Macromolecular Chemistry and Physics
Macromolecular Chemistry and Physics
5 years ago

Unexpected Large Depression of VPTT of a PNIPAM Microgel by Low Concentration of PVA

Unexpected Large Depression of VPTT of a PNIPAM Microgel by Low Concentration of PVA
Yongjun Zhang, Zhuo Tang, Ying Guan, Junying Weng
Many low molecular weight and polymeric additives are found to be able to shift the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM), however, a large change can only be observed at a high concentration of the additive. Particularly, poly(vinyl alcohol) (PVA), a polymeric additive, can only induce a very small change in the phase transition temperature of PNIPAM, even at a high concentration. Unexpectedly, it is found that a low concentration of PVA can dramatically reduce the volume phase transition temperature (VPTT) of the surface layer of poly(N-isopropylacrylamide-co-2-acrylamido-phenylboronic acid) (P(NIPAM-2-AAPBA)) microgel. The concentration of PVA is about three orders of magnitude lower than the required concentration for other additives to achieve a comparable decrease in phase transition temperature of PNIPAM. The lowered VPTT cannot be explained by a change in the ionization degree of the PBA groups, or cross-link density, or hydrophilicity–hydrophobicity balance of the gel. Instead, it is proposed that the adsorption of PVA chains onto the P(NIPAM-2-AAPBA) microgel spheres shortens the distance between the PVA and PNIPAM chains, allowing they influence the thermal behavior of PNIPAM more effectively and hence dramatically reducing the phase transition temperature of the latter. A low concentration of poly(vinyl alcohol) (PVA) can dramatically reduce the volume phase transition temperature of the surface layer of poly(N-isopropylacrylamide-co-2-acrylamido-phenylboronic acid) (P(NIPAM-2-AAPBA)) microgel. The adsorption of PVA chains onto the P(NIPAM-2-AAPBA) microgel spheres shortens the distance between the PVA and PNIPAM chains, allowing they influence the thermal behavior of PNIPAM more effectively and hence dramatically reducing the phase transition temperature of the latter.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/macp.201700364

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