Bioinspired core‐crosslinked micelles from thymine‐functionalized amphiphilic block copolymers: Hydrogen bonding and photo‐crosslinking study

Bioinspired core‐bound polymeric micelles, based on hydrogen bonding and photo‐crosslinking, of thymine have been prepared from poly(vinylbenzylthymine)‐b‐poly(vinylbenzyltriethylammonium chloride). The amphiphilic block copolymer was synthesized by 2,2‐tetramethylpiperidin‐1‐oxyl‐mediated living radical polymerization in water/ethylene glycol solution. Micelle characterization and critical micelle concentration measurements demonstrated that the hydrogen bonding of the attached thymine units stabilizes the micelles. Further, core‐crosslinked polymeric micelles were formed by ultraviolet (UV) radiation showing that the stability of the micelle could be controlled by the UV crosslinking of the attached thymines. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of a ‐shaped amphiphilic block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

The functionalization of monomer units in the form of macroinitiators in an orthogonal fashion yields more predictable macromolecular architectures and complex polymers. Therefore, a new ‐shaped amphiphilic block copolymer, (PMMA)₂–PEO–(PS)₂–PEO–(PMMA)₂ [where PMMA is poly(methyl methacrylate), PEO is poly (ethylene oxide), and PS is polystyrene], has been designed and successfully synthesized by the combination of atom transfer radical polymerization (ATRP) and living anionic polymerization. The synthesis of meso‐2,3‐dibromosuccinic acid acetate/diethylene glycol was used to initiate the polymerization of styrene via ATRP to yield linear (HO)₂–PS₂ with two active hydroxyl groups by living anionic polymerization via diphenylmethylpotassium to initiate the polymerization of ethylene oxide. Afterwards, the synthesized miktoarm‐4 amphiphilic block copolymer, (HO–PEO)₂–PS₂, was esterified with 2,2‐dichloroacetyl chloride to form a macroinitiator that initiated the polymerization of methyl methacrylate via ATRP to prepare the ‐shaped amphiphilic block copolymer. The polymers were characterized with gel permeation chromatography and ¹H NMR spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 147–156, 2007     

Novel amphiphilic block copolymers derived from the selective fluorination and sulfonation of poly(styrene‐block‐1,3‐cyclohexadiene)

Diblock copolymers of polystyrene‐block‐(1,3‐cyclohexadiene) (PS‐b‐PCHD), with varied molecular weights and compositions, were synthesized by sequential polymerization of styrene and 1,3‐cyclohexadiene (CHD) initiated by sec‐butyllithium in cyclohexane in the presence of appropriate additives during formation of the PCHD block. The residual double bonds in the PCHD block were saturated by addition of in situ generated difluorocarbene and/or hydrogen to enhance thermal and chemical stability. The fluorinated and/or hydrogenated polydiene blocks were chemically stable, allowing for controlled sulfonation of the PS blocks using acetyl sulfate. ¹H NMR and FT‐IR characterization confirmed successful fluorination/hydrogenation and sulfonation of the respective blocks. The resulting amphiphilic block copolymers consist of a semiflexible fluorine‐containing hydrophobic block having a bridged double ring structure and a hydrophilic sulfonated PS block. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of PEE‐PEO diblock copolymers with complementary end‐groups for hydrogen‐bond heteroassociation

Poly(ethylethylene‐b‐ethylene oxide) (PEE‐PEO) diblock copolymers with pyridine‐benzoic acid end‐groups for heterodimeric hydrogen bonding were designed as a possible means to noncentrosymmetric organizations by spontaneous self‐assembly. These end‐functionalized polymers were synthesized by anionic living polymerization with protected initiator and terminating reagents. A series of polymeric intermediates with different end‐groups was characterized by proton nuclear magnetic resonance, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and gel permeation chromatography. Preliminary studies of solid‐state organization by differential scanning calorimetry and small‐angle X‐ray scattering provided evidence for a long‐range order that was sensitive to chain length, copolymer composition, and end‐group structure. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 207–219, 2000     

Amphiphilic star‐block copolymers based on a hyperbranched core: Synthesis and supramolecular self‐assembly

Novel amphiphilic star‐block copolymers, star poly(caprolactone)‐block‐poly[(2‐dimethylamino)ethyl methacrylate] and poly(caprolactone)‐block‐poly(methacrylic acid), with hyperbranched poly(2‐hydroxyethyl methacrylate) (PHEMA–OH) as a core moiety were synthesized and characterized. The star‐block copolymers were prepared by a combination of ring‐opening polymerization and atom transfer radical polymerization (ATRP). First, hyperbranched PHEMA–OH with 18 hydroxyl end groups on average was used as an initiator for the ring‐opening polymerization of ε‐caprolactone to produce PHEMA–PCL star homopolymers [PHEMA = poly(2‐hydroxyethyl methacrylate); PCL = poly(caprolactone)]. Next, the hydroxyl end groups of PHEMA–PCL were converted to 2‐bromoesters, and this gave rise to macroinitiator PHEMA–PCL–Br for ATRP. Then, 2‐dimethylaminoethyl methacrylate or tert‐butyl methacrylate was polymerized from the macroinitiators, and this afforded the star‐block copolymers PHEMA–PCL–PDMA [PDMA = poly(2‐dimethylaminoethyl methacrylate)] and PHEMA–PCL–PtBMA [PtBMA = poly(tert‐butyl methacrylate)]. Characterization by gel permeation chromatography and nuclear magnetic resonance confirmed the expected molecular structure. The hydrolysis of tert‐butyl ester groups of the poly(tert‐butyl methacrylate) blocks gave the star‐block copolymer PHEMA–PCL–PMAA [PMAA = poly(methacrylic acid)]. These amphiphilic star‐block copolymers could self‐assemble into spherical micelles, as characterized by dynamic light scattering and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6534–6544, 2005     

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     

Synthesis of novel asymmetric dendritic‐linear‐dendritic block copolymers via “living” anionic polymerization of ethylene oxide initiated by dendritic macroinitiators

The first synthesis of asymmetric dendritic‐linear‐dendritic ABC block copolymers, that contain a linear B block and dissimilar A and C dendritic fragments is reported. Third generation poly(benzyl ether) monodendrons having benzyl alcohol moiety at their “focal” point were activated by quantitative titration with organometallic anions and the resulting alkoxides were used as initiators in the “living” ring‐opening polymerization of ethylene oxide. The reaction proceeded in controlled fashion at 40–50 °C affording linear‐dendritic AB block copolymers with predictable molecular weights (M_w = 6000–13,000) and narrow molecular weight distributions (M_w/M_n = 1.02–1.04). The propagation process was monitored by size‐exclusion chromatography with multiple detection. The resulting “living” copolymers were terminated by reaction either with HCl/tetrahydrofuran or with a reactive monodendron that differed from the initiating dendron not only in size, but also in chemical composition. The asymmetric triblock copolymers follow a peculiar structure‐induced self‐assembly pattern in block‐selective solvents as evidenced by size‐exclusion chromatography in combination with multi‐angle light scattering. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5136–5148, 2007     

Solid polymer electrolytes based on polystyrene‐polyether block copolymers having branched ether structure

To obtain solid polymer electrolytes (SPEs) having high ionic conductivity together with mechanical integrity, we have synthesized polystyrene (PSt)‐polyether (PE) diblock copolymers via one‐pot anionic polymerization. The PSt block is expected to aggregate to act as hard fillers in the SPE to enhance the mechanical property. The PE block consists of random copolymer (P(EO‐r‐MEEGE)) of ethylene oxide (EO) and 2‐(2‐methoxyethoxy) ethyl glycidyl ether (MEEGE) in different molar ratios ([EO]/[MEEGE] = 100/0, 86/14, 75/25, 68/32, and 41/59). The introduction of the MEEGE moiety in PEO reduced the crystallinity of PEO, and the fast motion of the MEEGE side chain caused plasticization of the PE block, thereby contributing to the fast ion transport. SPEs were fabricated by mixing the obtained diblock copolymer (PSE_x) and lithium bis(trifluoromethanesulfonyl) amide (LiTFSA) with [Li]/[O] = 0.05. Ionic conductivity of the obtained SPEs was dependent on the molar ratio of EO in the PE block (x) as well as the weight fraction of PE block (f_PE) in the block copolymer. PSE_0.86 (f_PE = 0.65) exhibited high ionic conductivity (3.3 × 10^?5 S cm^?1 at 30°C; 1.1 × 10^?4 S cm^?1 at 60°C) comparable with that of P(EO‐r‐MEEGE) (PE_0.85; f_PE = 1.00) (9.8 × 10^?5 S cm^?1 at 30°C; 4.0 × 10^?4 S cm^?1 at 60°C).     

Synthesis of arborescent polystyrene‐g‐[poly(2‐vinylpyridine)‐b‐polystyrene] core–shell–corona copolymers

Arborescent copolymers with a core‐shell‐corona (CSC) architecture, incorporating a polystyrene (PS) core, an inner shell of poly(2‐vinylpyridine), P2VP, and a corona of PS chains, were obtained by anionic polymerization and grafting. Living PS‐b‐P2VP‐Li block copolymers serving as side chains were obtained by capping polystyryllithium with 1,1‐diphenylethylene before adding 2‐vinylpyridine. A linear or arborescent (generation G0 – G3) PS substrate, randomly functionalized with acetyl or chloromethyl coupling sites, was then added to the PS‐b‐P2VP‐Li solution for the grafting reaction. The grafting yield and the coupling efficiency observed in the synthesis of the arborescent PS‐g‐(P2VP‐b‐PS) copolymers were much lower than for analogous coupling reactions previously used to synthesize arborescent PS homopolymers and PS‐g‐P2VP copolymers from the same types of coupling sites. It was determined from static and dynamic light scattering analysis that PS‐b‐P2VP formed aggregates in THF, the solvent used for the synthesis. This presumably hindered coupling of the macroanions with the substrate, and explains the low grafting yield and coupling efficiency observed in these reactions. Purification of the crude products was also problematic due to the amphipolar character of the CSC copolymers and the block copolymer contaminant. A new fractionation method by cloud‐point centrifugation was developed to purify copolymers of generations G1 and above. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1075–1085     

Synthesis and characterization of thermoresponsive amphiphilic block copolymers incorporating a poly(ethylene oxide‐stat‐propylene oxide) block

Amphiphilic BuO‐(PEO‐stat‐PPO)‐block‐PLA‐OH diblock and MeO‐PEO‐block‐(PEO‐stat‐PPO)‐block‐PLA‐OH triblock copolymers incorporating thermoresponsive poly(ethylene oxide‐stat‐propylene oxide) (PEO‐stat‐PPO) blocks were prepared by ring‐opening polymerization of lactide (LA) initiated by macroinitiators formed from treating BuO‐(PEO‐stat‐PPO)‐OH and MeO‐PEO‐block‐(PEO‐stat‐PPO)‐OH with AlEt₃. MeO‐PEO‐block‐(PEO‐stat‐PPO)‐OH was prepared by coupling MeO‐PEO‐OH and HO‐(PEO‐stat‐PPO)‐OH, followed by chromatographic purification. The cloud points of 0.2% aqueous solutions are between 36 and 46 °C for the diblock copolymers that contain a 50 wt % EO thermoresponsive block and 78 °C for the triblock copolymer that contains a 75 wt % EO thermoresponsive block. Variable temperature ¹H NMR spectra recorded on D₂O solutions of the diblock copolymers display no PLA resonances below the cloud point and fairly sharp PLA resonances above the cloud point, suggesting that desolvation of the thermoresponsive block increases the miscibility of the two blocks. Preliminary characterization of the micelles formed in aqueous solutions of BuO‐(PEO‐stat‐PPO)‐block‐PLA‐OH conducted using laser scanning confocal microscopy and pulsed gradient spin echo NMR point to significant changes in the size of the micellar aggregates as a function of temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5156–5167, 2005     

Synthesis of polymeric core–shell particles using surface‐initiated living free‐radical polymerization

An easy and novel approach to the synthesis of functionalized nanostructured polymeric particles is reported. The surfactant‐free emulsion polymerization of methyl methacrylate in the presence of the crosslinking reagent 2‐ethyl‐2‐(hydroxy methyl)‐1,3‐propanediol trimethacrylate was used to in situ crosslink colloid micelles to produce stable, crosslinked polymeric particles (diameter size ～ 100–300 nm). A functionalized methacrylate monomer, 2‐methacryloxyethyl‐2′‐bromoisobutyrate, containing a dormant atom transfer radical polymerization (ATRP) living free‐radical initiator, which is termed an inimer (initiator/monomer), was added to the solution during the polymerization to functionalize the surface of the particles with ATRP initiator groups. The surface‐initiated ATRP of different monomers was then carried out to produce core–shell‐type polymeric nanostructures. This versatile technique can be easily employed for the design of a wide variety of polymeric shells surrounding a crosslinked core while keeping good control over the sizes of the nanostructures. The particles were characterized with scanning electron microscopy, transmission electron microscopy, optical microscopy, dynamic light scattering, and Raman spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1575–1584, 2007     

Thermo‐ and pH‐induced self‐assembly of P(AA‐b‐NIPAAm‐b‐AA) triblock copolymers synthesized via RAFT polymerization

A series of environmentally sensitive ABA triblock copolymers with different block lengths were prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization from acrylic acid (AA) and N‐isopropylacrylamide (NIPAAm). The GPC and ¹H NMR analyses demonstrated the narrow molecular weight distribution and precise chemical structure of the prepared P(AA‐b‐NIPAAm‐b‐AA) triblock copolymers owing to the controlled/living characteristics of RAFT polymerization. The lower critical solution temperature (LCST) of the triblock copolymers could be tailored by adjusting the length of PAA block and controlled by the pH value. Under heating, the triblock copolymers underwent self‐assemble in dilute aqueous solution and formed nanoparticles revealed via TEM images. Physically crosslinked nanogels induced by inter‐/intra‐hydrogen bonding or core‐shell micelle particles thus could be obtained by changing environmental conditions. With a well‐defined structure and stimuli‐responsive properties, the P(AA‐b‐NIPAAm‐b‐AA) copolymer is expected to be employed as a nanocarrier for biomedical applications in controlled‐drug delivery and targeting therapy. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1109–1118     

One‐pot synthesis of linear‐hyperbranched diblock copolymers via self‐condensing vinyl polymerization and ring opening polymerization

The linear poly(ε–caprolacton)‐b‐hyperbrached poly(2‐((α‐bromobutyryl)oxy)ethyl acrylate) (LPCL‐b‐HPBBEA) has been successfully synthesized by simultaneous ring‐opening polymerization (ROP) of CL and self‐condensing vinyl polymerization (SCVP) of BBEA in one‐pot. The HPBBEA homopolymers were found to be formed in the polymerization because of the competitive reactions induced by initiation with bifunctional initiator, 2‐hydroxylethyl‐2′‐bromoisobutyrate (HEBiB), and inimer BBEA. The separation of LPCL‐b‐HPBBEA from the polymerization products was achieved by precipitation in methanol. With feed ratio increase of CL and BBEA to HEBiB, the molecular weights of PCL and HPBBEA blocks in the block copolymer enhanced; and the polymerization rate of CL started to decrease gradually after 12 h of polymerization, but the polymerization rate of BBEA was maintained until 24 h of polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7628–7636, 2008     

Synthesis and properties of polydimethylsiloxane-containing block copolymers via living radical polymerization

Polydimethylsiloxane (PDMS) block copolymers were synthesized by using PDMS macroinitiators with copper-mediated living radical polymerization. Diamino PDMS led to initiators that gave ABA block copolymers, but there was low initiator efficiency and molecular weights are somewhat uncontrolled. The use of mono- and difunctional carbinol–hydroxyl functional initiators led to AB and ABA block copolymers with narrow polydispersity indices (PDIs) and controlled number-average molecular weights (M_n's). Polymerization with methyl methacrylate (MMA) and 2-dimethylaminoethyl methacrylate (DMAEMA) was discovered with a range of molecular weights produced. Polymerizations proceeded with excellent first-order kinetics indicative of living polymerization. ABA block copolymers with MMA were prepared with between 28 and 84 wt % poly(methyl methacrylate) with M_n's between 7.6 and 35 K (PDI <1.30), which show thermal transitions characteristic of block copolymers. ABA block copolymers with DMAEMA led to amphiphilic block copolymers with M_n's between 9.5 and 45.7 K (PDIs of 1.25–1.70), which formed aggregates in solution with a critical micelle concentration of 0.1 g dm⁻³ as determined by pyrene fluorimetry experiments. Monocarbinol functional PDMS gave AB block copolymers with both MMA and DMAEMA. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1833–1842, 2001     

Synthesis and characterization of pH sensitive poly(glycidol)‐b‐poly(4‐vinylpyridine) block copolymers

Block copolymers of poly(glycidol)‐b‐poly(4‐vinylpyridine) were obtained by ATRP of 4‐vinylpyridine initiated by ω‐(2‐chloropropionyl) poly(glycidol) macroinitiators. By changing the monomer/macroinitiator ratio in the synthesis polymers with varied P4VP/PGl molar ratio were obtained. The obtained block copolymers showed pH sensitive solubility. It was found that the linkage of a hydrophilic poly(glycidol) block to a P4VP influenced the pK_a value of P4VP. DLS measurements showed the formation of fully collapsed aggregates exceeding pH 4.7. Above this pH values the collapsed P4VP core of the aggregates was stabilized by a surrounding hydrophilic poly(glycidol) corona. The size of the aggregates depended significantly upon the composition of the block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1782–1794, 2009     

Synthesis of miktoarm star amphiphilic block copolymers via combination of NMRP and ATRP and investigation on self‐assembly behaviors

The novel trifunctional initiator, 1‐(4‐methyleneoxy‐2,2,6,6‐tetramethylpip‐eridinoxyl)‐3,5‐bi(bromomethyl)‐2,4,6‐trimethylbenzene (TEMPO‐2Br), was successfully synthesized and used to prepare the miktoarm star amphiphilic poly(styrene)‐(poly(N‐isopropylacrylamide))₂ (PS(PNIPAAM)₂) via combination of atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMRP) techniques. Furthermore, the star amphiphilic block copolymer, poly (styrene)‐(poly(N‐isopropylacrylamide‐b‐4‐vinylpyridine))₂ (PS(PNIPAAM‐b‐P4VP)₂), was also prepared using PS(PNIPAAM)₂ as the macroinitiator and 4‐vinylpyridine as the second monomer by ATRP method. The obtained polymers were well‐defined with narrow molecular weight distributions (M_w/M_n ≤ 1.29). Meanwhile, the self‐assembly behaviors of the miktoarm amphiphilic block copolymers, PS(PNIPAAM)₂ and PS(PNIPAAM‐b‐P4VP)₂, were also investigated. Interestingly, the aggregate morphology changed from sphere‐shaped micelles (4.7 < pH < 3.0) to a mixture of spheres and rods (1.0 < pH < 3.0), and rod‐shaped nanorods formed when pH value was below 1.0. The LCST of PS(PNIPAAM)₂ (pH = 7) was about 31 °C and the LCST of PS(PNIPAAM‐b‐P4VP)₂ was about 35 °C (pH = 3). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6304–6315, 2009     

Aqueous self‐assembly of pullulan‐b‐poly(2‐ethyl‐2‐oxazoline) double hydrophilic block copolymers

The self‐assembly of a novel double hydrophilic block copolymer in water without the application of external triggers is described, namely pullulan‐b‐poly(2‐ethyl‐2‐oxazoline) (Pull‐b‐PEtOx). The biomacromolecules, Pull (8–38 kg mol^?1), is modified and conjugated to biocompatible PEtOx (22 kg mol^?1) via modular conjugation. Moreover, the molecular weight of the Pull blocks are varied to investigate the effect of molecular weight on the self‐assembly behavior. Spherical particles with sizes between 300 and 500 nm are formed in diluted aqueous solution (0.1–1.0 wt %) as observed via dynamic light scattering and static light scattering. Additionally, cryo scanning electron microscopy and laser scanning confocal microscopy are performed to support the finding from light scattering. The block ratio study shows an optimum ratio of Pull and PEtOx of 0.4/0.6 for self‐assembly in water in the concentration range of 0.1–1.0 wt %. At higher concentrations of 20 wt %, vesicular structures with sizes above 1 µm can be observed via optical microscopy. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3757–3766     

Synthesis of poly(p‐phenylene)‐poly(4‐diphenylaminostyrene) bipolar block copolymers with a well‐controlled and defined polymer chain structure

A poly(p‐phenylene) (PPP)‐poly(4‐diphenylaminostyrene) (PDAS) bipolar block copolymer was synthesized for the first time. A prerequisite prepolymer, poly(1,3‐cyclohexadiene) (PCHD)‐PDAS binary block copolymer, in which the PCHD block consisted solely of 1,4‐cyclohexadiene (1,4‐CHD) units, was synthesized by living anionic block copolymerization of 1,3‐cyclohexadiene and 4‐diphenylaminostyrene. To obtain the PPP‐PDAS bipolar block copolymer, the dehydrogenation of this prepolymer with quinones was examined, and tetrachloro‐1,2‐(o)‐benzoquinone was found to be an appropriate dehydrogenation reagent. This dehydrogenation reaction was remarkably accelerated by ultrasonic irradiation, effectively yielding the target PPP‐PDAS bipolar block copolymer. The hole and electron drift mobilities for PPP‐PDAS bipolar block copolymer were both on the order of 10^?3 to 10^?4 cm²/V·s, with a negative slope when plotted against the square root of the applied field. Therefore, this bipolar block copolymer was found to act as a bipolar semi‐conducting copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

AB2‐type amphiphilic block copolymers composed of poly(ethylene glycol) and poly(N‐isopropylacrylamide) via single‐electron transfer living radical polymerization: Synthesis and characterization

Novel AB₂‐type amphiphilic block copolymers of poly(ethylene glycol) and poly(N‐isopropylacrylamide), PEG‐b‐(PNIPAM)₂, were successfully synthesized through single‐electron transfer living radical polymerization (SET‐LRP). A difunctional macroinitiator was prepared by esterification of 2,2‐dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether (PEG). The copolymers were obtained via the SET‐LRP of N‐isopropylacrylamide (NIPAM) with CuCl/tris(2‐(dimethylamino)ethyl)amine (Me₆TREN) as catalytic system and DMF/H₂O (v/v = 3:1) mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography and ¹H NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions (PDI < 1.15). Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry. As a result, the phase transition temperature of PEG₄₄‐b‐(PNIPAM₅₅)₂ is similar to that in the case of PEG₄₄‐b‐PNIPAM₁₁₀; however, the corresponding enthalpy change is much lower, indicating the significant influence of the macromolecular architecture on the phase transition. This is the first study into the effect of macromolecular architecture on the phase transition using AB₂‐type amphiphilic block copolymer composed of PEG and PNIPAM. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4420–4427, 2009     

Synthesis and characterization of ABA‐type amphiphilic tri‐block copolymers through anionic polymerization using end functionalized poly(ethylene oxide) oligomers

ABA‐type amphiphilic tri‐block copolymers were successfully synthesized from poly(ethylene oxide) derivatives through anionic polymerization. When poly(styrene) anions were reacted with telechelic bromine‐terminated poly(ethylene oxide) ( 1 ) in 2:1 mole ratio, poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers were formed. Similarly, stable telechelic carbanion‐terminated poly(ethylene oxide), prepared from 1,1‐diphenylethylene‐terminated poly (ethylene oxide) ( 2 ) and sec‐BuLi, was also used to polymerize styrene and methyl methacrylate separately, as a result, poly (styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) and poly (methyl methacrylate)‐b‐poly(ethylene oxide)‐b‐poly(methyl methacrylate) tri‐block copolymers were formed respectively. All these tri‐block copolymers and poly(ethylene oxide) derivatives, 1 and 2 , were characterized by spectroscopic, calorimetric, and chromatographic techniques. Theoretical molecular weights of the tri‐block copolymers were found to be similar to the experimental molecular weights, and narrow polydispersity index was observed for all the tri‐block copolymers. Differential scanning calorimetric studies confirmed the presence of glass transition temperatures of poly(ethylene oxide), poly(styrene), and poly(methyl methacrylate) blocks in the tri‐block copolymers. Poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers, prepared from polystyryl anion and 1 , were successfully used to prepare micelles, and according to the transmission electron microscopy and dynamic light scattering results, the micelles were spherical in shape with mean average diameter of 106 ± 5 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011