Novel synthesis of rod‐coil block copolymers by combination of coordination polymerization and ATRP

Combination of coordination polymerization and atom transfer radical polymerization (ATRP) was applied to a novel synthesis of rod‐coil block copolymers. The procedure included the following steps: (1) monoesterification reaction of ethylene glycol with 2‐bromoisobutyryl bromide yielded a α‐bromo, ω‐hydroxy bifunctional initiator, (2) CpTiCl₃ (bifunctional initiator) catalyst was prepared from a mixture of trichlorocyclopentadienyl titanium (CpTiCl₃) and bifunctional initiator. Coordination polymerization of n‐butyl isocyanate initiated by such catalyst provided a well‐defined macroinitiator, poly(n‐butyl isocyanate)‐Br (PBIC‐Br), and (3) ATRP method of vinyl monomers using PBIC‐Br provided rod (PBIC)‐coil block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4037–4042, 2007     

Combining atom‐transfer radical polymerization and ring‐opening polymerization through bifunctional initiators derived from hydroxy benzyl alcohol—Preparation and characterization of initiators,macroinitiators, and block copolymers

A simple, one‐step procedure has been developed for the preparation of bifunctional initiators capable of polymerizing monomers suitable for atom‐transfer radical polymerization (ATRP) and ring‐opening polymerization (ROP). These bifunctional initiators were employed for making narrow disperse poly(styrene) macroinitiators, which were subsequently used for the ROP of various lactides to yield poly(styrene‐block‐lactide) copolymers. Thermogravimetric analysis (TGA) of these block copolymers are interesting in that it shows a two‐step degradation curve with the first step corresponding to the degradation of poly(lactide) segment and the second step associated with the poly(styrene) segment of the block copolymer. This nature of the block copolymer makes it possible to estimate the block copolymer content by TGA in addition to the ¹H NMR spectroscopic analysis. Thus, this study for the first time highlights the possibility of making porous materials by thermal means which are otherwise obtained by base hydrolysis. The bifunctional initiators were prepared by the esterification of 3‐hydroxy, 4‐hydroxy, and 3,5‐dihydroxy benzyl alcohols with α‐bromoisobutyryl bromide and 2‐bromobutyryl bromide. A mixture of products was obtained, which were purified by column chromatography. The esterified benzyl alcohols were employed in the polymerization of styrene under copper (Cu)‐catalyzed ATRP conditions to yield macroinitiators with low polydispersity. These macroinitiators were subsequently used in the ROP of L ‐, DL ‐, and mixture of lactides. The formation of block copolymers was confirmed by gel permeation chromatography (GPC), spectroscopic and thermal characterizations. The molecular weight of the block copolymers was always higher than the macroinitiator, and the GPC chromatogram was symmetrical indicating the uniform initiation of ROP by the macroinitiators. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 102–116, 2008     

The preparation of t‐butyl acrylate,methyl acrylate,and styrene block copolymers by atom transfer radical polymerization: Precursors to amphiphilic and hydrophilic block copolymers and conversion to complex nanostructured materials

Atom transfer radical polymerization conditions with copper(I) bromide/pentamethyldiethylenetriamine (CuBr/PMDETA) as the catalyst system were employed for the polymerization of tert‐butyl acrylate, methyl acrylate, and styrene to generate well‐defined homopolymers, diblock copolymers, and triblock copolymers. Temperature studies indicated that the polymerizations occurred smoothly in bulk at 50 °C. The kinetics of tert‐butyl acrylate polymerization under these conditions are reported. Well‐defined poly(tert‐butyl acrylate) (PtBA; polydispersity index = 1.14) and poly(methyl acrylate) (PMA; polydispersity index = 1.03) homopolymers were synthesized and then used as macroinitiators for the preparation of PtBA‐b‐PMA and PMA‐b‐PtBA diblock copolymers in bulk at 50 °C or in toluene at 60 or 90 °C. In toluene, the amount of CuBr/PMDETA relative to the macroinitiator was important; at least 1 equiv of CuBr/PMDETA was required for complete initiation. Typical block lengths were composed of 100–150 repeat units per segment. A triblock copolymer, composed of PtBA‐b‐PMA‐b‐PS (PS = polystyrene), was also synthesized with a well‐defined composition and a narrow molecular weight dispersity. The tert‐butyl esters of PtBA‐b‐PMA and PtBA‐b‐PMA‐b‐PS were selectively cleaved to form the amphiphilic block copolymers PAA‐b‐PMA [PAA = poly(acrylic acid)] and PAA‐b‐PMA‐b‐PS, respectively, via reaction with anhydrous trifluoroacetic acid in dichloromethane at room temperature for 3 h. Characterization data are reported from analyses by gel permeation chromatography; infrared, ¹H NMR, and ¹³C NMR spectroscopies; differential scanning calorimetry; and matrix‐assisted, laser desorption/ionization time‐of‐flight mass spectrometry. The assembly of the amphiphilic triblock copolymer PAA₉₀‐b‐PMA₈₀‐b‐PS₉₈ within an aqueous solution, followed by conversion into stable complex nanostructures via crosslinking reactions between the hydrophilic PAA chains comprising the peripheral layers, produced mixtures of spherical and cylindrical topologies. The visualization and size determination of the resulting nanostructures were performed by atomic force microscopy, which revealed very interesting segregation phenomena. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4805–4820, 2000     

Molecular structure of polymerization product containing phenyl- and diphenylsiloxy units

The molecular structure of the hydrolyzate, and of the prepolymers and polymerization products of phenyltrichlorosilane and diphenyldichlorosilane are investigated. ²⁹Si-NMR measurements reveal the kinds of component units and their ratio in each synthesis step. The molecular structure of the prepolymer chain end and the polymerization product are also discussed in relation to the change in the NMR spectra. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of graft copolymers based on polyepichlorohydrin via reversible addition-fragmentation chain transfer polymerization

In this study, synthesis of poly(epichlorohydrin-g-methyl methacrylate) graft copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization was reported. For this purpose, epichlorohydrin was polymerized by using HNO₃ via cationic ring-opening mechanism. A RAFT macroinitiator (macro-RAFT agent) was obtained by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin. The graft copolymers were synthesized using macro-RAFT agent as initiator and methyl methacrylate as monomer. The synthesis of graft copolymers was conducted by changing the time of polymerization and the amount of monomer-initiator concentration that affect the RAFT polymerization. The effects of these parameters on polymerization were evaluated via various analyses. The characterization of the products was determined using ¹H-nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared spectroscopy, gel-permeation chromatography, thermogravimetric analysis, elemental analysis, and fractional precipitation techniques. The block lengths of the graft copolymers were calculated by using ¹H-NMR spectrum. It was observed that the block length could be altered by varying the monomer and initiator concentrations.     

Anionic ring-opening polymerization of silacyclobutane derivatives

Anionic polymerizations of 1,1-dimethylsilacyclobutane, 1,1-diethylsilacyclobutane and 1-methyl-1-phenylsilacyclobutane were investigated. Addition of 5 mol % of butyllithium to a solution of 1,1-dimethylsilacyclobutane in THF-hexane (1 : 1) at −48°C provided poly(1,1-dimethylsilabutane) in 99% yield. M_n and M_w/M_n of the obtained polymer were 2400 and 1.10. This polymerization proceeded with a living nature. M_n increased in proportion as the yield of polymer increased. Addition of the second fresh feed of the monomer to the reaction mixture restarted polymerization of the second monomer at the same rate as in the initial stage. Addition of styrene to the living poly(1,1-dimethylsilabutane) provided a poly(1,1-dimethylsilabutane-b-styrene) block copolymer. It was also found that a polymerization of 1,1-diethylsilacyclobutane in THF-hexane at −48°C showed a living nature. In contrast, a polymerization of 1-methyl-1-phenylsilacyclobutane in THF at −78°C did not show a living nature. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3207–3216, 1997     

用新型茂钛催化剂制备的苯乙烯/丁二烯嵌段共聚物的结构表征

用CpTi(OBz)3/MAO催化体系合成的苯乙烯／丁二烯嵌段共聚合产物经丁酮、甲苯、四氢呋喃、氯仿连续抽提,并用已烷对丁酮的可溶级分进行再抽提;不同级分分别用GPC、^13C -NMR、DSC和WAXD等手段进行分析和表征。发现嵌段共聚物主要存在于氯仿可溶级分中,丁酮可溶级分基本上是无规聚苯乙烯和聚丁二烯组成的混合物（己烷可溶级分为聚丁二烯,不溶级分为无规模聚乙烯）。GPS谱图表明该嵌段共聚反应具有单催化活性中心的聚合特征,^13C-NMR谱图显示该嵌段共聚物分子链由间规聚苯乙链段和聚丁二烯链段组成,WAXD图谱显示嵌段共聚物有较高的结晶度。     

Photocrosslinkable liquid‐crystalline block copolymers with coumarin units synthesized with atom transfer radical polymerization

A new class of liquid‐crystalline (LC) homopolymers of poly{11‐[4‐(3‐ethoxycarbonyl‐coumarin‐7‐oxy)‐carbonylphenyloxy]‐undecyl methacrylate} containing a coumarin moiety as a photocrosslinkable unit with various polymerization degrees and their LC‐coil diblock and LC‐coil‐LC triblock copolymers with polystyrene as the coil segment was synthesized with the atom transfer radical polymerization method. All the homopolymers and block copolymers synthesized here exhibited narrow polydispersities, indicating well‐controlled living polymerization. Differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray diffraction confirmed that all the homopolymers and block copolymers exhibit a monolayer smectic A phase. Coumarin moieties in the polymers can be photodimerized under λ > 300 nm light irradiation to yield crosslinked network structures, which improve the thermal stability of a polymer nanostructure because of microphase separation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2197–2206, 2003     

Synthesis and characterization of amphiphilic triblock copolymers by iron‐mediated atom transfer radical polymerization

The atom transfer radical polymerization of methyl methacrylate (MMA) and n‐butyl methacrylate (n‐BMA) was initiated by a poly(ethylene oxide) chloro telechelic macroinitiator synthesized by esterification of poly(ethylene oxide) (PEO) with 2‐chloro propionyl chloride. The polymerization, carried out in bulk at 90 °C and catalyzed by iron(II) chloride tetrahydrate in the presence of triphenylphosphine ligand (FeCl₂ · 4H₂O/PPh₃), led to A–B–A amphiphilic triblock copolymers with MMA or n‐BMA as the A block and PEO as the B block. A kinetic study showed that the polymerization was first‐order with respect to the monomer concentration. Moreover, the experimental molecular weights of the block copolymers increased linearly with the monomer conversion, and the molecular weight distribution was acceptably narrow at the end of the reaction. These block copolymers turned out to be water‐soluble through the adjustment of the content of PEO blocks (PEO content >90% by mass). When the PEO content was small [monomer/macroinitiator molar ratio (M/I) = 300], the block copolymers were water‐insoluble and showed only one glass‐transition temperature. With an increase in the concentration of PEO (M/I = 100 or 50) in the copolymer, two glass transitions were detected, indicating phase separation. The macroinitiator and the corresponding triblock copolymers were characterized with Fourier transform infrared, proton nuclear magnetic resonance, size exclusion chromatography analysis, dynamic mechanical analysis, and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5049–5061, 2005     

Synthesis of well‐designed polymers carrying saccharide moieties via RAFT miniemulsion polymerization

Two hydrophobic vinyl saccharide monomers based on D ‐glucose and D ‐fructose were polymerized by employing the reversible addition‐fragmentation transfer (RAFT) miniemulsion polymerization technique to prepare well‐designed glycopolymers. Three dithiobenzoate‐RAFT agents [S?C(Ph)S? R], 1‐phenylethyl dithiobenzoate (PED), 2‐phenylprop‐2‐yl dithiobenzoate (PPD), and 2‐cyanoprop‐2‐yl dithiobenzoate (CPD), were used to control the growth of polymer chains. The best results were obtained in the presence of the PPD‐RAFT agent and the formed polymers have polydispersity index's (PDI) lower than 1.15. Under adequate miniemulsion polymerization conditions, a glycopolymer with PDI of 1.1 and molecular weight of 5 × 10⁴ g/mol has been successfully synthesized in a short reaction time of 100 min. Furthermore, some block copolymers containing saccharide segment with butyl or methyl methacrylate were prepared. Copyright © 2007 John Wiley & Sons, Ltd.     

One‐step synthesis of block‐graft copolymers via simultaneous reversible‐addition fragmentation chain transfer and ring‐opening polymerization using a novel macroinitiator

One‐step synthesis of block‐graft copolymers by reversible addition‐fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) by using a novel initiator was reported. Block‐graft copolymers were synthesized in one‐step by simultaneous RAFT polymerization of n‐butylmethacrylate (nBMA) and ROP of ε‐caprolacton (CL) in the presence of a novel macroinitiator (RAFT‐ROP agent). For this purpose, first epichlorohydrin (EPCH) was polymerized by using H₂SO₄ via cationic ring‐opening mechanism. And then a novel RAFT‐ROP agent was synthesized by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin (poly‐EPCH). By using the RAFT‐ROP agent, poly[CL‐b‐EPCH‐b‐CL‐(g‐nBMA)] block‐graft copolymers were synthesized. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one‐step polymerization reaction were evaluated. The block lengths of the block‐graft copolymers were calculated by using ¹H‐nuclear magnetic resonance (¹H NMR) spectrum. The block length could be adjusted by varying the monomer and initiator concentrations. The characterization of the products was achieved using ¹H NMR, Fourier‐transform infrared spectroscopy, gel‐permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, elemental analysis, and fractional precipitation (γ) techniques. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2651–2659     

Synthesis of carbosilane block copolymers by means of a living anionic polymerization of 1,1-diethylsilacyclobutane

Block polymerization of 1,1-diethylsilacyclobutane with styrene derivatives and methacrylate derivatives was investigated. Sequential addition of styrene to a living poly(1,1-diethylsilabutane), which was prepared from phenyllithium and 1,1-diethylsilacyclobutane in THF–hexane at −48°C, gave poly(1,1-diethylsilabutane)-b-polystyrene. Similarly, addition of 4-(tert-butyldimethylsiloxy)styrene to the living poly(1,1-diethylsilabutane) provided poly(1,1-diethylsilabutane)-b-poly(4-(tert-butyldimethylsiloxy)styrene). Poly(1,1-diethylsilabutane)-b-poly(methyl methacrylate) was obtained by treatment of living poly(1,1-diethylsilabutane) with 1,1-diphenylethylene followed by an addition of methyl methacrylate. Poly(1,1-diethylsilabutane)-b-poly(2-(tert-butyldimethylsiloxy)ethyl methacrylate) was also synthesized by adding 2-(tert-butyldimethylsiloxy)ethyl methacrylate to the living poly(1,1-diethylsilabutane) which was end-capped with 1,1-diphenylethylene in the presence of lithium chloride. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2699–2706, 1998     

Characterization of azo-containing polydimethylsiloxanes and their copolymers with methyl methacrylate

Azo group-containing polydimethylsiloxanes (PDMS–ACP), macroazoinitiators, were prepared by polycondensation reaction of 4,4′-azobis-4-cyanopentanoyl chloride (ACPC) with hydroxybutyl-terminated polydimethylsiloxane (PDMS) of varying molecular weights. The activation energy (E_a), activation enthalpy (ΔH^‡), and activation entropy (ΔS^‡) of the thermodecomposition of PDMS-ACP in toluene increased with increase in poly-dimethyl-siloxane chain length (SCL) in PDMS moieties, while the activation free energy (ΔG^‡) was independent on the SCL. The polydimethylsiloxane-poly(methyl methacrylate) block copolymers (PDMS-b-PMMA) were prepared by the use of PDMS-ACP macroazoinitiators, and they were characterized by ¹H-, ²⁹Si-, and ¹³C-nuclear magnetic resonance (NMR) spectroscopies. The microstructure and morphology of copolymers were investigated by proton spin–spin relaxation measurements and scanning electron microscopy (SEM). © 1996 John Wiley & Sons, Inc.     

甲基丙烯酸甲酯的反向原子转移自由基聚合反应 研究

在较低的温度(60℃)和较低的AIBN/CuCl~2/配位剂摩尔比(1:2:4)条件下,用乙腈为溶剂,实现了甲基丙烯酸甲酯(MMA)的反向原子转移自由基聚合(RATRP)。联二吡啶(bpy)为配位剂时,所合成的聚甲基丙烯酸甲酯(PMMA)的分子量分布可低至1.08。用1,10-菲咯啉(phen)代替bpy,MMA的聚合反应速率加快,但其分子量分布稍宽(1.40左右),并进一步研究了bpy和phen作为混合配位剂时对MMA反向ATRP聚合的影响。用RATRP反应所得的带有卤素端基的PMMA作为苯乙烯ATRP的大分子引发剂,成功地合成了具有预期结构的苯乙烯与甲基丙烯酸甲酯嵌段共聚物,大分子引发剂的引发效率接近于1,说明在RATRP过程中由自由基引发剂引发MMA进行一般自由基聚合反应的可能性甚微。     

Preparation and block copolymerization of oligodihexanoylchitin having hydroxy groups at both ends

The preparation of oligodihexanoylchitin (3) having hydroxy groups at the both ends was carried out by an acid hydrolysis of a parent dihexanoylchitin in a mixed solution of acetic acid and conc. hydrochloric acid (11 : 1 in volume) at a room temperature. After 13–21 h, the products were isolated and their molecular weights were calculated as 7400–1100 by GPC analyses. The structure of the product 3 was determined by ¹H and ¹³C-NMR and IR spectra. The IR spectra of the products yielded for longer hydrolysis times than 30 h, however, indicated the occurrence of the dehexanoylation. The block copolymerization of 3 with poly (propylene glycol) (PPG) using 4,4'-methylenedi (phenyl isocyanate) (MDI) as a coupling reagent gave the block copolymer 6 . The molecular weight of 6 as obrained by GPC was 52,000. © 1994 John Wiley & Sons, Inc.     

The synthesis of poly[6,8‐dioxabicyclo[3.2.1]octane‐b‐(ethylene glycol)‐b‐6,8‐dioxabicyclo[3.2.1]octane] by controlled cationic ring‐opening polymerization

The triblock copolymer poly[6,8‐dioxabicyclo[3.2.1]octane‐b‐(ethylene glycol)‐b‐6,8‐dioxabicyclo[3.2.1]octane] was prepared by the controlled cationic ring‐opening polymerization of 6,8‐dioxabicyclo[3.2.1]octane (6,8‐DBO) from a macroinitiator. The macroinitiator, poly(ethylene glycol) (PEG) di(1‐chloroethyl ether), was prepared via the addition of HCl to PEG divinyl ether and was characterized with ¹³C NMR, ¹H NMR, and gel permeation chromatography (GPC). Upon preparation, a small fraction of the chain ends underwent a cyclization reaction to form inactive chain ends. When the macroinitiator was used in polymerizations of 6,8‐DBO with ZnI₂ as an activator, linear kinetic plots were observed, a linear increase in the copolymer molecular weight with conversion was seen, and the molecular weight distributions of the copolymer samples remained constant at about 1.40. Confirmation of the triblock structure of the final product was obtained with ¹H NMR spectra, ¹³C DEPT spectra, and GPC chromatograms. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4081–4087, 2000     

Block copolymer preparation by atom transfer radical polymerization under emulsion conditions using a nanoprecipitation technique

Living‐radical polymerization of acrylates were performed under emulsion atom transfer radical polymerization (ATRP) conditions using latexes prepared by a nanoprecipitation technique previously employed and optimized for the polymerization of styrene. A macroinitiator of poly(n‐butyl acrylate) prepared under bulk ATRP was dissolved in acetone and precipitated in an aqueous solution of Brij 98 to preform latex particles, which were then swollen with monomer and heated. Various monomers (i.e. n‐butyl acrylate, styrene, and tert‐butyl acrylate) were used to swell the particles to prepare homo‐ and block copolymers from the poly(n‐butyl acrylate) macroinitiator. Under these conditions latexes with a relatively good colloidal stability were obtained. Furthermore, amphiphilic block copolymers were prepared by hydrolysis of the tert‐butyl groups and the resulting block copolymers were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The bulk morphologies of the polystyrene‐b‐poly(n‐butyl acrylate) and poly(n‐butyl acrylate)‐b‐poly(acrylic acid) copolymers were investigated by atomic force microscopy (AFM) and small angle X‐ray scattering (SAXS). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 625–635, 2008     

Removal of the copper catalyst from atom transfer radical polymerization mixtures by chemical reduction with zinc powder

Simple mixing of an atom transfer radical polymerization (ATRP) mixture with zinc powder was demonstrated to result in rapid decolorizing of the solution and precipitation of elemental copper, using small amounts of silica gel as seeding material. The experiments revealed that the chemical reduction of copper by wetted zinc powder (i.e., 0.325 g/mmol copper) is fast and completed within less than 5 min. UV spectra of the filtered polymer solution showed no any trace of copper. Terminal bromoalkyl groups of the polymers in the ATRP solution were determined to be unchanged by short‐term contact with zinc powder at room temperature and a nearly complete reductive dehalogenation takes place only after 24 h of interaction, as evidenced by reaction of elemental zinc with a model compound, ethyl bromoacetate. Indeed, poly(methyl methacrylate) (PMMA) sample (M_n: 7900, polydispersity index: 1.09) isolated from ATRP mixture after the copper removal a by short contact with zinc powder (i.e., 15 min) was determined “still living” as confirmed by chain extension with styrene, ethyl acrylate, and t‐butyl acrylate monomers to give block copolymers. The presence of acetic acid was demonstrated to accelerate reductive dehalogenation of PMMA end‐groups by zinc and yields nonliving polymer within 2 h. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Growth of poly(methyl methacrylate) brushes on silicon surfaces by atom transfer radical polymerization

Poly(methyl methacrylate) (PMMA) brushes are grown by surface‐initiated atom transfer radical polymerization on silicon surfaces at various polymerization temperatures. Kinetic studies show that the layer thickness scales linearly with the degree of polymerization of the polymers under some conditions, indicating a constant graft density of the surface‐attached chains. At high temperatures, the layer growth is a controlled process only for short reaction times, and after a rapid increase, the film growth levels off, and a constant thickness is obtained. At lower reaction temperatures, polymers with a lower polydispersity are obtained, but at the expense of a much slower growth rate. Accordingly, intermediate temperatures yield the highest film thickness on experimentally feasible timescales. The reinitiation of these surface‐grafted PMMA chains at room temperature to either extend the chains or grow a chemically different polyglycidylmethacrylate block demonstrates the presence of active ends and the living nature of the surface‐grafted PMMA chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1758–1769, 2006