Barrier films made with various lamellar block copolymers

The permeabilities of helium, nitrogen, and oxygen across lamellar block copolymers can be accurately estimated from the properties of the glassy and rubbery blocks. The copolymers tested include poly(styrene-b-isoprene-b-styrene), poly(styrene-b-butadience-b-styrene), and poly(lactide-b-isoprene-b-lactide). The results show improvements in barrier properties that tend to be larger than those expected from the resistances of lamellae in series. These increases are not as large as those achieved with impermeable fillers like mica and clay. The changes in film elastic modulus caused by glassy lamellae are also discussed.     

Characterizations of Some N—Substituted—salicylhydrazide in Mixtures by NMR Diffusion Ordered Spectroscopy

1 INTRODUCTION Metallacrown has emerged as inorganic host molecules. There has been considerable interest in metallacrown chemistry owing to its potential applications in chemically modified electrodes, anion-selective separation agents, liquid-crystal precursors and magnetic materials[1]. Multidentate ligands which can bridge two metal ions are used to synthesize metallacrowns. The cyclic repetition of the ligand bridging two metal ions generates the macrocyclic metal cluster. In the c…     

Analysis of Carbohydrate Mixtures by Diffusion Difference NMR Spectroscopy

Summary.  Diffusion difference NMR spectroscopy can be used as a fast and powerful tool to separate carbohydrates in a mixture by their translational diffusion properties. This method is of general interest for analyzing natural and synthetic mixtures and for monitoring and optimizing synthetic reactions. The proposed subtraction procedure applied to two varying diffusion encoded spectra can be combined with homo- and heteronuclear as well as with one- and multi-dimensional NMR experiments. Received November 26, 2001. Accepted November 30, 2001     

Using Fractionation and Diffusion Ordered Spectroscopy to Study Lignin Molecular Weight.

Recent reports demonstrate that applications of the biopolymer lignin can be helped by the use of a fraction of the lignin which has an optimal molecular weight range. Unfortunately, the current methods used to determine lignin's molecular weight are inconsistent or not widely accessible. Here, an approach that relies on 2D DOSY NMR analysis is described that provides a measure of lignin's molecular weight. Consistent results were obtained using this well-established NMR technique across a range of lignins.     

Characterization of propylene-ethylene block copolymers using solid state 13C-NMR spectroscopy

Commercial block copolymers of propylene with ethylene (PEBC) are multiphase systems comprising block and random copolymers as well as small amounts of homopolymers. At present, no satisfactory method exists for characterizing the “blocky” structure of these copolymers. This article aims to fulfill this need. Accordingly, the block and random copolymers of propylene with ethylene have been investigated using ¹³C CP/MAS NMR with high-power dipolar decoupling. Comparisons have been made between the spectra of block and random copolymers and it is shown possible to distinguish between them by means of an additional signal, appearing at 32.5δ, in block copolymers (attributable to block junctions). © 1992 John Wiley & Sons, Inc.     

The metathetic degradation of polyisoprene and polybutadiene in block copolymers using Grubbs second generation catalyst

A degradation study of polystyrene-polybutadiene-polystyrene and polyisoprene-polystyrene-polyisoprene in both dichloromethane and hexane solvents is presented. Alternative solvents for metathetic degradation provide the potential for greener chemistry, better selectivity, and control over the products. The catalyst concentration and solvent selection both determine the products formed. The degradation of polyisoprene and polybutadiene in a particular solvent was controlled by the solubility of polyisoprene/polybutadiene, and by its solubility relative to polystyrene. A large difference in solubility between the polymers in the selected solvent provides an additional driving force for block separation, encouraging reaction close to the interface between different blocks. Furthermore, solubility of the block copolymer speeds the degradation reaction. This tailoring of the reaction mechanism yields a new control over the products of polymer degradation.     

Solution-State 2D NMR Spectroscopy of Mixtures HyperpolarizedUsing Optically Polarized Crystals

The HYPNOESYS method (Hyperpolarized NOE System), which relies on the dissolution of optically polarized crystals, has recently emerged as a promising approach to enhance the sensitivity of NMR spectroscopy in the solution state. However, HYPNOESYS is a single-shot method that is not generally compatible with multidimensional NMR. Here we show that 2D NMR spectra can be obtained from HYPNOESYS-polarized samples, using single-scan acquisition methods. The approach is illustrated with a mixture of terpene molecules and a benchtop NMR spectrometer, paving the way to a sensitive, information-rich and affordable analytical method.     

Accelerating Diffusion‐Ordered NMR Spectroscopy by Joint Sparse Sampling of Diffusion and Time Dimensions

Diffusion‐ordered multidimensional NMR spectroscopy is a valuable technique for the analysis of complex chemical mixtures. However, this method is very time‐consuming because of the costly sampling of a multidimensional signal. Various sparse sampling techniques have been proposed to accelerate such measurements, but they have always been limited to frequency dimensions of NMR spectra. It is now revealed how sparse sampling can be extended to diffusion dimensions.     

Synthesis of polypeptide/inorganic hybrid block copolymers

Polypeptide/inorganic hybrid copolymers were obtained by a four-step synthetic approach combining (i) atom transfer polymerization of tert-butyl acrylate, (ii) chemical modification of the bromo end groups of ATRP-polymers into primary amino group using Gabriel reaction, (iii) ring opening polymerization of N_ε-trifluoroacetyl-l-lysine or γ-benzyl-l-glutamate N-carboxyanhydrides followed by (iv) the transamidification reaction using a large excess of (3-aminopropyl)trimethoxysilane to substitute the tert-butyl groups of the poly(tert-butyl acrylate) block. Products were characterized using ¹H NMR, FT-IR, DSC and MALDI-TOF MS. These techniques proved that polymerization of tert-butyl acrylate was controlled whatever the molecular weight targeted and that bromide was quantitatively converted to amino end group by a original method leading to the synthesis of copolymers in the presence of N-carboxyanhydrides as monomers. Amphiphilic polypeptide/inorganic hybrid copolymers were then achieved.     

Thermal transitions in associating aqueous block copolymers: light scattering,rheology and spectroscopy

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO–PPO–PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (¹H NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer–micelle equilibrium and the micelle–liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity–intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in ¹H NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle–liquid crystalline thermal transition. Similar results were obtained from the line width of ²H NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively.     

Surface patterns of block copolymers in thin layers after vapor treatment

A systematic study of formation of surface patterns in block copolymer thin layers after their exposure to solvent vapors was performed. The studied effect involves layers of thickness approximately equal to the ordering size of polymers - about 45 nm. Experiments were performed on three styrene - methacrylate derivative block copolymers, synthesized by living anionic polymerization: poly(4-octylstyrene)-block-poly(butyl methacrylate), poly(4-fluorostyrene)-block-poly(butyl methacrylate) and poly(p-octylstyrene)-block-poly(methyl methacrylate). The polymers were exposed to vapors of chloroform, 1,4-dioxane, hexane, acetone and tetrahydrofuran.     

Investigation of the microstructure of metallocene-catalyzed norbornene–ethylene copolymers using NMR spectroscopy

Norbornene–ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl) zirconium dichloride with MAO, and their microstructure was characterized with ¹H-NMR and ¹³C-NMR methods. From a Cosy ¹H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using ¹³C-¹H correlations, hmqc for one-bond correlations, and hmbc for two- or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy ¹H-NMR spectrum revealed a new crosspeak which, according to the corresponding ¹³C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1633–1638, 1998     

Design of water-soluble block copolymers containing poly(4-vinylpyridine) by atom transfer radical polymerization

The preparation of block copolymers consisting of poly(4-vinylpyridine) (P4VP) by atom transfer radical polymerization (ATRP) was investigated. The goal was to synthesize water-soluble block copolymers with poly(ethylene oxide) (PEO) as first block, a water-soluble polymer at any pH. First, a PEO macroinitiator was prepared for the ATRP block copolymerization of 4-vinylpyridine. In the second stage, the kinetic behaviour of this block copolymerization was investigated for two different types of PEO-macroinitiators and catalyst systems, based on CuCl or CuCl₂/Cu(0), with tris[2-(dimethylamino)ethyl]amine (Me₆-TREN) as the ligand. Various combinations of initiator and catalyst led to a controlled block copolymerization with optimized results obtained for chlorinated poly(ethylene glycol) monomethyl ether as macroinitiator, together with CuCl₂/Cu(0)/Me₆-TREN as catalyst system. With the latter system, narrow polydispersities (1.25) could be reached for PEO-P4VP block copolymers.     

Synthesis and characterization of sulphonated PEES copolymers by NMR spectroscopy

Two sulphonated PEES copolymers were synthesized by reacting 75 or 60 mol% silylated hydroquinone sulphonic acid and 25 or 40 mol% of hydroquinone with 4,4′-difluorodiphenyl sulphone. The number average molecular weights determined by GPC were 13.250 and 12.050 g/mol. In the FTIR spectra, in addition to the characteristic absorption bands due to aromatic skeleton, absorption bands associated with sulphonic acid groups were observed at ∼3500, 1172, 1080, 1026, and 706 cm⁻¹. In ¹H NMR, the aromatic proton resonance signals were observed between δ = 6.99 and 7.96 ppm. ¹³C{¹H} NMR spectra of these copolymers were complex and in order to resolve this, two-dimensional (2D) NMR techniques were utilized. Heteronuclear single quantum coherence (HSQC), total correlated spectroscopy (TOCSY), and heteronuclear multiple bond correlation (HMBC) were used for assigning the structure of the copolymers.     

Solid‐state 13C, 15N and 29Si NMR characterization of block copolymers with CO2 capture properties

Natural abundance solid‐state multinuclear (¹³C, ¹⁵N and ²⁹Si) cross‐polarization magic‐angle‐spinning NMR was used to study structures of three block copolymers based on polyamide and dimethylsiloxane and two polyamides, one of which including ferrocene in its structure. Assignment of most of the resonance lines in ¹³C, ¹⁵N and ²⁹Si cross‐polarization magic‐angle‐spinning NMR spectra were suggested. A comparative analysis of ¹³C isotropic chemical shifts of polyamides with and without ferrocene has revealed a systematic shift towards higher δ ‐values (de‐shielding) explained as the incorporation of paramagnetic ferrocene into the polyamide backbone. In addition, the ¹³C NMR resonance lines for ferrocene‐based polyamide were significantly broadened, because of paramagnetic effects from ferrocene incorporated in the structure of this polyamide polymer. Single resonance lines with chemical shifts ranging from 88.1 to 91.5 ppm were observed for ¹⁵N sites in all of studied polyamide samples. ²⁹Si chemical shifts were found to be around ?22.4 ppm in polydimethylsiloxane samples that falls in the range of chemical shifts for alkylsiloxane compounds. The CO₂ capture performance of polyamide‐dimethylsiloxane‐based block copolymers was measured as a function of temperature and pressure. The data revealed that these polymeric materials have potential to uptake CO₂ (up to 9.6 cm³ g^?1) at ambient pressures and in the temperature interval 30–40 °C. Copyright © 2016 John Wiley & Sons, Ltd.     

Interactions of amphiphilic block copolymers with lipid model membranes

Studies on interactions between amphiphilic block copolymers and lipid membranes have been focused traditionally on ABA triblock copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), widely due to their commercial availability. However, new architectures of amphiphilic block copolymer have been synthesized in recent years partially taking advantage of new polymerization techniques. This review focuses on amphiphilic block copolymers with potential biological activity and on model membrane systems used for studying interactions with such block copolymers. Experimental methods to study block copolymer–phospholipid interactions in Langmuir monolayers, liposomes, and planar bilayers are summarized. This work is intended to convey a better understanding of amphiphilic block copolymers used for in vitro and in vivo experiments in medicine and pharmacy. Recent developments and open questions are addressed.     

2H NMR研究嵌段共聚物溶致液晶相的结构演化与水分子动力学行为

采用2H NMR实验结合谱图线型的理论模拟方法研究了两亲性嵌段共聚物聚氧乙烯一聚氧丙烯一聚氧乙烯／氘代水／对二甲苯三元体系形成的不同液晶相的结构演化和水分子动力学行为．结果表明,对不同组分浓度的样品,2H谱线型发生明显的变化,对应体系从各向同性相、六角相和层状相间的系列结构转变．通过NMR弛豫模型获得了液晶相结构演化中序参数和分子运动相关时间的变化规律,理论模拟获得的自旋．晶格弛豫时间T1、自旋-自旋弛豫时乃等水分子动力学参数与实验测量结果吻合．结果表明：层状相四极劈裂及序参数随嵌段共聚物或二甲苯含量的增加呈现一个极大值,水分子的兀随着嵌段共聚物浓度增加而明显减小,而疋在六角相到层状相的转变中发生了明显的变化．研究表明,通过理论模拟2HNMR实验获得的谱图线型是研究液晶相结构演化和动力学的有力工具．     

Rapid Characterization of Molecular Diffusion by NMR Spectroscopy

An NMR‐based approach for rapid characterization of translational diffusion of molecules has been developed. Unlike the conventional method of acquiring a series of 2D ¹³C and ¹H spectra, the proposed approach involves a single 2D NMR spectrum, which can be acquired in minutes. Using this method, it was possible to detect the presence of intermediate oligomeric species of diphenylalanine in solution during the process of its self‐assembly to form nanotubular structures.     

环境响应性嵌段共聚物的合成、自组装及应用研究进展

近年来具有环境响应性的嵌段共聚物的研发受到了人们的广泛关注。该类型共聚物可以对外界环境刺激产生相应的结构、物理及化学性能的变化。根据外界环境刺激响应机理及类型的不同,可将其分为单一因素、双重因素以及三重因素刺激响应性嵌段共聚物三大类。针对每一类体系,本文重点综述了嵌段共聚物的设计合成、自组装以及应用等研究现状,并概括总结了各种有序聚集体(如胶束、囊泡等)随外界环境刺激(如pH、温度、光、CO_2、氧化还原剂等)所作出的响应性变化。最后,对智能型嵌段共聚物在药物控释、纳米容器制备、生物功能材料等方面潜在的应用价值和今后可能的发展方向进行了展望。