Mobility, Miscibility, and Microdomain Structure in Nanostructured Thermoset Blends of Epoxy Resin and Amphiphilic Poly(ethylene oxide)- b lock -poly(propylene oxide)- b lock -poly(ethylene oxide) Triblock Copolymers Characterized by Solid-State NMR (original) (raw)
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Colloid and Polymer Science, 2006
Nanostructuring of thermosetting systems using the concept of templating and taking advantage of the self-assembling capability of block copolymers is an exciting way for designing new materials for nanotechnological applications. In this first part of the work, reactive blends based on stoichiometric amounts of a diglycidylether of bisphenol-A epoxy resin and 4,4′-diaminodiphenylmethane cure agent modified with three poly(ethylene oxide)-co-poly (propylene oxide)-co-poly(ethylene oxide) block copolymers were studied. Cure advancement of these systems was analyzed by differential scanning calorimetry. The experimental results show a delay of cure rate, which increases as copolymer content and PEO molar ratio in the block copolymer rise. Infrared spectroscopy shows that PEO block is mainly responsible of physical interactions between the hydroxyl groups of growing epoxy thermoset and ether bonds of block copolymer. These interactions are mainly responsible for the delaying of cure kinetics. The molar ratio between blocks also has a critical influence on the delaying of the cure rate. A mechanistic approach of cure kinetics allows us to relate the delay of cure as a consequence of block copolymer adding to physical interactions between components.
Polymer, 2005
Diaminodiphenylmethane (DDM) curing at several temperatures of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin modified with a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer has been investigated in order to characterize the miscibility and morphological features. Two distinct phases are present for every blends studied except for DGEBA/DDM modified with 10 wt% PEO-PPO-PEO and cured at low temperature. Depending on the curing condition, phase separation takes place at micro or nanoscale due to competition among kinetic and thermodynamic factors. The mechanistic approach used for modeling the curing reactions shows that the formation of epoxy-hydroxyl complex and the auto catalytic process are slightly decreased whilst the noncatalytic process is favoured upon copolymer addition. Modifier addition delays curing process as the influence of both formation of epoxy-hydroxyl complex and catalytic process on reaction rate is higher than the influence of noncatalytic process. A thermodynamic model describing a thermoset/block copolymer considered as only one entity system is proposed. The LCST behaviour allows to elucidate nano or micro separated structures obtained at low and high curing temperatures, respectively. q Polymer 46 7082-7093 www.elsevier.com/locate/polymer 0032-3861/$ -see front matter q
The Journal of Physical Chemistry C, 2014
A variety of multiscale solid-state NMR techniques were used to characterize the heterogeneous structure and dynamics of the interphase and cross-linked network in nanostructured epoxy resin/block copolymer (ER/ BCP) blends, focusing on the role of ER-miscible blocks containing poly(ε-caprolactone) (PCL) or poly(ethylene oxide) (PEO) blocks having different intermolecular interactions with ER. 1 H spin-diffusion experiments indicate that the interphase thickness of PEO-containing blends is obviously smaller than that of PCL-containing blends. High-resolution 1 H fast magic-angle spinning (MAS) spin-exchange experiments reveal detailed interfacial mixing between ER and BCPs for the first time, and two different types of interphase structure are found. 1 H fast MAS double-quantum filter experiments provide a fast and convenient detection of interphase composition, including immobilized BCPs and partially cured or local damaged ER network. The driving force for the interphase formation and miscibility in PCL-containing blends was successfully determined by high-resolution 13 C CPMAS experiments, demonstrating the formation of hydrogen bonds between PCL and ER; competing hydrogen bonding interactions were also found when ER was blended with PEO-b-PCL (EOCL). A new calculation method is proposed to quantitatively determine the distribution of different blocks in the interphase and dispersed phase for PCL-containing blends in combination with 13 C CPMAS and 1 H spin-diffusion experiments. A 13 C T 1 spin−lattice relaxation experiment provides a quantitative determination of the amount of local destroyed network in the interphase. Furthermore, it is found that incorporation of BCPs induces unexpected enhanced rigidity of the cross-linked network. On the basis of NMR results, we propose a model to describe the unique structure and dynamics of the interphase and cross-linked network as well as their underlying formation mechanism in ER/BCP blends.
Polymer International, 2008
BACKGROUND: The goal of this work was to establish the minimum degree of epoxidation needed to develop nanostructured epoxy systems by modification with poly(styrene-block-butadiene-block-styrene) (SBS) triblock copolymers epoxidized to several degrees, and also to investigate the effect of polystyrene (PS) content on the final morphologies. By using two SBS copolymers, the influence of the weight ratio of the two blocks on the generated morphologies and mechanical properties was also analysed. RESULTS: Nanostructured thermosets were effectively obtained through reaction-induced microphase separation of PS blocks from the matrix. A minimum of 27 mol% of epoxidation, which corresponds to 4.8 wt% of epoxidized polybutadiene (PB) units in the overall mixture, was needed to ensure nanostructuring of final mixtures and thus their transparency. Hexagonally ordered nanostructures were achieved for PS contents of around 16-20 wt%, which agrees with our previous results for mixtures with other SBS copolymers with different ratios between blocks. The fracture toughness of the epoxy matrix was improved or at least retained with mixing.
Materials, 2016
In this study, we used diglycidyl ether bisphenol A (DGEBA) as a matrix, the ABA block copolymer poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (Pluronic F127) as an additive, and diphenyl diaminosulfone (DDS) as a curing agent to prepare flexible epoxy resins through reaction-induced microphase separation (RIMPS). Fourier transform infrared spectroscopy confirmed the existence of hydrogen bonding between the poly(ethylene oxide) segment of F127 and the OH groups of the DGEBA resin. Small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy all revealed evidence for the microphase separation of F127 within the epoxy resin. Glass transition temperature (T g) phenomena and mechanical properties (modulus) were determined through differential scanning calorimetry and dynamic mechanical analysis, respectively, of samples at various blend compositions. The modulus data provided evidence for the formation of wormlike micelle structures, through a RIMPS mechanism, in the flexible epoxy resin upon blending with the F127 triblock copolymer.
Macromolecules, 2014
Controlling nanodomain morphology of nanostructured epoxy thermosets is critical to modulate the mechanical properties of the cross-linked matrix. In this contribution, we demonstrate that this can be achieved by using a suitable block copolymer containing an epoxy soluble block with the ability to react toward the epoxy system during curing. For this purpose we designed an epoxidized poly-(styrene-b-isoprene-b-styrene) block copolymer incorporating amine-reactive functionalities (eSIS-AEP) in the epoxidized block as modifier for an epoxy system, which allowed the formation of nanostructured thermosets with controlled spherelike nanodomain morphology. The eSIS-AEP was obtained in two steps from poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer by controlled epoxidation of the olefinic block followed by partial oxirane ring-opening reaction using 1-(2-aminoethyl)piperazine as nucleophile. Before the curing reaction it was observed that poly(styrene) blocks self-assembled to form ordered spherelike nanostructures in blends of eSIS-AEP with epoxy precursors. Since the amine-reactive moiety was incorporated to the block copolymer so that it could react toward diglicidyl ether of bisphenol A (DGEBA) at a similar temperature than the DGEBA/hardener reaction, the epoxy miscible block of eSIS-AEP (ePI-AEP) was able to react with DGEBA during curing. Once the cross-linked network was formed, the initially obtained spherelike nanodomains were preserved, indicating that no reaction-induced microphase separation of ePI-AEP subchains occurred. A completely different scenario was ascertained for epoxidized SIS block copolymer, which conducted to nonspherical nanodomains due to the uncontrolled epoxidized poly(isoprene) demixing process during the curing reaction. These results demonstrate the importance of the epoxy soluble block being reactive toward the epoxy precursors to control the morphology of the obtained nanostructure.
European Polymer Journal, 2015
The network build-up process during curing of an epoxy resin using a hyperbranched poly(ethyleneimine) as crosslinking agent has been studied from a theoretical and experimental point of view. A systematic analysis taking into account the stoichiometry of the curing process has been performed. Conversion at gelation has been studied by thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). Crosslinking density has been studied by dynamomechanical analysis (DMA). Gel fraction after extraction in organic solvents has also been determined. The experimental results have been compared with a theoretical network build-up model based on the random recombination of structural fragments, showing good agreement between theory and experimental results, but deviations from the ideal epoxyamine polycondensation appear as a consequence of the dilution of the hyperbranched crosslinker in offstoichiometric formulations.
Polymer Engineering & Science, 2012
The compatibility of styrene-block-butadiene-block-styrene (SBS) triblockcopolymer in epoxy resin is increased by the epoxidation of butadiene segment, using hydrogen peroxide in the presence of an in situ prepared catalyst in water/dichloroethane biphasic system. Highly epoxidized SBS (epoxy content SBS >26 mol%) give rise to nanostructured blends with epoxy resin. The cure kinetics of micro and nanostructured blends of epoxy resin [diglycidyl ether of bisphenol A; (DGEBA)]/amine curing agent [4,4 0 -diaminodiphenylmethane (DDM)] with epoxidized styrene-block-butadieneblock-styrene (eSBS 47 mol%) triblock copolymer has been studied for the first time using differential scanning calorimetry under isothermal conditions to determine the reaction kinetic parameters such as kinetic constants and activation energy. The cure reaction rate is decreased with increasing the concentration of eSBS in the blends and also with the lowering of cure temperature. The compatibility of eSBS in epoxy resin is investigated in detailed by Fourier transform infrared spectroscopy, optical and transmition electron microscopic analysis. The experimental data of the cure behavior for the systems, epoxy/DDM and epoxy/ eSBS(47 mol%)/DDM show an autocatalytic behavior regardless of the presence of eSBS in agreement with Kamal's model. The