Molecular Mobility in Hyperbranched Polymers and Their Interaction with an Epoxy Matrix

Román, Frida; Colomer, P.; Hutchinson, John M.

doi:10.3390/ma9030192

Cited by 19 publications

(59 citation statements)

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“…For the DGEBA epoxy alone, a glass transition (α-relaxation) and two secondary relaxations, β and γ, have been reported [ 67 , 68 , 69 ]. The γ-relaxation in the pure epoxy and in the epoxy-amine system is related to the dynamics of dipoles localized in the epoxide end groups [ 68 ], or more generally, with the local motions of dipoles of unreacted species [ 70 ].…”

Section: Introductionmentioning

confidence: 99%

“…In a previous paper [ 69 ], we studied the molecular dynamics of the following systems by DRS and DMA: the pure HBPEI with a molecular weight of 2000 (PEI2000, trade name Lupasol PR8515, BASF); the neat epoxy resin (diglycidyl ether of bisphenol-A, DGEBA); the unreacted mixture of HBPEI and epoxy, denoted ELP; the ELP system during non-isothermal cure; and the fully cured system. The objective of the present work is to determine the effect of the molecular weight of the hyperbranched polymer (HBPEI) on its glass transition and secondary relaxations, and to investigate its relaxation behaviour when incorporated into an epoxy resin matrix.…”

Section: Introductionmentioning

confidence: 99%

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Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

2018

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Two different commercial hyperbranched poly(ethyleneimine)s (HBPEI), with molecular weights (MW) of 800 and 25,000 g/mol, and denoted as PEI800 and PEI25000, respectively, as well as the mixtures with a Diglycidyl Ether of Bisphenol-A (DGEBA) epoxy resin, have been studied using thermal analysis techniques (DSC, TGA), dielectric relaxation spectroscopy (DRS), and dynamic mechanical analysis (DMA). Only a single glass transition is observed in these mixtures by DSC. DRS of the HBPEIs shows three dipolar relaxations: γ, β, and α. The average activation energy for the γ-relaxation is similar for all HBPEIs and is associated with the motion of the terminal groups. The β-relaxation has the same average activation energy for both PEI800 and PEI25000; this relaxation is attributed to the mobility of the branches. The α-relaxation peak for all the HBPEIs is an asymmetric peak with a shoulder on the high temperature side. This shoulder suggests the existence of ionic charge trapped in the PEI. For the mixtures, the γ- and β-relaxations follow the behaviour of the epoxy resin alone, indicating that the epoxy resin dominates the molecular mobility. The α-relaxation by DRS is observed only as a shoulder, as a consequence of an overlap with conductivity effects, whereas by DMA, it is a clear peak.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

2018

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“…Previous studies have shown that PLA is a thermally degradable polymer as a consequence of the presence of ester groups of secondary alkyl moieties in the main chain, which can break by a thermal β-elimination process in the temperature interval from 200 to 250 °C [21,22]. The second stage, around 350 °C, is associated with the decomposition of the PEI core, as shown by Acebo et al [18] and by ourselves [19] in studies of the thermal degradation of PEI.…”

Section: Resultsmentioning

confidence: 92%

“…This relaxation is associated with motions of the lateral branches of PEI [19]. The average activation energy, calculated from the slope of the linear representation in Figure 7, is 92.7 ± 6.3 kJ/mol.…”

Section: Resultsmentioning

confidence: 99%

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

2017

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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.

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Deeper insights into the thermal properties of epoxy thermoset resins using torsion measurements

Smith

Lazzara

Fernando

2021

J of Applied Polymer Sci

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The glass transition temperature (T g ) of epoxy thermosets is a critical material property that depends on the component chemistry, the final cross-link density, and processing conditions. This study incorporates dynamic mechanical analysis (DMA) testing with a torsion clamp geometry on a TA Instruments DHR-2 and differential scanning calorimetry (DSC) to characterize five different two-component epoxy-amine systems. Investigation of the T g dependence on DMA frequency and heating shows that lowering the frequency from 1 to 0.01 Hz results in a T g very similar to that measured using DSC, while a heating rate of 0.3 C/min using DMA gives a T g comparable to the DSC measured value at 30 C/min. The DMA technique reveals secondary relaxation transitions and peak broadening in the tan(δ) plots of poorly mixed epoxy blends, quantified using full width at half maximum (FWHM) of tan(δ) peaks, and are indicative of a non-homogeneous cross-linked network and off-ratio blending, respectively. The increase in the FWHM due to poor mixing ranges from 8% to 96%. These parameters are easily measurable and quantifiable in DMA, but are not observed in DSC. The additional DMA insights are valuable for process development and failure analysis, and can improve the understanding of epoxies.

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Molecular Mobility in Hyperbranched Polymers and Their Interaction with an Epoxy Matrix

Cited by 19 publications

References 100 publications

Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

Study of Hyperbranched Poly(ethyleneimine) Polymers of Different Molecular Weight and Their Interaction with Epoxy Resin

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

Deeper insights into the thermal properties of epoxy thermoset resins using torsion measurements

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