Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) synthesis and properties

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) or P(EXA-r-tBA)-PCEA was synthesized by atom transfer radical polymerization. Reactivity ratios of EXA and tBA for copolymerization were determined. The specific refractive index increments of six diblocks were measured as a function of their composition. The diblocks were thermally stable and formed micelles in an automobile engine oil. Such micelles may be useful as an anti-friction additive in lubricating oils.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Preparation and properties of poly(ethylene glycol)-block-poly(acrylic acid)-coated cobalt nanocrystals

Reported in this paper are the preparation and properties of ?-Co nanocrystals coated by poly(ethylene glycol)-block-poly(acrylic acid) (PEG-b-PAA). These particles were prepared via the thermal decomposition of Co₂(CO)₈ at 185 °C in 1,2-dichlorobenzene, in the presence of the surfactant PEG-b-PAA and the co-surfactant trioctylphosphine oxide. At a given initial Co₂(CO)₈ concentration, the size of the particles increased with increasing Co₂(CO)₈-to-PEG-b-PAA molar ratio, and could be tuned between ∼5 and ∼20 nm. The size distribution of the particles narrowed as the Co₂(CO)₈ concentrations increased. The resultant particles were dispersible in a wide range of solvents, including chloroform, N,N-dimethylforamide, and water, which solubilized PEG. Magnetic measurements revealed that the particles possessed saturation magnetization close to that of bulk Co, suggesting high purity of the particles.     

Syntheses of well-defined poly(siloxane)-b-poly(styrene) and poly(norbornene)-b-poly(styrene) block copolymers using functional alkoxyamines

Functional alkoxyamines, 1-[4-(4-lithiobutoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (2) and 1-[4-(2-vinyloxyethoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (3) were prepared, and well-defined poly(hexamethylcyclotrisiloxane)-b-poly(styrene)[poly(D₃)-b-poly(St)] and poly(norbornene)-b-poly(St) [poly(NBE)-b-poly(St)] were prepared using the alkoxyamines. The first step was preparation of poly(D₃) and poly(NBE) macroinitiators, which were obtained by the ring-opening anionic polymerization of D₃ using 2 as an initiator and the ring-opening metathesis polymerization of NBE using 3 as a chain transfer. The radical polymerization of St by the poly(D₃) and poly(NBE) macroinitiators proceeded in the ‘living’ fashion to give well-defined poly(D₃)-b-poly(St) and poly(NBE)-b-poly(St) block copolymers.     

Re-assembly behaviors of polystyrene-b-poly(acrylic acid) micelles

The re-assembly behaviors of spherical micelles of the polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymer in different solvent mixtures were investigated using dynamic light scattering, transmission electron microscopy and atomic force microscopy. Depending on the nature of the solvent, PS-b-PAA micelles re-assembled from spheres to nanorings in toluene or to necklace-like aggregates in water induced by solvent evaporation. Systematic studies suggested that the re-assembly behaviors on a neutral surface are strongly correlated with the micellar surface components, the solvent polarity and the chain length of the micelle corona of the solvated blocks. We proposed that the formation of nanorings from PS-b-PAA micelles in toluene is mainly induced by the dewetting process of the solvent, while the necklace-like structure arises from the hydrogen bonding interactions among the partially dissociated PAA units.     

Water-dispersible fluorescent nanospheres from poly(solketal acrylate)-block-poly(2-hydroxyethyl acrylate)

Reported in this paper is the preparation of fluorescent nanospheres from poly(solketal acrylate)-block-poly(2-hydroxyethyl acrylate) or PSA-PHEA. The strategy involved the chemical derivation of the PHEA block to graft the fluorophore fluorosceinamine (Fl) first. A selective solvent for PSA was then used to induce micelle formation from the diblock with PSA as the corona and the fluorescein-tagged PHEA block as the core. Nanospheres with fluorescent cores were obtained after PHEA core crosslinking with succinyl chloride. Water-dispersible nanospheres were prepared after removing the acetonide groups from the PSA block by hydrolysis to yield poly(glyceryl acrylate). Such nanospheres may find applications in fluorescent in situ hybridization assays.     

Functionalization of amphiphilic coil-rod-coil triblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine) with florescence moiety and C60

We recently achieved quantitative synthesis of an amphiphilic coil-rod-coil triblock copolymer, poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine), by coupling in situ living diblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (P2VP-b-PHIC) using malonyl chloride in the presence of pyridine. This led to the introduction of an active methylene group that is a site for further functionalization in the rod block. The Michael addition reaction of the triblock copolymer with 7-(4-trifluoromethyl) coumarin acrylamide led to copolymer bearing a fluorescent pendent in the rod block. The fluorescent labeled copolymers were isolated in ∼94% yields. Similarly C₆₀ pendent was introduced to the rod block by the Bingel reaction. The yields of C₆₀ functionalized copolymers were ∼54%. The precursor and functionalized amphiphilic coil-rod-coil copolymer show diverse morphologies, such as micelles and vesicles by simply changing the solvent. For the C₆₀ functionalized block copolymer, structural constraints in micelles and vesicles prevented C₆₀ pendents to aggregate.     

Solvent induced morphologies of poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) triblock copolymers synthesized by atom transfer radical polymerization

Poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) (PMMA-PEO-PMMA) triblock copolymers were synthesized using atom transfer radical polymerization (ATRP) and halogen exchange ATRP. PEO-based macroinitiators with molecular weight from M_n = 2000 to 35,800 g/mol were used to initiate the polymerization of MMA to obtain copolymers with molecular weight up to M_n = 82,000 g/mol and polydispersity index (PDI) less than 1.2. The macroinitiators and copolymers were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. The melting temperature and glass transition temperature of the copolymers were measured by differential scanning calorimetry (DSC). Crystallinities of the PEO blocks were determined from the WAXS patterns of both homopolymers and block copolymers, which revealed the fragmentation of PEO blocks due to the folding of the PMMA chains. Interestingly, the fragmentation was less pronounced when cast on surfaces compared to that in bulk, as measured by GISAXS. Solvent casting was used to control the morphology of the copolymers, permitting the formation of various states including amorphous, induced micellar with a PMMA core and flower-like PEO arms, and a cross-linked gel. Atomic force microscopy (AFM) was used to visualize the different copolymer morphologies, showing micellar and amorphous states.     

Synthesis, characterization, and bulk crosslinking of polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) block terpolymers

We report on the synthesis and characterization of triblock terpolymers, polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) (PB-b-P2VP-b-PtBMA; BVT), via sequential living anionic polymerization in THF at low temperatures using sec-butyl lithium as initiator. In this work, 18 different BVT terpolymers were produced with volume fractions Φ_B : Φ_V : Φ_T in the range of 1 : 0.4…1.2 : 0.2…4.6. All polymers exhibit a very narrow molecular weight distribution (PDI < 1.1). They were characterized in terms of bulk morphology using small-angle X-ray scattering and transmission electron microscopy, unveiling mostly lamellar patterns or hexagonally arranged cylindrical structures. Some polymers displayed a partial gyroid structure coexisting with lamellar parts or cylinders with a non-continuous shell around the PB core and could serve as an interesting template for the facile generation of multi-compartmental self-assembled structures. In one case the middle block, P2VP, is forming a helix around the PB core. Crosslinking of the polybutadiene compartment of the bulk morphologies with an UV-photoinitiator was performed, followed by sonication-assisted dissolution of the aggregates to elucidate further use of the terpolymers for the generation of soft polymeric nanoparticles with controlled functionality. In that way, core-crosslinked cylindrical micelles could be generated and characterized.     

Adsorption kinetics and stability of poly(ethylene oxide)-block-polystyrene micelles on polystyrene surface

Herein, adsorption kinetics of poly(ethylene oxide)-block-polystyrene (PEO-b-PS) micelles from aqueous solution on PS thin films was investigated by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The stability of adsorbed micelles against water washing was enhanced by the strong physical interaction between the substrate-identical core blocks of micelles and the PS substrate. The adsorption kinetics was investigated and analyzed by a model considering both the effects of diffusion and micelles reorganization on the PS surface. The micelles adsorption process was well captured by this model which demonstrated that the micelles reorganized on the surface after adsorption. The fitting results exhibited that the micelles with longer core blocks had less tendency to reorganize on the surface while reorganization took more part in the adsorption process of the micelles with shorter core blocks. In the stability studies, micelles with shorter PS blocks could partially desorb from the PS substrate while micelles with longer PS blocks were totally hindered from desorption. Desorption process of micelles was evaluated by the hydrodynamics-induced rolling model. The results indicated that hydrodynamic force-induced partial slip of the micelles on the PS surface might be responsible for micelle desorption. Because of the hydrophilicity of adsorbed micelle layer, adsorption amount of BSA on the modified surface was greatly reduced comparing with that of the bare PS surface.     

Transition behavior and ionic conductivity of lithium perchlorate-doped polystyrene-b-poly(2-vinylpyridine)

We report the transition behavior and the ionic conductivity of ion-doped amorphous block copolymer, based on two compositionally different polystyrene-block-poly(2-vinylpyridine) copolymers (PS-b-P2VPs) that can self-assemble into nanostructures, where P2VP block is ionophilic to lithium perchlorate (LiClO₄). The transition temperatures of LiClO₄-doped PS-b-P2VP, like the order-to-disorder transition (T_ODT), were measured by small-angle X-ray scattering (SAXS) and depolarized light scattering (DPLS). The selective ionic coordination to the nitrogen units of P2VP block leads to the increase of the repulsive interactions between two block components from weak- to strong-segregation regime with increasing amount of LiClO₄, which results subsequently in the increased T_ODT. However, for a compositionally asymmetric PS-b-P2VP under lamellar morphology, the ionic conductivity by the addition of LiClO₄ was remarkably increased at higher temperatures, representing that the effective ionic coordination at the greater volume fraction of P2VP block component improves the ionic conductivity as the temperature approaches to a rubbery phase.     

Facile atom transfer radical homo and block copolymerization of higher alkyl methacrylates at ambient temperature using CuCl/PMDETA/quaternaryammonium halide catalyst system

Controlled polymerization of higher alkyl methacrylates, e.g. lauryl methacrylate (LMA) and stearyl methacrylate (SMA) has been successfully achieved by atom transfer radical polymerization (ATRP) at ambient temperature using CuCl/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA)/tricaprylylmethylammonium chloride (Aliquat^®336) as the catalyst system and ethyl 2-bromoisobutyrate or 2,2,2-trichloroethanol as the initiator. Although the bulk polymerization gives satisfactory control, the latter becomes better when anisole or THF is added into the system. Without AQCl the control was lost. A large deviation of molecular weight from theory has been observed which has been attributed to the very high-molecular weight of the dead polymers formed during the building-up of the persistent radical. The controlled polymers have been used as macroinitiators for block (di, tri and penta) ATR copolymerization with several methacrylates.     

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) pentablock copolymers from a combination of quasiliving carbocationic and atom transfer radical polymerization

Amphiphilic poly(acrylic acid-b-styrene-b-isobutylene-b-styrene-b-acrylic acid) (PAA-PS-PIB-PS-PAA) block copolymers were prepared using a combination of quasiliving carbocationic and atom transfer radical polymerization (ATRP) techniques. Poly(styrene-b-isobutylene-b-styrene) (PS-PIB-PS) block copolymer macroinitiators with targeted molecular weights and high degrees of chain end functionality (F_n>1.7) were prepared by quasiliving carbocationic polymerization of isobutylene followed by sequential addition of styrene. Poly(tert-butyl acrylate-b-styrene-b-isobutylene-b-styrene-b-tert-butyl acrylate) (PtBA-PS-PIB-PS-PtBA) pentablock terpolymers with targeted molecular weights and low polydispersities (PDIs) were synthesized from the PS-PIB-PS macroinitiators via ATRP of tBA using either a Cu(I)Cl/1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) or Cu(I)Cl/tris[2-(dimethylamino)ethyl]amine (Me₆TREN) catalyst system. Deprotection of the tert-butyl groups using trifluoroacetic acid at 25 °C resulted in the formation of PAA-PS-PIB-PS-PAA pentablock terpolymers. Comonomer composition of the final terpolymers, determined by ¹H-NMR spectroscopy, was very close to theoretical.     

Nanostructured polystyrene-block-poly(4-vinyl pyridine)(pentadecylphenol) thin films as templates for polypyrrole synthesis

Polypyrrole has been chemically synthesized on thin film nanostructures obtained from comb-shaped supramolecules of polystyrene-block-poly(4-vinyl pyridine) (PS-b-P4VP) hydrogen bonded with pentadecylphenol (PDP). PDP was washed from thin films of cylindrical and lamellar self-assembled comb-copolymer systems, which resulted in removal of the upper layers of microdomains, leaving single cylindrical and lamellar layers covering a substrate, with P4VP segregated at the bottom as well as at the free air interface. This P4VP was complexed with Cu²⁺ ions, after which chemical oxidation polymerization of pyrrole resulted in a thin polypyrrole layer covering the nanostructured block copolymer. The use of a catalytic amount of bipyrrole greatly improved the quality of the obtained product. The conductivity was measured to be ∼0.7 S cm⁻¹.     

Phase behavior of linear polystyrene-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) triblock terpolymers

Using sequential living anionic polymerization we synthesized well-defined linear ABC triblock terpolymers from polystyrene (PS), poly(2-vinylpyridine) (P2VP), and poly(tert-butyl methacrylate) (PtBMA). The length of the PtBMA block was systematically increased at constant block length ratios of the PS and P2VP blocks. The microdomain structures were characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). With increasing PtBMA block size we observe a systematic change in the bulk structure of the block copolymers.     

Structure and swelling behaviour of epoxy networks based on α,ω-diamino terminated poly(oxypropylene)-block-poly(oxyethylene)-block-poly(oxypropylene)

Structure and swelling behaviour of hydrophilic epoxy networks prepared from α,ω-diamino terminated poly(oxypropylene)-block-poly(oxyethylene)-block-poly(oxypropylene) and diglycidyl ether of brominated Bisphenol A in dependence on the initial molar ratio of reactive amino and epoxy groups has been investigated by small- and wide-angle X-ray scattering (SAXS and WAXS), differential scanning calorimetry (DSC) and dynamic mechanic analysis (DMA). Anomalous swelling behaviour of the networks in water has been found. The anomaly is attributed to the changing microphase separation in the networks controlled by their composition and crosslinking density, and inhomogeneous swelling on nanometer space scale.     

Synthesis and characterisation of hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) backbones via atom transfer radical polymerisation

Hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) (PMMA-b-PBA) backbones have been prepared via atom transfer radical polymerisation (ATRP) together with a nucleophilic substitution reaction. A hydroxyl-functionalised PMMA macroinitiator (HO-PMMA-Br) was prepared via ATRP at the optimised reaction temperature (60 °C) using 2-hydroxyethyl 2-bromoisobutyrate as the initiator. The high functionality of the bromo end group in the macroinitiator was confirmed by both ¹H NMR technique and a chain-extension reaction. Electrospray ionisation mass spectrometer proved to be a valuable tool for characterising PMMAs with a bromo end group (PMMA-Br), which provided signals corresponding to the intact polymers although multiply charged polymer chains were observed. The well-defined block copolymers HO-PMMA-b-PBA-Br were obtained by the ATRP of n-butyl acrylate using HO-PMMA-Br as a macroinitiator in a one-pot reaction at 100 °C. The kinetics as well as the dependence of the M_n,SEC and PDIs of the obtained block copolymers on the conversions of n-butyl acrylate in the chain-extension reaction suggested negligible radical termination during the reaction, demonstrating that the well-defined HO-PMMA-b-PBA-Br with a high functionality of bromo end group were obtained. The nucleophilic substitution reaction of a monohydroxyl-functionalised block copolymer HO-PMMA-b-PBA-Br with 5-amino-1-pentanol in dimethyl sulfoxide at room temperature was verified with ¹H and ¹³C NMR techniques, which resulted in a series of telechelic polymers HO-PMMA-b-PBA-OH with a functionality of hydroxyl groups up to 1.7 according to the gradient polymer elution chromatography.     

Phase segregation of poly(3-dodecylthiophene)-block-poly(methyl methacrylate) copolymers

We investigated, via small angle X-ray scattering (SAXS), the ordered-to-disordered transition temperature (T_ODT) of symmetric poly(3-dodecylthiophene)-block-poly(methyl methacrylate) copolymers (P3DDT-b-PMMA) with different molecular weights synthesized by anionic coupling reaction. When the molecular weight of P3DDT-b-PMMA was properly chosen, the T_ODT was observed within experimentally accessible temperature range (higher than the glass transition and melting temperature for PMMA and P3DDT, respectively, but lower than the thermal degradation temperature). We also measured the temperature dependence of Flory–Huggins interaction parameter (χ) between P3DDT and PMMA as χ = 0.1109 + 76.63/T, in which T is the absolute temperature.     

Analysis of poly(ethylene oxide)-b-poly(propylene oxide) block copolymers by MALDI-TOF mass spectrometry using collision induced dissociation

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to analyse the block length of commercially available block copolymers of poly(ethylene oxide) and poly(propylene oxide) (PEO-b-PPO) based on the fragmentation behaviour in collision induced dissociation (CID) experiments.MALDI-CID-TOF² analysis is a complex procedure depending on a number of different experimental parameters. Therefore, a step-by-step procedure was used starting with PEG and PPG standards, PEG-PPG blends and endgroup-functionalized PPGs, to understand the fragmentation behaviour of the different species. These results showed that characteristic fragment patterns of the homopolymers and PEG-PPG mixtures can be obtained that facilitate the interpretation of the fragment spectra of PEO-b-PPO di- and triblock copolymers. It was found that di- and triblock copolymers can be differentiated by their fragment spectra. In addition, the sequence of monomer units in the diblock copolymers could be determined.     

Comparison of morphologies and mechanical properties of crosslinked epoxies modified by polystyrene and poly(methyl methacrylate)) or by the corresponding block copolymer polystyrene-b-poly(methyl methacrylate)

Polystyrene (PS, M_n=28,400, PI=1.07), poly(methyl methacrylate) (PMMA, M_n=88,600, PI=1.03), and PS (50,000)-b-PMMA (54,000) (PI=1.04), were used as modifiers of an epoxy formulation based on diglycidyl ether of bisphenol A (DGEBA) and m-xylylene diamine (MXDA). Both PS and PMMA were initially miscible in the stoichiometric mixture of DGEBA and MXDA at 80 °C, but were phase separated in the course of polymerization. Solutions containing 5 wt% of each one of both linear polymers exhibited a double phase separation. A PS-rich phase was segregated at a conversion close to 0.02 and a PMMA rich phase was phase separated at a conversion close to 0.2. Final morphologies, observed by scanning electron microscopy (SEM), consisted on a separate dispersion of PS and PMMA domains. A completely different morphology was observed when employing 10 wt% of PS-b-PMMA as modifier. PS blocks with M_n=50,000 were not soluble in the initial formulation. However, they were dispersed as micelles stabilized by the miscible PMMA blocks, leading to a transparent solution up to the conversion where PMMA blocks began to phase separate. A coalescence of the micellar structure into a continuous thermoplastic phase percolating the epoxy matrix was observed. The elastic modulus and yield stress of the cured blend modified by both PS and PMMA were 2.64 GPa and 97.2 MPa, respectively. For the blend modified by an equivalent amount of block copolymer these values were reduced to 2.14 GPa and 90.0 MPa. Therefore, using a block copolymer instead of the mixture of individual homopolymers and selecting an appropriate epoxy-amine formulation to provoke phase separation of the miscible block well before gelation, enables to transform a micellar structure into a bicontinuous thermoplastic/thermoset structure that exhibits the desired decrease in yield stress necessary for toughening purposes.