Evaluation of the permeability and blood‐compatibility properties of membranes formed by physical interpenetration of chitosan with PEO/PPO/PEO triblock copolymers

In order to develop blood compatible membranes with controlled porosity, we have fabricated and examined the properties of physical interpenetrating network (PIN) of chitosan and poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO/PPO/PEO) triblock copolymers (Pluronics^®). Degree of equilibrium swelling, scanning electron microscopy, and electron spectroscopy for chemical analysis (ESCA) were used to characterize the bulk and surface properties. Vitamin B₁₂ and human serum albumin were used as permeability markers. Platelet adhesion and activation were used to determine the blood‐interaction properties of the PIN membranes. Unlike chitosan membranes that were nonporous, the chitosan‐Pluronic PIN membranes were highly porous with the pore size, depending on the type of incorporated Pluronic polyol. ESCA results showed a significant increase in the ? C ? O? signal of C1s spectra on the PIN membranes that correlates with the presence of PEO chains on the surface. The permeability coefficients of vitamin B₁₂ and albumin were higher in the chitosan‐Pluronic PIN membranes than in the control. The number of adherent platelets and the extent of activation were significantly reduced on the chitosan‐Pluronic PIN membranes. The decrease in platelet adhesion and activation correlated positively with the PEO chain length of the incorporated Pluronic polyols. The results of this study show that chitosan‐Pluronic PIN membranes offer a blood‐compatible alternative with a higher‐molecular‐weight cutoff for use in hemodialysis and related applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1274–1284, 2001     

PEO–PPO–PEO triblock copolymer/Nafion blend as membrane material for intermediate temperature DMFCs

This paper describes homogeneous triblock copolymer/Nafion blend membranes, which facilitate proton conduction in direct methanol fuel cells (DMFCs) at intermediate temperatures. The interaction between the two polymer components is investigated by FT-IR spectroscopy. The blend membranes show higher proton conductivity than recast Nafion under partially anhydrous conditions. Protons can be transported with the assistance of ether chain under such conditions at elevated temperature. In addition, the membranes exhibit more favourable methanol permeability and selectivity. This kind of blend membrane shows somewhat better performance in DMFC compared to bare recast Nafion at intermediate temperature (≥120 °C). This work is a first attempt in our group to design membrane materials with enhanced proton conductivity under conditions typical of intermediate temperature DMFCs.     

Effect of temperature and water on microphase separation of PCL–PEO–PCL triblock copolymers

Microphase separation of poly(ε-caprolactone-ethylene oxide-ε-caprolactone) (PCL–PEO–PCL), with block number-average molecular weights of 9,100–30,400–9,100 g/mol, was studied. Cylindrical morphology was observed in a solvent-cast sample. When the as-cast sample was heated above the melting points of both PEO and PCL blocks, a change in morphology was observed by Small Angle X-ray Scattering (SAXS). When this sample was cooled to room temperature in the ambient atmosphere, another morphology (lamellae) was observed with SAXS and Atomic Force Microscopy (AFM). This asymmetric change in morphology suggests a role of kinetics (microphase separation and crystallization) in determining the observed microstructures. Addition of water at room temperature also affected microphase separation of the block copolymer due to hydrophilicity of PEO. As the polymer concentration decreases from 100 to 60%, the morphology changes from cylinders to lamellae. Differential Scanning Calorimetry (DSC) data show that water addition decreases PEO crystallinity but PCL crystallinity remains.     

Crystallization behavior of oxyethylene/oxybutylene diblock and triblock copolymers

The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (E_mB_n diblock copolymers and E_mB_nE_m, B_nE_mB_n triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature (T_c) in non-isothermal crystallization was determined. It is found that the E_mB_n diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, φ_E, and the length, m, of the E block. Some block copolymers with extremely low T_c, which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike E_mB_n/B_h blends, there is no obvious relationship between T_c and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of χ_c/χ_ODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have χ_c/χ_ODT<3, in agreement with the previously reported critical value and consistent with their breakout crystallization behavior.     

Synthesis and characterization of PCL/PEG/PCL triblock copolymers by using calcium catalyst

Triblock copolymer PCL-PEG-PCL was prepared by ring-opening polymerization of ε-caprolactone (CL) in the presence of poly(ethylene glycol) catalyzed by calcium ammoniate at 60 °C in xylene solution. The copolymer composition and triblock structure were confirmed by ¹H NMR and ¹³C NMR measurements. The differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed the micro-domain structure in the copolymer. The melting temperature T_m and crystallization temperature T_c of the PEG domain were influenced by the relative length of the PCL blocks. This was caused by the strong covalent interconnection between the two domains. Aqueous micelles were prepared from the triblock copolymer. The critical micelle concentration was determined to be 0.4-1.2 mg/l by fluorescence technique using pyrene as probe, depending on the length of PCL blocks, and lower than that of corresponding PCL-PEG diblock copolymers. The ¹H NMR spectrum of the micelles in D₂O demonstrated only the -CH₂CH₂O- signal and thus confirmed the PCL-core/PEG-shell structure of the micelles.     

Controlled drug release carriers based on PCL/PEO/PCL block copolymers

In order to create a new drug delivery system, the ibuprofen-loaded triblock copolymer PCL/PEO/PCL (PCEC) microspheres with a low PEO content (<2?wt%) were prepared by oil in water (o/w) solvent evaporation technique. The influence of PEO content, molecular weight of a polymer matrix and drug loading on the ibuprofen release profiles were evaluated. The interactions between polymer matrix and ibuprofen were detected by FTIR analysis. The presence of hydrophilic PEO segment in PCL chains caused the decrease in particle size, which further had a great impact on the drug release kinetics, i.e., initially faster release and significantly higher quantity of released drug compared to neat PCL. Ibuprofen release behavior from polymer matrix was governed by a diffusion process. In vitro cytotoxicity tests revealed that empty PCL and PCEC microspheres were not toxic at low concentrations, while ibuprofen-loaded microspheres exhibited cytotoxicity correlated with amounts of incorporated drug.     

Synthesis and characterization of polyoxazoline-polysulfone triblock copolymers

Amphiphilic triblock poly(2-ethyl-2-oxazoline-b-sulfone-b-2-ethyl-2-oxazoline) (PEOX-b-PSF-b-PEOX) and poly(2-ethyl-2-oxazoline-co-ethyleneimine-b-sulfone-b-2-ethyl-2-oxazoline-co-ethyleneimine) (PEOXcoPEI-b-PSF-b-PEOXcoPEI) copolymers were synthesized for potential use as water purification membranes. Poly(arylene ether sulfone) (polysulfone) oligomers of controlled molecular weight were prepared by nucleophilic step polymerization of 4,4′-dichlorodiphenyl sulfone with a molar excess of bisphenol-A. The phenolate endgroups were then reacted with ethylene carbonate to afford telechelic aliphatic hydroxyethyl groups. These were tosylated to produce macroinitiators for ring-opening cationic polymerization of 2-ethyl-2-oxazoline. Subsequently, the pendent amides on the hydrophilic PEOX blocks were also hydrolyzed to generate positively charged PEOXcoPEI-b-PSF-b-PEOXcoPEI copolymers. Compositions with high polysulfone compositions relative to the hydrophilic blocks were of particular interest because they maintained good mechanical integrity in water. Water uptake at room temperature increased up to 18 wt% for copolymers with 22 wt% of the hydrophilic components. Solid-state thermal properties suggested some phase mixing of the components in the PEOX-b-PSF-b-PEOX copolymers but better phase separation of the blocks in the partially hydrolyzed PEOXcoPEO-b-PSF-b-PEOXcoPEI materials.     

Synthesis and characterization of nylon-polyisobutylenenylon triblock copolymers

Nylon-6-polyisobutylene-nylon-6 triblock copolymers have been synthesized by converting telechelic polyisobutylene diols to , -diisocyanate polyisobutylenes and using these macroactivators, in conjunction with strong base, to induce the subsequent anionic polymerization of -caprolactam. Pure block copolymer was obtained by suitable sequential extraction. Products were characterized by composition, molecular weight and DSC.     

Thermoreversible gelation of mixed triblock and diblock copolymers in n-octane

The thermoreversible gelation of blends of polystyrene-block-poly(ethylene/butylene)-block-polystyrene (SEBS) and polystyrene-block-poly(ethylene/propylene) (SEP) copolymers in n-octane was studied. The solvent is selective for the polyolefine blocks of the copolymers. The influence of the composition of the hybrid gels on the sol-gel transition and on the mechanical properties of the gels was analyzed. The sol-gel transition temperature increased with the concentration of both type of copolymers and did not depend on the hybrid gel composition for SEBS2 proportions higher than 50% at a total copolymer concentration higher than 6 wt%. The mechanical properties of the different gels were examined through oscillatory shear and compressive stress relaxation measurements. The elastic storage modulus increased with the triblock copolymer concentration but kept almost constant with the diblock copolymer concentration for SEBS concentrations higher than 5.0%. The stress relaxation rate was not dependent on the concentration of triblock and diblock copolymers, but the hybrid gels show lower stress relaxation rates than the pure SEBS2 gels. In the hybrid SEBS/SEP gels the SEP chains impart stability to the micelles or nodes of the network whereas the SEBS chains are responsible for the bridges that keep the gel as one-phase system.     

Deformation behavior of styrene-block-butadiene-block-styrene triblock copolymers having different morphologies

Deformation behavior of styrene-block-butadiene-block-styrene (SBS) triblock copolymers having different morphologies was investigated. Due to the combination of different methods which provide information on different deformation levels (macroscopic, microscopic and molecular) complex deformation mechanisms for each type of SBS block copolymer (including glassy-rubber alternating lamellae, rubber cylinders in glassy matrix and hard domains in soft matrix morphology) could be revealed. In combination with tensile tests, Fourier transform infrared (FTIR) spectroscopy was successfully applied to study the change of orientation in individual phases using the absorption bands at 1493 and 966 cm⁻¹ for polystyrene (PS) and polybutadiene (PB) phases, respectively. For all the block copolymers investigated the PB phase always oriented stronger than the PS phase because of its lower Young's modulus. However, differences in orientation in both phases were influenced by an appropriate stress distribution within the specimens during deformation, which, in fact, depends on the morphology of the polymers. Additionally, atomic force microscopy revealed local morphological changes during uniaxial stretching, which, in fact, depend on the arrangement of the structural units.     

Studies on the fluorescence quenching of anthracenes by polysilane copolymers

In this article, the room-temperature solution fluorescence quenching of electron-deficient anthracenes such as 9-cyanoanthracene (CNA), 9,10-dicyanoanthracene (DCNA), and 9,10-dichloroanthracene (DCLA) by polysilane copolymers was studied. The fluorescence quenching data was in conformity with the Stern-Volmer equation F₀/F = 1 + K_sv[Q], the F₀/F−[Q] straight lines were drawn, and the fluorescence quenching constants K_sv were obtained. By measuring the fluorescence lifetimes of the anthracenes, the fluorescence quenching rate constants k_q were calculated. Based on experiments and references, we tentatively proposed that for the same polysilane copolymer quencher the fluorescence quenching was caused mainly by the polysilane Si—Si chain and affected in a small degree by the side substituents attached to the Si—Si chain. In addition, it was observed that the order of the fluorescence quenching rate constants k_q of the above three electron-deficient anthracenes by the same polysilane copolymer was DCNA > CNA > DCLA, which is just in keeping with that of their electron deficiency. © 1996 John Wiley & Sons, Inc.     

Synthesis of biodegradable and biocompatible ABC triblock copolymers

A facile approach is offered to synthesize well‐defined amphiphilic ABC triblock copolymers composed of poly(ethylene glycol) monomethyl ether (MPEO) as A block, poly(L ‐lysine) (PLLys) as B block, and poly(ε‐caprolactone) (PCL) as C block by a combination of ring‐opening polymerization (ROP) and click reactions. The propargyl‐terminated poly(Z‐L ‐lysine)‐block‐poly(ε‐caprolactone) (MPEO‐PzLLys‐PCL) diblock copolymers were synthesized via the ring‐opening polymerization of N^ε‐carbobenzoxy‐L ‐lysine N‐carboxyanhydride (Z‐L ‐Lys NCA) in DMF at room temperature using propargyl amine as an initiator and the resulting amino‐terminated poly(Z‐L ‐lysine) then used in situ as a macroinitiator for the polymerization of ε‐caprolactone in the presence of stannous octoate as a catalyst. The triblock copolymers poly(ethylene glycol) monomethyl ether –block‐poly(Z‐L ‐lysine)‐block‐poly(ε‐caprolactone) (MPEO‐PzLLys‐PCL) were synthesized via the click reaction of the propargyl‐terminated PzLLys‐PCL and azido‐terminated poly(ethylene glycol) monomethyl ether (PEO‐N₃) in the presence of CuBr and 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) catalyst system. After the removal of Z groups of L ‐lysine units, amphiphilic and biocompatible ABC triblock copolymers MPEO‐PLLys‐PCL were obtained. The structural characteristics of these ABC triblock copolymers and corresponding precursors were characterized by NMR, IR, and GPC. These results showed the click reaction was highly effective. Therefore, a facile approach is offered to synthesize amphiphilic and biocompatible ABC triblock copolymers consisting of polyether, polypeptide and polyester. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Facile surface modification of PVDF microfiltration membrane by strong physical adsorption of amphiphilic copolymers

To endow the surface of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes with hydrophilicity and antifouling property, physical adsorption of amphiphilic random copolymers of poly(ethylene glycol) methacrylate (PEGMA) and poly(methyl methacrylate) (PMMA) (P(PEGMA‐r‐MMA)) onto the PVDF membrane was performed. Scanning electron microscopy (SEM) images showed that the adsorption process had no influence on the membrane structure. Operation parameters including adsorption time, polymer concentration, and composition were explored in detail through X‐ray photoelectron spectroscopy (XPS), static water contact angle (CA), and water flux measurements. The results demonstrated that P(PEGMA‐r‐MMA) copolymers adsorbed successfully onto the membrane surface, and hydrophilicity of the PVDF MF membrane was greatly enhanced. The antifouling performance and adsorption stability were also characterized, respectively. It was notable that PVDF MF membranes modified by facile physical adsorption of P(PEGMA₅₈‐r‐MMA₃₃) even showed higher water flux and better antifouling property than the commercial hydrophilic PVDF MF membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3112–3121, 2013     

Synthesis and self-assembly of polyimide/poly(dimethylsiloxane) brush triblock copolymers

A series of novel brush triblock copolymers containing ‘glassy’ fluorinated polyimide, poly((4,4′-hexafluoroisopropylidene diphthalic anhydride)-co-(2,3,5,6-tetramethyl-1,4-phenylenediamine)) (poly(6FDA-co-TMPD)), and ‘rubbery’ polydimethylsiloxane monomethacrylate (PDMS-MA) were synthesized and characterized. Well-defined difunctional poly(6FDA-co-TMPD) with α,ω-amino end-groups was initially prepared via step-growth polymerization using precise control of the diamine (TMPD) to dianhydride (6FDA) ratio. Subsequent functionalization with 2-bromoisobutyryl bromide afforded a telechelic macroinitiator suitable for atom transfer radical polymerization (ATRP). The macroinitiator and its diamino poly(6FDA-co-TMPD) precursor were characterized via gel permeation chromatography (GPC), ¹H nuclear magnetic resonance (NMR) spectroscopic analysis and matrix assisted laser desorption ionization time-of-flight (MALDI ToF) mass spectroscopy. ATRP of PDMS-MA using the macroinitiator in different molar ratios afforded a series of brush triblock copolymers with high monomer conversions (88–94%) and varying PDMS weight fractions. Self-assembly of the triblock brush copolymers in dimethylformamide (DMF) afforded nanoparticles with hydrodynamic diameters (d_H) ranging from 87 to 109 nm, as determined by dynamic light scattering (DLS) analysis. Cross-linking of the nanoparticles was achieved via hydrogen abstraction through the thermal degradation of benzoyl peroxide. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) revealed that the self-assemblies and their cross-linked derivatives had spherical morphologies.     

Synthesis of ultra-large mesoporous carbons from triblock copolymers and phloroglucinol/formaldehyde polymer

Ultra-large mesoporous carbon materials were synthesized with the use of triblock copolymers and phloroglucinol/formaldehyde polymer as filler under acid conditions. The carbons obtained by employing F127 as template and carbonizing at 600 °C exhibit large mesopores with a narrow pore-size distribution centered at 19.2 nm. With the assistance of decane as a swelling agent, the pore size of the P123-templated 600 °C-carbonized carbons could be enlarged from 11.5 to 14.7 nm. It is demonstrated that the low synthesis temperature and high reactivity of phloroglucinol are two key factors for the formation of large mesopores.     

Catalyst effect on the transesterification reactions between polycarbonate and polycaprolactone-B-polydimethylsiloxane triblock copolymers

Summary Transesterification reactions between bisphenol-A polycarbonate and polydimethylsiloxane-polycaprolactone block copolymers were studied in melt at 270°C. Influence of the composition of reaction mixture and the catalyst type on the formation and properties of the products obtained were investigated by spectroscopic, chromatographic and thermal methods. Both of the catalysts used, zinc acetate and lanthanum acetylacetonate are very efficient transesterification catalysts for the system studied. GPC and DSC results clearly show the formation of novel polymers displaying combined properties of the polycarbonate and the silicone-ester copolymer. Received: 22 June 1999/Accepted: 8 September 1999     

Syntheses of triblock polybutadiene–polydimethylsiloxane copolymers by coupling reactions

The reaction of epoxy‐telechelic polydimethylsiloxanes with polybutadienyllithium was used to prepare a series of low‐molecular‐weight polybutadiene‐block‐polydimethylsiloxane‐block‐polybutadiene copolymers. The copolymers were purified by repeated fractional precipitation/centrifugation and characterized with NMR, vapor pressure osmometry, size exclusion chromatography, and elemental analysis. The applicability of this method is discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3233–3240, 2006     

以三亚甲基碳酸酯和丙交酯为单体的三嵌段共聚物的合成和表征

以1,6-己二醇为引发剂,辛酸亚锡为催化剂,通过开环聚合制备了PLLA-b-PTMC-b-PLLA和PDLA-b-PTMC-b-PDLA两种三嵌段共聚物,采用核磁共振和红外光谱谱图对产物进行了验证表征,并使用DSC和TGA对共聚物的热力学性能进行了测试。结果表明,通过控制单体与引发剂的比例可以分别获得不同分子量和分子量分布的三嵌段聚合物。在DSC曲线上,PLA-b-PTMC-b-PLA三嵌段共聚物表现出两个玻璃化温度,熔融峰的高度与PLA部分的含量呈正相关,而当PTMC含量占绝大部分时,该熔融峰变得不明显。     

Influence of temperature on the tensile shear strength of joints bonded with polystyrene/polyisoprene triblock copolymers

ABA poly(styrene-b-isoprene) block copolymers (SIS) with various molecular characteristics were prepared. They were used as heat activated films in simple overlap glass joints. The influence of activation temperature on their tensile shear resistance at break was investigated. The decrease in viscosity with increasing temperature could not explain the observed maximum of joint resistance for a given temperature. A morphological interpretation which fits well the experimental observations is proposed.