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     

Concentration controlled multilevel self‐assembly of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) block copolymers investigated by AFM

Concentration dependent morphology of 3‐armed poly(ethylene glycol)‐b‐poly(ε‐caprolactone) copolymer aggregates in aqueous system was investigated by atomic force microscopy (AFM). The AFM results show that, at a low concentration, 4 × 10^?5 g/mL, spherical micelles occur, and unmicellized molecules are not distributed homogeneously in the copolymer aqueous solution. Unequal outspread clusters composed of wormlike aggregates are formed at a moderate copolymer concentration, 4 × 10^?4 g/mL, those wormlike aggregates are orderly packed in the clusters. At a high concentration of 0.05 g/mL, the copolymer aqueous system is indeed a gel at room temperature, outspread clusters of wormlike aggregates join together to forma network structure. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1412–1418, 2008     

Optimization of direct arylation polymerization conditions for the synthesis of poly(3‐hexylthiophene)

Direct arylation polymerization (DArP) is an emerging alternative to Stille and Suzuki polymerizations. This method is attractive as it allows preparation of high‐molecular‐weight conjugated polymers in good yield without the need to metallate monomers. Despite this promise, for poly(3‐hexylthiophene) (P3HT) and related polymers that have β‐protons on the thiophene ring, DArP is known to produce β‐defects, which make the polymer properties different from polymers produced by traditional methods. Here, we demonstrate that DArP conditions based on simple, inexpensive, and bench‐stable reagents can be tuned to limit the amount of defects and produce P3HT with properties remarkably similar to Stille P3HT. Specifically, lowering the reaction temperature, lowering the amount of catalyst, and using a bulkier carboxylate ligand is critical. Optimized conditions include reacting 2‐bromo‐3‐hexylthiophene with 0.25 mol % of Pd(OAc)₂, 1.5 equivalents of K₂CO₃, and 0.3 equivalents of neodecanoic acid in N,N‐dimethylacetamide at 70 °C and give DArP P3HT with ～60% yield, regioregularity of 93.5%, molecular weight of 20 kDa, polydispersity of 2.8, and melting point of 217 °C, providing a very close match to Stille P3HT, which is obtained with 70–80% yield, 91–94% regioregularity, molecular weight of 15–25 kDa, polydispersity of 2.5–2.8, and melting point of 214–221 °C. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2660–2668     

Minimization of the auxiliary reagent loading for direct arylation polymerization (DArP) of 2‐bromo‐3‐hexylthiophene

In this work, we present a powerful set of synthetic strategies aimed at minimization of auxiliary reagent loading for direct arylation polymerization (DArP) of 2‐bromo‐3‐hexylthiophene. As such, we report efficient lowering of Pd(OAc)₂ catalyst loading as well as loading of other auxiliary reagents, such as neodecanoic acid and N,N‐dimethylacetamide. Unprecedented low loadings of catalyst down to 0.0313% (313 ppm) were achieved, while producing polymer in high yield (91% after Soxhlet extraction), with a high molecular weight (24.2 kDa) and carefully controlled chemical structure thus making the optimized DArP protocol significantly more cost‐effective, convenient, sustainable, and environmentally friendly. The resulting polymer samples were thoroughly investigated in terms of their chemical structure as well as optical, thermal, chain ordering and electronic properties using GPC analysis, ¹H NMR, MALDI, UV–vis, GIXRD spectroscopy, DSC, and SCLC hole mobility measurements. The results demonstrate that the reagent lowering strategies increase the polymer regioregularity from 94.6 to 96.5% as evidenced by ¹H NMR spectra and corroborated by GIXRD, DSC, and UV–vis measurements. Additionally, polymer samples obtained at low reagent loading are more uniformly proton‐terminated as evidenced by ¹H NMR and MALDI end‐group analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1492–1499     

The effect of amide solvent structure on the direct arylation polymerization (DArP) of 2‐Bromo‐3‐hexylthiophene

In this work, we investigate the influence of the amide solvent chemical structure on the properties of poly(3‐hexylthiophene) (P3HT) prepared via direct arylation polymerization (DArP). Our findings indicate that for successful polymerization the amide must possess an acyclic aliphatic structure since cyclization of an amide results in a complete shutdown of DArP reactivity as evidenced by failed polymerization in N‐methylpyrrolidone, whereas the presence of an aromatic motif renders the amide solvent susceptible to C? H activation and leads to incorporation of the solvent structure into the P3HT backbone, as demonstrated on the example of N,N‐diethylbenzamide. Additionally, we observed that the steric bulk of alkyl substituents on both the nitrogen atom and the carbonyl group within the amide structure has to be delicately balanced for optimal DArP reactivity. In the optimal cases, P3HT is obtained in high yield, with high molecular weight and contains a minimal amount of structural defects. The obtained polymer samples were comprehensively studied in terms of their chemical structure, optical, thermal and solid‐state properties in thin films using GPC analysis, ¹H NMR, MALDI, UV–vis, GIXRD spectroscopy, and DSC. We additionally note a drastic difference of the amide solvent effect between DArP and Stille polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2494–2500     

Synthesis,reactivity, and optoelectronic properties of poly(3‐alkenylthiophene) diblock copolymers

Poly(3‐hexylthiophene)‐b‐poly(3‐pentenylthiophene) and poly(3‐hexylthiophene)‐b‐poly(3‐undecenylthiophene) diblock copolymers have been synthesized by McCullough method. X‐ray diffraction analysis of the diblock copolymers displayed all the reflection peaks specific to regioregular poly(3‐hexylthiophene), indicating that the presence of poly(3‐alkenylthiophene) block does not affect the packing of the polymer in the solid state. The synthesized diblock copolymers were subjected to hydroboration/oxidation and hydrosilation to demonstrate the reactivity of the alkenyl substituents. Furthermore, poly(3‐hexylthiophene)‐b‐poly(3‐pentenylthiophene) was used as a chain transfer agent for the ruthenium‐catalyzed ring‐opening metathesis polymerization of cyclooctene to generate a polycyclooctene graft copolymer, which was hydrogenated to give poly(3‐hexylthiophene)‐b‐poly(3‐pentenylthiophene‐g‐polyethylene). The opto‐electronic properties and the morphology of the synthesized polymers have been investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Exploring the synthesis and impact of end‐functional poly(3‐hexylthiophene)

In recent years, end‐functional poly(3‐hexylthiophene) (P3HT) has proven to be instrumental in the continued development and innovation within the broad conjugated polymer arena, enabling a variety of applications, particularly in organic electronics. The availability of P3HT with controlled molecular weights, low polydispersity, and importantly, a wide range of reactive end‐groups not only serves as a key building block for the preparation of conjugated block copolymers but also facilitates the development of hybrid nanocomposite materials via inorganic surface modification strategies. This Highlight focuses on the synthetic approaches to end‐functional P3HT and the impact of these systems in emerging technologies. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 831–841     

Regioregular Poly(3‐hexylthiophene) in a Novel Conducting Amphiphilic Block Copolymer

Regioregular poly(3‐hexylthiophene) has been successfully incorporated into a novel amphiphilic block copolymer. The amphiphilic nature of poly(3‐hexylthiophene)‐block‐poly(acrylic acid) has been investigated using spectroscopic methods and has yielded solvatochromic behavior in several solvents of varying polarity. Evidence suggests that a supramolecular, long range ordering of block copolymer occurs in polar solvents, resulting in the formation of aggregates. Despite relatively large amounts of non‐conductive blocks, the poly(3‐hexylthiophene) diblock copolymer yields a high conductivity of 1 S · cm⁻¹, and atomic force microscopy shows the formation of a highly organized nanofibrilar morphology in the solid state.

     

One‐pot synthesis of conjugated poly(3‐hexylthiophene)‐b‐poly(phenyl isocyanide) hybrid rod–rod block copolymers and its self‐assembling properties

In this article, the synthesis of a series of conjugated rod–rod block copolymers based on poly(3‐hexylthiophene) (P3HT) and poly(phenyl isocyanide) (PPI) building blocks in a single pot is presented. Ni‐catalyzed Grignard metathesis polymerization of 2,5‐dibromo‐3‐hexylthiophene and subsequent addition of 4‐isocyanobenzoyl‐2‐aminoisobutyric acid decyl ester in the presence of Ni(dppp)Cl₂ as a single catalyst afford P3HT‐b‐PPI with tunable molecular weights and compositions. In solid state, microphase separation occurred as differential scanning calorimetric analysis of P3HT‐b‐PPI revealed two glass transition temperatures. In solutions, the copolymers can self‐assemble into spherical aggregates with P3HT core and PPI shell in tetrahydrofuran and exhibit amorphous state in CHCl₃. However, atomic force microscopy revealed that the block copolymers self‐assemble into nanofibrils on the substrate. These unique features warrant the resultant conjugated rod–rod copolymers' potential study in organic photovoltaic and other electronic devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2939–2947     

Biocompatibility evaluation of self‐assembled micelles prepared from poly(lactide‐co‐glycolide)‐poly(ethylene glycol) diblock copolymers

In this work, a series of PLGA‐PEG diblock copolymers were synthesized by ring‐opening polymerization of L‐lactide and glycolide using mPEG as macroinitiator and stannous octoate as catalyst. Spherical micelles were obtained from the various copolymers by using co‐solvent evaporation method. The biocompatibility of micelles was evaluated with the aim of assessing their potential in the development of drug delivery systems. Various aspects of biocompatibility were considered, including MTT assay, agar diffusion test, release of cytokines, hemolytic test, dynamic clotting time, protein adsorption in vitro, and zebrafish embryonic compatibility in vivo. The combined results revealed that the micelles present good cytocompatibility and hemocompatibility in vitro. Moreover, the cumulative effects of micelles throughout embryos developing stages have no toxicity in vivo. It is thus concluded that micelles prepared from PLGA‐PEG copolymers present good biocompatibility as potential drug carrier.     

Properties of a novel thermal sensitive polymer based on poly(vinyl alcohol) and its layer‐by‐layer assembly

Structurally modified poly(vinyl alcohol) (PVA) was prepared as novel thermally sensitive polymers by partially acetalyzing and/or ionizing the commercially available PVA. Their aqueous solutions experience completely reversible polymer aggregation and dissolution above and below the lower critical solution temperature (LCST), respectively. The LCST of a partially acetalyzed PVA (APVA) can be readily controlled by the degree of acetalysis or the molecular weight of the starting PVA. Introduction of a small amount of cationic group onto the APVA backbone increases the LCST obviously, while the LCST is highly sensitive to NaCl concentration. Then APVA and cationic APVA multilayers are assembled on rayon to make a thermal responsive fiber. The atomic force microscopy (AFM) images of the surface reveal the increment of roughness stimulated by temperature. Copyright © 2007 John Wiley & Sons, Ltd.     

Crystallization and stereocomplexation governed self‐assembling of poly(lactide)‐b‐poly(ethylene glycol) to mesoscale structures

The stereocomplex formation between enantioselective poly(lactide) (PLA) homopolymers is well understood. In this report an attempt is made to analyze the influence on the self‐assembling of the stereocomplex of enantiomorphic PLA‐PEG di‐ and tri‐blocks in different solvents. Powder diffraction studies showed the poly(ethylene glycol) (PEG) and the PLA blocks crystallize separately forming unique supra structures like rods, discs and coiled coils with dimensions in the micrometer scale in length and sub‐micrometer scale in diameter. The influence of the solvents on the crystal formation was shown in the formation of uniform structures. Discs emerged from equimolar mixtures of the D ‐ and L ‐configured di‐ and tri‐block copolymers, in dioxan and acetonitrile and in water the stereocomplexes crystallized mainly as rods. In some cases the rods were observed as coiled coils. The shape, the hydrophobic/hydrophilic content and the PEG coated surface of the discs give them a future potential as matrix for the controlled and targeted delivery of bioactive agents. Copyright © 2005 John Wiley & Sons, Ltd.     

Switchable thin‐film surface prepared via a simple grafting‐to method using a polystyrene‐b‐poly(2‐vinylpyridine) copolymer

A polystyrene‐b‐poly(2‐vinylpyridine) block copolymer containing a methylhydridosilane linking group was chemically grafted to an 8‐trichlorosilyloctene monolayer via a simple one‐step hydrosilylation reaction. The resulting Y‐shaped thin film exhibited a low grafting density, which was characteristic of the grafting‐to technique. To further reduce the miscibility of the two arms, methyl iodide was reacted with the poly(2‐vinylpyridine) block to produce quaternary ammonium groups. The surfaces before and after quaternization were both solvent‐switchable when subjected to block‐selective solvents. Tensiometry, ellipsometry, attenuated total reflection/Fourier transform infrared, and atomic force microscopy were used to characterize the properties and morphology of both unquaternized and quaternized samples. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5608–5617, 2006     

Effects of Thermal Annealing Upon the Nanomorphology of Poly(3‐hexylselenophene)‐PCBM Blends

Grazing incidence X‐ray diffraction (GI‐XRD) is used to characterize the crystallographic dynamics of low molecular weight (LMW) and high molecular weight (HMW) poly(3‐hexylselenophene) (P3HS) films and blend films of P3HS with [6‐6‐]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) as a function of ‘step‐by‐step’ thermal annealing, from room temperature to 250 °C. The temperature‐dependent GIXRD data show how the melting point of P3HS crystallites is decreased by the presence of PCBM. P3HS crystallite domain sizes dramatically increase upon annealing to the P3HS melting temperature. The formation of well‐oriented HMW P3HS crystallites with the (100) plane parallel to the substrate (edge‐on orientation), when cooled from melt, are observed. We compare the behaviour of P3HS pure and blend films with that of poly(3‐hexyl)thiophene (P3HT) pure and PCBM blended films and suggest that the similar temperature dependent behaviour we observe may be a common to polythiophene and related polymers and their blends.

     

Palladium on carbon‐catalyzed direct C—H arylation polycondensation of 3,4‐ethylenedioxythiophene with various dibromoarenes

We have demonstrated a direct arylation polycondensation of 3,4‐ethylenedioxythiophene with 2,7‐dibromo‐9,9‐dioctylfluorene using palladium on carbon (Pd/C) as a catalyst. Pd/C is a low‐cost solid‐supported palladium catalyst, giving one of the effective catalytic systems for direct arylation. The Pd/C‐catalyzed direct arylation polycondensation with acetic acid/potassium carbonate in N,N‐dimethylacetamide furnished a high molecular weight π‐conjugated alternating copolymer of EDOT‐fluorene (M_n = 89,300, M_w/M_n = 3.27) in high yield. The polycondensation of EDOT with various dibromoarenes was also achieved, giving EDOT‐carbazole, EDOT‐dialylamine, and EDOT‐bithiophene polymers. Optical and electrochemical properties of the polymers were also discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1183–1188     

AFM Study of the Self‐Assembly Behavior of Hexa‐Armed Star Polymers with a Discotic Triphenylene Core

The six‐armed polystyrenes and poly(methyl methacrylate)s with a triphenylene core showed different self‐assembling patterns, isolated cylinders for polySt on mica and highly ordered cylindrical pores for polyMMA on a silicon wafer. With a decrease of polymer concentration in tetrahydrofuran (THF), the size and height of cylinders decreased for polySt, but for polyMMA, the size and depth of the cylindrical pores increased. Slow evaporation of the solvent and a low molecular weight favored the formation of regular patterns.

AFM images of self‐assembling patterns of polySt 1a on mica (A) and of polyMMA 2a on silicon wafer (B).     

Improving charge transport in poly(3‐hexylthiophene) transistors via blending with an alkyl‐substituted phenylene–thiophene–thiophene–phenylene molecule

A prototypical semiconducting bicomponent system consisting of a conjugated polymer, that is, poly(3‐hexylthiophene) (P3HT), blended with a small thiophene containing conjugated molecule, that is, an alkyl‐substituted bisphenyl‐bithiophene [phenylene–thiophene–thiophene–phenylene (PTTP)], has been used as an electroactive active layer in field‐effect transistors (FETs). The self‐assembly of this bicomponent system at surfaces has been studied at different length scales, from the nanoscale to the macroscale, and compared with the behavior of monocomponent films of PTTP and P3HT. The correlation between morphology and electric properties of the semiconducting material is explored by fabricating prototypes of FETs varying the relative concentrations of the two‐component blend. The maximum charge carrier mobility value, achieved with a few percent of PTTP component, is not simply due to a uniform dispersion of the molecules in the polymer matrix, but rather to the generation of very long percolation paths, whose composition and electrical properties can be tuned with the PTTP concentration. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Molecular composites composed of castor oil‐modified poly(ε‐caprolactone) and self‐assembled hydroxystearic acid fibers

After (R)‐12‐hydroxystearic acid (HSA) was mixed at 100 °C with the castor oil‐modified poly(ε‐caprolactone) (CO‐PCL) prepared by the ring‐opening polymerization of ε‐caprolactone in the presence of castor oil, the mixture was gradually cooled to room temperature to give a solidified CO‐PCL/HSA composite. The CO‐PCL/HSA sample showed an exothermic peak at around 67–71 °C which was lower than the melting point of HSA (76.8 °C), indicating the formation of mesogenic HSA aggregates. The rheological measurement of the CO‐PCL/HSA revealed the formation of HSA organogel at around 67–55 °C during the cooling process from the melt. Furthermore, the polarized and normal optical microscopic analyses of CO‐PCL/HSA on the cooling stage revealed that anisotropic fibrous materials are formed at around 60 °C and then the fibrous network propagated over the matrix polymer. The flexural modulus and storage modulus of the CO‐PCL/HSA composite increased with increasing HSA content. The CO‐PCL/HSA composite annealed at 60 °C for 2 h on the cooling process had a higher flexural and storage modulus than the sample without annealing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1281–1289, 2010