Synthesis,characterization, and property of amphiphilic fluorinated abc‐type triblock copolymers

Novel amphiphilic fluorinated ABC‐type triblock copolymers composed of hydrophilic poly(ethylene oxide) monomethyl ether (MeOPEO), hydrophobic polystyrene (PSt), and hydrophobic/lipophobic poly(perfluorohexylethyl acrylate) (PFHEA) were synthesized by atom transfer radical polymerization (ATRP) using N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA)/CuBr as a catalyst system. The bromide‐terminated diblock copolymers poly(ethylene oxide)‐block‐polystyrene (MeOPEO‐b‐PSt‐Br) were prepared by the ATRP of styrene initiated with the macroinitiator MeOPEO‐Br, which was obtained by the esterification of poly(ethylene oxide) monomethyl ether (MeOPEO) with 2‐bromoisobutyryl bromide. A fluorinated block of poly(perfluorohexylethyl acrylate) (PFHEA) was then introduced into the diblock copolymer by a second ATRP process to synthesize a novel ABC‐type triblock copolymer, poly(ethylene oxide)‐block‐polystyrene‐block‐poly(perfluorohexylethyl acrylate) (MeOPEO‐b‐PSt‐b‐PFHEA). These block copolymers were characterized by means of proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). Water contact angle measurements revealed that the polymeric coating of the triblock copolymer (MeOPEO‐b‐PSt‐b‐PFHEA) shows more hydrophobic than that of the corresponding diblock copolymer (MeOPEO‐b‐PSt). Bovine serum albumin (BSA) was used as a model protein to evaluate the protein adsorption property and the triblock copolymer coating posseses excellent protein‐resistant character prior to the corresponding diblock copolymer and polydimethylsiloxane. These amphiphilic fluoropolymers can expect to have potential applications for antifouling coatings and antifouling membranes. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of poly(N,N‐dimethylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N,N‐dimethylacrylamide) and its application for separation of proteins by capillary zone electrophoresis

A series of well‐defined triblock copolymers, poly(N, N‐dimethylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N, N‐dimethylacrylamide) (PDMA‐b‐PEO‐b‐PDMA) synthesized by atom transfer radical polymerization, were used as physical coatings for protein separation. A comparative study of EOF showed that the triblock copolymer presented good capillary coating ability and EOF efficient suppression. The effects of the M_r of PDMA block in PDMA‐b‐PEO‐b‐PDMA triblock copolymer and buffer pH on the separation of basic protein for CE were investigated. Moreover, the influence of the copolymer structure on separation of basic protein was studied by comparing the performance of PDMA‐b‐PEO‐b‐PDMA triblock copolymer with PEO‐b‐PDMA diblock copolymer. Furthermore, the triblock copolymer coating showed higher separation efficiency and better migration time repeatability than fused‐silica capillary when used in protein mixture separation and milk powder samples separation, respectively. The results demonstrated that the triblock copolymer coatings would have a wide application in the field of protein separation.     

PEG‐b‐PtBA‐b‐PHEMA well‐defined amphiphilic triblock copolymer: Synthesis,self‐assembly,and application in drug delivery

A series of well‐defined amphiphilic triblock copolymers, poly(ethylene glycol)‐b‐poly(tert‐butyl acrylate)‐b‐poly(2‐hydroxyethyl methacrylate) (PEG‐b‐PtBA‐b‐PHEMA), were synthesized via successive atom transfer radical polymerization (ATRP). ATRP of tBA was first initiated by PEG‐Br macroinitiator using CuBr/N,N,N′,N″,N′″‐pentamethyldiethylenetriamine as catalytic system to give PEG‐b‐PtBA diblock copolymer. This copolymer was then used as macroinitiator to initiate ATRP of HEMA, which afforded the target triblock copolymer, PEG‐b‐PtBA‐b‐PHEMA. The critical micelle concentrations of obtained amphiphilic triblock copolymers were determined by fluorescence spectroscopy using N‐phenyl‐1‐naphthylamine as probe. The morphology and size of formed aggregates were investigated by transmission electron microscopy and dynamic light scattering, respectively. Finally, an acid‐sensitive PEG‐b‐PtBA‐b‐P(HEMA‐CAD) prodrug via cis‐aconityl linkage between doxorubicin and hydroxyls of triblock copolymers with a high drug loading content up to 38%, was prepared to preliminarily explore the application of triblock copolymer in drug delivery. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of poly(dimethylsiloxane)‐containing diblock and triblock copolymers by the combination of anionic ring‐opening polymerization of hexamethylcyclotrisiloxane and nitroxide‐mediated radical polymerization of methyl acrylate,isoprene, and styrene

Poly(dimethylsiloxane)‐containing diblock and triblock copolymers were prepared by the combination of anionic ring‐opening polymerization (AROP) of hexamethylcyclotrisiloxane (D₃) and nitroxide‐mediated radical polymerization (NMRP) of methyl acrylate (MA), isoprene (IP), and styrene (St). The first step was the preparation of a TIPNO‐based alkoxyamine carrying a 4‐bromophenyl group. The alkoxyamine was then treated with Li powder in ether, and AROP of D₃ was carried out using the resulting lithiophenyl alkoxyamine at room temperature, giving functional poly(D₃) with M_w/M_n of 1.09–1.16. NMRPs of MA, St, and IP from the poly(D₃) at 120 °C gave poly(D₃‐b‐MA), poly(D₃‐b‐St), and poly(D₃‐b‐IP) diblock copolymers, and subsequent NMRPs of St from poly(D₃‐b‐MA) and poly(D₃‐b‐IP) at 120 °C gave poly(D₃‐b‐MA‐b‐St) and poly(D₃‐b‐IP‐b‐St) triblock copolymers. The poly(dimethylsiloxane)‐containing diblock and triblock copolymers were analyzed by ¹H NMR and size exclusion chromatography. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6153–6165, 2005     

Synthesis of poly(n‐butyl acrylate) homopolymer and poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) triblock copolymer via AGET emulsion ATRP using a cationic surfactant

Cationic emulsions of triblock copolymer particles comprising a poly(n‐butyl acrylate) (PⁿBA) central block and polystyrene (PS) outer blocks were synthesized by activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP). Difunctional ATRP initiator, ethylene bis(2‐bromoisobutyrate) (EBBiB), was used as initiator to synthesize the ABA type poly(styrene‐b‐n‐butyl acrylate‐b‐styrene) (PS‐PⁿBA‐PS) triblock copolymer. The effects of ligand and cationic surfactant on polymerizations were also discussed. Gel permeation chromatography (GPC) was used to characterize the molecular weight (M_n) and molecular weight distribution (MWD) of the resultant triblock copolymers. Particle size and particle size distribution of resulted latexes were characterized by dynamic light scattering (DLS). The resultant latexes showed good colloidal stability with average particle size around 100–300 nm in diameter. Glass transition temperature (T_g) of copolymers was studied by differential scanning calorimetry (DSC). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 611–620     

Synthesis of ABA‐triblock and star‐diblock copolymers with poly(2‐adamantyl vinyl ether) and poly(n‐butyl vinyl ether) segments: New thermoplastic elastomers composed solely of poly(vinyl ether) backbones

ABA‐type triblock copolymers and AB‐type star diblock copolymers with poly(2‐adamantyl vinyl ether) [poly(2‐AdVE)] hard outer segments and poly(n‐butyl vinyl ether) [poly(NBVE)] soft inner segments were synthesized by sequential living cationic copolymerization. Although both the two polymer segments were composed solely of poly(vinyl ether) backbones and hydrocarbon side chains, they were segregated into microphase‐separated structure, so that the block copolymers formed thermoplastic elastomers. Both the ABA‐type triblock copolymers and the AB‐type star diblock copolymers exhibited rubber elasticity over wide temperature range. For example, the ABA‐type triblock copolymers showed rubber elasticity from about ?53 °C to about 165 °C and the AB‐type star diblock copolymer did from about ?47 °C to 183 °C with a similar composition of poly(2‐AdVE) and poly(NBVE) segments in the dynamic mechanical analysis. The AB‐type star diblock copolymers exhibited higher tensile strength and elongation at break than the ABA‐type triblock copolymers. The thermal decomposition temperatures of both the block copolymers were as high as 321–331 °C, indicating their high thermal stability. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

From poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N‐isopropylacrylamide) triblock copolymer to poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide) hydrogels: Synthesis and rapid deswelling and reswelling behavior of hydrogels

Poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N‐isopropylacrylamide) (PNIPAAm‐b‐PEO‐b‐PNIPAAm) triblock copolymer was synthesized via the reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process with xanthate‐terminated poly(ethylene oxide) (PEO) as the macromolecular chain transfer agent. The successful synthesis of the ABA triblock copolymer inspired the preparation of poly(N‐isopropylacrylamide)‐block‐poly(ethylene oxide) (PNIPAAm‐b‐PEO) copolymer networks with N,N′‐methylenebisacrylamide as the crosslinking agent with the similar approach. With the RAFT/MADIX process, PEO chains were successfully blocked into poly(N‐isopropylacrylamide) (PNIPAAm) networks. The unique architecture of PNIPAAm‐b‐PEO networks allows investigating the effect of the blocked PEO chains on the deswelling and reswelling behavior of PNIPAAm hydrogels. It was found that with the inclusion of PEO chains into the PNIPAAm networks as midblocks, the swelling ratios of the hydrogels were significantly enhanced. Furthermore, the PNIPAAm‐b‐PEO hydrogels displayed faster response to the external temperature changes than the control PNIPAAm hydrogel. The accelerated deswelling and reswelling behaviors have been interpreted based on the formation of PEO microdomains in the PNIPAAm networks, which could act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the PNIPAAm networks. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) via a combination of ring‐opening olefin metathesis polymerization and grignard metathesis polymerization

Novel rod–coil–rod ABA triblock copolymers, poly(3‐hexylthiophene)‐block‐poly(ethylene)‐block‐poly(3‐hexylthiophene) (P3HT‐b‐PE‐b‐P3HT) were synthesized by using a combination of a Ru‐catalyzed ring‐opening metathesis polymerization of 1,4‐cyclooctadiene in the presence of a suitable chain transfer agent (CTA) and a Ni‐catalyzed Grignard metathesis polymerization of 5‐chloromagnesio‐2‐bromo‐3‐hexylthiophene followed by hydrogenation. Using this methodology, the molecular weights of the poly(butadiene) (PBD) or the P3HT blocks were controlled by adjusting the initial monomer/CTA or the initial monomer/macroinitiator ratio, respectively. In addition, the triblock structure was confirmed by selective oxidative degradation of the PBD block found in the intermediate P3HT‐b‐PBD‐b‐P3HT copolymer produced in the aforementioned method, followed by analysis of the degradation products. Thermal analysis and atomic force microscopy of P3HT‐b‐PE‐b‐P3HT revealed that the material underwent phase separation in the solid state, a feature which may prove useful for improving charge mobilities within electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3810–3817     

End‐group modification of poly(2,6‐dimethyl‐1,4‐phenylene ether) and in situ synthesis of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer

The preparation of poly(2,6‐dimethyl‐1,4‐phenylene ether)‐b‐poly(ethylene terephthalate) block copolymer was performed by the reaction of the 2‐hydroxyethyl modified poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE‐EtOH) with poly(ethylene terephthalate) (PET) by an in situ process, during the synthesis of the polyester. The yield of the reaction of the 2‐hydroxyethyl functionalized PPE‐EtOH with PET was close to 100%. A significant proportion of the PET‐b‐PPE‐EtOH block copolymer was found to have short PET block. Nevertheless, the copolymer structured in the shape of micelles (20 nm diameter) and very small domains with 50–200 nm diameter, whereas unmodified PPE formed much larger domains (1.5 μm) containing copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3985–3991, 2008     

Synthesis of amphiphilic block–graft copolymers [poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene)‐g‐poly(acrylic acid)] and their aggregation in water

Novel block–graft copolymers [poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene)‐g‐poly(tert‐butyl acrylate)] were synthesized by the atom transfer radical polymerization (ATRP) of tert‐butyl acrylate (tBA) with chloromethylated poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) (SEBS) as a macromolecular initiator. The copolymers were composed of triblock SEBS as the backbone and tBA as grafts attached to the polystyrene end blocks. The macromolecular initiator (chloromethylated SEBS) was prepared by successive hydrogenation and chloromethylation of SEBS. The degree of chloromethylation, ranging from 1.6 to 36.5 mol % according to the styrene units in SEBS, was attained with adjustments in the amount of SnCl₄ and the reaction time with a slight effect on the monodispersity of the starting material (SEBS). The ATRP mechanism of the copolymerization was supported by the kinetic data and the linear increase in the molecular weights of the products with conversion. The graft density was controlled with changes in the functionality of the chloromethylated SEBS. The average length of the graft chain, ranging from a few repeat units to about two hundred, was adjusted with changes in the reaction time and alterations in the initiator/catalyst/ligand molar ratio. Incomplete initiation was detected at a low conversion; moreover, for initiators with low functionality, sluggish initiation was overcome with suitable reaction conditions. The block–graft copolymers were hydrolyzed into amphiphilic ones containing poly(acrylic acid) grafts. The aggregation behavior of the amphiphilic copolymers was studied with dynamic light scattering and transmission electron microscopy, and the aggregates showed a variety of morphologies. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1253–1266, 2002     

Novel Amphiphilic Diblock and Triblock Liquid‐Crystalline Copolymers with Well‐Defined Structures Prepared by Atom Transfer Radical Polymerization

Summary: Based on a hydrophilic poly(ethylene oxide) macroinitiator (PEOBr), a novel amphiphilic diblock copolymer PEO‐block‐poly(11‐(4‐cyanobiphenyloxy)undecyl) methacrylate) (PEO‐b‐PMA(11CB)) was prepared by atom transfer radical polymerization (ATRP) using CuCl/1,1,4,7,10,10‐hexamethyltriethylenetriamine as a catalyst system. An azobenzene block of poly(11‐[4‐(4‐butylphenylazo)phenoxyl]undecyl methacrylate) was then introduced into the copolymer sequence by a second ATRP to synthesize the corresponding triblock copolymer PEO‐b‐PMA(11CB)‐b‐PMA(11Az). Both of the amphiphilic block copolymers had well‐defined structures and narrow molecular‐weight distributions, and exhibited a smectic liquid‐crystalline phase over a wide temperature range.

The amphiphilic triblock copolymer synthesized here.     

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     

Synthesis and characterization of well‐defined diblock and triblock copolymers of poly(N‐isopropylacrylamide) and poly(ethylene oxide)

Well‐defined diblock and triblock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) were successfully synthesized through the reversible addition–fragmentation chain transfer polymerization of N‐isopropylacrylamide (NIPAM) with PEO capped with one or two dithiobenzoyl groups as a macrotransfer agent. ¹H NMR, Fourier transform infrared, and gel permeation chromatography instruments were used to characterize the block copolymers obtained. The results showed that the diblock and triblock copolymers had well‐defined structures and narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight < 1.2), and the molecular weight of the PNIPAM block in the diblock and triblock copolymers could be controlled by the initial molar ratio of NIPAM to dithiobenzoate‐terminated PEO and the NIPAM conversion. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4873–4881, 2004     

Synthesis and characterizations of the four‐armed amphiphilic block copolymer S[poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate)]4

The polymers poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate] (PDMDMA) and four‐armed PDMDMA with well‐defined structures were prepared by the polymerization of (2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate (DMDMA) in the presence of an atom transfer radical polymerization (ATRP) initiator system. The successive hydrolyses of the polymers obtained produced the corresponding water‐soluble polymers poly(2,3‐dihydroxypropyl acrylate) (PDHPA) and four‐armed PDHPA. The controllable features for the ATRP of DMDMA were studied with kinetic measurements, gel permeation chromatography (GPC), and NMR data. With the macroinitiators PDMDMA–Br and four‐armed PDMDMA–Br in combination with CuBr and 2,2′‐bipyridine, the block polymerizations of methyl acrylate (MA) with PDMDMA were carried out to afford the AB diblock copolymer PDMDMA‐b‐MA and the four‐armed block copolymer S{poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate]‐block‐poly(methyl acrylate)}₄, respectively. The block copolymers were hydrolyzed in an acidic aqueous solution, and the amphiphilic diblock and four‐armed block copolymers poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate) were prepared successfully. The structures of these block copolymers were verified with NMR and GPC measurements. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3062–3072, 2001     

Stimuli‐responsive ABC triblock copolymers by sequential living cationic copolymerization: Multistage self‐assemblies through micellization to open association

Stimuli‐responsive ABC triblock copolymers with three segments with different phase‐separation temperatures were synthesized via sequential living cationic copolymerization. The triblock copolymers exhibited sensitive thermally induced physical gelation (open association) through the formation of micelles. For example, an aqueous solution of EOVE₂₀₀‐b‐MOVE₂₀₀‐b‐EOEOVE₂₀₀ [where EOVE is 2‐ethoxyethyl vinyl ether, MOVE is 2‐methoxethyl vinyl ether and EOEOVE is 2‐(2‐ethoxy)ethoxyethyl vinyl ether; the order of the phase‐separation temperatures was poly(EOVE) (20 °C) < poly(EOEOVE) (41 °C) < poly(MOVE) (70 °C)] underwent multiple reversible transitions from sol (<20 °C) to micellization (20–41 °C) to physical gelation (physical crosslinking, 41–64 °C) and, finally, to precipitation (>64 °C). At 41–64 °C, the physical gel became stiffer than similar diblock or ABA triblock copolymers of the same molecular weight. Furthermore, the ABC triblock copolymers exhibited Weissenberg effects in semidilute aqueous solutions. In sharp contrast, another ABC triblock copolymer with a different arrangement, EOVE₂₀₀‐b‐EOEOVE₂₀₀‐b‐MOVE₂₀₀, scarcely exhibited any increase in viscosity above 41 °C. The temperatures of micelle formation and physical gelation corresponded to the phase‐separation temperatures of the segment types in the ABC triblock copolymer. No second‐stage association was observed for AB and ABA block copolymers with the same thermosensitive segments found in their ABC counterparts. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2601–2611, 2004     

Synthesis of well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) triblock copolymer via a combination of polyhomologation,ring‐opening polymerization,and atom transfer radical polymerization

Well‐defined amphiphilic polymethylene‐b‐poly(ε‐caprolactone)‐b‐poly(acrylic acid) (PM‐b‐PCL‐b‐PAA) triblock copolymers were synthesized via a combination of polyhomologation, ring‐opening polymerization (ROP), and atom transfer radical polymerization (ATRP). First, hydroxyl‐terminated polymethylenes (PM‐OH; M_n = 1100 g mol^?1; M_w/M_n = 1.09) were produced by polyhomologation followed by oxidation. Then, the PM‐b‐PCL (M_n = 10,000 g mol^?1; M_w/M_n = 1.27) diblock copolymers were synthesized via ROP of ε‐caprolactone using PM‐OH as macroinitiator and stannous octanoate (Sn(Oct)₂) as a catalyst. Subsequently, the macroinitiator transformed from PM‐b‐PCL in high conversion initiated ATRPs of tert‐butyl acrylate (^tBA) to construct PM‐b‐PCL‐b‐P^tBA triblock copolymers (M_n = 11,000–14,000 g mol^?1; M_w/M_n = 1.24–1.26). Finally, the PM‐b‐PCL‐b‐PAA triblock copolymers were obtained via the hydrolysis of the P^tBA segment in PM‐b‐PCL‐b‐P^tBA triblock copolymers. The chain structures of all the polymers were characterized by gel permeation chromatography, proton nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Porous films of such triblock copolymers were fabricated by static breath‐figure method and observed by scanning electron microscope. The aggregates of PM‐b‐PCL‐b‐PAA triblock copolymer were studied by transmission electron microscope. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Novel synthesis of biodegradable amphiphilic linear and star block copolymers based on poly(ε‐caprolactone) and poly(ethylene glycol)

Biodegradable, amphiphilic, diblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol) (PCL‐b‐PEG), triblock poly(ε‐caprolactone)‐block‐poly(ethylene glycol)‐block‐poly(ε‐caprolactone) (PCL‐b‐PEG‐b‐PCL), and star shaped copolymers were synthesized by ring opening polymerization of ε‐caprolactone in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) or star poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. Polymerizations were carried out in toluene at room temperature to yield monomodal polymers of controlled molecular weight. The chemical structure of the copolymers was investigated by ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and DSC investigations. The effects of copolymer composition and molecular structure on the physical properties were investigated by GPC and DSC. For the same PCL chain length, the materials obtained in the case of linear copolymers are viscous whereas in the case of star copolymer solid materials are obtained with low T_g and T_m temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3975–3985, 2007     

High‐molecular‐weight symmetrical multiblock copolymers: Synthesis by RAFT polymerization and characterization

High‐molecular‐weight (MW) symmetrical multiblock copolymers, based on the hydrophobic monomers styrene (Sty) and methyl methacrylate (MMA), and the more polar monomer, 2‐vinyl pyridine (2VPy), were prepared using stepwise reversible addition‐fragmentation chain transfer polymerization. All copolymers shared a common poly(ethylene glycol) (PEG) midblock, introduced as a bifunctional macromolecular chain transfer agent. In total, five ABA triblock copolymers, five ABCBA pentablock terpolymers, and two ABCDCBA heptablock quaterpolymers (comprising four different monomer types) were synthesized. The MWs of the multiblock polymers were determined using gel permeation chromatography (GPC) and proton nuclear magnetic resonance (¹H NMR) spectroscopy, with the latter values being closer to the theoretically expected, whereas GPC MW distributions were relatively narrow, broadening with the number of blocks. The compositions of the synthesized polymers, as determined by ¹H NMR spectroscopy, were also close to the expected values. Finally, films cast from chloroform solutions of the pentablock terpolymers P2VPy‐b‐PSty‐b‐PEG‐b‐PSty‐b‐P2VPy, PSty‐b‐PMMA‐b‐PEG‐b‐PMMA‐b‐PSty, and P2VPy‐b‐PMMA‐b‐PEG‐b‐PMMA‐b‐P2VPy examined using transmission electron microscopy exhibited PSty and PMMA cylinders (first two) and lamellae (third terpolymer). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4957–4965     

A Molecular Dynamics Simulation on the Self‐Assembly of ABC Triblock Copolymers, 1. Effects of Block Composition in Symmetric Triblock Copolymers

The self‐assembly of ABC triblock copolymers in the microphase‐separated state is investigated using an isothermal‐isobaric molecular dynamics simulation. For the validation of our simulation scheme, ABA triblock copolymers are also simulated. We examine the effect of the composition (f_B) of symmetric triblock copolymers on the morphology realized in these copolymers, keeping other parameters fixed. For ABA triblock copolymers, the transition from lamellar to cylindrical morphologies is observed with increasing the composition from f_B = 0.5 to f_B = 0.75, and such behavior is supported by calculation results of scattering patterns. These simulated results agree well with experimental and theoretical ones, validating our simulation method. More complex structures are predicted for ABC triblock copolymers. If midblock B is the minor component, its structures are changed from lamellar, cylindrical, to spherical morphology at the interface between A/C lamellae as f_B decreases. For ABC triblock copolymers with the midblock B as the major component, the morphology of end blocks in the matrix composed of the midblock is changed from tricontinuous to spherical structures as f_B increases.     

Synthesis and characterization of side‐chain liquid crystalline ABC triblock copolymers with p‐methoxyazobenzene moieties by atom transfer radical polymerization

A series of novel side‐chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine‐terminated diblock copolymer poly(ethylene oxide)‐block‐polystyrene (PEO‐PS‐Br) was prepared by the ATRP of styrene initiated with the macro‐initiator PEO‐Br, which was obtained from the esterification of PEO and 2‐bromo‐2‐methylpropionyl bromide. An azobenzene‐containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side‐chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)‐block‐polystyrene‐block‐poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PEO‐PS‐PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442–4450, 2008