocks composed of randomly distributed DMAEMA and <i>n</i>-butyl methacrylate (<i>n</i>BMA) units were investigated. Oscillatory shear measurements revealed formation of dynamic networks with terminal relaxation times that can be controlled by tuning the ionization degree (α) of the DMAEMA units or the temperature up until 50 °C. A sol–gel transition could be induced by increasing the pH. Above 50 °C irreversible aggregation was observed. The behavior of these pH-sensitive cationic copolymers is compared with that of pH-sensitive anionic copolymers, revealing that incorporating stimuli-responsive hydrophilic units within the hydrophobic blocks of amphiphilic block copolymers may be a general way to control the exchange dynamics of the latter

Toward a Better Understanding of the Parameters that Lead to the Formation of Nonspherical Polystyrene Particles via RAFT-Mediated One-Pot Aqueous Emulsion Polymerization

The emulsion polymerization of styrene in the presence of hydrophilic poly­(methacrylic acid-<i>co</i>-poly­(ethylene oxide) methyl ether methacrylate), P­(MAA-<i>co</i>-PEOMA), macromolecular RAFT (reversible addition–fragmentation chain transfer) agents possessing a trithiocarbonate reactive group and 19 ethylene oxide subunits in the grafts was performed to create <i>in situ</i> P­(MAA-<i>co</i>-PEOMA)-<i>b</i>-polystyrene amphiphilic block copolymer self-assemblies. The system was studied using the following conditions: a pH of 5, two different compositions of the MAA/PEOMA units (50/50 and 67/33, mol/mol), different molar masses of the macroRAFT agents, and various concentrations of the latter targeting different molar masses for the polystyrene block. This work completes a previous one performed at pH 3.5, under otherwise similar experimental conditions, for which only spherical particles were obtained [Zhang et al. <i>Macromolecules</i> <b>2011</b>, <i>44</i>, 7584]. For both MAA/PEOMA compositions, the system led to different nano-object morphologies such as spherical micelles, nanofibers, and vesicles, depending directly on the molar masses of the hydrophilic and hydrophobic blocks. A pH of 5 was shown to be the best compromise to achieve nonspherical particles while keeping a good control over the chain growth

Patchy Supramolecular Bottle-Brushes Formed by Solution Self-Assembly of Bis(urea)s and Tris(urea)s Decorated by Two Incompatible Polymer Arms

In an attempt to design urea-based Janus nanocylinders through a supramolecular approach, nonsymmetrical bis­(urea)­s and tris­(urea)­s decorated by two incompatible polymer arms, namely, poly­(styrene) (PS) and poly­(isobutylene) (PIB), were synthesized using rather straightforward organic and polymer chemistry techniques. Light scattering experiments revealed that these molecules self-assembled in cyclohexane by cooperative hydrogen bonds. The extent of self-assembly was limited for the bis­(urea)­s. On the contrary, reasonably anisotropic 1D structures (small nanocylinders) could be obtained with the tris­(urea)­s (<i>N</i>_agg ∼ 50) which developed six cooperative hydrogen bonds per molecule. ¹H transverse relaxation measurements and NOESY NMR experiments in cyclohexane revealed that perfect Janus nanocylinders with one face consisting of only PS and the other of PIB were not obtained. Nevertheless, phase segregation between the PS and PIB chains occurred to a large extent, resulting in patchy cylinders containing well separated domains of PIB and PS chains. Reasons for this behavior were proposed, paving the way to improve the proposed strategy toward true urea-based supramolecular Janus nanocylinders

Borate and MAO Free Activating Supports for Metallocene Complexes

Fluorinated activating supports (AS) for metallocene complexes were prepared via treatment of silica with AlEt₃ or AlEt₂F followed by pyrolysis and combustion steps, and a subsequent fluorination step when AlEt₃ was used. This new family of activators appears to be universal for metallocene complexes leading to catalysts displaying high activities in ethylene polymerization without the addition of MAO. A productivity of 3200 g g_AS^–1 was obtained in 1 h with the catalyst <i>rac</i>-Et­(Ind)₂ZrCl₂/AS₈/Al­(<i>i</i>Bu)₃ at 80 °C under 10 bar of ethylene. An isotactic polypropylene with a melting transition at 145 °C was prepared using <i>rac</i>-Me₂Si­(2-Me-benz­(e)­Ind)₂ZrCl₂ activated by AS9 and Al­(<i>i</i>Bu)₃. The spherical particle morphology of polyolefins was particularly adapted to slurry processes employed in industry

Effect of the pH on the RAFT Polymerization of Acrylic Acid in Water. Application to the Synthesis of Poly(acrylic acid)-Stabilized Polystyrene Particles by RAFT Emulsion Polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylic acid (AA) in water was studied in detail at different pHs using 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA) as a control agent and 4,4′-azobis­(4-cyanopentanoic acid) (ACPA) as an initiator. Well-defined hydrophilic macromolecular RAFT agents (PAA-CTPPA) were obtained and further used directly in water for the polymerization of styrene. The corresponding polymerization-induced self-assembly (PISA) process was evaluated at different pHs and it was shown that working in acidic conditions (pH = 2.5) led to well-defined amphiphilic block copolymer particles (<i>Đ</i> < 1.4) of small size (below 50 nm). When the pH increased, the control over the growth of the polystyrene (PS) block was gradually lost. Chain extension experiments of PAA-CTPPA with <i>N</i>-acryloylmorpholine (NAM), a hydrosoluble and non-pH sensitive monomer, performed at different pHs showed that the very first addition–fragmentation steps that occurred in water were impeded when PAA was ionized leading to partial consumption of PAA-CTPPA and thus to PS molar masses higher than expected. Varying the PAA-CTPPA concentration at pH = 2.5 led in all cases to stable particles composed of well-defined block copolymers with PS segments of different molar masses

Thermal Reduction of NO_<i>x</i> with Recycled Plastics

This study develops technology for mitigation of NO_<i>x</i> formed in thermal processes using recycled plastics such as polyethylene (PE). Experiments involve sample characterization, and thermogravimetric decomposition of PE under controlled atmospheres, with NO_<i>x</i> concentration relevant to industrial applications. TGA–Fourier transform infrared (FTIR) spectroscopy and NO_<i>x</i> chemiluminescence serve to obtain the removal efficiency of NO_<i>x</i> by fragments of pyrolyzing PE. Typical NO_<i>x</i> removal efficiency amounts to 80%. We apply the isoconversional method to derive the kinetic parameters, and observe an increasing dependency of activation energy on the reaction progress. The activation energies of the process span 135 kJ/mol to 226 kJ/mol, and 188 kJ/mol to 268 kJ/mol, for neat and recycled PE, respectively, and the so-called compensation effect accounts for the natural logarithmic pre-exponential ln (<i>A</i>/min^–1) factors of ca. 19–35 and 28–41, in the same order, depending on the PE conversion in the experimental interval of between 5 and 95%. The observed delay in thermal events of recycled PE reflects different types of PE in the plastic, as measurements of intrinsic viscosity indicate that, the recycled PE comprises longer linear chains. The present evaluation of isoconversional activation energies affords accurate kinetic modeling of both isothermal and nonisothermal decomposition of PE in NO_<i>x</i>-doped atmosphere. Subsequent investigations will focus on the effect of mass transfer and the presence of oxygen, as reburning of NO_<i>x</i> in large-scale combustors take place at higher temperatures than those included in the current study

Phenolate Substituent Effects on Ring-Opening Polymerization of ε‑Caprolactone by Aluminum Complexes Bearing 2‑(Phenyl-2-olate)-6-(1-amidoalkyl)pyridine Pincers

Interaction of the 2-(phenyl-2-ol)-6-ketiminopyridines 2-(4′-R¹-C₆H₃-2′-OH)-6-{CMeN­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N (R¹ = H (<b>L1</b>_a-H), Bu^t (<b>L1</b>_b-H), Cl (<b>L1</b>_c-H), F (<b>L1</b>_d-H)) with AlMe₃ at elevated temperature and subsequent crystallization from acetonitrile affords the five-coordinate 2-(phenyl-2-olate)-6-(2-amidoprop-2-yl)­pyridine aluminum–methyl complexes [2-(4′-R¹C₆H₃-2′-O)-6-{CMe₂N­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N]­AlMe­(NCMe) (R¹ = H (<b>1a</b>), Bu^t (<b>1b</b>), Cl (<b>1c</b>), F (<b>1d</b>)), as their acetonitrile adducts, in good yield. In each case, complexation results in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino unit in <b>L1</b>-H. On the other hand, reactions of the aldimine-containing compounds 2-(4′-R¹-C₆H₃-2′–OH)-6-{CHN­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N (R¹ = H (<b>L1</b>_e-H), Bu^t (<b>L1</b>_f-H), Cl (<b>L1</b>_g-H)) afford as the major crystallized products [2-(4′-R¹C₆H₃-2′-O)-6-{CH­(Me))­N­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N]­AlMe­(NCMe) (R¹ = H (<b>2a</b>), Bu^t (<b>2b</b>), Cl (<b>2c</b>)), in which the migrated methyl group and aluminum–methyl are disposed mutually cis; evidence for the minor trans isomers <b>2a</b>′–<b>c</b>′ is presented. The ring-opening polymerization of ε-caprolactone employing <b>1</b> and <b>2</b> in the presence of PhCH₂OH proceeded efficiently, producing polymers of narrow molecular weight distribution with the catalytic activities highly dependent on the nature of the phenolate-containing 4-R¹ substituent with the F and Bu^t initiators showing the highest activities (<b>1b</b> ≈ <b>1d</b> > <b>1a</b> ≈ <b>1c</b> and <b>2b</b> > <b>2a</b> > <b>2c</b>); in general the CMe₂-containing series <b>1</b> were more active than CH­(Me)-containing <b>2</b> at 30 °C. The bimetallic complex [{2-(4′-Bu^t-C₆H₃-2′-O)-6-{CHMeN­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N}­AlMe­(μ-OMe)­AlMe₂] (<b>3</b>), the result of adventitious oxygenation, is also reported. The single-crystal X-ray structures are reported for <b>L1</b>_d-H, <b>L1</b>_f-H, <b>1a</b>–<b>d</b>, <b>2a</b>, <b>2b</b>/<b>2b</b>′, <b>2c</b>, and <b>3</b>

Phenolate Substituent Effects on Ring-Opening Polymerization of ε‑Caprolactone by Aluminum Complexes Bearing 2‑(Phenyl-2-olate)-6-(1-amidoalkyl)pyridine Pincers

Interaction of the 2-(phenyl-2-ol)-6-ketiminopyridines 2-(4′-R¹-C₆H₃-2′-OH)-6-{CMeN­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N (R¹ = H (<b>L1</b>_a-H), Bu^t (<b>L1</b>_b-H), Cl (<b>L1</b>_c-H), F (<b>L1</b>_d-H)) with AlMe₃ at elevated temperature and subsequent crystallization from acetonitrile affords the five-coordinate 2-(phenyl-2-olate)-6-(2-amidoprop-2-yl)­pyridine aluminum–methyl complexes [2-(4′-R¹C₆H₃-2′-O)-6-{CMe₂N­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N]­AlMe­(NCMe) (R¹ = H (<b>1a</b>), Bu^t (<b>1b</b>), Cl (<b>1c</b>), F (<b>1d</b>)), as their acetonitrile adducts, in good yield. In each case, complexation results in concomitant C–C bond formation via methyl migration from aluminum to the corresponding imino unit in <b>L1</b>-H. On the other hand, reactions of the aldimine-containing compounds 2-(4′-R¹-C₆H₃-2′–OH)-6-{CHN­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N (R¹ = H (<b>L1</b>_e-H), Bu^t (<b>L1</b>_f-H), Cl (<b>L1</b>_g-H)) afford as the major crystallized products [2-(4′-R¹C₆H₃-2′-O)-6-{CH­(Me))­N­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N]­AlMe­(NCMe) (R¹ = H (<b>2a</b>), Bu^t (<b>2b</b>), Cl (<b>2c</b>)), in which the migrated methyl group and aluminum–methyl are disposed mutually cis; evidence for the minor trans isomers <b>2a</b>′–<b>c</b>′ is presented. The ring-opening polymerization of ε-caprolactone employing <b>1</b> and <b>2</b> in the presence of PhCH₂OH proceeded efficiently, producing polymers of narrow molecular weight distribution with the catalytic activities highly dependent on the nature of the phenolate-containing 4-R¹ substituent with the F and Bu^t initiators showing the highest activities (<b>1b</b> ≈ <b>1d</b> > <b>1a</b> ≈ <b>1c</b> and <b>2b</b> > <b>2a</b> > <b>2c</b>); in general the CMe₂-containing series <b>1</b> were more active than CH­(Me)-containing <b>2</b> at 30 °C. The bimetallic complex [{2-(4′-Bu^t-C₆H₃-2′-O)-6-{CHMeN­(2″,6″-<i>i</i>-Pr₂C₆H₃)}­C₅H₃N}­AlMe­(μ-OMe)­AlMe₂] (<b>3</b>), the result of adventitious oxygenation, is also reported. The single-crystal X-ray structures are reported for <b>L1</b>_d-H, <b>L1</b>_f-H, <b>1a</b>–<b>d</b>, <b>2a</b>, <b>2b</b>/<b>2b</b>′, <b>2c</b>, and <b>3</b>

Poly(vinylidene chloride)-Based Amphiphilic Block Copolymers

The controlled/living free-radical copolymerization of vinylidene chloride (VDC) with methyl acrylate (MeA) or acrylic acid (AA) was studied by the reversible addition–fragmentation chain transfer (RAFT) technique using a trithiocarbonate RAFT agent. The reactions were performed in 1,4-dioxane solution at 30 °C and led to good control and high chain-end functionality. P­(VDC-<i>co</i>-MeA)-<i>b</i>-PAA, PAA-<i>b</i>-P­(VDC-<i>co</i>-MeA), and PAA-<i>b</i>-P­(VDC-<i>co</i>-AA) amphiphilic block copolymers were then prepared in the same conditions, starting either from a hydrophobic P­(VDC-<i>co</i>-MeA) macromolecular RAFT (macro-RAFT) agent or from a hydrophilic PAA one. The advantage of the first synthesis pathway relies on the very good transfer efficiency to trithiocarbonate-ended P­(VDC-<i>co</i>-MeA) and on the rapid consumption of the latter even when low percentages (10 mol %) of MeA comonomer are incorporated in the macro-RAFT agent. In contrast, for the second approach a rapid consumption of the macro-RAFT agent is only reached with 30 mol % of MeA in the comonomer feed, whereas with 10 mol % of MeA the transfer constant was determined to be only close to 1. Finally, we demonstrated that PAA-<i>b</i>-P­(VDC-<i>co</i>-AA) diblock copolymers might also be obtained with controlled features in a one-pot process

High-Temperature Rubbing: A Versatile Method to Align π‑Conjugated Polymers without Alignment Substrate

Mechanical rubbing of polymer films has been widely used in the liquid crystal display industry to prepare oriented alignment layers of polyimides. We show that this fast orientation method can be successfully applied to a large palette of different π-conjugated systems, i.e., p- and n-type semiconducting homopolymers and alternating copolymers. Transmission electron microscopy, grazing incidence X-ray diffraction and UV–vis absorption spectroscopy reveal that both, the temperature of the films during rubbing and the molecular weight of the polymer strongly influence the level of orientation. For polythiophenes and polyfluorenes, the dependence of the orientational order parameter on the rubbing temperature (<i>T</i>_rub) was determined. A strong increase of alignment with <i>T</i>_rub is explained by the progressive alignment of higher molecular weight fractions at higher <i>T</i>_rub. The disordering of alkyl side chains allows the hairy-rod shaped macromolecules to disentangle and align during rubbing. In addition, for certain conjugated polymers, the in-plane orientation, crystallinity, and polymorphism of the rubbed films can be substantially improved/modified by postdeposition thermal or solvent vapor annealing. This high level of orientation results in highly anisotropic optical and electronic properties (UV–vis absorption, fluorescence, charge transport)