PEO/LiClO4复合体系中PEO的等温结晶动力学研究

用差示扫描量热法研究了聚氧化乙烯(PEO)和PEO/LiClO4复合体系中PEO的等温结晶过程.用Avrami方程分析了PEO和复合体系中PEO的等温结晶动力学,得到PEO在不同体系中等温结晶时的动力学参数.PEO的Avrami指数n都趋近2.5,说明PEO晶体以三维方式依热成核生长.动力学参数表明,复合体系中的PEO以异相成核为主.LiClO4对PEO等温结晶过程的影响为:作为PEO结晶的成核剂而加快其结晶过程;增加了复合体系的粘度,缩短了PEO的半结晶时间,使其结晶总速率增大;降低了复合体系中PEO的绝对结晶度.PEO和复合体系中的PEO等温结晶时成核和生长活化能△E分别为59.28kJ/mol、70.85kJ/mol.     

分子量及其分布对聚丙烯力学性能和结晶行为的影响

通过机械共混的方法制备一系列不同分子量及其分布的聚丙烯，并对其力学性能和结晶行为进行了表征，研究了分子量及其分布对这些性能的影响以及力学性能和结晶行为的对应关系。通过实验发现，分子量及其分布对聚丙烯的结晶速率，结晶温度，结晶度，冲击强度，拉伸屈服强度，断裂伸长率等均有较大影响。     

不同分子量的聚氧化乙烯对聚乳酸结晶和力学性能的影响研究

聚乳酸(PLA)和其他可降解高分子材料熔融共混被认为是增韧PLA而不损失其可降解特性的最经济有效的方法。通过熔融共混法制备了PLA与聚氧化乙烯(PEO)的共混物,并采用DSC、XRD、SEM以及万能试验机等方法系统研究了不同分子量以及不同比例PEO对PLA微观结构和力学性能的影响。结果表明:在相同比例条件下,低分子量PEO与PLA的相容性要优于高分子量PEO,且对PLA结晶速率的提高更显著;PEO的加入提高了共混物的断裂伸长率,但伴随着拉伸强度的下降,且随PEO含量的增加,拉伸强度下降越明显。当PEO的分子量超过10万时,对PLA的增韧效果更加显著,且共混物的拉伸强度下降幅度较小。     

聚醚酰亚胺热焓松驰的分子量依赖关系

采用ＤＳＣ对不同分子量的聚醚酰亚胺的等温及动态热焓松驰行为进行了研究，并以ＫＷＷ方程对实验数据进行了非线性拟合。结果表明，分子量对热焓松驰的影响是由高分子端基引起自由体积的差异所致。     

聚醚酰亚胺热焓松弛的分子量依赖关系

采用ＤＳＣ对不同分子量的聚醚酰亚胺的等温及动态热焓松弛行为进行了研究，并以ＫＷＷ方程对实验数据进行了非线性拟合。结果表明，分子量对热焓松弛的影响是由高分子端基引起自由体积的差异所致。不同分子量的聚醚酰亚胺分子具有不同数量的端基，淬冷时端基数目的差异将产生不同数量的过剩自由体积，从而影响松弛热焓及松弛速率、低分子量的聚醚酰亚胺松弛相对较快，且起始热焓高，松弛的表观活化能亦较小。     

PCL-b-PMMA/PEO共混薄膜的微相分离形貌

通过聚氧化乙烯(PEO)与聚己内酯-聚甲基丙烯酸甲酯嵌段共聚物(PCL-b-PMMA)的共混来调节聚己内酯(PCL)与聚甲基丙烯酸甲酯(PMMA)嵌段的微相分离行为。采用原子力显微镜研究了PEO的质量分数和相对分子质量对PCL-b-PMMA/PEO共混薄膜微相分离形貌的影响。结果表明,共混薄膜形成了以PMMA/PEO为连续相,PCL呈柱状微区垂直于薄膜表面的微相分离形貌,PMMA/PEO链段无法在PCL柱状微区上方形成完全覆盖,导致薄膜表面形成许多孔洞。随着PEO含量增加,PCL链段聚集趋势增强,柱状微区尺寸不断增大;随着PEO相对分子质量的增加,PMMA/PEO在PCL微区上方形成的有效覆盖减少,薄膜表面的孔洞数量和尺寸增大;当PEO与不同嵌段比PCL-b-PMMA共混后,随嵌段共聚物中PCL链段体积分数增加,柱状微区向层状形态转变,薄膜表面孔洞消失。     

钴基非晶薄带交换偏置现象稳定性和可控性的研究

钴基(Co58Fe5Ni10Si11B16)非晶薄带在一定温度范围内做热磁处理之后,由于薄带内有少量磁性较硬结晶相析出,其磁矩对非晶软磁基体的钉扎作用使样品出现交换偏置行为。在研究过程中采用X射线衍射仪、高分辨透射电镜表征样品相组成及微观结构,利用冲击检流测量法测试其磁滞回线,通过扫描探针显微镜观测薄带表面磁畴,由此深入分析内在磁矩配置情况。结果表明,在利用横向冲击场调控钴基薄带交换偏置行为的过程中存在临界场。当横向冲击场低于临界场时,结晶相磁矩几乎不受其影响,交换偏置行为呈稳定状态;而大于临界场时,结晶相磁矩在其冲击作用下按自由能最小原则重新配置,交换偏置行为可通过调节横向冲击场的大小有效调控。     

聚乙二醇-聚硅氧烷哑铃形嵌段共聚物的合成与表征

金属钾和聚乙二醇1000在THF中反应生成醇钠,再加入环氧氯丙烷得到环氧基端基的聚乙二醇,经水解,重复以上步骤,分别得到了具有4和8羟基端基的聚乙二醇中间体。将不同数目羟基端基聚乙二醇和KOH、D4在100℃～140℃条件下进行开环聚合,即得具有线性-树状结构的聚乙二醇-聚硅氧烷哑铃形共聚物。用核磁共振、凝胶渗透色谱和原子力扫描电镜对所得共聚物的结构、性能及其在亲水表面的排列方式作了详细研究。结果表明,4和8羟基端基聚乙二醇的羟基官能度分别为3.96和7.70;共聚物的绝对数均分子量分别为4300g/mol、4700g/mol和5900g/mol;哑铃形共聚物在亲水介质表面可形成形态学不均一、表面较为粗糙的硅膜。     

POM/PEO共混物中PEO对POM非等温结晶的影响

利用DMA和DSC考察了POM/PEO共混物的相容性及PEO对POM非等温结晶的影响。结果表明,POM/PEO共混物只有一个玻璃化转变温度(Tg),与组分的关系符合Fox方程,POM与PEO在无定形态相容,PEO抑制了POM成核,降低了POM的结晶速度和共混物中POM的相对结晶度。PEO含量较高时POM结晶温度下降。     

聚氧化乙烯(PEO)及其与高氯酸锂复合体系的等温结晶动力学研究

用示差扫描量热法研究了PEO及其与高氯酸锂复合体系的等温结晶过程。用Avrami方程分析了PEO和复合体系中PEO的等温结晶动力学,得到了PEO在不同体系中等温结晶时的动力学参数。PEO的Avrami指数n都趋近2．5,说明PEO晶体以三维方式依热成核生长。动力学参数表明,复合体系中PEO结晶时以异相成核为主。LiClO4对PEO等温结晶过程的影响如下：作为PEO结晶的成核剂而加快其结晶过程;增加了复合体系的粘度,缩短了PEO的结晶半时间,使其结晶总速率增大;降低了复合体系中PEO的绝对结晶度。     

Fractionation and solvent-free MALDI-MS analysis of polymers using liquid adsorption chromatography at critical conditions in combination with a multisample on-target homogenization/transfer sample preparation method

A solvent-free homogenization/transfer matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) method is described for the preparation and precise transfer of up to 100 samples simultaneously on a single MALDI plate. This method is demonstrated using a poly(ethylene oxide) (PEO) mixture consisting of different molecular weights (500-6000) and end groups (PEO, dimethoxy-PEO, monomethoxy monomethacrylate-PEO, and dimethacrylate-PEO) that was fractionated using liquid adsorption chromatography at critical conditions. Off-line fractionation is performed prior to the on-target homogenization/transfer solvent-free sample preparation and MALDI mass analysis. The miniaturization of the solvent-free MALDI approach allowed analysis of less than 2 microg per PEO component per fraction corresponding to approximately 200 pmol for PEO 6000. The amounts of polymer sample used for LC separation and the quality of the MS results are equivalent to the "dry spray" method; however, three times more fractions were collected and analyzed with the newly developed hyphenated approach. The off-line method eliminates optimization of, for example, spray conditions or spreading of organic solvents on the MALDI plate that occurs with droplet deposition methods. The widespread applications of MALDI make this solvent-free, multisample method particularly important as it expands the capabilities for obtaining mass measurements with great efficiencies in areas with increased sample numbers. In addition, the solvent-free method is well suited for automated MALDI analysis as it virtually eliminates the "dead-spot" phenomenon.     

Review Spherulites: A personal perspective

Chain-folding is a central feature of the self-organizational aspect of polymer in the solid state, yet the ability of a polymer chain to organize into a folded morphology depends upon its length. The shorter chains seem to fold with relative ease in dilute solution crystallization, but in the melt where topological constraints are encountered, spherulitic crystallization is less facile especially in the higher molecular weight fractions. Polymer morphology and properties demonstrate this point clearly according to the experimental evidence, obtained from several sources and presented in this article. For topological and statistical reasons, longer chains are responsible for more interfacial disorder if the degree of crystallinity, density, mechanical behavior, fold surface free energy, transition from brittleness to toughness, and so on, may be used as guidelines. Spherulites of homopolymers or copolymers are undoubtedly less ordered than crystals of comparable MW fractions, if measured properties are a manifestation of morphology. The imperfections in spherulites are mainly associated with the quasi-amorphous interlamellar regions within them. Polymer crystallinity decreases as the molecular weight of polymer fractions increase at comparable crystallization temperatures or undercooling conditions. This trend is true for all polymers that have been studied extensively.     

Study of poly(methyl methacrylate)/poly(ethylene oxide) blends in solution. I

Determination of polymer-polymer interaction parameters (b₂₃) has been made by viscometry for poly(methyl methacrylate)/poly (ethylene oxide) blends, in solution, of a wide range of molecular weights of both polymers. The results obtained show that the compatibility of the polymer pair PMMA/PEO in 1.2-dichloroethane depends not only on the molecular weight of the samples used but also on the concentration of one polymer in relation to another.     

Polymer blends based on PEO and starch: Miscibility and spherulite growth rate evaluated through DSC and optical microscopy

The miscibility and PEO spherulite growth rate in PEO/starch blends (starch from cassava) were evaluated using the depression in the melting point (by DSC) and optical polarized microscope, respectively, and compared to pure PEO. The PEO/starch blend ratio changed from 100/0 to 60/40 (weight/weight). The starch induces changes in PEO crystallization on PEO/starch blends but the crystallization rates do not change linearly to the blend ratio. For 90/10, 80/20, 70/30, 65/35 and 60/40 ratios, lower values for the equilibrium melting temperature were observed as compared to the pure PEO. The obtained interaction parameter value was ? 0.25 by the use of Nishi–Wang equation. The depression in the equilibrium melting temperatures and the negative value for the polymer–polymer interaction parameter suggest that the blends are miscible in the molten state in the range of investigated ratios, except for the 95/05 ratio in which the equilibrium melting temperature increased relative to the pure PEO. The miscibility should be due to the H-bonds among the hydroxyl groups from starch and oxygen atoms of repeat units of PEO.     

Assessment of critical material attributes of polyethylene oxide for formulation of prolonged-release tablets

Abstract

Physicochemical evaluation of polyethylene oxide (PEO) polymers with various molecular weights was performed at molecular (polymeric dispersion) and bulk level (powders, polymeric films, and tablets) with the aim of specifying polymer critical material attributes with the main contribution to drug release from prolonged-release tablets (PRTs). For this purpose, grades of PEO with low, medium, and high viscosity were used for formulating PRTs with a good soluble drug substance (dose solubility volume 15?ml). The results revealed a good correlation (r²=0.88) between in?vivo data (pharmacokinetic parameters: C_max and AUC) and the elastic property of PEO films determined with the nanoindentation method, demonstrating that film level can also be used for the in?vivo prediction of drug dissolution. The study confirmed that polymer molecular weight and its viscosity are the most important critical material attributes affecting drug dissolution (in?vitro) and in?vivo bioavailability (e.g. C_max and AUC). Our research revealed that the nanoindentation technique can distinguish well between various types of polymers, classifying PEO as the most ductile and polyvinyl alcohol as the most brittle. Finally, our study provides an approach for the determination of exact physical attributes of PEO as a critical material attribute from clinically relevant data, and it therefore fulfills the basic principles of product development by Quality by Design.     

Composition-dependent physical properties of poly[(vinylidene fluoride)-co-trifluoroethylene]–poly(ethylene oxide) blends

Polymer blends based on poly(vinylidene fluoride-co-trifluoroethylene) copolymers, P(VDF-TrFE), and poly(ethylene oxide), PEO, with varying compositions have been prepared by solvent casting. In this way, P(VDF-TrFE) crystallizes from the solution while solvent evaporates, while PEO crystallizes from the melt during cooling to room temperature. The surface morphology of the polymer blends indicates the transition from the fibrillar microstructure typical of PVDF-TrFE to the spherulite structure characteristic of PEO. The vibration mode characteristics of P(VDF-TrFE) are not influenced by the presence of PEO in the polymer blend. Confinement of PEO in the P(VDF-TrFE) phase change the conformation of PEO from trans to helix, increasing this transformation for increasing P(VDF-TrFE) content in the polymer blends. Sequential crystallization of the two polymers produce separated amorphous phases whose independent cooperative conformational motions are revealed by two main dynamic-mechanical relaxations. No chemical interaction seems to exist between the polymers within the blend.     

Probing the effects of cone potential in the electrospray ion source: consequences for the determination of molecular weight distributions of synthetic polymers

Shifts in the relative intensities of oligomer ions are found to accompany changes in the cone potential in the electrospray ion source, which introduce uncertainties into average molecular weight determinations for polymer distributions. Similar shifts with changes in cone potential have long been recognized in the multiple-charge distributions of proteins and other biomolecules. In the case of multiple-charge distributions of a single, or small number of, species there are no major consequences for calculation of molecular weight; however, mass distributions and the averages thereof, are of major concern with synthetic polymers and understanding the shifts in relative intensities becomes critically important. We report here an evaluation of the effects of cone potentials on the molecular weight distributions of synthetic polymers, which we compare with the effects on charge-state distributions of peptides. The effects of cone potential have been modeled mathematically, from which we conclude that cone potentials exert a focusing effect dependent on the mass-to-charge ratios of ions. It is largely this focusing effect that determines the dependence of oligomer ion intensities upon cone potential in the ESI mass spectra of polymers. The influence of cone potential on molecular weight determinations of polymers of varying polydispersities (P(o)) is compared and discussed. For polymers with low polydispersities (e.g., narrow molecular weight poly(ethyleneglycol) standards with P(o) < 1.5), the variation in molecular weight determinations tends to be small (typically <5%), whereas with synthetic polymers with polydispersities greater than 2, variations in cone potential can influence molecular weight determinations significantly (by 100% or even more).     

Synthesis and characterization of spherical polymer brushes

The synthesis of spherical polymer brushes consisting of a nano-SiO₂ core modified by γ-methacryloxypropyl trimethoxy-silane and a shell of linear polyacrylamide by grafting polymerization was described. The spherical polymer brushes were characterized by Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and Thermo-gravimetric analysis (TGA). After cleavage of the ester group that connected the polymers to the surface, the molecular weight of the brushes was determined by Gel Permeation Chromatography (GPC). The results showed that the average diameter of spherical polymer brushes was ca. 140 nm while weight average molecular weight and surface grafting density were 1.407 × 10³ g/mol and 1.016 × 10^?4 mol/g respectively.     

Coupling thermal field-flow fractionation with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the analysis of synthetic polymers

Thermal field-flow fractionation (ThFFF) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) have been coupled to yield a powerful combination of techniques for polymer analysis. Thermal FFF's high molecular weight (MW) selectivity and sensitivity to chemical composition are used to separate polydisperse polymers and polymer mixtures into the narrow polydispersity and homogeneous chemical composition fractions essential for MALDI-TOFMS analyses. On the other hand, MALDI-TOFMS's ability to directly measure molecular weight alleviates the need for polymer standards for ThFFF. In this first-time coupling of ThFFF and MALDI-TOFMS, compatibility issues were addressed and optimum conditions and procedures were identified and developed to maximize the capabilities of the combined technique. Depending on the polymer MW and the method of MALDI sample deposition, fractions from 1-10 ThFFF runs were combined for MALDI-TOFMS analysis. Binary solvents were used to enhance ThFFF retention and resolution of low-MW (<15-kDa) polymers, and methods were developed to allow routine MALDI-TOFMS analyses of polystyrene polymers up to 575 kDa. Overall, the MW compatibility of the two techniques was extended from several kilodaltons to several hundred kilodaltons. Polymer fractions were collected after separation by ThFFF and analyzed either by MALDI-TOFMS or reinjection into the ThFFF system. Good agreement was observed between the MW distribution data obtained by MALDI-TOFMS and ThFFF. The application of ThFFF/MALDI-TOFMS to polydisperse polymers and polymer mixtures was demonstrated. This combined technique was also shown to be a viable means for preparing standards from the original polymer sample.     

Separation of long double-stranded DNA by nanoparticle-filled capillary electrophoresis

We present the first example of the analysis of long double-stranded (ds) DNA molecules by nanoparticle-filled capillary electrophoresis (NFCE). To avoid aggregation of the gold nanoparticles (GNPs) and to allow strong interactions with the DNA molecules, the gold nanoparticles were modified with poly(ethylene oxide) (PEO) via noncovalent bonding to form gold nanoparticle/polymer composites (GNPPs). The neutral GNPPs are heavy (approximately 2.0 x 10(8) g/mol for the 32-nm GNP) and thus slow the DNA molecules that they encounter during the electrophoretic process. Compared to linear polymer solutions, such as hydroxyethyl cellulose and PEO, the GNPPs provide greater efficiency and require significantly shorter times to separate long dsDNA. The separation of lambda-DNA (0.12-23.1 kbp) by NFCE at -250 V/cm was accomplished in 3 min. The ability to separate high molecular weight DNA markers (8.27-48.5 kbp) with plate numbers greater than 10(6) suggests that this novel method may hold great promise for the analysis of long-stranded DNA molecules such as chromosomes. Moreover, this method is simple and affordable when compared to those that use micro- and nanofabricated devices for separating long DNA molecules.