Physical properties of poly(cyclohexyl methacrylate)-b-poly(iso-butyl acrylate)-b-poly(cyclohexyl methacrylate) triblock copolymers synthesized by controlled radical polymerization

The microphase segregation of different poly(cyclohexyl methacrylate)-b-poly(iso-butyl acrylate)-b-poly(cyclohexyl methacrylate), PCH-b-PiBA-b-PCH, triblock copolymers obtained by atom transfer radical polymerization has been evaluated by dynamic mechanical thermal analysis through location of the two relaxations ascribed to cooperative motions of each block. Additionally, other secondary relaxations have been found, whose characteristics are also dependent on molecular weight of outer and rigid segments. The length of these hard blocks influences significantly the stiffness and microhardness found in these triblock copolymers. These two mechanical parameters increase as molecular weight of poly(cyclohexyl methacrylate) does. The morphological aspects have been examined by small angle X-ray scattering and atomic force microscopy.     

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.     

Synthesis of pH-Responsive Multilayer Micelles for Sustained Release of Folic Acid

Two novel triblock copolymers poly(hydroxypropyl acrylate)-b-poly (methyl methacrylate)-b-poly(N,N-dimethylaminoethyl methacrylate) and poly(hydroxypropyl acrylate)-b-poly(methyl methacrylate)-b-poly(acrylic acid) were successfully synthesized. In acetone media, using the electrostatic interactions between N,N-dimethylaminoethyl methacrylate and acrylic acid units, they could form spherically shaped multilayer micelles with pH-responsive, and have a mean diameter around 110 nm. The critical micelle concentration of it was determined to be 2.42 mg/L. In vitro release experiments, the folic acid-loaded micelles exhibited sustained release behavior and the drug release rate was affected by the pH value of release media. These results indicate that the multilayer micelles may serve as a novel intelligent drug delivery system.     

Functional coatings for anti-biofouling applications by surface segregation of block copolymer additives

Temperature responsive or bactericidal coatings with poly(n-butyl methacrylate) (PBMA) as bulk material and surface segregated poly(n-butyl acrylate)-block-poly-(N-isopropylacrylamide) (PBA-b-PNIPAAm) or poly(n-butyl acrylate)-block-quaternized poly(2-(dimethylamino)ethyl methacrylate) (PBA-b-PDMAEMAq) as additive were prepared via sequential solvent evaporation of polymer solutions in a solvent mixture. The degree of enrichment at the air surface of the coating and the functionality were examined for different molecular weight additives with different block ratios obtained via Atom Transfer Radical Polymerization (ATRP). The design of the block copolymers with an anchor block (PBA) which is compatible with the bulk polymer (PBMA) and water-compatible functional blocks (PNIPAAm and PDMAEMAq) along with the selection of suited solvent mixtures based on pre-estimation of the selective solubility and sequential evaporation via the Hansen solubility parameters and vapor pressures, respectively, were found to work very well. A small fraction of water in the solvent mixture had been crucial to obtain surface segregation of the functional block, e.g., a PNIPAAm surface with temperature-switchable wettability. Reversible temperature dependent wettability and long term stability of the functionalization, based on contact angle data, were obtained for an optimized PBA-b-PNIPAAm additive. Surface charge density, estimated from dye binding and zeta potential measurements, and killing efficiency against Staphylococcus aureus were investigated for PBA-b-PDMAEMAq as additive. Both block copolymer additives were found to dominate the surface properties and the functionality of the PBMA coating.     

Nanostructured thermosets from epoxy and poly(2,2,2-trifluoroethyl acrylate)-block-poly(glycidyl methacrylate) diblock copolymer: Demixing of reactive blocks and thermomechanical properties

Poly(2,2,2-trifluoroethyl acrylate)-block-poly(glycidyl methacrylate) (PTFEA-b-PGMA) diblock copolymer was synthesized via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. The reactive diblock copolymer was incorporated into epoxy to obtain the nanostructured thermosets. The morphology of the thermosets was investigated by means of atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). It is identified that the demixing of the reactive subchain (viz. PGMA) out of epoxy matrix occurred in the process of curing reaction, which exerted a profound impact on the glass transition temperatures of the nanostructured thermosets. The static contact angle measurements showed that the nanostructured thermosets displayed a significant enhancement in surface hydrophobicity as well as a reduction in surface free energy. The improvement in surface properties was attributed to the enrichment of the fluorine-containing block (i.e., PTFEA) of amphiphilic diblock copolymer on the surface of the thermosets, which was further evidenced by surface atomic force microscopy (AFM). The measurement of critical stress intensity factor (K_1C) showed that the fracture toughness of the materials was significantly enhanced by the inclusion of a small amount of PTFEA-b-PGMA diblock copolymer.     

Formation of nanostructures in thermosets containing block copolymers: From self-assembly to reaction-induced microphase separation mechanism

In this work, we investigated the effect of formation mechanisms of nanophases on the morphologies and thermomechanical properties of the nanostructured thermosets containing block copolymers. Toward this end, the nanostructured thermosets involving epoxy and block copolymers were prepared via self-assembly and reaction-induced microphase separation approaches, respectively. Two structurally similar triblock copolymers, poly(ε-caprolactone)-block-poly(butadiene-co-styrene)-block-poly(ε-caprolactone) (PCL-b-PBS-b-PCL) and poly(ε-caprolactone)-block-poly(ethylene-co-ethylethylene-co-styrene)-block-poly(ε-caprolactone) (PCL-b-PEEES-b-PCL) were synthesized via the ring-opening polymerization of ε-caprolactone (CL) with α,ω-dihydroxyl-terminated poly(butadiene-co-styrene) (HO-PBS-OH) and α,ω-dihydroxyl-terminated poly(ethylene-co-ethylethylene-co-styrene) (i.e., HO-PEEES-OH) as the macromolecular initiators, respectively; the latter was obtained via the hydrogenation reduction of the former. Both the triblock copolymers had the same architecture, the identical composition and close molecular weights. In spite of the structural resemblance of both the triblock copolymers, the formation mechanisms of the nanophases in the thermosets were quite different. It was found that the formation of nanophases in the thermosets containing PCL-b-PBS-b-PCL followed a reaction-induced microphase separation mechanism whereas that in the thermosets containing PCL-b-PEEES-b-PCL was in a self-assembly manner. The different formation mechanisms of nanophases resulted in the quite different morphologies, glass transition temperatures (T_g's) and fracture toughness of the nanostructured thermosets.     

Synthesis of amphiphilic triblock copolymers and application for morphology control of calcium carbonate crystals

A series of amphiphilic triblock copolymers poly(ethylene glycol)-block-poly(acrylic acid)-block-poly(n-butyl acrylate) (PEG-b-PAA-b-PnBA) differing only in the relative block lengths were synthesized by the acid-catalyzed elimination of the tert-butyl groups from poly(ethylene glycol)-block-poly(tert-butyl acrylate)-block-poly(n-butyl acrylate) (PEG-b-PtBA-b-PnBA), which was synthesized by atom-transfer radical polymerization (ATRP). The degree of polymerization, molecular weight and percentage of hydrolysis of the product PEG-b-PAA-b-PnBA were studied by gel permeation chromatography (GPC), NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to study the aggregation states of copolymers in water solution. The radii of the copolymer micelles shrink as Ca²⁺ is introduced into the solutions. The crystallization behaviors of calcium carbonate controlled by copolymer 1 (PEG₁₁₂-b-PAA₈₆-b-PnBA₆₀) and copolymer 2 (PEG₁₁₂-b-PAA₄₀-b-PnBA₇₂) differing mainly in the length of PAA block were systematically studied. It was found that the crystallization products are composed of calcite and vaterite, and the ratio of vaterite to calcite increases with increasing the concentration of copolymer 1. For copolymer 2, however, only calcite is obtained at all the concentration range investigated in this work.     

Influence of block composition on structural,thermal and mechanical properties of novel aliphatic polyester based triblock copolymers

A series of ABA type triblock copolymers [Poly(lactide)-block-poly(hexamethylene 2,3-O-isopropylidene tartarate)-block-poly(lactide)] PLA-b-PHIT-b-PLA based on renewable monomers l-tartaric acid and l-lactide have been synthesized and the effect of the PLA chain length on the properties of the triblock copolymers has been systematically investigated. The block nature of the copolymers was established by differential scanning calorimetry (DSC) which showed two glass transition temperatures (T_g) corresponding to PHIT and PLA blocks. Solution cast films of these triblock copolymers turned out to be brittle in nature and to overcome this, ε-caprolactone was copolymerized with l-lactide to generate a separate series of triblock copolymers [PLA-ran-PCL]-b-PHIT-b-[PLA-ran-PCL]. Our study systematically demonstrates that the PLA-to-PCL ratio in the outer block composition influences the mechanical properties via a delayed post-yield stress drop phenomenon. The study further elaborates the time-synchronized strain-field analysis of the novel triblocks to be a convincing approach for the characterization of micro-deformation modes.     

Preparation and self-assembly of double hydrophilic poly(ethylethylene phosphate)-block-poly[2-(succinyloxy)ethyl methacrylate] diblock copolymers for drug delivery

This work focuses on the synthesis and self-assembly of biodegradable and anionic double hydrophilic diblock copolymers (DHBCs) poly(ethylethylene phosphate)-block-poly[2-(succinyloxy)ethyl methacrylate] (PEEP-b-PSEMA) with different molecular weights and compositions, which were prepared via a combination of ring opening polymerization (ROP), atom transfer radical polymerization (ATRP) and polymer reaction. The chemical structures of these well-defined diblock copolymers were confirmed by ¹H NMR and FT-IR analyses. GPC results indicated that the copolymers showed symmetric peak and relatively narrow polydispersities. Subsequently, pH-responsive micellization behaviors of PEEP-b-PSEMA diblock copolymers were investigated by fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. The results demonstrated that these diblock copolymers were able to self-assemble into micelles with various sizes depending on the variation of pH values. Naproxen (NAP), a poorly water-soluble drug, was selected as the model drug and encapsulated into the core of micelles via dialysis method. The in vitro release behavior of NAP from these micelles was pH-dependent and could be accelerated in the presence of phosphodiesterase I which could promote the degradation of polyphosphoesters. Cytotoxicity tests by MTT assay showed that these block copolymers possessed favorable biocompatibility against HeLa cells, revealing that this kind of biodegradable, biocompatible and pH-responsive block copolymer would be served as a promising material for drug delivery.     

Design of responsive double-hydrophilic A-b-(B-co-C) diblock terpolymers with tunable thermosensitivity

Double-hydrophilic poly[(oligo(ethylene glycol) methacrylate)-co-methyl methacrylate]-b-poly(2-(diethylamino)ethyl methacrylate), P(EGMA-co-MMA)-b-PDEA, diblock terpolymers were designed and explored in aqueous media. Thanks to the thermosensitivity of the P(EGMA-co-MMA) statistical block and the pH sensitivity of the PDEA block, these terpolymers form two distinct micellar self-assemblies at different conditions of pH and temperature. The thermosensitivity of these terpolymers can be tuned by controlling the LCST of the statistical block through its monomer unit composition.     

Dissipative particle dynamics study on the multicompartment micelles self-assembled from the mixture of diblock copolymer poly(ethyl ethylene)-block-poly(ethylene oxide) and homopolymer poly(propylene oxide) in aqueous solution

Dissipative particle dynamics (DPD) method is applied to model the self-assembly of diblock copolymer poly(ethyl ethylene)-block-poly(ethylene oxide) (PEE-b-PEO) and homopolymer poly(propylene oxide) (PPO) in aqueous solution. In this study, several segments are coarse-grained into a single simulation bead based on the experimental density. For the self-assembly of pure diblock copolymer PEE-b-PEO in dilute solution, the DPD simulation results are in good agreement with experimental data of micelle morphologies and sizes. The chain lengths of the block copolymers and the volume ratios between PPO and PEE-b-PEO are varied to find the conditions of forming multicompartment micelles. The micelles with core-shell-corona structure and the micelles with two compartments are both formed from the mixture of PEE-b-PEO and PPO in aqueous solution.     

Reversible pH-Responsive Hydrogels of Softwood Kraft Lignin and Poly[(2-dimethylamino)ethyl Methacrylate]-based Polymers

Softwood kraft lignin (SKL) pH-responsive hydrogels were prepared through controlled aggregation using poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and poly(2-(dimethylamino)ethyl methacrylate)-block-poly(ethylene oxide)-block-poly(2-(dimethylamino) ethyl methacrylate) triblock copolymer (PDMAEMA-co-PEO-co-PDMAEMA). At low SKL concentrations, the SKL/polymer (PDMAEMA and PDMAEMA-co-PEO-co-PDMAEMA) aqueous solutions exhibited pH-dependent aggregation arising from the formation of strong intermolecular hydrogen bonds. Decreasing the SKL/polymer weight ratio resulted in the pH-reversible soluble-insoluble (S-I) transition to become a soluble-insoluble-soluble (S-I-S) transition, which upon increasing the SKL concentration resulted in hydrogel formation. Under neutral conditions relatively strong hydrogels were formed, which upon either increasing or decreasing solution pH resulted in the hydrogels collapsing to liquid solutions, but were readily reformed upon neutralization. The effects of polymer structure, concentration, and intermolecular interactions on solution behavior and gelation are thoroughly discussed.     

Micelles and ‘reverse micelles’ with a novel water-soluble diblock copolymer

A series of poly[2-(diisopropylamino)ethyl methacrylate]-block-poly[2-(N-morpholino)ethyl methacrylate], [PDPA-b-PMEMA], have been synthesized by using group transfer polymerization. These novel PDPA-b-PMEMA diblock copolymers dissolved molecularly in aqueous solution at low pH (<6.0) due to the protonation of all tertiary amine residues of both blocks and formed PDPA-core micelles at pH 7.5 by PMEMA block forming the micelle coronas. On the other hand, it was also observed that these diblock copolymers formed near-monodisperse ‘reverse micelles’, PMEMA-core micelles, in n-alkanes with or without requiring cosolvent depending on comonomer ratios. Dynamic light scattering studies indicated monodisperse or near-monodisperse micelles in both cases. The intensity-average radii of the PDPA-core and the PMEMA-core micelles were between 10 nm and 17 nm (polydispersity index, μ₂/Γ² < 0.08) and between 10 nm and 13 nm in n-hexane (μ₂/Γ² < 0.09), respectively.     

A facile way to prepare crystalline platelets of block copolymers by crystallization-driven self-assembly

Poly(ε-caprolactone)-block-poly[2-(dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) block copolymers were applied to fabricate elongated polymer platelets with axial length of 5–20 μm and thickness of ca. 10 nm by crystallization-driven self-assembly (CDSA). The block copolymer platelets composed of a crystallized PCL layer sandwiched between two PDMAEMA layers were obtained spontaneously by adding methanol, a selective solvent of PDMAEMA, into the block copolymer solution of THF at 25 °C. Therefore, this is a facile approach to generate lamellar nanoobjects of block copolymers. Effects of the block copolymer compositions on the morphologies of platelets were investigated. The presence of PDMAEMA segments along the lamellar surfaces was further confirmed by loading gold nanoparticles. Moreover, PEO-b-PCL-b-PDMAEMA triblock terpolymer could form spindle platelets by this approach. The crystalline platelets were characterized by the transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD).     

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.     

PBT-b-PEO-b-PBT triblock copolymers: Synthesis,characterization and double-crystalline properties

We demonstrated here a facile method to synthesize novel double crystalline poly(butylene terephthalate)-block-poly(ethylene oxide)-block-poly(butylene terephthalate) (PBT-b-PEO-b-PBT) triblock copolymers by solution ring-opening polymerization (ROP) of cyclic oligo(butylene terephthalate)s (COBTs) using poly(ethylene glycol) (PEG) as macroinitiator and titanium isopropyloxide as catalyst. The structure of copolymers was well characterized by ¹H NMR and GPC. TGA results revealed that the decomposition temperature of PEO in triblock copolymers increased about 30 °C to the same as PBT copolymers, after being end-capped with PBT polymers. These triblock copolymers showed double crystalline properties from PBT and PEO blocks, observed from DSC and WAXD measurements. The melting and crystallization peak temperatures corresponding to PBT blocks increased with PBT content. The crystallization of PBT blocks showed the strong confinement effects on PEO blocks due to covalent linking of PBT blocks with PEO blocks, where the melting and crystallization temperatures and crystallinity corresponding to PEO blocks decreased significantly with increment of PBT content. The confinement effect was also observed by SAXS experiments, where the long distance order between lamella crystals decreases with increasing PBT length. For the triblock copolymer with highest PBT content (PBT₅₄-b-PEO₂₂₇-b-PBT₅₄), this effect shows a 30 °C depression on PEO crystals' melting temperature and 77% on enthalpy, respectively, compared to corresponding PEO homopolymer. The crystal morphology was observed by POM, and amorphous-like spherulites were observed during PBT crystallization.     

Study on crystalline morphology of poly(l-lactide)-poly(ethylene glycol) diblock copolymer

Crystallization behavior, structural development and morphology evolution in a series of diblock copolymers of poly(l-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) were investigated via differential scanning calorimetry, wide-angle X-ray diffraction, polarized optical microscopy and atomic force microscopy. In these copolymers, both blocks are crystallizable and biocompatible. It was interesting that these PLLA-b-PEG diblock copolymers could form spherulites with banded textures, which was undercooling dependent. Single crystals with an abundance of screw dislocations were also observed via AFM. Such results indicated that these ringed spherulites and single crystals were formed during the crystallization of the PLLA blocks.     

Hydrolysis of poly(ester-ether-ester) block copolymers in the presence of endothelial cells: in vitro modulation of endothelin release

In previous papers, we studied the hydrolytic degradation of six poly(ester-ether-ester) block copolymers, i.e. three poly(ε-caprolactone)-block-poly(oxyethylene)-block-poly(ε-caprolactone) copolymers and three poly(l-lactide)-block-poly(oxyethylene)-block-poly(l-lactide) copolymers. Their degradation products, 6-hydroxyhexanoic acid and l-lactic acid, have now been found to modulate endothelin release by human umbilical vein endothelial cells, with no significant alteration of the vasoconstrictor-vasodilator balance previously determined. The influence of the same degradation products on the cell proliferation has also been determined and discussed. Received: 13 January 1997/Revised: 2 May 1997/Accepted: 3 May 1997     

Preparation of the Sulfonamide Containing Block Copolymer as Polymeric Sorbent for Removal of Mercury from Aqueous Solutions

A new sulfonamide containing polymeric sorbent for the removal of mercury ions from waste waters was prepared starting from poly(glycidyl methacrylate)-b-poly(ethylene glycol)-b-poly(glycidyl methacrylate) (PGMA- b -PEG- b -PGMA) triblock copolymer prepared by using the ATRP method. Epoxy groups on the block copolymer were functionalized with amino groups. Ammonia-functionalized PGMA- b -PEG- b -PGMA was treated with excess of benzenesulfonyl chloride to obtain a sulfonamide-based polymeric sorbent. The sulfonamide containing the polymeric sorbent with a 3.5 mmol · g^?1 total nitrogen content is able to selectively sorb mercury from aqueous solutions. The mercury sorption capacity of the resin is around 3.12 mmol g^?1 under non-buffered conditions. Experiments performed in identical conditions with several metal ions revealed that Cd(II), Pb(II), Zn(II), Fe(III), and Fe(II) also were extractable in quantities (0–0.45 mmol/g). The sorbed mercury can be eluted by repeated treatment with 4 M HNO₃ without hydrolysis of the sulfonamide groups.     

Contact Time and Temperature Dependencies of Tack in Polyacrylic Block Copolymer Pressure-Sensitive Adhesives Measured by the Probe Tack Test

The adhesion strength of an adhesive is affected by two factors: the development of interfacial adhesion and the cohesive strength of the adhesive. In order to evaluate the relative contributions of these two factors, the tack of polyacrylic block copolymer-based adhesives was measured using a probe tack test. For this purpose, three model adhesives were prepared: poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) triblock copolymer (A), a mixture of the triblock and poly(methyl ethacrylate)-block-poly(n-butyl acrylate) diblock copolymer (7/3, w/w) (B), and a mixtureof the triblock and poly(n-butyl acrylate) oligomer (8/2, w/w) (C). The tack measured at room temperature was in the order B ≈ C > A and increased gradually with an increase in the contact time. The temperature dependence of tack showed peak tack values above room temperature, and the peak tack temperature was in the order A > B > C. The storage and loss moduli measured by dynamic mechanical analysis were also in the order A > B > C. The molecular mobility of the poly(n-butyl acrylate) unit in the block copolymer measured by H-pulse NMR was in the order C> B > A. It was concluded from these results that the relative contribution of interfacial adhesion to the tack of the different systems was in the order C > B > A.