Polysulfide elastomer as well as preparation method and application thereof

Abstract

The invention discloses a polysulfide elastomer as well as a preparation method and application thereof, and belongs to the technical field of elastomer preparation. The preparation method of the polysulfide elastomer provided by the invention comprises the following steps: heating and melting sulfur and a dithiocarboxylic acid monomer, and adding a vinyl monomer for reaction to obtain carboxyl-containing polysulfide; and mixing the carboxyl-containing polysulfide and the epoxy group-containing compound, and curing at high temperature to obtain the polysulfide elastomer. According to the preparation method provided by the invention, the polysulfide elastomer can be endowed with adjustability and excellent thermal mechanical performance and dynamic performance, and efficient repeated processing and self-repairing can be carried out; the adhesive has excellent bonding strength on engineering materials, the preparation raw materials are easy to obtain, the synthesis process is simple, the product yield is high, and the adhesive can be used as a body material and an adhesive and has wide application prospects in automobiles, optical instruments, electronic products, shoes and clothing and medical instruments.

Description

Technical Field

[0001] This application belongs to the technical field of elastomer preparation, and particularly relates to a polysulfide elastomer, a preparation method thereof, and an application thereof. Background Art

[0002] Sulfur, as an extremely abundant element on Earth, widely exists in fields such as industrial production. However, millions of tons of sulfur are in surplus every year, which not only causes serious waste of resources but also brings a series of safety hazards. How to effectively utilize this surplus sulfur has become an urgent problem to be solved. To achieve the effective utilization of sulfur, many studies have been carried out by scientific researchers. In 2013, Pyun et al. reported the copolymerization of sulfur and unsaturated olefin monomers at high temperatures (temperature greater than 159 °C), and successfully synthesized sulfur-containing polymers. This process was named "inverse vulcanization", which showed great application value in fields such as heavy metal adsorption, electrode materials, and infrared lenses (Nature Chemistry, 2013, 5: 518 - 524). However, chain transfer occurs during the inverse vulcanization process, resulting in a low molecular weight of the product, making the sulfur-containing polymer lack mechanical strength and having obvious limitations in practical applications.

[0003] To improve the mechanical properties of sulfur-containing polymers, researchers have tried to use highly functional olefins as comonomers. For example, 1,3,5-triisopropenylbenzene (TIB) was selected to participate in the reaction. In this way, the network crosslinking density can be increased, and the glass transition temperature of the sulfur-containing polymer is higher than room temperature, thus showing certain mechanical strength (ACS Macro Letters, 2016, 5: 1152 - 1156). However, the reaction process of highly functional olefins is more complex, it is difficult to precisely control the reaction conditions, the crosslinked network is brittle, and the obtained product is not an elastomer.

[0004] The copolymerization of sulfur and olefin monomers containing functional groups has also been studied, and then a crosslinking agent is added for curing, hoping to obtain a crosslinked polysulfide elastomer (Green Chemistry, 2023, 25: 4544 - 4552; Angewandte Chemie International Edition, 2021, 60: 22900 - 22907). However, due to the polarity of functional olefin monomers, their compatibility with sulfur is poor, resulting in difficulties in the smooth progress of the inverse vulcanization reaction. Usually, a catalyst needs to be added and a higher reaction temperature (greater than 170 °C) is required. This not only easily triggers side reactions, reduces the product yield, but also makes the reaction conditions very harsh, increasing the production cost and operation difficulty.

[0005] In summary, currently, when using sulfur as a raw material to synthesize polysulfide elastomers, many challenges still remain, and it is difficult to synthesize polysulfide elastomers with good mechanical strength through simple and effective methods. Therefore, developing a method that can simply synthesize polysulfide elastomers with mechanical strength using sulfur raw materials has important practical significance and application value. Summary of the Invention

[0006] This application discloses a polysulfide elastomer, its preparation method and application, aiming to solve the technical problems of the existing harsh synthesis conditions, complicated preparation process, and poor comprehensive performance of the synthesized polysulfide elastomers.

[0007] To achieve the above object, the technical solution of this application is:

[0008] In the first aspect of this application, a preparation method of a polysulfide elastomer is provided. The preparation method includes:

[0009] After heating and melting sulfur and a dithiocarboxylic acid monomer, a vinyl monomer is added for reaction to obtain a carboxyl-containing polysulfide;

[0010] The carboxyl-containing polysulfide and a compound containing an epoxy group are mixed and cured at a high temperature to obtain the polysulfide elastomer.

[0011] Preferably, in combination with the first aspect, the dithiocarboxylic acid monomer is one of 3,3'-dithiobispropionic acid, lipoic acid, and dithiodiacetic acid.

[0012] Preferably, in combination with the first aspect, the vinyl monomer is one of styrene, α-methylstyrene, and 4-methylstyrene.

[0013] Preferably, in combination with the first aspect, the compound containing an epoxy group is one of 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, bisphenol A diglycidyl ether, and polyethylene glycol diglycidyl ether.

[0014] Preferably, in combination with the first aspect, the sulfur content is 20 - 50 wt%;

[0015] The content of the dithiocarboxylic acid monomer is 30 - 60 wt%;

[0016] The content of the vinyl monomer is 20 - 40 wt%.

[0017] Preferably, in combination with the first aspect, when the carboxyl-containing polysulfide and the compound containing an epoxy group react, the molar ratio of the epoxy group to the carboxyl group is 0.4 - 1.0.

[0018] Preferably, in combination with the first aspect, when sulfur and dithiocarboxylic acid monomer are heated and melted and then vinyl monomer is added for reaction, the reaction temperature is 119 - 150 °C and the time is 2 - 5 h.

[0019] Preferably, in combination with the first aspect, when the carboxyl - containing polysulfide and the epoxy - group - containing compound are subjected to high - temperature curing, they are cured at 100 - 120 °C for 8 - 12 h and then heated to 130 - 150 °C for 2 - 4 h.

[0020] The second aspect of the present application provides a polysulfide elastomer prepared by the preparation method described in the first aspect.

[0021] The third aspect of the present application provides the application of the polysulfide elastomer prepared by the preparation method described in the first aspect or the polysulfide elastomer described in the second aspect as a bulk material and an adhesive in automobiles, optical instruments, electronic products, shoes and clothing, and medical devices.

[0022] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application at least include:

[0023] The preparation method provided by the present application prepares carboxyl - containing polysulfide through bulk copolymerization of sulfur, dithiocarboxylic acid monomer, and vinyl monomer at high temperature; then, an epoxy - group - containing compound is used as a cross - linker to react with the carboxyl - containing polysulfide to obtain a cross - linked polysulfide elastomer. On the one hand, the dithiocarboxylic acid monomer can generate sulfur radicals at a temperature lower than the lower limit temperature (T f = 159 °C) of sulfur ring - opening, and then promote the S 8 ring - opening reaction. Therefore, the synthesis of carboxyl - containing polysulfide can be carried out under mild conditions without using a catalyst, and the product yield is high without separation and purification, with extremely high atom economy. On the other hand, by first preparing carboxyl - containing polysulfide and then cross - linking and curing it with an epoxy - group - containing compound, the polysulfide elastomer can be given adjustable and excellent thermomechanical properties and dynamic properties, and can be efficiently processed repeatedly and self - repaired; and it has excellent adhesive strength on three common engineering materials of stainless steel, aluminum, and glass, and the raw materials for preparation are easily available and the synthesis process is simple. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a DSC diagram of the carboxyl - containing polysulfide (A2) provided by the embodiment of the present application;

[0026] Figure 2 XRD pattern of carboxyl-containing polysulfide (A2) provided by an embodiment of the present application. Detailed implementation manners

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0028] In the following description of the present embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: the case where A exists alone, the case where B exists alone, and the case where A and B exist simultaneously. Where A and B may be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0029] In the following description of the present embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or its similar expression below refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b or c", or, "at least one (item) of a, b and c" can all represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or plural respectively.

[0030] Those skilled in the art should understand that in the following description of the embodiments of the present application, the sequence number does not mean the sequence of execution. Some or all steps can be executed in parallel or sequentially, and the execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0031] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0032] It should be noted that all raw material reagents in the embodiments of the present application are purchased on the market or prepared by conventional methods well known to those skilled in the art.

[0033] In a first aspect, an embodiment of the present application provides a method for preparing a polysulfide elastomer, and the preparation method includes:

[0034] After heating sulfur and dithiocarboxylic acid monomers to melt, vinyl monomers are added for reaction to obtain carboxyl-containing polysulfide;

[0035] The carboxyl-containing polysulfide and the compound containing epoxy groups are mixed and cured at high temperature to obtain the polysulfide elastomer.

[0036] Among them, on the one hand, the dithiocarboxylic acid monomer can generate sulfur radicals at a temperature lower than the lower limit temperature (T f = 159 °C) at which sulfur ring-opening occurs, and then promote the S 8 ring-opening reaction. Therefore, the synthesis of carboxyl-containing polysulfide can be carried out under mild conditions without using a catalyst, and the product yield is high without separation and purification, with extremely high atom economy. On the other hand, by first preparing carboxyl-containing polysulfide and then crosslinking and curing it with a compound containing epoxy groups, the polysulfide elastomer can be given adjustable and excellent thermomechanical properties and dynamic properties, and can be efficiently processed repeatedly and self-repaired; and it has high adhesion strength on three common engineering materials of stainless steel, aluminum, and glass, and the raw materials for preparation are easy to obtain and the synthesis process is simple.

[0037] It should be noted that in this application, the thermomechanical properties of the polysulfide elastomer are finely regulated within a wide range by changing the feed ratio of each monomer, the type and addition amount of the crosslinking agent, etc. The crosslinked polysulfide elastomer can be used as a matrix material with high mechanical properties, and based on the dynamics of S-S bonds, it can be efficiently processed repeatedly and self-repaired; in addition, due to the carboxyl groups and sulfur chain segments in the network, the polysulfide elastomer can be used as an adhesive and has excellent adhesion properties to a variety of matrix materials.

[0038] In the examples of this application, the dithiocarboxylic acid monomer is preferably one of 3,3'-dithiobispropionic acid, lipoic acid, and dithiodiacetic acid. The vinyl monomer is preferably one of styrene, α-methylstyrene, and 4-methylstyrene. The compound containing epoxy groups is preferably one of 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, bisphenol A diglycidyl ether, and polyethylene glycol diglycidyl ether. The sulfur content is preferably 20-50 wt%; the dithiocarboxylic acid monomer content is preferably 30-60 wt%; the vinyl monomer content is preferably 20-40 wt%. Among them, under the condition of heating and melting, the disulfide bond in the dithiocarboxylic acid monomer breaks first to generate sulfur radicals and promote sulfur (S 8) The eight-membered ring structure of () is opened to generate a polysulfide radical segment; the polysulfide radical segment attacks the double bond of the unsaturated monomer to form a reactive intermediate with a sulfur-carbon bond; then through continuous sulfur radical addition and chain transfer reactions (proton transfer and abstraction of α-H), a carboxyl group-containing polysulfide with a polysulfide segment as the backbone is obtained after chain termination. The hydrogen atom in the carboxyl group will attack one carbon atom of the epoxy group to open the epoxy ring and form a β-hydroxy ester crosslinking bond; at the same time, the carboxyl group can also undergo an esterification reaction with the generated hydroxyl group to further connect different molecular chains, thereby gradually forming a three-dimensional network structure and endowing the material with the characteristics of an elastomer.

[0039] In the embodiments of the present application, when the carboxyl group-containing polysulfide reacts with the epoxy group-containing compound, the molar ratio of the epoxy group to the carboxyl group is preferably 0.4-1.0. Among them, by controlling the molar ratio of the epoxy group to the carboxyl group, the formed crosslinked structure can be controlled, which determines the network structure of the polysulfide elastomer. When the molar number of the epoxy group is relatively large, more crosslinking points will be formed during the reaction, the crosslinking density increases, and the hardness and strength of the elastomer will increase, but the flexibility and elasticity will decrease; conversely, if the carboxyl group is relatively large, the crosslinking density is low, and the elastomer may be softer and have better elasticity, but the strength and hardness may be insufficient. Therefore, by controlling the molar ratio of the two, the crosslinking density can be adjusted to enable the polysulfide elastomer to obtain appropriate mechanical properties to meet different application requirements.

[0040] In the embodiments of the present application, when sulfur and the dithiocarboxylic acid monomer are heated and melted and then an ethylenically unsaturated monomer is added for reaction, the reaction temperature is preferably 119-150 °C, and the time is preferably 2-5 h. Among them, by controlling the reaction temperature and time, sufficient energy can be provided to break the disulfide bond in the dithiocarboxylic acid monomer, which can promote the opening of the eight-membered ring structure of sulfur and generate polysulfide radicals, preparing for subsequent radical addition reactions.

[0041] In the embodiments of the present application, when the carboxyl group-containing polysulfide and the epoxy group-containing compound are cured at a high temperature, they are cured at 100-120 °C for 8-12 h and then heated to 130-150 °C for 2-4 h. Among them, by controlling the temperature and time of crosslinking and curing, the reaction is started at a lower temperature first to reduce the possibility of side reactions, and then the temperature is raised to accelerate the reaction rate and promote the crosslinking reaction.

[0042] The second aspect of the present application provides a polysulfide elastomer prepared by the preparation method described in the first aspect. Based on the above preparation process, the polysulfide elastomer can be endowed with excellent thermomechanical properties, repeated processing properties, self-healing properties, and adhesion properties.

[0043] The third aspect of the present application provides the use of the polysulfide elastomer prepared by the preparation method described in the first aspect or the polysulfide elastomer described in the second aspect as a bulk material and an adhesive in automobiles, optical instruments, electronic products, shoes and clothing, and medical devices. Among them, based on the excellent thermomechanical properties, repeated processing properties, self-healing properties, and adhesion properties of the above polysulfide elastomer, it can be used as a bulk material and an adhesive, and is widely used in fields such as automobiles, optical instruments, electronic products, shoes and clothing, and medical devices, with strong product competitiveness.

[0044] The technical solutions of the present application will be further described below in conjunction with specific embodiments.

[0045] Example 1

[0046] This example provides a preparation method of carboxyl-containing polysulfide A1, which specifically includes:

[0047] Add 3 kg of sulfur and 3 kg of 3,3'-dithiodipropionic acid to a reaction kettle equipped with mechanical stirring, heat it to 119 °C to make it melt, and stir and react to form a uniform transparent melt; then add 4 kg of styrene, stir and react for 2 h to obtain carboxyl-containing polysulfide A1.

[0048] Example 2

[0049] This example provides a preparation method of carboxyl-containing polysulfide A2, which specifically includes:

[0050] Add 3 kg of sulfur and 4 kg of lipoic acid to a reaction kettle equipped with mechanical stirring, heat it to 140 °C to make it melt, and stir and react to form a uniform transparent melt; then add 3 kg of α-methylstyrene, stir and react for 4 h to obtain carboxyl-containing polysulfide A2.

[0051] Example 3

[0052] This example provides a preparation method of carboxyl-containing polysulfide A3, which specifically includes:

[0053] Add 5 kg of sulfur and 3 kg of dithiodiacetic acid to a reaction kettle equipped with mechanical stirring, heat it to 150 °C to make it melt, and stir and react to form a uniform transparent melt; then add 2 kg of 4-methylstyrene, stir and react for 5 h to obtain carboxyl-containing polysulfide A3.

[0054] Example 4

[0055] This example provides a preparation method of carboxyl-containing polysulfide A4, which specifically includes:

[0056] Add 2 kg of sulfur and 6 kg of dithiodiacetic acid to a reaction kettle equipped with mechanical stirring, heat to 150 °C to melt it, and stir to react to form a uniform transparent melt; then add 2 kg of 4-methylstyrene and stir to react for 3 h to obtain carboxyl-containing polysulfide A4.

[0057] Example 5

[0058] This example provides a preparation method of polysulfide elastomer, which specifically includes:

[0059] According to the formulations and process conditions of Samples 1-8 in Table 1: Stir and mix A1, A2, A3, A4 and the compound containing epoxy groups evenly, and then transfer the mixture to a silica gel mold for high-temperature curing. The curing temperature T 1 is 100-120 °C, and the curing time t 1 is 8-12 h. Heat up to the temperature T 2 is 130-150 °C, and the time t 2 is 2-4 h, and finally obtain the polysulfide elastomer.

[0060] Table 1 Formulation and Process Table

[0061]

[0062] In order to verify the yield of the carboxyl-containing polysulfide prepared in the example, the prepared carboxyl-containing polysulfide was subjected to DSC and XRD tests.

[0063] According to Figure 1 it is known that in the DSC curve, the endothermic peak of thioctic acid (TA) at 61.7 °C represents its melting point, and the endothermic peaks of S 8 at 107.1 °C and 121.2 °C are its crystal form transformation and melting peaks respectively. After the copolymerization reaction, no endothermic peaks of S 8 and TA monomers appear in the range of 60-130 °C, indicating that S 8 and TA react completely without residue.

[0064] According to Figure 2 it is known that the XRD results show that A2 is amorphous, and along with the disappearance of the diffraction peaks of TA and crystalline sulfur, this confirms that TA and S 8 react completely and successfully copolymerize to form an amorphous sulfur-rich copolymer.

[0065] In order to verify the comprehensive performance of the polysulfide elastomer prepared in the example, the prepared polysulfide elastomer was subjected to mechanical property, dynamic property and adhesion property tests. The determination standards for the tensile strength and elongation at break of the polysulfide elastomer are ISO37-2005, the test temperature is room temperature, and the tensile rate is 100 mm / min; the determination standard for the lap shear strength is GB / T 7124-2008.

[0066] The repeated processing experimental method is as follows: The polysulfide elastomer is crushed and sieved through a 80-mesh sieve. The obtained powder is hot-pressed at 120 °C and 20 MPa for 10 minutes to achieve repeated processing. The tensile strength and elongation at break of the reprocessed sample are divided by those of the original sample to obtain the recovery rate of the corresponding properties.

[0067] The healing experimental method is as follows: The crosslinked polysulfide elastomer is cut with a blade, and then the cut surfaces are butt-jointed and placed at 100 °C for 2 h for healing. The tensile strength of the healed sample is divided by that of the original sample to obtain the healing efficiency. The test results are shown in Table 2.

[0068] Table 2 Mechanical properties, dynamic properties and adhesion properties of the samples

[0069]

[0070]

[0071] According to the test results in Table 2, by comparing Samples 1-3, it can be seen that as the dosage of the crosslinking agent 1,6-hexanediol diglycidyl ether increases, the crosslinking density of the sample increases, and the glass transition temperature T g increases from 2.6 °C to 10.2 °C, resulting in an increase in the tensile strength of the sample from 1.47 MPa to 3.25 MPa, a gradual decrease in the elongation at break, an increase in the lap shear strength, and a decrease in the repeated processability and healing efficiency. By comparing Samples 4-6, it can be seen that the samples crosslinked with bisphenol A diglycidyl ether containing a rigid aromatic ring structure exhibit the highest tensile strength and T g and the lowest elongation at break, which is due to the fact that the rigid structure restricts the movement of molecular chains; while 1,6-hexanediol diglycidyl ether and polyethylene glycol diglycidyl ether containing flexible aliphatic chains endow the samples with lower tensile strength and T g and higher elongation at break. In addition, as the rigidity of the crosslinking agent increases, the lap shear strength of the sample increases, and the repeated processability and healing efficiency remain basically unchanged. By comparing Samples 7-8, it can be seen that when using the same type and quality of crosslinking agent, as the sulfur content increases and the carboxyl content decreases, Sample 7 has lower tensile strength and T g and higher elongation at break, lower lap shear strength, and higher repeated processability and healing efficiency.

[0072] Therefore, the preparation method provided by this application involves bulk copolymerization of sulfur, dithiocarboxylic acid monomers, and vinyl monomers at high temperature to prepare carboxyl-containing polysulfur, and then crosslinking and curing with a compound containing an epoxy group. This can endow the polysulfide elastomer with adjustable and excellent thermomechanical properties and dynamic properties, enabling efficient repeated processing and self-healing. Moreover, it has excellent adhesion strength in engineering materials, with easily obtainable raw materials, a simple synthesis process, and a high product yield. It can be used as a bulk material and an adhesive, and has broad application prospects in automobiles, optical instruments, electronic products, shoes and clothing, and medical devices.

[0073] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other, and the key point of each embodiment is to illustrate the differences from other embodiments.

[0074] The above embodiments are only used to illustrate the technical solutions of this application, rather than limiting this application. Although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. However, such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a polysulfide elastomer, characterized in that: The preparation method comprises: After sulfur and dithiocarboxylic acid monomers are heated and melted, vinyl monomers are added to react to obtain carboxyl-containing polysulfide; The polysulfide containing carboxyl group and the compound containing epoxy group are mixed and cured at high temperature to obtain the polysulfide elastomer.

2. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: The dithiocarboxylic acid monomer is one of 3,3'-dithiodipropionic acid, thioctic acid and dithiodiacetic acid.

3. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: The vinyl monomer is one of styrene, α-methylstyrene and 4-methylstyrene.

4. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: The epoxy group-containing compound is one of 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, bisphenol A diglycidyl ether, and polyethylene glycol diglycidyl ether.

5. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: The sulfur content is 20-50wt%; The dithiocarboxylic acid monomer content is 30-60wt%; The vinyl monomer content is 20-40 wt%.

6. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: When the carboxyl-containing polysulfide reacts with the epoxy-containing compound, the molar ratio of the epoxy group to the carboxyl group is 0.4-1.

0.

7. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: After the sulfur and dithiocarboxylic acid monomers are heated and melted, when the vinyl monomer is added for reaction, the reaction temperature is 119-150° C. and the reaction time is 2-5 hours.

8. The method for preparing a polysulfide elastomer according to claim 1, characterized in that: When the carboxyl-containing polysulfide and the epoxy-containing compound are cured at high temperature, the curing time is 8-12 hours at 100-120° C., and the temperature is raised to 130-150° C. for curing for 2-4 hours.

9. A polysulfide elastomer prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the polysulfide elastomer prepared by the preparation method according to any one of claims 1 to 8 or the polysulfide elastomer according to claim 9 as a bulk material and an adhesive in automobiles, optical instruments, electronic products, shoes and clothing, and medical devices.

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