The formation of bicontinuous microemulsions (BUEs) in ternary symmetric blends including two immiscible homopolymers A and B as well as a linear gradient copolymer G is verified by Monte Carlo simulations. Four phase diagrams as a function of segregation strength and blend composition are constructed to show the effects of compositional gradient. Compared with the blends of A/B/diblock copolymers, the BUE phase occupies a broader region in the phase diagram of the A/B/G blends and is replaced by the three-phase coexistence phases of A + B + L or A + B + D at a much lower chain length ratio. Moreover, the lamellar phase is formed at a higher value of segregation strength, has a shorter periodic length and lower orientational order, and spans a narrower range of the phase diagram. A “counteraction effect” is proposed to explain those discrepancies caused by gradient copolymers. 相似文献
Styrene/4-methylstyrene (S/MS) random and gradient copolymers were synthesized by nitroxide-mediated controlled radical polymerization (NM-CRP) and compared to random copolymers made by conventional free radical polymerization (ConvFRP). The gradient copolymers have molecular weight (MW) values approaching 85,000 g/mol, making these some of the higher MW gradient copolymers reported to date. Due to the proximity of the glass transition temperatures (Tg) of polystyrene (PS) and poly(4-methylstyrene) (PMS), there is no significant difference in Tg between the gradient and random copolymers, with both copolymer types yielding single Tgs that typically increase slightly with increasing MS content. While enthalpy relaxation studies demonstrate similarity in random copolymers made by NM-CRP and ConvFRP, they reveal significant differences between random and gradient copolymers. Gradient copolymers exhibit broad enthalpy recovery peaks, whereas random copolymers exhibit narrower enthalpy recovery peaks. The maxima in the enthalpy recovery peaks are at substantially lower temperature, as much as 17 °C, in the gradient copolymers as compared to random copolymers of equal overall composition. While random and gradient copolymers of a given overall composition exhibit similar enthalpy recovery values at a common physical aging time and quench depth relative to Tg, the major differences in the enthalpy recovery peaks indicate that differences in sequence distribution along the chain length can lead to unusual behavior in gradient copolymers relative to random copolymers. 相似文献
An easily obtained parameter for characterizing polymers is the molecular weight distribution (MWD). Polymers with different MWD have different properties. The MWD can be easily influenced with controlled polymerization technologies. Examples of how these methods influence the properties of block and gradient copolymers in wetting and dispersing additives are discussed. These wetting and dispersing additives are used to make solvent-borne paints and aqueous pigment concentrates. An advantage of modulation of the MWD is the ability to fine tune-specific properties, such as the compatibility or the wetting activity of the polymer. 相似文献
Nanoblends, in which dispersed-phase domains exhibit length scales of order 100 nm or less, are made using a continuous, industrially scalable, mechanical process called solid-state shear pulverization (SSSP). An 80/20 wt% polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend processed by SSSP and consolidated by platen pressing, without melt processing, exhibits a quasi-nanostructured morphology with many irregular, minor-phase domain sizes of ∼100 nm or less. After short-residence-time single-screw extrusion, the pulverized blend exhibits spherical dispersed-phase domains with a number-average diameter of 155 nm. Thus, SSSP followed by certain melt-processing operations can yield nanoblends. However, the pulverized blend exhibits significant coarsening of the dispersed-phase domains during long-term, high-temperature static annealing, indicating that SSSP followed by other melt processes may yield microstructured blends. In order to suppress coarsening, a styrene (S)/methyl methacrylate (MMA) gradient copolymer is synthesized by controlled radical polymerization. When 5 wt% S/MMA gradient copolymer is added to the PS/PMMA blend during SSSP, the resulting blend exhibits a nanostructure nearly identical to that of the blend without gradient copolymer, and coarsening is nearly totally suppressed during long-term, high-temperature static annealing. Thus, SSSP with gradient copolymer addition can yield compatibilized nanoblends. Morphologies obtained in the pulverized PS/PMMA nanoblend are compared with those in blends of PS/poly(n-butyl methacrylate) and PS/high-density polyethylene made using identical SSSP conditions, providing for commentary on the ability of SSSP to produce nanostructured blends as a function of blend components. 相似文献
Crystallization elution fractionation (CEF) is the newest crystallization-based technique for estimating the chemical composition distribution of ethylene/1-olefin copolymers. Understanding the separation mechanism of CEF for ethylene/propylene copolymers over their full compositional range is challenging because the crystallizabilities of the copolymer chains depend on the longest ethylene sequence and on longest isotactic propylene sequence. We developed a mathematical model to describe the CEF mechanism for ethylene/propylene copolymers over the entire compositional range using population balances for the crystallization and dissolution stages. The joint distribution of longest ethylene and isotactic propylene sequences determines how the copolymer populations crystallize and dissolve. The model was validated with experimental CEF profiles of ethylene/propylene copolymers varying from pure ethylene to propylene homopolymers. 相似文献
The controlled synthesis of low-Tg poly(2-ethylhexyl acrylate) (P2EHA) and derived random, block and blocky gradient copolymers via atom transfer radical polymerization (ATRP) is described. After optimizing the reaction conditions for the homopolymerization of 2EHA via ATRP, the synthesis of a variety of copolymers with poly(t-butyl acrylate) (PtBuA) was investigated. First, AB-block copolymers were targeted, starting from P2EHA and PtBuA as macroinitiators. Second, random copolymers of tBuA and 2EHA with different monomer ratios were synthesized. Finally, the synthesis of “blocky” gradient copolymers via a one-pot procedure was investigated, starting with the homopolymerization of tBuA, followed by the addition of 2EHA. The hydrolysis of the PtBuA-segments to poly(acrylic acid) (PAA), which was carried out with methanesulfonic acid, resulted in block, blocky gradient and random copolymers consisting of PAA and P2EHA. Solubility testing of the copolymers in slightly basic water (pH ∼ 9) demonstrated that the gradient structure significantly enhances solubility compared to the block copolymer structures with equal composition. The polymers have been characterized by MALDI-TOF MS, GPC and 1H NMR. 相似文献
Styrene (S)/4-hydroxystyrene (HS) copolymers are synthesized by hydrolysis of S/4-acetoxystyrene copolymer precursors; two gradient copolymer precursors are made by semi-batch, nitroxide-mediated controlled radical polymerization, and a random copolymer precursor is prepared by conventional free radical polymerization. Conventional heat curves from differential scanning calorimetry indicate two glass transition temperatures (Tgs) and a broad Tg in well-annealed 59/41 mol% and 25/75 mol% S/HS gradient copolymers, respectively, both of which contain short S end-blocks. In contrast, a narrow Tg is observed in a 57/43 mol% random copolymer. Each S/HS copolymer is added at 5 wt% by solution mixing to an 80/20 wt% polystyrene (PS)/polycaprolactone (PCL) blend and tested for its ability to compatibilize the blend during melt processing; the hydroxyl groups on the HS units can form hydrogen bonds with the PCL ester groups. The S/HS random copolymer fails as a compatibilizer while both gradient copolymers are good compatibilizers. Relative to the blend without copolymer, the blend with 59/41 mol% S/HS gradient copolymer also exhibits a major reduction in initial dispersed-phase domain size and irregularly shaped domains, which are indicators of a sharply reduced interfacial tension. In contrast, the blend with 25/75 mol% S/HS gradient copolymer has an average PCL domain size comparable to the blend without copolymer and a broad domain size distribution. The presence of S/HS copolymers in the blend leads to reduced PCL crystallization and melting temperatures as well as reduced enthalpies of crystallization and melting, consistent with some solubilization of copolymer in the PCL domain interiors. 相似文献
Thermo-responsive brush copolymers poly(methyl methacrylate (MMA)-co-2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM)-graft-(N-isopropyl-acrylamide) (NIPAAm)) were synthesized using Cu-mediated “living” radical polymerization (LRP) approach. Varied grafting densities of the brushes were obtained through adjusting backbone structure as random, gradient and block respectively. The effect of grafting densities on their thermo-responsive phase transition behaviors in aqueous solution and on surface were investigated in detail. The lower critical solution temperature (LCST) of brush copolymers in solution was adjusted as 35, 37 and 38 °C through random, gradient and block backbone structure respectively. Their structure tunable thermo-responsive phase transition in solution were further confirmed by the different micelle aggregation behaviors above LCST which monitored by transmission electron microscopy (TEM) images and dynamic light scattering (DLS). In addition, surfaces modified by the resulted brush copolymers have a temperature tunable wettability based on thermo-responsive phase transition in solid, the similar WCA variation range of three brush copolymers implies that the composition of backbone does not much affect the switchable wettability of surfaces. 相似文献
In this study, novel protein/biodegradable polymer blend biomaterials‐gelatin/poly(ethylene oxide) blend films with compositional gradients were successfully fabricated by a dissolution/diffusion method. Two kinds of compositional gradient films, which were different in gradient structure, were prepared. The compositional gradient structure in the films was characterized by polarized optic microscopy, ATR‐FTIR, and trans‐FT‐IR mapping measurement. In addition, the mechanical properties of the gradient films were characterized with reference to their gradient structure. It is found that the compositional gradient films have better mechanical properties than the pure gelatin film. These protein/biodegradable polymer compositional gradient films have a potential for many biomedical applications.
Well-defined statistical, gradient and block copolymers consisting of isobornyl acrylate (IBA) and n-butyl acrylate (nBA) were synthesized via atom transfer radical polymerization (ATRP). To investigate structure-property correlation, copolymers were prepared with systematically varied molecular weights and compositions. Thermomechanical properties of synthesized materials were analyzed via differential scanning calorimetry (DSC), dynamic mechanical analyses (DMA) and small-angle X-ray scattering (SAXS). Glass transition temperature (Tg) of the resulting statistical poly(isobornyl acrylate-co-n-butyl acrylate) (P(IBA-co-nBA)) copolymers was tuned by changing the monomer feed. This way, it was possible to generate materials which can mimic thermal behavior of several homopolymers, such as poly(t-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA) and poly(n-propyl acrylate) (PPA). Although statistical copolymers had the same thermal properties as their homopolymer equivalents, DMA measurements revealed that they are much softer materials. While statistical copolymers showed a single Tg, block copolymers showed two Tgs and DSC thermogram for the gradient copolymer indicated a single, but very broad, glass transition. The mechanical properties of block and gradient copolymers were compared to the statistical copolymers with the same IBA/nBA composition. 相似文献
Copolymers of ethylene with propylene, butene-1 and hexene-1 were prepared using a titanium–magnesium (TMC) or a vanadium–magnesium catalyst (VMC). The copolymers were examined for thermal stability by TGA, melting and crystallization behaviour by DSC and crystallinity by XRD. Fractionated samples of ethylene–hexene-1 copolymers were also similarly characterized. Results indicate that VMC produces copolymers with a higher degree of crystallinity and greater compositional homogeneity than TMC. 相似文献
A high performance liquid chromatography column (HPLC) Hypercarb® packed with porous graphite has proven to discriminate polyolefin molecules due to differences in their adsorption and desorption behaviour. While linear polyethylene (PE) and syndiotactic polypropylene (sPP) are adsorbed on the graphite packing, isotactic polypropylene (iPP) is not adsorbed. The column operates at 160 °C with 1-decanol as sample solvent and mobile phase. We have now tested this HPLC system for separations of random propene/1-alkene and ethylene/1-hexene copolymers: While copolymers of propene with 1-butene, 1-hexene and 1-octene copolymers eluted in size exclusion mode without adsorption, propene/1-octadecene and ethylene/1-hexene copolymers are strongly retained and eluted only after application of a linear gradient starting from 1-decanol and ending with pure 1,2,4-trichlorobenzene. The retention of propene/1-alkene (>11 carbons in the side chain) copolymers increases with the concentration of comonomer, making this HPLC system suitable to separate these copolymers according to their chemical composition. In contrast, the retention of ethylene/1-hexene samples decreases with increasing 1-hexene content. Branching in this case shortens the length of continuous methylene sequences of the polymer backbone, which are expected to adsorb in a planar conformation to the graphite layers. This is the first report on the separation of short chain branched polyolefins by high-temperature adsorption liquid chromatography. 相似文献
A new approach to gradient chromatography of polymers is presented, in which the sample is introduced at the end of the gradient and elutes within the elution volume range typical for size exclusion chromatography (SEC). Due to the gradient the samples are retarded and elute nearly independent of molar mass at the adsorption threshold. The concept was proven for a series of narrowly distributed poly(methy methacrylate)s (PMMA) in a chloroform-tetrahydrofuran (THF) SEC-gradient. The application of the SEC-gradient to a blend of PMMA and polystyrene standards of similar molar masses, which could not be separated by SEC due to their similar hydrodynamic sizes, resulted in a clear separation according to chemical composition. Since SEC-gradients allow dissolving the sample in strong eluents, which might result in breakthrough peaks in conventional gradients, the new approach is a valuable alternative to conventional gradient chromatography. 相似文献
In this paper, two methodologies for determining comonomer composition in ethylene 1-olefin copolymers, namely three detectors coupled to a temperature rising elution fractionation unit (3D-TREF) and size exclusion chromatography coupled to a Fourier transfer infrared detector (SEC-FTIR), are examined and compared. Because the two methods are based on different separation mechanisms, insight into the resin's molecular architecture is gained from two entirely different, yet complementary perspectives. The choice of which method to use will be determined by the specific structure vs. property issue under study. Comparative results from the analysis of copolymers produced by Ziegler-Natta, chromium and metallocene catalysts show that both the methods are useful for characterizing LLDPE resins. However, the 3D-TREF method may offer more insight into the heterogeneity of resin blends, particularly when the blend components have similar molecular weights. Although some MW-dependency information of the temperature fractions can be ascertained via viscometer and light scattering detectors, SEC-FTIR is the more appropriate method to detect compositional heterogeneity in resin blends that are composed of two or more resins with the same copolymer compositions, but with different molecular weights. 相似文献
Epoxy-functional spontaneous gradient copolymers of glycidyl methacrylate (G) and n-butyl acrylate (B) were synthesized via atom transfer radical polymerization (ATRP). The copolymerization reactions were carried out in toluene solution at 70 °C, using methyl 2-bromopropionate (MBrP) as initiator and copper chloride with N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalyst system. The kinetic behaviour of the statistical copolymerizations was studied in a wide composition interval with molar fractions of G ranging from 0.10 to 0.75. The synthesized copolymers were characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. 1H NMR was employed to determine the copolymer composition, demonstrating the gradient character of the copolymers along the main chain in the whole monomer conversion interval. Apart from this, the sequence distribution and stereoregularity were analyzed. These microstructural experimental data agreed well with those calculated from Mayo-Lewis terminal model (MLTM) and a Bernoullian statistic with an isotacticity parameter of σG = 0.28 and a coisotacticity parameter of σ = 0.30. 相似文献