Search

A facile method to prepare a self-healing polymeric material with tunable mechanical properties is developed. The material has a remarkable self-healing efficiency via the formation of multiple dynamic hydrogen bonds. It can resist the corrosion of various organic solvents and can also be readily processed into a range of shapes. [ABSTRACT FROM AUTHOR]

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.

By choosing poly(N,N-diethylacrylamide) which lacks the possibility to form intra- or inter-chain hydrogen bonds, we studied its chain association and dissociation in water by using laser light scattering (LLS), ultrasensitive differential scanning calorimetry (US-DSC) and Fourier transform infrared spectroscopy (FTIR). As the solution temperature increases, the average hydrodynamic radius (R(h)) and average radius of gyration (R(g)) decrease, indicating the intrachain shrinking. When the temperature is higher than its lower critical solution temperature (LCST, approximately 30 degrees C), the apparent weight-average molar mass (M(w,app)) increases, reflecting the interchain association. At the same time, FTIR study reveals that as the temperature increases, the area ratio of two absorption peaks, respectively, associated to one hydrogen bonded carbonyl >C=O...H-O-H and free carbonyl >C=O groups increases, while that related to two hydrated hydrogen bonded carbonyl groups decreases, indicating heating-induced dehydration. In the reversible cooling process, R(h), R(g), M(w,app) and area ratios of the absorption peak are similar to those in the heating process for each given temperature, indicating that there is no hysteresis in the interchain association and dissociation. This present study confirms that the hysteresis previously observed for a sister polymer, poly(N-isopropylacrylamide), is due to the formation of some additional hydrogen bonds in its collapsed state at temperatures higher than the LCST.