Self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers in aqueous solution

The associative behavior of monodisperse diblock copolymers consisting of a hydrophilic poly(ethylene oxide) block and a hydrophobic poly(epsilon-caprolactone) or poly(gamma-methyl-epsilon-caprolactone) block has been studied in aqueous solution. Copolymers have been directly dissolved in water. The solution properties have been studied by surface tension, in relation to mesoscopic analyses by NMR (self-diffusion coefficients), transmission electron microscopy, and small-angle neutron and X-ray scattering. The experimental results suggest that micellization occurs at low concentration (approximately 0.002 wt %) and results in a mixture of unimers and spherical micelles that exchange slowly. The radius of the micelles has been measured (ca. 11 nm), and the micellar substructure has been extracted from the fitting of the SANS data with two analytical models. The core radius and the aggregation number change with the hydrophobic block length according to scaling laws as reported in the scientific literature. The poly(ethylene oxide) blocks are in a moderately extended conformation in the corona, which corresponds to about 25% of the completely extended chain. No significant modification is observed when poly(gamma-methyl-epsilon-caprolactone) replaces poly(epsilon-caprolactone) in the diblocks.     

Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has been confirmed by surface tension measurements, whereas the influence of the surfactant on the copolymer self-assembling has been studied by measurement of the 1H NMR self-diffusion coefficients and by small-angle neutron scattering. As a rule, the surfactant decreases the heterogeneity of the micellar structures formed by the copolymer in water. Moreover, increasing the content of SDS results in the increasingly more important extension of the poly(ethylene oxide) (PEO) corona chains and the copolymer micelle deaggregation. The stability of the micelles against SDS increases with the length of the hydrophobic block. Preliminary two-dimensional NMR measurements with nuclear Overhauser enhancement have confirmed the spatial vicinity between SDS and the constitutive blocks of the copolymer.     

聚(对苯二甲酸丁二醇酯-co-对苯二甲酸环己烷二甲醇酯)-b-聚乙二醇嵌段共聚物的合成与表征

用熔融缩聚法合成了一系列聚(对苯二甲酸丁二醇酯-co-对苯二甲酸环己烷二甲醇酯)-b-聚乙二醇嵌段共聚物(PBCG),用NMR,GPC,DSC,TGA及力学性能测试等方法表征了材料的结构与性能.GPC分析显示,共聚物分子量均具有较为对称的单峰分布,多分散性指数低于1.70.¹³CNMR谱结果表明,随PCT摩尔分数(x_PCT)从10%增至60%,PBT平均序列长度由4.02降到1.41;而PCT平均序列长度则由1.17升至2.50,二者呈无规分布.受硬段平均序列长度及结晶能力影响,硬段熔点及结晶度在x_PCT为20%～30%处均达到最小值,可能是硬段间形成共晶所致.TGA分析显示,引入芳香族聚酯组分PCT确可提高材料的热稳定性.力学性能测试说明,降低结晶度有利于提高材料的断裂延伸率,相反,则有助于增强弹性模量,断裂强度及屈服强度.     

Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-g-poly(vinyl pyrrolidone): synthesis and characterization

Pluronic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers are grafted with poly(vinyl pyrrolidone) by free radical polymerization of vinyl pyrrolidone with simultaneous chain transfer to the Pluronic in dioxane. This modified polymer has both thermal responsiveness and remarkable capacity to interact with a wide variety of hydrophilic and hydrophobic pharmaceutical agents which is very attractive for medical applications. The chemical structure of the graft copolymers was characterized by FTIR and 1H NMR spectroscopy. Polymerization conditions such as initiators, feed ratio, and reaction times are studied to obtain the ideal graft copolymer.     

Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.     

Langmuir and Langmuir-Blodgett films of poly(ethylene oxide)-b-poly(epsilon-caprolactone) star-shaped block copolymers

Self-assembly of poly(ethylene oxide)-block-poly(epsilon-caprolactone) five-arm stars (PEO-b-PCL) was studied at the air/water (A/W) interface. The block copolymers consist of a hydrophilic PEO core with hydrophobic PCL chains at the star periphery. All the polymers have the same number of ethylene oxide repeat units (9 per arm), and the number of epsilon-caprolactone repeat units ranges from 0 to 18 per arm. The Langmuir monolayers were analyzed by surface pressure/mean molecular area isotherms, compression-expansion hysteresis experiments, and isobaric relaxation measurements, and the Langmuir-Blodgett (LB) films' morphologies were investigated by atomic force microscopy (AFM). PCL homopolymers crystallize directly at the A/W interface in a narrow surface pressure range (11-15 mN/m). In the same pressure region, the star-shaped block copolymers undergo a phase transition corresponding to the collapse and the crystallization of the PCL chains as shown by the presence of a pseudoplateau in the isotherms. The LB films were prepared by transferring the Langmuir monolayers onto mica substrates at various surface pressures. AFM imaging confirmed the formation of PCL crystals in the LB monolayers of the PCL homopolymers and of the copolymers, but also showed that the PCL segments can undergo additional crystallization after monolayer transfer during water evaporation. The PCL crystal morphologies were also strongly influenced by the surface pressure and by the PEO segments.     

聚乙烯基环己烷-聚乙烯-聚乙烯基环己烷三嵌段共聚物溶液的受限结晶研究

嵌段共聚物由于组分间的化学不相容性而发生微相分离,组装成各种有序的纳米结构,如球、圆柱、层及双连续结构等．半晶型嵌段共聚物由于引入了能结晶的组分,使体系中存在两种相互竞争的过程,即微相分离与结晶,所以能形成更为丰富的有序结构．聚乙烯基环己烷-聚乙烯-聚乙烯基环己烷[Poly(Vinylcyclohexane)-b-poly(ethylene)-b-poly(vinylcyclohexane),     

Multifunctional Poly(ethylene glycol)s

In the rapidly evolving multidisciplinary field of polymer therapeutics, tailored polymer structures represent the key constituent to explore and harvest the potential of bioactive macromolecular hybrid structures. In light of the recent developments for anticancer drug conjugates, multifunctional polymers are becoming ever more relevant as drug carriers. However, the potentially best suited polymer, poly(ethylene glycol) (PEG), is unfavorable owing to its limited functionality. Therefore, multifunctional linear copolymers (mf‐PEGs) based on ethylene oxide (EO) and appropriate epoxide comonomers are attracting increased attention. Precisely engineered via living anionic polymerization and defined with state‐of‐the‐art characterization techniques—for example real‐time ¹H NMR spectroscopy monitoring of the EO polymerization kinetics—this emerging class of polymers embodies a powerful platform for bio‐ and drug conjugation.     

聚对苯二甲酸丁二醇酯－co-聚丁二酸丁二醇酯-b-聚乙二醇嵌段共聚物的合成及表征

用熔融缩聚法合成了一系列基于聚对苯二甲酸丁二醇酯（PBT）、聚丁二酸丁 二醇酯（PBS）及聚乙二醇（PEG）的嵌段共聚物（PBT－co-PBS/PEG)。^1H NMR结 构分析显示,软段摩尔百分含量恒为20％。随组成中PBS含量增加,软段质量百分 含量略微升高,硬段PBT平均序列长度由2.80逐步减至1.23,PBS平均序列长度由1. 27逐步增加到4．76,无规度在1．1附近,两者呈无规分布。受组成及硬段平均序 列长度变化影响,材料内部呈微观相分离状态,DSC热分析曲线上可分别观察到软 、硬段熔点（Tm,s,Tm,h)及玻璃化转变温度（Tg,s,Tg,h)。硬段熔点及结晶度随 PBS含量升高而降低,在50－60mol％处达到最小值,则是PBS与PBT二者间形成共晶 所致。力学性能测试及水解降解实验表明,将脂肪族聚酯PBS引入PEGT／PBT共聚体 系,可赋予高分子链更好的柔韧性及亲水性,加快降解速率。     

Supramolecular hydrogels induced rapidly by inclusion complexation of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) block copolymers with alpha-cyclodextrin in aqueous solutions

On the basis of the synthesis of water-soluble poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL) block copolymers, the supramolecular hydrogels were fabricated rapidly in aqueous solutions by their inclusion complexation with alpha-cyclodextrin. X-ray diffraction (XRD) analyses confirmed the supramolecular self-assemblies of alpha-cyclodextrin threaded onto amphiphilic PCL-PEG-PCL block copolymers. The resulting hydrogels display a high degree of elasticity, with the storage modulus (G') greater than the loss modulus (G') over the entire range of frequency. Moreover, their viscosity greatly diminished as they were sheared. By controlling the molecular weight of the PEG component in the block copolymers and the content of the block copolymer, their rheological properties could be modulated. Such hydrogel materials have the potential to be used as tissue engineered scaffolds, biosensors in the human body, and carriers for controlled drug delivery.     

pH-induced micelle formation of poly(histidine-co-phenylalanine)-block-poly(ethylene glycol) in aqueous media

Poly[(L-histidine)-co-(L-phenylalanine)]-block-poly(ethylene glycol) (HF-b-PEG) diblock copolymers were synthesized to be used for preparation of pH-sensitive polymeric micelles. First, HF block was synthesized by ring opening copolymerization of L-histidine and L-phenylalanine N-carboxyanhydride, and then the resulting copolymer was coupled with PEG. The pKa value of diblock copolymer can be controlled by adjusting the histidine/phenylalanine ratio in HF block. It is observed that the block copolymers form micelles in aqueous media and that the micelles are spherical in shape with a unimodal distribution. The micelle is formed at pH higher than pKa of block copolymer while it is not formed at lower pH. This is because the protonation of histidine residue in the HF block converts the hydrophobic core into hydrophilic one at lower pH. Acid-Base titration profile of HF41(5600)-b-PEG, HF56(5500)-b-PEG, H(5100)-b-PEG and 0.1 N NaCl.     

Bacterial polyesters grafted with poly(ethylene glycol): Behaviour in aqueous media

An easy method for grafting of poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate) (PHOU) was developed. Oxidation of the pendant double bonds of PHOU into carboxyl groups to yield poly(3-hydroxyoctanoate-co-3-hydroxy-9-carboxydecanoate) (PHOD) and the esterification of the carboxyl side groups with poly(ethylene glycol) (PEG) were carried out in a single reaction solution. The grafting yield is dependent on the molar mass of the PEG graft. The maximum carboxyl group conversion (52%) was obtained with PEG M_n = 350 and decreased with increasing molar mass of PEG (19% for PEG M_n = 2000). Yields were determined by ¹H and ¹³C NMR. Short PEG grafts lowered the glass transition temperature (PHOD-g-PEG 350 −57 °C) compared to PHOD (−19 °C) and PHOU (−39 °C). This effect depends on the COOH conversion and PEG chain length. Grafting enhanced the hydrophilic character of the modified polymers making them soluble in polar solvents, such as alcohols and water/acetone mixtures. PHOD-g-PEG films were more stable towards hydrolytic degradation as PHOD films. No obvious modification of films was observed after more than 200 days at pH 7.2 and 37 °C. The molar mass of the grafted polymers decreased only slightly during this period, while PHOD films were hydrolyzed into soluble fragments.     

聚乙烯/聚乙二醇共混物中极性组分的表面富集

采用衰减全反射傅立叶变换红外光谱(FTIR-ATR)和扫描电子显微镜研究了极性组分聚乙二醇在聚乙烯／聚乙二醇共混物中的表面富集特性。研究结果认为不同组分表面自由能的差异以及聚乙烯基体的结晶异相排斥作用是导致聚乙二醇组分向共混物表面富集的主要驱动力，而极性组分相区的大小和分布则是影响其选择性迁移过程的重要因素。因此，可以通过添加合适相容剂的办法对聚乙二醇组分的表面富集程度进行有效的调控。     

Micellization and Thermogelation of Poly(ether urethane)s Comprising Poly(ethylene glycol) and Poly(propylene glycol)

A series of multiblock poly(ether urethane)s comprising poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) segments were synthesized. Their aqueous solutions exhibited thermogelling behavior at critical gelation concentrations (CGC) ranging from 8 to 12 wt%. The composition and structural information of the copolymers were studied by GPC and ¹H NMR. The critical micellization concentration (CMC) and thermodynamic parameters for micelle formation were determined at different temperatures. The temperature response of the copolymer solutions were studied and found to be associated with the composition of the copolymers.     

Poly(ethylene glycol)-based shape-memory polymers

Poly(ethylene glycol) (PEG) blends photo-curable and thermal activated shape-memory polymers (SMPs), with different activation temperature (T_switch), have been synthesized and characterized. PEG blends with different molecular weights were chain-end functionalized with isocyanate ethyl methacrylate and photo-cured with UV lamp. Degree of cross-linking of the blend network, determined by gel content measurement, resulted as higher than 95%. The thermal and thermomechanical properties of these SMPs PEG blends were characterized by differential scanning calorimetry and dynamic mechanical analysis. The shape-memory properties of the networks were quantified using thermomechanical three-point bending experiments and showed strain fixity rates higher than 99% and a minimum strain recovery ratio of 82%.     

Two-dimensional self-assembly of linear poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the air-water interface

The interfacial properties of amphiphilic linear diblock copolymers based on poly(ethylene oxide) and poly(epsilon-caprolactone) (PEO-b-PCL) were studied at the air-water (A/W) interface by surface pressure measurements (isotherms and hysteresis experiments). The resulting Langmuir monolayers were transferred onto mica substrates and the Langmuir-Blodgett (LB) film morphologies were investigated by atomic force microscopy (AFM). All block copolymers had the same PEO segment (Mn = 2670 g/mol) and different PCL chain lengths (Mn = 1270; 2110; 3110 and 4010 g/mol). Isothermal characterization of the block copolymer samples indicated the presence of three distinct phase transitions around 6.5, 10.5, and 13.5 mN/m. The phase transitions at 6.5 and 13.5 mN/m correspond to the dissolution of the PEO segments in the water subphase and crystallization of the PCL blocks above the interface similarly as for the corresponding homopolymers, respectively. The phase transition at 10.5 mN/m was not observed for the homopolymers alone or for their blends and arises from a brush formation of the PEO segments anchored underneath the adsorbed hydrophobic PCL segments. AFM analysis confirmed the presence of PCL crystals in the LB films with unusual hairlike/needlelike architectures significantly different from those obtained for PCL homopolymers.     

Potentiometric titration behavior of poly(ethylene glycol methyl ether)-b-poly(ethylenimine)

Poly(ethylene glycol methyl ether)-b-poly(ethylenimine hydrochloride) was characterized using potentiometric and viscosimetric titration methods. The average chemical compositions of the polyamine hydrochloride salts estimated by the acid-base titration,¹H-NMR, and elemental analysis were compared. The apparent dissociation constant, pK, and the inherent viscosity of the polyamine hydrochloride were found to be highly dependent on the degree of neutralization. Very strong coulombic interactions among the charged sites were observed at low pH's for this polymer.     

聚L-丙氨酸-聚乙二醇嵌段共聚物纳米胶束的研究

分别以氨基聚乙二醇和氨基聚乙二醇单甲醚为大分子引发剂,采用开环聚合的方法合成了两亲性聚L-丙氨酸-聚乙二醇(PAE)和聚L-丙氨酸-聚乙二醇单甲醚(PAME)两种嵌段共聚物,其结构经1H NMR,IR,DSC,GPC等表征;利用园二色技术研究了其在水溶液中的二级结构,用芘荧光探针技术研究了其胶束的形成及其临界胶束浓度(CMC),利用透射电镜研究了胶束的形态。结果表明,在水溶液中共聚物链以α-螺旋构象形式存在,在一定条件下嵌段共聚物PAE-1,PAE-2,PAME-1和PAME-2能够形成球形的稳定胶束,PAE-1形成胶束的CMC为3.36×10-5mol.L-1,CMC值受嵌段类型和共聚物中聚L-丙氨酸链段含量的影响。     

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.