Synthesis and physicochemical characterization of amphiphilic block copolymer self‐aggregates formed by poly(ethylene glycol)‐block‐poly(ϵ‐caprolactone)

Diblock copolymers with different poly(ε‐caprolactone) (PCL) block lengths were synthesized by ring‐opening polymerization of ε‐caprolactone in the presence of monomethoxy poly(ethylene glycol) (mPEG‐OH, MW 2000) as initiator. The self‐aggregation behaviors and microscopic characteristics of the diblock copolymer self‐aggregates, prepared by the diafiltration method, were investigated by using ¹H NMR, dynamic light scattering (DLS), and fluorescence spectroscopy. The PEG–PCL block copolymers formed the self‐aggregate in an aqueous environment by intra‐ and/or intermolecular association between hydrophobic PCL chains. The critical aggregation concentrations of the block copolymer self‐aggregate became lower with increasing hydrophobic PCL block length. On the other hand, reverse trends of mean hydrodynamic diameters were measured by DLS owing to the increasing bulkiness of the hydrophobic chains and hydrophobic interaction between the PCL microdomains. The partition equilibrium constants (K_v) of pyrene, measured by fluorescence spectroscopy, revealed that the inner core hydrophobicity of the nanoparticles increased with increasing PCL chain length. The aggregation number of PCL chain per one hydrophobic microdomain, investigated by the fluorescence quenching method using cetylpyridinium chloride as a quencher, revealed that 4–20 block copolymer chains were needed to form a hydrophobic microdomain, depending on PCL block length. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3520–3527, 2006     

Surfactant‐free nanoparticles of poly(DL‐lactide‐co‐glycolide) prepared with poly(L‐lactide)/ poly(ethylene glycol)

Surfactant‐free nanoparticles of poly(DL ‐lactide‐co‐glycolide) (PLGA) nanoparticles were prepared with or without poly(L ‐lactide)‐poly(ethylene oxide) (LE) diblock copolymer (abbreviated as PLGA/LE and PLGA nanoparticles) by dialysis method. LE diblock copolymer was used to make PLGA nanoparticles to alternate conventional surfactant. The size of PLGA and PLGA/LE nanoparticles was 295.3 ± 171.3 and 307.6 ± 27.2 nm, respectively, suggesting LE diblock copolymer might be coated onto the surface of nanoparticles. Observation of scanning electron microscope (SEM) showed that PLGA/LE nanoparticles have spherical shapes ranging ～ 200–500 nm. In ¹H‐NMR study, characteristic peaks of the methyl protons of PLGA disappeared in D₂O, whereas characteristic peaks of the methyl proton of both PEG and PLGA were shown in both CDCl₃ and D₂O, indicating that LE diblock copolymer coated on the surface of the PLGA nanoparticles. The higher the initial content of drug, the higher the drug contents and the lower the loading efficiency. PLGA/LE nanoparticles at higher drug contents resulted in slower adriamycin·HCl (ADR) release rate than that of lower drug contents. Also, slower release rate of ADR was achieved by entrapped into the PLGA/LE nanoparticles, whereas LE polymeric micelles showed rapid ADR release. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1116–1123, 2003     

Formation of silver nanoparticles created in situ in an amphiphilic block copolymer film

In this work, silver nanoparticles were synthesized with an amphiphilic diblock copolymer, polystyrene‐block‐poly(1‐vinyl‐2‐pyrrolidone) (PS‐b‐PVP), as a template film. First, microphase‐separated amphiphilic PS‐b‐PVP (70 : 30 wt %) was synthesized through atom transfer radical polymerization. The self‐assembled block copolymer film was used to template the growth of silver nanoparticles by the introduction of a silver trifluoromethanesulfonate precursor and an ultraviolet irradiation process. The in situ formation of silver nanoparticles with an average size of 4–6 nm within the block copolymer template film was confirmed with transmission electron microscopy, ultraviolet–visible spectroscopy, and wide‐angle X‐ray scattering. Fourier transform infrared spectroscopy also demonstrated the selective incorporation and in situ formation of silver nanoparticles within the hydrophilic poly(1‐vinyl‐2‐pyrrolidone) domains, which were mostly due to the stronger interaction strength of the silver with the carbonyl oxygens of poly(1‐vinyl‐2‐pyrrolidone) in the block copolymer. This work provides a simple route for the in situ synthesis of silver nanoparticles within a polymer film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Chemo‐enzymatic synthesis of poly(2,2,2‐trichloroethyl 10‐hydroxydecanate)‐block‐polystyrene combining enzymatic self‐condensation polymerization and ATRP

Enzymatic polymerization in a non‐natural environment is of interest as an environmentally friendly methodology as an alternative to the use of conventional chemical organometallic catalysts. Chemo‐enzymatic synthesis of the AB‐type diblock copolymer poly(2,2,2‐trichloroethyl 10‐hydroxydecanate)‐block‐polystyrene (PHD‐b‐PSt) was carried out by combining enzymatic self‐condensation polymerization (eSCP) and atom‐transfer radical polymerization (ATRP). Biocatalyst Novozyme 435 was successful in catalyzing the eSCP of a novel ω‐hydroxyester, i.e. 2,2,2‐trichloroethyl 10‐hydroxydecanate. The resulting ? CCl₃‐terminated PHD initiated the ATRP of styrene, a ‘living’/controlled radical polymerization. The analysis of the hydrolysate from the copolymer proved the presence of a block copolymer structure. In addition, the well‐defined diblock copolymer PHD‐b‐PSt self‐assembled into nanoscale micelles in aqueous solution. The chemo‐enzymatic synthesis of diblock copolymer PHD‐b‐PSt was achieved by the combination of eSCP and ATRP. The structures and composition of the block copolymer were characterized by means of NMR, infrared and gel permeation chromatography measurements. Differential scanning calorimetry analysis showed that a microphase‐separation structure was formed in the copolymer, which was caused by the crystallization of the PHD segments. As investigated with atomic force microscopy and dynamic light scattering, these micelles had a mean diameter and a spherical shape. To our knowledge, this is the first example of a chemo‐enzymatic synthesis based on eSCP and ATRP. Copyright © 2007 Society of Chemical Industry     

Nanostructured thermosets from self‐assembled amphiphilic block copolymer/epoxy resin mixtures: effect of copolymer content on nanostructures

Nanostructure formation in thermosets can allow the design of materials with interesting properties. The aim of this work was to obtain a nanostructured epoxy system by self‐assembly of an amphiphilic diblock copolymer in an unreacted epoxy/amine mixture followed by curing of the matrix. The copolymer employed was polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA). The thermoset system, formed by a diglycidyl ether of bisphenol A‐type epoxy resin and diaminodiphenylmethane hardener, was chosen to ensure the miscibility of most of the PMMA block until matrix gelation. Transparent materials with microphase‐separated domains were obtained for copolymer contents lower than 40 wt%. In systems containing 20 and 30 wt% block copolymer, the PS block formed spherical micelles or worm‐like structures before curing, which were stabilized through curing by the more compatible PMMA block phase. Nanostructured thermoset systems were successfully synthesized for self‐assembled amphiphilic block copolymer–epoxy/amine mixtures for copolymer contents lower than 40 wt%. Copyright © 2009 Society of Chemical Industry     

Amphiphilic block copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene: synthesis and self‐assembly

The triblock energetic copolymer poly(lactic acid)‐block‐(glycidylazide polymer)‐block‐polystyrene (PLA‐b‐GAP‐b‐PS) was synthesized successfully through atom‐transfer radical polymerization (ATRP) of styrene and ring‐opening polymerization of d,l ‐lactide. The energetic macroinitiator GAP‐Br, which was made from reacting equimolar GAP with α‐bromoisobutyryl bromide, firstly triggered the ATRP of styrene with its bromide group, and then the hydroxyl group on the GAP end of the resulting diblock copolymer participated in the polymerization of lactide in the presence of stannous octoate. The triblock copolymer PLA‐b‐GAP‐b‐PS had a narrow distribution of molecular weight. In the copolymer, the PS block was solvophilic in toluene and improved the stability of the structure, the PLA block was solvophobic in toluene and served as the sacrificial component for the preparation of porous materials, and GAP was the basic and energetic material. The three blocks of the copolymer were fundamentally thermodynamically immiscible, which led to the self‐assembly of the block copolymer in solution. Further studies showed that the concentration and solubility of the copolymer and the polarity of the solvent affected the morphology and size of the micelles generated from the self‐assembly of PLA‐b‐GAP‐b‐PS. The micelles generated in organic solvents at 10 mg mL^?1 copolymer concentration were spherical but became irregular when water was used as a co‐solvent. The spherical micelles self‐assembled in toluene had three distinct layers, with the diameter of the micelles increasing from 60 to 250 nm as the concentration of the copolymer increased from 5 to 15 mg L^?1. © 2017 Society of Chemical Industry     

Polydispersity control in ring opening metathesis polymerization of amphiphilic norbornene diblock copolymers

Ring opening metathesis polymerization (ROMP) with Grubbs's catalyst was used to synthesize narrow polydispersity (PDI)diblock copolymers of norbornene (NOR) and norbornenedicarboxylic acid (NORCOOH). Norbornene (NOR) and 5-norbornene-2,3,-dicarboxylic acid bis trimethylsilyl ester (NORCOOTMS) were used as precursor monomers for thepolymerization. [NORCOOTMS]_m/[NOR]_n was converted to [NORCOOH]_m/[NOR]_n by precipitating the polymer solution in a mixture of methanol, acetic acid, and water. The conversion to 5-norbornene-2,3-dicarboxylic acid was evidenced by ¹H NMR. By polymerizing the bulkier NORCOOTMS precursor monomer first, lower PDIs were observed for the completed [NORCOOH]_m/[NOR]_n block copolymers in comparison to copolymers where the NOR block was polymerized first. The PDI of the diblock copolymers of [NORCOOH]_m/[NOR]_n decreased with increase in block length ofthe precursor NORCOOTMS monomer. This study shows that the PDI can be controlled by selecting a monomer with appropriate functionality as the starting block of the block copolymer to control the rate of propagation, R_p, as an alternative of using additives to change the reactivity of the catalyst.     

Vulcanization of chlorobutyl rubber. II. A revised cationic mechanism of ZnO/ZnCl2 initiated crosslinking

Data relating to the ZnO/ZnCl₂‐accelerated vulcanization of chlorinated poly(isoprene‐coisobutylene) (CIIR or chloro‐butyl) is examined. ZnCl₂ and conjugated diene butyl units on the polymer chain are both precursors to crosslinking, and a revised cationic mechanism is proposed to account for crosslinking, taking into account the involvement of conjugated diene butyl in the process. It is demonstrated that Zn₂OCl₂ will catalyze dehydrohalogenation, and the formation of catalytic amounts of Zn₂OCl₂ by the reaction of ZnCl with ZnO, followed by H⁺ abstraction to give Zn₂OCl₂ and HCl, is essential in the overall crosslinking reaction sequence. The HCl is trapped by ZnO as ZnCl₂. It is proposed that the abstraction by Zn₂OCl₂ of HCl in a concerted reaction leads to Zn(OH)Cl and ZnCl₂. Zn(OH)Cl remains in the polymer as an unextractable salt, while 50% of the chlorine in the rubber is extracted as ZnCl₂ when compounds reach their equilibrium crosslink density. ZnCl₂ initiates crosslinking by the abstraction of chlorine from the chain, but a crosslink will only result when a carbocation on a dechlorinated isoprenoid unit is close to a conjugated diene butyl on an adjacent chain; if not, dehydrohalogenation will result in the formation of a further conjugated diene butyl unit at that point in the chain. The maximum crosslink density achieved is only 1/4 that theoretically possible, as crosslinking restricts chain movement and limits the number of chance meetings between carbocations on the polymer and conjugated diene butyl units. Zinc stearate promotes dehydrohalogenation, ZnCl₂ being the only chloro‐zinc salt formed. Reversion occurs in compounds where there is insufficient ZnO to trap all of the chlorine present in the rubber. HCl per se does not attack the polymer, but promotes reversion only in the presence of carbocations on the chain, i.e., during the crosslinking process. Trapping of HCl by ZnO prevents reversion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2302–2310, 2000     

Synthesis of functional poly(styrene)‐block‐(methyl methacrylate/methacrylic acid) by homogeneous reverse atom transfer radical polymerization: Spherical nanoparticles,thermal behavior,self‐aggregation,and morphological properties

This study investigates the use of homogeneous reverse atom transfer radical polymerization for the synthesis of polystyrene (PS) initiated by conventional radical peroxide with copper bromide in the lower oxidation state and a 2,2′‐bypyridine complex as the catalyst. In a second stage, an amphiphilic block copolymer containing methyl methacrylate (MMA) was synthesized via normal atom transfer radical polymerization in two steps, followed by partial hydrolysis of the methyl ester linkage of the MMA block under acidic conditions. The block copolymer PS₆₉₉‐b‐P(MMA₂₃₂/MAA₅₈) obtained had a narrow molecular weight dispersity (Ð < 1.3). The structure of the precursor, PS‐b‐PMMA, and resultant polymer, was characterized and verified by FTIR and ¹H‐NMR spectroscopy as well as size exclusion chromatography. The self‐aggregation of PS₆₉₉‐b‐P(MMA₂₃₂/MAA₅₈) in organic solvents was monitored by UV spectroscopy, whereas the morphology and size of the formed microaggregates were investigated by transmission electron microscopy and dynamic light scattering. The results indicate that this copolymer formed regular spherical reverse micelles with a core–shell structure. The atomic force micrographs of PS₆₉₉‐b‐P(MMA₂₃₂/MAA₅₈) showed a rough surface morphology owing to microphase separation of the block copolymer. In addition, thermal characterization was performed by differential scanning calorimetry and thermogravimetric analysis. The glass transition temperature of PS₆₉₉‐b‐P(MMA₂₃₂/MAA₅₈) decreased significantly (65°C), when compared to PS and PMMA, suggesting that an enhanced movement of the polymer chains resulted by the segregation of the hydrolyzed P(MMA₂₃₂/MAA₅₈) block. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of inorganic salts on viscosity of acrylonitrile‐N‐vinylpyrrolidone copolymer solutions

Effects of inorganic salts on viscosities of dimethyl sulphoxide (DMSO) solutions of acrylonitrile(AN)/N‐vinylpyrrolidone(N‐VP) copolymer are discussed. Viscosity was determined by the rotary viscosimeter. It was shown that the solution viscosity decreases quickly with addition of KCl and NaCl and the effect of NaCl is more prominent than that of KCl. As concentration of KCl and NaCl went beyond 0.025 mol/L, the viscosity showed a trend of increase. The viscosity increased considerably with addition of FeCl₃ and CuCl₂. Changes in solution viscosity became less obvious with addition of ZnCl₂. As temperature increased, the viscosity of the copolymer solution containing NaCl decreased most quickly and the copolymer solution consisting of FeCl₃ showed the slowest decrease. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3492–3495, 2003     

Synthesis and characterization of methyl methacrylate/styrene hyperbranched copolymers via living radical mechanism

Free‐radical copolymerizations of N,N‐diethylaminodithiocarbamoylmethylstyrene (inimer: DTCS) with a methyl methacrylate (MMA)/zinc chloride (ZnCl₂) complex were carried out under UV light irradiation. DTCS monomers play an important role in this copolymerization system as an inimer that is capable of initiating living radical polymerization of the vinyl group. The reactivity ratios (r₁ = 0.56 and r₂ = 0.52: DTCS [M₁]; MMA [M₂]) obtained for this copolymerization system were different from a corresponding model system (alternating copolymer) of a styrene and MMA/ZnCl₂ complex (r₁ = 0.25 and r₂ = 0.056). It was found that the hyperbranched copolymers produced exhibited a random branching structure. It was found that the Lewis acid ZnCl₂ formed the complex not only with MMA but also with the carbamate group of inimer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2490–2495, 2003     

A novel thermosensitive triblock copolymer from 100% renewably sourced poly(trimethylene ether) glycol

Bio‐based amphiphilic triblock copolymers with 100% renewably sourced poly(trimethylene ether) glycol (PO3G) as the hydrophobic blocks and statistical copolymer of 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol)methacrylate (OEGMA) [P(MEO₂MA‐stat‐OEGMA)] as the hydrophilic blocks are synthesized and characterized. It is found that the molar ratio of MEO₂MA/OEGMA among the resulting copolymers is approximately 70/30. The degree of polymerization (DP) of P(MEO₂MA‐stat‐OEGMA) block ranges from 16 to 90, and the DP of PO3G block is fixed at 35. The amphiphilic copolymers could form core‐shell micelles self‐assembly in aqueous solution at low concentrations, and the micelles are in spherical shape with sizes varying from 121 to 188 nm. With the increasing length of hydrophilic blocks, the critical micelle concentration increases from 2.15 to 13.8 mg L^?1, and the lower critical solution temperature improves from 32.5 to 38.4 °C. The in vitro doxorubicin (DOX) release study shows that all DOX‐loaded micelles have a higher release rate at 37 °C than that at 25 °C. Cytotoxicity test reveals that the blank micelles are nearly nontoxic. These results indicate that the block copolymer micelles containing 100% renewably sourced PO3G can serve as a potential drug delivery carrier. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46112.     

A novel method for preparing silver/poly(siloxane‐b‐methyl methacrylate) nanocomposites with multiple properties in the DMF‐toluene mixture solvent

A novel method for preparing silver/poly(siloxane‐b‐methyl methacrylate) (Ag/(PDMS‐b‐PMMA)) hybrid nanocomposites was proposed by using the siloxane‐containing block copolymers as stabilizer. The reduction of silver nitrate (AgNO₃) was performed in the mixture solvent of dimethyl formamide (DMF) and toluene, which was used to dissolve double‐hydrophobic copolymer, as well as served as the powerful reductant. The presence of the PMMA block in the copolymer indeed exerted as capping ligands for nanoparticles. The resultant nanocomposites exhibited super hydrophobicity with water contact angle of 123.3^° and the thermogravimetry analysis (TGA) revealed that the resultant nanocomposites with more PDMS were more heat‐resisting. Besides, the antimicrobial efficiency of the most desirable nanocomposite (Ag/PDMS₆₅‐b‐PMMA₃₀ loaded with 7.3% silver nanoparticle) could reach up to 99.4% when contacting with escherichia coli within 120 min. As a whole, the resultant nanocomposites by the integration of excellent properties of silver nanoparticles as well as siloxane‐block copolymers can be a promising for the development of materials with hydrophobic, heat‐resisting and outstanding antibacterial properties from the chemical product engineering viewpoint. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4780–4793, 2013     

Vulcanization of chlorobutyl rubber. I. The identification of crosslink precursors in compounds containing ZnO/ZnCl2

Chlorinated poly(isoprene‐coisobutylene) (CIIR or chloro‐butyl) was characterized by Nuclear Magnetic Resonance. Compounds with ZnO, ZnCl₂, and ZnO/ZnCl₂ were vulcanized in a DSC at a programmed heating rate and isothermally at 150°C in a press. Crosslink densities were determined by swelling and extracted ZnCl₂ analyzed by atomic absorption. ZnCl₂ formation precedes crosslinking, and at equilibrium only 50% of the chlorine in the rubber is extractable as ZnCl₂. ZnCl₂ promotes crosslinking, and its addition to formulations decreases but does not eliminate the induction period prior to crosslinking. Dehydrohalogenation, which is catalyzed by ZnCl₂ in an autocatalytic process, is accompanied by the formation of conjugated diene butyl on the polymer chain. It is demonstrated that both species, not only ZnCl₂, are necessary precursors to crosslink formation. Moist ZnCl₂ catalyzes dehydrohalogenation but not crosslinking, while ZnO does not promote either reaction. CIIR can be crosslinked to polybutadiene and to polyisoprene, no induction period applying when ZnCl₂ is present in the formulation, and high crosslink densities develop in blends precipitated from solution. Severe reversion occurs in formulations where there is insufficient ZnO to trap all of the HCl evolved. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2290–2301, 2000     

Preparation and characterization of mPEG‐g‐α‐zein biohybrid micelles as a nano‐carrier

A new kind of block copolymer micelles methoxy polyethylene glycol (mPEG) grafted α‐zein protein (mPEG‐g‐α‐zein) was synthesized. The chemical composition of mPEG‐g‐α‐zein was identified with the help of FT‐IR and ¹H‐NMR. The biohybrid polymer can self‐assemble into spherical core–shell nanoparticles in aqueous solution. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to investigate the self‐assembled morphology of mPEG‐g‐α‐zein. Dynamic light scattering (DLS) results showed that the particle size of mPEG‐g‐α‐zein was about 90 nm. Moreover, the nanoparticles had a very low critical micelle concentration value with only 0.02 mg/mL. Then, the anticancer drug curcumin (CUR) was encapsulated into the biohybrid polymer micelles. The in vitro drug release profile showed a zero‐order release of CUR up to 12 h at 37°C. Cell viability studies revealed that the mPEG‐g‐α‐zein polymer exhibited low cytotoxicity for HepG2 cells (human hepatoma cells). Consequently, the mPEG‐g‐α‐zein micelles can be used as a potential nano‐carrier to encapsulate hydrophobic drugs and nutrients. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42555.     

Thermoplastic hydrogel based on pentablock copolymer consisting of poly(γ‐benzyl L‐glutamate) and poloxamer

A thermoplastic hydrogel based on a pentablock copolymer composed of poly(γ‐benzyl L ‐glutamate) (PBLG) and poloxamer was synthesized by polymerization of BLG N‐carboxyanhydride, which was initiated by diamine‐terminated groups located at the ends of poly(ethylene oxide) (PEO) chains of the poloxamer, to attain a new pH‐ and temperature‐sensitive hydrogel for drug delivery systems. Circular dichroism measurements in solution and IR measurements in the solid state revealed that the polypeptide block existed in the α‐helical conformation, as in the PBLG homopolymer. The intensity of the wide‐angle X‐ray diffraction patterns of the polymers depended on the poloxamer content in the copolymer and showed basically similar reflections to the PBLG homopolymer. The melting temperature (T_m) of the poloxamer in the copolymer was reduced with an increase of the PBLG block in comparison with the T_m of the poloxamer, which is indicative of a thermoplastic property. The water contents of the copolymers were dependent on the poloxamer content in the copolymers, for example, those for the GPG‐2 (48.7 mol % poloxamer) and GPG‐1 (57.5 mol % poloxamer) copolymers were 31 and 41 wt %, respectively, indicating characteristics of a polymeric hydrogel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2649–2656, 2003     

Crystallization behavior of “wet brush” and “dry brush” blends of PS‐b‐PEO‐b‐PS/h‐PEO

The crystallization behavior of the blending system consists of homopolymer poly(ethylene oxide) (h‐PEO) with different molecular weights, and polystyrene‐block‐poly (ethylene oxide)‐block‐polystyrene (PS‐b‐PEO‐b‐PS) triblock copolymer has been investigated by DSC measurements. The crystallization of PEO block (b‐PEO) in block copolymer occurs under much lower temperature than that of the h‐PEO in the bulk (ΔT > 65 °C), which is attributed to the homogeneous nucleation crystallization behavior of the b‐PEO microdomains. In both the “dry‐brush” and the “wet brush” blending systems, the homogeneous nucleation crystallization temperature of PS‐b‐PEO‐b‐PS/h‐PEO blends increases due to the increase of the domain size. The heterogeneous nucleation crystallization temperatures of h‐PEO in the wet brush blending systems are higher than that of the corresponding h‐PEO in the bulk. At the same time, the heterogeneous nucleation crystallization temperature of b‐PEO10000 decreases from 43°C to 30°C and 40°C in the h‐PEO600 and h‐PEO2000 blending systems, respectively, because of the stretching of the PEO chains in the wet brush. However, this kind of phenomenon does not happen in the dry brush blending systems. The self‐seeding procedure was used to further ascertain the nucleation mechanism in the crystallization process. As a result, the self‐seeding domains have been confirmed, and the difference between the dry brush and wet brush systems has been observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Self‐assembled structures in blends of disordered and lamellar block copolymers: SAXS,SANS and TEM study

BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self‐assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS‐block‐dPMMA)₁/(dPS‐block‐PMMA)₂, were investigated using small‐angle X‐ray scattering, small‐angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution‐cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with M_n by D ～ M_n^2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene‐block‐polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single‐domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self‐assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene‐block‐polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry     

Nano ZnO as cure activator and reinforcing filler in natural rubber

Zinc oxide (ZnO) nanoparticles of size 20–90 nm and surface area 9.56 m²/g were synthesized from ZnCl₂ and Chitosan and characterized by X‐ray diffraction, high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Natural rubber (NR) vulcanizates containing nano ZnO was prepared by mill mixing and characterized by SEM, energy dispersive X‐ray analysis (EDAX), and HRTEM. Cure characteristics, free volume studies, bound rubber, crosslink density, and dynamic mechanical properties were evaluated and compared with that of NR vulcanizate containing conventional micro ZnO. Considering the cure characteristics, it was found that NR vulcanizate with 0.5 phr (parts per 100 g rubber) of nano ZnO showed low values of optimum cure time (t₉₀) and very high cure rate index compared with 5 phr of conventional micro ZnO. The study shows that micro ZnO can be successfully replaced with nano ZnO for accelerated sulfur vulcanization process in NR, and preparation of vulcanizate containing nano ZnO with better properties as that of micro ZnO. The optimum dosage of nano ZnO as a cure activator in NR vulcanization was found to be 0.5 phr compared with conventional grade micro ZnO. This will lead to substantial cost reduction in the manufacture of rubber products and alleviate environmental pollution due to excess ZnO in rubber compounds. POLYM. ENG. SCI., 2013 © 2013 Society of Plastics Engineers     

pH‐responsive poly(ethylene glycol)‐poly(ϵ‐caprolactone)‐poly(glutamic acid) polymersome as an efficient doxorubicin carrier for cancer therapy

The synthesis, characterization and potential application in the doxorubicin (Dox) delivery system of a biodegradable polypeptide‐based block copolymer, poly(ethylene glycol)₂₀₀₀‐poly(?‐caprolactone)₆₀₀₀‐poly(glutamic acid)₁₀₀₀ (PEG₂₀₀₀‐PCL₆₀₀₀‐PGA₁₀₀₀), was investigated. The copolymer was synthesized via ring‐opening polymerization and characterized by ¹H NMR and Fourier transform IR. The synthesized copolymer could self‐assemble into aggregates and the critical aggregation concentration was 0.23 mg mL^?1. Transmission electron microscopy indicated that spherical polymersomes formed with a desirable size about 180 nm. Therefore Dox was encapsulated into these polymersomes, and then we investigated its applications in a drug delivery system. These Dox‐loaded polymersomes (PolyDox) were characterized by dynamic light scattering, zeta potential and pH responsiveness measurements. In vitro drug release indicated that the release rate of drug from PolyDox was pH‐responsive and significantly decreased. The drug pharmacokinetic parameters were improved in comparison to the group treated with free Dox, which proved the prolonged Dox release from PolyDox. A WST‐1 assay indicated a low toxicity and good compatibility of copolymer to cells within 48 h. The results also showed that PolyDox appeared to induce a higher anti‐tumor effect. Cell uptake results indicated that PolyDox displayed higher cellular uptake in A549 cells. Endocytosis inhibition results demonstrated that the internalization of PolyDox was mostly mediated by the fluid‐phase endocytosis pathway. © 2017 Society of Chemical Industry