Molecular dynamics in polymer networks containing caprolactone and ethylene glycol moieties studied by dielectric relaxation spectroscopy

Copolymer networks with methacrylate main chain and caprolactone and ethylene glycol side groups were obtained by free radical copolymerisation of caprolactone methacrylate (CLMA) and poly(ethylene glycol) methacrylate (PEGMA). Dielectric relaxation spectroscopy was used to analyse molecular mobility of the different groups in the system. Only one main dielectric relaxation process was found in CLMA/PEGMA copolymer networks, located between those of the corresponding homonetworks, indicating that the system does not present phase separation. The copolymers show a secondary relaxation process at temperatures below −50 °C, which can be assigned to the overlapping of the corresponding secondary processes for the homopolymer networks; one of them was related to the local mobility of caprolactone units in CLMA and the second one was assigned to the twisting motions within ethylene glycol moiety in PEGMA. Besides the relaxation processes, the mobility of space charges has been analysed by means of conductivity and electric modulus formalisms.The support from the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER funds under the project MAT2012-38359-C03-01 is gratefully acknowledged.Sabater I Serra, R.; Escobar Ivirico, JL.; Romero Colomer, FJ.; Andrio Balado, A.; Gómez Ribelles, JL. (2014). Molecular dynamics in polymer networks containing caprolactone and ethylene glycol moieties studied by dielectric relaxation spectroscopy. Journal of Non-Crystalline Solids. 404:109-115. https://doi.org/10.1016/j.jnoncrysol.2014.08.013S10911540

Dielectric relaxation dynamics of high-temperature piezoelectric polyimide copolymers

Polyimide co-polymers have been prepared based on different diamines as co-monomers: a diamine without CN groups and a novel synthesized diamine with two CN groups prepared by polycondensation reaction followed by thermal cyclodehydration. Dielectric spectroscopy measurements were performed and the dielectric complex function, ac conductivity and electric modulus of the co-polymers were investigated as a function of CN group content in the frequency range from 0.1 Hz to 107 Hz at temperatures from 25 to 260 °C. For all samples and temperatures above 150ºC, the dielectric constant increases with increasing temperature due to increaseing conductivity. The α-relaxation is just detected for the sample without CN groups, being this relaxation overlapped by the electrical conductivity contributions in the remaining samples. For the copolymer samples and the polymer with CN groups an important Maxwell-Wagner-Sillars contribution is detected. The mechanisms responsible for the dielectric relaxation, conduction process and electric modulus response have been discussed as a function of the CN groups content present in the samples.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PESTC/FIS/UI607/2011 and grants SFRH/BD/ 62507/2009 (A.C.L.) SFRH/BD/68499/2010 (C.M.C.). The authors also thank funding from “Matepro – Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). RSS acknowledge the support of the Spanish Ministry of Economy and Competitiveness through the project MAT2012-38359-C03-01 (including the FEDER financial support). Authors also thank the Basque Country Government for financial support (ACTIMAT project, ETORTEK Program, IE13-380, and Ayudas para Grupos de Investigación del Sistema Universitario Vasco Program, IT718-13)

Dielectric relaxation dynamics in poly(vinylidene fluoride)/Pb(Zr0·53Ti0.47)O3 composites

Polymer-ceramic composites based on poly(vinylidene fluoride) and ceramic particles of the inorganic piezoelectric material Pb(Zr0.53Ti0.47)O3 were prepared with different particle concentrations and size by solution casting in the non-polar (α-) and polar (β-) phases of the polymer. The influence of amount and particle size on the overall dielectric response of α- and β-phase matrix composites was analyzed, focusing on the dielectric relaxation processes. The cooperative segmental motions within the PVDF amorphous phase (low-temperature β-relaxation), are strongly affected by the inclusion of the fillers, both in the α and β-phase matrix composites. The complex permittivity analyzed by the Havriliak-Negami equation model (NH) and the fragility parameter indicates that the PZT ceramic filler induces heterogeneity in the polymer matrix. For αPVDF/PZT composites, the strength of the relaxation process increases with increasing the filler amount and it is nearly independent on particle size. The behavior of the HN shape parameters, more noticeable for filler content of 20% or higher, shows that the relaxation dynamics is influenced by the polymer nucleation kinetics. PVDF/PZT composites in β-phase matrix exhibit a strong increase in the relaxation strength for PVDF/PZT composites with 40% of ceramic fillers, and the process becomes more symmetric when the amount of filler increases. The detected variations in the relaxation dynamics in both α- and β-phase matrix composites is strongly affected by the ceramic filler and the interface between the ceramic microparticles and the polymer.The authors thank the FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2019, and UID/EEA/04436/2019; and project PTDC/FIS-MAC/28157/2017. The author also thanks the FCT for financial support under grant SFRH/BPD/112547/2015 (C.M.C.). Financial support from the Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43 / AEI / 10.13039/501100011033 and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, are acknowledged. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008–2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. The authors thank Prof. R. Gregorio Filho, University Federal of S. Carlos, Brazil, for providing the ceramic particles

Molecular relaxation and ionic conductivity of ionic liquids confined in a poly(vinylidene fluoride) polymer matrix: Influence of anion and cation type

Blends of poly(vinylidene fluoride) (PVDF) and ionic liquids (ILs) with different cations and anions have been prepared by solvent casting. The IL content was the same in all blends of the series. Molecular relaxation and ionic conductivity have been systematically studied by broadband dielectric relaxation spectroscopy (BDS) in wide frequency (0.1 Hz-1 MHz) and temperature ranges (-120 to 150 degrees C) and the results have been analysed in terms of dielectric modulus M*(omega) and conductivity sigma*(omega) formalisms. The main relaxation process (beta-relaxation) of the amorphous phase of the blend that integrates amorphous polymer chain segments and IL molecules was observed. Significant differences in the Vogel-Fulcher-Tammann (VFT) fitting parameters in the PVDF/IL blends with different anions were detected. The conductivity sigma*(omega) formalism shows that it is strongly dependent on the miscibility of the IL with the amorphous PVDF chains and the type of anion. The Barton-Namikawa-Nakajima (BNN) relation sigma(0) similar to omega(c) is fulfilled for all PVDF/IL blends except for that containing 1-ethyl-3-methylimidazolium hydrogen sulfate, [Emim][HSO4]. The activation energy of the ac conductivity, calculated according to the Dyre model, decreases for all PVDF/IL blends with respect to neat PVDF. The structure of the cation of the IL has been found to exert less influence on the dielectric and conductivity properties of the blends.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013 and the Associated Laboratory Research Unit for Green Chemistry, Technologies and Clean Processes, LAQV (financed by national funds from FCT/MEC, UID/QUI/50006/2013 and ERDF under the PT2020, POCI-01-0145-FEDER-007265). The authors thank FEDER funds through the COMPETE 2020 Programme and National Funds through FCT under the projects PTDC/CTM-ENE/5387/2014, PTDC/EEI-SII/5582/2014 and PTDC/FIS-MAC/28157/2017. D.M.C., C.M.C., J.M.S center dot S.E. and P.M.R. also thank to the FCT for grants SFRH/BPD/121526/2016 and SFRH/BPD/112547/2015, and Investigator FCT contracts IF/00355/2012 and IF/0621/2015, respectively. Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-(1 and 3)-R (AEI/FEDER, UE) (including the FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, are acknowledged. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund

Dielectric relaxation spectrum of poly (ε-caprolactone) networks hydrophilized by copolymerization with 2-hydroxyethyl acrylate

The dielectric relaxation spectrum of polycaprolactone (PCL) networks hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) is investigated. PCL is a semicrystalline polyester with a complex relaxation spectrum that includes the main α relaxation and two secondary modes (β, γ) at lower temperatures. The overlapping of the different relaxational modes was split by using several Havriliak-Negami functions. Crosslinking the material modifies the dynamics of the main relaxation process as reflected by the parameters that characterize the Vogel behavior of the process and the dynamic fragility. The incorporation of HEA units in the network results in a material with microphase separation: two α processes are detected, the one corresponding to the PCL chains and the new one associated to nanometric regions that contain different amount of both comonomers. The incorporation of the HEA units in the system involves the presence of a new βsw relaxation due to the link of two side chains by water molecules through hydrogen bonding

Structure and dynamics in poly(L-lactide) copolymer networks

Poly(L-lactide) networks (PmLA) hydrophilized with different amounts of 2-hydroxyethyl acrylate (HEA) were investigated by dielectric relaxation spectroscopy, thermally stimulated depolarization currents, and differential scanning calorimetry. The incorporation of HEA units in the PmLA network, with the aim of modulating the water sorption capacity of the system, results in a material with a complex behavior. The system consists of phase-separated microdomains richer in one or the other comonomers that constitute the network. Initially, the addition of smalls amount of HEA units in the network gives rise to a one-phase, two-component system; however, when the amount of HEA in the system increases, a new phase (HEA-rich one) is formed containing some mLA chains that modify the main relaxation mode of these domains and the local dynamics of the system. The structure of the system has been analyzed by comparing the relaxational modes in the PmLA and PHEA homonetworks with those in the copolymer networks