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

Melting points have been measured for several ethylene oxide–propylene oxide block copolymers (sym-EPE) chosen from the Pluronic range. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by up to 4°C. The melting point depressions are much smaller than those observed for comparable sym-PEP block copolymers.     

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.     

Modification of the lyotropic liquid crystalline microstructure of amphiphilic block copolymers in the presence of cosolvents

This article reviews the results of recent investigations on the macroscopic (phase behavior) and microscopic (microstructure) aspects of the role of cosolvents on the self-assembly of amphiphilic copolymers. A comprehensive account of the systematic studies performed in ternary isothermal systems consisting of a representative poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymer (Pluronic P105, EO₃₇PO₅₈EO₃₇), water and a polar cosolvent (such as glycerol, propylene glycol or ethanol) is presented. The effect of cosolvents on the copolymer phase behavior is quantified in terms of the highest cosolvent/water ratio able to maintain the liquid crystalline structures. The effect of cosolvents on the microstructure of the lyotropic liquid crystals is quantified in terms of the degree of relative swelling per cosolvent content per copolymer content, a parameter that characterizes the given cosolvent and copolymer. The set of correlations on the cosolvent effects on the phase behavior or microstructure to the cosolvent physicochemical characteristics (such as octanol/water partition coefficient or solubility parameter) have led to the development of a hypothesis that accounts for the cosolvent effects on the self-assembly of PEO–PPO–PEO block copolymers and can be used to predict them. The rich structural diversity and the potential for a precise and convenient modification of the lyotropic liquid crystalline microstructure of the PEO–PPO–PEO block copolymers is discussed in comparison to the phase behavior of the low-molecular nonionic surfactants.     

Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(α‐olefin)

This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s‐PS), and elastomers, such as poly(ethylene‐co‐1‐octene) and poly(ethylene‐co‐styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ～270 °C to low glass‐transition temperature ～?60 °C. The chemistry involves two reaction steps, including the preparation of a borane group‐terminated polyolefin by the combination of a metallocene catalyst and a borane chain‐transfer agent as well as the interconversion of a borane terminal group to an anionic (? O^?K⁺) terminal group for the subsequent ring‐opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of α‐olefins to the ring‐opening polymerization of ethylene oxide. The well‐defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (M_w/M_n < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416–3425, 2002     

Hydrophilic poly(ethylene oxide)–aramide segmented block copolymers

The present paper discusses block copolymers with segments of either poly(ethylene oxide), poly(propylene oxide), or mixtures of poly(ethylene oxide)/poly(propylene oxide) and monodisperse aramide segments. The length of the polyether segments as well as the concentration of polyethylene oxide was varied. The synthesized copolymers were analyzed by DSC, FTIR, AFM and DMTA. In addition, the hydrophilicity was studied.The crystallinity of the monodisperse aramide segments was found to be high and the crystals, dispersed in the polyether phase, displayed a nano-ribbon morphology. The PEO segments were able to crystallize and this crystalline phase reduced the low-temperature flexibility. The PEO crystallinity and melting temperature could be strongly reduced by copolymerization with PPO segments. By using mixtures of PEO and PPO segments, hydrophilic copolymers with decent low-temperature properties could be obtained.     

Clouding Behavior of Ethylene Oxide‐Propylene Oxide Block Copolymer P85: The Effect of Additives

The characteristic feature of nonionic poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymers is that at higher temperatures they undergo clouding and liquid‐liquid phase separation. The clouding temperature of such block copolymers can be profoundly altered in the presence of various additives. In this work the effect of various additives on the clouding phenomenon of triblock copolymer P85[(EO)₂₆(PO)₃₉(EO)₂₆] is discussed.     

Segmented block copolymers based on poly(propylene oxide) and monodisperse polyamide‐6,T segments

Polyether(ester amide)s with poly(propylene oxide) (PPO) and monodisperse poly(hexamethylene terephthalamide) segments were synthesized, and their structure–property relations were investigated. The length of the amide segments was varied from diamide to tetraamide to hexaamide segments, and therefore the number hydrogen bonds per amide segment increased from two to four to six. PPO was end‐capped with 20 wt % ethylene oxide and had number‐average molecular weights of 1000, 2300, and 4000 g/mol (including ethylene oxide tips). The morphology of the poly‐ether(ester amide)s was studied with transmission electron microscopy and atomic force microscopy, the thermal properties were studied with differential scanning calorimetry and dynamic mechanical thermal analysis, and the tensile properties were studied with dumbbell samples. The elastic behavior of the block copolymers was investigated with tensile and compression tests. These segmented copolymers had two sharp transitions: a glass‐transition temperature (T_g) of the PEO–PPO–PEO phase [where PEO is poly(ethylene oxide)] and a melting temperature (T_m) of the amide segments. The amide segments crystallized in nanoribbons with a high aspect ratio 1000. T_m increased with the amide segment length and with decreasing PEO–PPO–PEO content (solvent effect). The modulus increased strongly with the amide content. This modulus increase could be described by the Halpin–Tsai fiber composite model. Increasing the amide segment length surprisingly also improved the elasticity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4769–4781, 2006     

High Tg polyimide nanofoams derived from pyromellitic dianhydride and 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane

New routes for the synthesis of high T_g thermally stable polymer foams with pore sizes in the nanometer regime have been developed. Foams were prepared by casting well-defined microphase-separated block copolymers comprised of a thermally stable block and a thermally labile material. At properly designed volume fractions the morphology provides a matrix of the thermally stable material with the thermally labile material as the dispersed phase. Upon thermal treatment, the thermally unstable block undergoes thermolysis generating pores, the size and shape of which are dictated by the initial copolymer morphology. Triblock copolymers comprised of a high T_g, amorphous polyimide matrix with poly(propylene oxide) as the thermally decomposable coblock, were prepared. The copolymer synthesis was conducted through the poly(amic acid) precursor and subsequent cyclodehydration to the polyimide by either thermal or chemical means. Dynamic mechanical analysis confirmed microphase separated morphologies for all copolymers, irrespective of the propylene oxide block lengths investigated. Upon decomposition of the thermally labile coblock, a 9–18% reduction in density was observed, consistent with the generation of a foam which was stable to 400°C. © 1996 John Wiley & Sons, Inc.     

Study on sequence distribution of segmented poly(urethane urea)s by 13C-NMR spectroscopy: Effect of polymerization procedures

The segmented poly(urethane urea) copolymers were synthesized by one- and two-step polymerization procedures. The copolymers were based on 4,4′-diphenylmethane diisocyanate, 3,5-diethyltoluene diamine, and ethylene oxide-capped poly(propylene oxide) diol. The mean sequence lengths of polyurethane soft block and polyurea hard block as well as the sequence distribution of the hard block in the copolymers were estimated from the signals of aromatic carbons in ¹³C-NMR spectra. The results indicated that two-step polymerization led to longer mean sequence lengths and broader hard block sequence distribution than one-step polymerization did. © 1996 John Wiley & Sons, Inc.     

Ethylene-propylene copolymerization initiated with solubilized ziegler-natta macromolecular complexes. II. Characterization of [styrene]-b-[ethylene-co-propylene] copolymers

Copolymerization of ethylene (E) with propylene (P) initiated with soluble (polystyrene)₁₀₀-butadiene₃-Li/TiCl₄ complexes leads to [St]-b-[E-co-P] diblock copolymers with a random [E-P] block. GPC and ¹³C-NMR analyses of copolymers with various compositions and block lengths disclose well-defined linear structures. From DSC measurements of such materials, three different endothermal transition regions are observed: two glass transition regions corresponding, respectively, to the T_g of styrenic and olefinic blocks, and one [E-P] block melting region in which propylene units play a primary role. Furthermore, an additional endotherm is observed, depending on the thermal history of the sample.     

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.     

Isotactic sequence lengths by ozonation of poly(propylene oxide)

Ozonation followed by lithium aluminum hydride reduction cleaved high molecular weight isotactic poly(propylene oxide) to crystalline polyglycols. From the melting point and molecular weight of the latter, the molar freezing point depression produced by end groups is found to be ca. 18°C./mole, as compared to that estimated for poly(ethylene glycols), K_f = 12°C./mole, from earlier data. By assuming syndiotactic placements (or other irregularities) would produce the same molar depression, the melting point of isotactic poly(propylene oxides) produced by various catalysts has been used to estimate the isotactic sequence lengths.     

Synthesis and characterization of polystyrene–poly(ethylene oxide)–heparin block copolymers

A procedure for the preparation of new block copolymers composed of a hydrophobic block of polystyrene, a hydrophilic spacer-block of poly(ethylene oxide) and a bioactive block of heparin was investigated. Polystyrene with one amino group per chain was synthesized by free radical oligomerization of styrene in dimethylformamide, using 2-aminoethanethiol as a chain transfer agent. This amino group was used in the coupling reaction with amino-telechelic poly(ethylene oxide) to produce an AB type diblock copolymer with one amino group per polystyrene (PSt)–poly(ethylene oxide) (PEO) chain. The amino-semitelechelic oligo-styrene was converted into the isocyanate-semitelechelic oligo-styrene using toluene 2,4-diisocyanate and subsequent coupling with H₂N–PEO–NH₂ afforded AB type block copolymers with terminal amino groups. The coupling of PSt–PEO–NH₂ with heparin was performed in a DMF–H₂O mixture, first by activating the heparin carboxylic groups with EDC at pH 5.1–5.2 and subsequently reacting the activated carboxylic groups with the amino groups of the PSt–PEO–NH₂ at pH 7.5. Depending on the molecular weights of the diblock copolymer used 25–29% w/w heparin was incorporated. These polymers will be further evaluated for their blood-compatibility.     

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 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     

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.     

Synthesis and bulk assembly behavior of linear–dendritic rod diblock copolymers

Dendritic rod structures can be formed via the branching of dendritic elements from a primary polymer backbone; such systems present an opportunity to create nanoscale material structures with highly functional exterior regions. In this work, we report for the first time the synthesis of a hybrid diblock copolymer possessing a linear–dendritic rod architecture. These block copolymers consist of a linear poly(ethylene oxide)–poly(ethylene imine) diblock copolymer around which poly(amido amine) branches have been divergently synthesized from the poly(ethylene imine) block. The dendritic branches are terminated with amine or ester groups for the full generations and half‐generations, respectively; however, the methyl ester terminal groups can also be readily converted into alkyl groups of various lengths, and this allows us to tune the hydrophilic/hydrophobic nature of the dendritic block and, therefore, the amphiphilic properties of the diblock copolymer and its tendencies toward microphase separation. The block copolymers exhibit semicrystallinity due to the presence of the poly(ethylene oxide) block; however, as the polymer fraction consisting of poly(ethylene oxide) decreases, the overall crystallinity also decreases, and it approaches zero at generation 2.0 and higher. The unfunctionalized block copolymers show weak phase segregation in transmission electron microscopy and differential scanning calorimetry at all generations. The addition of n‐alkyl chains increases phase segregation, particularly at high alkyl lengths. The generation 3.5 polymer with n‐dodecyl alkyl substitution has a rodlike or wormlike morphology consisting of domains of 4.1 nm, equivalent to the estimated cross section of the individual polymer chains. In this case, the nanometer scale of the polymer chains can be directly observed with transmission electron microscopy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2784–2814, 2004     

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     

Hydrophilic segmented block copolymers based on poly(ethylene oxide) and monodisperse amide segments

Segmented block copolymers based on poly(ethylene oxide) (PEO) flexible segments and monodisperse crystallizable bisester tetra‐amide segments were made via a polycondensation reaction. The molecular weight of the PEO segments varied from 600 to 4600 g/mol and a bisester tetra‐amide segment (T6T6T) based on dimethyl terephthalate (T) and hexamethylenediamine (6) was used. The resulting copolymers were melt‐processable and transparent. The crystallinity of the copolymers was investigated by differential scanning calorimetry (DSC) and Fourier Transform infrared (FTIR). The thermal properties were studied by DSC, temperature modulated synchrotron small angle X‐ray scattering (SAXS), and dynamic mechanical analysis (DMA). The elastic properties were evaluated by compression set (CS) test. The crystallinity of the T6T6T segments in the copolymers was high (>84%) and the crystallization fast due to the use of monodisperse tetra‐amide segments. DMA experiments showed that the materials had a low T_g, a broad and almost temperature independent rubbery plateau and a sharp flow temperature. With increasing PEO length both the PEO melting temperature and the PEO crystallinity increased. When the PEO segment length was longer than 2000 g/mol the PEO melting temperature was above room temperature and this resulted in a higher modulus and in higher compression set values at room temperature. The properties of PEO‐T6T6T copolymers were compared with similar poly(propylene oxide) and poly(tetramethylene oxide) copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4522–4535, 2007