Synthesis of functional star‐shaped poly(ethylene oxide) using the macromonomer technique

Functional poly(ethylene oxide) stars were prepared by free‐radical copolymerization of poly(ethylene oxide) macromonomers with divinylbenzene in water. The poly(ethylene oxide) arm was prepared by anionic polymerization using 2‐[2‐(N,N‐dimethylamino)ethoxy]ethanol potassium alkoxide as the initiator. These functional stars were converted into peripherally charged stars by quaternization of the peripheral tertiary amino groups with methyl iodide.     

Preparation of H‐shaped ABCAB terpolymers by atom transfer radical coupling

H‐shaped ABCAB terpolymers composed of polystyrene (PS) (A), poly(ethylene oxide) (PEO) (B), and poly(tert‐butyl acrylate) (PtBA) (C) were prepared by atom transfer radical coupling reaction using ABC star terpolymers as precursors, CuBr and N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as catalysts, and nanosize copper as the reducing agent. The synthesis of 3‐miktoarm star terpolymer PS‐PEO‐(PtBA‐Br) involved following steps: (1) the preparation of PS with an active and an ethoxyethyl‐ptotected hydroxyl group at the same end; (2) the preparation of diblock copolymer PS‐b‐PEO with ethoxyethyl‐protected group at the junction point through the ring‐opening polymerization (ROP) of EO; (3) after de‐protection of ethoxyethyl group and further modification of hydroxyl group, tBA was polymerized by atom transfer radical polymerization using PS‐b‐PEO with 2‐bromoisobutyryl functional group as macroinitiator. The H‐shaped terpolymer could be successfully formed by atom transfer radical coupling reaction in the presence of small quantity of styrene, CuBr/PMDETA, and Cu at 90 °C. The copolymers were characterized by SEC, ¹H NMR, and FTIR in detail. The optimized coupling temperature is 90 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 59–68, 2009     

Heteroarm H‐shaped terpolymers through the combination of the Diels–Alder reaction and controlled/living radical polymerization techniques

Heteroarm H‐shaped terpolymers (PS)(PtBA)–PEO–(PtBA)(PS) and (PS)(PtBA)–PPO–(PtBA)(PS) [where PS is polystyrene, PtBA is poly(tert‐butyl acrylate), PEO is poly(ethylene oxide), and PPO is poly(propylene oxide)], containing PEO or PPO as a backbone and PS and PtBA as side arms, were prepared via the combination of the Diels–Alder reaction and atom transfer radical and nitroxide‐mediated radical polymerization routes. Commercially available PEO or PPO containing bismaleimide end groups was reacted with a compound having an anthracene functionality, succinic acid anthracen‐9‐yl methyl ester 3‐(2‐bromo‐2‐methylpropionyloxy)‐2‐methyl‐2‐[2‐phenyl‐2‐(2,2,6,6‐tetramethylpiperidin‐1‐yloxy)ethoxycarbonyl]propyl ester, with a Diels–Alder reaction strategy. The obtained macroinitiator with tertiary bromide and 2,2,6,6‐tetramethylpiperidin‐1‐oxy functional end groups was used subsequently in the atom transfer radical polymerization of tert‐butyl acrylate and in the nitroxide‐mediated free‐radical polymerization of styrene to produce heteroarm H‐shaped terpolymers with moderately low molecular weight distributions (<1.31). The polymers were characterized with ¹H NMR, ultraviolet, gel permeation chromatography, and differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3947–3957, 2006     

Synthesis of well‐defined macromonomers by the combination of atom transfer radical polymerization and a click reaction

This article presents a new strategy for synthesizing a series of well‐defined macromonomers. Bromine‐terminated polystyrene and poly(t‐butyl acrylate) with predetermined molecular weights and narrow distributions were prepared through the atom transfer radical polymerization of styrene and t‐butyl acrylate initiated with ethyl 2‐bromoisobutyrate. Then, azido‐terminated polymers were obtained through the bromine substitution reaction with sodium azide. Catalyzed by CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine, the azido end group reacted with propargyl methacrylate via a 1,3‐dipolar cycloaddition reaction, and ω‐methacryloyl‐functionalized macromonomers were thus obtained. The end‐group transformation yields were rather high, as characterized by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra and ¹H NMR analysis. By this effective and facile approach, some novel macromonomers that otherwise are difficult to achieve, such as poly(ethylene oxide)‐block‐polystyrene, were easily prepared. Radical homopolymerizations of these macromonomers were performed, and a series of comb polymers were prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6103–6113, 2006     

Gradient graft copolymers derived from PEO‐based macromonomers

Atom transfer radical polymerization (ATRP) of two poly(ethylene oxide) (PEO) macromonomers, with different polymerization degrees (DP_n) and different end groups, was conducted in solution via the grafting through method. Selection of a PEO methacrylate with a methyl end‐group (PEOMeMA, DP_PEO = 23) and a PEO acrylate end‐capped by a phenyl ring (PEOPhA, DP_PEO = 4) for the copolymerization led to a spontaneous gradient of PEO grafts along the copolymer backbone. Such a composition was formed because of significantly different reactivities of the two PEO macromonomers. The resulting copolymer has PEOMeMA at one end of the polymer chain, gradually changing through hetero‐sequences of PEOPhA at the other chain end. An increase in the initial feed ratio of PEO acrylate reduced the rate of change in the shape of the gradient. Amorphous–crystalline structure in the copolymers was demonstrated by DSC and WAXS. The mechanical measurements of copolymers consisting of an amorphous PEOPhA and crystallizable PEOMeMA segments indicated elastomeric properties in the range of a soft rubber (G′ ～ 10⁴ Pa, G′ ? G″). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1347–1356, 2006     

Synthesis of amphiphilic ABC triblock copolymers by single electron transfer nitroxide radical coupling reaction in tetrahydrofuran

A series of ABC triblock copolymers, that is, polyisoprene‐block‐polystyrene‐block‐poly(ethylene oxide) (PI‐PS‐PEO), PI‐block‐poly(tert‐butyl acrylate)‐block‐PEO (PI‐PtBA‐PEO), and PI‐block‐poly(acrylic acide)‐block‐PEO (PI‐PAA‐PEO) were obtained by combination of anionic technique, atom transfer radical polymerization (ATRP), and single electron transfer nitroxide coupling (SETNRC) reaction. Anionic polymerization of isoprene followed by end capping with ethylene oxide yielded hydroxyl‐terminated PI. After esterification, PI with Br end group was used as a macroinitiator to initiate the polymerization of styrene and tBA by ATRP that was then trapped by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group in PEO by SETNRC reaction rapidly with high efficiency in tetrahydrofuran at room temperature. The effect of reaction time and polymer chain length on SETNRC reaction was discussed in detail. In the presence of Cu⁰/tris[2‐(dimethylamino)ethyl]amine, SETNRC between PI‐PS‐Br and PEO‐TEMPO was carried out with the efficiency of up to 91.6% in 2 h. With the increase in polymer chain length, the efficiency decreased fleetly. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of Well‐Defined Diblock Copolymers with Short Polypeptide Segments by Polymerization of N‐Carboxy Anhydrides

Summary: The ring‐opening polymerization of N‐carboxy anhydrides (NCA) of γ‐benzyl‐L ‐glutamate and β‐benzyl‐L ‐aspartate was studied in the presence of an ammonium chloride‐functionalized poly(ethylene oxide) macroinitiator, which possibly prevents side reactions such as NCA deprotonation. Although polymerization initiated by such macroinitiators was found to be quite slow, well‐defined conjugates of poly(ethylene oxide)‐block‐poly(γ‐benzyl‐L ‐glutamate) and poly(ethylene oxide)‐block‐poly(β‐benzyl‐L ‐aspartate) with polydispersity indexes as low as 1.05 were prepared. Moreover, the presence of ammonium chloride chain ends significantly prevented end‐group cyclization of poly(γ‐benzyl‐L ‐glutamate) after polymerization.

Gel permeation chromatograms recorded for the diblock copolymers of poly(ethylene oxide)‐block‐poly(γ‐benzyl‐L ‐glutamate) prepared by N‐carboxy anhydride polymerization initiated either by PEO‐NH₂ macroinitiator or PEO‐NHequation/tex2gif-stack-1.gifCl⁻ macroinitiator.     

Changes in the Hydration State of a Block Copolymer of Poly(N‐isopropylacrylamide) and Poly(ethylene oxide) on Thermosensitive Micellization in Water

A diblock copolymer of poly(N‐isopropylacrylamide) and poly(ethylene oxide) (PiPA‐b‐PEO) has been prepared by radical polymerization with a ceric ion initiation system. Its thermosensitive micellization has been investigated by means of IR and fluorescence spectroscopy. The PiPA segments are critically dehydrated above 33.5°C (5 wt.‐%) and associate through hydrophobic interaction to form the hydrophobic core of the micelle. In contrast, the change in the hydration state of the PEO segments upon micellization is small.     

Synthesis and Characterization of α,ω‐Heterofunctional Poly(ethylene oxide) Macromonomers

A novel α,ω‐heterofunctional poly(ethylene oxide) (PEO) macromonomer possessing methacryloyl and thienyl end groups was prepared by ring‐opening polymerization of ethylene oxide initiated by potassium thienylethoxide and termination of the living PEO ends with methacryloyl chloride. Incorporation of methacryloyl and thienyl groups was confirmed by free‐radical and oxidative polymerization processes, respectively, and by means of ¹H NMR analysis.

     

Synthesis of well‐defined macromonomers and comb copolymers from polymers made by atom transfer radical polymerization

Poly(n‐butyl acrylate) macromonomers with predetermined molecular weights (1300 < number‐average molecular weight < 23,000) and low polydispersity indices (<1.2) were synthesized from bromine‐terminated atom transfer radical polymerization polymers via end‐group substitution with acrylic acid and methacrylic acid. These macromonomers, having a high degree of end‐group functionalization (>90%), were radically homopolymerized to obtain comb polymers. A high macromonomer concentration, combined with a low radical flux, was needed to obtain a high conversion of the macromonomers and a reasonable degree of polymerization. By the traditional radical copolymerization of the hydrophobic macromonomers with the hydrophilic monomer N,N‐dimethylaminoethyl methacrylate (DMAEMA), amphiphilic comb copolymers were obtained. The conversions of the macromonomers and comonomer were almost quantitative under optimized reaction conditions. The molecular weights were high (number‐average molecular weight ≈70,000), and the molecular weight distribution was broad (polydispersity index ≈ 3.5). Kinetic measurements showed simultaneous decreases in the macromonomer and DMAEMA concentrations, indicating a relatively homogeneous composition of the comb copolymers over the whole molecular weight range. This was supported by preparative size exclusion chromatography. The copolymerization of poly(n‐butyl acrylate) macromonomers with other hydrophilic monomers such as acrylic acid or N,N‐dimethylacrylamide gave comb copolymers with multimodal molecular weight distributions in size exclusion chromatography and extremely high apparent molecular weights. Dynamic light scattering showed a heterogeneous composition consisting of small (6–9 nm) and large (23–143 nm) particles, probably micelles or other type of aggregates. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3425–3439, 2003     

Uniform PEO Star Polymers Synthesized in Water via Free Radical Polymerization or Atom Transfer Radical Polymerization

Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross‐linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple “arm‐first” method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross‐linked by divinylbenzene (DVB) using 2,2′‐azoisobutyronitrile (AIBN). Uniform star polymers ( < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross‐linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP.

     

Synthesis of double hydrophilic poly(ethylene oxide)‐b‐poly(2‐hydroxyethyl acrylate) by single‐electron transfer–living radical polymerization

In this study, the polymerization of (2‐hydroxyethyl) acrylate (HEA), in polar media, using Cu(0)‐mediated radical polymerization also called single‐electron transfer–living radical polymerization (SET‐LRP) is reported. The kinetics aspects of both the homopolymerization and the copolymerization from a poly(ethylene oxide) (PEO) macroinitiator were analyzed by ¹H NMR. The effects of both the ligand and the solvent were studied. The polymerization was shown to reach very high monomer conversions and to proceed in a well‐controlled fashion in the presence of tris[2‐(dimethylamino)ethyl]amine Me6‐TREN and N, N,N′, N″, N″‐pentamethyldiethylenetriamine (PMDETA) in dimethylsulfoxide (DMSO). SET‐LRP of HEA was also led in water, and it was shown to be faster than in DMSO. In pure water, Me₆‐TREN allowed a better control over the molar masses and polydispersity indices than PMDETA and TREN. Double hydrophilic PEO‐b‐PHEA block copolymers, exhibiting various PHEA block lengths up to 100 HEA units, were synthesized, in the same manner, from a bromide‐terminated PEO macroinitiator. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Oxazoline‐terminated macromonomers by the alkylation of 2‐methyl‐2‐oxazoline

Well‐defined macromonomers of poly(ethylene oxide) and poly(tert‐butyl methacrylate) were obtained by anionic polymerization induced directly by the carbanion issued from 2‐methyl‐2‐oxazoline. When ethylene oxide was added to this carbanion with lithium as the counterion, a new compound able to initiate the polymerization of ε‐caprolactone in an anionically coordinated way was synthesized, and this led to well‐defined poly(ε‐caprolactone) macromonomers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2440–2447, 2005     

Star polymers by cross‐linking of linear poly(benzyl‐L‐glutamate) macromonomers via free‐radical and RAFT polymerization. A simple route toward peptide‐stabilized nanoparticles

Poly(benzyl‐L ‐glutamate) (PBLG) macromonomers were synthesized by N‐carboxyanhydride (NCA) polymerization initiated with 4‐vinyl benzylamine. MALDI‐ToF analysis confirmed the presence of styrenic end‐groups in the PBLG. Free‐radical and RAFT polymerization of the macromonomer in the presence of divinyl benzene produced star polymers of various molecular weights, polydispersity, and yield depending on the reaction conditions applied. The highest molecular weight (M_w) of 10,170,000 g/mol was obtained in a free‐radical multibatch approach. It was shown that the PBLG star polymers can be deprotected to obtain poly(glutamic acid) star polymers, which form water soluble pH responsive nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Preparation of amphiphilic ternary block copolymers with PEO as the middle block and the effect of PEO position on the glass transition temperature (Tg) of copolymers

The copolymer of polystyrene‐block‐poly(ethylene oxide)‐block‐poly (tert‐butyl acrylate) (PS‐b‐PEO‐b‐PtBA) was prepared, the synthesis process involved ring‐opening polymerization (ROP), nitroxide‐mediated polymerization (NMP), and atom transfer radical polymerization (ATRP), and 4‐hydroxyl‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (HTEMPO) was used as parent compound. The PEO precursors with α‐hydroxyl‐ω‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy end groups(TEMPO‐PEO‐OH) were first obtained by ROP of EO using HTEMPO and diphenylmethylpotassium (DPMK) as the coinitiator. The TEMPO at one end of PEO chain mediated the polymerization of St using benzoyl peroxide as initiator. The resultant PS‐b‐PEO‐OH reacted further with 2‐bromoisobutyryl bromide and then initiated the polymerization of tBA in the presence of CuBr and PMDETA by ATRP. The ternary block copolymers PS‐b‐PEO‐b‐PtBA and intermediates were characterized by gel permeation chromatography, Fourier transform infrared, and nuclear magnetic resonance spectroscopy in detail. Differential scanning calorimetry measurements confirmed that the PS‐b‐PEO‐b‐PtBA with PEO as middle block can weaken the interaction between PS and PtBA blocks, the glass transition temperature (T_g) for two blocks were approximate to their corresponding homopolymers comparing with the PEO‐b‐PS‐b‐PtBA with PEO as the first block. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2624–2631, 2008     

ATRP合成大分子单体法制备核壳结构微球

以α-溴代丙酸乙酯(EPN-Br)为引发剂, N,N, N′,N″,N″-五甲基二亚乙基三胺(PMDETA)为配体,使甲基丙烯酸叔丁酯进行原子转移自由基聚合,合成了端基带溴原子的聚甲基丙烯酸叔丁酯(PtBMA-Br)大分子中间体,通过其与甲基丙烯酸的亲核取代反应,得到了末端C=C双键含量高的大分子单体（MAA-PtBMA）,其相对分子质量可控制在5400-12000g/mol的范围内,分子量分布≤1.20。以偶氮二异丁腈为自由基引发剂,在乙醇中使MAA-PtBMA大分子单体与苯乙烯（St）进行分散共聚,制得了甲基丙烯酸叔丁酯接枝聚苯乙烯（PtBMA-g-PSt）微米级共聚微球,该微球具有核壳结构。     

Synthesis and Liquid Crystalline Behavior of Random Copolymer of Poly(ethylene oxide) Macromonomer and Liquid Crystalline Monomer by the Photon Transmission Technique

Random copolymers of poly(ethylene oxide) macromonomer with p‐vinylbenzyl end‐functional group (PEOVB) and liquid crystalline monomer, namely 6‐(4‐cyanobiphenyl‐4′‐oxy)hexyl acrylate (COA), were prepared by conventional free radical polymerization. A living anionic polymerization technique was employed for the synthesis of PEO macromonomers bearing p‐vinylbenzyl moiety at one end. The photon transmission method was also applied to study the phase transitions of COA monomer and its random copolymer with PEO. It was found that, for both samples, the nematic‐smectic A transition is continuous, but the critical fluctuation regions do not allow to obtain 3D XY values. Instead, we have obtained the values close to mean field regime. Scaling of thermal hystersis for random copolymer sample near the nematic‐isotropic transition was studied as well. Thermal hysteresis loops were produced under linearly varying temperature. It was shown that the areas of the hysteresis loops scale with the temperature scanning rate with an exponent being equal to 0.614 which is in good agreement with the field‐theoretical value.     

Preparation of amphiphilic poly(ethylene oxide)‐block‐polystyrene macrocycles via glaser coupling reaction under CuBr/pyridine system

The amphiphilic cyclic poly(ethylene oxide)‐block‐polystyrene [c‐(PEO‐b‐PS)] was synthesized by cyclization of propargyl‐telechelic poly(ethylene oxide)‐block‐polystyrene‐block‐poly(ethylene oxide) (?? PEO‐b‐PS‐b‐PEO? ?) via the Glaser coupling. The hydroxyl‐telechelic ABA triblock PEO‐b‐PS‐b‐PEO was first prepared by successive living anionic polymerization of styrene and ring‐opening polymerization of ethylene oxide, and then the hydroxyl ends were reacted with propargyl bromide to obtain linear precursors with propargyl terminals. Finally, the intramolecular cyclization was conducted in pyridine under high dilution by Glaser coupling of propargyl ends in the presence of CuBr under ambient temperature, and the c‐(PEO‐b‐PS) was directly obtained by precipitation in petroleum ether with high efficiency. The cyclic products and their corresponding linear precursor ?? PEO‐b‐PS‐b‐PEO? ? were characterized by means of GPC, ¹H NMR, and FTIR. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Electron Transfer Reactions of Radical Anions with TEMPO: A Versatile Route for Transformation of Living Anionic Polymerization into Stable Radical‐Mediated Polymerization

Summary: The possibility of transforming a living anionic polymerization into a stable radical‐mediated radical polymerization (SFRP) was demonstrated. For this purpose, 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) alcoholate, formed by a one‐electron redox reaction between potassium naphthalene and TEMPO, was used to initiate the living anionic polymerization of ethylene oxide (EO). Poly(ethylene oxide) obtained in this way possessed TEMPO terminal units and was subsequently used as an initiator for the SFRP of styrene to give block copolymers.

A one‐electron redox reaction gives rise to TEMPO alcoholate, which is able to initiate the living anionic polymerization of ethylene oxide (EO).     

Synthesis of telechelics and block copolymers via “living” radical polymerization

Hydroxy‐telechelic poly(methyl methacrylate)s of molecular weights below 5000 were obtained by atom transfer radical polymerization (ATRP) of methyl methacrylate followed by end‐capping with allyl alcohol via atom transfer radical addition (ATRA). As initiators for the ATRP, monofunctional initiators with an additional hydroxy group in the molecule or bifunctional initiators were employed. The successful synthesis of the hydroxy‐telechelic PMMA was proved by determination of their molecular weight using MALDI‐TOF‐MS. The efficiency of the end‐capping reaction was determined by ¹H NMR spectroscopy using the allyl N‐(4‐tolyl)carbamate as end‐capping agent. Block copolymers comprising a poly(ethylene oxide) (PEO) block and a poly(methyl methacrylate) (PMMA) block were prepared by ATRP using a macroinitiator on the PEO basis. The dormant species of the macroinitiator consists of the phenyl chloroacetate moiety which shows a high rate of initiation. The successful synthesis of the poly(ethylene oxide)‐block‐poly(methyl methacrylate) was proved by ¹H NMR spectroscopy; the ratios of EO/MMA repeating units in the feed and the copolymer were nearly equal.