Manipulating Thermoresponsive Properties of Polycations in Water

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Title: Manipulating Thermoresponsive Properties of Polycations in Water
Author: Suvarli, Narmin
Contributor: University of Helsinki, Faculty of Science, Department of Chemistry
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
Thesis level: master's thesis
Abstract: This thesis reports the design and study of new series of thermoresponsive polycations with upper critical solution temperature (UCST) and lower critical solution temperature (LCST) type phase separation properties in water. The polymers were synthesized using reversible addition-fragmentation transfer polymerization process in presence of azobisisobutyronitrile (AIBN) as an initiator and 2-cyano-2-propylbenzoditionate (2-c-2-PBDT) as a chain transfer agent. Various solution properties of obtained polymers were studied. Transmittance measurements were utilized to determine the cloud point temperatures of poly[(4-vinylbenzyl)triethyl]ammonium chloride (P-VB-NEt3-Cl), poly[(4-vinylbenzyl)tripropyl]ammonium chloride (P-VB-NPr3-Cl), poly[(4-vinylbenzyl)tributyl]ammonium chloride (P-VB-NBu3-Cl) and poly[(4-vinylbenzyl)tripentyl]ammonium chloride (P-VB-NPen3-Cl) with several counterions (bis(trifluoromethane) sulfonimide, trifluoromethanesulfonate, CH3(CH2)4SO3 and CH3(CH2)11SO3) and anions belonging to Hofmeister series (Cl, NO3, SCN, H2PO4, SO4). P-VB-NEt3-Cl and P-VB-NPr3-Cl demonstrate both UCST and LCST type phase separation behavior depending on the chosen additive, whereas P-VB-NBu3-Cl and P-VB-NPen3-Cl only show LCST type phase transitions independent of the chosen anions. The phase transition temperature could be manipulated by varying the salt concentration of the polymer solutions; increasing the ionic strength causes the appearance of distinguishable transition in systems with no transition at low ionic strength. Combination of different anions in the system causes either increase or decrease of the cloud point temperature. The reversibility of the aforementioned transitions was studied and irreversibility of the transitions of polymer solutions with some anions was determined. Differential scanning calorimetry measurements were conducted to determine the enthalpy of heating of P-VB-NBu3-Cl and P-VB-NPen3-Cl with specific concentrations of counterions. Cononsolvency behaviour of P-VB-NBu3-Cl in water/DMF mixtures was studied, indicating that the turbidity occurs due to addition of either of solvents and remains regardless of temperature variation. Particle size measurements were conducted to explain the formation and behavior of particles depending on the temperature variation for P-VB-NBu3-Cl solutions with counterions.

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