Degradable low-dielectric eco-friendly epoxy-based thermosetting resin

Abstract

The present invention relates to a degradable, low-dielectric, eco-friendly epoxy-based thermosetting resin and a method for preparing same, the resin being prepared through steps including: converting isosorbide into isosorbide diglycidyl ether (ISDGE) through an epoxidation process with epichlorohydrin in the presence of a base; and polymerizing the ISDGE with a lactone-based curing agent by using a cationic initiator.

Description

Biodegradable low-dielectric eco-friendly epoxy-based thermosetting resin

[0001] The present invention relates to a degradable low-dielectric eco-friendly epoxy-based thermosetting resin and a method for manufacturing the same.

[0002] Plastic is an indispensable material for modern life and industrial development due to its low density, ease of processing, various useful functions, and low cost. However, as its use increases, it leaves a large carbon footprint, causing serious problems such as waste disposal and greenhouse gas emissions. In particular, only 16% of global plastic waste is recycled, while the remainder is landfilled, incinerated, or discharged into the ocean. Currently, plastic accounts for approximately 75% of global coastal waste, posing serious environmental and health threats. Due to its high durability and resistance, plastic has limited self-cleaning capabilities and accumulates in the environment; furthermore, it continuously decomposes due to the combined action of wind, waves, and ultraviolet radiation, forming microplastics. Microplastics are plastic debris smaller than 5 mm in size and are found in diverse marine environments worldwide. The high specific surface area and hydrophobicity of microplastics enable the efficient adsorption of persistent organic pollutants, such as toxic organic substances, endocrine disruptors, and decomposition byproducts. This poses a threat to both the global environment and human health, as microplastics can accumulate in marine organisms and be transmitted to humans through the food chain.

[0003] Conventional thermoplastic plastics such as polyethylene terephthalate, polypropylene, polyethylene, and polylactic acid are easy to reprocess and reshape when molded at high temperatures and solidify upon cooling. On the other hand, thermosetting resins with a three-dimensional cross-linked network structure are stronger than thermoplastic plastics but do not melt and decompose when heated, and are difficult to reshape after curing, making recycling difficult. Consequently, thermosetting polymer waste is disposed of through incineration or landfill, during which CO2 and hazardous substances are released into the atmosphere.

[0004] Despite these drawbacks, thermosetting resins are preferred over thermoplastics in extreme environments and high-end applications due to their high thermal and mechanical stability. Therefore, developing thermosetting plastics that can decompose under mild conditions is of great help in recycling and waste disposal. Among numerous thermosetting polymers, bisphenol A (BPA) diglycidyl ether (DGEBA) is the most widely used as a matrix for printed circuit boards (PCBs), electrically encapsulated structural adhesives, and fiber-reinforced polymers (FRP) thanks to its excellent adhesion, high mechanical strength, insulating properties, and superior heat and corrosion resistance. However, exposure to BPA, the primary raw material for DGEBA production, has harmful effects on the brains and prostates of fetuses, infants, and children.

[0005] Recently, biomass-derived renewable resources have garnered significant attention as alternatives to BPA. In particular, products made from biomass-derived isosorbide, lignin, and cellulose exhibit physical properties equivalent to or better than those of BPA-based polymers, and are expected to reduce environmental pollution by emitting less CO2. Therefore, these raw materials can be used to produce new sustainable thermosetting plastics. For these plastics to have practical value, the materials entering the supply chain must be bio-based and possess a structure that allows them to decompose easily under specific conditions.

[0006] Isosorbide is produced through the dehydration of sorbitol, a hydrogenated sugar obtained by reducing glucose, and is the most promising eco-friendly alternative to petroleum-based BPA.

[0007] The inventors have developed a degradable thermosetting polymer based on sustainable materials extracted from renewable natural resources. The BPA monomer used in conventional epoxy resins was replaced with biomass-derived isosorbide, a water-free sugar alcohol.

[0008] The present invention is intended to provide a biodegradable, low-dielectric, eco-friendly epoxy-based thermosetting resin based on sustainable materials extracted from renewable natural resources.

[0009] The present invention provides a degradable, low-dielectric, eco-friendly epoxy-based thermosetting resin prepared by comprising the steps of: converting isosorbide into isosorbide diglycidyl ether (ISDGE) through an epoxidation process with epichlorohydrin in the presence of a base; and polymerizing the isosorbide diglycidyl ether (ISDGE) and a lactone-based curing agent using a cationic initiator.

[0010] In addition, the present invention provides a method for manufacturing a low dielectric eco-friendly epoxy-based thermosetting resin, comprising the steps of: reacting isosorbide derived from renewable resources with epichlorohydrin in the presence of a base to produce isosorbide diglycidyl ether (ISDGE); and reacting the ISDGE with a lactone-based curing agent in the presence of a cationic initiator to form a cross-linked structure including ester bonds to produce a degradable thermosetting resin.

[0011] The thermosetting resin according to the present invention can exhibit a low dielectric constant of 2.6 and a low dielectric loss of 0.01 in the 10 GHz high-frequency band.

[0012] The prepreg produced by impregnating glass fibers with a thermosetting resin according to the present invention exhibits excellent adhesion to copper foil, allowing for the production of copper clad laminates (CCL), and the glass fibers can be recycled by completely decomposing them in a base.

[0013] According to the present invention, by manufacturing a biodegradable thermosetting resin based on an eco-friendly material, it is possible to reduce waste plastics and provide an excellent low-dielectric, low-loss material capable of responding to ultra-high frequency communication.

[0014] The thermosetting resin according to the present invention is a promising alternative to BPA-based epoxy thermosetting resins due to its low dielectric constant and flexibility, and is suitable for eco-friendly biodegradable electronic products. In addition, microplastics generated from conventional thermosetting resins are not expected to have a negative impact on human health when considering the sustainable network structure.

[0015] The thermosetting resin according to the present invention is expected to be applicable as a circuit board material for electronic devices in smart manufacturing fields such as autonomous vehicles, AI, multimedia, and healthcare, as well as in 5G / 6G communication.

[0016] Meanwhile, the scope of the present invention is not limited by the effects described above.

[0017] Figure 1 is a schematic diagram showing a) the ISDGE synthesis reaction, b) the cross-linking between ISDGE and lactone, and c) the structure and degradation of the cross-linked degradable thermosetting resin.

[0018] Figure 2 is a) 1 H NMR, b) 13 c) 3C NMR, c) FT-IR spectrum, d) gel transmission chromatogram of synthesized ISDGE.

[0019] FIG. 3 relates to FT-IR spectra recorded before and after curing of ISDGE after crosslinking with a) GBL, b) DVL, and c) ECL, d) differential scanning calorimetry curves of ISDGE and DGEBA cured with various lactones, e) thermogravimetric analysis, f) differential thermogravimetric analysis, and g) stress-strain curves of thermosetting resins cured with three lactones.

[0020] Figure 4 relates to a) residual mass fraction of isosorbide and DGEBA-based thermosetting resins according to time of exposure to a 3 wt% NaOH solution at 80°C, b) extension of a) to a time range of 0-12 hours, c) a photograph of the isosorbide-based thermosetting resin degraded after exposure to the NaOH solution, d) the degradation rate constant k of the ISDGE thermosetting resin cured with ceractone, and e) the degradation products identified through the high-performance liquid chromatography curve of the ISDGE cured with GBL.

[0021] FIG. 5 relates to a) the dielectric constant of ISDGE- and DGEBA-based thermosetting resins cured with ceractone, b) the tensile properties of prepregs made from ISDGE thermosetting resins cured with ceractone, c) a photograph showing the flexibility of ISDGE thermosetting resin-based prepregs completely decomposed in a 3 wt% NaOH solution at 80°C, d) a schematic diagram of copper clad laminate (CCL) manufacturing, e) the peel strength of CCLs derived from ISDGE and DGEBA cured with ceractone, and f) a photograph of a microstrip substrate with 0.5, 1, 2, and 5 cm strip lines.

[0022] The present invention will be described in detail as follows.

[0023] Meanwhile, each description and embodiment disclosed in this application may also be applied to other descriptions and embodiments. That is, all combinations of the various elements disclosed in this application fall within the scope of this application. Furthermore, the scope of this application should not be considered limited by the specific descriptions provided below.

[0024] The inventors synthesized an epoxy using isosorbide, an eco-friendly raw material extracted from corn, as a monomer, and produced a thermosetting polymer that is completely decomposed in a basic environment through a curing reaction with a lactone-based curing agent.

[0025] In the present invention, isosorbide was converted into isosorbide diglycidyl ether (ISDGE) through an epoxidation process with epichlorohydrin, and subsequently, a degradable thermosetting resin containing ester bonds was produced through a ring-opening reaction between a glycidyl group and a biomass-derived lactone.

[0026] In the present invention, the lactone-based curing agent may be one or more selected from gamma-butyrolactone (GBL), delta-valerolactone (DVL), or ε-caprolactone (ECL).

[0027] The above cation initiator may be ytterbium(III) trifluoromethanesulfonate (Yb(OTf)3).

[0028] The thermosetting resin according to the present invention may have a dielectric constant of 2.6 or less and a dielectric loss of 0.01 or less in the 10 GHz high frequency band.

[0029] The thermosetting resin according to the present invention can decompose by more than 90% by weight within 3 days under weakly basic conditions.

[0030] The thermosetting resin according to the present invention may have a tensile strength of about 3 MPa or more and a fracture strain of about 25% or more after curing.

[0031] The prepreg produced by impregnating a glass fiber reinforcing material with a thermosetting resin according to the present invention exhibits excellent adhesion to copper foil, enabling the production of CCL, and can regenerate glass fibers by completely decomposing them in a base.

[0032] The above prepreg can be laminated with copper foil to form a copper clad laminate (CCL) with a peel strength of about 10 N or more.

[0033] The thermosetting resin according to the present invention includes carboxyl groups and hydroxyl groups as products upon decomposition and can be decomposed by a surface erosion mechanism.

[0034] The thermosetting resin according to the present invention can be used in circuit boards for electronic devices for 5G or 6G communication.

[0035] In addition, the present invention provides a method for manufacturing a low dielectric eco-friendly epoxy-based thermosetting resin, comprising the steps of: reacting isosorbide derived from renewable resources with epichlorohydrin in the presence of a base to produce isosorbide diglycidyl ether (ISDGE); and reacting the ISDGE with a lactone-based curing agent in the presence of a cationic initiator to form a cross-linked structure including ester bonds to produce a degradable thermosetting resin.

[0036] The above lactone-based curing agent is one or more of gamma-butyrolactone (GBL), delta-valerolactone (DVL), or ε-caprolactone (ECL), and the above cation initiator may be Yb(OTf)3.

[0037] The thermosetting resin manufactured according to the above manufacturing method may have a dielectric constant of 2.6 or less and a dielectric loss of 0.01 or less in the 10 GHz high frequency band.

[0038] The thermosetting resin produced according to the above manufacturing method can decompose by more than 90% by weight within 3 days under weakly basic conditions.

[0039] In addition, the present invention provides an insulating material for circuit boards of electronic devices for 5G or 6G communication, comprising the low dielectric eco-friendly epoxy-based thermosetting resin.

[0040] In addition, the present invention provides a resin composition for manufacturing prepreg for printed circuit boards (PCBs) or copper clad laminates (CCL), comprising the above-mentioned low dielectric eco-friendly epoxy-based thermosetting resin.

[0041] In addition, the present invention provides an adhesive or encapsulant for eco-friendly electronic components or packages that require recycling or biodegradation, comprising the above-mentioned low dielectric eco-friendly epoxy-based thermosetting resin.

[0042] In addition, the present invention provides a substrate structure for a high-frequency antenna, a high-speed signal transmission line, or a radar system comprising the above-mentioned low-dielectric, eco-friendly epoxy-based thermosetting resin.

[0043] The present invention will be explained in more detail below through the following examples. However, these examples are intended to illustrate the invention and the scope of the invention is not limited to these examples.

[0044]

[0045] ingredient

[0046] Isosorbide, epichlorohydrin, NaOH, ytterbium (III) trifluoromethanesulfonate (Yb(OTf)3), and dichloromethane were purchased from Tokyo Chemical Industry Co., Ltd.

[0047] Isophorone diamine (IPD), NaN3, HCl, gamma-butyrolactone (GBL), delta-valerolactone (DVL), or ε-caprolactone (ECL) were purchased from Sigma-Aldrich, Inc.

[0048] Diglycidyl ether (DGEBA) (YD-128) was purchased from Kookdo Chemical Co.

[0049]

[0050] <Example 1>

[0051] ISDGE synthesis

[0052] ISDGE was synthesized according to a previously reported method (Fig. 1a). Isosorbide was converted to isosorbide diglycidyl ether (ISDGE) through an epoxidation process with epichlorohydrin in the presence of a base, according to standard procedures for the production of commercial epoxy resins.

[0053] Isosorbide (0.3 mol) and freshly distilled epichlorohydrin (3 mol) were placed in a three-necked flask equipped with a Dean-Stark water separation tube, magnetic stirrer, thermometer, and Liebig condenser. The mixture was heated to the reflux temperature (110–115°C) and stirred under continuous nitrogen flow to form halohydrins. Subsequently, a 50 wt.% aqueous NaOH solution (0.6 mol) was added dropwise while water continued to separate. After the addition was complete, the reaction mixture was maintained under vigorous stirring for 1 hour to induce a ring-closing reaction. The resulting solution was vacuum filtered, and the filtrate was collected and concentrated under reduced pressure using a rotary evaporator to remove residual epichlorohydrin. The resulting product had an epoxy equivalent weight of 225 g eq. -1 It was a yellow viscous liquid containing mainly oligomer-type epoxy resin, and the total yield was estimated to be about 97%.

[0054] Cationic polymerization of ISDGE and lactone

[0055] ISDGE and lactones (GBL, DVL, ECL) were polymerized using the cationic initiator Yb(OTF)3 (Fig. 1b).

[0056] A mixture containing ISDGE, lactone (GBL, DVL, ECL), and Yb(OTF)3 (1 wt.% relative to the mixture of ISDGE and lactone) was mechanically stirred, poured into a Teflon mold, cured in an oven at 150°C for 1 hour, and then post-cured at 160°C for 5 hours. The cured sample was cooled to room temperature.

[0057]

[0058] <Experimental Example 1> Hydrolysis Test

[0059] A degradability test was performed on a cured sample measuring 10 mm X 5 mm X 3 mm. After weighing the sample, it was placed in a 3 wt.% NaOH solution (20 mL) containing 0.04 wt.% NaN3 at a predetermined temperature. After a certain period, the sample was recovered by vacuum filtration, rinsed with deionized water, neutralized with 1 wt.% aqueous HCl, and dried overnight in a vacuum oven at 50 °C. The dried sample was weighed and placed back into the NaOH solution. This process was repeated until the sample was completely degraded.

[0060]

[0061] <Experimental Example 2> Characterization Analysis

[0062] Analysis equipment and experimental conditions

[0063] Chemical structure of ISDGE and cured thermosetting resin using FT-IR spectroscopy (Nicolet IS50, Thermo Fisher Scientific, Inc., USA; resolution 4 cm in transmission mode) -1 It was analyzed using a 32-scan (500-MHz Avance III HD500 spectrometer, Bruker Co., USA; solvent = dehydrated chloroform containing tetramethylsilane (99.8 at% D)).

[0064] The molecular weight (and distribution) of ISDGE was determined using gel permeation chromatography (1260 Infinity II, Agilent Technologies, Inc., USA) with a refractive index detector and tetrahydrofuran as the mobile phase at 1.0 mL min -1 It was measured at the flow velocity.

[0065] Number average molecular weight (Mn), weight average molecular weight (Mw), and dispersion index were calculated using linear polystyrene standards.

[0066]

[0067] The curing behavior of ISDGE and cured thermosetting resin was observed using DSC (DSC 4000, PerkinElmer Co., USA).

[0068] Seal the sample (5–10 mg) in an aluminum pan and apply a nitrogen flow (19.8 mL min 1 ) from 0 to 200℃ 10 ℃ min -1 The sample was heated at a rate of . The thermal stability of the thermosetting resin was evaluated using TGA (TGA 4000, PerkinElmer Co., USA), in which case the sample was heated from room temperature to 600°C at a rate of 10°C min -1 It was heated under nitrogen at a rate of . Tensile strength and adhesive strength were measured using a universal testing machine (LLOYD LD10, AMETEK Inc., USA) with a 10-kN load cell at room temperature at a crosshead speed of 10 mm min -1 It was measured as.

[0069]

[0070] Structural analysis of isosorbide diglycidyl ether (ISDGE)

[0071] Figure 1a shows the chemical reaction for ISDGE synthesis.

[0072] The successful synthesis of the synthesized ISDGE was confirmed through spectroscopic analysis. In the 1H nuclear magnetic resonance (NMR) spectrum of the synthesized ISDGE (Fig. 2a), 2.5–3.2 ppm signals were assigned to hydrogens of the epoxy ring and hydroether unit, and 4.41–4.72 ppm signals were assigned to hydrogens of the isosorbide ring.

[0073] Corresponding 13 In the 1C NMR spectrum (Fig. 2b), carbon signals of the glycidyl group appeared at 44.01, 50.32, and 69.85 ppm, and carbon signals of the isosorbide ring were observed at 72.0-75.0, 80.18, 80.44, 85.92, and 84.58 ppm.

[0074] In the related Fourier transform infrared (FT-IR) spectrum (Fig. 2c), OH (3480 cm⁻¹) -1 ), epoxy (910 cm -1 ) group and aliphatic ether CO bond (1090 and 1020 cm⁻¹) -1 A peak of ) appeared.

[0075] Figure 2d shows the gel permeation chromatogram (GPC) profile of ISDGE with the contributions of monomers and oligomers. The monomer proportion was estimated to be about 25%, and the remainder was attributed to oligomer epoxides.

[0076]

[0077] Ring splitting reaction mechanism

[0078] Figure 1b shows the process of preparing a degradable cross-linked thermosetting resin through cationic ring-cleaving polymerization of ISDGE and cyclic lactones (γ-butyrolactone (GBL), δ-valerolactone (DVL), ε-caprolactone (ECL)).

[0079] Rare earth metal compounds such as lanthanides, scandium, and ytterbium have excellent reactivity and selectivity, and are oxygen-friendly and exhibit high Lewis acidity; therefore, Yb(OTf)3 was used as a cationic initiator in a ring cleavage reaction to form a network structure composed of homo or copolymer (poly(ester-ether)) chains (Fig. 1c).

[0080] The polymerization of ISDGE provides a tetrafunctional homopolymer suitable for producing thermosetting resins, and the rings of ISDGE and lactone are cleaved to form a difunctional copolymer.

[0081] In the case of GBL, ring cleavage was not observed during the copolymerization process due to thermodynamic reasons, and intermediates labeled as spiro-orthoesters were produced. Consequently, the epoxy group content showed a positive correlation with crosslinking density, and the lactone content showed a positive correlation with molecular weight.

[0082]

[0083] Analysis of hardening behavior

[0084] Figures 3a-c show the FT-IR spectra of [ISDGE + lactone] mixtures in equal proportions before and after curing at 115°C, indicating that curing significantly affected the peaks of the major functional groups.

[0085] C=O band of GBL during the curing process (1770 cm⁻¹) -1 The intensity decreased, which is due to the GBL moiety reacting with the epoxy group, and the peak of the linear aliphatic ester group (1735 cm⁻¹) -1 It was confirmed that the lactone rings cleaved as the strength increased. In addition, after curing, the epoxy ring band (910 cm -1 ) disappeared, indicating that ISDGE was completely polymerized.

[0086] A similar phenomenon was observed in DVL and ECL. DVL (1745 cm -1 ) and ECL(1720 cm -1 The intensity of the C=O band of ) decreased after reacting with the glycidyl group of ISDGE, and hardened ISDGE / DVL (1731 cm -1 ) and ISDGE / ECL(1704 cm -1 The intensity of the peak of the linear ester group increased in ). As with the case of GBL, the glycidyl band (910 cm⁻¹) -1 The disappearance of ) indicated that complete hardening was achieved in both cases.

[0087]

[0088] Thermal properties

[0089] Figure 3d shows the differential scanning calorimetry (DSC) profiles of lactone-cured ISDGE and DGEBA, indicating that the curing temperature was significantly lower for lactone-cured ISDGE. This was explained by the fact that cyclic aliphatic epoxides such as ISDGE are generally more reactive because they have higher ring modification and basicity than the DGEBA monomer.

[0090] Figure 3e shows the results of thermogravimetric analysis (TGA), and compared to the thermosetting resin produced from DGEBA cured with IPD, the thermosetting resin produced by curing ISDGE with GBL and DVL showed slightly lower thermal stability, whereas the thermosetting resin produced from ISDGE cured with ECL showed similar thermal properties. The increased thermal stability of ISDGE cured with ECL was explained by the higher molecular weight of ECL compared to GBL and DVL.

[0091] Figure 3f shows the differential thermogravimetric profiles of lactone-cured epoxy resins, where the mass loss rates of ISDGE cured with GBL, DVL, and ECL were maximized at 310, 305, and 342°C, respectively. In particular, the profile of ISDGE cured with ECL showed a single peak, whereas the profiles of the samples cured with GBL and DVL exhibited shoulder peaks at approximately 218°C and 345°C, respectively. This phenomenon is attributed to the complex curing reaction between the epoxy compound and polylactone, which have different chemical structures and thermal properties. The analysis of thermal properties suggested that ISDGE cured with ECL has the potential to replace BPA-based thermosetting resins.

[0092] mechanical properties

[0093] Figure 3g shows the stress-strain curves of the cured thermosetting resin, indicating that all cured dumbbell-shaped specimens fractured immediately after reaching the maximum tensile stress.

[0094] The stress-strain curves showed significant nonlinearity before each sample reached maximum stress, but no clear yield point was observed. DGEBA hardened with IPD exhibited a high stress of 15.84 MPa and a strain of less than 0.3%.

[0095] In contrast, ISDGE cross-linked with gamma-butyrolactone (GBL) and delta-valerolactone (DVL) exhibited tensile strengths of 3.42 MPa and 3.16 MPa, respectively, and fracture strains of approximately 25% and 50%. ISDGE hardened with ECL showed the highest tensile strength (5.00 MPa) and approximately 90% strain among the lactone-hardened samples.

[0096]

[0097] Having excellent mechanical strength and elasticity simultaneously is a desirable characteristic for thermosetting resins used in flexible electronic products, but epoxy-based thermosetting resins and elastomers are difficult to achieve due to a lack of flexibility and strength, respectively. On the other hand, the bio-based thermosetting resin according to the present invention has demonstrated both high strength and excellent flexibility, and has the potential for various industrial applications.

[0098] Introducing hydrolyzable functional groups into thermosetting resins allows degradation to proceed under weak alkaline conditions. The ester groups of lactones can impart degradation potential to bio-based thermosetting resins and exhibit a much higher degradation rate compared to DGEBA-based thermosetting resins (Figs. 4a and b).

[0099] In particular, the ISDGE thermosetting resin cured with GBL showed the highest degradation rate and completely degraded within two days (Fig. 4c), while the ISDGE thermosetting resin cured with DVL and ECL completely degraded within three days. This phenomenon reflects the influence of the alkyl group length in the polyester backbone of the cured thermosetting resin.

[0100] In cross-linked epoxy network structures, as the alkyl spacer lengthens, the number of ester bonds per unit decreases, resulting in a slower decomposition rate. During the hydrolysis process, each ester bond forms a carboxyl and a hydroxyl group, and the carboxylic acid group promotes the cleavage of the ester bond, thereby inducing an autocatalytic reaction.

[0101] Despite being cured with lactone, the DGEBA-based thermosetting resin showed almost no degradation under basic conditions and maintained more than 83% of its initial weight even after three days, indicating a slower degradation rate than that of the isosorbide-based thermosetting resin. This indicates that the degradation rate of the ISDGE-based epoxy is higher than that of the BPA-based epoxy because it has higher hydrophilicity and a lower glass transition temperature.

[0102] Physical erosion of thermosetting resins associated with polyester hydrolysis can be described as total erosion or surface erosion in acidic / alkaline solutions. Total erosion involves overall mass loss, whereas surface erosion is confined only to the specimen surface through which the erosion front passes. Due to their superior hydrophilicity, ISDGE thermosetting resins came into closer contact with basic solutions and surfaces than DGEBA thermosetting resins, resulting in faster surface hydrolysis.

[0103] The degradation rate of degradable thermosetting resins was explained by referring to the hydrolysis mechanism of linear polyester. In general, solid-state kinetics models the dimensionless conversion rate a as a function of time and temperature under isothermal or temperature-controlled conditions (Equation (1)):

[0104] da / dt=kf(a),

[0105] Here, k is the degradation rate constant, and f(a) is the kinetic model. Based on optical images acquired during the degradation process, it was assumed that the bio-based thermosetting resin containing ester groups would follow a surface erosion mechanism in a basic solution (Fig. 4c).

[0106] This assumption added a shrinking volume model, while other models described the existing solid-state melting kinetics. Therefore, the shrinking volume model defines the dissolution of various crystal forms controlled by the shrinkage of the specimen volume as the solid-liquid interface moves into the specimen. Previous studies successfully applied this kinetic model to the dissolution reaction of BPA-based thermosetting resins under non-isothermal conditions and extended it to the decomposition of polymers containing ester groups in their backbones. The shrinking volume model is expressed as follows (Equation (2)):

[0107] f(a)=3(1a) 2 / 3

[0108] The shrinking volume model explained the degradation profile of the ISDGE thermosetting resin cured with GBL well (R2>0.99) (Fig. S1).

[0109] Other solid-state dissolution reaction kinetic models, such as n-th order reaction and 3D diffusion-based models (Table S1), did not fit the data as well as the shrinking volume model (Fig. S1). Fig. 4d shows the degradation rate constants of ISDGE-based thermosetting resins calculated using the shrinking volume model, indicating that this is consistent with the weight loss trend due to ester bond hydrolysis in ISDGE thermosetting resins. The rate constants of lactone-cured ISDGE thermosetting resins are GBL (15.5 mm -1 h -1 ) > DVL (9.8 mm -1 h -1 ) > ECL (8.7 mm -1 h -1 It decreased in the order of ). Therefore, it was concluded that lactone-cured ISDGE thermosetting resins can decompose rapidly under certain conditions.

[0110] To further characterize the degradation of the bio-based thermosetting resin, the hydrolysate was analyzed by high-performance liquid chromatography (HPLC). Figure 4e shows the UV-absorption chromatogram of the product generated by the degradation of GBL-cured ISDGE. The degradation product for HPLC measurement was prepared by completely degrading the ISDGE thermosetting resin and completely removing all solvents used for erosion. The separated degradation product was prepared by 20 μg mL of acetonitrile. -1 It was dissolved at a concentration of . Although the chemical structure of the decomposition product could not be determined precisely, it was confirmed that the hardened product was completely fragmented.

[0111] Comparison with HPLC trace results of ISDGE and GBL provided additional insights. Since NaOH is used in the degradation process, the presence of H+ or Na+ ions and the possibility of exchange between H and Na within the molecule must also be considered. Consequently, we hypothesized that monomeric and oligomer products of GBL and ISDGE-based oligomer ring opening were generated after the degradation of the ISDGE thermosetting resin (Fig. S2). Further research is needed to elucidate the chemical structures of these degradation products and to optimize the upcycling of thermosetting waste.

[0112] In FRP composites generally manufactured using conventional epoxy resins, micro / nano-sized fibers (e.g., glass and carbon) are impregnated into the polymer matrix, achieving superior performance by synergistically combining the beneficial properties of the polymer and fibers. Considering their low density, excellent mechanical properties, and high stiffness, these composites have numerous applications, such as those used in the aerospace, aircraft, and automotive industries, as well as in telecommunications devices.

[0113] Here, the inventors realized eco-friendly electronic products by focusing on the applicability of biodegradable bio-based thermosetting resins for the production of PCBs having glass fiber reinforced structures. As the use of 5G / 6G communication systems increases, low dielectric constant materials to reduce transmission loss have become essential for high-end electronic products. Therefore, the dielectric properties of ISDGE thermosetting resins at 10 GHz were evaluated.

[0114] Figure 5a shows the measured dielectric loss coefficient (dielectric constant, Dk) of lactone-cured ISDGE and DGEBA thermosetting resins. The DGEBA thermosetting resin cured using IPD exhibited a dielectric constant of 4.66 at 10 GHz, whereas lower values ​​of 3.31, 3.18, and 3 were obtained when curing was performed with GBL, DVL, and ECL, respectively.

[0115] In contrast, ISDGE thermosetting resins cured with GBL, DVL, and ECL had dielectric constants of 2.64, 2.57, and 2.54, respectively, which were significantly lower than those of the corresponding DGEBA thermosetting resins. The dielectric constant tended to decrease as the number of carbon atoms in the lactone increased, as the fraction of the non-polar region in the thermosetting resin increased simultaneously. In particular, due to their low dielectric constant of 2.6 or less, ISDGE thermosetting resins are suitable for high-speed communication components and other applications requiring low dielectric constant materials.

[0116] The physical properties of glass fiber reinforced prepreg impregnated with ISDGE thermosetting resin were determined using tensile tests to compare the effects of various types of epoxy and curing agents.

[0117] According to the resulting stress-strain curves (Fig. 5b), the DGEBA-prepreg hardened with IPD showed a high stress of 59.10 MPa and a strain of <0.02%, whereas the ISDGE-prepreg cross-linked with GBL, DVL, and ECL showed slightly improved strains of approximately 0.023, 0.026, and 0.048%, respectively.

[0118] In particular, the ISDGE prepreg cured with ECL exhibited tensile strength equivalent to that of DGEBA. Figure 5c shows the flexibility and degradability of the GBL-cured ISDGE prepreg with dimensions of 20 mm x 20 mm. Unlike DGEBA-based prepregs, this three-layer ISDGE prepreg composite can be easily bent. After immersion in a 3 wt% NaOH solution at 80°C for 48 hours, the ISDGE thermosetting prepreg completely degraded, and the three-layer clean glass fiber cloth was recovered by washing with deionized water and drying in an oven. Structural damage and degradation of physical properties of glass fibers are generally known as conflicting problems that complicate the reuse of glass fibers. Therefore, thermosetting resins that can degrade under mild conditions play an important role in ensuring the recyclability of high-quality clean glass fibers.

[0119] As a major PCB component, copper clad laminate (CCL), which has high thermal conductivity, low dielectric loss, and high peel strength, is in high demand in the upcoming 5G era.

[0120] Figure 5d illustrates the preparation of CCL containing a degradable isosorbide-based thermosetting resin. ISDGE, a lactone monomer, and an initiator were mixed and mechanically stirred for 2 hours to form a composite resin solution. Subsequently, a flat glass fiber cloth was uniformly impregnated with the prepared resin solution for 3 hours and then dried under vacuum for 2 hours. Three sheets of the resulting dried prepreg were neatly stacked between two copper foils and then heat-pressed at 3 MPa and 110°C to obtain CCL. The adhesion strength between the prepreg and the copper foil obtained through a 90° peel test (Figure S3) was 8.73, 12.89, and 14.60 N for DGEBA-based CCL cured with GBL, DVL, and ECL, respectively (Figure 5e). In contrast, ISDGE-based CCL cured with GBL and DVL exhibited peel strengths of 10.71 and 15.68 N, respectively. In particular, the peel strength of the ISDGE-based prepreg cured with ECL (23.80 N) significantly exceeded that of the corresponding DGEBA-based prepreg, indicating superior adhesion to copper foil.

[0121] Hydroxyl groups derived from isosorbide increase cohesion through hydrogen bonding with other ester and ether moietyes, thereby improving the adhesion of the cured epoxy. In particular, the oligomeric ISDGE was expected to feature much higher adhesion strength because it contained more hydroxyl groups than the monomeric ISDGE and DGEBA. It was used to prepare microstrip antenna patterns to demonstrate the practical applicability of CCL in 5G communication (Fig. 5f).

[0122] In the high-frequency band, the shape or length of the stripline significantly affects circuit performance. Microstrips were fabricated with stripline lengths of 0.5, 1, 2, and 5 cm using CCL to measure transmission loss. We are currently conducting further research to optimize pattern formation and are confident that isosorbide-based thermosetting resins can replace existing BPA-based epoxy resins.

[0123] The eco-friendly degradable thermosetting resins derived from isosorbide according to the present invention were prepared through cationic copolymerization of lactone and ISDGE, exhibited excellent flexibility and high degradation efficiency, and were completely degraded within 3 days in a weakly basic solution at 80°C.

[0124] Due to their high ester content and hydrophilicity, isosorbide-based thermosetting resins hydrolyzed faster than conventional DGEBA-based epoxy resins, and this hydrolysis was well reproduced by solid-state kinetics models. ISDGE-based thermosetting resins possessed high mechanical strength and low dielectric constants, and demonstrated strong adhesion to copper foil, showing great potential as viable alternatives to biomass-based degradable materials and BPA-based epoxy resins for future electronics.

[0125] Since hydrolysis is an essential aspect of polymer degradation, our results can be extended to the production of fully degradable thermosetting resins, which can help mitigate the problems of waste plastic accumulation or microplastic formation.

[0126]

[0127] From the foregoing description, those skilled in the art to which the present invention pertains will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. In this regard, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention should be interpreted as including all modifications or variations derived from the meaning and scope of the claims set forth below and their equivalents, rather than from the detailed description above.

Claims

1. A step of converting isosorbide into isosorbide diglycidyl ether (ISDGE) through an epoxidation process with epichlorohydrin in the presence of a base; and A degradable, low-dielectric, eco-friendly epoxy-based thermosetting resin prepared by including the step of polymerizing the above-mentioned isosorbide diglycidyl ether (ISDGE) and a lactone-based curing agent using a cationic initiator.

2. A low dielectric eco-friendly epoxy-based thermosetting resin according to claim 1, wherein the lactone-based curing agent is one or more selected from gamma-butyrolactone (GBL), delta-valerolactone (DVL), or ε-caprolactone (ECL).

3. A low dielectric, eco-friendly epoxy-based thermosetting resin according to claim 1, wherein the cation initiator is ytterbium(III) trifluoromethanesulfonate (Yb(OTf)3).

4. A low-dielectric, eco-friendly epoxy-based thermosetting resin according to claim 1, having a dielectric constant of 2.6 or less and a dielectric loss of 0.01 or less in the 10 GHz high-frequency band.

5. A low dielectric eco-friendly epoxy-based thermosetting resin according to claim 1, wherein the manufactured thermosetting resin is capable of decomposing by 90% or more by weight within 3 days under weakly basic conditions.

6. A low dielectric eco-friendly epoxy-based thermosetting resin according to claim 1, having a tensile strength of 3 MPa or more and a fracture strain of 25% or more after curing.

7. A low dielectric eco-friendly epoxy-based thermosetting resin that is impregnated into a glass fiber reinforcement and applicable in the form of prepreg, according to claim 1.

8. In claim 7, the prepreg is a low dielectric eco-friendly epoxy-based thermosetting resin that is laminated with a copper foil to form a copper clad laminate (CCL) having a peel strength of 10 N or more.

9. A low dielectric eco-friendly epoxy-based thermosetting resin according to claim 1, comprising carboxyl groups and hydroxyl groups as products upon decomposition and decomposing by a surface erosion mechanism.

10. A low dielectric eco-friendly epoxy-based thermosetting resin used in a circuit board for electronic devices for 5G or 6G communication, in any one of claims 1 to 9.

11. A step of preparing isosorbide diglycidyl ether (ISDGE) by reacting isosorbide derived from renewable resources with epichlorohydrin in the presence of a base; and A step comprising reacting the above ISDGE and a lactone-based curing agent in the presence of a cationic initiator to form a cross-linked structure containing ester bonds to produce a degradable thermosetting resin. Method for manufacturing a low dielectric eco-friendly epoxy-based thermosetting resin.

12. A method for manufacturing a low dielectric eco-friendly epoxy-based thermosetting resin according to claim 11, wherein the lactone-based curing agent is one or more of gamma-butyrolactone (GBL), delta-valerolactone (DVL), or ε-caprolactone (ECL), and the cation initiator is Yb(OTf)3.

13. A method for manufacturing a low dielectric eco-friendly epoxy-based thermosetting resin according to claim 11, wherein the manufactured thermosetting resin has a dielectric constant of 2.6 or less and a dielectric loss of 0.01 or less in the 10 GHz high-frequency band.

14. A method for manufacturing a low dielectric eco-friendly epoxy-based thermosetting resin according to claim 11, wherein the manufactured thermosetting resin is capable of decomposing by 90% or more by weight within 3 days under weakly basic conditions.

15. A low dielectric eco-friendly epoxy-based thermosetting resin comprising any one of claims 1 to 10, Insulating material for circuit boards of electronic devices for 5G or 6G communication.

16. A low dielectric eco-friendly epoxy-based thermosetting resin comprising any one of claims 1 to 10, Resin composition for manufacturing prepreg or copper clad laminate (CCL) for printed circuit boards (PCB).

17. A low dielectric eco-friendly epoxy-based thermosetting resin comprising any one of claims 1 to 10, Eco-friendly adhesives or encapsulating materials for electronic components or packaging that require recycling or biodegradation.

18. A low dielectric eco-friendly epoxy-based thermosetting resin comprising any one of claims 1 to 10, A substrate structure for a high-frequency antenna, a high-speed signal transmission line, or a radar system.

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