Morphology of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) assemblies in diluted aqueous solution and gel studied by atomic force microscopy

Morphologies of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) triblock copolymer self‐assemblies in the diluted solution and in gel were studied by atomic force microscopy (AFM). The copolymer self‐assembled into wormlike aggregates, of uniform diameter, in water. The wormlike aggregates arranged in order to form separate clusters in the diluted copolymer solution; at a higher copolymer concentration, the clusters became bigger and bigger, and packed together to form gel. Copyright © 2008 John Wiley & Sons, Ltd.     

Poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ϵ‐caprolactone) triblock copolymers: Synthesis and self‐assembly in aqueous solutions

Nontoxic and biodegradable poly(?‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(?‐caprolactone) triblock copolymers were synthesized by the solution polymerization of ?‐caprolactone in the presence of poly(ethylene glycol). The chemical structure of the resulting triblock copolymer was characterized with ¹H NMR and gel permeation chromatography. In aqueous solutions of the triblock copolymers, the micellization and sol–gel‐transition behaviors were investigated. The experimental results showed that the unimer‐to‐micelle transition did occur. In a sol–gel‐transition phase diagram obtained by the vial‐tilting method, the boundary curve shifted to the left, and the gel regions expanded with the increasing molecular weight of the poly(?‐caprolactone) block. In addition, the hydrodynamic diameters of the micelles were almost independent of the investigated temperature (25–55 °C). The atomic force microscopy results showed that spherical micelles formed at the copolymer concentration of 2.5 × 10^?4 g/mL, whereas necklace‐like and worm‐like shapes were adopted when the concentration was 0.25 g/mL, which was high enough to form a gel. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 605–613, 2007     

Syntheses and self‐assembly of poly(benzyl ether)‐b‐poly(N‐isopropylacrylamide) dendritic–linear diblock copolymers

This article describes the syntheses and solution behavior of model amphiphilic dendritic–linear diblock copolymers that self‐assemble in aqueous solutions into micelles with thermoresponsive shells. The investigated materials are constructed of poly(benzyl ether) monodendrons of the second generation ([G‐2]) or third generation ([G‐3]) and linear poly(N‐isopropylacrylamide) (PNIPAM). [G‐2]‐PNIPAM and [G‐3]‐PNIPAM dendritic–linear diblock copolymers have been prepared by reversible addition–fragmentation transfer (RAFT) polymerizations of N‐isopropylacrylamide with a [G‐2]‐ or [G‐3]‐based RAFT agent, respectively. The critical micelle concentration (cmc) of [G‐3]‐PNIPAM₂₂₀, determined by surface tensiometry, is 6.3 × 10^?6 g/mL, whereas [G‐2]‐PNIPAM₂₃₅ has a cmc of 1.0 × 10^?5 g/mL. Transmission electron microscopy results indicate the presence of spherical micelles in aqueous solutions. The thermoresponsive conformational changes of PNIPAM chains located at the shell of the dendritic–linear diblock copolymer micelles have been thoroughly investigated with a combination of dynamic and static laser light scattering and excimer fluorescence. The thermoresponsive collapse of the PNIPAM shell is a two‐stage process; the first one occurs gradually in the temperature range of 20–29 °C, which is much lower than the lower critical solution temperature of linear PNIPAM homopolymer, followed by the second process, in which the main collapse of PNIPAM chains takes place in the narrow temperature range of 29–31 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1357–1371, 2006     

Synthesis,pH‐ and temperature‐induced micellization and gelation of doubly hydrophilic triblock copolymer of poly(N,N‐dimethylamino‐2‐ethylmethacrylate)‐b‐poly(ethylene glycol)‐b‐poly(N,N‐dimethylamino‐2‐ethylmethacrylate) in aqueous solutions

A doubly hydrophilic triblock copolymer of poly(N,N‐dimethylamino‐2‐ethyl methacrylate)‐b‐Poly(ethylene glycol)‐b‐poly(N,N‐dimethylamino‐2‐ethylmethacrylate) (PDMAEMA‐b‐PEG‐b‐PDMAEMA) with well‐defined structure and narrow molecular weight distribution (M_w/M_n = 1.21) was synthesized in aqueous medium via atom transfer radical polymerization (ATRP) of N,N‐dimethylamino‐2‐ethylmethacrylate (DMAEMA) initiated by the PEG macroinitiator. The macroinitiator and triblock copolymer were characterized with ¹H NMR and gel permeation chromatography (GPC). Fluorescence spectroscopy, dynamic light scattering (DSL), transmittance measurement, and rheological characterization were applied to investigate pH‐ and temperature‐induced micellization in the dilute solution of 1 mg/mL when pH > 13 and gelation in the concentrated solution of 25 wt % at pH = 14 and temperatures beyond 80 °C. The unimer of R_h = 3.7 ± 0.8 nm coexisted with micelle of R_h = 45.6 ± 6.5 nm at pH 14. Phase separation occurred in dilute aqueous solution of the triblock copolymer of 1 mg/mL at about 50 °C. Large aggregates with R_h = 300–450 nm were formed after phase separation, which became even larger as R_h = 750–1000 nm with increasing temperature. The gelation temperature determined by rheology measurement was about 80 °C at pH 14 for the 25 wt % aqueous solution of the triblock copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5869–5878, 2008     

Self‐assembled complexes of poly(acrylic acid) and poly(styrene)‐block‐poly(4‐vinyl pyridine)

Polymer complexes were prepared from high molecular weight poly(acrylic acid) (PAA) and poly(styrene)‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) in dimethyl formamide (DMF). The hydrogen bonding interactions, phase behavior, and morphology of the complexes were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this A‐b‐B/C type block copolymer/homopolymer system, P4VP block of the block copolymer has strong intermolecular interaction with PAA which led to the formation of nanostructured micelles at various PAA concentrations. The pure PS‐b‐P4VP block copolymer showed a cylindrical rodlike morphology. Spherical micelles were observed in the complexes and the size of the micelles increased with increasing PAA concentration. The micelles are composed of hydrogen‐bonded PAA/P4VP core and non‐bonded PS corona. Finally, a model was proposed to explain the microphase morphology of complex based on the experimental results obtained. The selective swelling of the PS‐b‐P4VP block copolymer by PAA resulted in the formation of different micelles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1192–1202, 2009     

Association of hydrophobically α,ω‐end‐capped poly(2‐methyl‐2‐oxazoline) in water

The α,ω‐end‐capped poly(2‐methyl‐2‐oxazoline) (C_n‐POXZ‐C_n) have been synthesized by a one‐pot process using cationic ring‐opening polymerization with an appropriate initiator and terminating agent. The polymers bearing different alkyl groups C₁₂ and C₁₈ have molecular weight in the range of 2.4 × 10³ to 14 × 10³ with a small polydispersity index. The solution behavior of the free chains has been analyzed in a nonselective solvent, dichloromethane, by small‐angle neutron scattering and dynamic light scattering. These amphiphilic polymers associate in water to form flower‐like micellar structures. Critical micelle concentrations, investigated by fluorescence technique, are in the range of 0.03–0.5 g L^?1 and are dependent on the hydrophilic/lipophilic balance. The structural properties of the aggregates have also been investigated by viscometry. Intrinsic viscosities of these polymers are in the same range as that of the precursors poly(2‐methyl‐2‐oxazoline) (POXZ) and mono‐functionalized polymers. Large viscosity increase corresponding to intermicellar bridging was observed in the vicinity of the micelle overlap concentration. Addition of hydroxypropyl β‐cyclodextrin (HβCD) has dissociated the aggregates and the intrinsic viscosities of the HβCD‐end‐capped chains have become comparable with the ones of POXZ precursor chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2477–2485, 2010     

Competitive hydrogen bonding and self‐assembly in poly(2‐vinyl pyridine)‐block‐poly(methyl methacrylate)/poly(hydroxyether of bisphenol A) blends

Blends of poly(2‐vinyl pyridine)‐block‐poly(methyl methacrylate) (P2VP‐b‐PMMA) and poly(hydroxyether of bisphenol A) (phenoxy) were prepared by solvent casting from chloroform solution. The specific interactions, phase behavior and nanostructure morphologies of these blends were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this block copolymer/homopolymer blend system, it is established that competitive hydrogen bonding exists as both blocks of the P2VP‐b‐PMMA are capable of forming intermolecular hydrogen bonds with phenoxy. It was observed that the interaction between phenoxy and P2VP is stronger than that between phenoxy and PMMA. This imbalance in the intermolecular interactions and the repulsions between the two blocks of the diblock copolymer lead to a variety of phase morphologies. At low phenoxy concentration, spherical micelles are observed. As the concentration increases, PMMA begins to interact with phenoxy, leading to the changes of morphology from spherical to wormlike micelles and finally forms a homogenous system. A model is proposed to describe the self‐assembled nanostructures of the P2VP‐b‐PMMA/phenoxy blends, and the competitive hydrogen bonding is responsible for the morphological changes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1894–1905, 2009     

Synthesis and self‐assembling of poly(N‐isopropylacrylamide‐block‐poly(L‐lactide)‐block‐poly(N‐isopropylacrylamide) triblock copolymers prepared by combination of ring‐opening polymerization and atom transfer radical polymerization

Novel thermo‐responsive poly(N‐isopropylacrylamide)‐block‐poly(l ‐lactide)‐block‐poly(N‐isopropylacylamide) (PNIPAAm‐b‐PLLA‐b‐PNIPAAm) triblock copolymers were successfully prepared by atom transfer radical polymerization of NIPAAm with Br‐PLLA‐Br macroinitiator, using a CuCl/tris(2‐dimethylaminoethyl) amine (Me₆TREN) complex as catalyst at 25 °C in a N,N‐dimethylformamide/water mixture. The molecular weight of the copolymers ranges from 18,000 to 38,000 g mol^?1, and the dispersity from 1.10 to 1.28. Micelles are formed by self‐assembly of copolymers in aqueous medium at room temperature, as evidenced by ¹H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The critical micelle concentration determined by fluorescence spectroscopy ranges from 0.0077 to 0.016 mg mL^?1. ¹H NMR analysis in selective solvents confirmed the core‐shell structure of micelles. The copolymers exhibit a lower critical solution temperature (LCST) between 32.1 and 32.8 °C. The micelles are spherical in shape with a mean diameter between 31.4 and 83.3 nm, as determined by TEM and DLS. When the temperature is raised above the LCST, micelle size increases at high copolymer concentrations due to aggregation. In contrast, at low copolymer concentrations, decrease of micelle size is observed due to collapse of PNIPAAm chains. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3274–3283     

Synthesis and self‐association behavior of poly[bis(2‐(2‐methoxyethoxy)ethoxy)phosphazene]‐b‐poly(propyleneglycol) triblock copolymers

Amphilic triblock copolymers with varying ratios of hydrophilic poly[bis (methoxyethoxyethoxy)phosphazene] (MEEP) and relatively hydrophobic poly(propylene glycol) (PPG) blocks were synthesized via the controlled cationic‐induced living polymerization of a phosphoranimine (Cl₃P?NSiMe₃) at ambient temperature. A PPG block can function as either a classical hydrophobic block or a less hydrophobic component by varying the nature of a phosphazene block. The aqueous phase behavior of MEEP‐PPG‐MEEP block copolymers was investigated using fluorescence techniques, TEM, and dynamic light scattering (DLS). The critical micelle concentrations (cmcs) of MEEP‐PPG‐MEEP block copolymers were determined to be in the range of 3.7–16.8 mg/L. The mean diameters of MEEP‐PPG‐MEEP polymeric micelles, measured by DLS, were between 31 and 44 nm. The equilibrium constants of pyrene in these micelles ranged from 4.7 × 10⁴ to 9.6 × 10⁴. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 692–699, 2009     

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     

Supramolecular complexes of poly(3‐Hexylthiophene)‐block (and random)‐poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] copolymers with perylene bisimide

Block and random copolymers of poly(3‐hexylthiophene) and poly[3‐(2‐(6‐carboxyhexyl)methyl)thiophene] with side‐chain carboxylic functionality ((P3HT‐b‐P3COOH) and (P3HT‐r‐P3COOH) were developed by Grignard Metathesis (GRIM) polymerization. The carboxylic functionality was introduced in the side chain via the oxazoline route. Both the block and random polythiophene copolymers were complexed with pyridine functionalized perylene bisimide to obtain supramolecular block and random polymer complexes. The complex formation in both systems was confirmed by ¹H NMR, WXRD and SAXS studies. An expansion of d spacing upon complex formation was observed in both the block and random copolymer, which could be traced by WXRD. Hole and electron mobilities measured for the supramolecular complexes indicated values which were higher by an order of magnitude for the supramolecular block complex (μ_h ≈ 2.9 × 10⁻⁴ cm²/Vs; μ_e ≈ 3.1 × 10⁻⁶ cm²/Vs) as compared to the random (μ_h ≈ 1.4 × 10⁻⁵ cm²/Vs; μ_e ≈ 4.7 × 10⁻⁷ cm²/Vs) copolymer. These results are indicative of the higher degree of disorder prevailing in the films of random copolymer system compared to the block copolymer. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1574–1583     

Novel temperature‐ and pH‐responsive graft copolymers composed of poly(L‐glutamic acid) and poly(N‐isopropylacrylamide)

A series of novel temperature‐ and pH‐responsive graft copolymers, poly(L ‐glutamic acid)‐g‐poly(N‐isopropylacrylamide), were synthesized by coupling amino‐semitelechelic poly(N‐isopropylacrylamide) with N‐hydroxysuccinimide‐activated poly(L ‐glutamic acid). The graft copolymers and their precursors were characterized, by ESI‐FTICR Mass Spectrum, intrinsic viscosity measurements and proton nuclear magnetic resonance (¹H NMR). The phase‐transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering. The solution behavior of the copolymers showed dependence on both temperature and pH. The cloud point (CP) of the copolymer solution at pH 5.0–7.4 was slightly higher than that of the solution of the PNIPAM homopolymer because of the hydrophilic nature of the poly(glutamic acid) (PGA) backbone. The CP markedly decreased when the pH was lowered from 5 to 4.2, caused by the decrease in hydrophilicity of the PGA backbone. At a temperature above the lower critical solution temperature of the PNIPAM chain, the copolymers formed amphiphilic core‐shell aggregates at pH 4.5–7.4 and the particle size was reduced with decreasing pH. In contrast, larger hydrophobic aggregates were formed at pH 4.2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4140–4150, 2008     

Synthesis,properties, and field effect transistor characteristics of new thiophene‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline‐thiophene‐based conjugated polymers

Four new conjugated copolymers based on the moiety of bis(4‐hexylthiophen‐2‐yl)‐6,7‐diheptyl‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline (BTHTQ) were synthesized and characterized, including poly(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline) (PBTHTQ), poly‐(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl)‐[1,2,5]thiadiazolo‐[3,4‐g]quinoxaline‐alt‐2,5‐thiophene) (PTTHTQ), poly(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl) [1,2,5]‐thiadiazolo‐[3,4‐g]quinoxaline‐alt‐9,9‐dioctyl‐2,7‐fluore‐ne) (PFBTHTQ), and poly(6,7‐diheptyl‐4,9‐bis(4‐hexylthiophen‐2‐yl)‐[1,2,5]thiadiazolo[3,4‐g]quinoxaline‐alt‐1,4‐bis(decyloxy)phenylene) (PPBTHTQ). The λ_max of PBTHTQ, PTTHTQ, PFBTHTQ, and PPBTHTP thin films was shown at 780, 876, 734, and 710 nm, respectively, with the corresponding optical band gaps (E) of 1.31, 1.05, 1.40, and 1.43 eV. The relatively small band gaps of the synthesized polymers suggested the significance of intramolecular charge transfer between the donor and TQ moiety. The estimated hole mobilities of PBTHTQ, PTTHTQ, and PFBTHTQ‐based field effect transistor devices using CHCl₃ solvent were 8.5 × 10^?5, 8.5 × 10^?4, and 2.8 × 10^?5 cm² V^?1 s^?1, respectively, but significantly enhanced to 1.6 × 10^?4, 3.8 × 10^?3, and 1.5 × 10^?4 cm² V^?1 s^?1 using high boiling point solvent of chlorobenzene (CB). The higher hole mobility of PTTHTQ than the other two copolymers was attributed from its smaller band gap or ordered morphology [wormlike (chloroform) or needle‐like (CB)]. The characteristics of small band gap and high mobility suggest the potential applications of the BTHTQ‐based conjugated copolymers in electronic and optoelectronic devices. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6305–6316, 2008     

Excluded‐volume effects on the chain dimensions and transport coefficients of sodium poly(styrene sulfonate) in aqueous sodium chloride

Fifteen samples of sodium poly(styrene sulfonate) with weight‐average molecular weights of 3 × 10⁴ to 8 × 10⁵ have been studied by static and dynamic light scattering and viscometry in 0.05 and 0.5 M aqueous NaCl at 25 °C. The measured radii of gyration, translational diffusion coefficients, and intrinsic viscosities at the lower salt concentration exhibit molecular weight dependencies stronger than those predictable for uncharged flexible chains in the good solvent limit. These data and those at the higher NaCl concentration are analyzed, along with previous intrinsic viscosity data covering a broad molecular weight range, in the framework of the quasi‐two‐parameter (QTP) theory with the wormlike chain as the model. It is shown that the relevant theories for the expansion factors in the QTP scheme combined with these theories for the unperturbed wormlike chain are capable of describing the experimental data with a degree of accuracy similar to that known for nonionic flexible polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2728–2735, 2002     

Preparation of poly(ethylene oxide)‐block‐poly(isoprene) by nitroxide‐mediated free radical polymerization from PEO macroinitiators

Amphiphilic poly(ethylene oxide)‐block‐poly(isoprene) (PEO‐b‐PI) diblock copolymers were prepared by nitroxide‐mediated polymerization of isoprene from alkoxyamine‐terminal poly(ethylene oxide) (PEO). PEO monomethyl ether (M_n ≈ 5200 g/mol) was functionalized by esterification with 2‐bromopropionyl bromide with subsequent copper‐mediated replacement of the terminal bromine with 2,2,5‐trimethyl‐4‐phenyl‐3‐azahexane‐3‐nitroxide. The resulting PEO‐alkoxyamine macroinitiator was used to initiate polymerization of isoprene in bulk and in solution at 125 °C to yield PEO‐b‐PI block copolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.1). Polymerizations were first order in isoprene through 35% conversion. Micellar aggregates of PEO‐b‐PI in aqueous solution were crosslinked by treatment with a water‐soluble redox initiating system, and persistent micellar structures were observed in the dry state by AFM. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2977–2984, 2005     

Synthesis and characterization of poly(1,4‐bis((E)‐2‐(3‐dodecylthiophen‐2‐yl)vinyl)benzene) derivatives

New amorphous semiconducting copolymers, poly(9,9‐dialkylfluorene)‐alt‐(3‐dodecylthienyl‐divinylbenzene‐3‐dodecylthienyl) derivatives (PEFTVB and POFTVB), were designed, synthesized, and characterized. The structure of copolymers was confirmed by H NMR, IR, and elemental analysis. The copolymers showed very good solubility in organic solvents and high thermal stability with high T_g of 178–185 °C. The weight average molecular weight was found to be 107,900 with polydispersity of 3.14 for PEFTVB and 76,700 with that of 3.31 for POFTVB. UV–vis absorption studies showed the maximum absorption at 428 nm (in solution) and 435 nm (in film) for PEFTVB and at 430 nm (in solution) and 436 nm (in film) for POFTVB. Photoluminescence studies showed the emission at 498 nm (in solution) and 557 nm (in film) for PEFTVB and at 498 nm (in solution) and 536 nm (in film) for POFTVB. The solution‐processed thin‐film transistors showed the carrier mobility of 2 × 10^?4 cm² V^?1 s^?1 for PEFTVB‐based devices and 2 × 10^?5 cm² V^?1 s^?1 for POFTVB‐based devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3942–3949, 2010     

Synthesis and characterization of a biodegradable amphiphilic copolymer based on branched poly(ϵ‐caprolactone) and poly(ethylene glycol)

A novel biodegradable amphiphilic copolymer with hydrophobic poly(ε‐caprolactone) branches containing cholic acid moiety and a hydrophilic poly(ethylene glycol) chain was synthesized. The copolymer was characterized by FTIR, ¹H NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD) analysis. The amphiphilic copolymer could self‐assemble into micelles in an aqueous solution. The critical micelle concentration of the amphiphilic copolymer was determined by fluorescence spectroscopy. A nanoparticle drug delivery system with a regularly spherical shape was prepared with high encapsulation efficiency. The in vitro drug release from the drug‐loaded polymeric nanoparticles was investigated. Because of the branched structure of the hydrophobic part of the copolymer and the relatively fast degradation rate of the copolymer, an improved release behavior was observed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5256–5265, 2007     

Morphology control of poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) block copolymer by solvent blending

The use of mixed solvents provided an effective way to control the self‐assembly behavior and photophysical properties of a conjugated rod–coil block copolymer, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) (P3HT‐b‐PEO). It was shown that the balance between the π–π stacking of the P3HT and microphase separation of the copolymer could be dynamically controlled and shifted by solvent blending. Depending on the mixed solvent ratio (i.e., chloroform/methanol, anisole/chloroform, or anisole/methanol), the copolymer chains experienced different kinetic pathways, yielding a series of nanostructures such as disordered wormlike pattern, densely packed nanofibrils, and isolated nanofibrils. With the varying solvent selectivity, the P3HT‐b‐PEO chains displayed a hybrid photophysical property depending on the competition between intrachain and interchain excitonic coupling, resulting in the transformation between J‐ and H‐aggregation. Overall, this work offered an effective way to demonstrate the correlation and transformation between π–π stacking of P3HT and microphase separation, and how the conformation of P3HT chains influenced the photophysical properties of the copolymer during solvent blending. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 544–551     

Synthesis of four‐armed poly(ε‐caprolactone)‐block‐poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four‐armed poly(?‐caprolactone)‐block‐poly(ethylene oxide) (PCL‐b‐PEO) copolymers were synthesized by ring‐opening polymerization of ethylene oxide in the presence of four‐armed poly(?‐caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt₂) as a catalyst. The chemical structure of PCL‐b‐PEO copolymer was confirmed by ¹H NMR and ¹³C NMR. The hydroxyl end groups of the four‐armed PCL were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four‐armed architecture of the copolymer. Physicochemical properties of the four‐armed block copolymers differed from their starting four‐armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four‐armed block copolymer increased with PEO length and PEO content. The micelle formation of the four‐armed block copolymer was examined by a fluorescent probe technique, and the existence of the critical micelle concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. The cmc value increased with increasing PEO length. The absolute cmc values were higher than those for linear amphiphilic block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 950–959, 2004     

Poly(thieno[3,4‐b]‐1,4‐oxathiane) and poly(3,4‐ethylenedioxythiophene‐co‐thieno[3,4‐b]‐1,4‐oxathiane)/poly(styrene sulfonic sodium): Preparation,characterization, and optoelectronic performance

In this work, the asymmetrical analog of 3,4‐ethylenedioxythiophene (EDOT), thieno[3,4‐b]‐1,4‐oxathiane (EOTT), was synthesized and chemically polymerized first in aqueous solution using poly(styrene sulfonic sodium) (PSS) as the polyelectrolyte to yield poly(thieno[3,4‐b]‐1,4‐oxathiane) (PEOTT)/PSS. As‐formed film exhibited low electrical conductivity (～10^?4 S/cm). Alternatively, EOTT together with EDOT (in different molar ratio of 1:1 and 1:5) was copolymerized and the polymer poly(EOTT‐co‐EDOT)/PSS had electrical conductivity of 10^?1 S/cm. After dimethyl sulfoxide (DMSO) treatment, the electrical conductivity was enhanced to 10⁰ S/cm; however, the conductivity of the above homopolymer was reduced (～10^?5 S/cm). Raman spectroscopy was used to interpret conductivity enhancement or reduction after DMSO treatment. The conductivity decrease of PEOTT/PSS compared to poly(EOTT‐co‐EDOT)/PSS may arise from the conformational change of PEOTT backbone from the quasi‐planar to the distorted planar mode induced by PSS^–/PSSH through ionic interaction. Kinetic studies revealed that the copolymer had high coloration efficiencies (375 cm²/C), low switching voltages (?0.8 to +0.6 V), decent contrast ratios (45%), moderate response time (1.0 s), excellent stability, and color persistence. An electrochromic device employing poly(3‐methylthiophene) and poly(EOTT‐co‐EDOT)/PSS as the anode and cathode materials was also studied. From these results, poly(EOTT‐co‐EDOT)/PSS would be a promising candidate material for organic electronics. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2285–2297