Unusual Multilayered Structures in Poly(ethylene oxide)/Laponite Nanocomposite Films

Summary: The unusual structure of poly(ethylene oxide) (PEO) and Laponite clay in transparent nanocomposite films was investigated using scanning electron, atomic force, and optical microscopy, and X‐ray scattering. Each method is sensitive to different aspects of structural features and together they measure the resulting morphology and shear‐induced orientation. On nanometer length scales, clay platelets were found to orient in bundles while polymer crystallinity was suppressed. Microscopy led to the observation of unexpected and highly oriented multilayers on the micron length scale.

Scanning electron microscopy image of the freeze‐fractured surface of a poly(ethylene oxide)–Laponite film: the view on top of the x–y plane.     

Effects of hard‐segment polymers on CO2/N2 gas‐separation properties of poly(ethylene oxide)‐segmented copolymers

Poly(ethylene oxide)‐segmented polyurethanes (PEO‐PUs) and polyamides (PEO‐PAs) were prepared, and their morphology and CO₂/N₂ separation properties were investigated in comparison with those of PEO‐segmented polyimides (PEO‐PIs). The contents of the hard and soft segments in the soft and hard domains, W_HS and W_SH, respectively, were estimated from glass‐transition temperatures with the Fox equation. The phase separation of the PEO domains depended on the kind of hard‐segment polymer; that is, W_HS was in the order PU > PA ≫ PI for a PEO block length (n) of 45–52. The larger W_HS of PUs and PAs was due to hydrogen bonding between the oxygen of PEO and the NH group of urethane or amide. The CO₂/N₂ separation properties depended on the kind of hard‐segment polymer. Compared with PEO‐PIs, PEO‐PUs and PEO‐PA had much smaller CO₂ permeabilities because of much smaller CO₂ diffusion coefficients and somewhat smaller CO₂ solubilities. PEO‐PUs also had a somewhat smaller permselectivity because of a smaller solubility selectivity. This was due to the larger W_HS of PEO‐PUs and PEO‐PAs, that is, a greater contamination of PEO domains with hard urethane and amide units. For PEO‐PIs, with a decrease in n to 23 and 9, W_HS became large and CO₂ permeability decreased significantly, but the permselectivity was still at a high level of more than 50 at 35 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1707–1715, 2000     

Inverse gas chromatographic characterization of triblock copolymer of polystyrene–poly(ethylene oxide)–polystyrene

The thermodynamic properties of triblock copolymer of polystyrene–poly (ethylene oxide)–polystyrene (PS‐b‐PEO‐b‐PS) were investigated by means of inverse gas chromatography (IGC) using 15 different kinds of solvents as the probes. Some thermodynamic parameters, such as specific retention volume, molar heats of sorption, weight fraction activity coefficient, Flory‐Huggins interaction parameter, partial molar heats of mixing and solubility parameter were obtained to judge the interactions between PS‐b‐PEO‐b‐PS polymers and solvents and the solubility of the polymers in these solvents. It was found that increasing PEO content in PS‐b‐PEO‐b‐PS resulted in the increase in the solubility of PS‐b‐PEO‐b‐PS in alkanes and acetates solvents, but the solubility in alcohols had no change, and more PEO content in polymer caused a small decrease in the solubility parameter of PS‐b‐PEO‐b‐PS polymer, © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2015–2022, 2007     

Synthesis and self‐assembly morphologies of amphiphilic multiblock copolymers [poly(ethylene oxide)‐b‐polystyrene]n via trithiocarbonate‐embedded PEO macro‐RAFT agent

An amphiphilic multiblock copolymer [poly(ethylene oxide)‐b‐polystyrene]_n [(PEO‐b‐PS)_n] is synthesized by using trithiocarbonate‐embedded PEO as macro‐RAFT agent. PEO with four inserted trithiocarbonate (M_n = 9200 and M_w/M_n = 1.62) groups is prepared first by condensation of α, ω‐dihydroxyl poly(ethylene oxide) with S, S′‐Bis(α, α′‐dimethyl‐α″‐acetic acid)‐trithiocarbonate (BDATC) in the presence of pyridine, then a series of goal copolymers with different St units (varied from 25 to 218 per segment) are obtained by reversible addition‐fragmentation chain transfer (RAFT) polymerization. The synthesis process is monitored by size exclusion chromatography (SEC), ¹H NMR and FT‐IR. The self‐assembled morphologies of the copolymers are strongly dependent of the length of PS block chains when the chain length of PEO is fixed, some new morphologies as large leaf‐like aggregates (LLAs), large octopus‐like aggregates (LOAs), and coarse‐grain like micelles (CGMs) are observed besides some familiar aggregates as large compound vesicles (LCVs), lamellae and rods, and the effect of water content on the morphologies is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6071–6082, 2006     

Synthesis of branch‐ring‐branch tadpole‐shaped [linear‐poly(ε‐caprolactone)]‐b‐[cyclic‐poly(ethylene oxide)]‐b‐ [linear‐poly(ε‐caprolactone)] by combination of glaser coupling reaction with ring‐opening polymerization

A novel amphiphilic branch‐ring‐branch tadpole‐shaped [linear‐poly(ε‐caprolactone)]‐b‐[cyclic‐poly(ethylene oxide)]‐b‐[linear‐poly(ε‐caprolactone)] [(l‐PCL)‐b‐(c‐PEO)‐b‐(l‐PCL)] was synthesized by combination of glaser coupling reaction with ring‐opening polymerization (ROP) mechanism. The self‐assembling behaviors of (l‐PCL)‐b‐(c‐PEO)‐b‐(l‐PCL) and their π‐shaped analogs of poly(ε‐caprolactone)/poly(ethylene oxide)]‐b‐poly(ethylene oxide)‐b‐[poly(ε‐caprolactone)/poly(ethylene oxide) with comparable molecular weight in water were preliminarily investigated. The results showed that the micelles formed from the former took a fiber look, however, that formed from the latter took a spherical look. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis,characterization, effect of architecture on crystallization,and spherulitic growth of poly(L‐lactide)‐b‐poly(ethylene oxide) copolymers with different branch arms

Well‐defined poly(L ‐lactide)‐b‐poly(ethylene oxide) (PLLA‐b‐PEO) copolymers with different branch arms were synthesized via the controlled ring‐opening polymerization of L ‐lactide followed by a coupling reaction with carboxyl‐terminated poly(ethylene oxide) (PEO); these copolymers included both star‐shaped copolymers having four arms (4sPLLA‐b‐PEO) and six arms (6sPLLA‐b‐PEO) and linear analogues having one arm (LPLLA‐b‐PEO) and two arms (2LPLLA‐b‐PEO). The maximal melting point, cold‐crystallization temperature, and degree of crystallinity (X_c) of the poly(L ‐lactide) (PLLA) block within PLLA‐b‐PEO decreased as the branch arm number increased, whereas X_c of the PEO block within the copolymers inversely increased. This was mainly attributed to the relatively decreasing arm length ratio of PLLA to PEO, which resulted in various PLLA crystallization effects restricting the PEO block. These results indicated that both the PLLA and PEO blocks within the block copolymers mutually influenced each other, and the crystallization of both the PLLA and PEO blocks within the PLLA‐b‐PEO copolymers could be adjusted through both the branch arm number and the arm length of each block. Moreover, the spherulitic growth rate (G) decreased as the branch arm number increased: G_{6sPLLA‐b‐PEO} < G_{4sPLLA‐b‐PEO} < G_{2LPLLA‐b‐PEO} < G_{LPLLA‐b‐PEO}. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2034–2044, 2006     

Molecular weight dependence of phase behavior of PEO/P(EO‐b‐DMS) blends: Application of Sanchez‐Lacombe lattice fluid theory

Molecular weight dependence of phase separation behavior of the Poly (ethylene oxide) (PEO)/Poly(ethylene oxide‐block‐dimethylsiloxane) (P(EO‐b‐DMS)) blends was investigated by both experimental and theoretical methods. The cloud point curves of PEO/P(EO‐b‐DMS) blends were obtained by turbidity method. Based on Sanchez‐Lacombe lattice fluid theory (SLLFT), the adjustable parameter, (quantifying the interaction energy between different components), was evaluated by fitting the experimental data in phase diagrams. To calculate the spinodals, binodals, and the volume changes of mixing for these blends, three modified combining rules of the scaling parameters for the block copolymer were introduced. The calculated binodals with those modified combining rules show good agreement with the experimental data. Furthermore, the calculated volume changes during mixing decrease with increasing molecular weight of PEO, and the relationship between the volume changes and temperature is quite different for the mixtures with different molecular weight of PEO. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 452–459, 2008     

Synthesis of four‐armed poly(ε‐caprolactone)‐block‐poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four‐armed poly(?‐caprolactone)‐block‐poly(ethylene oxide) (PCL‐b‐PEO) copolymers were synthesized by ring‐opening polymerization of ethylene oxide in the presence of four‐armed poly(?‐caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt₂) as a catalyst. The chemical structure of PCL‐b‐PEO copolymer was confirmed by ¹H NMR and ¹³C NMR. The hydroxyl end groups of the four‐armed PCL were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four‐armed architecture of the copolymer. Physicochemical properties of the four‐armed block copolymers differed from their starting four‐armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four‐armed block copolymer increased with PEO length and PEO content. The micelle formation of the four‐armed block copolymer was examined by a fluorescent probe technique, and the existence of the critical micelle concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. The cmc value increased with increasing PEO length. The absolute cmc values were higher than those for linear amphiphilic block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 950–959, 2004     

Synthesis of amphiphilic tadpole‐shaped copolymers by combination of glaser coupling with living anionic polymerization and ring‐opening polymerization

The tadpole‐shaped copolymers polystyrene (PS)‐b‐[cyclic poly(ethylene oxide) (PEO)] [PS‐b‐(c‐PEO)] contained linear tail chains of PS and cyclic head chains of PEO were synthesized by combination of Glaser coupling with living anionic polymerization (LAP) and ring‐opening polymerization (ROP). First, the functionalized polystyrene‐glycerol (PS‐Gly) with two active hydroxyl groups at ω end was synthesized by LAP of St and the subsequent capping with 1‐ethoxyethyl glycidyl ether and then deprotection of protected hydroxyl group in acid condition. Then, using PS‐Gly as macroinitiator, the ROP of EO was performed using diphenylmethylpotassium as cocatalyst for AB₂ star‐shaped copolymers PS‐b‐(PEO‐OH)₂, and the alkyne group was introduced onto PEO arm end for PS‐b‐(PEO‐Alkyne)₂. Finally, the intramolecular cyclization was performed by Glaser coupling reaction in pyridine/Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine system under room temperature, and tadpole‐shaped PS‐b‐(c‐PEO) was formed. The target copolymers and their intermediates were well characterized by size‐exclusion chromatography, proton nuclear magnetic resonance spectroscopy, and fourier transform infrared spectroscopy in details. The thermal properties was also determined and compared to investigate the influence of architecture on properties. The results showed that tadpole‐shaped copolymers had lower T_m, T_c, and X_c than that of their precursors of AB₂ star‐shaped copolymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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

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

Water‐soluble poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) copolymer: Synthesis and characterization

Water‐soluble and photoluminescent block copolymers [poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) (PEO‐b‐PPV)] were synthesized, in two steps, by the addition of α‐halo‐α′‐alkylsulfinyl‐p‐xylene from activated poly(ethylene oxide) (PEO) chains in tetrahydrofuran at 25 °C. This copolymerization, which was derived from the Vanderzande poly(p‐phenylene vinylene) (PPV) synthesis, led to partly converted PEO‐b‐PPV block copolymers mixed with unreacted PEO chains. The yield, length, and composition of these added sequences depended on the experimental conditions, namely, the order of reagent addition, the nature of the monomers, and the addition of an extra base. The addition of lithium tert‐butoxide increased the length of the PPV precursor sequence and reduced spontaneous conversion. The conversion into PPV could be achieved in a second step by a thermal treatment. A spectral analysis of the reactive medium and the composition of the resulting polymers revealed new evidence for an anionic mechanism of the copolymerization process under our experimental conditions. Moreover, the photoluminescence yields were strongly dependant on the conjugation length and on the solvent, with a maximum (70%) in tetrahydrofuran and a minimum (<1%) in water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4337–4350, 2005     

The influence of variant PE‐b‐PEO segments on physical properties of LLDPE graft copolymers

A method was adopted to fix a series of polymers of PE‐b‐PEO with different PEO/PE segments on the chains of LLDPE. Maleic anhydride (MA) reacting with hydroxyl group of PE‐b‐PEO (mPE‐b‐PEO) was used as the intermediate. The structures of intermediates and graft copolymers were approved by ¹H NMR and FTIR. XPS analysis revealed a great amount of oxygen on the surface of grafted copolymers although the end group of PEO was fixed on the LLDPE chains through MA. Thermal properties of the graft copolymers as determined by differential scanning calorimetry (DSC) showed that PE segments in the grafted monomers could promote the heterogeneous nucleation of the polymer, increase T_c, and crystal growth rate. While the amorphous PEO segments which attached to the crystalline PE segments in LLDPE, impaired their ability to fit the crystal lattice, and depressed the crystallization of LLDPE backbones. In this study, it was also verified through the dynamic rheological data that increasing M_n of grafted monomers significantly increased the complex viscosity and enhanced the shear‐thinning behavior. Long‐branched chains formed by grafted monomers enhanced the complex moduli (G′ and G″) value and retarded relaxation rate. However, there were little influence on the rheological properties when increasing the amounts of PEO segments (or decreasing PE segments) of grafted monomers with similar molecular weight. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 506–515, 2008     

Preparation of amphiphilic poly(ethylene oxide)‐block‐polystyrene macrocycles via glaser coupling reaction under CuBr/pyridine system

The amphiphilic cyclic poly(ethylene oxide)‐block‐polystyrene [c‐(PEO‐b‐PS)] was synthesized by cyclization of propargyl‐telechelic poly(ethylene oxide)‐block‐polystyrene‐block‐poly(ethylene oxide) (?? PEO‐b‐PS‐b‐PEO? ?) via the Glaser coupling. The hydroxyl‐telechelic ABA triblock PEO‐b‐PS‐b‐PEO was first prepared by successive living anionic polymerization of styrene and ring‐opening polymerization of ethylene oxide, and then the hydroxyl ends were reacted with propargyl bromide to obtain linear precursors with propargyl terminals. Finally, the intramolecular cyclization was conducted in pyridine under high dilution by Glaser coupling of propargyl ends in the presence of CuBr under ambient temperature, and the c‐(PEO‐b‐PS) was directly obtained by precipitation in petroleum ether with high efficiency. The cyclic products and their corresponding linear precursor ?? PEO‐b‐PS‐b‐PEO? ? were characterized by means of GPC, ¹H NMR, and FTIR. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of comb‐like copolymers with amphiphilic poly(ethylene oxide)‐b‐polystyrene graft chains by combination of “graft from” and “graft onto” strategies

A novel method for preparation the comb‐like copolymers with amphihilic poly(ethylene oxide)‐block‐poly(styrene) (PEO‐b‐PS) graft chains by “graft from” and “graft onto” strategies were reported. The ring‐opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using α‐methoxyl‐ω‐hydroxyl‐poly(ethylene oxide) (mPEO) and diphenylmethyl potassium (DPMK) as coinitiation system, then the EEGE units on resulting linear copolymer mPEO‐b‐Poly(EO‐co‐EEGE) were hydrolyzed and the recovered hydroxyl groups were reacted with 2‐bromoisobutyryl bromide. The obtained macroinitiator mPEO‐b‐Poly(EO‐co‐BiBGE) can initiate the polymerization of styrene by ATRP via the “Graft from” strategy, and the comb‐like copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐PS] were obtained. Afterwards, the TEMPO‐PEO was prepared by ring‐opening polymerization (ROP) of EO initiated by 4‐hydroxyl‐2,2,6,6‐tetramethyl piperdinyl‐oxy (HTEMPO) and DPMK, and then coupled with mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐PS] by atom transfer nitroxide radical coupling reaction in the presence of cuprous bromide (CuBr)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) via “Graft onto” method. The comb‐like block copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐(PS‐b‐PEO)] were obtained with high efficiency (≥90%). The final product and intermediates were characterized in detail. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1930–1938, 2009     

Block copolymers of poly(ethylene oxide) and poly(vinyl alcohol) synthesized by the RAFT methodology

A methodology for the synthesis of well‐defined poly(ethylene oxide)‐block‐poly(vinyl alcohol) (PEO‐b‐PVA) and PVA‐b‐PEO‐b‐PVA polymers was reported. Novel xanthate end‐functionalized PEOs were synthesized by a series of end‐group transformations. They were then used to mediate the reversible addition–fragmentation chain transfer polymerization of vinyl acetate to obtain well‐defined poly(ethylene oxide)‐b‐poly(vinyl acetate) (PEO‐b‐PVAc) and PVAc‐b‐PEO‐b‐PVAc. When these block copolymers were directly hydrolyzed in methanol solution of sodium hydroxide, polymers with brown color were obtained, which was due to the formation of conjugated unsaturated aldehyde structures. To circumvent these side reactions, the xanthate groups were removed by adding a primary amine before hydrolysis and the products thus obtained were white powders. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy and FT‐IR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1901–1910, 2009     

Shape memory polymers with interconnected nanopores and high mechanical strength

The fabrication of shape memory polymers with both interconnected nanopores and high mechanical strength is challenging. In this work, porous shape memory polymers (PSMPs) were prepared based on the combination of crystallization and phase separation in a ternary blend of poly(l ‐lactic acid)/polyvinyl acetate/poly(ethylene oxide) (i.e., PLLA/PVAc/PEO). The phase separation between the PLLA and PVAc/PEO resulted in bicontinuous structures in microscale including a PLLA‐rich phase and a mixed PVAc/PEO phase. On one hand, the continuous PLLA‐rich phase contributed to the high mechanical strength and shape memory performance, in which tiny crystals and amorphous matrix of PLLA act as the shape fixed phase and reversible phase, respectively. On the other hand, the crystallization of PEO in the miscible PVAc/PEO blend produced submicrometer bicontinuous structures. The interconnected nanopores have been obtained by selective etching of the PEO. Our strategy opens a new avenue for fabricating PSMPs with both interpenetrated channels and high strength. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 125–130     

Synthesis of poly(N,N‐dimethylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N,N‐dimethylacrylamide) and its application for separation of proteins by capillary zone electrophoresis

A series of well‐defined triblock copolymers, poly(N, N‐dimethylacrylamide)‐block‐poly(ethylene oxide)‐block‐poly(N, N‐dimethylacrylamide) (PDMA‐b‐PEO‐b‐PDMA) synthesized by atom transfer radical polymerization, were used as physical coatings for protein separation. A comparative study of EOF showed that the triblock copolymer presented good capillary coating ability and EOF efficient suppression. The effects of the M_r of PDMA block in PDMA‐b‐PEO‐b‐PDMA triblock copolymer and buffer pH on the separation of basic protein for CE were investigated. Moreover, the influence of the copolymer structure on separation of basic protein was studied by comparing the performance of PDMA‐b‐PEO‐b‐PDMA triblock copolymer with PEO‐b‐PDMA diblock copolymer. Furthermore, the triblock copolymer coating showed higher separation efficiency and better migration time repeatability than fused‐silica capillary when used in protein mixture separation and milk powder samples separation, respectively. The results demonstrated that the triblock copolymer coatings would have a wide application in the field of protein separation.     

Effects of Br connected groups on atom transfer nitroxide radical coupling reaction and its application in the synthesis of comb‐like block copolymers

The effects of Br connected groups on atom transfer nitroxide radical coupling (ATNRC) reaction were investigated. Two precursors methoxyl poly(ethylene oxide)‐b‐poly(ethylene oxide‐co‐2‐bromoiso butyryloxy glycidyl ether) (mPEO‐b‐Poly(EO‐co‐BiBGE)) and methoxyl poly(ethylene oxide)‐b‐poly(2‐bromoiso butyryloxy glycidyl ether) (mPEO‐b‐Poly(BiBGE)) with different ? C(CH₃)₂Br density were designed and synthesized firstly, and then ATNRC reaction were completed between these precursors and 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy poly(ε‐caprolactone) (TEMPO‐PCL) in the presence or absence of St monomers, respectively. The results showed that the structure of Br connected groups showed an important effect on ATNRC reaction, and the ATNRC reaction with high efficiency could be realized by transforming the higher active Br connected groups into the lower one by the addition of small amount of St monomers. The final comb‐like block copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐(St_1.8‐b‐PCL)] and mPEO‐b‐[Poly(Gly)‐g‐(St_2.4‐b‐PCL)] with high coupling efficiency were obtained by this strategy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1633–1640, 2010     

Influence of Structural Features on the Cellular Uptake Behavior of Non‐Targeted Polyester‐Based Nanocarriers

The development of delivery systems efficiently uptaken by cells is of due importance since sites of drug action are generally localized in subcellular compartments. Herein, naked and core–shell polymeric nanoparticles (NPs) have been produced from poly(lactic‐co‐glycolic acid)—PLGA, poly(ethylene oxide)‐b‐poly(ε‐caprolactone)—PEO‐b‐PCL, and poly(ethylene oxide)‐b‐poly(lactic acid)—PEO‐b‐PLA. The nanostructures are characterized and the cellular uptake behavior is evaluated. The data evidence that cellular uptake is enhanced as the length of the hydrophilic PEO‐stabilizing shell reduces and that high negative surface charge restricts cellular uptake. Furthermore, NPs of higher degree of hydrophobicity (PEO‐b‐PCL) are more efficiently internalized as compared to PEO‐b‐PLA NPs. Accordingly, taking into account our recent published results 1 and the findings of the current investigation, there should be a compromise regarding protein fouling and cellular uptake as resistance to nonspecific protein adsorption and enhanced cellular uptake are respectively directly and inversely related to the length of the PEO‐stabilizing shell.

     

Tuning microdomain spacing with light using ortho‐nitrobenzyl‐linked triblock copolymers

Using sequential RAFT polymerization, single monomer insertion, and “click” chemistry, a series of triblock copolymers, poly(ethylene oxide)‐b‐polystyrene‐b‐poly(ethylene oxide), PEO‐b‐PS‐b‐PEO, were synthesized, where one of the two junction points is a UV cleavable ortho‐nitrobenzyl (ONB). Ordered patterns of PEO‐b‐PS‐b‐PEO were produced by solvent vapor annealing. Upon exposure to ultraviolet (UV) light, the PEO‐b‐PS‐b‐PEO was converted into a mixture of a PEO homopolymer and a PS‐b‐PEO diblock copolymer. It was found that the microdomain spacing could be tuned by adjusting the UV exposure time, due to the change in the copolymer architecture and the swelling of the PEO microdomain by the PEO homopolymer produced. By selective area exposure of the PEO‐b‐PS‐b‐PEO thin films, the domain spacing was changed over selected locations across the film, generating patterns of different microdomain sizes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 355–361.