Abstract
Poly(sodium styrenesulfonate)–block–poly(acrylic acid) (PNaSS–b–PAA) and poly(sodium styrenesulfonate)–block–poly(N-isopropylacrylamide) (PNaSS–b–PNIPAM) were prepared via reversible addition–fragmentation chain transfer (RAFT) radical polymerization using a PNaSS-based macro-chain transfer agent. The molecular weight distributions (Mw/Mn) of PNaSS–b–PAA and PNaSS–b–PNIPAM were 1.18 and 1.39, respectively, suggesting that these polymers have controlled structures. When aqueous solutions of PNaSS–b–PAA and PNaSS–b–PNIPAM were mixed under acidic conditions, water-soluble PNaSS–b–PAA/PNaSS–b–PNIPAM complexes were formed as a result of hydrogen bonding interactions between the pendant carboxylic acids in the PAA block and the pendant amide groups in the PNIPAM block. The complex was characterized by 1H NMR, dynamic light scattering, static light scattering, and transmission electron microscope measurements. The light scattering intensity of the complex depended on the mixing ratio of PNaSS–b–PAA and PNaSS–b–PNIPAM. When the molar ratio of the N-isopropylacrylamide (NIPAM) and acrylic acid (AA) units was near unity, the light scattering intensity reached a maximum, indicating stoichiometric complex formation. The complex dissociated at a pH higher than 4.0 because the hydrogen bonding interactions disappeared due to deprotonation of the pendant carboxylic acids in the PAA block.
Highlights
Non-covalent interactions, such as hydrophobic [1], electrostatic [2,3], van der Waals [4], and hydrogen bonding interactions [5,6], can be a driving force for the complex formation of polymers.In particular, hydrogen bonding interactions are an important driving force for the self-organization of natural polymers such as polysaccharides, proteins, and deoxyribonucleic acid (DNA).It is known that hydrogen bonding interactions between amide groups or poly(ethylene glycol) (PEG)and carboxylic acid groups promote self-association or complex formation in water [7,8,9]
The DPs of the poly(acrylic acid) (PAA) and PNIPAM blocks were 125 and 115, respectively. These values were calculated from 1 H NMR peak area intensities derived from the PAA or PNIPAM block and an area derived from the PNaSS block
From the significant reduction of the motional freedom for the PNIPAM block at pH 3, one can predict that the complexes are formed from PNaSS58 –b–PAA125 and PNaSS58 –b–PNIPAM115 owing to the hydrogen bonding interactions between the pendant carboxylic acids in the PAA block and the amide groups in the PNIPAM block
Summary
Non-covalent interactions, such as hydrophobic [1], electrostatic [2,3], van der Waals [4], and hydrogen bonding interactions [5,6], can be a driving force for the complex formation of polymers. 2017, 9, 367 the hydrogen bonding interactions between the PEG block in PNaSS–b–PEG–b–PNaSS and ofthe carboxylic acids in PMA. The PNIPAM (PNaSS–b–PEG–b–PNaSS) with poly(methacrylic acid) (PMA) Both PNaSS–b–PEG–b–PNaSS and PMA blocks of PNaSS-b-PNIPAM are assumed to associate above the lower critical solution temperature were synthesized via reversible addition–fragmentation chain transfer (RAFT) radical polymerization. The experimental b–PNIPAM complexes were formed through hydrogen bonding interactions between the PAA and data indicated that the PNaSS–b–PEG–b–PNaSS/PMA complex was spherical in shape. We focused on the complex formation behavior owing to the hydrogen bonding interactions as a function of the solution temperature instead of the solution pH
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