Synthesis and properties of polystyrene‐b‐poly(ethylene oxide)‐b‐polystyrene triblock copolymers

A series of well‐defined and property‐controlled polystyrene (PS)‐b‐poly(ethylene oxide) (PEO)‐b‐polystyrene (PS) triblock copolymers were synthesized by atom‐transfer radical polymerization, using 2‐bromo‐propionate‐end‐group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by ¹H‐NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass‐transition temperature (T_g) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer–toluene–water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 727–730, 2006     

Synthesis of poly(octadecyl acrylate‐b‐styrene‐b‐octadecyl acrylate) triblock copolymer by atom transfer radical polymerization

The synthesis of triblock copolymer poly(octadecyl acrylate‐b‐styrene‐b‐octadecyl acrylate), using atom transfer radical polymerization (ATRP), is reported. The copolymers were prepared in two steps. First, polystyrene was synthesized by ATRP using α,α′‐dichloro‐p‐xylene/CuBr/bpy as the initiating system; Second, polystyrene was further used as macroinitiator for the ATRP of octadecyl acrylate to prepare ABA triblock copolymers in the presence of FeCl₂·4H₂O/PPh₃ in toluene. Polymers with controlled molecular weight (M_n = 17,000–23,400) and low polydispersity index value (1.33–1.44) were obtained. The relationship between molecular weight versus conversion showed a straight line. The effect of reaction temperature on polymerization was also investigated, showing a faster polymerization rate under higher temperature. The copolymers were characterized by FTIR, ¹H‐NMR, DSC, and GPC and the crystallization behavior of the copolymers was also studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1539–1545, 2004     

Synthesis and characterization of poly(n‐butyl methacrylate)‐b‐polystyrene diblock copolymers by atom transfer radical emulsion polymerization

Poly(n‐butyl methacrylate) (PBMA)‐b‐polystyrene (PSt) diblock copolymers were synthesized by emulsion atom transfer radical polymerization (ATRP). PBMA macroinitiators that contained alkyl bromide end groups were obtained by the emulsion ATRP of n‐butyl methacrylate with BrCH₃CHCOOC₂H₅ as the initiator; these were used to initiate the ATRP of styrene (St). The latter procedure was carried out at 85°C with CuCl/4,4′‐di(5‐nonyl)‐2,2′‐bipyridine as the catalyst and polyoxyethylene(23) lauryl ether as the surfactant. With this technique, PBMA‐b‐PSt diblock copolymers were synthesized. The polymerization was nearly controlled; the ATRP of St from the macroinitiators showed linear increases in number‐average molecular weight with conversion. The block copolymers were characterized with IR spectroscopy, ¹H‐NMR, and differential scanning calorimetry. The effects of the molecular weight of the macroinitiators, macroinitiator concentration, catalyst concentration, surfactant concentration, and temperature on the polymerization were also investigated. Thermodynamic data and activation parameters for the ATRP are also reported. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2123–2129, 2005     

Synthesis of poly(cyclohexene oxide)‐block‐polystyrene by combination of radical‐promoted cationic polymerization,atom transfer radical polymerization and click chemistry

The combination of radical‐promoted cationic polymerization, atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of poly(cyclohexene oxide)‐block‐polystyrene (PCHO‐b‐PSt). Alkyne end‐functionalized poly(cyclohexene oxide) (PCHO‐alkyne) was prepared by radical‐promoted cationic polymerization of cyclohexene oxide monomer in the presence of 1,2‐diphenyl‐2‐(2‐propynyloxy)‐1‐ethanone (B‐alkyne) and an onium salt, namely 1‐ethoxy‐2‐methylpyridinium hexafluorophosphate, as the initiating system. The B‐alkyne compound was synthesized using benzoin photoinitiator and propargyl bromide. Well‐defined bromine‐terminated polystyrene (PSt‐Br) was prepared by ATRP using 2‐oxo‐1,2‐diphenylethyl‐2‐bromopropanoate as initiator. Subsequently, the bromine chain end of PSt‐Br was converted to an azide group to obtain PSt‐N₃ by a simple nucleophilic substitution reaction. Then the coupling reaction between the azide end group in PSt‐N₃ and PCHO‐alkyne was performed with Cu(I) catalysis in order to obtain the PCHO‐b‐PSt block copolymer. The structures of all polymers were determined. Copyright © 2010 Society of Chemical Industry     

Grafting studies onto cellulose by atom‐transfer radical polymerization

Styrene (Sty), methyl methacrylate (MMA), methacrylamide (MAm) and acrylomorpholine (AcM) were grafted onto powder cellulose by atom‐transfer radical polymerization. Cellulose chloroacetate (Cell‐ClAc), as a macro‐initiator, was first prepared by the reaction of chloroacetyl chloride with primary alcoholic OH groups on powder cellulose. CuBr and 1,2‐dipiperidinoethane were used as a transition‐metal compound and as a ligand, respectively. These reactions were monitored by FT‐IR and weight increase in Cell‐ClAc. In case of styrene, although some weight increase occurred, no evidence of grafting could be observed in the FT‐IR spectrum, while there were strong evidence of grafting with MMA, MAm and AcM. Cell‐graft‐MAm, Cell‐graft‐AcM and Cell‐graft‐MMA showed new carbonyl bands at 1665, 1640 and 1735 cm^?1, respectively. Dye‐uptake and dye‐absorption properties of cellulose, for alizarin yellow (basic dye) and bromocresol green (acidic dye), and its moisture‐ and water‐uptake capacities improved with the grafting, but some decrease was observed in thermal stability. Copyright © 2004 Society of Chemical Industry     

Atom transfer radical polymerization of styrene and methyl (meth)acrylates initiated with poly(dimethylsiloxane) macroinitiator: Synthesis and characterization of triblock copolymers

Poly(dimethylsiloxane)(PDMS)‐based triblock copolymers were successfully synthesized via atom transfer radical polymerization (ATRP) initiated with bis(bromoalkyl)‐terminated PDMS macroinitiator (Br‐PDMS‐Br). First, Br‐PDMS‐Br was prepared by reaction between the bis(hydroxyalkyl)‐terminated PDMS and 2‐bromo‐2‐methylpropionyl bromide. PSt‐b‐PDMS‐b‐PSt, PMMA‐b‐PDMS‐b‐PMMA and PMA‐b‐PDMS‐b‐PMA triblock copolymers were then synthesized via ATRP of styrene (St), methyl methacrylate (MMA) and methyl acrylate (MA), respectively, in the presence of Br‐PDMS‐Br as a macroinitiator and CuCl/PMDETA as a catalyst system at 80 ^oC. Triblock copolymers were characterized by FTIR, ¹H‐NMR and GPC techniques. GPC results showed linear dependence of the number‐average molecular weight on the conversion as well as the narrow polydispersity indicies (PDI < 1.57) for the synthesized triblock copolymers which was lower than that of Br‐PDMS‐Br macroinitiator (PDI = 1.90), indicating the living/controlled characteristic of the reaction. Also, there was a very good agreement between the number‐average molecular weight calculated from ¹HNMR spectra and that calculated theoretically. Results showed that resulting copolymers have two glass transition temperatures, indicating that triblock copolymers have microphase separated morphology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Poly(ethylene oxide)‐block‐polystyrene copolymers obtained by radical polymerization involving chain‐transfer processes

Poly(ethylene oxide)‐block‐polystyrene (PEO–PSt) block copolymers were prepared by radical polymerization of styrene in the presence of iodoacetate—terminated PEO (PEO‐I) as a macromolecular chain‐transfer agent. PEO‐I was synthesized by successively converting the OH end‐group of α‐methoxy ω‐hydroxy PEO to chloroacetate and then to the iodoacetate. The chain‐transfer constant of PEO‐I was estimated from the rate of consumption of the transfer agent versus the rate of consumption of the monomer (C_{tr, PEO‐I} = 0.23). Due to the involvement of degenerative transfer, styrene polymerization in the presence of PEO‐I displayed some of the characteristics of a controlled/‘living’ process, namely an increase in the molecular weight and decrease of polydispersity with monomer conversion. However, because of the slow consumption of PEO‐I due to its low chain‐transfer constant, this process was not a fully controlled one, as indicated by the polydispersity being higher than in a controlled polymerization process (1.65 versus < 1.5). The formation of PEO–PSt block copolymers was confirmed by the use of size‐exclusion chromatography and ¹H NMR spectroscopy. Copyright © 2004 Society of Chemical Industry     

Synthesis of poly(aryl ether sulfone)‐graft‐polystyrene and poly(aryl ether sulfone)‐graft‐[polystyrene‐block‐poly(methyl methacrylate)] through atom transfer radical polymerization

A new graft copolymers poly(aryl ether sulfone)‐graft‐polystyrene (PSF‐g‐PS) and poly(aryl ether sulfone)‐graft‐[polystyrene‐block‐poly(methyl methacrylate)] (PSF‐g‐(PS‐b‐PMMA)) were successfully prepared via atom transfer radical polymerisation (ATRP) catalyzed by FeCl₂/isophthalic acid in N,N‐dimethyl formamide. The products were characterized by GPC, DSC, IR, TGA and NMR. The characterization data indicated that the graft copolymerization was accomplished via conventional ATRP mechanism. The effect of chloride content of the macroinitiator on the graft copolymerization was investigated. Only one glass transition temperature (T_g) was detected by DSC for the graft copolymer PSF‐g‐PS and two glass transition temperatures were observed in the DSC curve of PSF‐g‐(PS‐b‐PMMA). The presence of PSF in PSF‐b‐PS or PSF‐g‐(PS‐b‐PMMA) was found to improve thermal stabilities. © 2002 Society of Chemical Industry     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Synthesis of amphiphilic poly(methyl methacrylate)‐block‐poly(methacrylic acid) diblock copolymers by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of 1‐(butoxy)ethyl methacrylate (BEMA) was carried out using CuBr/2,2′‐bipyridyl complex as catalyst and 2‐bromo‐2‐methyl‐propionic acid ester as initiator. The number average molecular weight of the obtained polymers increased with monomer conversion, and molecular weight distributions were unimodal throughout the reaction and shifted toward higher molecular weights. Using poly(methyl methacrylate) (PMMA) with a bromine atom at the chain end, which was prepared by ATRP, as the macro‐initiator, a diblock copolymer PMMA‐block‐poly [1‐(butoxy)ethyl methacrylate] (PMMA‐b‐PBEMA) has been synthesized by means of ATRP of BEMA. The amphiphilic diblock copolymer PMMA‐block‐poly(methacrylic acid) can be further obtained very easily by hydrolysis of PMMA‐b‐PBEMA under mild acidic conditions. The molecular weight and the structure of the above‐mentioned polymers were characterized with gel permeation chromatography, infrared spectroscopy and nuclear magnetic resonance. Copyright © 2005 Society of Chemical Industry     

Synthesis and characterization of novel polystyrene‐block‐polyurethane‐block‐polystyrene tri‐block copolymers through atom transfer radical polymerization

Background: Radical polymerization is used widely to polymerize more than 70% of vinyl monomers in industry, but the control over molecular weight and end group of the resulting polymers is always a challenging task with this method. To prepare polymers with desired molecular weight and end groups, many controlled radical polymerization (CRP) ideas have been proposed over the last decade. Atom transfer radical polymerization (ATRP) is one of the successful CRP techniques. Using ATRP, there is no report on the synthesis of polystyrene‐block‐polyurethane‐block‐polystyrene (PSt‐b‐PU‐b‐PSt) tri‐block copolymers. Hence this paper describes the method of synthesizing these tri‐block copolymers. To accomplish this, first telechelic bromo‐terminated polyurethane was synthesized and used further to synthesize PSt‐b‐PU‐b‐PSt tri‐block copolymers using CuBr as a catalyst and N,N,N,N″,N″‐pentamethyldiethylenetriamine as a complexing agent. Results: The ‘living’ nature of the initiating system was confirmed by linear increase of number‐average molecular weight and conversion with time. A semi‐logarithmic kinetics plot shows that the concentration of propagating radical is steady. The results from nuclear magnetic resonance spectroscopy, gel permeation chromatography and differential scanning calorimetry show that the novel PSt‐b‐PU‐b‐PSt tri‐block copolymers were formed through the ATRP mechanism. Conclusion: For the first time, PSt‐b‐PU‐b‐PSt tri‐block copolymers were synthesized through ATRP. The advantage of this method is that the controlled incorporation of polystyrene block in polyurethane can be achieved by simply changing the polymerization time. Copyright © 2007 Society of Chemical Industry     

Synthesis of block copolymers with thermodynamically compatible chain segments: di‐ and triblock copolymers of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)

Mono‐ and bifunctional poly(phenylene oxide) (PPO) macroinitiators for atom transfer radical polymerization (ATRP) were prepared by esterification of mono‐ and bishydroxy telechelic PPO with 2‐bromoisobutyryl bromide. The macroinitiators were used for ATRP of styrene to give block copolymers with PPO and polystyrene (PS) segments, namely PPO‐block‐PS and PS‐block‐PPO‐block‐PS. Various ligands were studied in combination with CuBr as ATRP catalysts. Kinetic investigations revealed controlled polymerization processes for certain ligands and temperature ranges. Thermal analysis of the block copolymers by means of DSC revealed only one glass transition temperature as a result of the compatibility of the PS and PPO chain segments and the formation of a single phase; this glass transition temperature can be adjusted over a wide temperature range (ca 100–199 °C), depending on the composition of the block copolymer. Copyright © 2005 Society of Chemical Industry     

Synthesis and characterization of amphiphilic block copolymers of methyl methacrylate with poly(ethylene oxide) macroinitiators formed by atom transfer radical polymerization

Amphiphilic ABA triblock copolymers of poly(ethylene oxide) (PEO) with methyl methacrylate (MMA) were prepared by atom transfer radical polymerization in bulk and in various solvents with a difunctional PEO macroinitiator and a Cu(I)X/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system at 85°C where X=Cl or Br. The polymerization proceeded via controlled/living process, and the molecular weights of the obtained block copolymers increased linearly with monomer conversion. In the process, the polydispersity decreased and finally reached a value of less than 1.3. The polymerization followed first‐order kinetics with respect to monomer concentration, and increases in the ethylene oxide repeating units or chain length in the macroinitiator decreased the rate of polymerization. The rate of polymerization of MMA with the PEO chloro macroinitiator and CuCl proceeded at approximately half the rate of bromo analogs. A faster rate of polymerization and controlled molecular weights with lower polydispersities were observed in bulk polymerization compared with polar and nonpolar solvent systems. In the bulk polymerization, the number‐average molecular weight by gel permeation chromatography (M_n,GPC) values were very close to the theoretical line, whereas lower than the theoretical line were observed in solution polymerizations. The macroinitiator and their block copolymers were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR, matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry, thermogravimetry (TG)/differential thermal analysis (DTA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). TG/DTA studies of the homo and block copolymers showed two‐step and multistep decomposition patterns. The DSC thermograms exhibited two glass‐transition temperatures at ?17.7 and 92°C for the PEO and poly(methyl methacrylate) (PMMA) blocks, respectively, which indicated that microphase separation between the PEO and PMMA domains. SEM studies indicated a fine dispersion of PEO in the PMMA matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 989–1000, 2005     

Synthesis of poly(fluorinated styrene)‐block‐poly(ethylene oxide) amphiphilic copolymers via atom transfer radical polymerization: potential application as paper coating materials

BACKGROUND: The surface of a substrate which comprises a fibrous material is brought into contact with a type of amphiphilic block copolymer which comprises hydrophilic/hydrophobic polymeric blocks. These amphiphilic copolymers have been synthesized by atom transfer radical polymerization (ATRP) technique. The atom transfer radical polymerization of poly(2,3,4,5,6‐pentafluorostyrene)‐block‐poly(ethylene oxide) (PFS‐b‐PEO) copolymers (di‐ and triblock structures) with various ranges of PEO molecular weights was initiated by a PEO chloro‐telechelic macroinitiator. The polymerization, carried out in bulk and catalysed by copper(I) chloride in the presence of 2,2′‐bipyridine ligand, led to A–B–A amphiphilic triblock and A–B amphiphilic diblock structures. RESULTS: With most of the macroinitiators, the living nature of the polymerizations led to block copolymers with narrow molecular weight distributions (1.09 < M_w/M_n < 1.33) and well‐controlled molecular structures. These block copolymers turned out to be water‐soluble through adjustment of the PEO block content (>90 wt%). Of all the block copolymers synthesized, PFS‐b‐PEO(10k)‐b‐PFS containing 10 wt% PFS was found to retard water absorption considerably. CONCLUSION: The printability of paper treated with the copolymers was evaluated with contact angle measurements and felt pen tests. The adsorption of such copolymers at the solid/liquid interface is relevant to the wetting and spreading of liquids on hydrophobic/hydrophilic surfaces. Copyright © 2009 Society of Chemical Industry     

MesoDyn modeling study of the phase morphologies of miktoarm poly(ethylene oxide)‐b‐poly(methyl methacrylate) copolymers doped with nanoparticles

Earlier studies have shown that poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blocks are compatible at 270 and 298 K, and that their Flory–Huggins interaction parameters have the same blending ratio dependence at both temperatures. At a much higher temperature (400 K), the behavior of PEO/PMMA blends is strikingly different as both components become incompatible, while the Flory–Huggins parameters are low. Here we investigate the effect of doping with nanoparticles on the degree of incompatibility of twelve miktoarm PEO‐b‐PMMA copolymers at 400 K. Since PEO tends to be semicrystalline and long chains aggregate easily, PEO‐rich and long‐chain copolymer blends feature the highest degree of incompatibility for all nanoparticle arrangements and present cubic phase morphologies. In addition, the largest nanoparticles can reinforce the microscopic phase separation of all PEO‐b‐PMMA copolymers. This shows that the main factor affecting the phase morphology is the size of the nanoparticles. Also, only the asymmetric Da3‐type PEO‐rich copolymers show a hexagonal cylindrical phase morphology, which illustrates the effect induced by the nanoparticles on the microscopic phase separation changes of the PEO‐b‐PMMA copolymers. These induced effects are also related to the composition and molecular architecture of the copolymers. © 2013 Society of Chemical Industry     

Semifluorinated ABA triblock copolymers: Synthesis,characterization, and amphiphilic properties

In this study a series of novel semifluorinated ABA triblock copolymers with different fluorinated segment lengths and different fluorocarbon side‐chain structures were synthesized via atom transfer radical polymerization (ATRP) and macroinitiator techniques. The macroinitiator, telechelic bromine terminated polystyrene, was obtained from bulk ATRP of styrene with α,α′‐dibromo‐p‐xylene as the initiator and cuprous bromide/α,α′‐bispyridine complex as the catalyst. The polymerization reactions of 2‐[(perfluorononenyl)oxy] ethyl methacrylate and ethylene glycol monomethacrylate monoperfluorooctanoate were initiated by the macroinitiator in the presence of additional catalyst. The characterization of the block copolymers was performed by gel permeation chromatography, ¹H‐NMR spectroscopy, and differential scanning calorimetry. The surface activities of the block copolymers in toluene were investigated with the Wilhelmy plate method. The solid surface energy of the block copolymers was determined by measurement of the contact angles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2625–2633, 2002     

Preparation and characterization of polystyrene–poly(ethylene oxide) amphiphilic block copolymers via atom transfer radical polymerization: Potential application as paper coating materials

Poly(ethylene oxide) (PEO) monochloro macroinitiators or PEO telechelic macroinitiators (Cl‐PEO‐Cl) were prepared from monohydroxyfunctional or dihydroxyfunctional PEO and 2‐chloro propionyl chloride. These macroinitiators were applied to the atom transfer radical polymerization of styrene (S). The polymerization was carried out in bulk at 140°C and catalyzed by Copper(I) chloride (CuCl) in the presence of 2,2′‐bipyridine (bipy) ligand (CuCl/bipy). The amphiphilic copolymers were either A‐B diblock or A‐B‐A triblock type, where A block is polystyrene (PS) and B block is PEO. The living nature of the polymerizations leads to block copolymers with narrow molecular weight distribution (1.072 < M_w/M_n < 1.392) for most of the macroinitiators synthesized. The macroinitiator itself and the corresponding block copolymers were characterized by FTIR, ¹H NMR, and SEC analysis. By adjusting the content of the PEO blocks it was possible to prepare water‐soluble/dispersible block copolymers. The obtained block copolymers were used to control paper surface characteristics by surface treatment with small amount of chemicals. The printability of the treated paper was evaluated with polarity factors, liquid absorption measurements, and felt pen tests. The adsorption of such copolymers at the solid/liquid interface is relevant to the wetting and spreading of liquids on hydrophobic/hydrophilic surfaces. From our study, it is observed that the chain length of the hydrophilic block and the amount of hydrophobic block play an important role in modification of the paper surface. Among all of block copolymers synthesized, the PS‐b‐PEO‐b‐PS containing 10 wt % PS was found to retard water absorption considerably. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4304–4313, 2006     

Reverse atom‐transfer radical polymerization of acrylonitrile catalyzed by FeCl3/iminodiacetic acid

FeCl₃ coordinated by iminodiacetic acid (IMA) was Changed used for the first time as the catalyst in azobisisobutyronitrile‐initiated reverse atom‐transfer radical polymerization (ATRP) of acrylonitrile (AN). An FeCl₃ to IMA ratio of 1:2 not only gave the best control of molecular weight and its distribution but also provided a rather rapid reaction rate. The effects of solvents on the polymerization of AN were also investigated. The rate of the polymerization in N,N‐dimethylformamide (DMF) was faster than in propylene carbonate or toluene. The molecular weight of polyacrylonitrile agreed reasonably well with the theoretical molecular weight in DMF. The rate of polymerization increased with increasing polymerization temperature and the apparent activation energy was calculated to be 54.8 kJ mol⁻¹. The reverse ATRP of AN did not show obvious living characteristics with CuCl₂ instead of FeCl₃. Copyright © 2005 Society of Chemical Industry     

Synthesis of double‐hydrophilic poly(methylacrylic acid)–poly(ethylene glycol)–poly(methylacrylic acid) triblock copolymers and their micelle formation

The aim of the work reported was to synthesize a series of double‐hydrophilic poly(methacrylic acid)‐block‐poly(ethylene glycol)‐block‐poly(methacrylic acid) (PMAA‐b‐PEG‐b‐PMAA) triblock copolymers and to study their self‐assembly behavior. These copolymeric self‐assembly systems are expected to be potential candidates for applications as carriers of hydrophilic drugs. Bromo‐terminated difunctional PEG macroinitiators were used to synthesize well‐defined triblock copolymers of poly(tert‐butyl methacrylate)‐block‐poly(ethylene glycol)‐block‐poly(tert‐butyl methacrylate) via reversible‐deactivation radical polymerization. After the removal of the tert‐butyl group by hydrolysis, double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers were obtained. pH‐sensitive spherical micelles with a core–corona structure were fabricated by self‐assembly of the double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers at lower solution pH. Transmission electron microscopy and laser light scattering studies showed the micelles were of nanometric scale with narrow size distribution. Solution pH and micelle concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible reason for the formation of the micelles is proposed. Copyright © 2010 Society of Chemical Industry     

Synthesis and characterization of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers with dibutylmagnesium as catalyst

Two series of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) triblock copolymers were prepared by the ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) and dibutylmagnesium in 1,4‐dioxane solution at 70°C. The triblock structure and molecular weight of the copolymers were analyzed and confirmed by ¹H NMR, ¹³C NMR, FTIR, and gel permeation chromatography. The crystallization and thermal properties of the copolymers were investigated by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). The results illustrated that the crystallization and melting behaviors of the copolymers were depended on the copolymer composition and the relative length of each block in copolymers. Crystallization exothermal peaks (T_c) and melting endothermic peaks (T_m) of PEG block were significantly influenced by the relative length of PCL blocks, due to the hindrance of the lateral PCL blocks. With increasing of the length of PCL blocks, the diffraction and the melting peak of PEG block disappeared gradually in the WAXD patterns and DSC curves, respectively. In contrast, the crystallization of PCL blocks was not suppressed by the middle PEG block. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009