Preparation Of PNIPA/CLAY Nanocomposite Hydrogel And Its Organic-inorganic Interaction

The thermosensitive poly(N-isopropyl acrylamide)(PNIPA)hydrogel has been widely used.Nanocomposite hydrogels are prepared by introducing nano inorganic particles into the hydrogel,which has a unique three-dimensional network structure and excellent properties.Inorganic nanoparticles are introduced into polymer matrix resulting in excellent comprehensive properties.Microscopic structure and dynamics behavior of the nanocomposites determines its macro performance,so how to clarify the effect of inorganic nanoparticles on the structure and dynamic behavior in the nanocomposites,and how to detect the organic-inorganic interface interaction and hydrogen bonding interaction on molecular level in nanocomposites are very important to the designation and preparation of polymer materials with excellent performances.In this paper,several advanced solid state NMR techniques,combined with TM-DSC and thermogravimetric analysis simulating decomposition dynamics methods to study hydrogen bonding interaction between the Clay surfaces and the polymer chains in the PNIPA/Clay nanocomposites,and the altra-elongation mechanism were investigated.The main research work is as follows:PNIPA/Clay nanocomposites with ultra-elongation properties was synthesized by situ radical polymerization,and the structure and performances were studied.The 1H MAS and 13C CPMAS,two-dimensional correlation spectroscopy(2D HETCOR),spin-lattice relaxation time experiment were used to investegated the organic-inorganic interaction mechanism in PNIPA/Clay nanocomposites.The results of 13C-1H 2D HETCOR experiments indicated that the existence of hydrogen bonding interaction between Clay surfaces and the polymer molecular chains.The results of 13C T1 experiments indicated that the motility of polymer molecular chains of PNIPA/Clay nanocomposites was lower than that of the virgin PNIPA,which shows that the movement of polymer molecular chains were limited for the introduction of the clay particles.Furthermore,the motility of polymer molecular chains of the water-containing systems were higher than that of the dry nanocomposites.That’s because the hydrogen bonding interaction between polymer chains were destroyed by the introduction of water molecules,which increased the chain mobility.Temperature-modulated differential scanning calorimetry(TM-DSC)were applied to study the thermodynamic performance and the confined dynamic behavior during the glass transition of pure PNIPA as well as PNIPA/Clay nanocomposites,respectively.The relaxation kinetics was characterized by determining the effective activation energies(E)and evaluating the sizes of cooperatively rearranging regions(Vg)during the glass transition.The values of Vg have been determined from the heat capacity(Cp)data.Thermogravimetric analysis(TGA)combined with the model-fitting methods were used to study the kinetic processes of the PNIPA/clay nanocomposite decomposition.The degradation reaction mechanism of the nanocomposites was explained by solving the degradation activation energy(E’).The glass transition emperature(Tg)of PNIPA was 139.9℃,while the values of Tg for PNIPA/Clay20 and PNIPA/Clay40 were 142.5℃ and 136.9℃,respectively.The value of E(227.6 kJ/mol)for the PNIPA/Clay20 nanocomposite was higher than that of the virgin PNIPA(168.9 kJ/mol).Moreover,the PNIPA/Clay20 nanocomposite was found to have a markedly larger value of Vg(8.23 nm3)as compared to the virgin PNIPA(3.41 nm3).The increase in E and Vg indicates an increase in molecular cooperitvity.This could be because of the generation of "hydrogen-bonded clusters"between polymer and clay sheets,which limited the segmental motion to a certain degree for the polymer chains near to the surfaces of clay sheets.However,the value of E(130.8 kJ/mol)for PNIPA/Clay40 was smaller than that of virgin PNIPA,and the value of Vg(3.54 nm3)for PNIPA/Clay40 also decreased.Furthermore,the values of E’ for PNIPA/Clay20 and PNIPA/Clay40 nanocomposite gels(105.2 kJ/mol and 108.2 kJ/mol,respectively)were lower than that of the virgin PNIPA(227.2 kJ/mol).That’s because the polymer chains were shorter with the increase of the clay content.