Co-reporter:Erlita Mastan and Junpo He
Macromolecules December 12, 2017 Volume 50(Issue 23) pp:9173-9173
Publication Date(Web):November 21, 2017
DOI:10.1021/acs.macromol.7b01662
A continuous process for the production of multiblock polymers via living anionic polymerization in a loop reactor is proposed by kinetic modeling. The process utilizes specific configurations of the loop reactors and feed inlets, thus producing multiblock polymers constituted by a blend of chains with varying number of blocks. The dependence of the product molecular parameters, such as length, composition of each block, and the block number distribution, on the residence time and the recirculation fraction is analyzed by numerical integration of differential mass balances. This dependence is subsequently translated into controllability of molecular parameters by changing the operation conditions such as the recirculation and inlet flow rates. In general, higher recirculation flow rate yields products with shorter block length but larger fraction of polymers possessing higher number of blocks and more significant compositional mixing in each block. An increase in the feed flow rates also increases the compositional mixing but gives longer block length with lower fraction of polymers possessing a higher number of blocks. While being discussed in terms of living anionic copolymerization of styrene and butadiene, the present strategy can be extended to any other living copolymerization of suitable monomer pairs, thus highlighting the use of reaction engineering to control the polymer structures.
Co-reporter:Shaohui Yang and Junpo He
Polymer Chemistry 2016 vol. 7(Issue 27) pp:4506-4514
Publication Date(Web):10 Jun 2016
DOI:10.1039/C6PY00810K
In this article, we report the synthesis of rod–coil diblock copolymers comprising substituted polyacetylene and poly(dimethylsiloxane) (PDMS) segments through a precursor approach based on living polymerization. The precursor was prepared by sequential anionic vinyl polymerization of a designed template monomer, 2,3-di(n-hexylphenyl)-1,3-butadiene (n-HD), and the anionic ring-opening polymerization of a cyclic monomer, hexamethylcyclotrisiloxane (D3). Block copolymers with well-defined molecular weights were obtained as demonstrated by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS). The polybutadiene segment of the precursor block copolymer was transformed into a substituted polyacetylene segment, or polyene, by dehydrogenation in the presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The self-assembly behavior of the resulting rod–coil diblock copolymers in dilute solution was investigated by using dynamic light scattering (DLS) and transmission electron microscopy (TEM). It was found that the block copolymers showed a strong tendency to form vesicular aggregates. In some cases intermediate morphologies were observed, such as large size particles and vesicles with loosely packed thick walls. These morphologies developed further into regular vesicles through orientational assembly of the polyacetylene segments, as indicated by the blue shift in UV-Vis and fluorescence spectra.
Co-reporter:Yunpeng Wang, Gang Qi, and Junpo He
ACS Macro Letters 2016 Volume 5(Issue 4) pp:547
Publication Date(Web):April 11, 2016
DOI:10.1021/acsmacrolett.6b00198
In this report, we synthesized layered amphiphilic dendrimer-like block copolymers containing a polystyrene core and poly(p-tert-butoxystyrene)/poly(p-hydroxylstyrene) shell (coded G4-PtBOS/G4-PHOS). The synthetic method is easy involving anionic polymerization, epoxidation, ring-opening reaction and hydrolysis reaction. The hydrolyzed G4-PtBOS was soluble in alkaline water and behaved as unimolecular micelle, as demonstrated by the results of DLS, cryo- and normal TEM, and pyrene entrapping experiment. The stability of the unimolecular micelles was investigated via ζ-potential measurements.
Co-reporter:Gang Qi, Yunhai Yu and Junpo He
Polymer Chemistry 2016 vol. 7(Issue 7) pp:1461-1467
Publication Date(Web):28 Dec 2015
DOI:10.1039/C5PY01674F
Herein, we report the synthesis of a hybrid material composed of a head-to-head substituted polyacetylene end-capped with [60]fullerene through anionic polymerization. The synthesis was carried out in three successive steps: anionic polymerization of 2,3-diphenyl-1,3-butadiene, anionic addition of the resulting living chains towards C60, and dehydrogenation of the polymer segment in the presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Since the precursor polymer is a coil-like polybutadiene derivative and the dehydrogenated polymer is a rod-like conjugated segment, the molecular hybrids underwent a change from a “coil-sphere” to “rod-sphere” conformation before and after dehydrogenation. The structure and properties of the molecular hybrids were investigated via1H NMR, FTIR, GPC, FLS, UV and TGA. The self-assembly behaviors of both molecular hybrids in THF were studied using DLS and TEM. Moreover, we also observed an obvious optical limiting property of the hybrid product, which indicates that it may potentially be utilized as a functional opto-electronic material.
Co-reporter:Jia Li and Junpo He
ACS Macro Letters 2015 Volume 4(Issue 4) pp:372
Publication Date(Web):March 16, 2015
DOI:10.1021/acsmacrolett.5b00125
We hereby report a strategy to synthesize sequence-regulated substituted polyacetylenes using living anionic polymerization of designed monomers, that is, 2,4-disubstituted butadienes. It is found that proper substituents, such as 2-isopropyl-4-phenyl, lead to nearly 100% 1,4-addition during the polymerization, thus, giving product with high regioregularity, precise molecular weight, and narrow molecular weight distribution. The product is convertible into sequence-regulated substituted polyacetylene by oxidative dehydrogenation using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Block copolymers containing polyacetylene segment are also prepared. Owing to the versatility of the anionic reactions, the present strategy can serve as a powerful tool of precise control on polymer chain microstructure, architecture, and functionalities in the same time.
Co-reporter:Linxiang Hong, Shaohui Yang, Junpo He
European Polymer Journal 2015 Volume 65() pp:171-190
Publication Date(Web):April 2015
DOI:10.1016/j.eurpolymj.2015.02.019
•An anionic inimer approach was developed for the synthesis of star-branched polymers.•Hyperbranched polymers were synthesized through self-condensing vinyl copolymerization of the anionic inimer.•Dendrimer-like polymers with orthogonal functionalities were synthesized in a fast, divergent, and living procedure.•Ultra high molecular weight dendrimer-like polymers were synthesized.•Cylindrical polymer brushes with high density of side chains were prepared.In this feature article, we describe the synthetic work in our laboratory on branched polymers through anionic polymerization reaction based on selective addition of organolithium toward a bifunctional 1,1-diphenylethylene derivative, 1,3-bis(1-phenylvinyl)benzene (MDDPE). Exclusive monoaddition was achieved using equal molar ratio of organolithium and MDDPE in THF, in which the solvent polarity played a decisive role for the addition behavior. The monoaddition was used in the synthesis of ABC- and ABCD-type miktoarm star polymers through successive reactions on the double bonds of MDDPE. The monoadduct, either with butyllithium or polymeric lithium, was also utilized as inimer or macroinimer to synthesize hyperbranched polymers, hyperbranched block copolymers or terpolymers, respectively, through self-condensing vinyl copolymerization (SCVCP) with vinyl monomer. A very specific application of the anionic inimer is the development of a continuous process for the synthesis of living dendrimer-like polymers. By this approach, dendrimer-like polystyrene of 5th generation can be synthesized within 12 h. Functionalization and copolymerization were also possible on the basis of living dendrimer-like polymers. We also developed another facile method for the synthesis dendrimer-like polymers using anionic “grafting-to” reaction. Dendritic products with extremely large molecular weights were obtained. In addition, the anionic “grafting-to” reaction was used in the synthesis of graft polymers with “V-shaped”, “Y-shaped”, “comb-on-comb” and dendritic side chains.
Co-reporter:Zehui Gao
Macromolecular Reaction Engineering 2015 Volume 9( Issue 5) pp:431-441
Publication Date(Web):
DOI:10.1002/mren.201400061
A Monte Carlo algorithm is developed to simulate the radical polymerization and copolymerization in microflow reactor. The algorithm couples the stochastic reaction process, based on Gillespie's theory, with material diffusion and flow. The simulation results agree well with the experimental kinetic data reported in the literature. The method can be used to predict the polymerization kinetics, molecular weight and molecular weight distribution, and composition and sequence length distribution (both instantaneous and cumulative) of the polymer products obtained from microflow reactors. The effects of various reaction parameters, such as flow rate, initial concentration, and temperature, on the polymerization kinetics are also discussed.
Co-reporter:Hefeng Zhang, Chengke Qu, Junpo He
Polymer 2015 Volume 64() pp:240-248
Publication Date(Web):1 May 2015
DOI:10.1016/j.polymer.2015.02.004
•Cylindrical polymer brushes with dendritic side chains were prepared by a divergent grafting-to approach.•Only a living block copolymer, PI-b-PSLi, was used as the precursor for side chains and branching agents.•The approach facilitated fast synthesis of molecular brushes and afforded high density of side chains.We report in this paper an easy method for the synthesis of cylindrical polymer brushes with dendritic side chains through anionic reaction. The synthesis is accomplished by iteratively grafting a living block copolymer, polyisoprene-b-polystyrenyllithium (PI-b-PSLi), to the main chain and subsequently to the branches in a divergent way. PI segment is short and serves as a precursor for multifunctional branching unit. The grafting reaction involves two successive steps: i) epoxidation of internal double bonds of PI segments, either in main chain or side chains; ii) ring-opening addition to the resulting epoxy group by the living PI-b-PSLi. Repeating the two steps affords a series of cylindrical polymer brushes with up to 3rd generation and extremely high molecular weight. The branching multiplicity depends on the average number of oxirane groups per PI segment, usually ca. 8 in the present work. The high branching multiplicity leads to tremendous increase in molecular weights of the cylindrical products with generation growth. Several series of cylindrical polymer brushes with tunable aspect ratios are prepared using backbones and branches with controlled lengths. Shape anisotropy is investigated in dilute solution using light scattering technique. Worm-like single molecular morphology with large persistence length is observed on different substrates by atomic force microscopy.
Co-reporter:Chengke Qu
Science China Chemistry 2015 Volume 58( Issue 11) pp:1651-1662
Publication Date(Web):2015/11/01
DOI:10.1007/s11426-015-5476-9
The synthesis of sequence controlled polymers received increasing interest in polymer science. This mini review focuses on the principle and methods developed to control the sequence in polymer products from various polymerization mechanisms and processes. Typical examples are discussed to explicate the progress in this research field.
Co-reporter:Lei Yang and Junpo He
Chemical Communications 2014 vol. 50(Issue 99) pp:15722-15725
Publication Date(Web):28 Oct 2014
DOI:10.1039/C4CC07647H
We have developed a method to prepare covalently functionalised graphene using ferric perchlorate as the catalyst. The resulting functionalised graphene was characterised by Raman spectroscopy, TGA, XPS, AFM, and dispersibility tests in organic or aqueous media.
Co-reporter:Zhenhua Ju and Junpo He
Chemical Communications 2014 vol. 50(Issue 62) pp:8480-8483
Publication Date(Web):15 May 2014
DOI:10.1039/C4CC01377H
Nanospheres with an internal bicontinuous structure were obtained through hierarchical self-assembly of a dendritic block terpolymer in selective solvents. The self-assembly underwent a unique three stage process involving unimolecular micelle formation, multimicelle aggregation and microphase separation within a self-confined space. Reversible phase inversion of the nanospheres in response to the solvent environment was observed.
Co-reporter:Yang Zhang, Jia Li, Xiaohong Li, and Junpo He
Macromolecules 2014 Volume 47(Issue 18) pp:6260-6269
Publication Date(Web):September 14, 2014
DOI:10.1021/ma501283b
Substituted polyacetylenes with alkylphenyl side groups and head-to-head regioregularity were prepared through anionic living polymerization of template monomers and subsequent dehydrogenation process. The template monomers have the structure of 2,3-disubstituted-1,3-butadienes prepared by palladium-catalyzed Kumada coupling of the corresponding vinyl bromides. Anionic polymerizations of the template monomers produced narrow disperse substituted polybutadiene precursors with exclusive 1,4-enchainment. The precursors were converted into soluble polyacetylene derivatives via two methods, e.g., bromination followed by elimination of HBr, and direct dehydrogenation by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), both resulting in dark colored products with significant red shift in UV spectra. The obtained head-to-head polyacetylene derivatives exhibited highly thermal stability, possibly due to trans-rich and/or head-to-head chain configurations. The microstructures of the poly(2,3-dialkylphenyl butadiene) precursors were analyzed in detail using NMR spectroscopy with regard to the solvent effect during polymerization. Block copolymers containing substituted polyacetylene segments were prepared through sequential anionic polymerization of different monomers, followed by dehydrogenation transformation. The present synthesis may serve as a new strategy for tailoring molecular structures of polyacetylene-based polymers by virtue of anionic living polymerization techniques.
Co-reporter:Hefeng Zhang, Jian Zhu, Junpo He, Feng Qiu, Hongdong Zhang, Yuliang Yang, Hyojoon Lee and Taihyun Chang
Polymer Chemistry 2013 vol. 4(Issue 3) pp:830-839
Publication Date(Web):30 Oct 2012
DOI:10.1039/C2PY20742G
We report here an easy method for the synthesis of dendrimer-like polymers with high branching functionality (1 → 8). The synthetic process involves iterative grafting reactions in a divergent way. A multi-functional core containing short segments of polyisoprene (PI), either as a star-like block copolymer of isoprene and styrene or as a linear triblock copolymer of isoprene, styrene and isoprene (coded G1), is epoxidized on the double bonds and grafted with a living block copolymer, polyisoprene-b-polystyrenyllithium (PI-b-PSLi), again with a short PI segment, through the ring-opening reaction of oxirane by polymeric anions. The resulting graft polymer, G2, possesses a definite number of PI segments at the periphery. These PI segments are further epoxidized followed by the ring-opening addition of PI-b-PSLi, affording G3. Repeating the process leads to the synthesis of a dendrimer-like polystyrene up to 5th generation with a polydispersity lower than 1.21, as measured by SEC. A feature of the process is the easily accessible high chain density in the final product, although defects exist due to steric hindrance in the reactions of high generations. The solution properties of the dendritic products are investigated using viscometry and dynamic and static laser light scattering on the molecular conformation. The results support a compact globular conformation model for the dendrimer-like products. In addition, the chain density of the products from the star-like core is higher than that of products from a linear triblock core. AFM results show that the dendritic products adopt flattened conformations and tend to form lateral sphere-like aggregates on mica substrate.
Co-reporter:Chao Zhang, Yuliang Yang, and Junpo He
Macromolecules 2013 Volume 46(Issue 10) pp:3985-3994
Publication Date(Web):May 10, 2013
DOI:10.1021/ma4006457
A method of direct switching from anionic polymerization into RAFT-based polymerization was developed. The transformation involved in situ addition of living carbanionic species, end-capped with DPE, toward CS2 and subsequent reaction with alkyl bromides, resulting in macro-RAFT agents (macro-CTAs). The macro-CTAs were used to mediate RAFT polymerization of (functional) vinyl monomers. These processes were performed in a continuous way without isolation of the intermediate. Diblock or ABA-type triblock copolymers, composed of polydiene segment and functional acrylate (2-hydroxyethyl acrylate, HEA) or acrylamide (N-isopropylacrylamide, NIPAM), were synthesized by RAFT polymerization mediated by PI macro-CTAs. The successful preparation of block copolymers was demonstrated by the self-assembly of amphiphilic diblock copolymer PI75-b-PNIPAM199 in water (selective solvent for PNIPAM) or heptane (selective solvent for PI). The obtained block copolymers are cleavable into homopolymer components due to the presence of the thiocarbonylthio moieties at their joint points. The block copolymers are also “clickable” as a whole onto Au nanoparticles through Au–sulfur complexation.
Co-reporter:Chao Xie, Zhenhua Ju, Chao Zhang, Yuliang Yang, and Junpo He
Macromolecules 2013 Volume 46(Issue 4) pp:1437-1446
Publication Date(Web):February 13, 2013
DOI:10.1021/ma3025317
Anionic macroinimer is prepared through selective monoaddition of polyisoprenyllithium (PILi) toward 1,3-bis(1-phenylvinyl)benzene (MDDPE) in THF/cyclohexane mixture. The resulting macroinimer, possessing a living anion and a diphenylethylene (DPE) group at the same end of the PI chain, undergoes self-condensing vinyl copolymerization (SCVCP) with styrene after the solvent has been switched from mixture of THF/cyclohexane into pure cyclohexane. Dendritic block copolymers of styrene and isoprene are obtained, in which PI chains are linked to the branch points. The molecular weights of the dendritic products mainly depend on the ratio of monomer to macroinimer, whereas PI chain length has only slight effects. The PI segments are subsequently epoxidized and grafted with PILi or polystyrenyllithium (PSLi) to give dendritic polymer brushes. Both dendritic block copolymers and dendritic polymer brushes show decreased intrinsic viscosities. Dendritic block copolymer of styrene and isoprene undergoes a specially slow process of self-assembly, from unimolecular micelles and intermediate compound micelles to large compound micelles, in mixed solvent (n-heptane/THF = 19/1, v/v). In addition, conversion of large compound micelles into lamellar structure is observed for the first time in self-assembly of dendritically branched polymers.
Co-reporter:Deqin Fan, Chao Zhang, Junpo He, Rong Hua, Yang Zhang and Yuliang Yang
Journal of Materials Chemistry A 2012 vol. 22(Issue 35) pp:18564-18571
Publication Date(Web):16 Jul 2012
DOI:10.1039/C2JM33467D
We report here redox reactions between graphene oxide (GO) and mercaptans, which reduces GO to reduced graphene oxide (RGO) and oxidizes mercaptans into disulfides. The reduction processes of GO using various mercaptans as the reducing agents are investigated through XPS, TGA, FT-IR, Raman and EA analysis. The degree of reduction of RGO depends on molecular structure of mercaptans and is controlled by the reaction time. The redox reaction is also employed to oxidize mercaptans into disulfides in medium to high yields under moderate conditions. The mechanism of the redox reaction may involve nucleophilic ring opening of oxirane on GO by alkylthio moiety, followed by addition of another alkylthio group, leaving the resulting disulfide. The reduction of the hydroxy group could be more complex, involving both radical and anionic processes.
Co-reporter:Deqin Fan, Ying Liu, Junpo He, Yanwu Zhou and Yuliang Yang
Journal of Materials Chemistry A 2012 vol. 22(Issue 4) pp:1396-1402
Publication Date(Web):23 Nov 2011
DOI:10.1039/C1JM13947A
Porous graphene monolith and porous composites of graphene oxide (GO) and silica were prepared by thermolytic cracking of graphene-coated, or GO/silica-coated polystyrene (PS) spheres. The spheres were synthesized through in situprecipitation polymerization of styrene using GO and poly(vinylpyrrolidone) as stabilizing agents. During polymerization, GO adsorbed to the surface of the PS particle due to its amphiphilicity as well as spontaneous grafting on GO basal plane. The GO-coated PS spheres were either reduced by hydrazine to graphene-coated PS spheres, or underwent a sol–gel reaction with tetraethyloxysilane (TEOS). These materials were finally subjected to thermolytic cracking in a thermogravimetry instrument or in a furnace under nitrogen up to 550 or 700 °C, resulting in graphene-based porous materials in which the pores are surrounded by graphene or GO/silica walls. The factors affecting the specific surface area were discussed. The method may serve as a new approach to fabricate 3D graphene-based porous materials.
Co-reporter:Hefeng Zhang, Junpo He, Chao Zhang, Zhenhua Ju, Jia Li, and Yuliang Yang
Macromolecules 2012 Volume 45(Issue 2) pp:828-841
Publication Date(Web):December 29, 2011
DOI:10.1021/ma2024039
A continuous anionic living process for the fast synthesis of dendrimer-like star polymers is described. The process is based on the selective addition of sec-butyllithium (s-BuLi) toward 1,3-bis(1-phenylethenyl)benzene (MDDPE), which gives stoichiometric monoadduct in tetrahydrofuran (THF). The monoadduct, an anionic inimer-like molecule, is then used as the branching agent in the synthesis of dendrimer-like star polymers. Thus, α,ω-bifunctional polystyryllithium (G1.0), initiated by a difunctional anionic initiator, undergoes addition reaction with the monoadduct to form a tetrafunctional species, which is able to initiate the polymerization of styrene to form a four-arm star with terminal polystyryl anions (G2.0). Repeating addition/polymerization in an alternate way leads to the formation of a dendrimer-like star polystyrene up to the fifth generation, G5.0. The process is performed in a continuous way without separation of the intermediate species. The synthetic procedure of dendritic polystyrene is greatly accelerated, e.g., G5.0 with 32 terminal groups being obtained within 12 h. Because the product is living, it is employed as a dendritic precursor to prepare dendrimer-like star block copolymers such as PS-b-PI, PS-b-PMMA, and dendrimer-like star polymer with a graft-on-graft periphery. The solution properties of the dendrimer-like star products, such as viscosity as a function of molecular weight and globular shape, are investigated using viscometry and laser light scattering. The morphology of the individual molecules is observed using AFM and TEM.
Co-reporter:Changxi Li;Yanwu Zhou;Yuankai Gu;Yuliang Yang
Journal of Polymer Science Part A: Polymer Chemistry 2011 Volume 49( Issue 6) pp:1351-1360
Publication Date(Web):
DOI:10.1002/pola.24554
Abstract
Radical-induced oxidation of reversible addition-fragmentation chain transfer (RAFT) agents is investigated with respect to the effect of molecular structure on oxidation rate. The radicals are generated by homolysis of either azobisisobutyronitrile or alkoxyamine and transformed in situ immediately into peroxy radicals through transfer to molecular oxygen. It is found that the oxidation rate depends on the structure of Z- and R-group of thiocarbonylthio compounds. For dithioesters with identical Z-phenyl substituent, the oxidation rate decreases in the order of cyanoisopropyl (C(Me)2CN) > cumyl (C(Me)2Ph) > phenylethyl (CH(Me)Ph) > 2-methoxy-1-methyl-2-oxoethyl (CH(Me) C(O)OCH3) > benzyl (CH2Ph). For dithioesters with identical R-group, the oxidation rate decreases in the order of Z = phenyl− ∼ benzyl− > RS− (trithiocarbonates) > RO− (xanthates). The stability of the RAFT agents toward oxidation correlates well with the chain transfer abilities as those previously reported by Rizzardo and coworkers. The priority of the oxidation reaction over the RAFT process, and the subsequent influence on RAFT polymerization are also investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Co-reporter:Yizheng Wang;Deqin Fan;Yuliang Yang
Colloid and Polymer Science 2011 Volume 289( Issue 17-18) pp:1885-1894
Publication Date(Web):2011 November
DOI:10.1007/s00396-011-2506-9
Silica nanoparticles (NSiO2) are modified with mixed polymer brushes derived from a block copolymer precursor, poly(methyl methacrylate)-b-poly(glycidyl methacrylate)-b-poly(tert-butyl methacrylate) with short middle segment of PGMA, through one step “grafting-onto” approach. The block polymer precursors are prepared via reversible addition–fragmentation chain transfer-based polymerization of methyl methacrylate, glycidyl methacrylate, and tert-butyl methacrylate. The grafting is achieved by the reaction of epoxy group in short PGMA segment with silanol functionality of silica. After hydrolysis of poly(tert-butyl methacrylate) segment, amphiphilic NSiO2 with “V-shaped” polymer brushes possessing exact 1:1 molar ratio of different arms were prepared. The functionalized particles self-assemble at oil/water interfaces to form stable large droplets with average diameter ranging from 0.15 ± 0.06 to 2.6 ± 0.75 mm. The amphiphilicity of the particles can be finely tuned by changing the relative lengths of poly(methyl methacrylate) and poly(methacrylic acid) segments, resulting in different assembly behavior. The method may serve as a general way to control the surface property of the particles.
Co-reporter:Yanwu Zhou, Junpo He, Changxi Li, Linxiang Hong, and Yuliang Yang
Macromolecules 2011 Volume 44(Issue 21) pp:8446-8457
Publication Date(Web):October 4, 2011
DOI:10.1021/ma201570f
The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates, and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-elimination, α-elimination, and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z- or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens result in faster decomposition rate or lower decomposition temperature. Thus, the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z = phenyl) −CH2Ph (5) > −PS (PS-RAFT 15) > −C(Me)HPh (2) > −C(Me)2C(═O)OC2H5 (7) > −C(Me)2Ph(1) > −PMMA (PMMA-RAFT 16) > −C(Me)2CN (6). For those possessing identical leaving group such as 1-phenylethyl, the stability decreases in the order of O-ethyl (11) > –N(CH2CH3)2 (13) > –SCH(CH3)Ph (8) > −Ph (2) > −CH2Ph (4) > −PhNO2 (3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.
Co-reporter:Yuankai Gu, Junpo He, Changxi Li, Changming Zhou, Shijie Song and Yuliang Yang
Macromolecules 2010 Volume 43(Issue 10) pp:4500-4510
Publication Date(Web):April 27, 2010
DOI:10.1021/ma1000139
Block copolymerization of vinyl acetate (VAc) and vinyl neo-decanoate (VNDc) is carried out in the presence of a disulfide, isopropylxanthic disulfide (DIP), using 2,2′-azoisobutyronitrile (AIBN) as the radical initiator. The polymerization proceeds in a controlled/“living” style, as illustrated by stepwise increase in molecular weight and relatively narrow molecular weight distribution of the final product. The reaction mechanism is investigated in detail for the system of VAc homopolymerization in the presence of DIP. The results of chromatography, NMR, and mass spectra reveal that there exists two kinds of RAFT agents, that is, S-(cyano)isopropyl O-isopropyl xanthate and diisopropyl dithiocarbonate, the former coming from the reaction of 2-cyano-isopropyl radical with DIP and the latter being formed in situ during a series of radical process participated by the monomer. High efficiency of the cross initiation is achieved for the sequential polymerization. The block lengths are well controlled by the ratio of monomer to RAFT agents. The resulting block copolymer, PVAc-b-PVNDc, is hydrolyzed to prepare PVOH-b-PVNDc. These block copolymers, before and after hydrolysis, undergo self-assembly in solution and phase separation in bulk state.
Co-reporter:Weijie Zhao;Ming Fang;Junyu Chen;Wei Tang;Yuliang Yang
Journal of Polymer Science Part A: Polymer Chemistry 2010 Volume 48( Issue 19) pp:4141-4149
Publication Date(Web):
DOI:10.1002/pola.24156
Abstract
Tandem atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP) were used to synthesize a polystyrene-co-poly(acrylic acid) (poly(St-co-AA)) network, in which the two components were interconnected by covalent bond. First, a specific cross-linker, 1,4-bis(1′-(4″-acryloyloxy-2″,2″,6″,6″-tetramethylpiperidinyloxy)ethyl)benzene (di-AET), a bifunctional alkoxyamine possessing two acrylate groups, was copolymerized with tert-butyl acrylate through ATRP to prepare a precursor gel. The gel was then used to initiate the NMRP of styrene to prepare poly(St-co-(t-BA)) conetwork, in which the cross-linkages are composed of polystyrene segments. Finally, the poly(St-co-(t-BA)) conetwork was hydrolyzed to produce amphiphilic poly(St-co-AA) conetwork. The resulting gels show swelling ability in both organic solvent and water, which is characteristic of amphiphilic conetworks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4141–4149, 2010
Co-reporter:Junyu Chen, Junpo He, Yuefei Tao, Chengming Li, Yuliang Yang
Polymer 2010 Volume 51(Issue 21) pp:4769-4775
Publication Date(Web):1 October 2010
DOI:10.1016/j.polymer.2010.08.044
Thermosensitive gel is synthesized through controlled/“living” free radical copolymerization of styrene and DVB mediated by an alkoxyamine inimer, 2,2,6,6-tetramethyl-1-(1′-phenylethoxy)-4-(4′-vinylbenzyloxy)-piperidine (V-ET). The inimer plays the role of both incorporating “T-shaped” inter-chain linkages and mediating the polymerization. First order kinetics is observed for crosslinking polymerizations before gel point, indicating a constant concentration of propagating radicals. Monomer conversion at the gel point depends on the feed ratio of DVB to V-ET. Higher amount of V-ET results in later gel point due to smaller molecular weight of the primary chains that depends inversely on the concentration of nitroxide. The resulting gel contains permanent and labile crosslinking points formed by DVB units and alkoxyamine moieties, respectively. Therefore, the gels exhibit gel–sol transition within a narrow temperature range. The gel properties, such as the swelling ratio and gel–sol transition temperature, can be controlled by changing the feed ratio of DVB to V-ET. The microenvironments in different gels, or at different temperatures, are investigated by ESR spectroscopy.
Co-reporter:Wei Sun, Junpo He, Xiaojun Wang, Chao Zhang, Hongdong Zhang and Yuliang Yang
Macromolecules 2009 Volume 42(Issue 19) pp:7309-7317
Publication Date(Web):September 1, 2009
DOI:10.1021/ma9006768
An anionic inimer (a monomer with an initiating site) is prepared by monoaddition of sec-butyllithium and 1,3-bis(1-phenylethenyl)benzene (MDDPE) in tetrahydrofuran (THF) at low temperature. The selectivity of monoaddition is high, yielding nearly quantitative formation of the inimer. The inimer is able to initiate the polymerization of styrene, forming different architectures of the products in THF and cyclohexane. In the former, linear product with larger-than-expected molecular weight is obtained whereas, when the solvent is switched from THF to cyclohexane, dendritic polymer is obtained through the copolymerization of the inimer and styrene. The resulting products are characterized by size exclusion chromatography equipped with a multiangle light scattering detector and a viscometer. Smaller radius of gyration and intrinsic viscosity are measured for the dendritic product. The mechanism of forming dendritic structure by the solvent-switching process is discussed according to Müller’s theory.
Co-reporter:Jianli Cheng, Junpo He, Changxi Li and Yuliang Yang
Chemistry of Materials 2008 Volume 20(Issue 13) pp:4224
Publication Date(Web):June 13, 2008
DOI:10.1021/cm800357g
Nanodiamond (ND) particles were functionalized with V-shaped polymer brushes of polystyrene and poly(t-butyl methacrylate) (PtBMA) through the reaction of surface carboxylic groups of NDs toward epoxy functionalities located in the middle of the polymer precursor, an ABC-type triblock copolymer. The block copolymer was prepared through sequential radical polymerizations of tBMA, glycidyl methacrylate (GMA), and styrene mediated by a reversible addition−fragmentation chain transfer process, in which the lengths of different segments are well-controlled by virtue of the living nature of the reaction. The polymerization product, PtBMA-b-PGMA-b-PS, carried a short block of PGMA in the middle, which was used for subsequent reaction with -COOH on the convex surface of the NDs. This grafting-onto approach through a center-linking process functionalized nanoparticles with V-shaped polymer brushes possessing an exact 1:1 molar ratio of different arms. Furthermore, ND particles with amphiphilic functionalities were prepared after hydrolysis of the PtBMA segment. The obtained polymer grafted ND was characterized by electron microscopy (TEM and SEM), NMR and IR spectroscopy, and TGA. The product not only formed stable dispersions in organic solvents such as tetrahydrofuran, toluene, and chloroform but also self-assembled at oil−water interfaces to form flat films or large droplets of water-in-oil and oil-in-water. The mechanism of self-assembly at liquid−liquid interfaces is discussed.
Co-reporter:Wei Sun;Fengping Yu;Chao Zhang;Yuliang Yang
Journal of Polymer Science Part A: Polymer Chemistry 2008 Volume 46( Issue 16) pp:5518-5527
Publication Date(Web):
DOI:10.1002/pola.22872
Abstract
Well-defined comb-on-comb copolymers of styrene, isoprene, and α-methyl-styrene are prepared through cascade “grafting-onto” methods. The polymer main chain is prepared by nitroxide-mediated radical polymerization while the branches are prepared by anionic polymerization. The “grafting-onto” approach employs the coupling chemistry of macromolecular anions, such as polystyryllithium, polyisoprenyllithium, or poly(α-methylstyryl)lithium, toward either benzyl chloride or epoxy ring on precursor backbones. Thus a series of ABA-, ABB-, and ABC-type comb-on-comb copolymers are prepared and characterized by gel permeation chromatography equipped with a multi-angle laser light scattering detector and a viscometer. Unusual “U-shaped” dependences of radius of gyration, Rg, on molecular weight are observed for comb-on-comb products, which are attributable to delayed elution of the densely grafted copolymers from GPC columns. The result also shows that the comb-on-comb copolymers exhibit morphologies from hard sphere to cylindrical rod, depending on the length ratio of the main chain to the branches. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5518–5527, 2008
Co-reporter:Junpo He;Yong Ao;Xueqin Han;Yang Liu;Xiaojun Wang;Deqin Fan;Jiangtao Xu;Yuliang Yang
Journal of Polymer Science Part A: Polymer Chemistry 2007 Volume 45(Issue 3) pp:374-387
Publication Date(Web):8 DEC 2006
DOI:10.1002/pola.21798
A model reaction of dithioester and alkoxyamine is proposed to probe the reversible addition–fragmentation chain transfer (RAFT) process. The kinetics of the model reaction is analyzed and compared with that of pure alkoxyamine homolysis with a Monte Carlo simulation. Although the pure alkoxyamine obeys the law of persistent radical effect, the model reaction results in higher concentration of the persistent radical during the main period of the reaction. However, for a very fast RAFT process or a very low addition rate constant, the time dependence of the persistent radical concentration is quite close to that of pure alkoxyamine. Furthermore, the cross termination between the intermediate and alkyl radicals causes a retardation effect for the model reaction when the intermediate is relatively long-lived. The Monte Carlo simulation indicates that it is feasible to measure the individual rate constants of the RAFT process, such as the rate constant of addition, with a large excess of alkoxyamine. In addition, the special feature of the system with different leaving groups in the alkoxyamine and dithioester is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 374–387, 2007
Co-reporter:Fengping Yu;Xiaojun Wang;Yuliang Yang;Guangzheng Gao
Journal of Polymer Science Part A: Polymer Chemistry 2007 Volume 45(Issue 17) pp:4013-4025
Publication Date(Web):17 JUL 2007
DOI:10.1002/pola.22155
A combination of nitroxide-mediated radical polymerization and living anionic polymerization was used to synthesize a series of well-defined graft (co)polymers with “V-shaped” and “Y-shaped” branches. The polymer main chain is a copolymer of styrene and p-chloromethylstyrene (PS-co-PCMS) prepared via nitroxide-mediated radical polymerization. The V-shaped branches were prepared through coupling reaction of polystyrene macromonomer, carrying 1,1-diphenylethylene terminus, with polystyryllithium or polyisoprenyllithium. The Y-shaped branches were prepared throughfurther polymerization initiated by the V-shaped anions. The obtained branches, carrying a living anion at the middle (V-shaped) or at the end of the third segment (Y-shaped), were coupled in situ with pendent benzyl chloride of PS-co-PCMS to form the target graft (co)polymers. The purified graft (co)polymers were analyzed by size exclusion chromatography equipped with a multiangle light scattering detector and a viscometer. The result shows that the viscosities and radii of gyration of the branched polymers are remarkably smaller than those of linear polystyrene. In addition, V-shaped product adopts a more compact conformation in dilute solution than the Y-shaped analogy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4013–4025, 2007
Co-reporter:Xiaojun Wang;Yuliang Yang
Journal of Polymer Science Part A: Polymer Chemistry 2007 Volume 45(Issue 21) pp:4818-4828
Publication Date(Web):14 SEP 2007
DOI:10.1002/pola.22229
ABCD-type 4-miktoarm star copolymers of styrene (St), α-methylstyrene (αMSt), tert-butyl methacrylate (tBuMA), and 4-vinylpyridine (4VP) were synthesized via anionic polymerization using 1,3-bis(1-phenylvinyl)benzene (m-DDPE) as the linking molecule. The synthetic route was rationally designed with respect to the reactivity of individual propagating anion towards the double bond of m-DDPE. Thus the synthesis includes several consecutive key reactions, for example, the monoaddition of polystyryllithium towards m-DDPE, the polymerization of tBuMA initiated by the resulting monoadduct to produce a diblock macromonomer, the coupling of the macromonomer with poly(α-methylstyryl)lithium to form a 3-arm star anion, and the polymerization of 4-vinylpyridine initiated by the star anion. These reactions were conducted either in a one-pot process, in which the diblock macromonomer was in situ coupled with poly(α-methylstyryl)lithium, or in a batch polymerization process, in which the same diblock macromonomer was separated. The final product was hydrolyzed to produce a zwitterionic miktoarm star copolymer, which was soluble at lower pH but insoluble in neutral and basic solution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4818–4828, 2007
Co-reporter:Yunhai Yu, Junpo He
European Polymer Journal (January 2017) Volume 86() pp:
Publication Date(Web):January 2017
DOI:10.1016/j.eurpolymj.2016.11.020
•Regioblock PS with high regiospecificity, controlled MW and Ð were synthesized.•Regioblock PS were thoroughly characterized using 1H and 13C NMR and GPC.•Soluble living poly(2,3-diphenylbutadienyl)lithium was obtained in mixed solvent.•Thermal properties and fluorescence spectra of regioblock and H-T PS were compared.In this study, we synthesized for the first time a well-defined model polymer of regioblock polystyrene (PS) comprising pure head-to-tail and head-to-head blocks through living anionic block copolymerisation of styrene and 2,3-diphenyl-1,3-butadiene (DPB), followed by hydrogenation using Na/isopropanol reagent. In the polymerisation of DPB, it was critical to use a mixed solvent of cyclohexane with a small amount of THF to attain high solubility. Since DPB polymerized exclusively in 1,4-addition manner, the resulting block copolymers were readily transformed into the regioblock PS by hydrogenation of the residual double bonds in the main chain. The structure of the regioblock PS thus synthesized were confirmed by carefully characterizing with GPC, 1H NMR, 13C NMR, UV–Vis and Raman spectra.
Co-reporter:Deqin Fan, Ying Liu, Junpo He, Yanwu Zhou and Yuliang Yang
Journal of Materials Chemistry A 2012 - vol. 22(Issue 4) pp:NaN1402-1402
Publication Date(Web):2011/11/23
DOI:10.1039/C1JM13947A
Porous graphene monolith and porous composites of graphene oxide (GO) and silica were prepared by thermolytic cracking of graphene-coated, or GO/silica-coated polystyrene (PS) spheres. The spheres were synthesized through in situprecipitation polymerization of styrene using GO and poly(vinylpyrrolidone) as stabilizing agents. During polymerization, GO adsorbed to the surface of the PS particle due to its amphiphilicity as well as spontaneous grafting on GO basal plane. The GO-coated PS spheres were either reduced by hydrazine to graphene-coated PS spheres, or underwent a sol–gel reaction with tetraethyloxysilane (TEOS). These materials were finally subjected to thermolytic cracking in a thermogravimetry instrument or in a furnace under nitrogen up to 550 or 700 °C, resulting in graphene-based porous materials in which the pores are surrounded by graphene or GO/silica walls. The factors affecting the specific surface area were discussed. The method may serve as a new approach to fabricate 3D graphene-based porous materials.
Co-reporter:Deqin Fan, Chao Zhang, Junpo He, Rong Hua, Yang Zhang and Yuliang Yang
Journal of Materials Chemistry A 2012 - vol. 22(Issue 35) pp:NaN18571-18571
Publication Date(Web):2012/07/16
DOI:10.1039/C2JM33467D
We report here redox reactions between graphene oxide (GO) and mercaptans, which reduces GO to reduced graphene oxide (RGO) and oxidizes mercaptans into disulfides. The reduction processes of GO using various mercaptans as the reducing agents are investigated through XPS, TGA, FT-IR, Raman and EA analysis. The degree of reduction of RGO depends on molecular structure of mercaptans and is controlled by the reaction time. The redox reaction is also employed to oxidize mercaptans into disulfides in medium to high yields under moderate conditions. The mechanism of the redox reaction may involve nucleophilic ring opening of oxirane on GO by alkylthio moiety, followed by addition of another alkylthio group, leaving the resulting disulfide. The reduction of the hydroxy group could be more complex, involving both radical and anionic processes.
Co-reporter:Zhenhua Ju and Junpo He
Chemical Communications 2014 - vol. 50(Issue 62) pp:NaN8483-8483
Publication Date(Web):2014/05/15
DOI:10.1039/C4CC01377H
Nanospheres with an internal bicontinuous structure were obtained through hierarchical self-assembly of a dendritic block terpolymer in selective solvents. The self-assembly underwent a unique three stage process involving unimolecular micelle formation, multimicelle aggregation and microphase separation within a self-confined space. Reversible phase inversion of the nanospheres in response to the solvent environment was observed.
Co-reporter:Lei Yang and Junpo He
Chemical Communications 2014 - vol. 50(Issue 99) pp:NaN15725-15725
Publication Date(Web):2014/10/28
DOI:10.1039/C4CC07647H
We have developed a method to prepare covalently functionalised graphene using ferric perchlorate as the catalyst. The resulting functionalised graphene was characterised by Raman spectroscopy, TGA, XPS, AFM, and dispersibility tests in organic or aqueous media.
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