Solution Behavior of Responsive Cationic Polymers

This thesis combines anion responsive polymeric ionic liquids (PILs) with thermoresponsive polymers. The polymers have been synthesized with controlled radical polymerization methods. A water-insoluble PIL was used as a macro-chain transfer agent in synthesis of block copolymers with poly(N-isopropyl acrylamide) (PNIPAm). PNIPAm chains of various lengths were grown to the same PIL-block. These polymers show a lower cirical solution temperature (LCST) type behavior, typical to PNIPAm. The PIL block and the PNIPAm block interact strongly, no phase transition can be observed for the block copolymers with short PNIPAm chains. The block copolymers form complex aggregates in water. The hydrophobic PIL-homopolymer can be used to make stable particles in salt free water. Also triblock copolymers with a long central PNIPAm block and short water soluble PIL blocks were synthesized. These polymers also show interactions between the PIL and PNIPAm blocks. This can be seen for example as reduced enthalpy of phase transition for the triblock copolymers compared to the PNIPAm homopolymer. The triblock copolymers form complex aggregates at elevated temperatures. The LCST-type phase transtiton of weakly cationic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) can be modified with bis(trifluoromethane)sulfonamide (NTf2) ions. The presence of NTf2 induces also an upper critical solution temperature (UCST) type transition for PDMAEMA, if the polymer is charged enough. NTf2 turns PDMAEMA to a stronger base, presumably due to the effective screening of charges. NTf2 induces an UCST-type transition for strong polycations in the presence of an added electrolyte. The phase behavior of the polycation-NTf2 system can be influenced by addition of sodium chloride. Similar transition can also be induced by trifluoromethanesulfonate (OTf), though OTf is needed in much higher concetrations. This allows the use of OTf as the only salt. The NTf2-polycation interactions influence the phase behavior of copolymers of N-isopropyl acrylamide (NIPAm) and strongly cationic (3-acrylamidopropyl) trimethylammonium chloride (AMPTMA). With low AMPTMA content, the copolymers show LCST-type behavior in the presence of NTf2 and a copolymer with high AMPTMA-content shows UCST-type behavior. If NIPAm and AMPTMA are copolymerized in nearly equal amounts, both transitions may coexist.Tutkimus yhdistää polymeeriset ioninesteet (PIL) ja lämpöherkät polymeerit. Kaikki polymeerit syntetisoitiin kontrolloiduilla radikaalipolymerointimenetelmillä. PIL-tyyppiset polymeerit ovat ioninesteiden, eli matalalla sulavien suolojen, polymeroituja muotoja. Ne ovat tyypillisesti polykationeja ja niiden ominaisuuksiin voidaan suuresti vaikuttaa vastaionin valinnalla. Tässä työssä keskityttiin erityisesti mahdollisuuteen tehdä polykationeista veteen liukenemattomia sopivan anionin avulla. Tutkimuksessa syntetisoitiin lohkopolymeerejä joissa toisena lohkona on PIL ja toisena lohkona poly(N-isopropyyliakryyliamidi) (PNIPAm). PNIPAm on vesiliukoinen matalissa lämpötiloissa, mutta lämpötilan ylittäessä 32 °C, se muuttuu liukenemattomaksi. Toisin sanoen sillä on alempi kriittinen liuoslämpötila (LCST). Rippumatta siitä oliko PIL-lohko vesiliukoinen vai ei, havaittiin, että lohkot vuorovaikuttavat keskenään ja muodostavat monimutkaisia rakenteita. Myös toisen tunnetun LCST-polymeerin, poly(2-dimetyyliaminoetyyli metakrylaatin) (PDMAEMA), vesiliuoksia tutkittiin hydrofobisen vastaionin läsnä ollessa. Hydrofobisena anionina käytettiin bis(trifluorometyyli)sulfonamidia (NTf2). PDMAEMA on heikko emäs; sen varautuneisuutta ja täten myös LCST-käytöstä pystytään säätämään pH:n avulla. Sen LCST-käytökseen vaikuttaa myös NTf2:n konsentraatio, vaikutuksen voimakkuuden riippuessa pH:sta. Happamassa liuoksessa havaittiin myös ylempi kriittinen liuoslämpötila (UCST) joissain NTf2-konsentraatioissa. PDMAEMAlle happamassa liuoksessa havaittua UCST-käytöstä tutkittiin kahdella vahvalla polykationilla ja hydrofobisilla anioneilla. Vastaava käytös havaittiin myös kyseisille polykationeille, mutta ainoastaan liuoksen ionivahvuuden ollessa riittävän korkea. PDMAEMAn kaltainen käytös NTf2-pitoisessa liuoksessa havaittiin myös N-isopropyyli akryylamidin ja (3-akryyliamidopropyyli)trimetyyliammonium kloridin (AMPTMA) kopolymeereille. Tässä tapauksessa NTf2:n ja polymeerin vuorovaikutusta säädeltiin AMPTMA-pitoisuudella pH:n sijaan. AMPTMAn homopolymeerillä ja korkeimman AMPTMA-pitoisuuden kopolymeerillä on UCST-käytös, mikä on yhteneväistä aiempien havaintojen kanssa. Mikäli kumpaakin komonomeeriä on suunnilleen yhtä paljon, kopolymeerilla on sekä LCST- että UCST-käytös. Kopolymeerien liuoskäyttäytymistä pystytään säätelemään myös natriumkloridin konsentraatiolla

Upper or lower critical solution temperature, or both? : Studies on cationic copolymers of N-isopropylacrylamide

The solution properties of statistical copolymers of N-isopropyl acrylamide (NIPAm) and cationic (3-acrylamidopropyl) trimethylammonium chloride (AMPTMA) have been studied. The phase behavior of the copolymers in aqueous solutions is strongly affected by the addition of lithium bis(trifluoromethane)sulfonimide (LiNTf2), NaCl, or both. Hydrophobic NTf2 counter ions bind to the AMPTMA repeating units. By adjusting the balance between hydrophobic and electrostatic interactions the transition temperature of the copolymers may be tuned over a wide temperature range. It was observed that a homopolymer PAMPTMA undergoes an UCST-type phase separation in an aqueous solution in the presence of both NaCl and LiNTf2. When AMPTMA and NIPAm are present in the copolymer in nearly equal amounts both LCST and UCST can coexist. It was observed that the effect of LiNTf2 is similar to that of the salts in the kosmotropic end of the Hofmeister series for PNIPAm.Peer reviewe

Phase Separation of Aqueous Poly(diisopropylaminoethyl methacrylate) upon Heating

Poly(diisopropylaminoethyl methacrylate) (PDPA) is a pH- and thermally responsive water-soluble polymer. This study deepens the understanding of its phase separation behavior upon heating. Phase separation upon heating was investigated in salt solutions of varying pH and ionic strength. The effect of the counterion on the phase transition upon heating is clearly demonstrated for chloride-, phosphate-, and citrate-anions. Phase separation did not occur in pure water. The buffer solutions exhibited similar cloud points, but phase separation occurred in different pH ranges and with different mechanisms. The solution behavior of a block copolymer comprising poly(dimethylaminoethyl methacrylate) (PDMAEMA) and PDPA was investigated. Since the PDMAEMA and PDPA blocks phase separate within different pH- and temperature ranges, the block copolymer forms micelle-like structures at high temperature or pH.Poly(diisopropylaminoethyl methacrylate) (PDPA) is a pH-and thermally responsive water-soluble polymer. This study deepens theunderstanding of its phase separation behavior upon heating. Phase separationupon heating was investigated in salt solutions of varying pH and ionicstrength. The effect of the counterion on the phase transition upon heating isclearly demonstrated for chloride-, phosphate-, and citrate-anions. Phaseseparation did not occur in pure water. The buffer solutions exhibited similarcloud points, but phase separation occurred in different pH ranges and withdifferent mechanisms. The solution behavior of a block copolymer comprisingpoly(dimethylaminoethyl methacrylate) (PDMAEMA) and PDPA wasinvestigated. Since the PDMAEMA and PDPA blocks phase separate withindifferent pH- and temperature ranges, the block copolymer forms micelle-likestructures at high temperature or pHPeer reviewe

Well-dispersed clay in photopolymerized poly(ionic liquid) matrix

This contribution presents a methodology for combining the solvating power of ionic liquids with polymer composite synthesis. A polymerizable ionic liquid was used as solvent to disperse clay, after which the mixture was polymerized into a solid polymer-clay composite. Polymer-clay composites were prepared with filler load-ings up to 10 wt%. The addition of clay as filler enhanced mechanical properties; tensile strength and stiffness of the materials exhibited appreciable improvements. The glass transition temperature of the materials shifted to slightly higher temperatures due to the hindered segmental motions of the polymer chains. The improvements were the highest at approximately 5 wt% filler content. When the filler content was increased further, excessive aggregate formation impaired the material properties.Peer reviewe

Tough Materials Through Ionic Interactions

This article introduces butyl acrylate-based materials that are toughened with dynamic crosslinkers. These dynamic crosslinkers are salts where both the anion and cation polymerize. The ion pairs between the polymerized anions and cations form dynamic crosslinks that break and reform under deformation. Chemical crosslinker was used to bring shape stability. The extent of dynamic and chemical crosslinking was related to the mechanical and thermal properties of the materials. Furthermore, the dependence of the material properties on different dynamic crosslinkers-tributyl-(4-vinylbenzyl)ammonium sulfopropyl acrylate (C4ASA) and trihexyl-(4-vinylbenzyl)ammonium sulfopropyl acrylate (C6ASA)-was studied. The materials' mechanical and thermal properties were characterized by means of tensile tests, dynamic mechanical analysis, differential scanning calorimetry, and thermogravimetric analysis. The dynamic crosslinks strengthened the materials considerably. Chemical crosslinks decreased the elasticity of the materials but did not significantly affect their strength. Comparison of the two ionic crosslinkers revealed that changing the crosslinker from C4ASA to C6ASA results in more elastic, but slightly weaker materials. In conclusion, dynamic crosslinks provide substantial enhancement of mechanical properties of the materials. This is a unique approach that is utilizable for a wide variety of polymer materials.Peer reviewe

Clay Composites by In Situ Polymerization of Ionic Liquid-Based Dispersions

Flexible composite materials were prepared by in situ copolymerization of ionic liquid like monomers-namely 1-vinyl-3- ethyl imidazolium bis(trifluoromethane)sulfonimide (M1) and 1-(2-acryloyloxyundecyl)-3-methylimidazolium bis(trifluoromethane)sulfonimide (M2) that were cross-linked with 1,1 '-octane-1,8-diylbis(3-vinyl imidazolium) di[bis(trifluoromethane)sulfonimide] (CL). Mixtures of polymerizable ionic liquids were used to disperse organo-modified montmorillonite clay as a filler. Polymerization of the mixtures resulted in copolymer composites. The glass transition temperature of the composites could be tuned in the range of -2-127 degrees C by varying the ratio of the ionic liquid monomers M1 and M2, which is presented in the article for the first time along with its homopolymer. The mechanical properties were significantly enhanced by using a copolymer matrix instead of either of the respective homopolymers. The toughest M1-M2 copolymer composite exhibited a toughness of 5.3 +/- 1.4 MPa, while the toughnesses of corresponding poly(M1) and poly(M2) films were 0.6 +/- 0.2 and 0.5 +/- 0.003 MPa, respectively. The composite could be filled uniformly with large amounts of montmorillonite clay. The copolymer matrix was able to take up large amounts of clay while still exhibiting mechanical properties that surpassed the unfilled matrix.Peer reviewe

Polycation-PEG Block Copolymer Undergoes Stepwise Phase Separation in Aqueous Triflate Solution

A block copolymer poly(ethylene glycol)-b-poly(vinylbenzyltrimethylammonium triflate), PEG-PVBTMA-OTf, and a homopolymer PVBTMA-OTf were synthesized through RAFT reactions. The polymers were studied in aqueous triflate solutions with varying temperatures, changing also the polymer and salt concentrations. The hydrophobic triflate anion turns polycations thermoresponsive, and they show an UCST. In the block copolymer, the interaction between the PEG and the cationic block makes the phase separation occur in distinct steps. Upon cooling, transparent solutions first turn turbid and then partially clear at T-cL. The T-cL is not observed in a mixed solution of PVBTMA-OTf and PEG macro-CTA. By considering the interplay between ionic, hydrogen bonding, and hydrophobic interactions, an overall picture of the complex phase separation processes is suggested.Peer reviewe

Stimuli-Responsive Nanodiamond–Polyelectrolyte Composite Films

Nanodiamonds (NDs) can considerably improve the mechanical and thermal properties of polymeric composites. However, the tendency of NDs to aggregate limits the potential of these non-toxic, mechanically- and chemically-robust nanofillers. In this work, tough, flexible, and stimuli-responsive polyelectrolyte films composed of cross-linked poly(butyl acrylate-co-dimethylaminoethyl methacrylate) (P(BA-co-DMAEMA)) were prepared by photopolymerization. The effects of the added carboxylate-functionalized NDs on their mechanical and stimuli-responsive properties were studied. When the negatively charged NDs were added to the polymerization media directly, the mechanical properties of the films changed only slightly, because of the uneven distribution of the aggregated NDs in the films. In order to disperse and distribute the NDs more evenly, a prepolymerized polycation block copolymer complexing agent was used during the photopolymerization process. This approach improved the mechanical properties of the films and enhanced their thermally-induced, reversible phase-transition behavior

An enzymatic biomimetic system : enhancement of catalytic efficiency with new polymeric chiral ionic Liquids synthesised by controlled radical polymerisation

Correction to the affiliations. Mistake made by original Journal.Peer reviewe

Poly(2-propyl-2-oxazoline)s in Aqueous Methanol : To Dissolve or not to Dissolve

At room temperature, poly(N-isopropylacrylamide) (PNIPAM) is soluble in water and methanol, but it is not soluble in certain water/methanol mixtures. This phenomenon, known as cononsolvency, has been explored in great detail experimentally and theoretically in an attempt to understand the complex interactions occurring in the ternary PNIPAM/water/co-nonsolvent system. Yet little is known about the effects of the polymer structure on cononsolvency. To address this point, we investigated the temperature-dependent solution properties in water, methanol, and mixtures of the two solvents of poly(2-cyclopropyl-2-oxazoline) (PcyPOx) and two structural isomers of PNIPAM (M-n similar to 11 kg/mol): poly(2-isopropyl-2-oxazoline) (PiPOx) and poly(2-n-propyl-2-oxazoline) (PnPOx). The phase diagram of the ternary water/methanol/poly(2-propyl-2-oxazolines) (PPOx) systems, constructed based on cloud point (T-CP) measurements, revealed that PnPOx exhibits cononsolvency in water/methanol mixtures. In contrast, methanol acts as a cosolvent for PiPOx and PcyPOx in water. The enthalpy, Delta H, and temperature, T-max, of the coil-to-globule transition of the three polymers in various water/methanol mixtures were measured by high-sensitivity differential scanning calorimetry. T-max follows the same trends as T-CP, confirming the cononsolvency of PnPOx and the cosolvency of PiPOx and PcyPOx. Delta H decreases linearly as a function of the methanol content for all PPOx systems. Ancillary high-resolution H-1 NMR spectroscopy studies of PPOx solutions in D2O and methanol-d(4), coupled with DOSY and NOESY experiments revealed that the n-propyl group of PnPOx rotates freely in D2O, whereas the rotation of the isopropyl and cyclopropyl groups of PiPOx and PcyPOx, respectively, is limited due to steric restriction. This factor appears to play an important role in the case of the PPOxs/water/methanol ternary system.Peer reviewe