Dielectric spectroscopy study of EMA–EGDM crosslinking system at sol–gel transition (original) (raw)

Influence of solvent on the network structure formed by free radical polymerization of tri-ethylene glycol dimethacrylate: A dielectric study

Journal of Non-Crystalline Solids, 2010

Molecular mobility of a series of tri-ethylene glycol dimethacrylate (TrEGDMA) samples polymerized with different amounts of ethyl acetate up to 40% (w/w) as diluent was investigated by dielectric relaxation spectroscopy. In the first measuring scan, the samples show three secondary relaxation processes: a c process related to the twisting motions within the ethylene glycol moiety as found in the unreacted monomer, a b process assigned to hindered rotations of carboxylic groups residing in non-bonded ends of the monomers linked to the network only by one side of the molecule; and additionally, at higher temperatures, a third process was detected designated as b pol , ascribed to a p flip of the ester unit accompanied by a restricted main chain rearrangement. While the c and the b pol processes remain in the second scan, the b relaxation goes to extinction due to post-polymerization that took place at the highest temperatures scanned in the previous run, leading to complete polymerization of the network. The strength of c and b relaxation measured in the first scan increases with the amount of solvent present in the initial mixture, nevertheless, in any case, b relaxation completely disappears in the second scan.

Dielectric Properties of Bio-Based Diphenolate Ester Epoxies

ACS applied materials & interfaces, 2018

Thermoset bio-based diglycidyl ether of diphenolate esters (DGEDP) exhibit comparable mechanical properties as petroleum-derived diglycidyl ether of bisphenol A (DGEBA), whereas DGEDP is derived from levulinic acid, a safe and readily renewable feedstock. To determine the potential replacement of DGEBA as dielectric materials, a series of DGEDP-esters (i.e., methyl, ethyl, propyl, and butyl esters) were synthesized and studied. Broadband dielectric spectroscopy revealed that DGEDP-propyl has the highest dielectric constant in the series, comparable to DGEBA. Differences in the dielectric properties of DGEDP-esters is attributed to the interplay of segmental, small local, and side-chain motions on one hand and free volume and steric hindrance on the other.

Molecular relaxation in cross-linked poly(ethylene glycol) and poly(propylene glycol) diacrylate networks by dielectric spectroscopy

Polymer, 2007

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-T g 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.

Dielectric and mechanical relaxation processes in methyl acrylate/tri-ethyleneglycol dimethacrylate copolymer networks

European Polymer Journal, 2007

The dielectric properties of methylacrylate (MA)/tri-ethyleneglycol dimethacrylate (TrEGDMA) copolymers at different compositions, ranging from 0 to 100, were measured between À120 and 150°C over the frequency range 0.1 Hz-1 MHz. In the given frequency range, three relaxation processes were detected by dielectric relaxation spectroscopy in homo poly-TrEGDMA and copolymers: the a process associated with the glass transition, and two secondary processes due to localized mobility. In PMA only one secondary process was observed besides the alpha relaxation process. The influence of copolymerization going from PMA, monofunctional softer component with a glass transition determined calorimetrically as 284 K, to poly-TrEGDMA, higher glass transition component, bifunctional, that also forms a dense network due to cross linking, reflects mainly in the alpha process that shifts to higher temperatures and becomes broader. The raise and broadening in the glass transition with TrEGDMA increase was also observed by dynamic mechanical thermal analysis and differential scanning calorimetry. The glass transition temperature of poly-TrEGDMA was not detected calorimetrically but a value of 429 K was estimated from the best fit of the Fox equation. In what concerns the secondary relaxation process detected in poly-TrEGDMA and copolymers at the lowest temperatures, it is related with local twisting motions of ethyleneglycol moieties, being designated as c relaxation, while the process detected in the medium temperature range is associated with the rotation of the carboxylic groups as in poly(alkyl methacrylates), designated as b relaxation. This process is detected at much lower temperatures in homo PMA in the same temperature region than the above mentioned c relaxation. The copolymerization influences mainly the a process while the c process remains almost unaffected in copolymers relative to homo poly-TrEGDMA. The b process is largely determined by the presence o the tri-ethylene glycol dimethacrylate monomeric units even in copolymers with the lowest TrEGDMA content.

Dielectric behaviour of acrylic ester-organic solvent mixtures

Journal of Chemical Sciences, 1997

A~tracL Dielectric constants and refractive indices of fifteen binary mixtures containing methyl methacrylate (MMA), ethyl methacrylate (EMA) or butyl methacrylate (BMA), with hexane, heptane, carbon tetrachloride, chlorobenzene or o-dichlorobenzene are measured at 303.15 K. The excess dielectric constants, c ~, excess molar polarizations, P2 and excess orientation polarizations, P~ were calculated from the measured properties of the pure and mixed components. An attempt was also made to provide qualitative interpretation of the complex molecular interactions involved based on the sign and magnitude of the excess dielectric function.

Dielectric Relaxation in Ethylene Glycol-Dimethyl Sulfoxide Mixtures as a Function of Composition and Temperature

2012

Using time domain reflectometry, the complex dielectric spectra between 10 MHz to 20 GHz has been measured in the whole composition range at 10, 20, 30 and 40 o C for the binary mixtures of ethylene glycol and dimethyl sulfoxide. For all the mixtures, only one dielectric loss peak was observed in this frequency range. The relaxation in these mixtures can be described by a single relaxation time using the Debye model. A systematic variation is observed in dielectric constant (ε0) and relaxation time (τ). The excess permittivity (ε E ), excess inverse relaxation time (1/τ) E , Kirkwood correlation factor (g) and thermodynamic parameters viz. enthalpy of activation (∆H) and Gibbs free energy of activation (∆G) have been determined, to confirm the formation of hydrogen bonded homogeneous and heterogeneous cooperative domains, the dynamics of solute -solute interaction and the hindrance to molecular rotation in the hydrogen bonded glass forming ethylene glycol -dimethyl sulphoxide system.

Simultaneous kinetic and microdielectric studies of some epoxy-amine systems

Journal of Polymer Science Part B-polymer Physics, 1998

Three reactive epoxy-amine systems based on diglycidyl ether of bisphenol A (DGEBA) with 4,4Ј-diaminodiphenylsulfone (DDS), 4,4Ј-methylenebis [3-chloro 2,6diethylaniline] (MCDEA), and 4,4Ј-methylenebis [2,6-diethylaniline] (MDEA), were studied during isothermal curings at 140 and 160°C. The simultaneous kinetic and dielectric studies allow to express conductivity, , in terms of conversion, x, and of glass transition temperature, T g . The conductivity, 0 , of the initial monomer mixture and, ϱ of the fully cured network are measured. It is found that:

Kinetics of free radical polymerization probed by dielectric relaxation spectroscopy under high conductivity conditions

Polymer, 2011

Polymerization kinetics of tri-ethylene glycol dimethacrylate (TrEGDMA)/2,2-azobis-isobutyronitrile (AIBN) mixtures (0.1% w.t.) at different temperatures was investigated by using dielectric relaxation spectroscopy. The dielectric spectra at the polymerization temperatures studied are dominated by high conductivity leading us to employ the electric modulus representation in order to extract information about the evolution of the system during isothermal reaction. An intense peak appears in the imaginary component of the complex dielectric modulus which is related to conductivity. The variation of the strength of this peak and of its relaxation time with the polymerization time allows us to determine the polymerization degree evolution and the moment in which vitrification is attained, which can be compared with results obtained by temperature modulated DSC in a previous work (Viciosa MT, Hoyo JQ, Dionísio M, Gómez Ribelles JL. Journal of Thermal Analysis and Calorimetry 2007; 90:407e414).