首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
The variation of refractive index increments with molecular weight has been studied using solutions of polystyrene (2.2 × 103 < Mw < 1.8 × 106), poly(ethylene glycol) (1.0 × 103 < Mw < 2.0 × 104), and poly(dichlorophenylene oxide) (3.3 × 103 < Mw < 4.8 × 105) in toluene and poly(propylene glycol) (1.2 × 103 < Mw < 4.0 × 103) in benzene. The refractive index increments of polyglycols containing aliphatic ether moieties are negative in these solvents. However, poly(dichlorophenylene oxide) polymers, which contain aromatic ether moieties, give positive values. Linear and branched halogenated poly(phenylene oxide)s show an asymptotic approach of the refractive index increment to the same limiting value, but the approach is more rapid for the branched polymer.  相似文献   

2.
The zone‐drawing (ZD) method was applied three times to the melt‐spun poly(L ‐lactic acid) (PLLA) fibers of low molecular weight (Mv = 13,100) at different temperatures under various tensions. The mechanical properties and superstructure of the ZD fibers were investigated. The resulting ZD‐3 fiber had a draw ratio of 10.5, birefringence of 37.31 × 10−3, and crystallinity of 37%, while an orientation factor of crystallites remarkably increased to 0.985 by the ZD‐1. The Young's modulus and tensile strength of the ZD‐3 fiber respectively attained 9.1 GPa and 275 MPa, and the dynamic storage modulus was 10.4 GPa at room temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 991–996, 1999  相似文献   

3.
Microporous regenerated cellulose gel particles were prepared by mixing cellulose cuoxam with silk fibroin aspore former, and the mean pore size and pore volume of the pallicles were 525 nm and 7.27 mL g~(-1), respectively. Apreparative size-exclusion chromatography (SEC) column (550 mm×20 mm) packed with the cellulose gel particles wasused for the fractionation of two polysaccharides Dextran 07 (M_w = 7.14×10~4, d= 1.7) and Dextran 50(M_w = 50.5×10~4,d = 3.8) in water phase. The fractionation range of the stationary phase covered M_w from 3×10~3 to 1.1×10~6. The dailythroughput was 2.9 g for Dextran 07 (D07) and 4.3 g for Dextran 50 (D50) with a flow-rate of 1.5 mL min~(-1). The fractionsobtained by using the SEC were analyzed by an analytical SEC combined with laser light scattering (LLS), and thepolydispersity indices of fractions for Dextran 07 and Dextran 50 were determined to be 1.34-1.57 and 1.53-3.36,respectively. The preparative SEC is a simple, rapid, and suitable means not only for the fractionation of polysaccharides inwater but also for other polymers in organic solvents.  相似文献   

4.
Eight 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride‐4,4′‐diamino‐3,3′‐dimethylbiphenyl (6FDA‐OTOL) fractions and seven 2,2′‐bis[4‐(3,4‐dicarboxyphenoxy) phenyl] propane dianhydride‐4,4′‐diamino‐3,3′‐dimethylbiphenyl (BISADA‐OTOL) fractions in cyclopentanone at 30 °C were characterized by a combination of viscometry and static and dynamic laser light scattering (LLS). In static LLS, the angular dependence of the absolute scattered intensity led to the weight‐average molar mass (Mw), the z‐average root mean square radius of gyration, and the second virial coefficient. In dynamic LLS, the Laplace inversion of each measured intensity–intensity time correlation function resulted in a corresponding translational diffusion coefficient distribution [G(D)]. The scalings of 〈D〉 (cm2/s) = 8.13 × 10−5 Mw−0.47 and [η] (dL/g) = 2.36 × 10−3 Mw0.54 for 6FDA‐OTOL and 〈D〉 (cm2/s) = 3.02 × 10−4 Mw−0.60 and [η] (dL/g) = 2.32 × 10−3 Mw0.53 for BISADA‐OTOL were established. With these scalings, we successfully converted each G(D) value into a corresponding molar mass distribution. At 30 °C, cyclopentanone is a good solvent for BISADA‐OTOL but a poor solvent for 6FDA‐OTOL; this can be attributed to an ether linkage in BISADA‐OTOL. Therefore, BISADA‐OTOL has a more extended chain conformation than 6FDA‐OTOL in cyclopentanone. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2077–2080, 2000  相似文献   

5.
The data on the effect of polymerization temperature of 1‐hexene within the 30–70 °C range in the presence of a highly active supported titanium–magnesium catalyst on molecular weight characteristics and microtacticity of polyhexene, with cocatalyst composition being additionally varied (AlEt3 or Al(i‐Bu)3), in the absence and presence of an external stereoregulating electron‐donating compound and hydrogen, are reported. Polymerization conditions, making it possible to specifically regulate molecular weight and molecular weight distribution of polyhexene over a broad range ((Mw = 7 × 104–2.2 × 106 g mol−1; Mw/Mn = 3.7–33) and regulate isotacticity of polyhexene (content of mmmm pentads from 56% to 96%), while retaining high catalyst activity, are determined.  相似文献   

6.
A method was developed for the synthesis of arborescent polystyrene by “click” coupling. Acetylene functionalities were introduced on linear polystyrene (Mn = 5300 g/mol, Mw/Mn = 1.05) by acetylation and reaction with potassium hydroxide, 18‐crown‐6 and propargyl bromide in toluene. Polymerization of styrene with 6‐tert‐butyldimethylsiloxyhexyllithium yielded polystyrene (Mn = 5200 g/mol, Mw/Mn = 1.09) with a protected hydroxyl chain end. Deprotection, followed by conversions to tosyl and azide functionalities, provided the side chain material. Coupling with CuBr and N,N,N′,N″,N″‐pentamethyldiethylenetriamine proceeded in up to 94% yield. Repetition of the grafting cycles led to well‐defined (Mw/Mn ≤ 1.1) polymers of generations G1 and G2 in 84% and 60% yield, respectively, with Mn and branching functionalities reaching 2.8 × 106 g/mol and 460, respectively, for the G2 polymer. Coupling longer (Mn = 45,000 g/mol) side chains with acetylene‐functionalized substrates was also examined. For a linear substrate, a G0 polymer with Mn = 4.6 × 105 g/mol and Mw/Mn = 1.10 was obtained in 87% yield; coupling with the G0 (Mn = 52,000 g/mol) substrate produced a G1 polymer (Mn = 1.4×106 g/mol, Mw/Mn = 1.38) in 28% yield. The complementary approach using azide‐functionalized substrates and acetylene‐terminated side chains was also investigated, but proceeded in lower yield. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1730–1740  相似文献   

7.
The present article considers the coil‐to‐globule transition behavior of atactic and syndiotactic poly(methyl methacrylates), (PMMA) in their theta solvent, n‐butyl chloride (nBuCl). Changes in Rh in these polymers with temperature in dilute theta solutions were investigated by dynamic light scattering. The hydrodynamic size of atactic PMMA (a‐PMMA‐1) in nBuCl (Mw: 2.55 × 106 g/mol) decreases to 61% of that in the unperturbed state at 13.0°C. Atactic PMMA (a‐PMMA‐2) with higher molecular weight (Mw: 3.3 × 106 g/mol) shows higher contraction in the same theta solvent (αη = Rh(T)/Rh (θ) = 0.44) at a lower temperature, 7.25°C. Although syndiotactic PMMA (s‐PMMA) has lower molecular weight than that of atactic samples (Mw: 1.2 × 106), a comparable chain collapse was observed (αη = 0.63) at 9.0°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2253–2260, 1999  相似文献   

8.
The tensile strength of oriented polyethylene filaments is discussed in relation to molecular weight. Short-term tensile properties at room temperature were obtained in our laboratory and from the literature for polymer samples covering the molecular weight (M w) range from 54 × 103 to 4 × 106, and polydispersities ranging from 1.1 to 15.6, oriented by solid-state extrusion, melt spinning/drawing, solution spinning/drawing, and “surface growth.” It was found that both the molecular weight and its distribution markedly affected tensile strength. The breaking stress σ of highly oriented fibers varied with molecular weight roughly as σ ∝, M0.4, at constant M w/M n over the entire range studied. Reduction of polydispersity from 8 to 1.1 by an increase of M n with M w approximately constant at 105 increased tensile strength of oriented polyethylene filaments by a factor of nearly 2.  相似文献   

9.
Rigid‐rod poly(4′‐methyl‐2,5‐benzophenone) macromonomers were synthesized by Ni(0) catalytic coupling of 2,5‐dichloro‐4′‐methylbenzophenone and end‐capping agent 4‐chloro‐4′‐fluorobenzophenone. The macromonomers produced were labile to nucleophilic aromatic substitution. The molecular weight of poly(4′‐methyl‐2,5‐benzophenone) was controlled by varying the amount of the end‐capping agent in the reaction mixture. Glass‐transition temperatures of the macromonomers increased with increasing molecular weight and ranged from 117 to 213 °C. Substitution of the macromonomer end groups was determined to be nearly quantitative by 1H NMR and gel permeation chromatography. The polymerization of a poly(4′‐methyl‐2,5‐benzophenone) macromonomer [number‐average molecular weight (Mn) = 1.90 × 103 g/mol; polydispersity (Mw)/Mn = 2.04] with hydroxy end‐capped bisphenol A polyaryletherketone (Mn = 4.50 × 103 g/mol; Mw/Mn = 1.92) afforded an alternating multiblock copolymer (Mn = 1.95 × 104 g/mol; Mw/Mn = 6.02) that formed flexible, transparent films that could be creased without cracking. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3505–3512, 2001  相似文献   

10.
The morphology of one novel “homogeneous composite” and some conventional CaCO3-particulate-filled polyethylenes (PEs) has been investigated by transmission and scanning electron microscopy. It is found that for three different linear polyethylenes (M w = 37,000, 200,000, and 1.5 × 106) studied, ordering on the scale of spherulites was absent in the CaCO3-filled polymer. However, PE lamallae were observed growing normal to the filler interface. Changes in molecular weight of the polyethylene result in easily observed differences in morphology, while DSC studies indicate that crystallinity decreases in the presence of filler for the two lower-molecular-weight polyethylenes.  相似文献   

11.
To synthesize polyesters and periodic copolymers catalyzed by nonafluorobutanesulfonimide (Nf2NH), we performed ring‐opening copolymerizations of cyclic anhydrides with tetrahydrofuran (THF) at 50–120 °C. At high temperature (100–120 °C), the cyclic anhydrides, such as succinic anhydride (SAn), glutaric anhydride (GAn), phthalic anhydride (PAn), maleic anhydride (MAn), and citraconic anhydride (CAn), copolymerized with THF via ring‐opening to produce polyesters (Mn = 0.8–6.8 × 103, Mn/Mw = 2.03–3.51). Ether units were temporarily formed during this copolymerization and subsequently, the ether units were transformed into esters by chain transfer reaction, thus giving the corresponding polyester. On the other hand, at low temperature (25–50 °C), ring‐opening copolymerizations of the cyclic anhydrides with THF produced poly(ester‐ether) (Mn = 3.4–12.1 × 103, Mw/Mn = 1.44–2.10). NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectra revealed that when toluene (4 M) was used as a solvent, GAn reacted with THF (unit ratio: 1:2) to produce periodic copolymers (Mn = 5.9 × 103, Mw/Mn = 2.10). We have also performed model reactions to delineate the mechanism by which periodic copolymers containing both ester and ether units were transformed into polyesters by raising the reaction temperature to 120 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   

12.
Poly(3-hydroxybutyrate) (P3HB), a biologically produced, biodegradable natural polyester, exhibits excellent thermal and barrier properties but suffers from mechanical brittleness, largely limiting its applications. Here we report a mono-material product design strategy to toughen stereoperfect, brittle bio or synthetic P3HB by blending it with stereomicrostructurally engineered P3HB. Through tacticity ([mm] from 0 to 100 %) and molecular weight (Mn to 788 kDa) tuning, high-performance synthetic P3HB materials with tensile strength to ≈30 MPa, fracture strain to ≈800 %, and toughness to 126 MJ m−3 (>110× tougher than bio-P3HB) have been produced. Physical blending of the brittle P3HB with such P3HB in 10 to 90 wt % dramatically enhances its ductility from ≈5 % to 95–450 % and optical clarity from 19 % to 85 % visible light transmittance while maintaining desirably high elastic modulus (>1 GPa), tensile strength (>35 MPa), and melting temperature (160–170 °C). This P3HB-toughening-P3HB methodology departs from the traditional approach of incorporating chemically distinct components to toughen P3HB, which hinders chemical or mechanical recycling, highlighting the potential of the mono-material product design solely based on biodegradable P3HB to deliver P3HB materials with diverse performance properties.  相似文献   

13.
Interactions of cation/anion and cation/polymer in poly(N‐vinyl pyrrolidone) (PVP):silver triflate (AgCF3SO3) electrolytes with different weight‐average molecular weights (Mw's) of 1 × 106 (1 M), 3.6 × 105 (360 K), 4 × 104 (40 K), and 1 × 104 (10 K) have been studied with IR and Raman spectroscopies. According to the change of the C?O peak, coordination of silver ions by C?O in a low Mw (10 or 40 K) PVP matrix tend to be always thermodynamically favorable than high Mw (1 M or 360 K) PVP, demonstrating that the polymer matrix of low Mw dissolves silver salts more effectively. In addition, silver cations interact with both larger SO and smaller CF3 to form ion pairs, and the former interaction is stronger than the latter in a monomer or low Mw polymer matrix (40 K, 10 K), as demonstrated by theoretical ab initio calculation or experimental spectroscopy, respectively. However, CF3 interacts more favorably with silver cation than SO in high Mw (1 M and 360 K) PVP, which is ascribed to the steric effect of the bulky SO anion by highly entangled polymer chains. Despite the superior dissolving property of the low Mw polymer matrix, the membranes consisting of low Mw PVP and AgCF3SO3 exhibited poor separation performance for propylene/propane mixtures in comparison with those of high Mw, presumably because of the poor mechanical property for membrane formation in low Mw PVP. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1813–1820, 2002  相似文献   

14.
Second virial coefficients A2 and third virial coefficients A3 for benzene solutions of ten polystyrene fractions ranging in weight-average molecular weight Mw from 104 to 2 × 107 at 25°C were determined by light scattering. The third coefficient is represented approximately by A3 = 8.0 × 10?6 M mol g?3 cm6 for Mw above 105. In this molecular weight region, the factor g defined by A3/AMw/ This trend of g is consistent with predictions of early two-parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for Mw ? 2 × 105) and the mean-field two-parameter theory of Stockmayer and Casassa.  相似文献   

15.
Cloud point measurements were made for binary systems of polystyrene (PS) + methyl acetate (MA) and polystyrene (PS) + selectively deuterated MA: CD3COOCH3 and CH3COOCD3 with three PS samples of Mw = 4.0 × 105, 2.0 × 106, and 13.2 × 106. All systems are characterized by the phase diagrams with upper and lower critical temperature. H/D isotope effects on miscibility for both selectively deuterated acetates are very large and appeared to be independent of the site of deuterium substitution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2140–2143, 2009  相似文献   

16.
Short-range interactions between chain units of random copolymers in solution may be influenced by the composition or precisely by the distribution of sequence lengths of the same monomer units. Steric factors were derived for random copolymers of styrene and acrylonitrile with different compositions from the relation between the limiting viscosity number and the molecular weight. Mark-Houwink relations were obtained in methyl ethyl ketone (MEK) or in N,N′-dimethylformamide (DMF) at 30°C. for random copolymers containing 0.383 (Co-1) and 0.626 (Co-2) mole fraction of acrylonitrile, the expressions are: [η] = 3.6 X 10?4 M w0.62, for Co-1 in MEK; [η] = 5.3 X 10?4 M w0.61, for Co-2 in MEK; [η] = 1.2 × 10?4M w0.77 for Co-2 in DMF. With the Stockmayer-Fixman expression, these correlations become, respectively: [η]/M1/2 = 1.24 × 10?3 + 8.0 × 10?7 M1/2; and [η]/M1/2 = 1.70 × 10?3 + 6.3 × 10?7 M1/2; and [η]/M1/2 = 1.68 × 10?3 + 31.3 × 10?7 M1/2. From the unperturbed mean-square end-to-end distances, 〈L20, determined from the first terms of the latter expressions, together with 〈L20f calculated by assuming the completely free rotation, gives the steric factor σ = (〈L20/〈L20f)1/2 as 2.25 ± 0.05 for Co-1, and 2.31 ± 0.10 for Co-2. These values of σ are close to those for polystyrene (σ = 2.22 ± 0.05) and for polyacrylonitrile (σ = 2.20 ± 0.05). Therefore, it is concluded that the dimensions of random copolymers of styrene and acrylonitrile in solution are not significantly influenced by the composition. In other words, the unperturbed dimensions are not affected by a change in the alternation tendency between styrene units with phenyl side groups having a large molar volume and acrylonitrile units with nitrile groups responsible for the electrostatic interactions. On the other hand, the long-range interactions reflect the effect of sequence length. The Huggins constant and the second virial coefficient obtained from the light-scattering measurements have optimum values at about 0.5 mole fraction of acrylonitrile, where the greatest tendency for alternation seems to exist.  相似文献   

17.
RuH2(PPh3)4 catalyzed Tishchenko type polyaddition of terephthal-aldehyde gives aromatic polyester ( 1 ), which contains three structural units, [OCH2 C6H4 CH2O] ( 1a ), [OCH2 C6H4 CO] ( 1b ), and [CO C6H4 CO] ( 1c ). 1H-NMR spectrum shows the presence of the three units in a 1 : 2 : 1 ratio. Isophthalaldehyde also undergoes similar polyaddition to give another aromatic polyester ( 2 ), while 1,12-dodecanedial gives an aliphatic polyester ( 3 ) containing the following structural units: [OCH2 (CH2)10 CH2O] ( 3a ), [OCH2 (CH2)10 CO] ( 3b ), and [CO (CH2)10 CO] ( 3c ). The above polymers have Mn of 2.7 × 103−5.4 × 103 and Mw of 4.3 × 103 − 9.7 × 103, respectively. Mixtures of terephthalaldehyde and 1,12-dodecanedial produce copolymers, which contain the units 1a–1c and 3a–3c in a random sequence. In the copolymerization, terephthalaldehyde shows a strong tendency to give 1c units, whereas 1,12-dodecanedial predominantly affords 3a units. SmI2 also catalyzes polyaddition of terephthalaldehyde to give the corresponding polyester with Mn of 1.7 × 103 and Mw of 3.7 × 103, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1265–1273, 1997  相似文献   

18.
Polymer diffusion across interfaces at room temperature (21°C) was analyzed by direct nonradiative energy transfer (DET) in labeled latex films. Two modellatex polymers were examined: poly(butyl methacrylate) [PBMA, Mw = 3.5 × 104, Tg (dry) = 21°C] and a copolymer of 2-ethylhexyl methacrylate with 10 wt % (acetoacetoxy)-ethyl methacrylate [P(EHMA-co-AAEM), Mw = 4.8 × 104, Tg (dry) = −7°C]. Little energy transfer due to polymer diffusion was detected for the P(EHMA-co-AAEM) latex samples in the dispersed state or dried to solids content below ca. 90%, but above 90% solids, diffusion occurs among particles. For PBMA, diffusion occurs only after the film is dried (>97% solids) and aged. In the dry PBMA films, it requires 4–5 days at 21°C to reach a significant extent of mixing (fm = 0.3–0.4). This corresponds to an estimated penetration depth dapp of 30–40 nm and a mean apparent diffusion coefficient (Dapp) of 5 × 10−4 nm2/s. The corresponding Dapp value for the dry P(EHMA-co-AAEM) sample is 5 × 10−2 nm2/s, and it takes about 25–40 min for this polymer to reach fm of 0.3–0.4 with dapp of 20–30 nm. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1129–1139, 1998  相似文献   

19.
We measured the cloud-point curves of eight-arm star polystyrene (sPS) in methylcyclohexane (MCH) for polymer samples of three total molecular masses [weight-average molecular weight (Mw) × 10−3 = 77, 215, or 268]. We found a downward shift of 5–15 K in the critical temperature (Tc) of the star polymer solutions with respect to linear polystyrene (PS) solutions of the same Mw. The shift in Tc became smaller as Mw increased. The critical volume fraction for eight-arm sPS in MCH was equal within experimental uncertainty (10–40%) to that of linear PS in MCH. For sPS of Mw = 77,000 in MCH, we studied the mass density (ρ) as a function of temperature (T). As for linear polymers in solution, the difference in ρ between coexisting phases (Δρ) could be described over t = (TcT)/Tc for 1.1 × 10−4 < t < 4.7 × 10−3 with the Ising value of the exponent β in the expression Δρ = B tβ. Both ρ(T) above Tc and the average value of ρ below Tc were linear functions of temperature; no singular corrections were observed. The measurements of the shear viscosity (η) near Tc for sPS (Mw = 74,000) in MCH indicated a strong critical anomaly in η, but the data were not precise enough for a quantitative analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 129–145, 2004  相似文献   

20.
N-Vinyl-2-pyrrolidone(I) has been copolymerized with vinylferrocene(II) and vinylcyclopentadienyl manganese tricarbonyl(III) in degassed benzene solutions with the use of azobisisobutyronitrile (AIBN) as the initiator. The polymerizations proceed smoothly, and the relative reactivity ratios were determined as r1 = 0.66, r2 = 0.40 (for copolymerization of I with II, M1 defined as II) and r1 = 0.14 and r2 = 0.09 (for copolymerization of I with III, M1 defined as III). These copolymers were soluble in benzene, THF, chloroform, CCl4, and DMF. Molecular weights were determined by viscosity and gel-permeation chromatography studies (universal calibration technique.) The copolymers exhibited values of M?n between 5 × 103 and 10 × 103 and M?w between 7 × 103 and 17 × 103 with M?w/M?n < 2. Upon heating to 260°C under N2, copolymers of III underwent gas evolution and weight loss. The weight loss was enhanced at 300°C, and the polymers became in creasingly insoluble. Copolymers of vinylferrocene were oxidized to polyferricinium salts upon treatment with dichlorodicyanoquinone (DDQ) or o-chloranil (o-CA) in benzene. Each unit of quinone incorporated into the polysalts had been reduced to its radical anion. The ratio of ferrocene to ferricinium units in the polysalts was determined. The polysalts did not melt at 360°C and were readily soluble only in DMF.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号