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1.
The full‐chain dynamics and the linear viscoelastic properties of monodisperse, entangled linear and star polymers are simulated consistently via an equilibrium stochastic algorithm, based on a recently proposed full‐chain reptation theory 1 that is able to treat self‐consistently mechanisms of chain reptation, chain‐length fluctuations, and constraint release. In particular, it is the first time that the full‐chain simulation for star polymers is performed without subjecting to the great simplifications usually made. To facilitate the study on linear viscoelasticity, we employ a constraint release mechanism that resembles the idea of tube dilation, in contrast to the one used earlier in simulating flows, where constraint release was performed in a fashion similar to double reptation. Predictions of the simulation are compared qualitatively and quantitatively with experiments, and excellent agreement is found for all investigated properties, which include the scaling laws for the zero‐shear‐rate viscosity and the steady‐state compliance as well as the stress relaxation and dynamic moduli, for both polymer systems. The simulation for linear polymers indicates that the full‐chain reptation theory considered is able to predict very well the rheology of monodisperse linear polymers under both linear viscoelastic and flow conditions. The simulation for star polymers, on the other hand, strongly implies that double reptation alone is insufficient, and other unexplored mechanisms that may further enhance stress relaxation of the tube segments near the star center seem crucial, in explaining the linear viscoelasticity of star polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 248–261, 2000 相似文献
2.
Xiang Hao Kaixiang Yang Hairong Wang Feng Peng Haiyang Yang 《Angewandte Chemie (International ed. in English)》2020,59(11):4314-4319
Non‐Newtonian fluids are ubiquitous in daily life and industrial applications. Herein, we report an intelligent fluidic system integrating two distinct non‐Newtonian rheological properties mediated by an autocatalytic enzyme reaction. Associative polyelectrolytes bearing a small amount of ionic and alkyl groups are engineered: by carefully balancing the charge density and the hydrophobic effect, the polymer solutions demonstrate a unique shear thickening property at low pH while shear thinning at high pH. The urea‐urease clock reaction is utilized to program a feedback‐induced pH change, leading to a strong upturn of the nonlinear viscoelastic properties. As long as the chemical fuel is supplied, two distinct non‐Newtonian states can be achieved with a tunable lifetime span. As a proof of concept, we demonstrate how the physical energy‐driven nonequilibrium properties can be manipulated by a chemical‐fueled process. 相似文献
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A new approach is proposed to describe the spinodal decomposition, in particular, in polymer binary blends. In the framework of this approach, the spinodal decomposition is described as a relaxation of one‐time structure factor S(q,t) treated as an independent dynamic object (a peculiar two‐point order parameter). The dynamic equation for S(q,t), including the explicit expression for the corresponding effective kinetic coefficient, is derived. In the first approximation this equation is identical to the Langer equation. We first solved it both in terms of higher transcendental functions and numerically. The asymptotic behaviour of S(q,t) at large (from the onset of spinodal decomposition) times is analytically described. The values obtained for the power‐law growth exponent for the large‐time peak value and position of S(q,t) are in good agreement with experimental data and results of numerical integration of the Cahn‐Hilliard equation. 相似文献
4.
Kohji Ohno Benjamin Wong David M. Haddleton 《Journal of polymer science. Part A, Polymer chemistry》2001,39(13):2206-2214
The synthesis of 21‐arm methyl methacrylate (MMA) and styrene star polymers is reported. The copper (I)‐mediated living radical polymerization of MMA was carried out with a cyclodextrin‐core‐based initiator with 21 independent discrete initiation sites: heptakis[2,3,6‐tri‐O‐(2‐bromo‐2‐methylpropionyl]‐β‐cyclodextrin. Living polymerization occurred, providing well‐defined 21‐arm star polymers with predicted molecular weights calculated from the initiator concentration and the consumed monomer as well as low polydispersities [e.g., poly(methyl methacrylate) (PMMA), number‐average molecular weight (Mn) = 55,700, polydispersity index (PDI) = 1.07; Mn = 118,000, PDI = 1.06; polystyrene, Mn = 37,100, PDI = 1.15]. Functional methacrylate monomers containing poly(ethylene glycol), a glucose residue, and a tert‐amine group in the side chain were also polymerized in a similar fashion, leading to hydrophilic star polymers, again with good control over the molecular weight and polydispersity (Mn = 15,000, PDI = 1.03; Mn = 36,500, PDI = 1.14; and Mn = 139,000, PDI = 1.09, respectively). When styrene was used as the monomer, it was difficult to obtain well‐defined polystyrene stars at high molecular weights. This was due to the increased occurrence of side reactions such as star–star coupling and thermal (spontaneous) polymerization; however, low‐polydispersity polymers were achieved at relatively low conversions. Furthermore, a star block copolymer consisting of PMMA and poly(butyl methacrylate) was successfully synthesized with a star PMMA as a macroinitiator (Mn = 104,000, PDI = 1.05). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2206–2214, 2001 相似文献
5.
Hector Lopez Hernandez Abigail K. Grosskopf Lyndsay M. Stapleton Gillie Agmon Eric A. Appel 《Macromolecular bioscience》2019,19(1)
Drug delivery and cell transplantation require minimally invasive deployment strategies such as injection through clinically relevant high‐gauge needles. Supramolecular hydrogels comprising dodecyl‐modified hydroxypropylmethylcellulose and poly(ethylene glycol)‐block‐poly(lactic acid) have been previously demonstrated for the delivery of drugs and proteins. Here, it is demonstrated that the rheological properties of these hydrogels allow for facile injectability, an increase of cell viability after injection when compared to cell viabilities of cells injected in phosphate‐buffered saline, and homogeneous cell suspensions that do not settle. These hydrogels are injected at 1 mL min?1 with pressures less than 400 kPa, despite the solid‐like properties of the gel when at rest. The cell viabilities immediately after injection are greater than 86% for adult human dermal fibroblasts, human umbilical vein cells, smooth muscle cells, and human mesenchymal stem cells. Cells are shown to remain suspended and proliferate in the hydrogel at the same rate as observed in cell media. The work expands on the versatility of these hydrogels and lays a foundation for the codelivery of drugs, proteins, and cells. 相似文献
6.
Satu Strandman Minna Luostarinen Satu Niemel Kari Rissanen Heikki Tenhu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4189-4201
Two novel multifunctional initiators for atom transfer radical polymerization (ATRP) were synthesized by derivatization of tetraethylresorcinarene. The derivatization induced a change in the conformation of the resorcinarene ring, which was confirmed by NMR spectroscopy. The initiators were used in ATRP of tert‐butyl acrylate and methyl methacrylate, producing star polymers with controlled molar masses and low polydispersities. Instead of the expected star polymers with eight arms, polymers with four arms were obtained. Conformational studies on the initiators by rotating‐frame nuclear Overhauser and exchange spectroscopy NMR and molecular modeling suggested that of eight initiator functional groups on tetraethylresorcinarene, four are too close to each other to be able to initiate the chain growth. Starlike poly(tert‐butyl acrylate) macroinitiators were used further in the block copolymerization of methyl methacrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4189–4201, 2004 相似文献
7.
We show that Shaffer's version of the bond fluctuation model can be used to simulate three‐arm star polymers. We report a simulation study of both single stars and melts of star polymers with arm lengths up to 90 monomer units (approximately twice the entanglement crossover length for linear chains). Center‐of‐mass self‐diffusion of single stars is Rouse‐like (D ˜ N–1). Due to a limited range of molecular weights we cannot distinguish between a power‐law and an exponential dependence of the star‐melt self‐diffusion coefficient on arm length. 相似文献
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Katrina M. Knauer Yaling Zhu Robson F. Storey Sarah E. Morgan 《Journal of Polymer Science.Polymer Physics》2016,54(9):916-925
The phase behavior of (PS‐PIB)2‐s‐PAA miktoarm star terpolymers with varying volume fractions of PAA was investigated directly by transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering, and indirectly by thermogravimetric analysis and degree of water sorption. The microdomains of (PS‐PIB)2‐s‐PAA demonstrate a unique and unexpected progression from highly ordered cylinders, to lower ordered spheres, to gyroid structures with increasing PAA content from 6.6 to 47 wt %. Interestingly, the phase behavior in the miktoarm star polymer system is significantly different from that reported previously for the linear counterpart of similar composition (PAA‐PS‐PIB‐PS‐PAA), where a steady progression from cylindrical to lamellar morphology was observed with increasing PAA content. At low PAA concentrations, the morphology is driven primarily by the relative solubility of the components, while at high PAA content the molecular architecture dominates. Thermal annealing demonstrated the thermodynamic stability of the morphologies, indicating the potential for design of novel microstructures for specific applications through precise control of architecture, composition, and interaction parameters of the components. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 916–925 相似文献
11.
In this article we discuss the state of the art in the field of second‐order non‐linear optical polymers. More specifically, we highlight those results that we think made an important contribution to the field, combined with some of our own results. We start with a general overview of all the aspects involved in characterizing second‐order non‐linear optical polymers, from thin film formation and poling to second‐harmonic generation and electro‐optic measurements on such systems. Next, we review the second‐order non‐linear optical properties of selected polymer systems such as poly(vinyl ether)s, polystyrenes, polymethacrylates, main‐chain polymers and high Tg polymers like polyimides and polymaleimides. Finally, we discuss some new polymer systems that might become important in the field of non‐linear optics in the near future. 相似文献
12.
Xingzhu Wang Hailiang Zhang Erqiang Chen Xiayu Wang Qifeng Zhou 《Journal of polymer science. Part A, Polymer chemistry》2005,43(15):3232-3244
A series of novel multi‐armed (di‐, tri‐ and tetra‐armed) mesogen‐jacketed liquid crystal polymers (MJLCPs) were synthesized by atom transfer radical polymerization (ATRP) of {2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}(MPCS) using di‐, tri‐ and tetrafunctional initiator, respectively. The results show that the number average molecular weight (Mn,GPC) was increased versus monomer conversion, and the polydispersities were quite narrow (<1.19), which is the characteristic of controlled polymerization. The chemical structures of these multi‐armed mesogen‐jacketed liquid crystal polymers were confirmed by 1H NMR. The liquid crystalline behavior of these multi‐armed MJLCPs with arms ranging from two to four was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide‐angle X‐ray diffraction (WAXD). It was found that liquid crystalline phases appeared simply when the number molecular weights (Mn,GPC) of these multi‐armed MJLCPs was higher than a certain critical values, that is, Mn,GPC > 1.87 × 104 g/mol, 1.84 × 104 g/mol, 2.69 × 104 and 3.68 × 104 g/mol, which were initiated by coil difunctional initiator, hard difunctional initiator, trifunctional initiator and tetrafunctional initiator, respectively. All the liquid crystalline phase was found to be stable up to the decomposition temperature of these multi‐armed MJLCPs. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3232–3244, 2005 相似文献
13.
Thomas G. McKenzie Jing M. Ren Dave E. Dunstan Edgar H. H. Wong Greg G. Qiao 《Journal of polymer science. Part A, Polymer chemistry》2016,54(1):135-143
Core cross‐linked star (CCS) polymers with radiating arms composed of high‐order multiblock copolymers have been synthesized in a one‐pot system via iterative copper‐mediated radical polymerization. The employed “arm‐first” technique ensures the multiblock sequence of the macroinitiator is carried through to the star structure with no arm defects. The versatility of this approach is demonstrated by the synthesis of three distinct star polymers with differing arm compositions, two with an alternating ABABAB block sequence and one with six different block units (i.e. ABCDEF). Owing to the star architecture, CCS polymers in which the arm composition consists of alternating hydrophilic–hydrophobic (ABABAB) segments undergo supramolecular self‐assembly in selective solvents, whereas linear polymers with the same block sequence did not yield self‐assembled structures, as evidenced by DLS analysis. The combination of microstructural and topological control in CCS polymers offers exciting possibilities for the development of tailor‐made nanoparticles with spatially defined regions of functionality. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 135–143 相似文献
14.
O. Altintas B. Yankul G. Hizal U. Tunca 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6458-6465
We report a simple preparation of three‐armed (A3‐type) star polymers based on the arm‐first technique, using a click‐reaction strategy between a well‐defined azide‐end‐functionalized polystyrene, poly(tert‐butyl acrylate), or poly(ethylene glycol) precursor and a trisalkyne‐functional initiator, 1,1,1‐tris[4‐(2‐propynyloxy)phenyl]ethane. The click‐reaction efficiency for A3‐type star formation has been investigated with gel permeation chromatography measurements (refractive‐index detector). The gel permeation chromatography curves have been split with the deconvolution method (Gaussian area), and the efficiency of A3‐type star formation has been found to be 87%. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6458–6465, 2006 相似文献
15.
Paweł Chmielarz 《先进技术聚合物》2017,28(12):1787-1793
The vitamin B6‐based macroinitiator was prepared for the first time by the transesterification reaction of pyridoxine with 2‐bromoisobutyryl bromide. A pyridoxine‐based star‐shaped block copolymer with a hydrophilic pyridoxine core and a dual hydrophilic poly(2‐(dimethylamino)ethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) arms was synthesized for the first time via a simplified electrochemically mediated atom transfer radical polymerization, utilizing only 20 ppm of catalyst complex. The rate of the polymerizations was controlled by applying appropriate potential/current values during electrolysis to prevent the possibility of intermolecular coupling of the polymer stars. The asymmetric star polymers showed narrow molecular weight distribution (? = 1.09–1.13). 1H NMR spectral results confirm the formation of star‐like block (co)polymers. These new vitamin B6‐based eagle‐shaped star (co)polymers may find biomedical and biosensor applications as pH‐sensitive and thermo‐sensitive drug delivery systems. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
16.
Marisa Spiniello Anton Blencowe Greg G. Qiao 《Journal of polymer science. Part A, Polymer chemistry》2008,46(7):2422-2432
A series of fluorescently labeled core cross‐linked star (CCS) polymers were synthesized via the “arm‐first” approach, employing atom transfer radical polymerization (ATRP) to control the resulting architecture. The initiator p‐toluenesulfonyl chloride (TsCl) was used to synthesize “living” poly(methyl methacrylate) (PMMA) macroinitiator, which was subsequently cross‐linked to generate the CCS polymers. Divinylbenzene (DVB) was used as the cross‐linker and 7‐[4‐(trifluoromethyl)coumarin] methacrylamide ( F1 , λex = 343 nm) was added as a fluorescent labeling monomer. A range of PMMA/DVB/ F1 based CCS polymers were synthesized with the core domain made selectively fluorescent by using varying amounts of monomer F1 . The core functionalized stars were characterized using gel permeation chromatography (GPC) equipped with multi‐angle laser light scattering (MALLS), refractive index (RI), and UV–visible detectors. The fluorescence quantum yield (ΦF) and the amount of fluorescent monomer incorporated into the core were quantified by UV–visible and fluorescence spectrophotometry. It was recognized that the overall molecular weights of the stars produced, along with their core molecular weight, decreased as the mol % of monomer F1 was increased relative to cross‐linker. Visual confirmation of F1 incorporation was obtained by fluorescence microscopy of thin polymer films cast on glass substrates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2422–2432, 2008 相似文献
17.
Craig L. Homrighausen Teddy M. Keller 《Journal of polymer science. Part A, Polymer chemistry》2002,40(1):88-94
The syntheses and characterization of linear silarylene‐siloxane‐diacetylene polymers 3a–c and their thermal conversion to crosslinked elastomeric materials 4a–c are discussed. Inclusion of the diacetylene unit required synthesis of an appropriate monomeric species. 1,4‐Bis(dimethylaminodimethylsilyl)butadiyne [(CH3)2N? Si(CH3)2? C?C? C?C? (CH3)2Si? N(CH3)2] 2 was prepared from 1,4‐dilithio‐1,3‐butadiyne and 2 equiv of dimethylaminodimethylchlorosilane. The linear polymers were prepared via polycondensation of 2 with a series of disilanol prepolymers. The low molecular weight silarylene‐siloxane prepolymers 1a–c (terminated by hydroxyl groups) were synthesized via solution condensation of an excess amount of 1,4‐bis(hydroxydimethylsilyl)benzene with bis(dimethylamino)dimethylsilane. The linear polymers were characterized by 1H and 13C NMR, Fourier transform infrared spectroscopy, gel permeation chromatography, thermogravimetric analysis (TGA), and DSC. The elastomers exhibited long‐term oxidative stability up to 330 °C in air as determined by TGA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 88–94, 2002 相似文献
18.
Harry W. Gibson Aurica Farcas Jason W. Jones Zhongxin Ge Feihe Huang Matthew Vergne David M. Hercules 《Journal of polymer science. Part A, Polymer chemistry》2009,47(14):3518-3543
Dibenzo‐24‐crown‐8‐terminated polystyrene ( 5 ) was chain extended to “dimeric” 8 by pseudorotaxane formation with a ditopic guest, α,ω‐bis[p‐(N‐benzylammoniomethyl)phenoxy]heptane bis(hexafluorophosphate) ( 7 ). The three‐armed star polymer 11 was similarly formed by complexation of the dibenzo‐24‐crown‐8‐terminated polystyrene ( 5 ) with a tritopic secondary ammonium salt, 1,3,5‐tris[p‐(benzylammoniomethyl)phenyl]benzene tris(hexafluorophosphate) ( 10 ). Another three‐armed star polymer 13 was self‐assembled from dibenzo‐24‐crown‐8‐terminated polystyrene ( 5 ) and a tetratopic paraquat compound, 1,2,4,5‐tetrakis{p‐N‐[(N′‐methyl‐4,4′‐bipyridinium)methylphenyl]}benzene octakis(hexafluorophosphate) ( 12 ). The above chain extension and star polymer formation processes seemed to be cooperative; that is, the second and third complexation steps proceed with stepwise higher efficiencies than statistically expected. Dibenzo‐24‐crown‐8‐terminated polystyrene ( 5 ) was chain extended with secondary ammonium terminated polystyrene 14 , forming 16 , and also self‐assembled with a secondary ammonium ion terminated polyisoprene 15 to form supramolecular block copolymer 17 . These processes were examined by NMR, mass spectrometry and viscometery. Thus, although binding in these systems is not particularly strong (association constants <104 M?1), these examples provide proof‐of‐principle that pseudorotaxane formation is a viable concept for chain extension and self‐assembly of novel types of block copolymers and star polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3518–3543, 2009 相似文献
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Aydan Dag Hakan Durmaz Okan Sirkecioglu Gurkan Hizal Umit Tunca 《Journal of polymer science. Part A, Polymer chemistry》2009,47(9):2344-2351
The click chemistry strategy is successfully applied for the preparation of three‐arm star (A3) ring opening metathesis polymers. A well‐defined monoazide end‐functionalized poly(N‐ethyl oxanorbornene) and a poly(N‐butyl oxanorbornene) obtained via ring opening metathesis polymerization using first generation Grubbs' catalyst are simply clicked with the trisalkyne core affording the synthesis of target star polymers. The obtained star polymers are characterized via nuclear magnetic resonance spectroscopy and gel permeation chromatography (GPC). The deconvolution analyses of GPC traces reveal that the click reaction efficiency for the star formation strongly depends on the chemical nature and the molecular weight of ROM polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2344–2351, 2009 相似文献