Ion-Specific Effects On Polymers: From Homopolymers To Copolymers

In this paper,we investigated the specific ion effects present in polymer solutions.The main research contents are as follows:(1)The study of ion specificities of charged-neutral random copolymers is of great importance for understanding specific ion effects on natural macromolecules.In the present work,we have investigated the specific anion effects on the thermoresponsive behavior of poly([2-(methacryloyloxy)ethyl trimethylammonium chloride]-co-Nisopropylacrylamide)[P(METAC-co-NIPAM)]random copolymers.Our study demonstrates that the anion specificities of the P(METAC-co-NIPAM)copolymers are dependent on their chemical compositions.The specific anion effects on the copolymers with high mole fractions of poly(N-isopropylacrylamide)(PNIPAM)are similar to those on the PNIPAM homopolymer.As the mole fraction of PNIPAM decreases to a certain value,a V-shaped anion series can be observed in terms of the anion-specific cloud point temperature of the copolymer,as induced by the interplay between different anion-polymer interactions.Our study also suggests that both the direct and the indirect anion-polymer interactions contribute to the anion specificities of the copolymers.This work would improve our understanding of the relationship between the ion specificities and the ion-macromolecule interactions for naturally occurring macromolecules.(2)We have prepared a series of statistical copolymers of poly(sulfobetaine methacrylate-co-N-isopropylacrylamide)(P(SBMA-co-NIPAM)),and have investigated the specific anion effects on these polymers.PNIPAM and PSBMA exhibit the lower critical solution temperature(LCST)and the upper critical solution temperature(UCST)behaviors in aqueous solutions,respectively.The anion binding affinity to the LCST-type polymers is dominated by the anion-NIPAM interactions,whereas the anion binding affinity to the UCST-type polymers is dominated by the anion-SBM A interactions.As the strength of interactions for the latter is significantly higher than that for the former,stronger anion specificities of the UCST-type polymers than those of the LCST-type polymers are observed at a same salt concentration.Thus,our work demonstrates that the anion binding affinity determines the strength of specific anion effects on these thermosensitive polymers.(3)We have prepared a kind of stable PSBMA cocervate droplets in aqueous solutions.As PSBMA possesses the 'anti-polyelectrolyte' behavior,the UCST property.and a good biocompatibility,we have studied the release behavior of bovine serum albumin(BSA)from PSBMA cocervate droplets under different temperatures and ionic strengths.Our results show that no significant changes in the secondary structure of BSA can be observed before and after the protein release,indicating a good biocompatible environment during the protein loading and release processes.Based on these studies,we have further investigated the specific anion effects on the release behavior of BSA from the PSBMA cocervate droplets.All in all,the studies on ion specificities from homopolymers to copolymers in this thesis will improve our understanding of the mechanisms of specific ion effects on polymers.