Recent Advances in Helical Polyisocyanide-based Block Copolymers:Preparation,Self-assembly and Circularly Polarized Luminescence

Polyisocyanides and their block copolymers have widespread applications in many fields due to their unique helix and self-assembly properties.At first,the latest progress in the preparation of helical polyisocyanide-based block copolymers via the method of one-pot sequential controlled synthesis and stepwise polymerization was highlighted in this minireview.Various categories of helical polyisocyanide-based copolymers including amphiphilic block copolymers,UV-response block copolymers,π-conjugated block copolymers,etc.,have been prepared successfully.Moreover,recent advances in the self-assembly and circularly polarized luminescence performance of amphiphilic andπ-conjugated helical polyisocyanide-based copolymers have been introduced,respectively.We hope this minireview will not only inspire more interest in developing helical polyisocyanide-based copolymers,but also encourage further progress in the field of building artificial functional materials.

Optically Active Helical Polyisocyanides Bearing Chiral Phosphine Pendants: Facile Synthesis and Application in Enantioselective Rauhut-Currier Reaction

Three novel enantiopure phenyl isocyanide monomers with BH3-protected phosphine functional group were designed and synthesized. Polymerization of these monomers using a alkyne-Pd（II） complex as a catalyst led to the formation of respective helical polyisocyanides in high yields with controlled molecular weights（Mns） and narrow molecular weight distributions（Mw/Mns）. Removing the protecting BH3 groups afforded helical poly（phenyl isocyanide）s bearing phosphine pendants. Thanks to the chiral induction of monomer, the isolated helical polyisocyanides showed high optical activity, as revealed by circular dichroism（CD） and absorption spectroscopies and polarimetry. The helical structures of these polymers were quite stable in various organic solvents with different polarities and in a wide temperature range. Moreover, these helical polymers could be used as organocatalysts and showed good performance in enantioselective cross Rauhut-Currier reaction. The enantiomeric excess（ee） values of the isolated products of cross Rauhut-Currier reaction could be up to 90%. The polymer organocatalysts could be easily recovered from the reaction mixtures and reused at least five times in the reaction without significant loss of their enantioselectivities and catalytic activities.

Controlling the gelation temperature of biomimetic polyisocyanides

Thermosensitive polymers show an entropy-driven transition from a well-solvated to a poorly solvated polymer chain, resulting in a more compact globular conformation. The transition at the lower critical solution temperature（LCST） is often sharp, which allows for a wide range of smart material applications.At the LCST, oligo（ethylene glycol）-substituted polyisocyanides（PICs） form soft hydrogels, composed of polymer bundles similar to biological gels, such as actin, fibrin and intermediate filaments. Here, we show that the LCST of PICs strongly depends linearly on the length of the ethylene glycol（EG） tails; every EG group increases the LCSTand thus the gelation temperature by nearly 30 ℃. Using a copolymerisation approach, we demonstrate that we can precisely tailor the gelation temperature between 10 ℃ and 60 ℃and, consequently, tune the mechanical properties of the PIC gels.

Polythiophene-block-poly(phenyl isocyanide) Copolymers: One-pot Synthesis, Properties and Applications

Conjugated block copolymers have gained increasing interests in recent years. Development of a novel method for facile synthesis of conjugated block copolymers with desired structures and functions is greatly desired. In this mini review, we summarized the recent advances in one-pot synthesis of conjugated block copolymers containing π-conjugated polythiophene and helical polyisocyanide segments by using a nickel（Ⅱ） complex as single catalyst. The sequential living polymerization of the two monomers proceeded in a controlled manner, affording expected block copolymers in high yields with controlled molecular weights（Mns） and narrow molecular weight distributions（Mw/Mns）. By using this method, a family of block copolymers with expected structure and tunable compositions can be facilely prepared. Introducing functional groups onto the pendant, these block copolymers can exhibit interesting self-assembly property, tunable light emission and multi-responsiveness.

Halogen effects on phenylethynyl palladium(Ⅱ) complexes for living polymerization of isocyanides: a combined experimental and computational investigation

Phenylethynyl palladium(Ⅱ) complexes have proven to be effective catalysts for coordination polymerization of isocyanides. In this work, two new phenylethynyl palladium(Ⅱ) initiators bearing bromide(1b) and iodide(1c) were synthesized and applied for living polymerization of aryl and alkyl isocyanides. The coordinated halogen anions can significantly influence the kinetics of polymerization, with the observed order of reaction rates being 1c(Ⅰ)>1 b(Br)>1a(Cl). Impressively, 1c not only accelerates the reaction rate in both the initiation stage and propagation stage, but also can polymerize less active monomers that cannot be reacted by 1a. DFT calculations were then employed to understand the detailed mechanism and the halogen effects in this insertion polymerization process.

Enantiomer-selective Living Polymerization of rac-Phenyl Isocyanide Using Chiral Palladium Catalyst

We report the polymerization of phenyl isocyanides with the chiral palladium（II） initiating system. The resulting polymers with optically active properties were obtained by polymerization of the racemic isocyanide monomer （rac-1）, and enantiomerically unbalanced polymerization of the monomer was found, providing substantial evidence for the enantiomer-selective polymerization of rac- 1 mediated through chiral catalyst. A comparison between the enantiomerically pure monomers, 4-isocyanobenzoyl-L-alanine decyl ester （1 s） and 4-isocyanobenzoyl-D-alanine decyl ester （1 r）, revealed a drastic discrepancy in the reactivity ratio of their homopolymerizations. It turned out that the monomer reactivity ratio of ls was higher than that of lr with chiral ligands. The results clearly demonstrated the inclination for incorporation of the ls enantiomer during the polymerization process and thus resulted in the enantiomer-selective polymerization in this system. The effects of the catalyst chirality on the optically active properties of polymerization were investigated, and it was concluded that the formation of higher-ordered conformation with a handed helicity might be attributed to the chiral induction of chiral palladium（II） catalyst. Moreover, the polymers obtained through the enantiomer-selective polymerization of the enantiomerically pure monomer were with a significant improvement of the optical activity if the chirality of the monomer and the catalyst matched with each other.

Chiral Recognition and Resolution Based on Helical Polymers

Helical polymers have attracted a great deal of attention and been extensively investigated due to their various applications.One of the most importa nt applicati ons of helical polymers is chiral recog nition and resolutio n ofe nan tiomersforthe reas on that a pair of e nan tiomers is comm only with differe nt physiological and toxicological behaviors in biological systems.Helical polymers usually prese nt un expected high chiral recogniti on ability to a variety of racemic compo unds.Whatzs more,the chiral recog nition and resolution abilities of the system are depe ndent on the highly ordered helical structures of the helical polymers.This mini review mainly focuses on the recent progress in chiral recognition and resolution based on helical polymers.The synthetic methodology for helical polymers is firstly discussed briefly.Then recent advances of chiral recog nition and resoluti on systems based on helical polymers,especially polyacetylenes and polyisocya nides,are described.We hope this mini review will in spire more in terest in developing helical polymers and en courage further advances in chiral-related disciplines.

Cell-matrix reciprocity in 3D culture models with nonlinear elasticity

Three-dimensional(3D)matrix models using hydrogels are powerful tools to understand and predict cell behavior.The interactions between the cell and its matrix,however is highly complex:the matrix has a profound effect on basic cell functions but simultaneously,cells are able to actively manipulate the matrix properties.This(mechano)reciprocity between cells and the extracellular matrix(ECM)is central in regulating tissue functions and it is fundamentally important to broadly consider the biomechanical properties of the in vivo ECM when designing in vitro matrix models.This manuscript discusses two commonly used biopolymer networks,i.e.collagen and fibrin gels,and one synthetic polymer network,polyisocyanide gel(PIC),which all possess the characteristic nonlinear mechanics in the biological stress regime.We start from the structure of the materials,then address the uses,advantages,and limitations of each material,to provide a guideline for tissue engineers and biophysicists in utilizing current materials and also designing new materials for 3D cell culture purposes.