Living Crystallization-Driven Self-Assembly of Oligo(p-phenylene vinylene)-Containing Block Copolymers:Impact of Branched Structure of Alkyl Side Chain ofπ-Conjugated Segment

The structure of side chains ofπ-conjugated segments is a critical factor determining living crystallization-driven self-assembly(CDSA),a versatile platform to generate fiber-like nanostructures with precise length and composition.Herein,we design and synthesize three block copolymers(BCPs)containing same corona-forming poly(N-isopropyl acrylamide)(PNIPAM)segment,but different core-formingπ-conjugated oligo(p-phenylene vinylene)(OPV)with linear pentyl(l-OPV),racemic 2-methyl butyl(r-OPV)and stereo-regular chiral(S)-2-methyl butyl(c-OPV)side chains,respectively.By using these BCPs of l-OPV-b-PNIPAM_(47),r-OPV-b-PNIPAM_(47)and c-OPV-b-PNIPAM_(47)as model,we aim to get a deep insight into how steric and stereo-regular effect induced by branched alkyl side chains of OPV segment affects the living CDSA.The results showed that l-OPV-b-PNIPAM_(47)exhibits typical characteristics of self-seeding and seeded growth of living CDSA to give uniform fiber-like micelles of controlled length.On the contrary,r-OPV-b-PNIPAM_(47)and c-OPV-b-PNIPAM_(47)with branched racemic and stereo-regular chiral alkyl side chains are more prone to self-nucleation during the micellar elongation to give short and polydisperse fiber-like micelles.The obvious selfnucleation during the micellar elongation of r-OPV-b-PNIPAM_(47)and c-OPV-b-PNIPAM_(47)is due to the increase of steric repulsion with OPV units induced by branched alkyl side chains,not the stereo-irregular effect of racemic alkyl side chains.

Crystallization-driven Self-assembly of Isotactic Polystyrene in N,N-Dimethylformamide

Herein we demonstrate crystallization-driven self-assembly ofisotactic polystyrene （iPS） with high isotacticity and narrow molecular weight distribution and crystallization-induced switching of the morphology of iPS aggregates in N, N-dimethylformamide （DMF）. The formation and morphology switching of the self-assembled aggregates of iPS are investigated by means of dynamic light scattering （DLS）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC） and wide angle X-ray diffraction （WXRD）. The results reveal that cooling DMF solution of iPS promotes iPS chains to self-assemble into spherical aggregates with a gelled core cross-linked by microcrystals, which is surrounded by solvent-swollen corona. Furthermore, crystallization induces the deformation of iPS aggregates from spherical to plate-like or nest-like.

Preparation and cellular uptake behaviors of uniform fiber-like micelles with length controllability and high colloidal stability in aqueous media

Fragmentation/disassembly of fiber-like micelles generated by living crystalline-driven self-assembly(CDSA)is usually encountered in aqueous media,which hinders the applications of micelles.Herein,we report the generation of uniform fiber-like micelles consisting of a𝜋Л-conjugated oligo(p-phenylenevinylene)core and a crosslinking silica shell with grafted poly(ethylene glycol)(PEG)chains by the combination of living CDSA,silica chemistry and surface grafting-onto strategy.Owing to the presence of crosslinking silica shell and the outmost PEG chains,the resulting micelles exhibit excellent dispersity and colloidal stability in PBS buffer,BSA aqueous solution and upon heating at 80℃ for 2 h without micellar fragmentation/disassembly.The micelles also show negligible cytotoxicity toward both HeLa cervical cancer and HEK239T human embryonic kidney cell lines.Interestingly,micelles with Ln of 156 nm show the“stealth”property with no significant uptake by HeLa cells,whereas some certain amounts of micelles with Ln of 535 nm can penetrate into HeLa cells,showing length-dependent cellular uptake behaviors.These results provide a route to prepare uniform,colloidally stable fiber-like nanostructures with tunable length and functions derived for biomedical applications.