Phase behavior,crystallization, and nanostructures in thermoset blends of epoxy resin and amphiphilic star‐shaped block copolymers

This article reports thermoset blends of bisphenol A‐type epoxy resin (ER) and two amphiphilic four‐arm star‐shaped diblock copolymers based on hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO). 4,4′‐Methylenedianiline (MDA) was used as a curing agent. The first star‐shaped diblock copolymer with 70 wt % ethylene oxide (EO), denoted as (PPO‐PEO)₄, consists of four PPO‐PEO diblock arms with PPO blocks attached on an ethylenediamine core; the second one with 40 wt % EO, denoted as (PEO‐PPO)₄, contains four PEO‐PPO diblock arms with PEO blocks attached on an ethylenediamine core. The phase behavior, crystallization, and nanoscale structures were investigated by differential scanning calorimetry, transmission electron microscopy, and small‐angle X‐ray scattering. It was found that the MDA‐cured ER/(PPO‐PEO)₄ blends are not macroscopically phase‐separated over the entire blend composition range. There exist, however, two microphases in the ER/(PPO‐PEO)₄ blends. The PPO blocks form a separated microphase, whereas the ER and the PEO blocks, which are miscible, form another microphase. The ER/(PPO‐PEO)₄ blends show composition‐dependent nanostructures on the order of 10?30 nm. The 80/20 ER/(PPO‐PEO)₄ blend displays spherical PPO micelles uniformly dispersed in a continuous ER‐rich matrix. The 60/40 ER/(PPO‐PEO)₄ blend displays a combined morphology of worm‐like micelles and spherical micelles with characteristic of a bicontinuous microphase structure. Macroscopic phase separation took place in the MDA‐cured ER/(PEO‐PPO)₄ blends. The MDA‐cured ER/(PEO‐PPO)₄ blends with (PEO‐PPO)₄ content up to 50 wt % exhibit phase‐separated structures on the order of 0.5–1 μm. This can be considered to be due to the different EO content and block sequence of the (PEO‐PPO)₄ copolymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 975–985, 2006     

Phase behavior,crystallization, and morphology in thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin and poly(ϵ‐caprolactone)

Thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin (PEG‐ER) and poly(?‐caprolactone) (PCL) were prepared via an in situ curing reaction of poly(ethylene glycol) diglycidyl ether (PEGDGE) and maleic anhydride (MAH) in the presence of PCL. The miscibility, phase behavior, crystallization, and morphology of these blends were investigated. The uncured PCL/PEGDGE blends were miscible, mainly because of the entropic contribution, as the molecular weight of PEGDGE was very low. The crystallization and melting behavior of both PCL and the poly(ethylene glycol) (PEG) segment of PEGDGE were less affected in the uncured PCL/PEGDGE blends because of the very close glass‐transition temperatures of PCL and PEGDGE. However, the cured PCL/PEG‐ER blends were immiscible and exhibited two separate glass transitions, as revealed by differential scanning calorimetry and dynamic mechanical analysis. There existed two phases in the cured PCL/PEG‐ER blends, that is, a PCL‐rich phase and a PEG‐ER crosslinked phase composed of an MAH‐cured PEGDGE network. The crystallization of PCL was slightly enhanced in the cured blends because of the phase‐separated nature; meanwhile, the PEG segment was highly restricted in the crosslinked network and was noncrystallizable in the cured blends. The phase structure and morphology of the cured PCL/PEG‐ER blends were examined with scanning electron microscopy; a variety of phase morphologies were observed that depended on the blend composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2833–2843, 2004     

Hydrogen bonding interactions,crystallization, and surface hydrophobicity in nanostructured epoxy/block copolymer blends

Hydrogen bonding interactions, phase behavior, crystallization, and surface hydrophobicity in nanostructured blend of bisphenol A‐type epoxy resin (ER), for example, diglycidyl ether of bisphenol A (DGEBA) and poly(ε‐caprolactone)‐block‐poly(dimethyl siloxane)‐block‐poly(ε‐caprolactone) (PCL–PDMS–PCL) triblock copolymer were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, transmission electron microscopy, small‐angle X‐ray scattering, and contact angle measurements. The PCL–PDMS–PCL triblock copolymer consisted of two epoxy‐miscible PCL blocks and an epoxy‐immiscible PDMS block. The cured ER/PCL–PDMS–PCL blends showed composition‐dependent nanostructures from spherical and worm‐like microdomains to lamellar morphology. FTIR study revealed the existence of hydrogen bonding interactions between the PCL blocks and the cured epoxy, which was responsible for their miscibility. The overall crystallization rate of the PCL blocks in the blend decreased remarkably with increasing ER content, whereas the melting point was slightly depressed in the blends. The surface hydrophobicity of the cured ER increased upon addition of the block copolymer, whereas the surface free energy (γ_s) values decreased with increasing block copolymer concentration. The hydrophilicity of the epoxy could be reduced through blending with the PCL–PDMS–PCL block copolymer that contained a hydrophobic PDMS block. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 790–800, 2010     

The effect of compatibilization and rheological properties of polystyrene and poly(dimethylsiloxane) on phase structure of polystyrene/poly(dimethylsiloxane) blends

The compatibilization effect of polystyrene (PS)‐poly(dimethylsiloxane) (PDMS) diblock copolymer (PS‐b‐PDMS) and the effect of rheological properties of PS and PDMS on phase structure of PS/PDMS blends were investigated using a selective extraction technique and scanning electron microscopy (SEM). The dual‐phase continuity of PS/PDMS blends takes place in a wide composition range. The formation and the onset of a cocontinuous phase structure largely depend on blend composition, viscosity ratio of the constituent components, and addition of diblock copolymers. The width of the concentration region of the cocontinuous structure is narrowed with increasing the viscosity ratio of the blends and in the presence of the small amount diblock copolymers. Quiescent annealing shifts the onset values of continuity. The experimental results are compared with the volume fraction of phase inversion calculated with various theoretical models, but none of the models can account quantitatively for the observed data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 898–913, 2004     

High‐performance thin film composite membranes with well‐defined poly(dimethylsiloxane)‐b‐poly(ethylene glycol) copolymer additives for CO2 separation

A series of well‐defined diblock copolymers (BCPs) consisting of poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) were synthesized and blended with commercially available PEBAX® 2533 to form the active layer of thin‐film composite (TFC) membranes, via spin‐coating. BCPs with a PEG component ranging from 1 to 10 kDa and a PDMS component ranging from 1 to 10 kDa were synthesized by a facile condensation reaction of hydroxyl terminated PEG and carboxylic acid functionalized PDMS. The BCP/PEBAX® 2533 blends up to 50 wt % on cross‐linked PDMS gutter layers were tested at 35 °C and 350 kPa. TFC membranes containing BCPs of 1 kDa PEG and 1–5 kDa PDMS produced optimal results with CO₂ permeances of approximately 1000 GPU which is an increase up to 250% of the permeance of pure PEBAX® 2533 composite membranes, while maintaining a CO₂/N₂ selectivity of 21. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1500–1511     

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

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

Radical‐cured block copolymer‐modified thermosets

Poly(ethylene‐alt‐propylene)‐b‐poly(ethylene oxide) (PEP‐PEO) diblock copolymers were synthesized and added at 4 wt % to 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloxypropoxy)phenyl]propane (BisGMA), a monomer that cures using free radical chemistry. In separate experiments, poly(ethylene glycol) dimethacrylate (PEGDMA) was combined as a secondary monomer with BisGMA and the monomers were loaded with 4 wt % PEP‐PEO. The diblock copolymers self‐assembled into well‐dispersed spherical micelles with PEP cores and PEO coronas. No appreciable change in the final extent of cure of the thermosets was caused by the addition of diblock copolymer, except in the case of BisGMA, where the addition of the block copolymer increased extent of cure by 12%. Furthermore, the extent of cure was increased by 29% and 37% with the addition of 25 and 50 wt % PEGDMA, respectively. Elastic modulus and fracture resistance were also determined, and the values indicate that the addition of block copolymers does not significantly toughen the thermoset materials. This finding is surprising when compared with the large increase in fracture resistance seen in block copolymer‐modified epoxies, and an explanation is proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Self‐assembly of oligo(p‐phenylenevinylene)‐block‐poly(ethylene oxide) in polar media and solubilization of an oligo(p‐phenylenevinylene) homooligomer inside the assembly

Rod–coil amphiphilic diblock copolymers, consisting of oligo(p‐phenylenevinylene) (OPV) as a rod and hydrophobic block and poly(ethylene oxide) (PEO) as a coil and hydrophilic block, were synthesized by a convergent method. The aggregation behavior of the block copolymers in a selective solvent (tetrahydrofuran/H₂O) was probed with the absorption and emission of the OPV block. With increasing H₂O concentration, the absorption maximum was blueshifted, the emission from the molecularly dissolved OPV decreased, and that from the aggregated OPV increased. This indicated that the OPV blocks formed H‐type aggregates in which the OPV blocks aligned in a parallel orientation with one another. The transmission electron microscopy observation revealed that the block copolymers with PEO weight fractions of 41 and 62 wt % formed cylindrical aggregates with a diameter of 6–8 nm and a length of several hundreds nanometers, whereas the block copolymer with 79 wt % PEO formed distorted spherical aggregates with an average diameter of 13 nm. Furthermore, the solubilization of an OPV homooligomer with the block copolymer was studied. When the total polymer concentration was less than 0.1 wt %, the block copolymer solubilized OPV with a 50 mol % concentration. The structure of the aggregates was a cylinder with a relatively large diameter distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1569–1578, 2005     

Synthesis of amphiphilic poly(methyl methacrylate‐ b‐ethylene oxide) copolymers from monohydroxy telechelic poly(methyl methacrylate) as macroinitiator

The synthesis of well‐defined poly(methyl methacrylate)‐block‐poly(ethylene oxide) (PMMA‐b‐PEO) dibock copolymer through anionic polymerization using monohydroxy telechelic PMMA as macroinitiator is described. Living anionic polymerization of methyl methacrylate was performed using initiators derived from the adduct of diphenylethylene and a suitable alkyllithium, either of which contains a hydroxyl group protected with tert‐butyldimethylsilyl moiety in tetrahydrofuran (THF) at ?78 °C in the presence of LiClO₄. The synthesized telechelic PMMAs had good control of molecular weight with narrow molecular weight distribution (MWD). The ¹H NMR and MALDI‐TOF MS analysis confirmed quantitative functionalization of chain‐ends. Block copolymerization of ethylene oxide was carried out using the terminal hydroxyl group of PMMA as initiator in the presence of potassium counter ion in THF at 35 °C. The PMMA‐b‐PEO diblock copolymers had moderate control of molecular weight with narrow MWD. The ¹H NMR results confirm the absence of trans‐esterification reaction of propagating PEO anions onto the ester pendants of PMMA. The micellation behavior of PMMA‐b‐PEO diblock copolymer was examined in water using ¹H NMR and dynamic light scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2132–2144, 2008     

Effect of incorporated CdS nanoparticles on the crystallinity and morphology of poly(styrene‐b‐ethylene oxide) diblock copolymers

Surface‐modified CdS nanoparticles selectively dispersed in hexagonally packed poly(ethylene oxide) (PEO) cylinders of poly(styrene‐b‐ethylene oxide) (PSEO) block copolymers were prepared. The photoluminescence and ultraviolet–visible characteristics of the presynthesized CdS nanoparticles in N,N‐dimethylformamide and in PEO domains of the PSEO block copolymers were determined. Because of strong interactions between the CdS nanoparticles and PEO chains, as shown by Fourier transform infrared spectroscopy, the incorporation of the CdS nanoparticles prevented the PEO cylinders from properly crystallizing; this was confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. The intercylinder distance between the swollen and reduced‐crystallinity CdS/PEO cylinders in turn increased, as confirmed by small‐angle X‐ray scattering and transmission electron microscopy. At a high CdS concentration (43 wt % or 8.3 vol % with respect to PEO), however, the hexagonally packed cylindrical nanostructure of the PSEO diblock copolymers was destroyed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1220–1229, 2005     

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     

Highly ordered nanoporous thin films by blending of PSt‐b‐PMMA block copolymers and PEO additives as structure directing agents

Herein, we present a simple method for producing nanoporous templates with a high degree of lateral ordering by self‐assembly of block copolymers. A key feature of this approach is control of the orientation of polymeric microdomains through the use of hydrophilic additives as structure directing agents. Incorporation of hydrophilic poly(ethylene oxide) (PEO) moieties into poly(styrene‐b‐methyl methacrylate) (PSt‐b‐PMMA) diblock copolymers gives vertical alignment of PMMA cylinders on the substrate after solvent annealing. Because of the miscibility between PEO and PMMA, PEO additives were selectively positioned within PMMA microdomains and by controlling the processing conditions, it was found that ordering of PSt‐b‐PMMA diblock copolymers could be achieved. The perpendicular orientation of PMMA cylinders was achieved by increasing the molecular size of the PEO additives leading to an increased hydrophilicity of the PMMA domains and consequently to control the orientation of microdomains in PSt‐b‐PMMA block copolymer thin films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8041–8048, 2008     

Miscible blends of poly(ethylene oxide) with brush copolymers of poly(vinyl alcohol)‐graft‐poly(l‐lactide)

Even though poly(ethylene oxide) (PEO) is immiscible with both poly(l ‐lactide) (PLLA) and poly(vinyl alcohol) (PVA), this article shows a working route to obtain miscible blends based on these polymers. The miscibility of these polymers has been analyzed using the solubility parameter approach to choose the proper ratios of the constituents of the blend. Then, PVA has been grafted with l ‐lactide (LLA) through ring‐opening polymerization to obtain a poly(vinyl alcohol)‐graft‐poly(l ‐lactide) (PVA‐g‐PLLA) brush copolymer with 82 mol % LLA according to ¹H and ¹³C NMR spectroscopies. PEO has been blended with the PVA‐g‐PLLA brush copolymer and the miscibility of the system has been analyzed by DSC, FTIR, OM, and SEM. The particular architecture of the blends results in DSC traces lacking clearly distinguishable glass transitions that have been explained considering self‐concentration effects (Lodge and McLeish) and the associated concentration fluctuations. Fortunately, the FTIR analysis is conclusive regarding the miscibility and the specific interactions in these systems. Melting point depression analysis suggests that interactions of intermediate strength and PLOM and SEM reveal homogeneous morphologies for the PEO/PVA‐g‐PLLA blends. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1217–1226     

Annealing effect on performance and morphology of photovoltaic devices based on poly(3‐hexylthiophene)‐b‐poly(ethylene oxide)

Novel block copolymers, poly(3‐hexylthiophene)‐b‐poly(ethylene oxide) (P3HT‐b‐PEO) were synthesized via Suzuki coupling reaction of P3HT and PEO homopolymers. The copolymers were characterized by NMR, gel permeation chromatography, differential scanning calorimeter, and UV–vis measurements. A series of devices based on the block copolymers with a fullerene derivative were evaluated after thermal or solvent annealing. The device using P3HT‐b‐PEO showed higher efficiency than using P3HT blend after thermal annealing. Phase‐separated structures in the thin films of block copolymer blends were investigated by atomic force microscopy to clarify the relationship between morphologies constructed by annealing and the device performance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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

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

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

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

Hydrophilic–hydrophobic AB diblock copolymers containing poly(trimethylene carbonate) and poly(ethylene oxide) blocks

AB‐type block copolymers with poly(trimethylene carbonate) [poly(TMC); A] and poly(ethylene oxide) [PEO; B; number‐average molecular weight (M_n) = 5000] blocks [poly(TMC)‐b‐PEO] were synthesized via the ring‐opening polymerization of trimethylene carbonate (TMC) in the presence of monohydroxy PEO with stannous octoate as a catalyst. M_n of the resulting copolymers increased with increasing TMC content in the feed at a constant molar ratio of the monomer to the catalyst (monomer/catalyst = 125). The thermal properties of the AB diblock copolymers were investigated with differential scanning calorimetry. The melting temperature of the PEO blocks was lower than that of the homopolymer, and the crystallinity of the PEO block decreased as the length of the poly(TMC) blocks increased. The glass‐transition temperature of the poly(TMC) blocks was dependent on the diblock copolymer composition upon first heating. The static contact angle decreased sharply with increasing PEO content in the diblock copolymers. Compared with poly(TMC), poly(TMC)‐b‐PEO had a higher Young's modulus and lower elongation at break. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4819–4827, 2005     

Morphological study on water‐borne conducting polyaniline‐poly(ethylene oxide) blends

Conducting polyaniline‐poly(ethylene oxide) blends were prepared from their aqueous solutions. The blends displayed an electrical conductivity percolation threshold as low as 1.83 wt % of polyaniline loading. As demonstrated by scanning electron microscopy, polarized optical microscopy, and wide‐angle X‐ray diffraction studies, the conducting polyaniline took a fibrillar morphology in the blend, and it existed only in the amorphous phase of poly(ethylene oxide). A three‐phase model combining morphological factors instead of a two‐phase model was proposed to explain the low‐conductivity percolation threshold. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 605–612, 2002; DOI 10.1002/polb.10114     

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     

New super‐tough poly(butylene terephthalate) materials based on compatibilized blends with metallocenic poly(ethylene‐octene) copolymer

New super‐tough poly(butylene terephthalate) (PBT)/poly(ethylene‐octene) copolymer (PEO) blends containing 2 wt% poly(ethylene‐co‐glycidyl methacrylate) (EGMA) as a compatibilizer were obtained by extrusion and injection molding. The blends comprised of an amorphous PBT‐rich phase with some miscibilized EGMA, a pure PEO amorphous phase, and a crystalline PBT phase that was not influenced by the presence of either PEO or EGMA. The blends showed a fine particle size up to 20 wt% PEO content. Super‐tough blends were obtained with PEO contents equal to or higher than 10%. The maximum toughness was very high (above 710 J/m) and was attained with 20% PEO without chemical modification of the commercial components used. Copyright © 2003 John Wiley & Sons, Ltd.