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1.
The average relaxation time τ0, relaxation times corresponding to segmental motion τ1 and group rotations τ2, of a series of binary mixtures of poly(ethylene glycols) (PEG 200+PEG 300, PEG 400+PEG 600, PEG 1500+PEG 4000, PEG 6000+PEG 9000, PEG 200+PEG 1500, PEG 300+PEG 4000, PEG 400+PEG 6000 and PEG 600+PEG 9000) have been carried out in dilute solutions of benzene and carbon tetrachloride at 9·83GHz. The effect on chain flexibility due to inter- and intra-molecular association in these binary mixtures is discussed by comparing relaxation times of these mixtures with their individual relaxation times in solution. It is inferred that the extent of hydrogen bonding in different binary mixtures is not similar and is influenced by solvent environment, but there is correlation between τ0 and τ1 values in all these binary mixtures, which may be because of hydrogen bonding. The observed τ2 values in all these mixtures suggests that the chain-ends remain excluded from the intermolecular association and τ2 is independent of the polymer constituents of the mixture and solvent. It is also equal to the τ2 values of the individual polymers. © 1998 SCI.  相似文献   

2.
Molecular dynamics of binary mixtures of poly(propylene glycol) (PPG) and poly(ethylene glycol)s (PEGs) of varying molecular weight due to molecular interactions, chain coiling and elongation in dilute solution under various conditions, ie varying number of monomer units of PEG, method of mixing of polymers and solvent environment, has been explored using microwave dielectric relaxation times. The average relaxation time τo, relaxation time corresponding to segmental motion τ1 and group rotations τ2, of a series of binary mixtures of poly(propylene glycol) 2000 and poly(ethylene glycol) of varying molecular weight (ie PPG 2000 + PEG 200, PPG 2000 + PEG 300, PPG 2000 + PEG 400, and PPG 2000 + PEG 600 mixed by equal volume in the pure liquid states, and PPG 2000 + PEG 1500, PPG 2000 + PEG 4000 and PPG 2000 + PEG 6000 mixed equal weights in solvent) have been determined in dilute solution in benzene and carbon tetrachloride at 10.10 GHz and 35 °C. A comparison of the results of these binary systems of highly associating molecules shows that the molecular dynamics corresponding to rotation of a molecule as a whole and segmental motion in dilute solutions are governed by the solvent density when the solutes are mixed in their pure liquid state. Furthermore, the molecular motion is independent of solvent environment when the polymers are added separately in the solvent for the preparation of binary mixtures. It has also been observed that there is a systematic elongation of the dynamic network of the species formed during mixing of pure liquid polymers in lighter environment of solvent with increasing PEG monomer units, while the elongation behaviour of the same species in the heavier environment of carbon tetrachloride solvent is in contrast to the elongation behaviour of the polymeric species formed in pure PEG. The role of rotating methyl side‐groups in the PPG molecular chain has been discussed in term of the breaking and reforming of hydrogen bonds in complex polymeric species for the segmental motion. In all these mixtures, the relaxation time corresponding to group rotations is independent of the solvent environment and constituents of the binary mixtures. The effect of chain flexibility and coiling in these binary mixtures is discussed by comparing the relaxation times of the mixtures with their individual relaxation times in dilute solutions measured earlier in this laboratory. © 2001 Society of Chemical Industry  相似文献   

3.
This paper reports the results of a systematic study of microwave dielectric relaxation times of poly(ethylene glycols), average molecular weight 200–9000, in dilute solutions of benzene at 9·83GHz. These results are compared with the values of relaxation times obtained earlier in carbon tetrachloride solutions. This shows that the average relaxation times τ0 and the relaxation time corresponding to segmental reorientation τ1 are influenced by the solvent environment. The variation in chain flexibility in these polymers with the increase in degree of polymerization and formation of intra- and inter-molecular hydrogen bonding in benzene and carbon tetrachloride solutions is discussed with the help of relaxation data. The relaxation time τ2 corresponding to group rotations has been determined. It is found that the τ2 value is independent of solvent environment and degree of polymerization, and may be attributed to the rotation of chain −OH end-groups around the C−O bonds in dynamic equilibrium, with the formation of a five-membered ring due to intra-molecular hydrogen bonding at the end of the chain. © 1998 SCI.  相似文献   

4.
Dielectric complex permittivity of propylene glycol (PG), poly(propylene glycol) (PPG-2000) and their mixtures with concentration of 25, 50 and 75 vol% of PG were measured in the frequency range 10 MHz-4 GHz at 25°C using time domain reflectometry (TDR). For these molecules and their mixtures, only one frequency independent dielectric loss peak was observed. The relaxation for these systems is described by a single relaxation time using Debye model. The large value of observed relaxation time for PG molecules shows the formation of molecular clusters. It is found that the relaxation time for PG-PPG mixtures is smaller in comparison to the relaxation times of PG and PPG molecules, and it linearly increases with the concentration of the PG in the mixtures. The values of relaxation times of PG-PPG mixtures are discussed particularly with respect to the solvent (PG) behaviour, which can be assigned to unaffected, loosely affected and tightly bound solvent and also with respect to the PPG chain coiling. As a peculiar feature the observed relaxation time is direct evidence of the interchange of solvent-solvent to solvent-polymer interaction.  相似文献   

5.
This paper reports the measured values of dielectric permittivity ε′ and dielectric loss ε″ of ethylene glycol, diethylene glycol and poly(ethylene glycol)s of average molecular weight 200, 300, 400 and 600 g mol−1 in the pure liquid state. The measurements have been carried out in the frequency range 200 MHz to 20 GHz at four different temperatures of 25, 35, 45 and 55 °C. The complex plane plots (ε″ versus ε′) of these molecules are Cole–Cole arcs. The static dielectric constant ε0, high‐frequency limiting dielectric constant ε, average relaxation time τ0 and distribution parameter α have been determined from these plots. The value of the Kirkwood correlation factor g and the dielectric rate free energy of activation ΔF have also been evaluated. The dependence of relaxation time on molecular size and viscosity has been discussed. A comparison has also been made with the dielectric behaviour of these molecules in dilute solutions of non‐polar solvents, which were carried out earlier in this laboratory. The influences of intermolecular hydrogen bonding and molecular chain coiling on the dielectric relaxation of these molecules have been recognized. © 2000 Society of Chemical Industry  相似文献   

6.
陈晓明 《化学工程师》2012,26(3):14-16,32
测定了聚乙二醇(PEG)在十二烷基硫酸钠(SDS)和琥珀酸双-2-乙己酯磺酸钠(AOT)水溶液中的粘度,讨论了SDS和AOT在水溶液中聚集形态的差异对PEG与SDS和AOT相互作用的不同影响,结果表明:PEG-SDS与PEG-AOT体系粘度均明显增加,而PEG-SDS与PEG-AOT体系粘度变化机制不同,根本原因是表面活性剂在高分子溶液中聚集行为不同,SDS分子在PEG链上聚集,形成类胶束,使高分子链带电,表现出聚电解质的粘度行为;PEG链吸附于AOT囊泡,不同PEG链对囊泡的吸附可能造成高分子链更加伸展,PEG特性粘数增大,使溶液粘度上升。  相似文献   

7.
The molecular relaxation characteristics of rubbery amorphous crosslinked networks based on poly(ethylene glycol) diacrylate [PEGDA] and poly(propylene glycol) diacrylate [PPGDA] have been investigated using broadband dielectric spectroscopy. Dielectric spectra measured across the sub-glass transition region indicate the emergence of an intermediate “fast” relaxation in the highly crosslinked networks that appears to correspond to a subset of segmental motions that are more local and less cooperative as compared to those associated with the glass transition. This process, which is similar to a distinct sub-Tg relaxation detected in poly(ethylene oxide) [PEO], may be a general feature in systems with a sufficient level of chemical or physical constraint, as it is observed in the crosslinked networks, crystalline PEO, and PEO-based nanocomposites.  相似文献   

8.
Poly(ethylene terephthalate) copolymers were prepared by melt polycondensation of dimethyl terephthalate and excess ethylene glycol with 10–40mol% (in feed) of poly(ethylene glycol) (E) and poly(tetramethylene glycol) (B), with molecular weight (MW) of E and B 200–7500 and 1000, respectively. The reduced specific viscosity of copolymers increased with increasing MW and content of polyglycol comonomer. The temperature of melting (Tm), cold crystallization and glass transition (Tg) decreased with the copolymerization. Tm depression of copolymers suggested that the E series copolymers are the block type at higher content of the comonomer. Tg was decreased below room temperature by the copolymerization, which affected the crystallinity and the density of copolymer films. Water absorption increased with increasing content of comonomer, and the increase was much higher for E1000 series films than B1000 series films. The biodegradability was estimated by weight loss of copolymer films in buffer solution with and without a lipase at 37°C. The weight loss was enhanced a little by the presence of a lipase, and increased abruptly at higher comonomer content, which was correlated to the water absorption and the concentration of ester linkages between PET and PEG segments. The weight loss of B series films was much lower than that of E series films. The abrupt increase of the weight loss by alkaline hydrolysis is almost consistent with that by biodegradation.  相似文献   

9.
Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1495–1505, 1997  相似文献   

10.
H. Block  J.J. Gosling  S.M. Walker 《Polymer》1984,25(10):1465-1468
The effect of large electric fields (≤0.8 MV m?1) on solutions of poly(n-hexylisocyanates) of differing molecular weights is described. Non-linear dielectric effects are observed and their magnitudes are in fair agreement with those predicted theoretically for inflexible dipolar molecules of low polarizability. Small enhancements of relaxation frequencies are also caused by the application of large electric fields.  相似文献   

11.
E. Piorkowska  R. Masirek 《Polymer》2006,47(20):7178-7188
Plasticization of semicrystalline poly(l-lactide) (PLA) with a new plasticizer - poly(propylene glycol) (PPG) is described. PLA was plasticized with PPG with nominal Mw of 425 g/mol (PPG4) and 1000 g/mol (PPG1) and crystallized. The plasticization decreased Tg, which was reflected in a lower yield stress and improved elongation at break. The crystallization in the blends was accompanied by a phase separation facilitated by an increase of plasticizer concentration in the amorphous phase and by annealing of blends at crystallization temperature. The ultimate properties of the blends with high plasticizer contents correlated with the acceleration of spherulite growth rate that reflected accumulation of plasticizer in front of growing spherulites causing weakness of interspherulitic boundaries. In PLA/PPG1 blends the phase separation was the most intense leading to the formation of PPG1 droplets, which facilitated plastic deformation of the blends that enabled to achieve the elongation at break of about 90-100% for 10 and 12.5 wt% PPG1 content in spite of relatively high Tg of PLA rich phase of the respective blends, 46.1-47.6 °C. Poly(ethylene glycol) (PEG), long known as a plasticizer for PLA, with nominal Mw of 600 g/mol, was also used to plasticize PLA for comparison.  相似文献   

12.
聚乙二醇/聚己内酯三嵌段共聚物的合成与表征   总被引:3,自引:0,他引:3  
以甲苯二异氰酸酯 (TDI)为偶联剂 ,合成了聚乙二醇 (PEG) /聚己内酯 (PCL)两亲性三嵌段共聚物 (PEG-b-PCL -b -PEG ,PECL) ,采用IR、1 H-NMR、DSC和WAXD分析和研究了PECL的结构与性能。实验结果表明 ,PECL的结构和组成与设计相一致 ,结晶度和熔点均低于均聚物 ,且随着PECL中PCL嵌段含量的增加 ,PCL嵌段熔点升高。透射电镜照片显示PECL纳米粒呈核 /壳结构的球形。  相似文献   

13.
Enthalpic relaxation data are presented on poly(ethylene terephthalate), poly(ethylene naphthalate) and their copolymers. Analysis of these data allows the determination of the amount of energy absorbed at the glass transition, Qt, and the location of the enthalpic recovery peak, Tmax, as a function of the time of ageing of the samples. Ageing measurements were carried out for periods of up to 2016 h and at temperatures between 40 °C and 110 °C, depending upon the chemical composition of the system being investigated. The enthalpic relaxation rates are influenced by the chemical structure and reflect the effects of local order pinning the chains and influencing the rate of enthalpic recovery. © 2000 Society of Chemical Industry  相似文献   

14.
Naoki Nakajima  Yoshito Ikada 《Polymer》1995,36(26):4961-4965
The effect of antioxidants contained in poly(ethylene glycol) (PEG) on cell fusion was studied using L929 cells in the monolayer state. Hydroquinone monomethyl ether (HQME), 2-mercaptobenzimidazole (MB), butyl hydroxyanisole (BHA) and 2,6-di-(t-butyl)-4-methylphenol (BHT) were chosen from the antioxidants that have currently been used to protect commercially available PEG from oxidation. Cell culture was conducted in 40% w/w aqueous solution of PEG with a molecular weight of 3000 in the presence of different concentrations of antioxidants. BHA clearly enhanced membrane fusion of L929 cells with increasing concentration in PEG solution, whereas HQME, MB and BHT had no significant effect on cell fusion. The enhancement of cell fusion by BHA might be ascribed to balanced hydrophobicity and high water solubility in comparison with the other three antioxidants.  相似文献   

15.
A polyblend of poly(ortho esters)–poly(ethylene glycol) (POE–PEG) was prepared. The release behavior of the acetanilide‐loaded film of the POE–PEG polyblend was studied. Blending POE with water‐soluble PEG can promote the release of drug in pH 7.4 PBS buffer at 37°C, while POE has plasticizing effect on PEG. Infrared and X‐ray diffraction studies reveal that there is some interaction between POE and acetanilide. The SEM micrographs disclose that the porosity of the drug‐loaded film enhances with an increase immersing time. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 303–309, 1999  相似文献   

16.
Contour maps of dielectric loss tangent within the ranges 0.1 Hz to 3 MHz and ?175 °C to +190 °C are presented for a commercial poly(ethylene terephthalate) (PET) in two initial states of crystallinity. Individual absorption regions resemble those for poly(butylene terephthalate) and are attributed to carbonyl‐driven α‐ and β‐relaxation processes and to Maxwell–Wagner–Sillars polarizations. Possible causes are considered for the asymmetry and structure apparent in the α‐peak of partially crystalline PET. © 2001 Society of Chemical Industry  相似文献   

17.
Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide (PEO) and poly(propylene oxide) (PPO) was evaluated by building up temperature-concentration phase diagrams. We have studied bifunctional triblock copolymers (HO-PEO-PPO-PEO-OH) and monofunctional diblock copolymers (R-PEO-PPO-OH and R-PPO-PEO-OH, where R length is linear C4 and C12–14). The cloud points of the polymer solutions depended on EO/PO ratio, polarity, R length and position of the hydrophilic and hydrophobic segments along the molecule. Such factors influence on the solutions behavior was also analyzed in terms of critical micelle concentration (CMC), which was obtained from surface tension vs. concentration plots. Salts (NaCl and KCl) added into the polymer solutions change the solvent polarity decreasing the cloud points. On the other hand, the cloud points of the polymer solutions increased as a hydrotrope (sodium p-toluenesulfonate) was added. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1767–1772, 1997  相似文献   

18.
The intrinsic viscosity of polystyrene–poly(ethylene oxide) (PS–PEO) and PS–poly(ethylene glycol) (PEG) blends have been measured in benzene as a function of blend composition for various molecular weights of PEO and PEG at 303.15 K. The compatibility of polymer pairs in solution were determined on the basis of the interaction parameter term, Δb, and the difference between the experimental and theoretical weight-average intrinsic viscosities of the two polymers, Δ[η]. The theoretical weight-average intrinsic viscosities were calculated by interpolation of the individual intrinsic viscosities of the blend components. The compatibility data based on [η] determined by a single specific viscosity measurement, as a quick method for the determination of the intrinsic viscosity, were compared with that obtained from [η] determined via the Huggins equation. The effect of molecular weights of the blend components and the polymer structure on the extent of compatibility was studied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1471–1482, 1998  相似文献   

19.
Bicomponent melt blown (MB) microfiber nonwovens of poly(propylene) (PP) and poly(ethylene terephthalate) (PET) were produced in this study. It is interesting to analyze the polymer distribution uniformity across the web because it affects many end‐use properties. By utilizing the technique of differential scanning calorimetry (DSC), a standard working line between heat of fusion and weight percentage was constructed for mixtures of PP and PET components. The fitted equations were used for determination of a component percentage in a certain position across the MB web. Measurements were conducted from DSC re‐heating curves to achieve accurate results. The distribution of polymer varies with polymer mass ratio and processing conditions. The overall uniformity increased with the percentage of PP. When PP is the minor component in the polymer pair, it exhibits notably higher percentage in edge areas across the MB web. These results suggest the phase interface distortion of the polymer melt occurred at the entrance of the MB coat‐hanger die tip. The polymer distribution uniformity is improved by adjusting temperature profile of the MB die. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2885–2889, 2002  相似文献   

20.
K. Pathmanathan  G.P. Johari  R.K. Chan 《Polymer》1986,27(12):1907-1911
The complex relative permittivity of poly(propylene oxide) (PPO) of molecular weight 4000 containing 1.23 wt% water has been measured in the temperature range 77 to 325 K and frequency range 12 Hz to 500 kHz, and the results are compared with the corresponding study of pure PPO-4000. On the addition of water, all the three processes, namely the β-process (at T < Tg) and the - and ′-processes (at T > Tg), are shifted to higher temperatures. The strength of the β-process remained unchanged but that of the and ′-processes increased. The halfwidths of the three processes remained unchanged on dilution with water. The decrease in the relaxation rate of the β-process is suggested to be due to hydrogen bonding of the ---CH(CH3)---O---CH2--- group with water molecules. Water antiplasticizes PPO-4000 and this is interpreted as due to the increased chain length when the chain ends become linked via hydrogen bonds. The static permittivity is increased by 30% on addition of 1.23 wt% water.  相似文献   

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