The double thermosensitive and narrow dispersed PNIPAm110-PEO100-PPO65-PEO100-PNIPAm110 pentablock terpolymer was synthesized by the typical atomic transfer radical polymerization (ATRP) method with N-isopropylacrylamide (NIPAm) as the monomer and modified poly(ethylene oxide)100−poly(propylene oxide)65−poly(ethylene oxide)100 (PEO100-PPO65-PEO100) block copolymer as the macroinitiator. Microdifferential scanning calorimetry (micro-DSC) data showed that the pentablock terpolymer exhibited two low critical solution temperatures (LCSTs) at 31 and 34 °C in the aqueous solution, which can be attributed to the thermal phase transition of the PPO block and PNIPAm block, respectively. The chain conformation of the pentablock terpolymer in aqueous solution was then studied in detail by using a combination of static and dynamic laser light scattering (SLS-DLS). The SLS-DLS results indicated that the loose “associates” and single coil chains coexisted in the aqueous solution at the low temperature, where the PEO, PPO, and PNIPAm blocks were soluble in water. These phenomena were inconsistent with those observed in other PEO-containing block copolymer systems. At the high temperature above the LCSTs of PPO and PNIPAm blocks (38−60 °C), the pentablock terplymer chains formed large and stable core−shell micelles with collapsed PPO and PNIPAm cores and swollen PEO shells. The TEM and cryo-TEM experiments provided visual images, which confirmed the formation of loose “associates” at 21 °C and large stable micelles at 38 °C. Increase of concentration hindered the formation of “associate” at low temperature, but the micelles formed at high temperature were almost independent of the solution concentration investigated.

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.

Hollow silica nanospheres with mesoporous shells were successfully fabricated with a new one-pot strategy by using a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAm), as a reversible template without the need of further calcination or chemical etching. By simply regulating the solution temperature with respect to the lower critical solution temperature (LCST) of PNIPAm, PNIPAm chains can reversibly form aggregates or dissolve in aqueous solution. The thermosensitive character makes PNIPAm chains behave as soft templates for the formation of core-shell silica nanospheres at elevated temperature (>LCST), and they will then diffuse out of the cores at lower temperature (

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Three PLA x -PEG 44 diblock copolymers with fixed hydrophilic PEG block and various lengths of hydrophobic PLA block were synthesized via ring-opening polymerization. The micelle formation and micelle morphologies of the PLA x -PEG 44 copolymers in selective solvents were investigated by using cryogenic transmission electron microscopy (cryo-TEM) and light scattering techniques. PLA x -PEG 44 diblock copolymers in aqueous solution form various micelle structures when increasing x from 56 to 212 in order to minimize the overall free energy of the systems. The micelles transform from wormlike micelles for PLA 56 -PEG 44 into vesicles for PLA 212 -PEG 44 . Interestingly, vesicular structures with various morphologies, such as large polydisperse vesicles, entrapped vesicles, hollow concentric vesicles, ellipsoidal vesicles, open bending lamellae, vesicles with irregular shapes, etc., were found to be coexisting in PLA 212 -PEG 44 THF/H 2 O and PLA 212 -PEG 44 dioxane/H 2 O mixtures with 30 and 40 wt % water contents. Toroid micelles with new morphologies were also observed. These observations indicate that the vesicular micelles of amphiphilic block copolymers in mixed solvents fluctuate from time to time and are able to kinetically form different shapes of morphologies in the solutions. The membrane fluctuation of PLA 212 -PEG 44 vesicles in mixed solvent was verified by dynamic light scattering.