Copolymers In Water Research Articles

Supramolecular Dynamics as Origin for Thermally Induced Insoluble‐to‐Soluble‐to‐Insoluble Transitions of Copolymers in Water

The synthesis of cationic mono-(6-O-(1-vinylimidazolium))-ß-cyclodextrin with toluenesulfonate as the corresponding anion is described. Free-radical copolymerization of the resulting host-guest complex with N-isopropylacrylamide or N,N-diethylacrylamide yielded copolymers showing a temperature-controlled solubility window in water. The impact of different anionic guests and salt concentrations on solubility behavior was investigated via turbidity measurements.

Aqueous RAFT polymerization ofN-isopropylacrylamide-mediated with hydrophilic macro-RAFT agent: Homogeneous or heterogeneous polymerization?

Aqueous RAFT polymerization of N-isopropylacrylamide (NIPAM) mediated with hydrophilic macro-RAFT agent is generally used to prepare poly(N-isopropylacrylamide) (PNIPAM)-based block copolymer. Because of the phase transition temperature of the block copolymer in water being dependent on the chain length of the PNIPAM block, the aqueous RAFT polymerization is much more complex than expected. Herein, the aqueous RAFT polymerization of NIPAM in the presence of the hydrophilic macro-RAFT agent of poly(dimethylacrylamide) trithiocarbonate is studied and compared with the homogeneous solution RAFT polymerization. This aqueous RAFT polymerization leads to the well-defined poly(dimethylacrylamide)-b-poly(N-isopropylacrylamide)-b-poly(dimethylacrylamide) (PDMA-b-PNIPAM-b-PDMA) triblock copolymer. It is found, when the triblock copolymer contains a short PNIPAM block, the aqueous RAFT polymerization undergoes just like the homogeneous one; whereas when the triblock copolymer contains a long PNIPAM block, both the initial homogeneous polymerization and the subsequent dispersion polymerization are involved and the two-stage ln([M]o/[M])-time plots are indicated. The reason that the PNIPAM chain length greatly affects the aqueous RAFT polymerization is discussed. The present study is anticipated to be helpful to understand the chain extension of thermoresponsive block copolymer during aqueous RAFT polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Synthesis, micellization and gelation of temperature‐responsive star‐shaped block copolymers

A series of amphiphilic temperature‐responsive star‐shaped poly(D,L‐lactic‐co‐glycolic acid)‐b‐methoxy poly(ethylene glycol) (PLGA‐mPEG) block copolymers with different arm numbers were synthesized via the arm‐first method. Gel permeation chromatography data confirmed that star‐shaped PLGA‐mPEG copolymers had narrow polydispersity index, indicating the successful formation of star‐shaped block copolymers. Indirectly, the 1H NMR spectra in two kinds of solvents and dye solubilization method had confirmed the formation of core‐shell micelles. Further, core‐shell micelles with sizes of about 30–50 nm were directly observed by transmission electron microscopy. Subsequently, the micellar sizes and distributions as a function of concentrations and temperature were measured. At various copolymer concentrations, individual micelles with size of 20–40 nm and grouped micelles with size of 600–700 nm were found. Micellar mechanism of star‐shaped block copolymers in aqueous solution was simultaneously discussed. In addition, sol–gel transition of star‐shaped block copolymers in water was also investigated via the inverting test method. The critical gel temperature (CGT) and critical gel concentration (CGC) values of two‐arm, three‐arm and four‐arm copolymer solutions were markedly higher than ones of one‐arm copolymer. Moreover, the same CGC values of copolymer solution with different molecular weight and the same arm composition were ~15 wt %, and CGT values increased from ~38 to ~47°C with increasing arm numbers. Finally, the temperature‐dependent micellar packing gelation mechanism of star‐shaped block copolymer was schematically illustrated. Copyright © 2013 John Wiley & Sons, Ltd.

Spectroscopical properties of a DTAF-labeled hydrophilic–hydrophobic copolymer in water and surfactant micelles

Emulsion copolymerization of hydrophilic α-tert-butoxy-ω-vinylbenzyl-polyglycidol macromonomer with styrene yields core–shell microspheres and a water-soluble copolymer fraction. This copolymer has a higher content of hydrophilic polyglycidol attested by 1H NMR. Further information is acquired by labeling the copolymer with 5-(4,6-dichlorotriazinyl)aminofluorescein (DTAF) and making absorption and fluorescence studies. The acquired data on aqueous solution of labeled copolymer without (L) and with micelles of dodecyltrimethylammonium chloride (LD), sodium dodecylsulfate (LS) and hexaethyleneglycol mono n-dodecyl ether (LE) reveal that the dianionic and anionic tautomers of the DTAF-label are apparent and concordant with the recorded spectrophotometric pKa values. The emission intensities, quantum yields and lifetimes obey the sequence LE < LS < L < LD. They are along with the increasingly deprotonated forms of the fluorophore and unveil that the micelle-label interactions depend on the surfactant.

Synthesis and self‐assembly of amphiphilic star‐block copolymers consisting of polyethylene and poly(ethylene glycol) segments

AbstractWe report on the synthesis and self‐assembly in water of well‐defined amphiphilic star‐block copolymers with a linear crystalline polyethylene (PE) segment and two or three poly(ethylene glycol) (PEG) segments as the building blocks. Initially, alkynyl‐terminated PE (PE‐) is synthesized via esterification of pentynoic acid with hydroxyl‐terminated PE, which is prepared using chain shuttling ethylene polymerization with 2,6‐bis[1‐(2,6‐dimethylphenyl) imino ethyl] pyridine iron (II) dichloride/methylaluminoxane/diethyl zinc and subsequent in situ oxidation with oxygen. Then diazido‐ and triazido‐terminated PE (PE‐(N3)2 and PE‐(N3)3) are obtained by the click reactions between PE‐ and coupling agents containing triazido or tetraazido, respectively. Finally, the three‐arm and four‐arm star‐block copolymers, PE‐b‐(PEG)2 and PE‐b‐(PEG)3, are prepared by click reactions between PE‐(N3)2 or PE‐(N3)3 and alkynyl‐terminated PEG. The self‐assembly of the resultant amphiphilic star‐block copolymers in water was investigated by dynamic light scattering, transmission electron microscopy, and atomic force microscopy. It is found that, in water, a solvent selectively good for PEG blocks; these star‐block copolymer chains could self‐assemble to form platelet‐like micelles with insoluble PE blocks as crystalline core and soluble PEG blocks as shell. The confined crystallization of PE blocks in self‐assembled structure formed in aqueous solution is investigated by differential scanning calorimetry. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Antibacterial vesicles by direct dissolution of a block copolymer in water

A novel thermo- and pH-responsive antimicrobial diblock copolymer has been synthesized and directly dissolved in water to form polymer vesicles upon simply raising the temperature. Compared to individual polymer chains, polymer vesicles exhibit much better antimicrobial efficacy against both Gram-negative and Gram-positive bacteria under physiological conditions with neither quaternary ammonium moieties nor the loading of any external antibiotics as a result of their increased local concentration of cationic charge.

Molecular Weight Effect on the Quaternization of Poly(4-vinylpyridine) with Alkylbromide

The objective of this work is to study the influence of molecular weight on the quaternization of poly(4-vinylpyridine) (P4VP) with octyl and dodecyl bromide. The P4VP with different molecular weight was synthesized by radical polymerization. The molecular weight was determined by viscosimetric and light scattering. A set of copolymers containing the poly(4-vinylpyridine) of different molecular weights quaternized with octyl and dodecyl bromide (C8Br and C12Br) were prepared. In order to determine the solubility limit of each copolymer; phase diagrams were established according to the water percentage in the mixture water-ethanol. Empiric laws for the rate maximum (Tmax) and Mw were proposed. We have considered six P4VP samples in wide intervals of molecular weights: 0.75.104 to 94.104 g/mol. The ratio between the high size and the small size is 106.7. The maxima rate of quaternization (Tmax) and the initial constants rate k0 increase with P4VP molecular weights. Critical time for the quaternization kinetics is 360 h, which is independent of Mw. The length of alkyl chain from C8 does not affect the quaternization kinetics. The solubility of copolymers in water decreases with macromolecular weight,which is not the case for P4VP homopolymer.

Low friction and high load bearing capacity layers formed by cationic-block-non-ionic bottle-brush copolymers in aqueous media

Efficient lubricants should be able to build surface layers that result in low friction and high load bearing capacity. In this work we show how this can be achieved in aqueous media by means of adsorption of a diblock copolymer consisting of a cationic anchor block without side chains and an uncharged and hydrophilic bottle-brush block that protrudes into solution. Surface and friction forces were measured between negatively charged silica surfaces coated with adsorbed layers of the cationic diblock copolymer, utilizing the atomic force microscope colloidal probe technique. The interactions between the surfaces coated with this copolymer in water are purely repulsive, due to a combination of steric and electrostatic double-layer forces, and no hysteresis is observed between forces measured on approach and separation. Friction forces between the diblock copolymer layers are characterized by a low friction coefficient, μ ≈ 0.03–0.04. The layers remain intact under high load and shear due to the strong electrostatic anchoring, and no destruction of the layer was noted even under the highest pressure employed (about 50 MPa). Addition of NaCl to a concentration of 155 mM weakens the anchoring of the copolymer to the substrate surface, and as a result the friction force increases.

Synthesis and ring-opening polymerisation of a new alkyne-functionalised glycolide towards biocompatible amphiphilic graft copolymers

A new functional dilactone, 3-(2-propynyl)-1,4-dioxane-2,5-dione (4), was synthesized from ethyl glyoxalate and propargyl bromide via a 4-step reaction sequence. Ring-opening (co)polymerisation of the alkyne-functionalised monomer 4 with L-lactide was carried out in dichloromethane at 30 °C using N,N-dimethylaminopyridine as a catalyst and benzyl alcohol as an initiator. The resulting alkyne-functionalised copolyesters were characterized by 1H NMR, size exclusion chromatography (SEC) and MALDI-TOF spectroscopy. Azide end-functionalised PEG was then grafted onto the polyester backbone with multiple pendant alkyne moieties using copper-catalysed azide–alkyne cycloaddition (click chemistry). The graft copolymers were characterized by 1H NMR, SEC and DOSY NMR. The aggregation behavior of the copolymers in water was investigated by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The critical aggregation concentration was in the range of 10–50 mg L−1. The nano-sized objects were rod-like in shape with a diameter of 100 nm and a length of around 400 nm.

Single-walled carbon nanotube induced re-entrant hexagonal phases in a Pluronic block copolymer system

We report a new single-walled carbon nanotube (SWNT)-induced re-entrant lyotropic phase behavior of Pluronic F127 block copolymers in water which show two hexagonal phase regions. The small angle X-ray scattering measurements show that as the concentration is increased from 5 to 100 wt% by evaporation, the F127–SWNT/water system exhibits isotropic–hexagonal–(FCC/hex)–BCC–hexagonal–lamellar phase transitions, which is in contrast to the F127/water system showing isotropic–FCC–BCC–hexagonal-lamellar phase transitions. This clearly indicates that, in the F127–SWNT/water system, the 1sthexagonal phase is induced by the presence of long one-dimensional SWNTs and the 2ndhexagonal phase originates from the phase behavior of F127 itself. The presence of SWNTs also induced the shifts of phase transition concentrations and the change of domain sizes. The SWNTs in the hexagonal phases are located in the hydrophobic core (PPO domain) of F127 cylinders, making their orientation parallel to the [001] direction. The possible orientations of SWNTs (which maintain their individuality or very small bundle state) in the FCC and BCC phases were identified based on the epitaxial transitions between corresponding phases (hexagonal to FCC, FCC to BCC, and BCC to hexagonal): [110] in the FCC and 〈111〉 in the BCC.

Photocleavable glycopolymer aggregates

We present here a water soluble diblock glycopolymer, poly(spiropyran methacrylate)-block-poly(3-O-4-vinylbenzoyl-D-glucopyranose) (PSP-b-PBG), synthesized by the conventional atom transfer radical polymerization (ATRP) technique. Irradiation with UV light results in switching of the hydrophobic colorless spiropyran (SP) form to zwitterionic purple coloured merocyanine (MC) increasing the overall polarity of the glycopolymer, resulting in its enhanced affinity towards water. The MC form reverts back to the SP form in the dark or under visible light irradiation, restoring the amphiphilic nature of the polymer. Vesicular aggregates formed by this diblock copolymer in water could be dissociated and reconstructed by alternate UV and visible light irradiation. The ability of these polymersomes to efficiently encapsulate, release and re-encapsulate a hydrophobic dye was also explored.

RAFT-mediated one-pot aqueous emulsion polymerization of methyl methacrylate in presence of poly(methacrylic acid-co-poly(ethylene oxide) methacrylate) trithiocarbonate macromolecular chain transfer agent

The polymerization-induced self-assembly of amphiphilic block copolymers in water was performed following a reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization mechanism in emulsion. Poly(methacrylic acid-co-poly(ethylene oxide) methyl ether methacrylate), P(MAA-co-PEOMA), with a trithiocarbonate reactive end-group was selected as the water-soluble living precursor and synthesized in situ via a RAFT aqueous solution polymerization process. The study focused on the polymerization of methyl methacrylate (MMA) at pH 3.5, 5 and 7 and its copolymerization with various proportions of styrene (S) at pH 3.5. In the homopolymerization of MMA, the reaction was well-controlled at pH 3.5, while a low blocking efficiency was observed at higher pH. The systems led to spherical micelles, fibers and then vesicles when the molar mass of the hydrophobic block was increased, irrespective of the pH of the aqueous phase. In the case of the copolymerization with styrene at pH 3.5 and in chain length conditions leading to fibers for the homopolymerization of MMA, the control was very good but the final morphology was that of spherical particles only, at all compositions studied, exactly like in the homopolymerization of styrene performed under similar experimental conditions [Zhang et al. Macromolecules 2011; 44:7584–93]. The results were interpreted on the basis of an influence of the polymerization kinetics, especially in the early stage of the reaction in the aqueous phase.

Self‐Assembly of Amphiphilic Block Copolymers in Ternary Solvent Mixtures: Lyotropic Liquid Crystalline Phase Behavior and Structure

AbstractThe effects of the simultaneous addition of two organic solvents (glycerol and ethanol) on the lyotropic liquid crystalline (LLC) phase behavior and structure formed by PEO–PPO–PEO amphiphilic block copolymers in water are examined. Glycerol and ethanol have been selected because of their opposite effect: structure promoting and structure dissolving, respectively. Lattice parameters of Pluronic P105 (EO37PO58EO37) and F127 (EO100PO70EO100) LLC samples in the presence of any type and amount of E+G solvents decrease with increasing volume fraction of the PPO‐rich domains. Lattice parameters for the two block copolymers fall on the same line when normalized with the square root of polymer molecular weight, suggesting weak block segregation.

Preparation of cellulose-graft-poly(ɛ-caprolactone) nanomicelles by homogeneous ROP in ionic liquid

Self-associating cellulose-graft-poly(ɛ-caprolactone) (cellulose-g-PCL) copolymers were successfully synthesized via homogeneous ring-opening polymerization (ROP) of ɛ-CL onto softwood dissolved pulp substrate in ionic liquid 1-N-butyl-3-methylimidazolium chloride ([Bmim]Cl). An organic catalyst N,N-dimethylamino-4-pyridine (DMAP) was compared with the traditional metal-based catalyst (Sn(Oct)2) as the catalyst of the reaction, and exhibited higher catalytic activity. By controlling the cellulose:ɛ-CL feed ratio and reaction temperature, the molecular architecture of the copolymers can be altered, as evidenced by FT-IR, 1H NMR, 13C NMR, TGA and XRD. The self-assembly behavior of the copolymers in water was investigated and characterized using fluorescence probe, dynamic light scattering (DLS) and SEM. The results showed that the cellulose-g-PCL copolymers could form nanosized micelles (approximately 20–100nm) in water, and the micelle size and critical micelle concentration (CMC) can be controlled by varying the grafting ratio of PCL. These cellulose-based nanomicelles are expected to be useful in broad application fields.

Dynamic Origin and Thermally Induced Evolution of New Self‐Assembled Aggregates from an Amphiphilic Comb‐Like Graft Copolymer: A Multiscale and Multimorphological Procedure

In the past several decades, the self-assembly of block copolymers in selective solvents has attracted extensive interest due to the formation of various aggregates including spherical and cylindrical micelles, vesicles, tubes, helices, toroids, and other complex forms. Research has been focused on aggregates with spherical, flowerlike, tubular or sheet-like superstructures, obtained through the hierarchical self-assembly of Janus micelles or Janus nanoparticles, owning to their formation mechanisms and potential applications in biomedical materials and new nanodevices. The self-assembled aggregates can also be constructed from amphiphilic comb-like graft copolymers in water or organic solvents. Despite that many interesting aggregates including petal-like micelles, spindle-like micelles, wormlike micelles, chiral helices, and so on, are obtained by the change of structural and environmental parameters, in most cases conventional spherical micelles and vesicles are observed. In comparison with block copolymers, self-assembled aggregates of amphiphilic comb-like graft copolymers reveal the morphological characteristics of obviously low diversity and complexity. Considering the shape plays a crucial role in determining physical and chemical properties of aggregates, the controlled fabrication and switch of morphologies have been paid a great attention, which has been implemented by regulating the conditions, such as solvent, pH, redox, and so on. Typically, crystallization is an important factor utilized to control the self-assembly of semicrystalline block copolymers consisting of the crystallizable block and amorphous block, which has been actively researched recently. Inspired by this specific class of copolymer, we have designed an amphiphilic comb-like graft copolymer consisting of poly(p-dioxanone) (PPDO) as a crystallizable hydrophobic side chain and poly(vinyl alcohol) (PVA) as a hydrophilic main chain, and found that this copolymer presented an unique self-assembled behavior. In fact, recently we reported a “star anise”-like nanoaggregate from a PPDO-based branched alternating multi-block copolymer. Herein, by directly dispersing this PPDO-based amphiphilic comb-like graft copolymer into water, more complex and regular aggregates with a well-defined snowflake-like superstructure was obtained, and their origin involving a dynamically disorder–order change from nanoto submicroscale was visualized. Moreover, the aggregates showed thermally induced multimorphological evolution from a snowflake-like to cluster-like structure. As an original and significant work, this superstructure enriches the self-assembled morphology of amphiphiles, especially comb-like macromolecules. Furthermore, the direct water phase self-assembled strategy of PPDO-based amphiphilic copolymers and temperature-adjusted morphological change could provide a new idea to construct complex multimorphological and multiscale objects. The precursors of the copolymers were synthesized through ring-opening polymerization and the acylation, respectively. The copolymers were prepared in DMSO by a coupling reaction between carboxyl groups presenting on PPDO chain-end and hydroxyl groups of PVA (Scheme 1). The information of the molecular structure of copolymers is listed in the Supporting Information, Table S1. The self-assembly was achieved by adding PVA500-g5.6%PPDO15 to water at room temperature, heating the system to homogenous phase (to erase the thermal history), and aging it at 25 8C. Tests of dynamic light scattering (DLS) indicated the presence of monodispersed and stable particles with 791 nm of intensity-averaged hydrodynamic diameter ( ) and a polydispersity index (PDI) of 0.053 (Figure 1a, their and PDI after 7 days was shown in the Supporting Information, Figure S1). Transmission electron microscopy (TEM) images revealed well-defined snowflakelike aggregates having about 260 nm of average thickness, 530 nm of average width, and 620 nm of average length, respectively (marked by short arrows in Figure 1band 1c). For monodisperse spherical aggregates, they have same diffusion coefficient in every direction, and their size from CONTIN analysis is independent of scattering angles. Conversely, for the anisotropic or polydisperse aggregates, the results of DLS are dependent of scattering angles. By multi-angle DLS experiment, we found that the diameter and apparent [a] G. Wu, Dr. S.-C. Chen, Dr. X.-L. Wang, Dr. K.-K. Yang, Prof. Y.-Z. Wang National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan) State Key Laboratory of Polymer Materials Engineering College of Chemistry, Sichuan University 29 Wangjiang Road, Chengdu 610064 (P.R. China) Fax: (+86)28-85410259 E-mail : chensichong@scu.edu.cn yzwang@scu.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201103961.

Thermoresponsive Hydrogel of Diblock Methylcellulose: Formation of Ribbonlike Supramolecular Nanostructures by Self-Assembly

This article provides detailed insight into the thermoresponsive gelation mechanism of industrially produced methylcellulose (MC), highlighting the importance of diblock structure with a hydrophobic sequence of 2,3,6-tri-O-methyl-glucopyranosyl units for this physicochemical property. We show herein, for the first time, that well-defined diblock MC self-assembles thermoresponsively into ribbonlike nanostructures in water. A cryogenic transmission electron microscopy (cryo-TEM) technique was used to detect the ribbonlike nanostructures formed by the diblock copolymers consisting of hydrophilic glucosyl or cellobiosyl and hydrophobic 2,3,6-tri-O-methyl-cellulosyl blocks, methyl β-D-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-celluloside 1 (G-236MC, DP(n) = 10.7, DS = 2.65), and methyl β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-celluloside 2 (GG-236MC, DP(n) = 28.2, DS = 2.75). Rheological measurements revealed that the gel strength of a dispersion of GG-236MC (2, 2.0 wt %) in water at 70 °C was 3.0 times stronger than that of commercial MC SM-8000, although the molecular weight of GG-236MC (2) having M(w) = 8 × 10(3) g/mol was 50 times smaller than that of SM-8000 having M(w) = 4 × 10(5) g/mol. Cryo-TEM observation suggested that the hydrogel formation of the diblock copolymers could be attributed to the entanglement of ribbonlike nanostructures self-assembled by the diblock copolymers in water. The cryo-TEM micrograph of GG-236MC (2) at 5 °C showed rectangularly shaped nanostructures having a thickness from 11 to 24 nm, although G-236MC (1) at 20 °C showed no distinct self-assembled nanostructures. The ribbonlike nanostructures of GG-236MC (2) having a length ranging from 91 to 864 nm and a thickness from 8.5 to 27.1 nm were detected above 20 °C. Small-angle X-ray scattering measurements suggested that the ribbonlike nanostructures of GG-236MC (2) consisted of a bilayer structure with a width of ca. 40 nm. It was likely that GG-236MC (2) molecules were oriented perpendicularly to the long axis of the ribbonlike nanostructure. In addition, wide-angle X-ray scattering measurements revealed that GG-236MC (2) in its hydrogel formed the same crystalline regions as 2,3,6-tri-O-methylcellulose. The influence of the DP of diblock MC with a DS of around 2.7 on the gelation behavior will be discussed.

Preparation, Characterization and Antimicrobial Activity of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-g-Poly(N-vinylpyrrolidone) Copolymers

Graft polymerization of N-vinylpyrrolidone onto poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV was carried out in solution. The evidence of grafting was provided by FTIR, and 1H-NMR. The DSC results showed that the cold crystallization temperature from the glass state increased with increase of grafting %. TGA analysis revealed that the thermal stability of the host PHBV was improved remarkably with increasing extent of grafting. The swelling of the graft copolymer in water increases with increasing G%. The antibacterial activity of PHBV-g-PVP copolymers was improved dramatically with the extent of grafting. The biodegradability of PHBV and its graft copolymers was investigated in active soil.

Solution Behavior of Double-Hydrophilic Block Copolymers in Dilute Aqueous Solution

The self-assembly of double-hydrophilic poly(ethylene oxide)–poly(2-methyl-2-oxazoline) diblock copolymers in water has been studied. Isothermal titration calorimetry, small-angle X-ray scattering, and analytical ultracentrifugation suggest that only single polymer chains are present in solution. In contrast, light scattering and transmission electron microscopy detect aggregates with radii of ca. 100 nm. Pulsed field gradient NMR spectroscopy confirms the presence of aggregates, although only 2% of the polymer chains undergo aggregation. Water uptake experiments indicate differences in the hydrophilicity of the two blocks, which is believed to be the origin of the unexpected aggregation behavior (in accordance with an earlier study by Ke et al. [Macromolecules2009, 42, 5339–5344]). The data therefore suggest that even in double-hydrophilic block copolymers, differences in hydrophilicity are sufficient to drive polymer aggregation, a phenomenon that has largely been overlooked or ignored so far.

Temperature-responsive photoluminescence of quinoline-labeled poly(N-isopropylacrylamide) in aqueous solution

The pH- and temperature-responsive optical properties of a quinoline-labeled poly(N-isopropylacrylamide) copolymer are explored in aqueous solution and compared to the respective behavior of a similar quinoline-labeled poly(N,N-dimethylacrylamide) copolymer. These copolymers, P(NIPAM-co-SDPQ) and P(DMAM-co-SDPQ), were prepared through free radical copolymerization of 2,4-diphenyl-6-(4-vinylphenyl)quinoline (SDPQ) with the thermosensitive N-isopropylacrylamide (NIPAM) and the hydrophilic N,N-dimethylacrylamide (DMAM), respectively. Both copolymers exhibit the well-known pH-controlled optical response of quinoline unit in aqueous solution and the emitted color changes from blue to green upon decreasing pH. Nevertheless, a ∼20nm emission shift is observed upon heating the aqueous P(NIPAM-co-SDPQ) solution, regardless of pH, due to the formation of hydrophobic microdomains (Nile Red probing), as a consequence of the Lower Critical Solution Temperature (LCST) behavior of this copolymer in water. Interestingly, this LCST behavior also imposes the partial deprotonation of the otherwise protonated SDPQ unit at pH=2 and the emission of the basic form appears upon increasing temperature, suggesting that the acid/base equilibrium of the quinoline unit is significantly temperature-controlled, when introduced in the thermosensitive poly(N-isopropylacrylamide) chain.

Size controlled polymersomes by continuous self-assembly in micromixers

The formation of vesicles based on the self-assembly of amphiphilic poly(butadiene)-b-poly(ethylene oxide) (PB130-b-PEO66) block copolymer in water has been studied using THF as co-solvent. To obtain a highly controlled mixing process for the polymer/THF- and the water-phase, we employed micro mixers with different mixing geometries. The high impact of this preparation method on the self-assembling process was verified by TEM and DLS characterization of the obtained structures. Spherical micelles, vesicles and worm-like micelles were found depending on the parameters of mixing. By additional parameter adjustment in the vesicle regime, the size of the assembled vesicles was controlled between 45 and 100 nm. This demonstrates the continuous preparation of narrowly distributed vesicle structures with controlled sizes.