Preparing cyclic polymers at high concentrations via self-folding cyclization technique by adjusting the contents of hydrophilic units in linear precursors

Cyclic polymers are a class of polymers that feature endless topology,and the synthesis of cyclic polymers has attracted the attention of many researchers.Herein,cyclic polymers were efficiently constructed by self-folding cyclization technique at high concentrations.Linear poly((oligo(ethylene glycol)acrylate)-co-(dodecyl acrylate))(P(OEGA-co-DDA))precursors with different ratios of hydrophilic and hydrophobic moieties were synthesized by reversible addition-fragmentation chain transfer(RAFT)polymerization using a bifunctional chain transfer agent with two anthryl end groups.The amphiphilic linear precursors underwent the self-folding process to generate polymeric nanoparticles in water.By irradiating the aqueous solution of the nanoparticles with 365 nm UV light,cyclic polymers were synthesized successfully via coupling of anthryl groups.The effects of the ratios of hydrophilic and hydrophobic moieties in linear P(OEGA-co-DDA)copolymers and polymer concentration on the purity of the obtained cyclic polymers were explored in detail via ^(1)H nuclear magnetic resonance(^(1)H NMR),dynamic light scattering(DLS),UV‒visible(vis)analysis,three-detection size exclusion chromatography(TD-SEC)and transmission electron microscopy(TEM).It was found that by adjusting the content of the hydrophilic segments in linear precursors,single chain polymeric nanoparticles(SCPNs)can be generated at high polymer concentrations.Therefore,cyclic polymers with high purity can be constructed efficiently.This method overcomes the limitation of traditional ring-closure method,which is typically conducted in highly dilute conditions,providing an efficient method for the scalable preparation of cyclic polymers.

Scalable preparation and direct visualization of cyclic polymers via self-folding cyclization technique

Cyclic polymers exhibit distinct properties compared with their linear counterparts due to the lack of chain ends.However,the scalable synthesis of cyclic polymers remains a major challenge,especially for ring-closure method.Herein,we report a novel strategy for large-scale preparation of cyclic polymers,which relies on the prior self-folding of anthracene-telechelic amphiphilic random copolymers(poly((oligo(ethylene glycol)acrylate)-co-(dodecyl acrylate)),P(OEGA-co-DDA))into single-chain polymeric nanoparticles(SCPNs)in water.Subsequent ultraviolet(UV)-induced cyclization occurs in the hydrophobic nano-domain.The formation of SCPNs leads to a shortened distance between the end groups of the linear precursors and spatially separated cyclization loci,and significantly enhances the efficiency of UV-induced cyclization.This self-folding technique permits access to the synthesis of cyclic polymers not only with high molecular weights(M_(n)>10^(5) g/mol),but also in a decent scale(40 g/L),breaking through the limitations of ring-closure method.Furthermore,the dense pendants of the copolymers can magnify the macromolecules by increasing the mass density along the backbones,thus making the polymers more readily detectable by the microscopy.The transmission electron microscopy(TEM)and atomic force microscopy(AFM)images allow us to observe the topological structures directly and provide crucial evidence to confirm the cyclization.

Synthesis and Pyrolysis of Soluble Cyclic Hf-Schiff Base Polymers

Soluble Hf-containing polymers are significant processable precursors for the fabrication of ultra-high temperature ceramics.In this work,cyclic Hf-Schiff base polymers were synthesized via direct polymerization of hafnium alkoxide and bis-salen monomers.The defined structure and molecular weight of the polymers were characterized by NMR spectroscopy,gel permeation chromatography and MALDI-TOF mass spectroscopy.The feed ratio of monomers regulated the molecular weight and solubility of the polymers.This synthetic strategy features simple operation under ambient conditions,efficient reaction with high yield and cyclic polymers as the main products.The Hf-Schiff base polymers were converted to HfC/C materials after pyrolysis under argon at 1600°C,which was identified by XRD measurements,elemental analyses and Raman spectroscopy.This work will inspire more precise and efficient synthesis and applications of metallopolymers.

Synthesis of High Performance Cyclic Olefin Polymers Using Highly Efficient WCl6-based Catalyst System

Cyclic olefin polymers（COPs） with high glass transition temperature, high transparency（higher than 80%） in the visible light range, excellent thermal stability and outstanding mechanical properties have been synthesized by effective ring opening metathesis polymerization（ROMP） of exo-1,4,4 a,9,9 a,10-hexahydro-9,10（1′,2′）-benzeno-l,4-methanoanthracene（HBM） and dicyclopentadiene（DCPD） or norbornene（NBE） using WCl6/i-Bu3Al/ethanol/1-hexene catalyst system, followed by hydrogenation of double bonds. 1-Hexene acted as a molecular weight controller in the polymerization reaction, tuning the number-average molecular weight（Mn） of P-HBM from 5.8 × 10^4 to 41.1 × 10^4. The monomer composition and thermal properties of the copolymers were characterized by nuclear magnetic resonance（NMR）, differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA）. The saturated polymers exhibited high decomposition temperatures（Td） around 340 ℃ and glass transition temperatures（Tg） in the range from 117.5 ℃ to 219.7 ℃. What is more, tensile tests indicated that the mechanical properties of the COPs could be effectively tuned in a wide range by introducing varying amount of small cyclic olefin such as DCPD or NBE.

One-step synthesis of cyclic polypyrazole and the self-assembly vesicles driven by hydrogen bond

The synthesis of cyclic polymer is an important topic in polymer chemistry. Herein, we report a one-step method to prepare cyclic polypyrazoles. Monomers with two functional groups, diazo and alkyne, were synthesized and polymerized via 1,3-diploar cycloaddition in bulk under heating without any catalyst.Polypyrazoles with molecular weights in the range of 3800-4400 g/mol and yields in the range of 78.8-98.7% were successfully synthesized. No chain end group was detected by LC-QTOF-MS and FTIR, which proves the cyclic structure of polypyrazoles. What is noteworthy is that the cyclic polypyrazoles can selfassemble into vesicles during the reprecipitation process, which was proved by the results of SEM and TEM. The reason for that is the formation of intermolecular hydrogen bond between NH and ester groups.

Differences in Crystallization Behaviors between Cyclic and Linear Polymer Nanocomposites

Cyclic polymers exhibit fascinating crystallization behaviors owing to the absence of chain ends and more compact conformations.In the current simulation,dynamic Monte Carlo simulations were performed to reveal the underlying mechanism of the effect of chain topology and chain length on crystallization of polymer in solutions containing one-dimensional nanofiller.Simulation results suggested that the filled cyclic polymers exhibit higher melting temperature,higher crystallization temperature,and faster crystallization rate than the analogous linear polymers of identical chain length,especially in the systems with relatively short chains.Based on the Thomson-Gibbs equation,we theoretically analyzed the difference in the melting point between the cyclic and linear polymers under different chain lengths,and derived the dependence of the ratio of the melting point of the linear polymers to that of its cyclic analogs on chain length.In addition,it was also observed that the nanofiller can induce the formation of nanohybrid shish-kebab structure during isothermal crystallization of all systems.

Recent Advances of CuAAC Click Reaction in Building Cyclic Polymer

Cyclic polymers have attracted more and more attentions in recent years because of their unique topological structures and characteristic properties in both solution and bulk state. There are relatively few reports on cyclic polymers, partly because of the more demanding synthetic procedures. In recent years, 'click' reaction, especially Cu(I)-catalyzed azide-alkyne cycloaddition(CuAAC), has been widely utilized in the synthesis of cyclic polymer materials because of its high efficiency and low susceptibility to side reactions. In this review, we will focus on three aspects:(1) Constructions of monocyclic polymer using CuAAC 'click' chemistry;(2) Formation of complex cyclic polymer topologies through CuAAC reactions;(3) Using CuAAC 'click' reaction in the precise synthesis of molecularly defined macrocycles. We believe that the CuAAC click reaction is playing an important role in the design and synthesis of functional cyclic polymers.

Special Odd-Even Effect of Degree of Oligomerization on Properties of Cyclic Oligoesters

We demonstrate here seven pure cyclic samples, which belongs to two series of oligoesters, cyclic oligo（trimethylene terephthalate）s （COTTs） and cyclic oligo（butylene terephthalate）s （COBTs）, showing odd-even effect of degree of oligomerization （repeating units number） on properties. The pentamer of COTT and trimer of COBT show much lower melting temperature, and the trimer of COTT and trimer of COBT show significant lower refractive index, which can be ascribed to the low packing density of cyclic oligoesters with odd number of degree of oligomerization. Our results reveal the discrete property change as a function of cyclic size of oligomers, which can be used to design materials with special properties.

Polymer Synthesis Based on Self-Accelerating 1,3-Dipolar Cycloaddition Click Reactions

This review reports our recent work on developing polymer synthesis methods based on a self-accelerating double-strain-promoted 1,3-dipole-alkyne cycloaddition(DSPDAC)click reaction.In DSPDAC,the cycloaddition of 1,3-dipole with the first alkyne of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne(DIBOD)activates the second unreacted alkyne,which reacts with 1,3-dipole much faster than the original alkyne of DIBOD.When using DIBOD and bis-dipole compounds as monomer pairs,the self-accelerating property of DSPDAC allows us to develop a stoichiometric imbalance-promoted step-growth polymerization method.It could produce polymers with ultrahigh molecular weight in the presence of excess DIBOD monomers.When using DIBOD to ring-close linear polymers with 1,3-dipole end groups,the self-accelerating property of DSPDAC facilitates us to develop a unique bimolecular ring-closure method.It could efficiently prepare pure cyclic polymers in the presence of excess DIBOD small linkers to linear polymer precursors.