Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41428-023-00802-8

International / domestic magazine：Domestic journal  

DOI： 10.1016/j.polymer.2023.126280

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

During bulk free-radical polymerization of methyl methacrylate below the glass-transition temperature of poly(methyl methacrylate), the relative fraction of monomer and polymer changes as the reaction proceeds. The liquid monomer is eventually converted to a solid glassy polymer. In other words, polymerization-induced vitrification or glass transition occurs. This process was traced by small-angle neutron scattering (SANS). The scattering profile discontinuously changes at the vicinity of vitrification. This discontinuous change was correlated with a sudden reaction acceleration known as the Trommsdorff effect. Ornstein-Zernike analysis revealed that the intensity at q = 0 (I(0)) and the correlation length of concentration fluctuation (xi) suddenly increase at the discontinuous change of the scattering profile. The obtained data implies that the increased heterogeneity (i.e., microscopic concentration fluctuation) is intimately related to the Trommsdorff effect.

DOI： 10.1021/acs.macromol.3c00176

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

It has been reported that the hydration state of biocompatible polymers, such as poly(ethylene glycol) (PEG), affects their bioinertness. PEGylated dendrimers have been studied for use as drug carriers. In our previous study, the hydration behaviors of PEG and PEGylated dendrimers were analyzed using differential scanning calorimetry (DSC) to investigate the relationship between hydration and in vivo behaviors. In this study, the hydration behaviors of PEG and PEGylated dendrimer were analyzed using X-ray diffraction (XRD) and infrared (IR) spectroscopy. According to the XRD analysis, ice was formed and melted in the PEG/water mixture with a 20% water content below 0 degrees C during the heating process; however, PEG crystals were formed in the PEG/water mixture containing 70% water. The XRD and IR results of the PEGylated dendrimer/water mixture were similar to those of the PEG/water system containing 70% water. Our IR spectral studies indicated that the hydration state of the PEGylated dendrimer was different from that of PEG containing 20% water. These results suggested that a comprehensive study is important for the analysis of such eutectic mixtures of PEG compounds and water.

DOI： 10.1038/s41428-022-00700-5

Authorship：Lead author,　Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

International / domestic magazine：Domestic journal  

Publishing type：Research paper (scientific journal)  

The acrylate copolymers consisting of 4-hydroxybutyl acrylate (HBA), 2-(tert-butoxy-carbonyloxy)ethyl acrylate (BHEA) or 4-(tert-butoxycarbonyloxy)butyl acrylate (BHBA), and 2-ethylhexyl acrylate (2EHA) as the repeating units were synthesized by radical copolymerization. The performance as the pressure-sensitive adhesives (PSAs) used for a dismantlable adhesion system was investigated. The glass transition temperatures and the adhesive properties were precisely controlled by the comonomer composition of the copolymers. It was confirmed that the deprotection of the tert-butoxycarbonyl (BOC) group rapidly proceeded for the BOC-containing acrylate copolymers as the PSAs. It resulted in the decrease of the adhesion strength during a debonding process by heating. The thermal stability during use and the quick response for on-demand debonding were simultaneously achieved by the use of alkyl p-toluenesulfonates as the thermally latent acids (TLAs).

DOI： 10.1016/j.polymer.2022.125416

Publishing type：Research paper (scientific journal)  

New kind of polymer composites, i.e., co-continuous network polymers (CNP), were fabricated by the filling of the continuous pores of an epoxy monolith (EM) with a cross-linked acrylate polymer. The internal structures of EM and CNP were non-destructively observed by X-ray CT imaging. The mechanical properties of EM were highly dependent on the pore and epoxy frame sizes. Increasing the molar ratio of the amino groups to glycidyl groups during the monolith fabrication process created a coarser co-continuous structure. It greatly enhanced the stretching property of EM. Filling the pores of EM with a rubbery cross-linked acrylate polymer as the second component increased the maximum strength of CNP, independent of the pore size. Furthermore, the gap for-mation at the boundary between the hard phase and the soft phase of CNP was observed by X-ray CT imaging for the broken test piece used for a tensile test. We discussed a mechanism for the deformation and fracture of EM and CNP.

DOI： 10.1016/j.polymer.2022.125433

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

The physical properties of polymers are significantly affected by relaxation processes. Recently, we reported that poly(diethyl fumarate) (PDEF) shows two thermal anomalies on DSC measurement, despite the fact that it is a homopolymer. We attribute these two relaxations alpha relaxation and beta relaxation, respectively. In this study, we investigate the two relaxations of fumarate-containing polymers by DSC, solid-state NMR, and X-ray scattering. The two relaxations are present even in a copolymer of diethyl fumarate and ethyl acrylate with fumarate segments of 30%. We used poly(methyl methacrylate) (PMMA) as a model polymer for comparison, since there are detailed investigations of its dynamics and physical properties. Solid-state NMR indicates that the very local relaxation of poly(fumarate)s is not significantly different from that of PMMA. The tensile test showed that PDEF is still brittle at above beta relaxation temperature and below alpha relaxation temperature. It was revealed that a structural anisotropy appeared when PDEF was extended at around alpha relaxation temperature. We discuss the effect of the glassy packing of the rigid polymer chain including the DEF segments on the strong beta relaxation behavior. Our data provide insight into the microscopic mechanism of beta relaxation of vinyl polymers.

DOI： 10.3390/polym14224876

PubMed

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

It has been demonstrated that nano- or micro-structured polymeric materials have huge potential as advanced materials. However, most of the current fabricating methods have limitations either in cost or in size. Here, we investigate the bulk polymerization of methyl methacrylate in the presence of poly(ethylene glycol) (PEG). We found that phase separation occurs during bulk polymerization. After removal of PEG via sonication, microscopic structures of poly(methyl methacrylate), including porous structures, co-continuous monolith structures, or particle aggregation structures, are formed. These structures can be controlled by the amount of PEG added and the reaction temperature. The results are summarized in phase diagrams. The addition of PEG significantly affects the reaction kinetics. Phase separation is coupled with the reaction acceleration known as the Trommsdorff effect. As a result, the reaction completes in a shorter time when the PEG amount is higher. We demonstrate surface coating to fabricate an amphiphobic surface, repelling both water and oil. The methods presented here have the potential to fabricate microscopic structures in large areas cost-effectively.

DOI： 10.1021/acsomega.2c04690

PubMed

Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

Dynamical behavior and glass transitions in copolymers of diisopropyl fumarate (DiPF) with 1-adamantyl acrylate (AdA) or n-butyl acrylate (nBA) are investigated by dielectric relaxation spectroscopy (DRS) to elucidate the effect of structural constraint due to the absence of a CH2 spacer on the dynamics. DRS measurements revealed that the two copolymers exhibit three dynamical processes: alpha-, beta-, and gamma-processes. The relaxation time of the beta-process can be described by the Vogel-Fulcher-Tammann (VFT) law in addition to the alpha-process. Hence, two glass transition temperatures, T-g, can be evaluated from alpha-and beta-processes. The AdA and nBA fraction dependence of T(g)s is consistent with that obtained by dynamical mechanical analysis. The Vogel temperature of the alpha-process is nearly equal to that of the beta-process for the PDiPF homopolymer. With the increase in the AdA fraction, the difference in the Vogel temperature between the alpha-and beta-processes increases. This result suggested that there is an intrinsic correlation between the alpha- and beta-processes for PDiPF, and the correlation changes with the AdA fraction. From the nBA fraction dependence of the beta-process, the beta-process of PDiPF can be related to the segmental motion of the main chain. Nevertheless, PDiPF exhibits a solid-like property up to the T-g, which is related to the alpha-process. The physical origins of other processes also were discussed.

DOI： 10.1016/j.polymer.2022.124671

Publishing type：Research paper (scientific journal)  

Reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(tert-butoxycarbonyloxy)ethyl methacrylate (BHEMA) is carried out using 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid as the RAFT agent. The polymers with a controlled molecular weight and polydispersity are produced when a large amount of the RAFT agent is used. The RAFT polymerization of isobutyl methacrylate is also carried out using poly(2-(tert-butoxycarbonyloxy)ethyl methacrylate) (PBHEMA) as the macro-RAFT agent in order to synthesize diblock copolymers with a narrow molecular weight distribution. It is revealed that the control of the polymerization of BHEMA is achieved under limited polymerization conditions. Then, the acid-catalyzed deprotection of tert-butoxycarbonyloxy groups of PBHEMA is performed in the presence of trifluoroacetic acid at room temperature to obtain polymers with a hydroxy group in the side chain. The hydroxy-containing polymers are further reacted with 2-isocyanatoethyl acrylate and methacrylate to synthesize precursor polymers used for a thermally curing system.

DOI： 10.1002/macp.202100336

Publishing type：Research paper (scientific journal)  

<title>Abstract</title>High-performance polymer materials that can exhibit distinguished mechanical properties have been developed based on material design considering energy dissipation by sacrificial bond dissociation. We now propose co-continuous network polymers (CNPs) for the design of tough polymer materials. CNP is a new composite material fabricated by filling the three-dimensionally continuous pores of a hard epoxy monolith with any cross-linked polymer having a low glass transition temperature (<italic>T</italic>_g). The structure and mechanical properties of the CNPs containing epoxy resins, thiol-ene thermosets, and polyacrylates as the low-<italic>T</italic>_g components were investigated by differential scanning calorimetry, dynamic mechanical analysis, tensile tests as well as scanning electron microscopic observations and non-destructive 3D X-ray imaging in order to clarify a mechanism for exhibiting an excellent strength and toughness. It has been demonstrated that the mechanical properties and fractural behavior of the CNPs significantly depend on the network structure of the filler polymers, and that a simultaneous high strength and toughness are achieved via the sacrificial fracture mechanism of epoxy-based hard materials with co-continuous network structures.

DOI： 10.1038/s41598-021-80978-2

PubMed

Other URL： http://www.nature.com/articles/s41598-021-80978-2

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

Poly(2-(tert-butoxycarbonyloxy)ethyl methacrylate) (PBHEMA) is converted to poly(2-hydroxyethyl methacrylate) with the release of isobutene and carbon dioxide gasses when it is heated at a high temperature over 200 degrees C. The deprotection of PBHEMA is accelerated by the addition of an acid, but it is simultaneously disadvantageous for the storage and handling of the polymer at an ambient temperature. In this study, we propose the use of thermal acid generators, i.e., thermally latent acids (TLAs) as the catalysts to control a reaction rate and a working temperature for the deprotection of PBHEMA. We investigated the thermal deprotection behavior of some sulfonates including isopropyl p-toluenesulfonate (IPTS) and cyclohexyl p-toluenesulfonate (CHTS). The kinetic parameters for the deprotection, which provides p-toluenesulfonic acid (TsOH) as the reaction product, were determined by thermogravimetric (TG) analysis under the isothermal condition. A remarkable autocatalytic effect actually resulted in a rapid deprotection to produce TsOH in a narrow temperature range under the non-isothermal conditions. The additive effect of the TLAs on the deprotection of the BOC groups contained in the side chain of PBHEMA was similarly investigated. It was revealed that the deprotection of PBHEMA rapidly proceeded by the addition of IPTS and CHTS under the heating conditions over 100 degrees C. PBHEMA was stable at a temperature below the onset temperature of the deprotection of the TLAs. The deprotection kinetics of PBHEMA and a detailed mechanism for the control of the reactions in the presence of the TLAs were clarified.

DOI： 10.1016/j.polymdegradstab.2022.110127

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

Bulk polymerization directly provides glassy polymers from liquid monomers and has been used for many engineering applications. Recently, it has drawn attention for potential use as a resin for fiber-reinforced plastics and additive manufacturing. For such applications, detailed and precise information of the reaction kinetics, including non-ideal conditions, is required. Here, we investigate the reaction kinetics of isothermal bulk polymerization using differential scanning calorimetry (DSC) at a broad temperature ranged from 40 degrees C to 90 degrees C. 2,2'-Azobis(isobutyronitrile) (AIBN) or 2,2'-Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) is used as an initiator. We analyze the data focusing on the onset of sudden reaction acceleration known as Trommsdorff effect. Because of the reaction kinetics and the nature of Trommsdorff effect, a higher temperature does not always lead to a shorter time for the completion of the reaction. We discuss the reaction kinetics in conjunction with the molecular weight distributions.

DOI： 10.1002/kin.21564

Publishing type：Research paper (scientific journal)  

Recently the beta relaxation draws attention because it may act as a precursor of the alpha relaxation and potentially influences a wide range of properties. In many cases, the weak intensity of the beta relaxation limits the experimental investigation. Herein, the beta relaxation of poly(diethyl fumarate) (PDEF) using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and dielectric spectroscopy is investigated. Originating from the absence of methylene spacer in the main chain, polyfumarates possess an intense beta relaxation. Unlike common vinyl polymers, PDEF shows two distinct steps in DSC measurement corresponding to alpha and beta relaxations. Interestingly, the relative intensities of alpha and beta relaxations depend on the thermal history. The beta relaxation of PDEF obtained by dielectric spectroscopy at high temperature is similar to that of poly(methyl methacrylate) (PMMA). However, the beta relaxation of PDEF follows the VFT equation rather than the Arrhenius equation at low temperatures. The analysis of PDEF/PMMA blend suggests the local orientation of PDEF chain plays a vital role in the intense beta relaxation.

DOI： 10.1002/macp.202100124

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/macp.202100124

Publishing type：Research paper (scientific journal)  

The reaction kinetics during bulk free radical polymerization is still not fully understood. As the reaction proceeds, many parameters, including monomer/polymer fraction, radical concentration, viscosity, and temperature, change in a non-equilibrium manner. In this study, we investigate the bulk polymerization of methyl methacrylate, focusing on a sudden acceleration in reaction kinetics known as the Trommsdorff effect. Dielectric spectroscopy shows that a temperature increase occurs at the vicinity of polymerization-induced vitrification. At the same timing as the temperature increase, the polymerization solution becomes heterogeneous. This heterogenization causes a decrease in transmittance at a wavelength of 400 nm. We discuss phenomena related to the Trommsdorff effect, including the kinetic heterogenization, vitrification, change in the amorphous structure, and the formation of discontinuously high-molecular-weight polymers.

DOI： 10.1021/acs.macromol.0c02260

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

Copyright © 2020 American Chemical Society. A monolith bonding system has a high reliability for dissimilar material bonding. The epoxy monolith layer fabricated on a substrate guarantees bond strength by the anchor effect, regardless of the compatibility of the used materials. Designing a high-performance monolith bonding system requires the suppression of an interfacial failure between the monolith and the substrate. In this study, silane and phosphine coupling agents containing amino and epoxy groups were used to construct a robust interfacial structure between the monolith and the substrates such as glass and metals. The internal and interfacial monolith structures were characterized by three-dimensional X-ray imaging as a nondestructive observation method in addition to the scanning electron microscopy of the sample cross sections. The modification of the substrate-monolith interface using the coupling agents improved the strength of dissimilar material bonding of the glass and metal substrates in combination with thermoplastic resins such as poly(ethylene terephthalate) and polycarbonate bisphenol-A.

DOI： 10.1021/acs.langmuir.0c01481

PubMed

Publishing type：Research paper (scientific journal)  

© 2020 Elsevier Ltd Poly(diisopropyl fumarate) (PDiPF) has dynamic mechanical properties different from the relaxation processes of conventional vinyl polymers, due to the absence of a methylene spacer in the main chain. In this study, we investigated the relaxation behavior of PDiPF using dielectric spectroscopy (DS), differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA). We have demonstrated that the β relaxation of PDiPF has unusual characteristics originating from the absence of a methylene spacer; for example, the β relaxation of PDiPF follows the Vogel–Fulcher–Tammann (VFT) equation, causes a clear step in the DSC curve, and enhances the microscopic packing of the polymer chains in the solid state. These β relaxation behaviors of PDiPF reflect the enlarged cooperative rearranging region (CRR).

DOI： 10.1016/j.polymer.2020.122479

Publishing type：Research paper (scientific journal)  

© 2020 Wiley Periodicals, Inc. We carried out the thermal curing of the copolymers of N-allylmaleimide (AMI) and 2-ethylhexyl acrylate (2EHA) using 1,3,4,6-tetra(2-mercaproethyl)glycoluril (G1), 1,3,4,6-tetra(3-mercaptopropyl)glycoluril (G2), 1,3,4,6-tetraallylglycoluril (G3), triallylisocyanurate (TAIC), and pentaerythritol tetrakis(3-mercaptobutyrate) (PEMB) as the crosslinkers. Based on the results for the analysis of thiol–ene reactions monitored by IR spectroscopy, it was confirmed that the curing rate significantly depended on the combination of the used crosslinkers. The insoluble fraction after curing was more than 90% for the systems using the glycoluril crosslinkers, while the conversion of the allyl groups was suppressed due to the rigid structure of these crosslinkers. The heat resistance and the mechanical properties of the crosslinked polymers were investigated by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, and mechanical tensile tests. For the products cured using the glycoluril crosslinkers, the glass transition temperature (Tg) and the maximum temperature of thermal decomposition (Tmax) were 54–59 °C and 395–409 °C, respectively, being higher than those for the cured product prepared with PEMB and TAIC as the conventional crosslinkers. The elasticity (75–139 MPa), the maximum strength (3.0–4.1 MPa), and the adhesion strength (6.7–10.7 MPa) for the polymers cured with the glycoluril crosslinkers, determined by the mechanical tensile and single lap-shear adhesion tests, were higher than those for cured materials produced with PEMB. Thus, the thermal and mechanical properties of the maleimide copolymers were efficiently enhanced by crosslinking using the rigid glycoluril compounds. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 923–931.

DOI： 10.1002/pol.20190188

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/pol.20190188

Kind of work：Single Work  

Authorship：Lead author,　Corresponding author   Kind of work：Joint Work  

Kind of work：Single Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

In this study, we propose a convenient method for the synthesis of double-network gels by the one-shot radical polymerization for their application to rapid optical tissue clearing. Double-network gels were produced during the radical polymerization of acrylamide (AAm) and sodium styrenesulfonate (SS) in the presence of N,N'-methylenebisacrylamide and sodium divinylbenzenesulfonate as the cross-linkers by simultaneous addition, that is, one-shot polymerization accompanying the delay of polymerization for a second network monomer. We analyzed the polymerization process based on the consumption rates of each monomer during the reactions in the absence of the cross-linkers in order to estimate the repeating unit structure of the resulting polymers. We then fabricated the AAm/SS gels by the polymerization of AAm and SS in the presence of the cross-linkers. We analyzed the swelling, viscoelastic, and mechanical properties of the produced gels to investigate their network structure. Finally, we demonstrated the validity of the double-network gels for the application to rapid optical tissue clearing.

DOI： 10.1021/acsomega.9b02493

Publishing type：Research paper (scientific journal)  

Four dialkyl fumarates containing bulky adamantyl ester groups, i.e., di(1-adamantyl) fumarate (1), bis(3,5-dimethyl-1-adamantyl) fumarate (2), 1-adamantyl isopropyl fumarate (3), and 3,5-dimethyl-1-adamantyl isopropyl fumarate (4), were polymerized to obtain poly( dialkyl fumarate)s (PDRFs) with rigid chain structures. We carried out the conventional radical polymerization of these adamantane-containing DRFs in the presence of a radical initiator either in toluene or in bulk at 80 or 60 degrees C. Reversible addition-fragmentation chain transfer (RAFT) polymerization was also performed using 1,1'-(1,2ethanediyl) bis[2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate] and 2,2,2-trifluoroethyl 2-[[(dodecylthio)thioxymethyl]thio]-2-methylpropionate as the chain transfer agents (CTAs). Triblock copolymers consisting of rigid and flexible segments were synthesized by the polymerization of 2-ethylhexyl acrylate, which was used as the second monomer, using the PDRFs as the macro-CTA containing trithiocarbonate groups at the chain ends. The excellent thermal stability of the adamantane-containing PDRFs was confirmed by thermogravimetric analysis in a nitrogen stream. The alignment of the rigid PDRF chains in the solid-state was revealed based on the appearance of a peak in the small angle regions of the X-ray diffraction profiles.

DOI： 10.1038/s41428-019-0228-x

Publishing type：Research paper (scientific journal)  

Due to the absence of a methylene spacer in the main chain, poly(substituted methylene)s with rigid structures possess some distinguished properties including a unique beta-relaxation process. In this study, two series of random copolymers of diisopropyl fumarate (DiPF) with 1-adamantyl acrylate (AdA) and n-butyl acrylate (nBA) with various compositions were synthesized. The relaxation behavior of the copolymers was investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The alpha-relaxation temperature of the copolymers decreased as the acrylate content increased. Depending on the glass transition temperature (T-g) of the counterpart copolymers, that is, T-g = 156 degrees C for the homopolymer of AdA and T-g = -53 degrees C for the homopolymer of nBA, the beta-relaxation temperature from the DiPF segments systematically shifted. While the beta-relaxation temperature increased when copolymerized with AdA, the temperature decreased when copolymerized with nBA. Both copolymers maintained a high storage modulus of more than 10MPa in the range between the alpha- and ss-relaxation temperatures. The merging of the alpha and beta processes at an intermediate composition was also observed. The random copolymerization of DiPF and acrylates enables us to fine tune the properties associated with the beta-relaxation of DiPF segments.

DOI： 10.1038/s41428-019-0226-z

Publishing type：Research paper (scientific journal)  

Infusible liquid resins that polymerize into a thermoplastic are desirable for many applications. Similar to unsaturated and vinylester thermosetting systems, they consist of polymers dissolved in reactive monomer. This work presents a method to decrease cycle time by tuning the molecular weight and concentration of the predissolved polymer in the resin. Variation of these properties allows precise control of the viscosity which in turn controls the time at which peak exotherm is reached, the maximum temperature for a given part thickness, and cure time. Predictive models for the viscosity dependence on molecular weight, polymer concentration, shear rate, and temperature are developed. Two fiberglass panels are fabricated and tested; one with a lower molecular weight (M-w similar to 30 kg mol(-1)) poly(methyl methacrylate) dissolved in methyl methacrylate and the second with higher molecular weight (M-w similar to 500 kg mol(-1)) predissolved polymer in the resin. Mechanical properties are indistinguishable but the lower molecular weight panel cures up to three times faster. (c) 2019 Wiley Periodicals, Inc.

DOI： 10.1002/app.48006

Publishing type：Research paper (scientific journal)  

In organic synthesis and polymer materials chemistry, a tert-butoxycarbonyl (BOC) group is often used as one of tools for the protection of functional groups. In this study, we carried out radical polymerization of 2-(tert-butoxycarbonyloxy)ethyl methacrylate (BHEMA) and copolymerizations of BHEMA with methyl methacrylate (MMA), n-butyl methacrylate (nBMA), isobutyl methacrylate (iBMA), tert-butyl methacrylate (tBMA), dodecyl methacrylate (DMA), alpha-methylstyrene (AMS), and limonene (Lim) as the 1,1-disubstituted ethylene monomers and investigated the thermal decomposition behavior of the obtained polymers. On the basis of the results of thermogravimetric (TG) analysis in nitrogen at the heating rate of 10 degrees C/min, it was revealed that the deprotection of the BOC group in the polymer side chains occurred at ca. 200 degrees C accompanying the quantitative elimination of isobutene and carbon dioxide, independent of the structures of the repeating units. The following main-chain decomposition of the residual copolymers resulted in a small amount of residue less than 1% at 500 degrees C. Poly(2-hydroxyethyl methacrylate) was synthesized via the deprotection of the BOC group of PBHEMA. (C) 2019 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2019.05.027

Authorship：Lead author  

Publishing type：Research paper (scientific journal)  

Void detection in fiber-reinforced composites traditionally relies on precise density measurements before and after the physical removal of the polymer matrix; consequently, this method only provides data on the total volume of voids within the material without information about void sizes, shapes, and distributions. Despite advances in X-ray computed tomography, it is still challenging to quantitatively and convincingly characterize void content due to the complex X-ray physics of divergent, broad-spectrum laboratory X-ray sources. Here, we demonstrate that by using aligned high-energy and low-energy X-rays, dual-energy X-ray computed tomography provides high-quality images and phase-based segmentation that allows for clear distinction between air, polymer matrix, and reinforcing fibers. We verify the method on several fiber-reinforced composite samples: epoxy-glass fiber composites fabricated by vacuum-assisted resin transfer molding and by light resin transfer molding (light resin transfer molding), and a carbon fiber composite fabricated via vacuum-assisted resin transfer molding.

DOI： 10.1177/0021998319827091

Publishing type：Research paper (scientific journal)  

Reactive thermoplastics are advantageous for wind turbine blades because they are recyclable at end of life, have reduced manufacturing costs, and enable thermal joining and shaping. However, there are challenges with manufacturing wind components from these new materials. This work outlines the development of manufacturing processes for a thick glass fiber-reinforced acrylic thermoplastic resin wind turbine blade spar cap, with consideration given to effects of the exothermic curing reaction on thick composite parts. Comparative elastic properties of these infusible thermoplastic materials with epoxy thermoset materials, as well as thermoplastic coupon components, are also included. Based on the results of this study it is concluded that the thermoplastic resin system is a viable candidate for the manufacturing of wind turbine blades using vacuum-assisted resin transfer molding. Significant gains in energy savings are realized avoiding heated molds, ability for recycling, and providing an opportunity for utilizing thermal welding.

DOI： 10.1007/s10443-019-9760-2

Authorship：Lead author,　Corresponding author  

Publishing type：Research paper (scientific journal)  

We report on the phase separation of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) during bulk free-radical polymerization. The phase separation is induced when the reaction is initiated at room temperature by the redox reaction of benzoyl peroxide in the presence of an amine. During the reaction, the ratio of MMA and PMMA changes continuously. Separation into MMA-rich and PMMA-rich phases coincides with the onset of the Trommsdorff effect. At room temperature, the interface between the two phases remains, even after drying the remaining monomer. When the sample is annealed above the glass transition temperature T-g, the interface disappears. Due to the frozen dynamics of the polymer chains, subsequent cooling below T-g does not result in further phase separation. This result provides evidence for the existence of rich, thermodynamically stable states, which are typically suppressed due to the frozen dynamics of polymers at temperatures below the T-g, after thermal processing above the T-g.

DOI： 10.1038/s41428-018-0142-7

Publishing type：Research paper (scientific journal)  

For the first time ever, a styrene-free, biobased formulation suitable for infusion processing of thermoplastic composites is reported. Biobased polylactide (PLA) is soluble in methyl methacrylate (MMA) and this new styrene free system is suitable for fabricating composite parts. Rheology is critically important in transfer molding; therefore, single chain properties are related to concentrated solutions of PLA in MMA. Multiple angle laser light scattering (MALLS) provides molecular weights, radii of gyration, and second virial coefficients for PLAs of varying molecular weight dissolved in MMA. The Flory interaction parameter is described by chi = 0.40 +/- 0.04. Dilute solution viscometry (DSV) gives the Mark-Houwink relationship at 30 degrees C as [eta] = 0.017M(eta)(0.73). The expansion factors calculated from DSV and MALLS agree reasonably well (alpha = 1.45 +/- 0.25). The values of a, chi, and alpha indicate that MMA is a good solvent for PLA. The Carreau Yasuda viscosity and Andrade-Eyring temperature models enable a quantitative description of the specific viscosity, eta(sp), as a function of the intrinsic viscosity normalized concentration, c[eta]. The quantitative description provides a powerful and generally applicable approach to formulating resins useful for composite fabrication. A new environmentally superior resin system is used to fabricate a composite panel using vacuum-assisted resin transfer molding.

DOI： 10.1021/acssuschemeng.8b04229

Publishing type：Research paper (scientific journal)  

Thermoplastic resin systems have long been discussed for use in large-scale composite parts but have yet to be exploited by the energy industry. The use of these resins versus their thermosetting counterparts can potentially introduce cost savings due to non-heated tooling, shorter manufacturing cycle times, and recovery of raw materials from the retired part. Because composite parts have high embedded energy, recovery of their constituent materials can provide substantial economic benefit. This study determines the feasibility of recycling composite wind turbine blade components that are fabricated with glass fiber reinforced Elium (R) thermoplastic resin. Several experiments are conducted to tabulate important material properties that are relevant to recycling, including thermal degradation, grinding, and dissolution of the polymer matrix to recover the constituent materials. Dissolution, which is a process unique to thermoplastic matrices, allows recovery of both the polymer matrix and full-length glass fibers, which maintain their stiffness (190 N/(mm g)) and strength (160 N/g) through the recovery process. Injection molded regrind material is stiffer (12 GPa compared to 10 GPa) and stronger (150 MPa compared to 84 MPa) than virgin material that had shorter fibers. An economic analysis of the technical data shows that recycling thermoplastic-glass fiber composites via dissolution into their constituent parts is commercially feasible under certain conditions. This analysis concludes that 50% of the glass fiber must be recovered and resold for a price of $0.28/kg. Additionally, 90% of the resin must be recovered and resold at a price of $2.50/kg. (C) 2018 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jclepro.2018.10.286

Kind of work：Joint Work  

Venue：Indianapolis