Synthesis and characterization of well-defined comb-like branched polymers

Well-defined comb-like branched polymers having one branch in each repeating unit have been successfully synthesized by the coupling reaction of living polystyrene (PS) and polyisoprene (PI) anions with 1, 1-diphenylethenyl (DPE) groups along PS backbone prepared via atom transfer radical polymerization (ATRP) of 4-vinylbenzyloxy benzophenone (Sc) followed by Wittig reaction. The resulting comb-like branched polymers were characterized by IR, ¹H-NMR, gel permeation chromatography (GPC) and static light scattering (SLS) in detail. The effect of living chains and DPE group molar ratio on grafting efficiency was discussed. The results show the coupling reaction of living chains and DPE groups was highly effective, and the coupling efficiency can be controlled via the feed molar ratios of living chains and DPE groups. Moreover, the effect of molecular weights of backbone (PSe) and PSLi or PILi on grafting efficiency was also discussed. The results show that when excess living polymers were used, the almost quantitative grafting efficiency could be achieved. __________ Translated from Acta Polymerica Sinica (China), 2007, (3): 203–208 [译自: 高分子学报]     

Studies on the blends of polycarbonate and highly branched polystyrene

A highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4‐(chloromethyl) styrene with styrene using the self‐condensing atom transfer radical polymerization method. The addition of this highly branched polystyrene as a melt modifier for polycarbonate (PC) was attempted. Indeed, the results show that the addition of highly branched polystyrene can decrease the melt viscosity of PC with little change in mechanical properties, although the blends do exhibit lower thermal stability compared with pure PC. Extrapolation shows that all of the blends have an initial weight loss temperature above 450°C with a statistic heat‐resistant index T_s above 225°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2425–2430, 2004     

Novel ionic liquids as reaction medium for ATRP of acrylonitrile in the absence of any ligand

Atom transfer radical polymerization (ATRP) of acrylonitrile (AN) with ethyl 2-bromoisobutyrate (EBiB) as the initiator was firstly approached in the absence of any ligand in three novel ionic liquids, 1-methylimidazolium acetate ([mim][AT]), 1-methylimidazolium valerate ([mim][VT]) and 1-methylimidazolium caproate ([mim][CT]), respectively. All the polymerizations in the ionic liquids proceeded in a well-controlled manner. The polymerization in [mim][AT] not only showed the best control of molecular weight and its distribution but also provided a rather rapid reaction rate with the molar ratio of [AN]:[FeBr₂]:[EBiB] at 200:2:1. The resulting polyacrylonitrile was successfully used as the macroinitiator to proceed the chain extension polymerization in [mim][AT]. After simple purification, all the ionic liquids and FeBr₂ could be recycled and reused and had no effect on the living nature of polymerization.     

支化聚苯乙烯的合成及其与ABS的共混

以对氯甲基苯乙烯(CMS)、苯乙烯、2,2′-联吡啶(Bpy)和CuCl组成过渡金属催化原子转移自由基聚合制备支化聚苯乙烯(BPS)。研究了少量BPS的引入对丙烯腈-丁二烯-苯乙烯共聚物(ABS)熔体流动性能和热性能的影响。以Bpy/CuCl作为络合催化剂,CMS和苯乙烯可顺利自缩合乙烯基聚合合成BPS。在ABS中加入少量的BPS后,共混物的拉伸强度小幅提高,耐热性能基本保持不变,而熔体黏度降低7%～18%,改善了ABS的加工性能。     

Trapping polystyrene radicals using nitrones: Synthesis of polymers with mid-chain alkoxyamine functionality

Polystyrene radicals were formed in the presence of NtBPN under a variety of reaction conditions and reactant ratios, forming polymer dimers of twice the molecular weight of the monobrominated polystyrene (PStBr) precursors. The polystyrene radicals were generated by the activation of the monohalogentated polystyrene precursors, prepared by atom transfer radical polymerization (ATRP). The extent of radicals trapped by the nitrone, and therefore containing mid-chain alkoxyamine functionality, was determined by thermolysis of the polymer dimers, with the C-O bond in this functionality being cleaved and reverting the chains back to the approximate size of the precursors. Polymer dimers could also be formed simply by radical-radical combination of the chain-ends, which is conventional atom transfer radical coupling (ATRC) and thus contains a head-to-head C-C bond, rendering them inert to thermolysis under conditions that cleave the C-O bond. It was found that near quantitative alkoxyamine mid-chain functionality could be achieved by activating the PStBr in the presence of 10 equivalents of nitrone, 5 equivalents of copper bromide, and 2 equivalents of copper metal. Further reducing the amount of copper metal led to incomplete coupling, while increasing the equivalents beyond 2 generated polymer dimers with less than quantitative mid-chain functionality. Monochlorinated polystyrene (PStCl) precursors gave much poorer coupling results compared to reactions with PStBr, which is consistent with the stronger C-Cl bond resisting activation and the formation of the polystyryl radicals.     

High-pressure atom transfer radical polymerization of methyl methacrylate for well-defined ultrahigh molecular-weight polymers

The feasibility of high-pressure atom transfer radical polymerization (ATRP) for synthesizing well-defined polymers of extraordinarily high molecular weights was demonstrated. ATRP of methyl methacrylate (MMA) under pressures up to 500 MPa was investigated at 60 °C. The addition of a small amount of a Cu(II)Cl₂/ligand complex along with the general benefits of high pressure of enhancing propagation and suppressing termination brought about an excellent control of polymerization even with an extremely low concentration of ATRP initiator. For example, there was produced PMMA with a number-average molecular weight M_n of 3.6 × 10⁶ and a polydispersity index of 1.24, which had never been achieved by conventional ATRP.     

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)₂-PEO-(PMMA)₂ has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)₂-CHCOOCH₂CH₂OH with an active hydroxyl group. The chlorine was removed to yield the (PS)₂-CHCOOCH₂CH₂OH ((PS)₂-OH). The hydroxyl group of the (PS)₂-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)₂-PEO-OH. The (PS)₂-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)₂-PEO-OCCHCl₂ ((PS)₂-PEO-DCA). The asymmetric H-shaped block polymer (PS)₂-PEO-(PMMA)₂ was prepared via ATRP of MMA at 130 °C using (PS)₂-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)₂-PEO-(PMMA)₂, were confirmed by ¹H NMR, GPC and FT-IR.     

原子转移自由基聚合合成支化聚丙烯腈

以二乙烯苯为支化单体,α-溴代异丁酸叔丁酯为引发剂,CuBr和2,2'-联吡啶为催化体系,利用本体和溶液原子转移自由基聚合合成了支化聚丙烯腈.采用核磁共振谱仪、凝胶渗透色谱仪和多角度激光光散射仪等测试了聚合物结构、相对分子质量及其分布.用无水乙酸钠对支化聚丙烯腈进行末端改性,得到了在硫氰酸钠水溶液中性能稳定、可长期保存的支化聚丙烯腈,而改性对聚合物的耐热性能没有影响.     

One-pot synthesis of star polymer by ATRP of bismaleimide and an excess of styrene with a conventional initiator

A pragmatic one-pot approach to the synthesis of star polymers is reported using atom transfer radical copolymerization (ATRcP) of a bismaleimide and an excess of styrene (St) initiated with a conventional ATRP initiator.     

Synthesis of well-defined star polymers and star block copolymers from dendrimer initiators by atom transfer radical polymerization

Novel polyarylether dendrimers with 1,3,5-tri(4-hydroxyphenoxy)benzene core, polybenzylether interior, and benzyl 2-bromoisobutyrate surface group (CMGn-Br, n=1-3, with functionality of 6, 12, and 24, respectively) were prepared by convergent procedure. ATRP of tert-butyl acrylate (tBA) and styrene (St) with CMGn-Br dendrimer initiators in the presence of CuBr/pentamethyldiethylenetriamine catalytic system was investigated in detail, and a series of well-defined dendrimer-like star PtBA and PSt with precise arm numbers were synthesized under suitable conditions. The quantitative initiation of the dendrimer initiators was demonstrated by high initiation efficiency, ¹H NMR spectra, hydrolysis, and MALLS/SEC approach. Star block copolymers comprising PSt and PtBA segments with low polydispersity (1.08<M_w/M_n<1.18) were also successfully synthesized using functional macroinitiators by block copolymerization. In addition, the thermal properties of the resultant polymers were characterized by DSC and TGA.     

Synthesis and photoluminescent property of star polymers with carbzole pendent and a zinc porphyrin core by ATRP

Styrene-type monomer 9-(4-vinylbenzyl)-9H-carbazole (VBCz) and methacrylate-type monomer 2-(9H-carbazole-9-yl)-ethyl methacrylate (CzEMA) were polymerized to star polymers respectively via atom transfer radical polymerization (ATRP) using zinc 5,10,15,20-tetrakis(4-(2-methyl-2-bromopropoxy) phenyl) porphyrin as an initiator. The emission spectra of two star polymers (star poly(VBCz) and star poly(CzEMA)) in the solid state displayed red light emission, while those of two monomers showed blue light emission. The result demonstrates that effective energy transfer occurs from the carbazole to the Zn porphyrin core. However, two star polymers in DMF solution emit week red light and strong UV light at 350-400 nm, it points that energy transfer cannot occur from the carbazole to the Zn porphyrin core effectively. They exhibit good thermal stability with T_{d poly(VBCz)} = 374 °C and T_{d poly(CzEMA)} = 297 °C at 5% weight loss. The DSC curves show that the glass transition temperature of styrene-type (T_{g poly(VBCz)} = 177 °C) was better than that of methacrylate-type (T_{g poly(CzEMA)} = 148 °C).     

Controlled synthesis of linear and comb-like glycopolymers for preparation of honeycomb-patterned films

Honeycomb-patterned films can be facilely prepared by the breath figure method. However, it is still ambiguous how the polymer structure affects the morphologies of the films. In this work, poly(styrene-co-2-(2-,3-,4-,6-tetra-O-acetyl-β-d-glucosyloxy) ethyl methacrylate) (PS-co-AcGEMA) with well-defined linear and/or comb-like structures were synthesized by atom transfer radical polymerization (ATRP). These glycopolymers were used as precursors for the fabrication of pattern films by the breath figure method. The regularity and pore size of the films are greatly influenced by the polymer structure and the solution concentration. Highly ordered pattern films can be prepared from the comb-like glycopolymer and the linear block glycopolymers with relatively long PAcGEMA segment. Further studies of lectin recognition on the honeycomb-patterned films demonstrate that the glucose-containing films can specifically recognize Con A. These bioactive honeycomb-patterned films have potential applications as templates, picoliter beakers for bioanalysis and cell culture materials.     

“活性”自由基聚合的研究现状及发展趋势

以原子转移自由基聚合为重点,结合作者在这一领域的研究成果,简要综述了“活性”（可控）自由基聚合进展。     

Novel fluorescent polynorbornenes with multi-functional armed structure by using highly stable block macroinitiators via a combination of living ring-opening metathesis polymerization and atom transfer radical polymerization

Novel organosoluble fluorescent polynorbornenes with multi-functional armed structure were designed and prepared by using highly stable block macroinitiators via a combination of living ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). A bromo-containing functional norbornene (NBMBr) was prepared from the Diels-Alder reaction of cyclopentadiene and allyl bromide. The diblock copolymer of 5-(N-carbazolyl methyl)bicycle[2.2.1]hept-2-ene (CbzNB) and NBMBr was successfully prepared using living ROMP and used as a novel macroinitiator [poly(CbzNB-b-NBMBr)] for ATRP. Carbazoyl-containing multi-functional armed copolymer with poly(methyl methacrylate) (PMMA) was prepared by using poly(CbzNB-b-NBMBr) as a macroinitiator for ATRP. Strong fluorescence emissions (370-450 nm) were observed in the low excimer-forming multi-functional armed fluorescent polynorbornenes. The fact is that low excimer-forming carbazole-containing polymeric compound would apparently be favorable in photoconductive materials. The multi-functional armed structure make this compound an attractive candidate for applications as multi-modified hole transport materials in molecular electronic devices. Multi-modification could be further considered to be carried out by using such a functional bromo group at the end of multi-arms.     

New macromolecular silane coupling agents synthesized by living anionic polymerization; grafting of these polymers onto inorganic particles and metals

New macromolecular silane coupling agents, which are end-triethoxysilylated poly(styrene) and poly(tert-butylmethacrylate), were investigated as possible inorganic particle and metal surface treatment agents. These polymers containing poly(styrene) and poly(tert-butylmethacrylate) as the main chain, were prepared by living anionic polymerization. Grafting of the polymers onto inorganic particles and metals was performed via the hydrolysis of the triethoxysilyl group using either acidic or basic catalyst. n-Butylphosphate was used as the catalyst for grafting onto inorganic substances having an acidic surface such as silica. However, in the case of grafting onto inorganic substances having a basic surface, tetrabutylammoniumhydroxide was employed as the catalyst. Contrary to expectations, grafting onto titania was successful even in the absence of a catalyst. Particles grafted with these polymers showed excellent dispersibility in organic medium, in which the polymers are soluble. This phenomenon is in contrast to that for particles treated with polymers possessing triethoxysilyl groups at random positions of the chain or those treated with trimethylsilyl groups. Surface tension measurements of metal substrates coated with the grafted polymers, were found to be identical to the values obtained for the bulk polymers.     

Polymerization of styrene and cyclization to macrocyclic polystyrene in a one-pot,two-step sequence

Dibrominated polystyrene (BrPStBr) was produced by atom transfer radical polymerization (ATRP) at 80 °C, using the bifunctional initiator benzal bromide to afford the telechelic precursor. The ATRP reaction was stopped around 40% monomer conversion and directly converted into an radical trap-assisted atom transfer radical coupling (RTA-ATRC) reaction by lowering the temperature to 50 °C, and adding the radical trap 2-methyl-2-nitrosopropane (MNP) along with additional catalyst, reducing agent, and ligand to match ATRC-type reaction conditions. In an attempt to induce intramolecular coupling, rather than solely intermolecular coupling and elongation, the total reaction volume was increased by the addition of varying amounts of THF. Cyclization, along with intermolecular coupling and elongation, occurred in all cases, with the extent of ring closure a function of the total reaction volume. The cyclic portion of the coupled product was found to have a 〈G〉 value around 0.8 by GPC analysis, consistent with the reduction in hydrodynamic volume of a cyclic polymer compared to its linear analog. Analysis of the sequence by ¹H NMR confirmed that propagation was suppressed nearly completely during the RTA-ATRC phase, with percent monomer conversion remaining constant after the ATRP phase.     

Facile atom transfer radical homo and block copolymerization of higher alkyl methacrylates at ambient temperature using CuCl/PMDETA/quaternaryammonium halide catalyst system

Controlled polymerization of higher alkyl methacrylates, e.g. lauryl methacrylate (LMA) and stearyl methacrylate (SMA) has been successfully achieved by atom transfer radical polymerization (ATRP) at ambient temperature using CuCl/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA)/tricaprylylmethylammonium chloride (Aliquat^®336) as the catalyst system and ethyl 2-bromoisobutyrate or 2,2,2-trichloroethanol as the initiator. Although the bulk polymerization gives satisfactory control, the latter becomes better when anisole or THF is added into the system. Without AQCl the control was lost. A large deviation of molecular weight from theory has been observed which has been attributed to the very high-molecular weight of the dead polymers formed during the building-up of the persistent radical. The controlled polymers have been used as macroinitiators for block (di, tri and penta) ATR copolymerization with several methacrylates.     

Study of optically active methacrylates containing 1,1′‐binaphthyl side‐groups polymerized by anionic,group transfer and free radical methods

Optically active and racemic poly(meth)acrylates with pendant 1,1′‐binaphthalene moiety of 2‐methacryloyloxy‐ and 2‐acryloyloxy‐2′‐methoxy‐1,1′‐binaphthalene (MAMBN and AMBN) were synthesized by anionic, group transfer and free radical polymerization methods. Their polymerizability and chiroptical properties are somewhat different, depending on the three types of polymerization methods used. The yields for poly(MAMBN)s are lower than for poly(AMBN)s. The optical rotation of the optically active polymers is identical to that of the corresponding monomers. The values of specific rotation of optically active poly(AMBN)s are much larger than those of optically active poly(MAMBN)s. © 2002 Society of Chemical Industry     

Modification of carbon nanotubes with well-controlled fluorescent styrene-based polymers using the Diels-Alder reaction

A simple and single-step “grafting to” approach based on the Diels-Alder (DA) reaction is described to functionalize multi-wall carbon nanotubes (MWCNTs) with polystyrene (PSt). Thus, several fluorescent and furfuryl functionalized PSts, synthesized by the atom transfer radical polymerization (ATRP) of styrene, furfuryl methacrylate and low proportion of a fluorescent monomer, were covalently attached onto the pristine nanotubes. Furfuryl (diene) groups allowed the chemical attachment of the PSt polymer onto the as-synthesized MWCNTs by a DA reaction. On the other hand, the incorporation of fluorescent groups in the polymer has two main advantages. It permits to determine the attachment of the polymer onto the nanotubes and, in further applications, it will allow to follow the dispersion of these modified MWCNTs in a matrix. The efficiency of the functionalization was verified by FTIR, Raman spectroscopy, TEM, AFM and fluorescence techniques.     

Advances in RAFT polymerization: the synthesis of polymers with defined end-groups

This paper provides an overview and discusses some recent developments in radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization). Guidelines for the selection of RAFT agents are presented. The utility of the RAFT process is then illustrated with several examples of the synthesis of polymers with reactive end-groups. Thus, RAFT polymerization with appropriately designed trithiocarbonate RAFT agents is successfully applied to the synthesis of narrow polydispersity carboxy-functional poly(methyl methacrylate) and primary amino-functional polystyrene. Methods for removing the thiocarbonylthio end-group by aminolysis, reduction and thermal elimination are discussed. It is shown that the thiocarbonylthio end-group can be cleanly cleaved by radical induced reduction with tri-n-butylstannane, to leave a saturated chain end, or by thermolysis, to leave an unsaturated chain end.