Synthesis And Properties Of Helical Polystyrene Derivatives With Amino Acid Side Groups

Helical structures are ubiquitous,from plants visible to the naked eye and nebulae in the stars to microscopic DNA double-helix structures,proteins and collagen.After continuous intensive research,scientists have synthesized a series of helical polymers,with helical polystyrene being one of the research hot spots.It has been found that vinyl polymers with regular conformation can adopt a helical conformation in the crystalline or gel state.However,only very short fragments of helical conformations can exist in the solution due to the small helical conformational inversion energy barrier.It has been assumed that the formation of stable helical conformations of vinyl polymers in solution usually requires chain rigidity and spatial regularity.Interestingly,biopolymers such as polypeptides can maintain their helical conformation through hydrogen bonding,and in particular,intramolecular and intermolecular hydrogen bonding can facilitate the formation of secondary polymer structures.Thus,We have tried to prepare helical polystyrene derivatives containing amino acid side groups and investigated their properties.The primary studies are as follows.1.A series of styrene derivative monomers containing amino acid side groups were synthesized by amidation reactions,followed by reversible addition-rupture chain transfer（RAFT）polymerization to prepare polymers with controllable molecular weight and narrow molecular weight distribution.Spin,circular dichroism（CD）and UV spectra of the monomers and polymers indicated that the increase in the optical activity of the polymers was due to the asymmetric induction of chiral amide side groups,forming an excess of single-handed helical conformations.In addition,temperature,solvent polarity and side group spatial site resistance affect the helical conformation of the polymers by influencing the hydrogen bonding between adjacent repeating units.2.Block polymers with controlled molecular weight,narrow molecular weight distribution,and helical conformation were prepared by RAFT polymerization.Similarly,temperature,solvent polarity and side group space resistance affect the helical conformation of the block polymers by influencing the hydrogen bonding between adjacent repeating units.Using their amphiphilic nature,spherical micelles with helical polystyrene core layers are obtained by self-assembly in tetrahydrofuran（THF）/methanol（CH₃OH）system.In addition,atomic force microscopy（AFM）showed that the self-assembly resulted in a change in the helical conformation of the assemblies.3.Block polymer nanoparticles containing helical conformation were prepared by RAFT polymerization-induced self-assembly（PISA）.Vesicles with different nanoparticle sizes were obtained to varying ratios of the THF/CH₃OH system,while nanoparticle polystyrene with different morphologies was obtained at different polystyrene block ratios.The morphology of the assemblies changed from spherical micelles to vesicles as the degree of polymerization（Dp）of polystyrene blocks increased.In addition,AFM showed that the helical conformation of the assemblies changed for different solvent ratios and block ratios.4.Block copolymer nanoparticles containing helical conformation were prepared by cross-linking polymerization of block copolymers with ethylene glycol dimethacrylate（EDGMA）crosslinker to induce self-assembly via RAFT cross-linking polymerization.In addition to obtaining more advanced morphological vesicles,nanofibers with a tight helical conformation were obtained.