Chain End-functionalization Of Helical Polyisocyanides And Its Application In Synthesis Of Crosslinked Porous Polyisocyanides

Inspired by the helical structure of nature,artificial helical polymers have attracted great research interest.Helical polyisocyanide is one of C1 polymers,in which each C atom in the main chain is connected with the N atom of the side group by double bond.Due to the dense side groups and the large steric hindrance of the side groups,the main chain of polyisocyanide spontaneously twists into a rigid rod-shaped helical structure.At present,polyisocyanide has been widely used in asymmetric catalysis,chiral separation,circularly polarized light and biomedicine.However,most of helical polyisocyanides are functionalized from the design of monomer structure,while synthesis of functional polyisocyanides by post polymerization modification is limited.In this thesis,a method for the preparation of functional polyisocyanide via chain end-functionalization strategy is proposed.Furthermore,benefitting from the rigid rod structure of polyisocyanide,functional porous materials were prepared by crosslinking the chain end of polyisocyanide,and their properties in iodine adsorption and chiral separation were carefully studied.The main research contents are divided into the following parts:1.The chain end-functionalization method of helical polyisocyanide was established.A family of helical polyisocyanides with controlled Mn and low polydispersity bearing a Pd(II)complex on the chain end was readily prepared via the Pd(II)-mediated living polymerization of isocyanide monomers.The ligand exchange of the Pd(II)complex with Wei-phos provides a terminal Pd(II)-complex with high activity,which can promote the Sonogashira coupling reaction with many terminal alkyne derivatives.Taking advantage of this method,a series of interesting functional groups can be facilely installed onto the end of helical polyisocyanides.Moreover,a couple of hybrid block copolymers can also be obtained via the Sonogashira coupling reaction of the Pd(II)-terminated helical polyisocyanides with different functional polymers.This method can not only install interesting functionalities onto the chain end of helical polyisocyanides but also remove the transition metal residue simultaneously facilely.2.A precision synthesis of helical polyisocyanide-b-polyaryl alkyne block copolymer was developed.The controlled synthesis ofπ-conjugated polyisocyanide-b-polyphenyleneethylene(PPI-b-PPE)copolymers via chain extension of ethynyl 4-iodobenzene initiated by Pd(II)-terminated helical polyisocyanide(PPI).The results showed that the copolymerization reaction was also a living polymerization with controllable Mn.A series of block copolymers with different components,different Mn,and narrow Mw/Mn can be obtained.It is also found that in-situgenerated block copolymers self-assembled into various supramolecular in THF architectures depending on the PPE length.The helical PPI segment induced the block copolymers with an appropriate PPE length self-assemble into helical nanofibers with a controlled size and defined helicity.Interestingly,the chiral assemblies of the block copolymers exhibit intense optical activity and emit clear circularly polarized luminescence.3.The controllable synthesis of cross-linked porous polymers was realized by using polyisocyanide chain end-functionalization strategy.First,tetrahedral four-arm star polyisocyanides with predictable molecular weight and low dispersity were synthesized by four arm alkyne-Pd(II)catalyst.Then,the chain end of polyisocyanide was crosslinked by the chain end-functionalization technology,yielding well-defined porous organic frameworks with a designed pore size and narrow distribution.It was found that porous polymers of appropriate pore size were observed to efficiently capture radioactive iodine in both aqueous and vapor phases.More than 98%of iodine could be captured within 1minute from a saturated aqueous solution(capacity of up to 3.2 g g~-1),and an adsorption capacity of up to 574 wt%of iodine in vapor was measured within 4 hours.Moreover,the polymers could be recovered and recycled for iodine capture for at least six times,while maintaining high performance.4.With rigid helical polyisocyanide as the backbone,chiral separation materials were fabricated.Firstly,ABA-type triblock copolymer was synthesized by living polymerization of isocyanide monomers,in which A segment could be crosslinked by crosslinking agent.The obtained cross-linked polymer was porous,and its pore size could be adjusted by changing the chain length of the B segment.When the B block was with a single chiral helical structure,the porous polymer was optically active and presented excellent performance in chiral separation for a variety of racemic compounds.What’s more,it could also adsorb organic dyes efficiently in aqueous phase.