Abstract
Water-soluble copolymers of N-acryloyl-N′-ethylpiperazine (AcrNEP) with methyl methacrylate (MMA) were synthesized to high conversion by free-radical solution polymerization. The composition of the copolymers was determined using Fourier Transform Infra-red Spectroscopy (FTIR). Copolymers containing AcrNEP content above 44 mol% were readily soluble in water and exhibited the critical solution temperature behavior. The copolymers were strongly responsive to changes in pH of the external medium due to the presence of tertiary amine functions that could be protonated at low pH. The influence of various factors such as copolymer composition, pH, temperature, salt and surfactant concentration on the LCST of the copolymers were systematically studied. The intrinsic viscosity of the copolymers in dimethyl formamide decreased with increase in temperature due to a decrease in thermodynamic affinity between polymer chains and solvent molecules. The viscosity behavior of the copolymers in sodium chloride solution was similar to that of classical polyelectrolytes and hydrophobically modified polyacrylate systems.
Highlights
Water-soluble polymers that respond to external stimuli such as pH, temperature, electrolytes, illumination, electric and magnetic field are called as smart, stimuli-responsive, intelligent, or environmentally sensitive polymers [1,2,3]
These polymers are soluble in water at low temperatures but separate from solution when the temperature is raised above a certain temperature called the lower critical solution temperature (LCST)
With increase in temperature the hydrogen bonds are broken and hydrophobic interaction between the polymer chains become dominant leading to a phase separation of the polymer from the solution
Summary
Water-soluble polymers that respond to external stimuli such as pH, temperature, electrolytes, illumination, electric and magnetic field are called as smart, stimuli-responsive, intelligent, or environmentally sensitive polymers [1,2,3]. Poly(N-isopropyl acrylamide) (PNIPAM) is one of the most widely studied thermo-responsive polymer, which undergoes phase separation in water around 32 °C [6,7,8,9,10]. This polymer has both hydrophilic and hydrophobic groups. The synthesis of a ‘stimuli’-responsive piperazine-containing new copolymers is reported These copolymers are water soluble and exhibit interesting LCST behavior. The phase transition of the copolymers is sensitive to a number of factors such as monomer composition, pH, temperature, salts, and surfactants The influence of these factors is described in detail in this report
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