Synthesis and characterization of poly(N-isopropylacrylamide) with different initiators and the kinetics analysis of its lower critical solution temperature (LCST) behavior

• Main Authors: Ya-Ting Chang, 張雅婷
• Other Authors: Chorng-Shyan Chern
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/79192648027664350019

碩士 === 國立臺灣科技大學 === 化學工程系 === 105 === PNIPAm is a temperature-responsive polymer that undergoes a reversible lower critical solution temperature (LCST) phase transition from a swollen hydrated state to shrunken solid state. This work studied the effects of different initiators on the molecular weight and LCST of Poly(N-isopropylacrylamide) (PNIPAm). The common initiator azobisisobutyronitrile (AIBN) and sodium persulfate (SPS) which used in other polymerization systems were empolyed here. In addition , barbituric acid (BTA) also can initiate free radical polymerization with the reactive groups one >CH2 and two >NH groups in its structure. Thus, the polymerization and characterization of N-isopropylacrylamide (NIPAm) with novel initiator BTA was investigated. We also copolymerized hydrophilic and hydrophobic monomer with NIPAm respectively for adjusting the LCST behavior of PNIPAm, and find that both 2-hydroxyethyl acrylate (2-HEA) and 2-ethylhexyl acrylate (2-EHA) can decrease the LCST of PNIPAm. The LCST behavior of the aqueous solutions of polymers and copolymers was measured by differential scanning calorimetry (DSC). The technique of NMR, GPC and EPR were employed to study the reactivity of BTA. Further, non-isothermal LCST phase transition kinetics of PNIPAm was investigated by the DSC technique. The advanced isoconversional method (model-free method) can be used to determine the effective activation energy of non-isothermal sol-gel behavior of PNIPAm. The sol-gel transition process of increasing temperature involved forming PNIPAm nucleation and particle growth, and then particle shrink and aggregate simultaneously；on the other hand, the sol-gel transition of cooling PNIPAm related to form the hydrogen-bonding between H2O and PNIPAm and particle swelling and dissolution in H2O. The detail of the phase transition mechanism will show in this study .