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     

Improved self‐assembly of poly(dimethylsiloxane‐b‐ethylene oxide) using a hydrogen‐bonding additive

Block copolymers with increased Flory–Huggins interaction parameters (χ) play an essential role in the production of sub‐10 nm nanopatterns in the growing field of directed self‐assembly for next generation lithographic applications. A library of PDMS‐b‐PEO block copolymers were synthesized by click chemistry and their interaction parameters (χ) determined. The highest χ measured in our samples was 0.21 at 150 °C, which resulted in phase‐separated domains with periods as small as 7.9 nm, suggesting that PDMS‐b‐PEO is a prime candidate for sub‐10 nm nanopatterning. To suppress PEO crystallization, PDMS‐b‐PEO was blended with (l )‐tartaric acid (LTA) which allows for tuning of the self‐assembled morphologies. Additionally, it was observed that the order‐disorder transition temperature (T_ODT) of PDMS‐b‐PEO increased dramatically as the amount of LTA in the blend increased, allowing for further control over self‐assembly. To understand the mechanism of this phenomenon, we present a novel field‐based supramolecular model, which describes the formation of copolymer‐additive complexes by reversible hydrogen bonding. The mean‐field phase separation behavior of the model was calculated using the random phase approximation (RPA). The RPA analysis reproduces behavior consistent with an increase of the effective χ in the PDMS‐b‐(PEO/LTA suprablock). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2200–2208     

Poly(N‐vinyl pyrrolidone)‐block‐Poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) triblock copolymers: Synthesis via RAFT/MADIX process,self‐assembly behavior,and photophysical properties

Poly(N‐vinyl pyrrolidone)‐block‐poly(N‐vinyl carbazole)‐block‐poly(N‐vinyl pyrrolidone) (PVP‐b‐PVK‐b‐PVP) triblock copolymers were synthesized via sequential reversible addition‐fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. First, 1,4‐phenylenebis(methylene)bis(ethyl xanthate) was used as a chain transfer agent to mediate the radical polymerization of N‐vinyl carbazole (NVK). It was found that the polymerization was in a controlled and living manner. Second, one of α,ω‐dixanthate‐terminated PVKs was used as the macromolecular chain transfer agent to mediate the radical polymerization of N‐vinyl pyrrolidone (NVP) to obtain the triblock copolymers with various lengths of PVP blocks. Transmission electron microscopy (TEM) showed that the triblock copolymers in bulks were microphase‐separated and that PVK blocks were self‐organized into cylindrical microdomains, depending on the lengths of PVP blocks. In aqueous solutions, all these triblock copolymers can self‐assemble into the spherical micelles. The critical micelle concentrations of the triblock copolymers were determined without external adding fluorescence probe. By analyzing the change in fluorescence intensity as functions of the concentration, it was judged that the onset of micellization occurred at the concentration while the FL intensity began negatively to deviate from the initial linear increase with the concentration. Fluorescence spectroscopy indicates that the self‐assembled nanoobjects of the PVP‐b‐PVK‐b‐PVP triblock copolymers in water were capable of emitting blue/or purple fluorescence under the irradiation of ultraviolet light. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1852–1863     

Competitive specific interactions in miscible blends of poly(hydroxyether terephthalate ester) and poly(4‐vinyl pyridine)

The miscibility of poly(hydroxyether terephthalate ester) (PHETE) with poly(4‐vinyl pyridine) (P4VP) was established on the basis of thermal analysis. Differential scanning calorimetry showed that each blend displayed a single glass‐transition temperature (T_g), which is intermediate between those of the pure polymers and varies with the composition of blend. The T_g‐composition relationship can be well described with Kwei equation with k = 1 and q = ?30.8 (K), suggesting the presence of the intermolecular specific interactions in the blend system. To investigate the intermolecular specific interactions in the blends, the model compounds such as 1,3‐diphenoxy‐2‐propanol, 4‐methyl pyridine, and ethyl benzoate were used to determine the equilibrium constants, according to Coleman and Painter model, to account for the association equilibriums of several structural moieties, using liquid Fourier transform infrared difference spectroscopy. In terms of the difference in the association equilibrium constant, it is proposed that there are the competitive specific interactions in the blends, which were confirmed by means of Fourier transform infrared spectroscopy of the blends. It is observed that upon adding P4VP to the system, the ester carbonyls of PHETE that were H‐bonded with the hydroxyl groups were released because of the formation of the stronger interchain association via the hydrogen bonding between the hydroxyls of PHETE and tertiary nitrogen atoms of P4VP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1618–1626, 2006     

Synthesis and self‐assembly of novel amphiphilic copolymers poly(lactic acid)‐block‐poly(ascorbyl acrylate)

In this study, a novel type of amphiphilic block copolymers poly(lactic acid)‐block‐poly(ascorbyl acrylate) (PLA‐block‐PAAA) with biodegradable poly(lactic acid) as hydrophobic block and poly(ascorbyl acrylate) (PAAA) as hydrophilic block was successfully developed by a combination of ring‐opening polymerization and atom transfer radical polymerization, followed by hydrogenation under normal pressure. The chemical structures of the desired copolymers were characterized by ¹H NMR and gel permeation chromatography. The thermal physical properties and crystallinity were investigated by thermogravimetric analysis, differential scanning calorimetry, and wide angle X‐ray diffraction, respectively. Their self‐assembly behavior was monitored by fluorescence‐probe technique and turbidity change using UV–vis spectrometer, and the morphology and size of the nanocarriers via self‐assembly were detected by cryo‐transmission electron microscopy and dynamic light scattering. These polymeric micelles with PAAA shell extending into the aqueous solution have potential abilities to act as promising nanovehicles for targeting drug delivery. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and self‐assembly of helical polypeptide‐random coil amphiphilic diblock copolymer

Three amphiphilic rod‐coil diblock copolymers, poly(2‐ethyl‐2‐oxazoline‐b‐γ‐benzyl‐L ‐glutamate) (PEOz‐b‐PBLG), incorporating the same‐length PEOz block length and various lengths of their PBLG blocks, were synthesized through a combining of living cationic and N‐carboxyanhydride (NCA) ring‐opening polymerizations. In the bulk, these block copolymers display thermotropic liquid crystalline behavior. The self‐assembled aggregates that formed from these diblock copolymers in aqueous solution exhibited morphologies that differed from those obtained in α‐helicogenic solvents, that is, solvents in which the PBLG blocks adopt rigid α‐helix conformations. In aqueous solution, the block copolymers self‐assembled into spherical micelles and vesicular aggregates because of their amphiphilic structures. In helicogenic solvents (in this case, toluene and benzyl alcohol), the PEOz‐b‐PBLG copolymers exhibited rod‐coil chain properties, which result in a diverse array of aggregate morphologies (spheres, vesicles, ribbons, and tube nanostructures) and thermoreversible gelation behavior. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3108–3119, 2008     

Coarse‐grained molecular dynamics simulations of stereoregular poly(methyl methacrylate)/poly(vinyl chloride) blends

The stereoregular poly(methyl methacrylate)/poly(vinyl chloride) blends with a wide formulation range are extensively simulated using the coarse‐grained (CG) molecular dynamics (MD) method. To improve the representability, the bonded CG potentials are re‐parameterized against the atomistic simulated melt systems whereas the nonbonded CG potentials are adopted as developed in our previous work. Based on the CG potentials, the MD simulations reproduce all the local distributions of pure systems and the miscibility of mixed systems. Moreover, the global conformational properties are also closer to the target ones than those obtained using the previous CG potentials. The changes in density and volume upon mixing are computed together with the energies of mixing. They are all negative over the entire composition range and indicate stronger intermolecular interactions between distinct components than those between identical components. In particular, it is found that upon mixing the changes in density are insensible to chain tacticity but the changes in volume and the energies of mixing do, which quantitatively confirms that both inter‐molecular interactions and free‐volumes mainly contribute to the observed phase behaviors. Such models and methods reported herein can be used to quickly optimize formulations of polymer blends. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 203–212     

Direct observation of morphological development during the spin‐coating of polystyrene–poly(methyl methacrylate) polymer blends

We present results of the direct observation, in real‐space, of the phase separation of high molecular weight polystyrene and poly(methyl methacrylate) from ortho‐xylene using our newly developed technique of high speed stroboscopic interference microscopy. Taking a fixed concentration (3 wt % in o‐xylene) at a fixed composition (1:4 by weight) and by varying the rotational rate during the spin‐coating process, we are able to observe the formation of a range of phase separated bicontinuous morphologies of differing length‐scales. Importantly, we are able to show that the mechanism by which the final phase separated structure is formed is through domain coarsening when rich in solvent, before vitrification occurs and fixes the phase separated structure. The ability to directly observe morphological development offers a route toward controlling the length‐scale of the final morphology through process control and in situ feedback, from a single stock solution. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B Polym. Phys. 2013, 51, 875–881     

Specific interactions and phase behavior of ternary poly(2‐vinylpyridine)/poly(N‐vinyl‐2‐pyrrolidone)/bisphenol A blends

Hydrogen‐bonding interactions between bisphenol A (BPA) and two proton‐accepting polymers, poly(2‐vinylpyridine) (P2VPy) and poly(N‐vinyl‐2‐pyrrolidone) (PVP), were examined by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The Flory–Huggins interaction‐energy densities of BPA/P2VPy and BPA/PVP blends were determined by the melting point depression method. The interaction parameters for both BPA/P2VPy and BPA/PVP blend systems were negative, demonstrating the miscibility of BPA with P2VPy as well as PVP. The miscibility of ternary BPA/P2VPy/PVP blends was examined by DSC, optical observation, and solid‐state nuclear magnetic resonance spectroscopy. The experimental phase behavior of the ternary blend system agreed with the spinodal phase‐separation boundary calculated using the determined interaction‐energy densities. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1125–1134, 2002     

Real time laser interference microscopy for bar‐spread polystyrene/poly(methyl methacrylate) blends

We demonstrate that real‐time laser interference microscopy can be used to directly observe the dynamics of film formation and phase separation processes for a bar‐spread polystyrene/poly(methyl methacrylate) blend. The ability to dynamically image laser interference patterns allows compete drying curves and polymer content to be determined throughout the film formation process. The polymer content at which phase separation structure first is observed in the interference micrograph sequence is in good agreement with calculated spinodal curves. Morphology evolution proceeds from phase separation onward via coarsening and coalescence to arrive at the final domain structure. In comparison, spin coating the same polymer blend results in structure evolution being quenched further from equilibrium due to the faster drying rate. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 985–992     

Synthesis and self‐assembly of diblock copolymers composed of poly(3‐hexylthiophene) and poly(fluorooctyl methacrylate) segments

Regioregular poly(3‐hexylthiophene)‐b‐poly(1H,1H‐dihydro perfluorooctyl methacrylate) (P3HT‐b‐PFOMA) diblock copolymers were synthesized by atom transfer radical polymerization of fluorooctyl methacrylate using bromoester terminated poly(3‐hexylthiophene) macroinitiators in order to investigate their morphological properties. The P3HT macroinitiator was previously prepared by chemical modification of hydroxy terminated P3HT. The block copolymers were well characterized by ¹H NMR spectroscopy and gel permeation chromatography. Transmission electron microscopy was used to investigate the nanostructured morphology of the diblock copolymers. The block copolymers are able to undergo microphase separation and self‐assemble into well‐defined and organized nanofibrillar‐like micellar morphology. The development of the morphology of P3HT‐b‐PFOMA block copolymers was investigated after annealing in solvent vapor and also in supercritical CO₂. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Segmental and secondary dynamics in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) blends

Broadband dielectric spectroscopy was used to study the segmental (α) and secondary (β) relaxations in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) (PVPh/PMMA) blends with PVPh concentrations of 20–80% and at temperatures from ?30 to approximately glass‐transition temperature (T_g) + 80 °C. Miscible blends were obtained by solution casting from methyl ethyl ketone solution, as confirmed by single differential scanning calorimetry T_g and single segmental relaxation process for each blend. The β relaxation of PMMA maintains similar characteristics in blends with PVPh, compared with neat PMMA. Its relaxation time and activation energy are nearly the same in all blends. Furthermore, the dielectric relaxation strength of PMMA β process in the blends is proportional to the concentration of PMMA, suggesting that blending and intermolecular hydrogen bonding do not modify the local intramolecular motion. The α process, however, represents the segmental motions of both components and becomes slower with increasing PVPh concentration because of the higher T_g. This leads to well‐defined α and β relaxations in the blends above the corresponding T_g, which cannot be reliably resolved in neat PMMA without ambiguous curve deconvolution. The PMMA β process still follows an Arrhenius temperature dependence above T_g, but with an activation energy larger than that observed below T_g because of increased relaxation amplitude. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3405–3415, 2004     

A roadmap for poly(ethylene oxide)‐block‐poly‐ε‐caprolactone self‐assembly in water: Prediction,synthesis, and characterization

Numerical self‐consistent field (SCF) lattice computations allow a priori determination of the equilibrium morphology and size of supramolecular structures originating from the self‐assembly of neutral block copolymers in selective solvents. The self‐assembly behavior of poly(ethylene oxide)‐block‐poly‐ε‐caprolactone (PEO‐PCL) block copolymers in water was studied as a function of the block composition, resulting in equilibrium structure and size diagrams. Guided by the theoretical SCF predictions, PEO‐PCL block copolymers of various compositions have been synthesized and assembled in water. The size and morphology of the resulting structures have been characterized by small‐angle X‐ray scattering, cryogenic transmission electron microscopy, and multiangle dynamic light scattering. The experimental results are consistent with the SCF computations. These findings show that SCF is applicable to build up roadmaps for amphiphilic polymers in solution, where control over size and shape are required, which is relevant, for instance, when designing spherical micelles for drug delivery systems © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 330–339     

Diblock copolymer–azobenzene complexes through hydrogen bonding: Self‐assembly and stable photoinduced optical anisotropy

We have demonstrated the preparation of a series of photoaddressable supramolecular block copolymers by mixing a carboxy‐terminated azobenzene derivative, 6‐[4‐(4′‐cyanophenylazo)phenyloxy]hexanoic acid (AZO), and two polystyrene‐b‐poly(4‐vinylpiridine) (PS‐b‐P4VP) block copolymers. AZO can be selectively attached to the P4VP block of PS‐b‐P4VP through hydrogen bonding interactions. The assembly of AZO with vinylpyridine group‐containing polymers was initially investigated on a model system composed of P4VP homopolymer and AZO. Homogeneous liquid crystalline materials were obtained for ratios of AZO to vinylpyridine repeating unit, x, lower or equal to 0.50. Mixtures with higher x resulted in heterogeneous materials showing clear macrophase separation. Accordingly, a series of hydrogen‐bonded complexes of PS‐b‐P4VP and AZO, PS‐b‐P4VP(AZO)_x, with x = 0.25 and x = 0.50 were prepared. Lamellar and spherical morphologies were observed for the complexes based on PS24‐b‐P4VP9.5 (M_n,PS = 24,000, M_n,P4VP = 9500) and PS24‐b‐P4VP1.9 (M_n,PS = 24,000, M_n,P4VP = 1900), respectively. Photoinduced orientation of the azobenzene units was obtained in films of P4VP(AZO)_x and PS‐b‐P4VP(AZO)_x with x = 0.25 and 0.50 by using 488 nm linearly polarized light and characterized through birefringence and dichroism measurements. This investigation shows a versatile and less laborious approach to azobenzene‐containing polymer materials with low chromophore content, of interest in optical application. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Free-radical polymerization induced macrophase separation in poly(methyl methacrylate)/dimethacrylate blends: Experiment and modeling

This work presents the analysis of a polymerization-induced macrophase separation taking place during free-radical copolymerization of styrene and dimethacrylate in the presence of poly(methyl methacrylate) (PMMA) as a modifier. The PMMA does not participate in the polymerization but induces phase separation in the course of the reaction. An experimental study based on real-time static light scattering measurements with the aim of monitoring the phase behavior during the isothermal copolymerization is firstly presented. Then, an original and innovative contribution is made by modeling the evolution of the unstable region of the phase diagram as a function of conversion and by predicting phase separation in spinodal condition. The analysis is performed using an expression for the free energy of a reactive network-forming mixture based on the Flory–Rehner lattice model for swollen gels. The accuracy of the proposed model is verified by the good agreement found between its predictions and the experimental results.     

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 and self‐assembly of amphiphilic brush‐dendritic‐linear poly[poly(ethylene glycol) methyl ether methacrylate]‐b‐ polyamidoamine‐b‐poly(ε‐caprolactone) copolymers

A series of novel amphiphilic brush‐dendritic‐linear poly[poly(ethylene glycol) methyl ether methacrylate]‐b‐polyamidoamine‐b‐poly(ε‐caprolactone) copolymers (PPEGMEMA‐b‐D_m‐b‐PCL) (m = 1, 2, and 3: the generation number of dendron) were synthesized by the combination techniques of click chemistry, atom transfer radical polymerization (ATRP), and ring‐opening polymerization (ROP). The brush‐dendritic copolymers bearing hydrophilic brush PPEGMEMA and hydrophobic dendron polyamidoamine protected by the tert‐butoxycarbonyl (Boc) groups [D_m‐(Boc) (m = 1, 2, and 3)] were for the first time prepared by ATRP of poly(ethylene glycol) methyl ether methacrylate monomer (PEGMEMA) initiated with the dendron initiator, which was prepared from 2′‐azidoethyl‐2‐bromoisobutyrate (AEBIB) and D_m‐(Boc) terminated with a clickable alkyne by click chemistry. Then, the brush‐dendritic copolymers with primary amine groups (PPEGMEMA‐b‐D_m) were obtained from the removal of the protected Boc groups of the brush‐dendritic copolymers in the presence of trifluoroacetic acid. The brush‐dendritic‐linear PPEGMEMA‐b‐D_m‐b‐PCL copolymers were synthesized from ROP of ε‐caprolactone monomer using PPEGMEMA‐b‐D_m as the macroinitiators and stannous octoate as catalyst in toluene at 130 °C. To the best of our knowledge, this is the first report that integrates hydrophilic brush polymer PPEGMEMA with hydrophobic polyamidoamine (PAMAM) dendron and PCL to form amphiphilic brush‐dendritic‐linear copolymers. The amphiphilic brush‐dendritic‐linear copolymers can self‐assemble into spherical micellar structures in aqueous solution. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Effect of side chain and backbone length on lamellar spacing in polystyrene‐block‐poly(dimethyl siloxane) brush block copolymers

We report the synthesis of polystyrene‐block‐poly(dimethyl siloxane) (PS‐b‐PDMS) brush block copolymers (BBCPs) through sequential ROMP of norbornene‐modified macromonomers (‐NB) and explore the effect of side chain length (N_sc) and total backbone degree of polymerization (N_bb) on the self‐assembly of lamellar morphologies. Group I (PS‐NB M_n = 2.9 kg/mol, PDMS‐NB M_n = 4.8 kg/mol) exhibits asymmetric side chains, while Group II (PS‐NB M_n = 4.7 kg/mol, PDMS‐NB M_n = 4.8 kg/mol) possess a more symmetric arrangement. Both families rapidly self‐assemble into well‐ordered lamellar morphologies with domain spacings (d₀) ranging from d₀ = 54 to 140 nm. The scaling relationship between d₀ and N_bb (d₀ ~N_bb^α) was determined as the measure of backbone flexibility. Exponents of α = 0.71 and α = 0.81 are observed for Groups I and II, respectively, indicating the BBCPs adopt an extended backbone conformation. The presence of a low T_g side chain such as PDMS increases apparent flexibility of the backbone. The interplay between contrasting characteristics of the side chains is discussed and reveals the importance of understanding the physical consequences of block architecture on controlling BBCP assembly. These findings provide necessary information for future investigations of complex phases and well‐defined nanostructures fabricated using the brush architecture. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 691–699     

Synthesis and characterization of polythiophene block copolymer and fullerene derivative capable of “three‐point” complementary hydrogen bonding interactions and their application in bulk‐heterojunction solar cells

We report the synthesis and characterization of a polythiophene block copolymer (P4) selectively functionalized with diaminopyrimidine moieties and a thymine tethered fullerene derivative (F1). Self‐assembly between P4 and F1 through “three‐point” complementary hydrogen bonding is studied by ¹H NMR spectroscopy and differential scanning calorimetry. A large Stern‐Volmer constant (K_SV) of 1.2 × 10⁵ M^?1 is observed from fluorescence quenching experiments, revealing strong complexation between these two components. Solar cells employing P4 and F1 at different weight ratios as active layers are fabricated and tested; corresponding thin film morphologies are studied in detail by optical imaging and atomic force microscopy. Correlations between polymer complex structures, film morphologies, and device performance are discussed. Thermal stability of benchmark poly(3‐hexylthiophene) bulk heterojunction solar cells is found to be improved by the addition of a few weight percent of P4/F1 complexes as compatibilizers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3339–3350     

Crew‐cut aggregates from self‐assembly of blends of polystyrene‐b‐poly(acrylic acid) block copolymers and homopolystyrene in solution

The formation and morphological characteristics of crew‐cut aggregates from blends of polystyrene‐b‐poly(acrylic acid) diblock copolymer and polystyrene homopolymer in solution were studied by static light scattering, transmission electron microscopy and size exclusion chromatography. The crew‐cut aggregates, consisting of a polystyrene core and a poly(acrylic acid) corona, were prepared by direct dissolution of the polymer blends in a selective solvent mixture consisting of 93 wt % dimethylformamide and 7 wt % water. It is found that the aggregation behavior depends strongly on the relative volume fractions of the block copolymer and homopolymer in the blends. This is a result of the difference in solubility between the copolymer and the homopolymer in solution which, in turn, influences their miscibility and mutual solubility and consequently the morphology of the formed crew‐cut aggregates. Specifically, when the homopolymer fraction is low, it is mainly dissolved in the cores of the crew‐cut aggregates formed by the block copolymer. When the homopolymer fraction exceeds its solubility limit in the copolymer micelles, aggregates of another type are formed which contain a major fraction of the homopolymer. These aggregates are usually much larger than the primary micelles and have an internal structure due to the formation of reverse micelles from the dissolved block copolymer chains. The importance of thermodynamic vs. kinetic aspects during the formation of the crew‐cut aggregates is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1469–1484, 1999