Method for analyzing sulfur cross-linking form

Abstract

To easily and accurately analyze a sulfur cross-linking form included in a polymer composition by using pulsed NMR.SOLUTION: Provided is a method for analyzing a sulfur cross-linking form in a polymer composition having sulfur cross-linking, including the steps of: causing the polymer composition to swell; measuring the swollen polymer composition by using pulse method NMR; performing analysis on the transverse relaxation decay curve by using the inverse Laplace transformation or the Weibull function to obtain the distribution of spin-spin relaxation time (T2); attributing a plurality of peaks in the distribution to one or more of monosulfide, a disulfide bond, and a polysulfide bond, on the basis of molecular mobility; and quantifying one or more or the combination of the monosulfide bond, disulfide bond, and polysulfide bond in the polymer composition on the basis of the intensity ratio of the distribution peaks.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a method for analyzing sulfur bridge morphology. [Background technology]

[0002] The rubber elasticity of polymer compositions, such as sulfur-crosslinked rubber materials, is determined by their crosslink density, and rubber elasticity increases in proportion to the crosslink density. Strictly speaking, it is the effective network chain concentration that contributes to rubber elasticity. Crosslink density is the number of crosslink points per unit weight or unit volume, and effective network chain concentration is the number of molecular chains separated by crosslink points. Various methods have been used to analyze crosslink density. Representative methods include determining crosslink density from the equilibrium swelling using the Flory-Rehner equation and determining crosslink density from the elongation stress using elasticity theory equations. However, the values ​​obtained by these methods are amplified by reinforcing agents and therefore are larger than the true crosslink density.

[0003] Patent Document 1 discloses a method using NMR to determine crosslink density by performing NMR measurements on a rubber composition containing a filler and analyzing the resulting transverse magnetization decay curve to determine the residual dipole coupling constant. Non-Patent Document 1 also discloses a method for evaluating crosslink density from the reciprocal of the spin-spin relaxation time (T2) obtained by analyzing the transverse magnetization decay curve, and states that this method is hardly affected by reinforcing agents and therefore can evaluate the true crosslink density. Non-Patent Document 2 also discloses that the average value of 1 / T2 correlates well with crosslink density over a wide range, including for deteriorated samples.

[0004] As described above, various methods for analyzing crosslink density are known, but the physical properties of polymer compositions containing sulfur crosslinks are not determined solely by crosslink density. The sulfur crosslinking form, such as monosulfide bonds, disulfide bonds, and polysulfide bonds, changes the physical properties of polymer compositions depending on their form. For example, rubber containing many monosulfide bonds has excellent heat resistance and residual strain, while rubber containing many polysulfide bonds has excellent flex fatigue resistance and abrasion resistance. Patent Document 2, for example, discloses a method for predicting physical properties by analyzing crosslink structure. It uses solid-state NMR with magic angle spinning to determine the proportion of heat-resistant crosslinked structures α and heat-sensitive crosslinked structures β among all crosslinked structures of isoprene-based rubber, and predicts heat degradation resistance based on this proportion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6135971 [Patent Document 2] Patent No. 5580856 [Non-patent literature]

[0006] [Non-Patent Document 1] "Nuclear Magnetic Resonance (NMR) Spectroscopy in Soft Material Analysis (2) The Role of Pulsed NMR in Soft Material Analysis" J. Iwabuki, Journal of the Society of Rubber Science and Technology of Japan, Vol. 87, No. 5 (2014), 195-202 [Non-patent document 2] "Evaluation of the state of isoprene rubber and prediction of its fracture properties using pulsed NMR," Hitoshi Iwabuki, Takuya Ishida, Journal of the Society of Rubber Science and Technology of Japan, Vol. 91, No. 8 (2018), 301-308 Summary of the Invention [Problem to be solved by the invention]

[0007] In the development of polymer compositions such as rubber materials, it is necessary to control not only the crosslink density but also the sulfur crosslink morphology to achieve the required physical properties. For example, static physical properties such as hardness, elongation stress, and elongation can often be described as a function of crosslink density, but for practical properties such as dynamic properties, heat resistance, residual strain, flexural fatigue resistance, and abrasion resistance, the sulfur crosslink morphology as well as the crosslink density are important.

[0008] Conventionally, methods for quantifying sulfur cross-linking forms have generally been based on the use of reagents capable of selectively cleaving sulfur cross-links, such as the thiolamine method. However, analytical methods using such reagents are very expensive when commissioned to analytical laboratories. Furthermore, in consideration of the environmental impact, it is advisable to refrain from using such reagents.

[0009] The technology disclosed herein has been made in view of the above points, and its purpose is to easily and accurately analyze and quantify sulfur crosslinking forms, such as monosulfide bonds, disulfide bonds, and polysulfide bonds, contained in a polymer composition by using pulsed NMR, without using any special reagents that selectively cleave sulfur crosslinks. [Means for solving the problem]

[0010] The present disclosure relates to a method for analyzing the sulfur crosslinking morphology in a sulfur-crosslinked polymer composition. This analysis method includes the steps of swelling a polymer composition, measuring the swollen polymer composition using pulsed NMR, analyzing the transverse relaxation decay curve using an inverse Laplace transform or a Weibull function to obtain a distribution of spin-spin relaxation times (T2), attributing multiple distribution peaks in the distribution to one or more peaks of monosulfide bonds, disulfide bonds, and polysulfide bonds, or a combination thereof, based on molecular mobility, and quantifying the number of monosulfide bonds, disulfide bonds, and polysulfide bonds, or a combination thereof, in the polymer composition, based on the intensity ratio of the distribution peaks.

[0011] As a result of extensive research by the present inventors, the analytical method disclosed herein analyzes decay curves obtained using pulsed NMR. This eliminates the need for reagents capable of selectively cleaving sulfur crosslinks, as in the conventional thiolamine method, thereby reducing the environmental impact. Pulsed NMR measurement also has the advantage of not requiring the use of reagents capable of selectively cleaving sulfur crosslinks, as in the conventional thiolamine method. Furthermore, analysis using an inverse Laplace transform or a Weibull function enables accurate quantification of monosulfide bonds, disulfide bonds, and polysulfide bonds. Furthermore, in a dry polymer composition, physical crosslinks and entanglements affect the T2 value, diluting the contribution of chemical crosslinks to the T2 value. However, swelling the polymer composition prevents the contribution of such physical crosslinks, significantly improving the accuracy of evaluating the form of sulfur crosslinks, which are chemical crosslinks.

[0012] The distribution is preferably obtained by performing an inverse Laplace transform on the transverse relaxation decay curve.

[0013] The inverse Laplace transform of the transverse relaxation curve yields a natural T2 distribution with broadened peaks, whereas analysis using the Weibull function does not yield broadened peaks. The inverse Laplace transform provides a better fit with more T2 components than analysis using the Weibull function. Therefore, when obtaining the distribution of spin-spin relaxation times (T2), analysis accuracy can be improved by using the inverse Laplace transform rather than the Weibull function.

[0014] The measurement using the pulsed NMR may be performed using a spin echo method.

[0015] Among the distribution peaks, one peak (the peak with the shortest T2 or the peak with the lowest molecular mobility) may be assigned as a peak representing the sum of monosulfide bonds and disulfide bonds, and the monosulfide bonds and disulfide bonds in the polymer composition may be quantified in total based on the intensity ratio of the distribution peaks.

[0016] Based on the quantified results, the dynamic properties of the polymer composition may be predicted. [Effects of the Invention]

[0017] As described above, according to the present disclosure, sulfur cross-linking forms such as monosulfide bonds, disulfide bonds, and polysulfide bonds contained in a polymer composition can be easily and accurately analyzed and quantified by pulsed NMR without using any special reagents. [Brief explanation of the drawings]

[0018] [Figure 1] 10 is a graph showing the relationship between analytical values ​​and νt. [Figure 2] 1 is an example of a graph showing the distribution of T2 obtained by separating into two components using a Weibull function in a swollen state. [Figure 3] 10 is a graph showing the relationship between intensity F1 and ν1+ν2 in the distribution of T2 obtained by separating it into two components using a Weibull function in a swollen state. [Figure 4] 1 is an example of a graph showing the distribution of T2 obtained by separating it into three components using a Weibull function in a swollen state. [Figure 5] 10 is a graph showing the relationship between intensity F1 and ν1+ν2 in the distribution of T2 obtained by separating it into three components using a Weibull function in a swollen state. [Figure 6] 1 is a graph showing the relationship between F1 and v1+v2 obtained by the Weibull function in a dry state. [Figure 7] 1 is a graph showing the distribution of T2 obtained by inverse Laplace transform in the swollen state. [Figure 8] 10 is a graph showing the relationship between intensity F1 and ν1+ν2 in the distribution of T2 obtained by inverse Laplace transform in a swollen state. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure provides a method for analyzing sulfur crosslinking forms, such as monosulfide bonds, disulfide bonds, and polysulfide bonds, contained in a polymer composition, by using pulsed NMR without using any special reagents.

[0020] Here, the monosulfide bond is a sulfur-bridged form (-S n -), a disulfide bond is a bond with a sulfur linkage number n=2, and a polysulfide bond is a bond with a sulfur linkage number n≧3.

[0021] The present invention utilizes the following facts: polysulfide bonds, monosulfide bonds, disulfide bonds, in that order: 1) the distance between bonds becomes shorter, 2) the free volume near the bonds becomes smaller, 3) the mobility of rubber molecular chains decreases, and 4) spin-spin relaxation becomes faster.

[0022] The method for analyzing the sulfur crosslinking morphology of the present disclosure includes the following steps (1) to (5). (1) A step of swelling a polymer composition. (2) A step of measuring the swollen polymer composition using pulsed NMR. (3) A step of analyzing the transverse relaxation decay curve using an inverse Laplace transform or a Weibull function to obtain a distribution of spin-spin relaxation times (T2). (4) A step of assigning, based on molecular mobility, multiple distribution peaks in the distribution as peaks of one or more monosulfide bonds, disulfide bonds, and polysulfide bonds, or a combination thereof. (5) A step of quantifying one or more monosulfide bonds, disulfide bonds, and polysulfide bonds, or a combination thereof, in the polymer composition based on the intensity ratio of the distribution peaks.

[0023] Each step will be described in detail below.

[0024] <1. Swelling process> The polymer composition is immersed in an appropriate solvent to swell. In the dry state, physical crosslinks and entanglements affect spin-spin relaxation, diluting the contribution of chemical crosslinks to spin-spin relaxation. However, in the swollen state, the contribution of physical crosslinks to T2 can be prevented. Evaluation of crosslink density by T2 takes advantage of the fact that crosslinks restrict the movement of rubber molecules. As will be described in more detail below with reference to Figure 1, crosslink density can also be evaluated using the average 1 / T2 value obtained by NMR measurement of a polymer composition in the dry state. However, the average 1 / T2 value in the dry state is larger than the average 1 / T2 value obtained for the same polymer composition in the swollen state. This is because physical crosslinks and entanglements affect spin-spin relaxation in the dry state. Diluting the contribution of chemical crosslinks to spin-spin relaxation by physical crosslinks and entanglements is undesirable for evaluating the morphology of sulfur crosslinks, which are chemical crosslinks. If the contribution of physical crosslinks to spin-spin relaxation increases, it may even be impossible to evaluate crosslink density by spin-spin relaxation. Therefore, it is preferable to first carry out a swelling step in which the polymer composition is swelled with a good solvent.

[0025] In the swelling step, a general swelling method can be used, and the solvent for swelling can be selected depending on the type of polymer composition. Examples of the solvent for swelling include deuterated solvents and carbon tetrachloride. Various organic solvents can be used as the deuterated solvent, but deuterated toluene is preferred.

[0026] <2. Pulse NMR measurement process> Pulsed NMR is a means for observing the spin relaxation (spin-spin relaxation and spin-lattice relaxation) of hydrogen nuclei, and analyzing the spin relaxation can provide information about molecular mobility, such as the spin-spin relaxation time (transverse relaxation time, T2) and the spin-lattice relaxation time (longitudinal relaxation time, T1). In this disclosure, transverse relaxation is considered to be spin-spin relaxation, and the time constant of the transverse relaxation is T2.

[0027] Methods for measuring the transverse relaxation decay curve include the solid echo method (pulse sequence: 90°x-τ-90°y), the Hahn echo method (pulse sequence: 90°x-τ-180°y), and the Carr-Purcell-Meiboom-Gill (CPMG) method, which is an extension of the Hahn echo method. In this disclosure, the sulfur bridge morphology can be analyzed using either the Hahn echo method or the CPMG method. The Hahn echo method is more preferable. In this disclosure, the Hahn echo method and the CPMG method are collectively referred to as the spin echo method.

[0028] <3. Analysis of decay curve> [Analysis using Weibull function] In a multi-component system with components that exhibit different molecular motions, the observed spin-spin relaxation M(t) is expressed as the superposition of the spin-spin relaxation of each component using the Weibull function, as shown in equation (1) below.

[0029]

number

[0030] M 0i is the signal intensity of component i at t=0, and Wi is the Weibull coefficient of component i, which takes a value between 1 and 2. If the molecular motion is sufficiently fast, W=1, and if the molecular motion is sufficiently slow, W=2. In the case of rubber compositions, W often takes a value between 1 and 2. The component fraction F of each T2 component i For this, the following equation (2) holds true.

[0031]

number

[0032] When calculating the crosslink density, the polymer composition is considered to be composed of crosslinked and non-crosslinked components, and the obtained decay curve is separated into two components with different molecular mobility. The Hahn echo method can separate the curve into the HS component, which is a network component formed by chemical and physical crosslinking, and the HL component, which is a non-network component. The HS component is a component with fast relaxation (low molecular mobility), and the HL component is a component with slow relaxation (high molecular mobility).

[0033] It is known that the product of 1 / T2 of the crosslinked component and the fraction F of the crosslinked component is an effective parameter for many polymer compositions with crosslinked structures (Iwabuki Jin, "Analysis of Organic Materials by NMR, Its Pretreatment and Data Interpretation," Technical Information Association, p. 417). In general, the product of T2 and fraction of non-crosslinked components is much smaller than that of crosslinked components, and their contribution to the average 1 / T2 is small. Therefore, it is possible to evaluate crosslink density by considering only the crosslinked components. However, in the case of degraded polymer compositions, the contribution of non-crosslinked components increases, making it more appropriate to use the average 1 / T2 value.

[0034] As the number of components increases, the residual between the measurement data and the regression data becomes smaller. However, in the analysis method disclosed herein, the average value of 1 / T2 and the total network chain concentration (ν t ) is the correlation coefficient between the average value of 1 / T2 and ν t The correlation coefficient is almost the same as that of the crosslink density. The evaluation of crosslink density can be adequately determined by roughly binarizing the molecular mobility.

[0035] As a result of investigating the relationship between the parameters obtained by pulsed NMR measurement and the sulfur crosslink morphology, the inventors of the present application found that it is possible to analyze the sulfur crosslink morphology by separating the swollen rubber into two components using the Weibull function. To further increase the accuracy of the analysis, it is preferable to separate it into three or more components using the Weibull function, and it is even more preferable to separate it into multiple components using the inverse Laplace transform.

[0036] [Analysis using inverse Laplace transform] The spin-spin relaxation time T of each Lorentzian relaxation when the decay curve is a superposition of Lorentzian relaxations (relaxations with Wi=1) 2i and component fraction F i can be obtained by inverse Laplace transform. The distribution of spin-spin relaxation times T2 can be obtained by inverse Laplace transforming the relaxation phenomenon observed by pulsed NMR measurement. The CONTIN method, for example, is a commonly used algorithm for numerical analysis, but the analytical method used for the inverse Laplace transform is not limited to this.

[0037] Inverse Laplace transform is performed by fixing Wi to 1 in equation (1) and setting the number of components to 100-200, or even more in some cases. Inverse Laplace transform of transverse relaxation curves, such as the CONTIN method, produces a natural T2 distribution with broadened peaks, whereas analysis using the Weibull function produces no broadened peaks. Inverse Laplace transform allows for good fitting with many T2 components.

[0038] <4. Peak assignment process> The multiple peaks in the distribution obtained are assigned based on molecular mobility. 2i , vertical axis F i It is considered that the shorter the T2 distribution peak, the lower the mobility, and the longer the T2 peak, the higher the mobility. The molecular mobility of monosulfide bonds, disulfide bonds, and polysulfide bonds increases in the order of monosulfide bonds, disulfide bonds, and polysulfide bonds. Therefore, for example, one peak among multiple distribution peaks, the distribution peak with the shortest T2, can be assigned to a monosulfide bond, a disulfide bond, or a combination of monosulfide bonds and disulfide bonds, etc. Furthermore, for example, the distribution peak with the longest T2 can be assigned to a polysulfide bond.

[0039] <5.Quantification process> By determining the intensity ratio of the distribution peaks, one or more of monosulfide bonds, disulfide bonds, and polysulfide bonds, or a combination thereof, in the polymer composition can be quantified. For example, if one of the multiple distribution peaks with the shortest T2 is regarded as the sum of monosulfide bonds and disulfide bonds and the intensity of that distribution peak is designated as F1, then v1 + v2, which is the sum of the network chain concentration (v1) attributed to monosulfide bonds and the network chain concentration (v2) attributed to disulfide bonds, shows a good correlation with F1. [Example]

[0040] The analytical method of the present disclosure will be specifically explained below based on examples, but the technology of the present disclosure is not limited thereto. Table 1 shows the formulations of the vulcanized rubbers used as polymer compositions for the analysis. The vulcanized rubbers of compositions 1 to 14 were formulated with various crosslinking accelerators to change the sulfur crosslinking form.

[0041] [Table 1]

[0042] [Reagents used to prepare vulcanized rubber] Details of each reagent listed in Table 1 are shown below. Natural rubber (KGR-3) Butadiene rubber: UBEPOL BR (registered trademark) 150 manufactured by UBE Corporation Carbon black: CONRAX® N774 Zinc oxide: Two types of zinc oxide manufactured by Seido Chemical Industry Co., Ltd. Stearic acid: NOF Corporation, Tsubaki stearic acid beads Anti-aging agent 1: 2-mercaptobenzimidazole (MBI), manufactured by Ouchi Shinko Chemical Co., Ltd. Antioxidant 2: (1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) Paraffin wax Vulcanization accelerator 1: Noccela MSA (N-oxydiethylene-2-benzothiazolyl sulfenamide), manufactured by Ouchi Shinko Chemical Co., Ltd. Vulcanization accelerator 2: Noccela TT (tetramethylthiuram disulfide), manufactured by Ouchi Shinko Chemical Co., Ltd. Vulcanization accelerator 3: Tetraethylthiuram disulfide (TETD) Vulcanization accelerator 4: Tetramethylthiuram monosulfide (TMTM) Vulcanization accelerator 5: 1,3-diphenylguanidine (DPG) Sulfur: Hosoi Chemical Co., Ltd., finely powdered sulfur, 325 mesh The vulcanized rubber can be produced by any method generally used for producing vulcanized rubber, but in this example, it was produced by the following method.

[0043] [Production of vulcanized rubber] Using a Banbury mixer, materials other than sulfur and vulcanization accelerator were mixed for each of compositions 1 to 14 according to the formulations in Table 1. Next, sulfur and vulcanization accelerator were added to the resulting mixture, and the mixture was mixed using an open roll to obtain an unvulcanized rubber mixture. The resulting unvulcanized rubber mixture was then poured into a 2 mm thick mold and press-vulcanized at 170°C for 5 minutes to obtain vulcanized rubber. The vulcanized rubber was subjected to Soxhlet extraction using deuterated toluene to remove any remaining sol.

[0044] [Swelling of vulcanized rubber] The vulcanized rubbers of compositions 1 to 14 were each equilibrated with deuterated toluene at 40°C.

[0045] [Pulse NMR measurement] Each of the vulcanized rubbers of compositions 1 to 14 was filled into a test tube together with deuterated toluene, and pulsed NMR measurements were carried out. The pulsed NMR measurement equipment and measurement conditions were as follows: Equipment: Bruker minispec mq20 Sample volume: approx. 0.3 mL Observed nucleus: 1H Pulse sequence: Hahn echo Measurement temperature: 40℃ As a comparative sample, the vulcanized rubber that was not swollen was measured at 50°C.

[0046] [Comparative study of dry and swollen states] Figure 1 shows the analytical values ​​(average value of 1 / T2) when the sample is separated into two components, HS and HL, using the Weibull function, and the total network chain concentration (ν t ) is a graph showing the relationship between the ν t It is known that there is a linear relationship between the crosslink density obtained in the dry state and the crosslink density obtained by the swelling method. As shown in Figure 1, the slopes of the linear curves in the dry state and the swollen state are almost the same, and it can be said that there is a high correlation between the crosslink density obtained in the dry state and the crosslink density obtained by the swelling method. It is possible to evaluate the crosslink density even in the dry state. However, the average value of 1 / T2 in the dry state is larger than the average value of 1 / T2 in the swollen state. For the same total network chain concentration ν t =100 mol / m 3 When comparing the samples, the analytical value for the dry state is approximately 0.2ms higher than that for the swollen state. -1 This is large, and when converted to a network chain concentration, it is approximately 100 mol / m 3 This difference is considered to be due to the contribution of physical cross-linking and entanglement, which dilutes the information on the chemical sulfur cross-linking form. For example, ν t For a sample with a cross-linking ratio of 100, the ratio of chemical cross-linking to physical cross-linking is 0.3:0.2 in the dry state, meaning that the contribution of the chemical cross-linking that is the subject of evaluation is only 60%. Therefore, it can be said that it is preferable to evaluate the cross-linking form by measuring in a swollen state, where the influence of physical entanglement is eliminated.

[0047] [Analysis using Weibull function] Figure 2 is an example of a graph showing the distribution of spin-spin relaxation times (T2) for composition 1 measured in a swollen state and separated into two components using a Weibull function. Analysis using the Weibull function assumes that each T2 component has uniform molecular mobility, so the peaks in the T2 distribution obtained from analysis using the Weibull function are flat, and the component fractions given by equation (2) represent the peak intensities.

[0048] Figure 3 shows the relationship between the peak intensity F1 on the shorter T2 side and ν1 + ν2 when Composition 1 was measured in a swollen state and separated into two components using a Weibull function. The coefficient of determination R for the exponentially fitted curve 2 was 0.896, which was a good correlation.

[0049] Figure 4 is an example of a graph showing the distribution of spin-spin relaxation times (T2) for composition 1 measured in a swollen state and separated into three components using a Weibull function. The separation into three components using the Weibull function is thought to represent a cross-linked component with low mobility, a cross-linked component with high mobility, and a non-cross-linked component, or a cross-linked component, a component intermediate between the cross-linked and non-cross-linked components, and a non-cross-linked component.

[0050] Figure 5 shows the relationship between the fraction F1 of the cross-linked component with the lowest mobility and v1 + v2 when Composition 1 is measured in a swollen state and separated into three components using a Weibull function. The coefficient of determination R of the approximation curve using an exponential function 2 was 0.966, which indicates an improvement in correlation compared to Figure 3.

[0051] Figure 6 shows the relationship between the peak intensity F1 on the shorter T2 side and v1 + v2 when NMR measurement was performed on composition 1 in a dry state and the two components were separated using a Weibull function. The correlation is low, making it difficult to evaluate the state of sulfur crosslinking.

[0052] [Analysis using inverse Laplace transform] Figure 7 shows the distribution of spin-spin relaxation times (T2) for composition 1, obtained by inverse Laplace transform using the analysis software RelaTE manufactured by Yamamoto Metal Works. The three peaks, from the shortest T2 side, are thought to correspond to low mobility cross-linked components, high mobility cross-linked components, and non-cross-linked components. The three distribution peaks shown in Figure 7 were observed in all samples.

[0053] The distribution peaks shown in Figure 7 were named Peak 1, Peak 2, and Peak 3 from the shortest T2 side, and the intensities of each peak were normalized. These normalized intensities were designated F1, F2, and F3 from the lowest molecular mobility side. Note that F1 + F2 + F3 = 1.

[0054] Figure 8 shows the relationship between the intensity F1 and ν1 + ν2 in the distribution obtained by inverse Laplace transform. The coefficient of determination R of the exponential approximation curve 2 was 0.968, which was a better correlation than the relationship between F1 and ν1 + ν2 in Figure 5. Similar to the results in Figure 5, Peak 1, which has the lowest molecular mobility (shortest T2) in the distribution obtained by inverse Laplace transform, is thought to be the network component (ν1 + ν2) composed of monosulfide bonds and disulfide bonds.

[0055] Comparing the compositions and analytical results in Table 1, for example, between Compositions 3, 4, and 5, we can see that increasing the sulfur content tends to decrease v1 + v2. This is because sulfur has an eight-membered ring structure, and the greater the sulfur content, the longer the sulfur atoms bond to the rubber polymer molecules. This is consistent with common knowledge about rubber. Similarly, TMTD (tetramethylthiuram disulfide bis(dimethylthiocarbamoyl) disulfide) and TMTM (tetramethylthiuram monosulfide) release sulfur and bond to the polymer molecules with shorter sulfur atom chains. This confirms that v1 + v2 changes depending on the amount and type of crosslinking accelerator, which is consistent with common knowledge about rubber. However, as in the examples of the present disclosure, it is common knowledge that crosslinking accelerators are combined in multiple types and amounts to adjust various performance characteristics such as rubber physical properties, scorch resistance, and processability. It is therefore extremely difficult to predict the mono / poly ratio in such cases. The analytical method of the present disclosure is an effective means for determining this.

[0056] As shown in Figure 7, the inverse Laplace transform of the decay curve gives a solution in which each peak has width and a natural distribution, whereas the distribution in Figure 5 does not have any broadening of the peaks. The inverse Laplace transform is preferable to using the Weibull function because it provides a good fit with many T2 components. The three peaks observed in Figure 7 suggest the validity of the three-component separation using the Weibull function. However, because the peak intensity on the side with the highest molecular mobility is small and can be considered to be a heterogeneous structure consisting mainly of two components, it is thought that a certain degree of cross-linking state analysis would have been possible even with the two-component separation using the Weibull function.

[0057] Comparing Figures 3 and 6 reveals that the correlation between F and ν is better in the swollen state than in the dry state. This is because, in the dry state, differences in mobility due to crosslinking morphology are less apparent due to physical crosslinking (entanglement), whereas swelling can reveal differences in mobility due to crosslinking morphology. Furthermore, comparing Figures 3 and 5 reveals that when using a Weibull function, using three components rather than two improves the correlation. This is because two components cannot adequately accommodate the mobility distribution expanded by swelling. Therefore, when using a Weibull function, it is preferable to perform analysis using three components rather than two. Furthermore, comparing Figures 5 and 8 reveals that the correlation is better when using the inverse Laplace transform than when using the Weibull function. However, when a relaxation component with Wi > 1 exists, applying the inverse Laplace transform is inappropriate. Within the scope of the present disclosure, the decay curves can be considered as a superposition of Lorentzian relaxations. However, applying the inverse Laplace transform to a decay curve containing non-Lorentzian relaxations results in a worse fitting than when using the Weibull function.

Claims

1. A method for analyzing the sulfur crosslinking form in a polymer composition having sulfur crosslinks, comprising: Swelling the polymeric composition; measuring the swollen polymer composition using pulsed NMR; The transverse relaxation decay curve was analyzed using the inverse Laplace transform or the Weibull function to determine the spin-spin relaxation time (T ２ ) distribution; a step of assigning a plurality of distribution peaks of the distribution as peaks of one or more of monosulfide bonds, disulfide bonds, and polysulfide bonds, or combinations thereof, based on molecular mobility; and quantifying one or more of monosulfide bonds, disulfide bonds, and polysulfide bonds, or a combination thereof, in the polymer composition based on the intensity ratio of the distribution peaks.

2. The method for analyzing sulfur bridge morphology according to claim 1 , wherein the distribution is obtained by performing an inverse Laplace transform on a transverse relaxation decay curve.

3. 3. The method for analyzing sulfur bridge morphology according to claim 1, wherein the measurement using pulsed NMR is performed using a spin echo method.

4. 3. The method for analyzing a sulfur crosslinking morphology according to claim 1 or 2, wherein one peak among the distribution peaks is assigned as a peak representing a sum of monosulfide bonds and disulfide bonds, and the monosulfide bonds and disulfide bonds in the polymer composition are quantified in total based on an intensity ratio of the distribution peaks.

5. The method for analyzing sulfur crosslinking morphology according to claim 1 or 2, wherein the dynamic characteristics of the polymer composition are predicted based on the quantification results.

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