Complex Dynamics of a Fluorinated Vinylidene Cyanide Copolymer Highlighted by Dielectric Relaxation Spectroscopy (original) (raw)
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European Polymer Journal, 2011
Aiming to develop new dielectric polymers containing CN and F groups with strong dipole moments, a novel copolymer of acrylonitrile (AN) and 2,2,2-trifluoroethyl acrylate (ATRIF) was synthesized in acetonitrile by free radical process as well as the respective homopolymer (poly(ATRIF)). The copolymer's composition and microstructure were analyzed by FTIR, 1 H and 13 C NMR spectroscopy and SEC. The molar incorporation of AN determined in the copolymer by NMR was 58 mol%. Thermogravimetric analysis of poly(AN-co-ATRIF) copolymer showed good thermal stability comparatively to the fluorinated homopolymer.
Dielectric relaxations in amorphous polymers with complex chain architectures
Journal of Non-Crystalline Solids, 2002
By combining thermostimulated current and dynamic dielectric spectroscopies, the dielectric properties characteristic of the molecular mobility can be described over a very broad frequency range. The study of dielectric relaxations of phosphorus-containing dendrimers in the sub-glass transition region, and of poly(n-alkyl methacrylates) at and above the glass transition region allows us to gain insight into the molecular dynamics of complex architecture systems. From these sets of data we make an attempt to propose a structural interpretation of molecular mobility through the glass transition.
Dielectric behaviour of copolymers based on 2,2,2-trifluoroethyl methacrylate and cyano co-monomers
European Polymer Journal, 2009
In the frame of a research aiming at developing new dielectric polymers containing CACN and CAF substituents with strong dipole moment, statistical copolymers based on cyano monomers such as acrylonitrile (AN), methacrylonitrile (MAN), methylvinylidene cyanide (MVCN) and 2,2,2-trifluoroethylmethacrylate (MATRIF), were synthesized and characterized. Elemental analysis has shown that the molar percentages of AN and MAN in the copolymers were 45 mol.%, while only 5 mol.% of MVCN was incorporated in the poly(MVCN-co-MATRIF) copolymer. These copolymers exhibit glass transition temperatures, T g , in the range of 70-90°C. The dynamic dielectric analyses and their complex permittivities of these copolymers were studied versus the temperature and the frequency.
The European Physical Journal E, 2012
The aim of this study is to analyze the mobility of polymer chains in semicrystalline poly(vinylidene fluoride) (PVDF). PVDF crystallizes from the melt in the α crystalline phase. The transformation from the α phase to the electroactive β phase can be induced by stretching at temperatures in the range between 80 and 140 • C. The spherulitic structure of the crystalline phase is deformed during stretching to form fibrils oriented in the direction of the strain. The amorphous phase confined among the crystalline lamellae is distorted as well and some degree of orientation of the polymer chains is expected. Dynamicmechanical and dielectric spectroscopy measurements were performed in PVDF films stretched to strain ratios up to 5 at temperatures between 80 and 140 • C. Dynamic-mechanical measurements were conducted between −60 • C and melting and in this temperature range the relaxation spectra show the main relaxation of the amorphous phase (called β-relaxation) and at higher temperatures a relaxation related to crystallites motions (αc-relaxation). Although the mean relaxation times of the β-relaxation are nearly equal in PVDF before and after crystal phase transformation, a significant change of shape of the relaxation spectrum proves the effect of chain distortion due to crystal reorganization. In stretched PVDF the elastic modulus of the polymer in the direction of deformation is significantly higher than in the transversal one, as expected by chain and crystals fibril orientation. The recovery of the deformation when the sample is heated is related with the appearance of the α c-relaxation. Dielectric spectroscopy spectrum shows the main relaxation of the amorphous phase and a secondary process (γ-relaxation) at lower temperatures. Stretching produces significant changes in the relaxation processes, mainly in the strength and shape of the main relaxation β. The Havriliak-Negami function has been applied to analyze the dielectric response.
Dielectric properties of block copolymers based on vinylidene fluoride and cyano comonomers
Journal of Non-Crystalline Solids, 2010
The syntheses of poly(vinylidene fluoride)-b-poly(AN, MAN, VCN) (PVDF-b-PM CN ) block copolymers, using the iodine transfer polymerization (ITP) of acrylonitrile (AN), methacrylonitrile (MAN) and vinylidene cyanide (VCN), in the presence of PVDF-I, are presented. In a first step, the ITP of vinylidene fluoride (or 1,1-difluoroethylene, VDF) with C 6 F 13 I initiated by tert-butyl peroxypivalate is achieved. This ITP led to two different isomeric oligomers (PVDF-I) bearing either ACH 2 I or ACF 2 I end-groups. Second step, those fluorinated blocks were used latter as macromolecular chain transfer agents to achieve the ITP with cyanide monomers (M CN ). The characterization of synthesized samples by 19 F and 1 H NMR spectroscopy allowed determining the average degree of polymerization. These block copolymers were characterized by SEC chromatography (4160-51100 g/mol) and by wide angle X-ray diffraction. Their thermal stabilities were studied using thermogravimetric analysis (TGA). The melting and glass transition temperatures as well as the degree of crystallinity were characterized by means of DSC. The influence of the copolymer compositions on dielectric properties has also been investigated. Dielectric analyses show several relaxations processes associated with long-range molecular motions, which are associated to the glass transition temperatures of both blocks (PVDF block and poly(cyano monomer blocks)). These behaviors are discussed in terms of dielectric proprieties as a function of molecular composition and mobility.
Macromolecules, 2008
In this paper, we show that it is possible to predict the dielectric loss spectrum of methoxy groups in amorphous poly(vinyl methyl ether) from their rotational energy profiles obtained by a simple quasistatic technique described in our previous paper. Kramers' transition rate theory is used with a slight modification to account for the nonquadratic profiles encountered and short molecular dynamics runs are used to obtain the moment of inertia and rotational frictional coefficient of a methoxy group. The predicted dielectric loss spectrum and its temperature dependence are in good agreement with experimental observations with no adjustable parameters other than those specified in the force field. It is found that the width of the dielectric loss spectrum is essentially due to the spread of activation energies with a negligible contribution from the spread of relaxation time prefactors.
The European Physical Journal E, 2001
The complex dielectric permittivity has been measured for three poly(ethylenglycol)-bpoly(propylenglycol)-b-poly(ethylenglycol) copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10% and 20%, respectively). Only the noncrystalline sample shows the normal mode relaxation together with the segmental (α-relaxation) and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described by a VFT equation with the same value of T 0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the β-relaxation has been found. Near T g the β-relaxation time is close to the primitive time of the coupling model. PACS. 64.70.Pf Glass transitions -77.22.Gm Dielectric loss and relaxation
Physical Review B, 2001
The high-energy electron irradiated poly͑vinylidene fluoride-trifluoroethylene͒, P͑VDF-TrFE͒, copolymer exhibits many features resembling the relaxor ferroelectric behavior. In polymer systems, there are local dipolar motions at the monomer or unit cell scale, which manifest themselves as various relaxation processes. In this paper we investigate the relationship between the relaxor ferroelectric behavior, especially, Vogel-Fulcher ͑V-F͒ behavior and these local dipolar relaxation processes in irradiated P͑VDF-TrFE͒ 65/35-mol % copolymer. In order to cover the change in polarization dynamics of the copolymer system, the dielectric behavior of copolymer is measured over a broad frequency ͑0.01 Hz-10 MHz͒ and temperature ͑Ϫ40 to 80°C͒ range. The results indicate that there is an increased coupling among the local dipolar motions with reduced temperature in the crystalline region. On the other hand, the randomness introduced in the irradiation prevents the formation of a polar phase, on both the macroscale and the microscale, in the polymer. The observed relaxor behavior is a consequence of the competition of these two effects. The results further show that the V-F process of the irradiated copolymer system is different from the glass transition, which occurs in the amorphous phase of the copolymer.
The European Physical Journal E, 2011
The effect of the structure of copolymers (random, alternate or diblock) on their dynamics has been studied by dielectric spectroscopy. Six copolymers of styrene and methyl methacrylate (three diblocks, one alternate and two random) have been studied. The results show that the sub-T g transitions of the diblock samples can be described by one asymmetric Havriliak-Negami (HN) function, while two are necessary for the rest of the copolymers ( and relaxations). The characteristic times of the sub-T g relaxations show an Arrhenius temperature dependence and there is a strong coupling of the and relaxations at high temperatures. The deconvolution of the merging relaxations has been made in the framework of the Williams Ansatz set out in terms of Havriliak-Negami distributions. Because the 2D 2 H-NMR results excluded any significant contribution from the rotation of the methoxy group of the methacrylate group around the C-OCH 3 bond, the relaxation may be assigned to the rotation of the methyl methacrylate group in a styrene-rich environment. The Molecular Dynamics simulations of a poly(methyl methacrylate) homopolymer and of the alternate copolymer are in qualitative agreement with the experimental results, although they predict smaller values for the activation energy of the sub-T g relaxations.