Melting behavior of ethylene oxide–propylene oxide (sym-PEP) block copolymers

Melting points and lamellar thicknesses have been measured for ethylene oxide–propylene oxide block copolymers (sym-PEP) with central poly(ethylene oxide) block lengths of 70–100 chain units and end poly(propylene oxide) block lengths of 0–30 chain units. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by an amount (up to 15°C) which increases as the poly(propylene oxide) block length increases. Most samples have more than one melting transition, which can be assigned to variously folded chain crystals. End interfacial free energies σ_e for the various crystals have been estimated by use of Flory's theory of melting of block copolymers. For a given crystal type (e.g., once-folded-chain) σ_e is higher the longer the chain length of the end poly(propylene oxide) blocks. For a given copolymer σ_e is lower, the more highly folded the poly(ethylene oxide) chain.     

Synthesis and characterization of ABA‐type amphiphilic tri‐block copolymers through anionic polymerization using end functionalized poly(ethylene oxide) oligomers

ABA‐type amphiphilic tri‐block copolymers were successfully synthesized from poly(ethylene oxide) derivatives through anionic polymerization. When poly(styrene) anions were reacted with telechelic bromine‐terminated poly(ethylene oxide) ( 1 ) in 2:1 mole ratio, poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers were formed. Similarly, stable telechelic carbanion‐terminated poly(ethylene oxide), prepared from 1,1‐diphenylethylene‐terminated poly (ethylene oxide) ( 2 ) and sec‐BuLi, was also used to polymerize styrene and methyl methacrylate separately, as a result, poly (styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) and poly (methyl methacrylate)‐b‐poly(ethylene oxide)‐b‐poly(methyl methacrylate) tri‐block copolymers were formed respectively. All these tri‐block copolymers and poly(ethylene oxide) derivatives, 1 and 2 , were characterized by spectroscopic, calorimetric, and chromatographic techniques. Theoretical molecular weights of the tri‐block copolymers were found to be similar to the experimental molecular weights, and narrow polydispersity index was observed for all the tri‐block copolymers. Differential scanning calorimetric studies confirmed the presence of glass transition temperatures of poly(ethylene oxide), poly(styrene), and poly(methyl methacrylate) blocks in the tri‐block copolymers. Poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers, prepared from polystyryl anion and 1 , were successfully used to prepare micelles, and according to the transmission electron microscopy and dynamic light scattering results, the micelles were spherical in shape with mean average diameter of 106 ± 5 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Crystallization of polystyrene–poly(ethylene oxide) multiblock copolymers

The heat of fusion of poly(ethylene oxide) blocks has been measured by DSC on twelve polystyrene–poly(ethylene oxide) multiblock (AB)_n copolymers and two ABA triblock copolymers after conditioning at various times and temperatures. Regardless of the length of polystyrene blocks, copolymers with poly(ethylene oxide) blocks with M?_n = 404 showed no heat of fusion, those with M?_n = 900 almost no peaks, those with M?_n = 1960 small broad peaks, and those with M?_n = 5650 clearly observable peaks. the greatest heat of fusion measured for block copolymers was 60–70% of the value for hompolymer. Small-angle x-ray patterns are given. The relation between crystal growth and block length is discussed.     

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     

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.     

Study of molecular motion of block copolymers in solution by high-resolution proton magnetic resonance

Molecular motions of hydrophobic–hydrophilic water-soluble block copolymers in solution were investigated by high-resolution proton magnetic resonance (NMR). Samples studied include block copolymers of polystyrene–poly(ethylene oxide), polybutadiene–poly(ethylene oxide), and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide). NMR measurements were carried out varying molecular weight, temperature, and solvent composition. For AB copolymers of polystyrene and poly(ethylene oxide), two peaks caused by the phenyl protons of low-molecular-weight (M?_n = 3,300) copolymer were clearly resolved in D₂O at 100°C, but the phenyl proton peaks of high-molecular-weight (M?_n = 13,500 and 36,000) copolymers were too broad to observe in the same solvent, even at 100°C. It is concluded that polystyrene blocks are more mobile in low-molecular-weight copolymer in water than in high-molecular-weight copolymer in the same solvent because the molecular weight of the polystyrene block of the low-molecular-weight copolymer is itself small. In the mixed solvent D₂O and deuterated tetrahydrofuran (THF-d₈), two peaks caused by the phenyl protons of the high-molecular-weight (M?_n = 36,000) copolymer were clearly resolved at 67°C. It is thought that the molecular motions of the polystyrene blocks are activated by the interaction between these blocks and THF in the mixed solvent.     

Double hydrophilic block copolymers of sodium(2‐sulfamate‐3‐carboxylate)isoprene and ethylene oxide

Poly(sodium(2‐sulfamate‐3‐carboxylate)isoprene)‐b‐poly(ethylene oxide) and poly(ethylene oxide)‐b‐poly(sodium(2‐sulfamate‐1‐carboxylate)isoprene)‐b‐poly(ethylene oxide) double hydrophilic block copolymers were prepared by selective post polymerization reaction of the polyisoprene block, of poly(isoprene‐b‐ethylene oxide) diblocks or poly(ethylene oxide‐b‐isoprene‐b‐ethylene oxide) triblock precursors, with N‐chlorosulfonyl isocyanate. The precursors were synthesized by anionic polymerization high vacuum techniques and had narrow molecular weight distributions and predictable molecular weights and compositions. The resulting double hydrophilic block copolymers were characterized by FTIR and potentiometric titrations in terms of the incorporated functional groups. Their properties in aqueous solutions were studied by viscometry and dynamic light scattering. The latter techniques revealed a complex dilute solution behavior of the novel block copolymers, resulting from the polyelectrolyte character of the functionalized PI block and showing a dependence on solution ionic strength and pH. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 606–613, 2006     

Melting points of homogeneous random copolymers of ethylene and 1-alkenes

Melting points of copolymers of ethylene and 1-alkenes ranging from 1-butene to 1-octadecene have been determined. The copolymers were prepared by means of a homogeneous Et₃Al₂Cl₃/VOCl₃ initiating system so that in individual samples, comonomer contents do not vary with molecular weight. Evidence is presented for a random distribution of comonomer units in the copolymers. Melting points determined by differential scanning calorimetry are essentially independent of branch length at low comonomer contents. At higher comonomer contents (5–9 mol% 1-alkene), melting points decrease in the order 1-butene > 1-octene > 1-octadecene copolymers. The weight fraction of ethylene sequences drops to less than 60% in copolymers with 1-octadecene of high comonomer content and this results in a reduction in the crystallite thicknesses attained by these copolymers.     

β‐Lactam functionalized poly(isoprene‐b‐ethylene oxide) amphiphilic block copolymers

Amphiphilic block copolymers containing β‐lactam groups on the polyisoprene block were synthesized from poly(isoprene‐b‐ethylene oxide) (IEO) diblock copolymer precursors, prepared by anionic polymerization. β‐Lactam functionalization was achieved via reaction of the polyisoprene (PI) block with chlorosulfonyl isocyanate and subsequent reduction. The resulting block copolymers were molecularly characterized by SEC, FTIR, and NMR spectroscopies and DSC. Functionalization was found to proceed in high yields, altering the solubility properties of the PI block and those of the functionalized diblocks. Hydrogen bond formation is assumed to be responsible for the decreased crystallinity of the poly(ethylene oxide) block (PEO) in the bulk state as indicated by DSC measurements. The self‐assembly behavior of the β‐lactam functionalized poly(isoprene‐b‐ethylene oxide) copolymers (LIEO) in aqueous solutions was studied by dynamic light scattering (DLS), static light scattering (SLS), fluorescence spectroscopy, and atomic force microscopy (AFM). Nearly spherical loose aggregates were formed by the LIEO block copolymers, having lower aggregation numbers and higher cmc values compared to the IEO precursors, as a result of the increased polarity of the β‐lactam rings incorporated in the PI blocks. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 24–33, 2010     

Organizing thermodynamic data obtained from multicomponent polymer electrolytes: Salt‐containing polymer blends and block copolymers

The objective of this review is to organize literature data on the thermodynamic properties of salt‐containing polystyrene/poly(ethylene oxide) (PS/PEO) blends and polystyrene‐b‐poly(ethylene oxide) (SEO) diblock copolymers. These systems are of interest due to their potential to serve as electrolytes in all‐solid rechargeable lithium batteries. Mean‐field theories, developed for pure polymer blends and block copolymers, are used to describe phenomenon seen in salt‐containing systems. An effective Flory–Huggins interaction parameter, χ_eff , that increases linearly with salt concentration is used to describe the effect of salt addition for both blends and block copolymers. Segregation strength, χ_effN , where N is the chain length of the homopolymers or block copolymers, is used to map phase behavior of salty systems as a function of composition. Domain spacing of salt‐containing block copolymers is normalized to account for the effect of copolymer composition using an expression obtained in the weak segregation limit. The phase behavior of salty blends, salty block copolymers, and domain spacings of the latter systems, are presented as a function of chain length, composition and salt concentration on universal plots. While the proposed framework has limitations, the universal plots should serve as a starting point for organizing data from other salt‐containing polymer mixtures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1177–1187     

Poly(ethylene oxide)-poly(styrene oxide)-poly(ethylene oxide) copolymers: Micellization, drug solubilization, and gelling features

Two new poly(ethylene oxide)-poly(styrene oxide) triblock copolymers (PEO-PSO-PEO) with optimized block lengths selected on the basis of previous studies were synthesized with the aim of achieving a maximal solubilization ability and a suitable sustained release, while keeping very low material expense and excellent aqueous copolymer solubility. The self-assembling and gelling properties of these copolymers were characterized by means of light scattering, fluorescence spectroscopy, transmission electron microscopy, and rheometry. Both copolymers formed spherical micelles (12-14 nm) at very low concentrations. At larger concentration (>25 wt%), copolymer solutions showed a rich phase behavior, with the appearance of two types of rheologically active (more viscous) fluids and of physical gels depending on solution temperature and concentration. The copolymer behaved notably different despite their relatively similar block lengths. The ability of the polymeric micellar solutions to solubilize the antifungal drug griseofulvin was evaluated and compared to that reported for other structurally-related block copolymers. Drug solubilization values up to 55 mg g⁻¹ were achieved, which are greater than those obtained by previously analyzed poly(ethylene oxide)-poly(styrene oxide), poly(ethylene oxide)-poly(butylene oxide), and poly(ethylene oxide)-poly(propylene oxide) block copolymers. The results indicate that the selected SO/EO ratio and copolymer block lengths were optimal for simultaneously achieving low critical micelle concentrations (cmc) values and large drug encapsulation ability. The amount of drug released from the polymeric micelles was larger at pH 7.4 than at acidic conditions, although still sustained over 1 day.     

Synthesis and aqueous solution properties of functionalized and thermoresponsive poly(D,L-lactide)/polyether block copolymers

Tri- and pentablock amphiphilic copolymers containing hydrophobic poly(D,L-lactide) block(s) and hydrophilic polyethers were synthesized in order to obtain new precursor architectures suitable for drug delivery systems. Polyglycidol-6-poly(ethylene oxide)-b-poly(D,L-lactide) possess high hydroxyl functionality provided by the linear polyglycidol block. Thus very stable hydroxyl functionalized micelles in aqueous media were obtained. On the other hand poly(D,L-lactide)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(D,L-lactide) form temperature sensitive aggregates. The copolymers obtained were analyzed by SEC and NMR, and their aqueous solution properties were followed by cloud point measurements and determination of critical micellization temperature. TEM was used for particles visualization.     

THERMAL ANALYSIS OF POLYPROPYLENE-b-POLYETHYLENE DIBLOCK COPOLYMERS AND CORRESPONDING BLENDS

Difference in thermal behavior of presumed polypropylene-b-polyethylene block copolymers(PP-PE) and corresponding PP+PE blends was studied. Different views in the literature were unified in our observation that faster cooling rate yielded only one exothermal peak for the blends, while slower cooling rates revealed both PP and PE exothermal peaks. Further details on when a single or double exothermal peaks would appear are discussed. Melting and crystallization temperatures for both PP and PE in blends were found to be a few degrees higher than for PP and PE in block copolymers. Thus, thermal analysis can be used to identify PP-PE block copolymers. These phenomena and the lower △H_f-values of PP and PE in block copolymers than the △H_f-values of pure homo-PP and -PE (for PE even more so) are explained in terms of restricted block movement due to covalent bond between blocks and of crystallization processes in block copolymers. The presence of block structure in the PP-PE samples studied is inferred.     

Thermoresponsive Copolymers of Ethylene Oxide and N,N‐Diethyl Glycidyl Amine: Polyether Polyelectrolytes and PEGylated Gold Nanoparticle Formation

The synthesis of diblock as well as gradient copolymers of N,N‐diethyl glycidyl amine (DEGA) with ethylene oxide (EO) via anionic ring‐opening polymerization is presented. The polymers exhibit low polydispersities (≤1.13) and molecular weights in the range of 3300–10 200 g mol⁻¹. In PEG‐co‐PDEGA copolymers, incorporation of 4%–29% DEGA results in tailorable cloud point temperatures in aqueous solution and melting points depending on DEGA content. mPEG‐b‐PDEGA block copolymers can be quaternized to generate cationic double‐hydrophilic polyelectrolyte copolymers with polyether backbone. Furthermore, mPEG‐b‐PDEGA has been used as dual reducing and capping agent for gold nanoparticle synthesis.     

Synthesis and Characterization of New Block Copolymers with Poly(ethylene oxide) and Poly[3(S)‐sec‐butylmorpholine‐2,5‐dione] Sequences

Four different types of polydepsipeptide‐polyether block copolymers were synthesized via ring‐opening polymerization of 3(S)‐sec‐butylmorpholine‐2,5‐dione (BMD) in the presence of hydroxytelechelic poly(ethylene oxide) (PEO) with stannous octoate as a catalyst.The polymers were an AB block copolymer, an ABA block copolymer, an (A)₂B star shaped copolymer and an (A)₂B(A)₂ copolymer, where A is a poly[3(S)‐sec‐butylmorpholine‐2,5‐dione] (PBMD) and B a poly(ethylene oxide) block. The molar ratio of BMD to PEO was varied to obtain copolymers with different weight fractions of PBMD blocks ranging from 59.8 to 96.7 wt.‐%. The crystallinity of the PEO phase in the copolymers decreases in the following order: AB > (A)₂B > ABA > (A)₂B(A)₂ . The static contact angle θ decreases with increasing PEO content in the block copolymers.     

Modular Synthesis of Functional Block Copolymers

Summary: The free‐radical addition of ω‐functional mercaptans to the vinyl double bonds of 1,2‐polybutadiene‐block‐poly(ethylene oxide) copolymers was used for modular synthesis of well‐defined functional block copolymers. The modification reaction proceeds smoothly and yields quantitatively functionalized block copolymers (¹H NMR and FT‐IR spectroscopy) without disturbing the molecular‐weight distribution of the parent copolymer (PDI < 1.09, size exclusion chromatography).

The modular synthetic pathway towards the functional block copolymers reported here.     

Cytotoxicity of nonionic amphiphilic copolymers

The purpose of this study is to ascertain the relationship between the structure of an amphiphilic nonionic polymer and its toxicity for cells (cytotoxicity) growing in a culture. To this end, 16 polymers of different architectures and chemical structures are tested, namely, linear triblock copolymers of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronics); diblock copolymers of propylene oxide, ethylene oxide, and hyperbranched polyglycerol; alternating and diblock copolymers of ethylene oxide and dimethylsiloxane; and two surfactants containing linear (Brij-35) or branched (Triton X-100) aliphatic chains. Polymer-cell interaction is assayed in a culture medium in the absence of serum. Effective concentrations of the polymers causing 50% cell death, EC₅₀, vary within three orders of magnitude. Toxic concentrations of the alternating copolymer, Triton X-100, and Brij-35 are lower than their CMC values. In contrast, all block copolymers, regardless of their chemical structures, become toxic at concentrations above the CMC; that is, they acquire cytotoxicity only in the micellar form. The EC₅₀ values of the copolymers depend on their hydrophilic-liphophilic balance (HLB) through the following empirical formula: EC₅₀ × 10⁶ = 8.71 × HLB^2.1. This relationship makes it possible to predict the cytotoxic concentration region of a block copolymer of a known structure.     

Synthesis and thermal properties of diblock copolymers utilizing non-covalent interactions

Diblock copolymers of poly(styrene) and poly(ethylene oxide) were prepared utilizing a bisterpyridine ruthenium complex as non-covalent interaction for the connection of the two blocks. Apart from the synthesis and characterization of four metallo-supramolecular block copolymers, first studies on the thermal properties of the block copolymers have been performed. A complex crystallization behavior was observed and is described in a qualitative fashion. The influence of the metal complex on the thermal stability of the metallo-supramolecular block copolymers remains a question for further investigation.     

Oligomers Derived from 2-Oxazolines

This paper describes the synthesis and properties of oligomer chains derived from 2-oxazolines. First, poly(styrene-g-N-acetyl-ethylenimine) was prepared, and its hydrolysis gave poly(styrene-g-ethylenimine) which showed good chelating properties. Secondly, ABA type triblock copolymers were prepared in which an N-acylethylenimine chain is used as A block and ethylene oxide chain is employed as B block. These triblock copolymers showed good compatibility with Nylon 6, which were shown to posecess effective anti-electrostatic properties for Nylon 6. Thirdly, AB type block copolymers from 2-oxazolines have been prepared by using living polymerization technique. These block copolymers are soluble in water and showed good surfactant nature as reflected by surface tension (γ), when A block is consisted from N-acetyl- or N-propionylethylenimine chain (hydro-philic) and B block is made of N-tridecanoyl or N-aroylethylenimine chain (lipophilic). Finally, graft copolymers of cellulose diacetate having N-acetylethylenimine chain were prepared. It has been found by using a rheovibron that these graft copolymers are compatible with poly(vinyl chloride).     

Synthesis and characterization of liquid‐crystalline block copolymers with cyanoterphenyl moieties by atom transfer radical polymerization

A series of new mesomorphic block copolymers composedofdifferentmacroinitiators, including poly(ethylene oxide), polystyrene, and poly(ethylene oxide)‐b‐polystyrene,and polymethacrylate with a pendent cyanoterphenyl group were synthesized through atom transfer radical polymerization. The number‐average molecular weights of the three diblock copolymers, determined by gel permeation chromatography, were 10,254, 9,772, and 15,632 g mol^?1, and their polydispersity indices were 1.17, 1.28, and 1.34. The mesomorphic and optical properties of all the block copolymers were investigated, and they possessed a smectic A phase with mesophasic ranges wider than 100 °C. Moreover, X‐ray diffraction patterns provided evidence of the smectic A phase and the corresponding interdigitated packing of all the polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4593–4602, 2006