Polyphenylene sulfide / polyhedral oligomeric silsesquioxane nano-composite foam material as well as preparation method and application thereof

Abstract

The invention discloses a polyphenylene sulfide / polyhedral oligomeric silsesquioxane nano composite foam material as well as a preparation method and application thereof. The foam material comprises polyphenylene sulfide and polyhedral oligomeric silsesquioxane, wherein the polyhedral oligomeric silsesquioxane is connected with the polyphenylene sulfide through a-C-O-C bond, the polyhedral oligomeric silsesquioxane is connected with the polyphenylene sulfide through a-C-O-C bond, and the mass of the polyhedral oligomeric silsesquioxane is 0-4.5% of the mass of the polyphenylene sulfide and is not 0. Octaphenyl polyhedral oligomeric silsesquioxane (O-POSS) is adopted to prepare a POSS-coated PPS nano composite material, an entanglement structure is formed in a matrix through thermal oxidation treatment to improve the foaming behavior of PPS, and then a large amount of low-THz-loss air is introduced into the nano composite material by applying an scCO2 foaming technology, so that the material has low dielectric property and ultrahigh THz transmittance, and the material can be applied to the field of microwave dielectric materials, such as microwave dielectric materials, microwave dielectric materials, microwave dielectric materials, microwave dielectric materials, microwave dielectric materials, microwave dielectric materials, microwave dielectric materials, microwave dielectric materials and microwave dielectric materials. And the terahertz antenna has huge application potential in the fields of terahertz antennas and future 6G communication.

Description

Technical Field

[0001] The invention relates to a polyphenylene sulfide / polyhedral oligomeric silsesquioxane nano composite foam material and a preparation method and application thereof, belonging to the technical field of foaming materials. Background Art

[0002] With the vigorous development of wireless communication technology, it is foreseeable that the millimeter wave (mmW) used in the fifth generation of communication (5G) will be difficult to meet the explosive growth of data capacity and the rapid increase in signal transmission rate. Therefore, in order to meet the needs of the sixth generation of communication (6G), it is urgent to develop spectrum resources in higher frequency bands. The terahertz (THz) band, that is, the electromagnetic wave band with a frequency between 0.1THz and 10THz, has been considered to be an ideal electromagnetic band for 6G communication because of its unique properties such as high transmission information volume, high penetration, and high security. However, the extremely high frequency of THz causes a significant increase in signal transmission loss when electromagnetic waves pass through dielectric materials. In addition, for THz antennas, due to the extremely high signal frequency, the surge in signal transmission loss leads to a significant shortening of the available signal transmission distance. Therefore, the development of ultra-low THz loss materials is the key point for the application of THz in 6G.

[0003] In the wireless communication industry, the dielectric constant (D k ) and dielectric loss (D f ) is an important factor affecting the signal transmission process. k As D f The lower the D of the dielectric material, the better the wireless communication quality will be. k and D f It is an effective method to improve the quality of terahertz (THz) communication. So far, improving the low dielectric properties of materials by adding polyhedral oligomeric silsesquioxane (POSS) has attracted increasing attention. POSS is an organic-inorganic hybrid material with a unique molecular cage structure (1 to 3 nanometers). Its empirical formula is RSiO 3 / 2 For POSS with specific "R" groups that can react with the polymer matrix, the interfacial interaction is enhanced, which greatly improves the compatibility of POSS with the polymer matrix. For example, Peng et al. used POSS as a crosslinker to modify fluorinated polyimide (PI) to make D k and D f to 2.4 and 0.0017 (at 1 kHz), respectively. Zhang et al. synthesized a tetra(epoxy)-terminated open cage POSS and copolymerized it with hexafluorobisphenol A to prepare a low dielectric nanocomposite material, making D k and D fJoseph et al. prepared a polystyrene (PS) composite material containing hybrid silica spheres composed of POSS. The D k However, improving the dielectric properties of nanocomposites by simply adding POSS is still very limited and it is difficult to meet the requirements of THz communication for low transmission loss.

[0004] The dielectric constant of air (D k ) and dielectric loss (D f )Minimum(D k =1,D f ≈0), therefore, introducing air into the polymer matrix can significantly reduce D k and D f . Supercritical carbon dioxide (scCO2) foaming technology can introduce a large amount of air into the matrix without using residual foaming agent, and the resulting porous material has a fine and uniform honeycomb structure, so it has great advantages in the field of low dielectric modification. For example, Zhang used fluorinated ethylene propylene (FEP) as the matrix and achieved a D of 0.00015 through scCO2 foaming. f (at 10 GHz). Ma used scCO2 foaming to convert the D f The value is reduced to about 0.0015 (at 10 GHz). Shi used poly(arylether nitrile) (PEN) as the matrix and foamed D k and D f They are reduced to 1.26 and 0.0025 (at 1 kHz) respectively. However, the above materials have disadvantages such as poor heat resistance and high water absorption. Polyphenylene sulfide (PPS) has excellent comprehensive properties, such as low D k and low D f , high heat resistance, excellent solvent resistance, self-flame retardancy and low water absorption, etc., making it a potential material for the next generation of communications (6G). However, in order to meet the requirements of 6G communications, the low dielectric properties of PPS must be improved. Therefore, combining PPS with scCO2 foaming technology has great potential in developing new materials that meet the requirements of 6G communications. However, due to the high crystallinity and low melt strength of PPS, it is extremely difficult to prepare PPS porous materials with high expansion ratio and regular honeycomb structure by scCO2 foaming. Therefore, in order to overcome the difficulties in preparing PPS foam materials, PPS must be modified to adjust its crystallinity and enhance its melt strength, thereby improving its foaming behavior.

[0005] According to the equivalent medium theory, when the size of the porous structural unit is less than 1 / 10 of the wavelength of the incident electromagnetic wave, the porous material can be regarded as a uniform material. At 1 terahertz (THz), the wavelength of the electromagnetic wave is 300 microns, while the honeycomb size of the porous material prepared by scCO2 foaming can reach less than 30 microns. Therefore, when the THz signal passes through the porous dielectric material with a honeycomb size less than 30 microns, the THz loss mainly comes from the honeycomb wall. The addition of polyhedral oligomeric silsesquioxane (POSS) can introduce molecular cavities into the polymer matrix, and then through scCO2 foaming, these molecular cavities can be dispersed in the honeycomb wall, thereby reducing the THz loss generated by the honeycomb wall. In addition, due to the unique cage structure of POSS and the reactivity of its functional groups, a complex coupling effect is generated between POSS and the polymer matrix, which has a great influence on the final performance of the resulting nanocomposite. Therefore, in-depth research on this coupling effect becomes the key to developing high-performance porous nanocomposites suitable for THz communication through scCO2 foaming. Summary of the invention

[0006] The purpose of the present invention is to provide a polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material and a preparation method and application thereof. Octaphenyl polyhedral oligomeric silsesquioxane (O-POSS) is used to prepare a POSS@PPS nanocomposite material, and a tangled structure is formed in a matrix through thermal oxidation treatment to improve the foaming behavior of PPS. Then, a large amount of low THz loss air is introduced into the nanocomposite material using scCO2 foaming technology, so that the nanocomposite material has low dielectric properties and ultra-high THz transmittance.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material comprises polyphenylene sulfide and polyhedral oligomeric silsesquioxane; wherein the polyhedral oligomeric silsesquioxane and the polyphenylene sulfide and the polyhedral oligomeric silsesquioxanes are connected via -COC- bonds, and the mass of the polyhedral oligomeric silsesquioxane is 0-4.5% of the mass of the polyphenylene sulfide and is not 0.

[0009] Preferably, the polyphenylene sulfide is a mixture of polyphenylene sulfides containing different contents of isophenylene structure in the main chain, wherein the content of isophenylene structure is 5-25%.

[0010] The method for preparing any of the above polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam materials is to blend polyphenylene sulfide and polyhedral oligomeric silsesquioxane, perform thermal oxidation treatment after sample preparation, and then perform supercritical foaming to obtain the composite foam material.

[0011] Preferably, the polyphenylene sulfide is obtained by mixing a polyphenylene sulfide containing 8-12% of isophenyl structure in the main chain with a polyphenylene sulfide containing 15-25% of isophenyl structure in the main chain in a mass ratio of 1:(0.8-1.2).

[0012] Preferably, the amount of polyhedral oligomeric silsesquioxane added is 0-4.5% of the mass of polyphenylene sulfide and is not 0, preferably 0.5-3%.

[0013] Preferably, the blending conditions are: 250-350° C., 3-10 min, 30-120 rpm.

[0014] Preferably, the sample preparation conditions are: 250-350°C, 5-20MPa.

[0015] Preferably, the conditions for the thermal oxidation treatment are: 200-300° C., 5-20 h in air atmosphere.

[0016] Preferably, the supercritical foaming conditions are: foaming agent CO2, 200-300°C, 8-20MPa, and pressure maintenance for 30-90min.

[0017] Application of any of the above polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam materials in terahertz antennas.

[0018] The beneficial effects of the present invention are:

[0019] The present application adopts octaphenyl polyhedral oligomeric silsesquioxane (O-POSS) to prepare POSS@PPS nanocomposite materials, and forms an entangled structure in the matrix by thermal oxidation treatment to improve the foaming behavior of PPS. Then, a large amount of air with low THz loss is introduced into the nanocomposite material by scCO2 foaming technology to ensure that it has low dielectric properties and ultra-high THz transmittance. In the present application, loading O-POSS has a complex coupling effect on the crystallization and rheological behavior of PPS, which greatly affects the foaming behavior of PPS. First, the added POSS and the generated branching points can be regarded as heterogeneous crystal nucleus points, which are conducive to the crystallization of PPS, but the grafted POSS will produce a large steric hindrance effect, making it difficult for PPS to crystallize. Secondly, thermal oxidation produces a branched structure in PPS, while POSS inhibits the formation of an entangled structure in PPS. Since the branched structure contributes to the elastic behavior of PPS and is conducive to scCO2 foaming, loading POSS will deteriorate the foaming behavior of PPS. Therefore, the addition of POSS greatly affects the foaming behavior of PPS by changing the crystallization and viscoelastic behavior of PPS, indicating that proper regulation of POSS in the PPS matrix is ​​crucial for POSS@PPS porous nanocomposites. Accordingly, a new POSS@PPS porous material with ultrahigh terahertz transmittance was prepared by optimizing the coupling effect of POSS to the PPS matrix. For this porous material, its dielectric constant (D k ) and dielectric loss (D f ) is only 1.1 and 0.004 at 0.62 THz, and the THz transmittance is significantly increased from 70.4% to 97.5% (at 0.62 THz). Therefore, the available THz signal transmission distance is significantly increased from only 6.98 meters (PPS substrate) to 387.4 meters (new porous nanocomposite substrate). Therefore, this strategy of combining POSS and scCO2 foaming can effectively guide the development of low-dielectric materials for future 6G communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of thermal oxidation between PPS molecular chains and between PPS molecular chains and POSS (a), and the structure of POSS@PPS nanocomposite after thermal oxidation (b);

[0021] Figure 2 XPS broad spectrum (a) and O1s peak spectra of original PPS (b) and treated samples (c) to (f);

[0022] Figure 3DSC curves of original PPS, treated samples without POSS addition, and treated nanocomposites (1POSS, 3POSS, and 5POSS): (a) secondary heating curve; (b) cooling curve, and the changes of Tg (a) and Tm (b);

[0023] Figure 4 SSA curves (a) and percentage of melting peak at 250 °C (b) of original PPS, treated samples without POSS addition and treated nanocomposites;

[0024] Figure 5 Differential scanning calorimetry (DSC) curves: (a) isothermal crystallization curve at 138 °C, (b) corresponding relative crystallinity curve, and (c) calculated Avrami diagram;

[0025] Figure 6 Rheological curves of original PPS, treated samples without POSS addition and treated nanocomposites: (a) storage modulus; (b) loss modulus; (c) loss tangent tanδ; (d) complex viscosity;

[0026] Figure 7 (a) vanGurp-Palmen (vGP) graph; (b) Cole-Cole curve; (c) Han graph;

[0027] Figure 8 (a) to (d) the cell morphology at the optimal foaming temperature, and the summarized foam properties of (e) expansion ratio, (f) cell size and (g) cell density;

[0028] Fig. 9 (a) D k , (b) D f and (c) THz transmittance of treated-0POSS and treated nanocomposites;

[0029] Fig.10 Transmission electron microscopy (TEM) images of POSS@PPS nanocomposites: (a) and (a') 1POSS; (b) and (b') 3POSS; and (c) and (c') 5POSS (white circles indicate well-dispersed POSS, while red circles indicate aggregated POSS);

[0030] Fig.11 (a) to (c) dielectric constant, dielectric loss and terahertz transmittance of porous materials with different POSS contents at 0.62 THz, and (d) projection of terahertz transmittance on the porosity axis;

[0031] Fig.12Antenna performance: (a) efficiency, (b) gain, and (c) signal transmission distance. DETAILED DESCRIPTION

[0032] The wireless communication industry is developing towards a higher frequency electromagnetic band, so the terahertz (THz) band has become the target frequency band for the next generation of wireless communication. Such a high frequency of THz causes a sharp increase in the signal loss of wireless communication equipment (such as antennas), so a material with more stringent low dielectric properties is required. For this reason, the present application makes full use of supercritical carbon dioxide (scCO2) foaming technology and polyhedral oligomeric silsesquioxane (POSS) to modify the polyphenylene sulfide (PPS) matrix, and develops a novel porous nanocomposite material with excellent low dielectric properties and ultra-high terahertz transmittance. In this system, after scCO2 foaming, the molecular cavity generated by POSS can be dispersed in the pore wall, reducing the terahertz loss generated by the pore wall, and giving the porous material excellent dielectric properties. However, POSS, as a special component, has a complex coupling effect on the thermal oxidation process of PPS, which has a great influence on the foaming behavior of PPS. By optimizing the coupling behavior of POSS in the PPS matrix, the dielectric constant (1.13 at 0.62THz) and dielectric loss (0.004 at 0.62THz) of the prepared porous nanocomposite material were greatly reduced, and the corresponding terahertz transmittance was increased from 70.4% to 97.5% (at 0.62THz). Applying this low terahertz transmission loss material to terahertz antennas can significantly increase the available terahertz signal transmission distance from only 6.98 meters (PPS substrate) to 387.4 meters (new porous nanocomposite substrate).

[0033] Material

[0034] The polyphenylene sulfide (PPS) used in the experiment contains 10% and 20% isophenyl structure in the main chain. Octaphenyl polyhedral oligomeric silsesquioxane (O-POSS, molecular weight Mn = 1033.51 g / mol, CAS No.: 5256-79-1) was purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai). Carbon dioxide and nitrogen (CO2 & N2, purity > 99%) from Linde Gas (Chengdu) Co., Ltd. were used as foaming gas and protective gas, respectively.

[0035] Preparation of POSS@PPS nanocomposites

[0036] First, PPS and O-POSS were dried in a vacuum oven at 90 ° C for 4 hours. Then, PPS containing 10% isophthalic structure and PPS containing 20% ​​isophthalic structure were mixed in a mass ratio of 50 / 50wt%, and then mixed with 1%, 3% and 5% O-POSS (based on the mass of PPS) in an XSS-300 internal mixer (Shanghai Kechuang Rubber Plastic Machinery Equipment Co., Ltd., China) under the mixing conditions of 290 ° C, 6 minutes, and 60 rpm. The original PPS and the resulting mixture were pressed into 5cm×8cm×0.05cm strips with a flat vulcanizer under the conditions of 290 ° C and 10MPa. Finally, the strips were placed in an oven at 250 ° C and placed in air for 12 hours to obtain the treated samples. The treated samples were named treated-0POSS, treated-1POSS, treated-3POSS and treated-5POSS, respectively. The untreated PPS was named original PPS.

[0037] Preparation of porous materials by scCO2 foaming

[0038] Porous materials with different expansion ratios were prepared by scCO2 foaming. The temperature was set in the range of 238℃~265℃, CO2 was filled into the chamber to 15MPa using a high-pressure plunger pump, and then the pressure was maintained at the target temperature for 60 minutes. Subsequently, the nucleation and growth of bubbles were induced by rapid pressure release.

[0039] Chemical structure analysis of POSS@PPS nanocomposites

[0040] In the PPS molecular chain, the sulfide bond is stable, while the hydrogen in the benzene ring is active. Figure 1 As shown in the (a) area, during the thermal oxidation process, the hydrogen on the benzene ring in the PPS molecular chain is replaced by oxygen free radicals, and then an oxygen bridge (-COC-) is generated. After that, a grafting reaction between different PPS molecular chains occurs in the PPS matrix, forming Figure 1 The entangled structure shown in area (b) is shown in Figure 1. Figure 1 As shown in the middle (a) area, the side reaction produces -SO- and -SO2- in the PPS molecular chain and correspondingly enhances its rigidity. For O-POSS with eight phenyl functional groups, the hydrogen in O-POSS is also replaced by oxygen radicals during the thermal oxidation process and then connected to the PPS molecular chain by forming oxygen bridges. Therefore, Figure 1 As shown in the middle (b) area, O-POSS is grafted onto the PPS molecular chain (POSS-g-PPS) or connected to another O-POSS (POSS-POSS). Therefore, O-POSS consumes oxygen radicals and inhibits the reaction between PPS and oxygen, thereby also inhibiting the formation of entangled structures in the PPS matrix.

[0041] Figure 2 The middle (a) area shows the XPS broad spectrum including O1s (531.9 eV), C1s (284.4 eV) and S2p (162.2 eV). By analyzing the peak separation of the O1s peak, the effect of adding POSS on the reaction between PPS and oxygen is explored. Figure 2 The (b) to (f) region shows the peak spectrum of O1s, showing three peaks: -COC- (532.3 eV), -SO- (531.7 eV) and -SO2- (530.8 eV). The peak of O1s can explain the change in the proportion of oxygen-containing functional groups, and further indicate the effect of adding POSS on the reaction of PPS with oxygen during thermal oxidation. The elemental composition and the proportion of functional groups are summarized in Table 1. Since the original PPS was hot-pressed (i.e., treated at high temperature) before XPS characterization, Figure 2 As shown in (a) and (b) and Table 1, the original PPS surface also contains oxygen elements and oxygen-containing functional groups. Figure 2 It can be clearly seen in the middle (a) area and Table 1 that the intensity of the O1s peak and the proportion of oxygen-containing functional groups increased significantly, which proves that oxygen has reacted with PPS after thermal oxidation. Figure 2The middle (a) area shows that the O1s peak intensity of the treated nanocomposites is lower than that of the treated samples without POSS addition. Table 1 summarizes the proportion of oxygen bridges (-COC-) and the total proportion of sulfoxide / sulfone groups (-SO- and -SO2-, treated-1POSS: 12.90%, treated-5POSS: 12.01%). The results show that these proportions decrease with the increase of POSS content. This result indicates that the addition of POSS inhibits the reaction between PPS and oxygen, thereby limiting the formation of entangled structures in PPS. The inhibitory effect of POSS can be explained from two aspects. On the one hand, the thermal oxidation process is a long annealing process, so thermal oxidation and crystallization occur simultaneously. For POSS@PPS nanocomposites, the added POSS and the branch points generated by thermal oxidation can serve as heterogeneous nucleation points, which is conducive to the formation of more complete crystalline regions of PPS during the long thermal oxidation process. However, the crystalline region significantly hinders the diffusion of oxygen into the PPS matrix, so the reaction between the PPS molecular chain and oxygen free radicals is inhibited. On the other hand, the interaction between the Si-O bond in POSS and the oxygen molecule makes the benzene ring in POSS more likely to react with oxygen free radicals. Therefore, the number of oxygen free radicals that react with the PPS molecular chain is reduced, and the addition of POSS inhibits the reaction of PPS with oxygen. In addition, the -SO2- group is generated by the oxidation of the -SO- group. As shown in Table 1, the proportion of -SO- in the nanocomposites treated with different treatments is similar, but the proportion of -SO2- is significantly reduced after the addition of POSS. This can also indicate that the addition of POSS can inhibit the reaction of PPS with oxygen.

[0042] Table 1 Element composition and functional group ratio

[0043]

[0044] Crystallization behavior of POSS@PPS nanocomposites

[0045] The addition of POSS and the thermal oxidation of PPS have a great influence on its crystallization behavior. Figure 3 The DSC curves of the original PPS, the treated sample without POSS addition, and the treated nanocomposite are shown, as well as T g and T m The crystallization parameters of the samples are summarized in Table 2. The oxygen bridges generated by thermal oxidation can introduce branched structures into the PPS matrix, and these branching points can be regarded as heterogeneous crystal nucleation points, thereby improving the crystallization ability of the treated samples without POSS addition. Figure 3As shown in the middle (b), the crystallization peak of the sample without POSS addition during cooling is larger than that of the original PPS. However, due to the entangled structure and sulfoxide / sulfone groups generated by thermal oxidation, the movement of the PPS molecular chain is restricted and the rigidity is increased, which makes the X c (Crystallinity) is lower than that of the original PPS, as shown in Table 2. For the treated nanocomposites, although the addition of POSS can enhance the formation of heterogeneous crystal nuclei, the grafted POSS will produce steric hindrance to the PPS molecular chain, so Figure 3 As shown in the middle (b) area, the crystallization behavior of the treated nanocomposites deteriorates and is lower than that of the treated samples without POSS addition. In addition, as shown in Table 2, with the increase of POSS content, the T c The crystallization temperature decreased from 162.5°C to 137.3°C, which indicates that the supercooling of the treated nanocomposites increased with the increase of POSS content. Therefore, the addition of POSS reduces the crystallization ability of the nanocomposites.

[0046] from Figure 3 It can be seen from regions (c) and (d) that after thermal oxidation treatment, the oxygen bridge restricts the movement of the molecular chain, and the sulfoxide / sulfone group increases the rigidity of the molecular chain, which makes the T of the sample without POSS added g (glass transition temperature) is significantly higher than that of pristine PPS. The oxygen bridges and sulfoxide / sulfone groups subsequently reduce the regularity of the molecular chain, thereby lowering the T m On the other hand, by adding POSS into the PPS matrix, T g Reduce T m This can be explained by the fact that the addition of POSS inhibits the reaction between PPS and oxygen. Table 1 shows that with the increase of POSS content, the ratio of -COC- and -SO2- in the matrix decreases, that is, the mobility of the molecular chain increases, the rigidity decreases, and the regularity increases. Therefore, after loading POSS, T g Reduce T m Increase.

[0047] Continuous self-nucleation and annealing (SSA) is an effective method to characterize the crystallization differences between different segments and is a key parameter for supercritical carbon dioxide (scCO2) foaming. The SSA curve and the peak area percentage of the melting peak at 250°C are shown in Figure 2. Figure 4 As shown. Figure 4As shown in the figure, compared with the original PPS, the main melting point of the treated sample without POSS added shifts to a lower temperature after thermal oxidation, and the percentage of the melting peak at 250°C also decreases. This is attributed to the entangled structure and sulfoxide / sulfone groups generated in the PPS matrix by thermal oxidation. The entangled structure in PPS restricts the movement of the PPS molecular chain, while the sulfoxide / sulfone groups increase the rigidity of the PPS molecular chain, thereby weakening the crystallization ability of the PPS matrix. Therefore, the main melting peak shifts to a lower temperature. After loading POSS, from Figure 4 It can be seen in the middle (b) area that with the increase of POSS content, the percentage of melting peak at 250 ° C increases, which indicates that at a higher POSS content, PPS has a better completed crystallization area. This can be explained by the promotion of POSS on the nucleation of PPS molecular chain and the inhibition of PPS molecular chain reaction with oxygen (less entangled structure and less sulfoxide / sulfone groups).

[0048] In order to further study the effect of adding POSS on the crystallization of PPS, isothermal crystallization experiments were carried out to further study the parameters of half-crystallization time and crystallization rate. The obtained isothermal crystallization curves and their corresponding calculation results are shown in Figure 2. Figure 5 As shown, the relevant parameters are summarized in Table 2. Since the added POSS can serve as a heterogeneous crystal nucleus point, the n value increases with the increase of POSS content. Figure 5 In the middle (a) region, the crystallization peak of the treated sample without POSS addition is located on the left side of the original PPS (isothermal crystallization time is shorter), as shown in Table 2, which indicates a faster crystallization rate (higher k value) and a shorter half-crystallization time (t 1 / 2 The reason is that the branch points formed by thermal oxidation in the treated samples without POSS can serve as heterogeneous crystal nucleation points, which is conducive to the crystallization of PPS. Therefore, the crystallization rate of PPS increases after thermal oxidation. However, after loading POSS, Figure 5 As shown in the middle (a) area, the crystallization peak moves to the right, as shown in Table 2, the k value decreases, and t 1 / 2 This can be explained by the reaction between POSS and PPS. The added POSS is grafted onto the PPS molecular chain after thermal oxidation and creates a large steric hindrance to the PPS molecular chain, making it difficult for the PPS molecular chain to arrange into a lattice. Therefore, as the POSS content increases, the k value decreases and t 1 / 2 The value increases.

[0049] Table 2 Crystallization parameters of original PPS, treated samples without POSS addition and treated nanocomposites

[0050]

[0051] *ΔHm: melting enthalpy of the secondary heating process; X c: PPS crystallinity; T m : melting point of the secondary heating process; Tc: crystallization temperature of the cooling process; Tcc: crystallization temperature of the secondary heating process; n: Avrami index; k: total isothermal crystallization rate constant; t 1 / 2 : Half crystallization time.

[0052] Topological structure analysis

[0053] The rheological curves of the original PPS, the treated PPS (0POSS) and the treated nanocomposites (including storage modulus G', loss modulus G", loss tangent tanδ and complex viscosity η) are shown in Figure 2. Figure 6 As shown. Figure 6 It can be seen in the (a) and (b) regions that after thermal oxidation treatment (compared with the original PPS after treatment), G' and G" increased significantly, which proves that a branched structure was obtained in the PPS matrix after thermal oxidation treatment. Figure 6 The tanδ and η shown in regions (c) and (d) show that the tanδ of the original PPS is lower than that of the treated sample, indicating that the matrix exhibits more elastic properties and indicating the presence of a branched structure in the treated sample, which gives the matrix a higher η. Figure 6 As shown in the middle (d) area, the typical shear thinning behavior of the treated sample also indicates the presence of branched structures in the PPS matrix. Figure 6 It can be observed in regions (a) and (b) that with the increase of POSS content, the G' and G" of the treated samples decrease, indicating that POSS inhibits the formation of branched structures in PPS. Figure 6 As shown in areas (c) and (d), the treated samples have an increase in tanδ, a decrease in η, and a decrease in the degree of shear thinning behavior, which also indicates that the addition of POSS to the PPS matrix inhibits the formation of branched structures.

[0054] like Figure 7 As shown in the (a) to (c) area, the van Gurp-Palmen (vGP) diagram, Cole-Cole curve and Han diagram are introduced to further describe the effects of thermal oxidation and POSS addition on rheological behavior. For the vGP diagram, when δ is 0° or 90°, it means that the matrix behaves as an ideal elastic matrix (0°) or an ideal viscous matrix (90°), respectively. Therefore, according to Figure 7 In the vGP graph shown in area (a), the δ of the original PPS is close to 90°, indicating that it has typical viscous properties and a linear structure. After thermal oxidation treatment, the δ of the treated sample without POSS addition is significantly reduced, indicating that it exhibits more elastic properties and a branched structure is formed in the PPS matrix. Figure 7It can be observed in region (a) that the addition of POSS increases the δ of the nanocomposite, making it exhibit more viscous properties, which reflects that the addition of POSS to the PPS matrix suppresses the formation of branched structures.

[0055] The Cole-Cole curve can be used to analyze the relaxation process of molecular chains. The Cole-Cole curves of the original PPS, the treated sample without POSS addition, and the treated nanocomposite are shown in Figure 2. Figure 7 As shown in the middle (b) area. It can be observed that the shape of the curve of the original PPS is close to a semicircle, indicating that its molecular chain is easy to relax. After thermal oxidation treatment, the shape of the curve of the treated sample without POSS addition bends upward, which indicates that the relaxation of the molecular chain becomes more difficult, indicating that a branched structure is formed in the PPS matrix. However, after adding POSS, the shape of the curve tends to be a semicircle, which reflects the enhancement of the relaxation ability of the molecular chain and proves that POSS inhibits the formation of a branched structure in the PPS matrix during thermal oxidation.

[0056] In addition, for the Han diagram, the structure of the molecular chain (such as linear or branched chain) can be reflected by the slope of the curve, where the slope of the linear polymer curve is 2, while the slope of the branched polymer is less than 2. Figure 7 In the Han graph shown in area (c), the slopes of the curves of the treated samples are all smaller than that of the original PPS, indicating that a branched structure is formed in PPS after thermal oxidation treatment. However, as the POSS content increases, the slope of the curve increases from 1.21 (treated samples without POSS addition) to 1.35 (treated samples with 5% POSS addition), indicating that the addition of POSS inhibits the formation of branched structures in PPS.

[0057] POSS@PPS foam nanocomposite

[0058] Foam morphology analysis

[0059] The cell morphology of the obtained foam is as follows Figure 8 The corresponding expansion ratio, cell size and cell density are shown in (a) and (d) respectively. Figure 8As shown in the (e) and (g) areas. It can be observed that the pore morphology of the treated sample without POSS addition (treated-0POSS), the treated sample with 1% POSS addition (treated-1POSS) and the treated sample with 3% POSS addition (treated-3POSS) is significantly better than that of the treated sample with 5% POSS addition (treated-5POSS). The reason is that the addition of POSS inhibits the reaction of PPS with oxygen during thermal oxidation and inhibits the formation of branched structures in the PPS matrix. Therefore, the melt strength of the treated sample with 5% POSS addition is too low to maintain a stable pore structure. Correspondingly, the low melt strength leads to a decrease in the expansion rate, as shown in Figure 2. Figure 8 As shown in the middle (e) area, as the POSS content increases, the maximum expansion ratio of the treated samples decreases (treated samples without POSS added: 11.2, treated samples with 1% POSS added: 7.49, treated samples with 3% POSS added: 3.47, treated samples with 5% POSS added: 1.78). As for the cell size and cell density, since POSS can serve as a heterogeneous bubble nucleation point during the supercritical CO2 foaming process, the cell density increases with the increase of POSS content (the increase in cell density leads to a decrease in cell size), as shown in Fig. Figure 8 As shown in areas (f) and (g).

[0060] Dielectric properties and terahertz transmittance

[0061] Dielectric properties are the key factors affecting the terahertz transmittance of dielectric materials. The dielectric constants (D k ), dielectric loss (D f ) and the terahertz transmittance as Fig. 9 As shown in the (a) to (c) region. Thermal oxidation introduces branch structures into the PPS matrix, restricting the vibration of the dipoles, so the dielectric constant of PPS decreases after thermal oxidation. However, adding POSS to the PPS matrix inhibits the formation of branch structures, resulting in an increase in the dielectric constant of the treated sample with increasing POSS content. As for dielectric loss, the interface generated by the agglomerated POSS is as follows Fig.10 As shown in Figure 2, the dielectric loss of the treated nanocomposites also increases with the increase of POSS content, as Fig. 9As shown in the middle (b) area. However, it is worth noting that the dielectric loss of the treated nanocomposite is lower than that of the treated sample without POSS added, because the addition of POSS introduces molecular cavities (air, dielectric loss is about 0) in the PPS matrix. Therefore, in order to obtain better low dielectric properties of nanocomposites, the content of POSS must be optimized. As for the terahertz transmittance, due to the lower terahertz dielectric loss of the treated nanocomposite, its terahertz transmittance is higher than that of the treated sample without POSS added, as shown in Fig. 9 As shown in area (c).

[0062] Compared with adding POSS, supercritical CO2 foaming can introduce a large amount of air with low terahertz loss into the matrix, and the porosity of the foam material is higher than that of adding POSS, which is more important for improving the low dielectric properties because the dielectric constant of air (D k ) and dielectric loss (D f ) is the lowest. The dielectric constant, dielectric loss and terahertz transmittance of porous materials at 0.62 terahertz are as follows Fig.10 As shown in the (a) and (c) areas. Fig.11 As shown in the (a) and (b) regions, as the porosity increases, the dielectric constant and dielectric loss of the porous material show a downward trend, and the porous material can achieve an ultra-low dielectric constant of 1.1 and an ultra-low dielectric loss of 0.004 at 0.62 THz. Fig.11 As shown in the middle (c) area, the terahertz transmittance of the obtained porous material increased from 70.4% to 97.5% (at 0.62 THz). In addition, it is worth noting that at similar porosity, the addition of POSS can achieve higher terahertz transmittance. When the porosities of treated-0POSS, treated-1POSS and treated-3POSS were 50%, 60% and 52.4%, respectively, the terahertz transmittances of the above samples were 85.9%, 88.6% and 90.3%, respectively. This is attributed to the reduction of terahertz loss in the cell wall. The added POSS can introduce nanoscale pores into the matrix, and then these nanoscale pores can be dispersed into the cell wall after supercritical CO2 foaming. Therefore, the terahertz loss generated when the terahertz wave passes through the cell wall is reduced, and porous materials with higher POSS content can achieve higher terahertz transmittance at lower porosity. However, the terahertz transmittance of treated-5POSS with a porosity of 44.4% is 81.1%, and the decrease in terahertz transmittance can be explained by the agglomerated POSS and poor pore morphology. The interfaces between the agglomerated POSS lead to increased terahertz losses, while the poor pore morphology makes the treated-5POSS foam unable to act as a uniform material when the terahertz wave passes through. Therefore, at low porosity (about 50%), the terahertz transmittance of treated-5POSS is lower than that of other samples.

[0063] Terahertz patch antenna applications

[0064] Antennas are key devices for wireless communications, and their signal transmission distance has a significant impact on their applications. In order to demonstrate the advantages of POSS@PPS porous materials as terahertz antenna substrates, a simple patch antenna model was used to simulate the transmission performance of terahertz signals. The antenna efficiency, antenna gain, and terahertz signal transmission distance obtained are shown in Figure 2. Fig.12 As shown. Fig.12 It can be seen in areas (a) and (b) that due to the improvement in dielectric properties, the antenna efficiency and antenna gain of the treated nanocomposite (solid sample without supercritical CO2 foaming) are higher than those of the treated-0POSS solid sample. Therefore, the terahertz signal transmission distance of the treated nanocomposite (solid sample) is also higher than that of the treated-0POSS solid sample. For the treated nanocomposite (solid sample), the treated-5POSS solid sample deteriorates due to the low dielectric properties, resulting in reduced antenna efficiency and antenna gain, so the terahertz signal transmission distance is also reduced. After supercritical CO2 foaming, a large amount of low-loss air is introduced into the matrix, thereby giving the matrix excellent low dielectric properties. Therefore, Fig.12 As shown in the figure, with the increase of porosity, the antenna efficiency and antenna gain also increase, and the terahertz signal transmission distance also increases accordingly. By optimizing the POSS content and foam morphology, the antenna efficiency is increased from 30% to 89.5%, the antenna gain is increased from 2.9dBi to 10.2dBi, and the corresponding terahertz signal transmission distance is also significantly increased, from 6.98 meters to 387.4 meters.

[0065] In summary, in this application, octaphenyl polyhedral oligomeric silsesquioxane (POSS) and thermal oxidation process were used to prepare POSS@PPS nanocomposites with branched structures, and then supercritical CO2 foaming technology was used to prepare POSS@PPS nanocomposites with ultra-low dielectric constant (D k ) and dielectric loss (D f)(@THz) and POSS@PPS porous materials with ultra-high THz transmittance. The octaphenyl property causes O-POSS to have a coupling effect on the crystallization and rheological behavior of the polyphenylene sulfide (PPS) matrix. First, the added POSS and branch points can serve as heterogeneous crystal nucleation points, which is beneficial to the crystallization of PPS. However, the POSS grafted onto the PPS molecular chain has a large steric hindrance effect, which reduces the crystallization rate of PPS. Secondly, after thermal oxidation, the rheological behavior of PPS shows elastic characteristics due to the branched structure. However, POSS inhibits the formation of branched structures in the PPS matrix, causing the rheological behavior of PPS to transform into viscous characteristics. Therefore, in order to improve the foaming behavior of PPS, its crystallization and rheological behavior are adjusted by optimizing the coupling effect of POSS. Finally, the obtained new porous material has excellent dielectric properties and transmittance in the THz band. The D k and D f The terahertz transmittance was significantly increased from 70.4% to 97.5% (@0.62 THz) when the obtained porous material was applied to terahertz antennas. When solid PPS was used as the substrate, the available terahertz signal transmission distance was only 6.98 meters. When the substrate was replaced with a new porous material (expansion ratio of 7.5, POSS content of 1wt%), the distance increased significantly to 387.4 meters. In summary, this new POSS@PPS porous material has great potential in the future 6G communication field.

[0066] The above is only a preferred implementation of the patent of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the patent of the present invention. These improvements and modifications should also be regarded as the scope of protection of the patent of the present invention.

Claims

1. A polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material, characterized in that: It comprises polyphenylene sulfide and polyhedral oligomeric silsesquioxane; wherein the polyhedral oligomeric silsesquioxane and the polyphenylene sulfide and the polyhedral oligomeric silsesquioxanes are connected via -COC- bonds, and the mass of the polyhedral oligomeric silsesquioxane is 0-4.5% of the mass of the polyphenylene sulfide and is not 0.

2. The polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 1, characterized in that: The polyphenylene sulfide is a mixture of polyphenylene sulfides containing different contents of isophenyl structure in the main chain, wherein the content of isophenyl structure is 5-25%.

3. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to any one of claims 1 to 2, characterized in that: The method comprises the steps of blending polyphenylene sulfide and polyhedral oligomeric silsesquioxane, subjecting the sample to thermal oxidation treatment, and then subjecting the sample to supercritical foaming to obtain a composite foam material.

4. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 3, characterized in that: The polyphenylene sulfide is obtained by mixing a polyphenylene sulfide containing 8-12% of isophenyl structure in the main chain with a polyphenylene sulfide containing 15-25% of isophenyl structure in the main chain in a mass ratio of 1:(0.8-1.2).

5. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 3, characterized in that: The added amount of the polyhedral oligomeric silsesquioxane is 0-5% of the mass of the polyphenylene sulfide and is not 0.

6. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 3, characterized in that: The blending conditions are: 250-350°C, 3-10min, 30-120rpm.

7. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 3, characterized in that: The sample preparation conditions are: 250-350℃, 5-20MPa.

8. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 3, characterized in that: The conditions of thermal oxidation treatment are: 200-300°C, 5-20h in air atmosphere.

9. The method for preparing the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to claim 3, characterized in that: The conditions for supercritical foaming are: foaming agent CO2, 200-300°C, 8-20MPa, and pressure maintenance for 30-90min.

10. Use of the polyphenylene sulfide / polyhedral oligomeric silsesquioxane nanocomposite foam material according to any one of claims 1 to 2 in a terahertz antenna.

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