Polymerization-induced Self-assembly Of Block Copolymers Through Complementary Hydrogen Bonds

Stimuli-responsive polymer is a class of polymers that can change their structures by receiving external stimuli(temperature,pH,light,redox,etc.).These polymers have developed rapidly in the past few decades and have been widely used in biomedicine,smart device fabrication,and other fields.Among them,thermal-responsive polymers are a special kind of polymers because they have a critical solution temperature: lower critical solution temperature(LCST)or upper critical solution temperature(UCST),and LCST-type polymers are more common in the literature.The pH-responsive polymers are typically pyridine-containing block copolymers.Due to the pyridine structure’s various properties,such as hydrogen bond acceptors,pH sensitivity,easy functionalization,and metal ion coordination,it can self-assemble into a variety of Polymer nano-assemblies with different morphologies and highly ordered structures have broad application prospects.Herein,a novel pyridine-containing block copolymer(PEG-PMPA)based on polyethylene glycol(2000)was synthesized and utilized the complementary hydrogen bonding interaction between pyridine and amide bonds to drive PMPA chains in the block copolymer.segment extension.Through nuclear magnetic resonance spectroscopy(NMR),gel chromatography(GPC),Fourier transform infrared spectroscopy(FT-IR),ultraviolet-visible spectrophotometer(UV-Vis),transmission electron microscopy(TEM)and other characterization methods,the system the synthesis,thermodynamic properties and mechanism of polymerization-induced self-assembly of pyridine-containing monomers and polymers were studied,and the following conclusions were drawn:(1)Preparation and chemical composition analysis of new block copolymers containing pyridine: First,2-aminomethyl pyridine was used as raw material to obtain amidated pyridine polymerized monomer(MPA),and then one-end modified polyethylene glycol was synthesized.The macromolecular chain transfer agent(PEG2K-CTA)of alcohol(2000)monomethyl ether was used to prepare a series of block copolymers(PEG-PMPA)with different monomer molar ratios through PISA in aqueous phase.It was found that the relative weight-average molecular mass of PEG-PMPA was 6.6-21.5 k Da,and the relative polymerization dispersity was 1.14-1.19.By controlling the degree of block polymerization and solid content,the morphology of the assembly can be precisely regulated(spherical micelles→one-dimensional micelles→twodimensional micelles→vesicles).(2)The mechanism of PISA and the thermal response behavior of pyridine-containing block copolymers: salts can induce phase separation of the block copolymer aqueous solution,resulting in LCST.We speculate that the salt may polarize the adjacent water molecules,weaken the hydrogen bond between the water molecule and the amide,and then strengthen the intermolecular hydrogen bond between the pyridine and the amide.At the same time,we further proved the existence of complementary hydrogen bonds and their driving role in the PISA process by tests such as variable temperature infrared.(3)Study on pH responsiveness of pyridine-containing block copolymers: block copolymers have remarkable pH responsiveness,and changing the pH of the solution can not only control the dissociation and assembly of the assembly,but also precisely control the LCST of the block copolymer.