Abstract
Multiarm star polymers, denoted PEIx-PLAy and containing a hyperbranched poly(ethyleneimine) (PEI) core of different molecular weights x and poly(lactide) (PLA) arms with y ratio of lactide repeat units to N links were used in this work. Samples were preconditioned to remove the moisture content and then characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). The glass transition temperature, Tg, is between 48 and 50 °C for all the PEIx-PLAy samples. The dielectric curves show four dipolar relaxations: γ, β, α, and α′ in order of increasing temperature. The temperatures at which these relaxations appear, together with their dependence on the frequency, allows relaxation maps to be drawn, from which the activation energies of the sub-Tg γ- and β-relaxations and the Vogel–Fulcher–Tammann parameters of the α-relaxation glass transition are obtained. The dependence of the characteristic features of these relaxations on the molecular weight of the PEI core and on the ratio of lactide repeat units to N links permits the assignation of molecular motions to each relaxation. The γ-relaxation is associated with local motions of the –OH groups of the poly(lactide) chains, the β-relaxation with motions of the main chain of poly(lactide), the α-relaxation with global motions of the complete assembly of PEI core and PLA arms, and the α′-relaxation is related to the normal mode relaxation due to fluctuations of the end-to-end vector in the PLA arms, without excluding the possibility that it could be a Maxwell–Wagner–Sillars type ionic peak because the material may have nano-regions of different conductivity.
Highlights
Cured epoxy resins are thermosets exhibiting a cross-linked structure with excellent electrical properties, good chemical and corrosion resistance, low shrinkage, and high tensile strength and modulus
With an appropriate selection of PLA arms, which contain rigid esters of secondary alkyl groups in the structural units, materials with higher glass transition temperature can be obtained, compared with the use of similar stars with poly(ε-caprolactone) (PCL) arms with primary ester linkages. Such materials formed by a multifunctional core of PEI of different molecular weights and multiple branches of PLA, denoted PEIx-PLAy where x represents the molecular weight of the poly(ethyleneimine) and y represents the ratio of lactide repeat units to N links, were used as chemical modifiers in the anionic curing of diglycidylether of bisphenol A (DGEBA) epoxy resins
Endothermic peak due to melting at 148–175 ◦ C [23,24,26,27]. In this present andand discuss the results of dielectric relaxation spectroscopy
Summary
Cured epoxy resins are thermosets exhibiting a cross-linked structure with excellent electrical properties, good chemical and corrosion resistance, low shrinkage, and high tensile strength and modulus. The densely branched architecture and high molecular weight of poly(ethyleneimine) create significant mobility restrictions, which have a strong effect on the glass transition temperature and on the degree of cross-linking of the cured materials [17]. With an appropriate selection of PLA arms, which contain rigid esters of secondary alkyl groups in the structural units, materials with higher glass transition temperature can be obtained, compared with the use of similar stars with poly(ε-caprolactone) (PCL) arms with primary ester linkages Such materials formed by a multifunctional core of PEI of different molecular weights and multiple branches of PLA, denoted PEIx-PLAy where x represents the molecular weight of the poly(ethyleneimine) and y represents the ratio of lactide repeat units to N links, were used as chemical modifiers in the anionic curing of DGEBA epoxy resins.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.