The solution behaviors and microstructures of poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) pentablock terpolymers with various PNIPAm block lengths in dilute and concentrated aqueous solutions were investigated by micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and synchrotron small angle X-ray scattering (SAXS). Two lower critical solution temperatures (LCSTs) were observed for PNIPAmx-P123-PNIPAmx pentablock terpolymers in dilute solutions, which corresponded to LCSTs of PPO and PNIPAm blocks, respectively. The LCST of PPO block shifted from 24.4 °C to 29 °C when the length x of PNIPAm block increased from 10 to 97. The LCST of PNIPAm is around 34.5 °C-35.3 °C and less dependent on the block length x. The PNIPAmx-P123-PNIPAmx pentablock terpolymers formed "associate" structures and micelles with hydrophobic PNIPAm and PPO blocks as cores and soluble PEO blocks as coronas in dilute aqueous solutions at 20 °C and 40 °C, respectively, regardless of the relative lengths of PNIPAm, PPO and PEO blocks. The size of "associate" structures of PNIPAmx-P123-PNIPAmx pentablock terpolymers at 20 °C increased with increasing the length of PNIPAm block. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels formed in concentrated aqueous solutions (40 wt%) were strongly dependent on the environmental temperatures and relative lengths of PNIPAm, PPO and PEO blocks as revealed by SAXS. Increasing the length of PNIPAm block weakened the order structures of PNIPAmx-P123-PNIPAmx hydrogels. The microstructures of PNIPAmx-P123-PNIPAmx hydrogels changed from mixed fcc and hex structures for PNIPAm10-P123-PNIPAm10 to isotropic structure for PNIPAm97-P123-PNIPAm97. Increasing temperature led to the transition from mixed hex and fcc structure to pure hex structure for PNIPAm10-P123-PNIPAm10 hydrogel at temperature above the LCSTs.

The chain conformations and adsorption behaviors of four thermo-sensitive poly(N-isopropylacrylamide)x-poly(propylene oxide)36-poly(N-isopropylacrylamide)x (PNIPAmx-PPO36-PNIPAmx) triblock copolymers with x values of 15, 33, 75, and 117 in dilute aqueous solutions were investigated by combined techniques of micro-differential scanning calorimetry (micro-DSC), static and dynamic light scattering (SLS & DLS), and the quartz crystal microbalance (QCM). PNIPAm15-PPO36-PNIPAm15 only exhibited the lower critical solution temperature (LCST) of the PPO block, i.e. 25 °C, because the PNIPAm block with x = 15 was too short to maintain its own LCST. With middle lengths x of 33 and 75, the LCSTs of PPO and PNIPAm blocks were observed, respectively. For the longest PNIPAm block with x = 117, only LCST of PNIPAm block dominated, i.e. 32.3 °C. DLS results revealed that the four PNIPAmx-PPO36-PNIPAmx triblock copolymers formed "associate" structures in their dilute aqueous solutions at 20 °C, which was well below the LCSTs of the PPO and PNIPAm blocks. QCM results indicated that the adsorption time constant decreased with increasing adsorption temperature but tended to increase with increasing length x of the PNIPAm block. A complex adsorption behavior with large adsorption amounts was only observed at the corresponding LCST of the PNIPAm block for PNIPAmx-PPO36-PNIPAmx with longer PNIPAm blocks with x = 33, 75, and 117. Furthermore, the adsorbed PNIPAmx-PPO36-PNIPAmx layers obtained at 20 °C were rigid with less energy dissipation.

The effects of concentration, relative block length and environmental temperature as well as the surface chemical and wetting properties of solid substrates on the adsorption behaviors and mechanisms of a series of pentablock terpolymer poly(N-isopropylacrylamide)x-poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20-poly(N-isopropylacrylamide)x (PNIPAmx-PEO20-PPO70-PEO20-PNIPAmx or PNIPAmx-P123-PNIPAmx) with x of 10, 63 and 97 on gold were studied by using a quartz crystal microbalance (QCM) technique. It was found that increasing the solution concentration did not alter the adsorption mechanism of thickness growth mode but increase the adsorption amount of PNIPAm97-P123-PNIPAm97 on a bare gold substrate at 20 °C. Increasing the length x of PNIPAm block decreased the adsorption rate constant and shifted the adsorption mechanism from the densification adsorption process for PNIPAm10-P123-PNIPAm10 to the thickness growth mode for PNIPAm63-P123-PNIPAm63 and PNIPAm97-P123-PNIPAm97 on bare (unmodified) gold substrate at 20 °C. The adsorption mechanisms of PNIPAm97-P123-PNIPAm97 at 20 °C on the hydrophobic and hydrophilic gold surfaces were the thickness growth mode and densification adsorption process, respectively. A complex adsorption behavior with large adsorption amounts was observed at the lower critical solution temperature (LCST) of PNIPAm block, i.e. 34.7 °C, for the adsorption of PNIPAm97-P123-PNIPAm97 not only on hydrophobic gold substrates but also on hydrophilic gold substrates. The adsorption mechanism of PNIPAm97-P123-PNIPAm97 micelles at 45 °C was the densification adsorption process regardless of the surface wetting and chemical properties of gold substrate. Overall, the adsorption behavior and mechanism of PNIPAmx-P123-PNIPAmx pentablock terpolymers were mainly determined by the interactions of the pentablock terpolymers with different chain conformations in dilute aqueous solutions at various temperatures and the gold substrates with surface wetting and chemical properties.