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1.
We report that lithium salts in lithium-ion batteries effectively modify the physical properties of poly (methyl methacrylate) (PMMA). The glass transition temperature (Tg) is an indicator of the heat resistance of amorphous polymers. The anionic species of the salts strongly affected the glass transition behavior of PMMA. We focused on the additive effects of various lithium salts, such as LiCF3SO3, LiCOOCF3, LiClO4, and LiBr, on the Tg of PMMA. The large anions of the former three salts caused them to form macroscopic aggregates that acted as fillers in the PMMA matrix and to combine the PMMA domains, increasing Tg. On the other hand, LiBr salts dispersed microscopically in the PMMA matrix at the molecular scale, leading to the linking of the PMMA chains. Thus, the addition of LiBr to PMMA increased Tg as well as the relaxation time in the range of glass to rubber transition.  相似文献   

2.
To have a better insight into the effect of interaction between polymer matrix and clay on the properties of nanocomposite, poly(methyl methacrylate)/clay nanocomposites were prepared by a heterocoagulation method. Using a reactive cationic emulsifier, methacryloyloxyethyltrimethyl ammonium chloride (METAC), a strong polymer–clay interaction was obtained with the advantage of keeping a consistent polymer matrix property. X‐ray diffraction and transmission electronic microscopy indicated an exfoliated structure in nanocomposites. The glass transition temperature (Tg) of the nanocomposites was measured by DSC and DMA. The DMA results showed that with a strong interaction, PMMA–METAC nanocomposite showed a 20 °C enhancement in glass transition temperature (Tg), whereas a slight increase in Tg was observed for PMMA–cetyl trimethylammonium bromide (CTAB)/clay nanocomposite with a weak interaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 733–738, 2010  相似文献   

3.
An amphiphilic comb‐like copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly((oxyethylene)9 methacrylate) (POEM) side chains, PVC‐graft‐POEM was synthesized via atom transfer radical polymerization. This comb copolymer was complexed with LiCF3SO3 to form a solid polymer electrolyte. FTIR and FT‐Raman spectroscopy indicate that lithium salts are dissolved in the ion conducting POEM domains of microphase‐separated graft copolymer up to 10 wt % of salt concentration. Microphase‐separated structure of the materials and the selective interaction of lithium ions with POEM domains were revealed by transmission electron microscopy, wide angle X‐ray scattering, and differential scanning calorimetry. The maximum ionic conductivity of 4.4 × 10?5 S/cm at room temperature was achieved at 10 wt % of salt concentration, above which salts are present as less mobile species such as ion pairs and higher order ionic aggregates, as characterized by FT‐Raman spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1443–1451, 2009  相似文献   

4.
We investigated the effects of lithium bromide (LiBr) on the structure and properties of polyamide 6 (PA6). The strong ion–dipole interactions between lithium cations and the amide groups in PA6 greatly increased the glass transition temperature (Tg) and retarded the crystallization rate of PA6. As a result, compression-molded PA6 blends were highly transparent and had high Tg values. The rheological terminal region was obvious in the blends because the ion–dipole interactions weakened at high temperatures. This indicates that the melt processability was barely affected by LiBr. We also evaluated the optical anisotropy of the polymer to determine its suitability as a functional optical film. We found that hot-stretched blend films had large positive orientation birefringence with significantly weak wavelength dispersion, which can be attributed to the enhanced anisotropic polarizability of PA6. We also found that the stress-optical coefficient in the glassy region decreased with increasing LiBr content. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1513–1520  相似文献   

5.
The soluble poly(methyl methacrylate‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PMMA–POSS) hybrid nanocomposites with improved Tg and high thermal stability were synthesized by common free radical polymerization and characterized using FTIR, high‐resolution 1H NMR, 29Si NMR, GPC, DSC, and TGA. The POSS contents in the nanocomposites were determined based on FTIR spectrum, revealing that it can be effectively adjusted by varying the feed ratio of POSS in the hybrid composites. On the basis of the 1H NMR analysis, the number of the reacted vinyl groups on each POSS molecules was determined to be about 6–8. The DSC and TGA measurements indicated that the hybrid nanocomposites had higher Tg and better thermal properties than the pure PMMA homopolymer. The Tg increase mechanism was investigated using FTIR, displaying that the dipole–dipole interaction between PMMA and POSS also plays very important role to the Tg improvement besides the molecular motion hindrance from the hybrid structure. The thermal stability enhances with increase of POSS content, which is mainly attributed to the incorporation of nanoscale inorganic POSS uniformly dispersed at molecular level. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5308–5317, 2007  相似文献   

6.
Broadband dielectric spectroscopy was used to study the segmental (α) and secondary (β) relaxations in hydrogen‐bonded poly(4‐vinylphenol)/poly(methyl methacrylate) (PVPh/PMMA) blends with PVPh concentrations of 20–80% and at temperatures from ?30 to approximately glass‐transition temperature (Tg) + 80 °C. Miscible blends were obtained by solution casting from methyl ethyl ketone solution, as confirmed by single differential scanning calorimetry Tg and single segmental relaxation process for each blend. The β relaxation of PMMA maintains similar characteristics in blends with PVPh, compared with neat PMMA. Its relaxation time and activation energy are nearly the same in all blends. Furthermore, the dielectric relaxation strength of PMMA β process in the blends is proportional to the concentration of PMMA, suggesting that blending and intermolecular hydrogen bonding do not modify the local intramolecular motion. The α process, however, represents the segmental motions of both components and becomes slower with increasing PVPh concentration because of the higher Tg. This leads to well‐defined α and β relaxations in the blends above the corresponding Tg, which cannot be reliably resolved in neat PMMA without ambiguous curve deconvolution. The PMMA β process still follows an Arrhenius temperature dependence above Tg, but with an activation energy larger than that observed below Tg because of increased relaxation amplitude. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3405–3415, 2004  相似文献   

7.
Stable to atmospheric moisture, adhesive and transparent polymer electrolytes have been prepared by blending poly(methyl methacrylate) (PMMA) with poly(propylene glycol)-425/LiCF3SO3 complexes. The blending of the polymers has been achieved by a method developed in our laboratory: free radical polymerization of methylmethacrylate in the polyether/salt matrix. A series of polymer blend complexes varying in PMMA content (up to 20% by weight) and oxygen/metal ratios (25, 16, and 8) have been synthesized and their properties studied. All the samples prepared in this study were found to be optically clear unlike the higher molecular weight poly(propylene glycol)-2000 (PPG-2000) system which required a minimum salt concentration to compatibilize a specific amount of PMMA with PPG. The mechanisms by which the salt holds the otherwise incompatible polymers together in a single phase have been investigated by FT-IR. Our studies show a weak coupling of the ether oxygens in the PPG with the ester groups of the PMMA through the lithium cations. Discrete changes has been observed in the FT-IR spectrum of PMMA when doped with the lithium salt hitherto unnoticed with other dopants. Gel permeation chromatography results of the PMMA samples isolated from the solid electrolytes indicate the molecular weight to vary between 43000 and 121000 with relatively narrow distributions, 1.6?2.0. The ionic conductivities of the polymer blend electrolytes were fairly high (10?5 S/cm) at room temperature. The PMMA neither significantly influenced the Tg of the blend complexes nor effected the ionic conductivities drastically. The ionic conductivity as a function of temperature followed the empirical Vogel-Tammann-Fulcher equation. The blending of PMMA with PPG/LiCF3SO3 complexes was found to impart good adhesiveness to the solid electrolytes while making them stable to atmospheric moisture. © 1992 John Wiley & Sons, Inc.  相似文献   

8.
Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (Tg) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated Tg's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The Tg composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003  相似文献   

9.
2,3,4,5,6‐Pentafluoro and 4‐trifluoromethyl 2,3,5,6‐tetrafluoro styrenes were readily copolymerized with methyl methacrylate (MMA) by a free radical initiator. The copolymers were soluble in tetrahydrofuran and acetone. The films obtained were transparent and flexible. The glass transition temperatures (Tgs) of the copolymers were found positively deviated from the Gordon–Taylor equation. The positive deviation could be accounted for by dipole–dipole intrachain interaction between the methyl ester group of MMA and the highly fluorinated aromatic moiety, which resulted in a decrease in the segmental mobility of the polymer chains and the enhanced Tg values of the copolymers. The water absorption of PMMA was greatly decreased by copolymerization of MMA with the highly fluorinated styrenes. With as little as 10 mol % of pentafluoro styrene content in the copolymer, the water absorption was decreased to one‐third of that for pure PMMA. The fluorinated styrenes‐MMA copolymers were thermally stable up to 420 °C under air and nitrogen atmospheres. With 50 mol % of MMA in the copolymer, the copolymer was still stable up to 350 °C. Since these copolymers contain a large number of fluorine atoms, the light absorption in the region of the visible to near infrared is decreased in comparison with nonfluorinated polymers. Thus, these copolymers may be suitable for application in optical devices, such as optical fibers and waveguides. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010  相似文献   

10.
We have prepared polymer electrolytes composed of poly(methyl methacrylate-co-lithium methacrylate) ionomer (P(MMA-co-LiMA)), low molecular weight PEG, and LiCF3SO3 salt. The ion groups in P(MMA-co-LiMA) could enhance the miscibility between the MMA units and PEG in the polymer electrolytes. This miscibility enhancement made the pathway of ion transport less tortuous, and consequently led to the increase in ion conductivity. The maximum ambient ion conductivities in these systems were measured to be in the range of 10−4–10−5 S/cm. The polymer electrolytes became transparent at the higher ion content owing to the enhanced miscibility. The mechanical stability of the polymer electrolytes was also improved through the introduction of ion groups into the PMMA. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 991–997, 1998  相似文献   

11.
Poly(methyl methacrylate) (PMMA) was anchored to multiporous poly(vinylidine fluoride) (PVDF) surface via electron beam preirradiation grafting technique to prepare PVDF/PMMA brushes. The conformation of the PVDF/PMMA brushes was verified through Attenuated total reflection‐Fourier transform infra red spectroscopy (ATR‐FTIR), energy dispersive X‐ray spectroscopy (EDX), and scanning electron microscopy (SEM). Thermal stability of PVDF/PMMA brushes was characterized by thermo gravimetric analysis (TGA). The degradation of PVDF/PMMA brushes showed a two‐step pattern. PVDF/PMMA brushes membrane could be used as polymer electrolyte in lithium‐ion rechargeable batteries after it was activated by uptaking 1 M LiPF6/EC‐DMC (ethylene carbonate/dimethyl carbonate; EC:DMC = 1:1 by volume) electrolyte solution. The activated membrane showed high ionic conductivity, 6.1 × 10?3 S cm?1 at room temperature, and a good electrochemical stability up to 5.0 V. The excellent performances of multiporous PVDF‐g‐PMMA membranes suggest that they are suitable for application in high‐performance lithium‐ion batteries. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 751–758, 2008  相似文献   

12.
Commercial polydisperse atactic poly(methyl methacrylate) (PMMA) exhibits a decreased glass transition temperature (Tg) when the film thickness is less than ~60 nm, whereas more model atactic PMMA shows an increased Tg in thin films supported on clean silicon wafers. NMR indicates no difference in tacticity, so the divergent thin film behavior appears related to the relative distribution of molecular mass. Extraction of some low molecular weight PMMA components from the commercial sample results in a significant modification of the thin film Tg compared with the initial PMMA fraction. The extracted sample exhibits initially a slight decrease in Tg as the film thickness is reduced below ~60 nm, but then Tg appears to increase for films thinner than 20 nm. These results illustrate the sensitivity of polymer thin film properties to low‐molecular mass components and could explain some of the contradictory reports on the Tg of polymer thin films that exist in the literature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010  相似文献   

13.
The polymer electrolytes composed of poly(acrylonitrile‐co‐lithium methacrylate) [P(AN‐co‐LiMA)], ethylene carbonate (EC), and LiClO4 salts have been prepared. The ion groups in the P(AN‐co‐LiMA) were found to prevent EC from crystallization through their ion–dipole interactions with the polar groups in the EC. This suppression of the EC crystallization could lead to the enhancement of the ion conductivity at subambient temperature. The polymer electrolytes based on the PAN ionomer with 4 mol % ion content exhibited ion conductivities of 2.4 × 10−4 S/cm at −10°C and 1.9 × 10−3 S/cm at 25°C by simply using EC as a plasticizer. In the polymer electrolytes based on the PAN ionomer, ion motions seemed to be coupled with the segmental motions of the polymer chain due to the presence of the ion–dipole interaction between the ion groups in the ionomer and the polar groups in the EC, while the ion transport in the PAN‐based polymer electrolytes was similar to that of the liquid electrolytes. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 247–252, 1999  相似文献   

14.
Fluoroalkyl methacrylates, 2,2,2‐trifluoroethyl methacrylate ( 1 ), hexafluoroisopropyl methacrylate ( 2 ), 1,1,1,3,3,3‐hexafluoro‐2‐methyl‐2‐propyl methacrylate ( 3 ), and perfluoro t‐butyl methacrylate ( 4 ) were synthesized. Homopolymers and copolymers of these fluoroalkyl methacrylates with methyl methacrylate (MMA) were prepared and characterized. With the exception of the copolymers of MMA and 2,2,2‐trifluoroethyl methacrylate ( 1 ), the glass transition temperatures (Tgs) of the copolymers were found to deviate positively from the Gordon‐Taylor equation. The positive deviation from the Gordon‐Taylor equation could be accounted for by the dipole–dipole intrachain interaction between the methyl ester group and the fluoroalkyl ester group of the monomer units. These Tg values of the copolymers were found to fit with the Schneider equation. The fitting parameters in the Schneider equation were calculated, and R2 values, the coefficients of determination, were almost 1.0. The refractive indices of the copolymers, measured at 532, 633, and 839 nm wavelengths, were lower than that of PMMA and showed a linear relationship with monomer composition in the copolymers. 2 and MMA have a tendency to polymerize in an alternating uniform monomer composition, resulting in less light scattering. This result suggests that the copolymer prepared with an equal molar ratio of 2 and MMA may have useful properties with applications in optical devices. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4748–4755, 2008  相似文献   

15.
Copolymers of methyl methacrylate (MMA) with 2,3,5,6‐tetrafluorophenyl methacrylate (TFPMA), pentafluorophenyl methacrylate (PFPMA), and 4‐trifluoromethyl‐2,3,5,6‐tetrafluorophenyl methacrylate (TFMPMA) were investigated. All the three systems showed a random copolymerization character. The composition, glass transition temperature (Tg), and refractive index of the copolymers obtained were studied. Tgs of TFPMA/MMA and PFPMA/MMA copolymers were found to deviate positively from the Gordon–Taylor equation. However, Tgs of TFMPMA/MMA copolymers were well fit with the Gordon–Taylor equation. These results indicated the existence of interaction between MMA and either TFPMA or PFPMA units in copolymers. This interaction resulted in the enhancement of the Tg of MMA polymers through the copolymerization with TFPMA and PFPMA. The refractive index and the light transmittance of copolymers were close to those of PMMA. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
The free volume behaviour of the polyacrylonitrile/lithium triflate system is investigated over the composition range 0–75 wt % salt. The addition of salt, up to 45 wt %, to the PAN polymer substantially increases the free volume as measured by the orthopositronium pickoff lifetime, τ3. Beyond this salt concentration (i.e., 45–70 wt %) the free volume remains approximately constant. This constant free volume region corresponds to a region of high ionic conductivity in the glassy state, making these materials polymer‐based fast ion conductors, that is, having a decoupling ratio Rτ ≫1. The high salt content in these fast ion conductors results in a high susceptibility to polar solvents such as water. For all compositions, water absorption results in a free volume increase attributed to plasticization; however, in the fast ion conducting region, a significantly larger free volume response due to plasticization is measured and may be connected to a percolation morphology in these samples. Salt addition is shown to lower the Tg, as measured by positron annihilation lifetime spectroscopy (PALS). Tg is 115°C for PAN and 85°C for 66 wt % lithium triflate. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 341–350, 2000  相似文献   

17.
Polymer dielectrics generally have comparatively low dielectric constant, operating temperatures, and/or high dielectric loss, which limits their uses especially in harsh environment. In this article, a novel trilayered nanocomposite film (TNF) was constructed via solution‐casting and, subsequently, hot‐pressing process, which was composed of two outer layers of polyvinylidene fluoride (PVDF, high dielectric constant) and a middle layer of polymethyl methacrylate (PMMA, high glass transition temperature, Tg). The two outer layers of TNF were filled with barium strontium titanate nanoparticles to further increase the dielectric constant of PVDF. The PMMA in the middle layer was used to largely suppress the dielectric loss and simultaneously improve the temperature tolerance of TNF. Results show that the introduction of PMMA induced oriented crystal formation in the interface regions between PVDF and PMMA components. Moreover, most of the impurity ions were dramatically immobilized by partly oriented α crystals and high Tg PMMA layer until the temperature exceeded 120 °C. Therefore, the TNFs showed a high‐temperature tolerance and notably decreased loss, which are promising for widespread energy storage applications where harsh working conditions are present. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1043–1052  相似文献   

18.
In this research, thin, soft and flexible free standing films can be obtained from poly (methyl methacrylate) (PMMA)/50% epoxidised natural rubber (ENR 50)/lithium triflate (LiCF3SO3) blends. However, phase separation is observed on the surface of the films which indicates that the blending is not homogeneous. The blend became more homogeneous when ethylene carbonate (EC) plasticizer is introduced into the blend system. However, the anti-plasticization effect of EC on ENR 50 occurs at lower concentration of EC at which the rubber became coagulated due to immiscibility of the rubber with EC plasticizer during solution casting. These ENR 50 coagulates can be observed as large solid structures in the Field Emission Scanning Electron Microscope (FESEM) micrographs of the EC-plasticized rubber-based electrolytes. The presence of these coagulates, hinder the migration of lithium ions in the system and also trap the lithium ions within the coil. This in turn reduced the number of free lithium ions that contribute to the ionic conduction. As a result, the conductivity of the un-plasticized PMMA/ENR 50/LiCF3SO3 film dropped drastically by two orders of magnitude.  相似文献   

19.
Polymer composites composed of poly(methyl methacrylate) (PMMA) and silica (14 nm diameter) have been investigated. The influences of sample preparation and processing have been probed. Two types of sample preparation methods were investigated: (i) solution mixture of PMMA and silica in methyl ethyl ketone and (ii) in situ synthesis of PMMA in the presence of silica. After removing all solvent or monomer, as confirmed using thermogravimetric analysis, and after compression molding, drops in Tg of 5–15 °C were observed for all composites (2–12% w/w silica) and even pure polymer reference samples. However, after additional annealing for 72 h at 140 °C, all previously observed drops in Tg disappeared, and the intrinsic Tg of bulk, pure PMMA was again observed. This is indicative of nonequilibrium trapped voids being present in the as‐molded samples. Field‐emission scanning electron microscopy was used to show well‐dispersed particles, and dynamic mechanical analysis was used to probe the mechanical properties (i.e., storage modulus) of the fully equilibrated composites. Even though no equilibrium Tg changes were observed, the addition of silica to the PMMA matrices was observed to improve the mechanical properties of the glassy polymer host. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2270–2276, 2007  相似文献   

20.
Nanostructured amorphous bulk polymer samples were produced by processing them with small molecule hosts. Urea (U) and gamma‐cyclodextrin (γ‐CD) were utilized to form crystalline inclusion compounds (ICs) with low and high molecular weight as‐received (asr‐) poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), and their blends as included guests. Upon careful removal of the host crystalline U and γ‐CD lattices, nanostructured coalesced (c‐) bulk PVAc, PMMA, and PVAc/PMMA blend samples were obtained, and their glass‐transition temperatures, Tgs, measured. In addition, non‐stoichiometric (n‐s)‐IC samples of each were formed with γ‐CD as the host. The Tgs of the un‐threaded, un‐included portions of their chains were observed as a function of their degree of inclusion. In all the cases, these nanostructured PVAc and PMMA samples exhibited Tgs elevated above those of their as‐received and solution‐cast samples. Based on their comparison, several conclusions were reached concerning how their molecular weights, the organization of chains in their coalesced samples, and the degree of constraint experienced by un‐included portions of their chains in (n‐s)‐γ‐CD‐IC samples with different stoichiometries affect their chain mobilities and resultant Tgs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1041–1050  相似文献   

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