Dielectric spectroscopy of novel thiol-ene/epoxy thermosets obtained from allyl-modified hyperbranched poly(ethyleneimine) and diglycidylether of bisphenol A
[EN] Dielectric Thermal Analysis (DETA) of a series of new thermoset obtained by click chemistry was performed. The new thermosets were obtained by a dual-curing process consisting in a first photochemical thiol-ene, followed by a thermal thiol-epoxy starting from an allyl-terminated hyperbranched p...
| Authors: | ; ; ; ; ; |
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| Format: | Article |
| Publication date: | 2019 |
| Country: | España |
| Institution: | Universitat Politècnica de València (UPV) |
| Repository: | RiuNet. Repositorio Institucional de la Universitat Politécnica de Valéncia |
| Language: | English |
| OAI Identifier: | oai:riunet.upv.es:10251/147310 |
| Online Access: | https://riunet.upv.es/handle/10251/147310 |
| Access Level: | Open access |
| Keyword: | Thermoset Epoxy resin Hyperbranched polymers Dielectric analysis Segmental cooperativity INGENIERIA DE LOS PROCESOS DE FABRICACION MAQUINAS Y MOTORES TERMICOS CIENCIA DE LOS MATERIALES E INGENIERIA METALURGICA |
| Summary: | [EN] Dielectric Thermal Analysis (DETA) of a series of new thermoset obtained by click chemistry was performed. The new thermosets were obtained by a dual-curing process consisting in a first photochemical thiol-ene, followed by a thermal thiol-epoxy starting from an allyl-terminated hyperbranched poly(ethyleneimine) (HBPEI) and different proportions of diglycidylether of bisphenol A (DGEBA) and the corresponding stoichiometric proportions of pentaerythritol tetrakis (3-mercaptopropionate, PETMP). The dielectric behaviour was obtained experimentally supressing the conductive effects. Two sub-Tg intramolecular non-cooperative gamma and beta relaxations and an intermolecular cooperative alpha-relaxation were detected. The gamma-relaxation was ascribed to the dipole orientation of the terminal thiol groups. Two gamma relaxations gamma(epo) and gamma(ene) were observed, according to the influence of the surroundings. Only thermosets with a content of flexible HBPEI/PETMP domains higher than a 50% w/w showed the gamma(ene) relaxation at lower temperatures and higher frequencies. The beta-relaxation was a non-Johari-Goldstein relaxation, ascribed to the dipole transfer of the linear -CH2-O-(C=O)-CH2-CH2- groups of the thiol constrained in the glassy state. The alpha-relaxation was ascribed to the long-term segmental movements of the thermosets, occurring during the transition from the glassy to the rubbery stage. A synergic effect of reducing the rigidity and compactness of the thermosets by the reduction of aromatic moieties of the DGEBA/PETMP units, and the increase of the flexibility induced by the addition of HBPEI/PETMP units affected the macromolecular movement of the thermosets. |
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