Effects of end groups on the thermal response of poly(N‐isopropylacrylamide) microgels

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) microgels were prepared through soap-free emulsion polymerization using 2, 2 0 -azobisobutyronitrile and potassium persulfate as initiator respectively. The thermal response of microgels was researched by measuring the transmittance and the hydrodynamic diameter of the microgels at different temperatures. The result shows that the different structure of the end groups of polymer that come from residues of initiator result in the different thermal response of PNIPAM microgels. The LCST (lower critical solution temperature) of AIBN-initiator microgels is 5 C lower than that of the KPS-initiator microgels, whereas the AIBN-initiated PNIPAM microgels have better thermal response sensitivity. The scanning electron microscope characterization shows that the morphology of AIBN-initiated PNIPAM microgels is more regular than that of KPS-initiated. Furthermore, the T g of the microgels was measured by differential scanning calorimeter and the result indicates that the end groups influences the T g of microgels severely. This work demonstrated that the hydrophobic end group coming from initiators can decreases the LCST of PNIPAM microgels and increases the thermal response sensitivity, which providing a newly simple but effective method to regulate the thermal response of PNIPAM microgels.

Lower critical solution temperature sensitivity to structural changes in poly(N‐isopropyl acrylamide) homopolymers

“…The poly( N ‐isopropyl acrylamide) (PNIPAM) is one of the most investigated thermoresponsive polymers due to its unique features, sharp LCST, reversible and close to physiological body temperature (around 33 °C) . In addition, its LCST behavior can be modulated by different methods, which can be classified depending on adjusting the molecular features or/and the use of external agents, such as addition of additives or diverse solvents .…”

“…The first one can easily be achieved by the synthetic route, which defines the molecular characteristics of the polymer, such as polymerization degree, polydispersity, and the end‐group effect. These molecular features will affect, and partially define, the final LCST behavior, as well as other parameters such as tacticity, addition of monomers, or postmodification of structures …”

Thermoresponsive poly(γ‐propyl‐l‐glutamate)‐graft‐(oligo ethylene glycol)s: Synthesis, characterization, and properties

“…Thermoresponsive polymers are a class of polymers which undergo a solution phase transition on temperature variations . They have been extensively studied for their potential applications as biomedical materials, including thermoresponsive nanoparticles and hydrogels, and also in enhanced oil recovery . Most known examples of thermoresponsive polymers with solution phase transition temperatures (i.e., cloud point temperatures) are poly( N ‐isopropylacrylamide) (PNIPAM), poly( N , N ‐diethylacrylamide), polyethers and poly(2‐oxazoline)s .…”

RAFT preparation and the aqueous self-assembly of amphiphilic poly(octadecyl acrylate)- block -poly(polyethylene glycol methyl ether acrylate) copolymers

“…The presence of the RAFT end-group had a more significant effect on the CAC value for the amphiphilic brush diblock copolymers with a larger hydrophobic domain (i.e., 10 P(ODA) units on average), where the hydrophobic domain contributed approximately 20% of the polymer mass, compared with those with a smaller hydrophobic domain (i.e., 6 P(ODA) units on average) where the hydrophobic domain contributed approximately 10% (i.e., a tenth) of the polymer mass, as the CACs post-reduction varied only with the copolymer series with 10 P(ODA) units on average. In this case, P(ODA) 10 -b-P(PEGA-OMe) 23 The presence of RAFT end-groups has also been reported to affect the self-assembly behaviour of poly(N-isopropylacrylamide) (PNIPAM) [76,[83][84][85][86]. PNIPAM is a thermo-sensitive polymer commonly used to form hydrogels, which exhibits a phase transition at the lower critical solution temperature (LCST) around 32 • C. The LCST was reported to be influenced by the presence of additives, secondary copolymerisation monomer and modification of the end-group of the polymer chain [68][69][70][71].…”