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Materials 2017, 10(2), 127; doi:10.3390/ma10020127

Study of the Molecular Dynamics of Multiarm Star Polymers with a Poly(ethyleneimine) Core and Poly(lactide) Multiarms

Laboratori de Termodinàmica i Físicoquímica, TERFIQ, Departament de Màquines i Motors Tèrmics, ESEIAAT, Universitat Politècnica de Catalunya, Barcelona Tech, Carrer Colom 11, Terrassa 08222, Spain
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Academic Editor: Ming Hu
Received: 19 December 2016 / Revised: 27 January 2017 / Accepted: 28 January 2017 / Published: 4 February 2017
(This article belongs to the Special Issue Thermal Sciences and Thermodynamics of Materials)
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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. View Full-Text
Keywords: dielectric relaxation spectroscopy (DRS); multiarm star polymers; poly(lactide) (PLA); poly(ethyleneimine) (PEI); differential scanning calorimetry (DSC) dielectric relaxation spectroscopy (DRS); multiarm star polymers; poly(lactide) (PLA); poly(ethyleneimine) (PEI); differential scanning calorimetry (DSC)
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Román, F.; Colomer, P.; Calventus, Y.; Hutchinson, J.M. Study of the Molecular Dynamics of Multiarm Star Polymers with a Poly(ethyleneimine) Core and Poly(lactide) Multiarms. Materials 2017, 10, 127.

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