AbstractsChemistry

Solution Behavior of Responsive Cationic Polymers

by Erno Karjalainen




Institution: University of Helsinki
Department: Department of Chemistry, Laboratory of Polymer Chemistry
Year: 2015
Keywords: polymeerikemia
Record ID: 1139812
Full text PDF: http://hdl.handle.net/10138/154668


Abstract

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…