Disclosure of Invention
The present invention provides a high molecular polymer obtained by co-brominating aromatic and aliphatic chains and a preparation method thereof, in order to solve the above-mentioned disadvantages in the background art.
Therefore, the invention provides a high molecular polymer with aromatic and aliphatic chains jointly brominated, wherein the high molecular polymer is prepared by the two-stage bromination of a styrene butadiene polymer, and the general formula of the molecular structure of the high molecular polymer is as follows:
(C8H3+mBrn)x.(C4H6Br2)y.(C4H6Br2)z.(C8H3+mBrn)x
the molecular structure contains both aliphatic bromine and aromatic bromine, and x in the molecular structure is the number of styrene structural units; y is the number of 1, 4-butadiene structural units; z is the number of 1, 2-butadiene structural units; the value of m is 0-4; the value of n is 1 to 5.
The invention also provides a preparation method of the aromatic and aliphatic chain co-brominated high molecular polymer, which comprises the following specific steps:
(1) bromination of aliphatic chains: adding styrene butadiene polymer into an organic solvent, stirring for dissolving, preparing a quaternary ammonium bromide salt solution from liquid bromine and quaternary ammonium salt in the organic solvent for later use, controlling the reaction temperature, pouring the prepared quaternary ammonium bromide salt solution into the styrene butadiene polymer solution for a bromination reaction, adding water into the reaction solution, washing with water to recover the quaternary ammonium salt, recycling, and dehydrating and drying an organic layer by using a drying agent for later use;
(2) aromatic bromination: adding a composite catalyst and a brominating agent into the organic layer which is subjected to the aliphatic chain bromination in the step (1), controlling the reaction temperature, and performing a two-stage bromination reaction;
(3) and (3) post-treatment: and (3) adding a reducing agent into the high molecular polymer system prepared in the step (2) to remove residual bromine, adding a neutralizing agent to adjust the pH value to be neutral, recovering the organic solvent through steam stripping, and separating to obtain a powdery high molecular polymer product.
Preferably, in the step (1), the organic solvent is one or more of dichloromethane, dichloroethane, chloroform, carbon tetrachloride and chlorobenzene, and the mass ratio of the organic solvent to the styrene butadiene polymer is (5-10): 1.
Preferably, in the step (1), the quaternary ammonium salt is one or more of tetraethylammonium bromide, tetrabutylammonium bromide, benzyltriethylammonium chloride, benzyltrimethylammonium bromide and hexadecyltrimethylammonium bromide, and the molar ratio of the liquid bromine to the quaternary ammonium salt is 1 (0.5-1).
Preferably, in the step (1), the mass ratio of the liquid bromine to the styrene butadiene polymer is (6.5-8.5): 3.
preferably, the method is characterized in that in the step (1), the reaction temperature is 10-20 ℃, and the reaction time is 10-15 hours.
Preferably, in the step (1), the drying agent is one or more of anhydrous sodium sulfate, anhydrous barium sulfate, calcium oxide and a 5A molecular sieve.
Preferably, in the step (2), the composite catalyst and the brominating agent act to realize bromination of the benzene ring structure, and are one or more of the following combinations:
(1) the composite catalyst is a composite catalyst of an azo compound and a peroxide compound, the azo compound is at least one of azodiisobutyronitrile and azodiisoheptonitrile, the peroxide compound is at least one of benzoyl and dicumyl peroxide, the brominating agent is one or more of N-bromosuccinimide, dibromohydantoin and tetrabromocycloketone, the dosage of the composite catalyst is 5-10% of that of a styrene butadiene polymer, and the mass ratio of the brominating agent to the styrene butadiene polymer is (0.5-1) 1;
(2) the composite catalyst is a composite catalyst of iron powder and one of aluminum trichloride, ferric trichloride, stannic chloride and antimony trichloride, the brominating agent is at least one of liquid bromine and bromine chloride, the using amount of the composite catalyst is 5-10% of that of the styrene butadiene polymer, and the mass ratio of the brominating agent to the styrene butadiene polymer is (0.5-1): 1.
Preferably, in the step (2), the reaction temperature is 30-50 ℃ and the reaction time is 10-15 hours.
Preferably, in the step (3), the reducing agent is one or more of a sodium sulfite solution, a sodium bisulfite solution, a sodium thiosulfate solution and a hydrazine hydrate solution, and the concentration of the reducing agent is 10-25%; the neutralizer is one or more of sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, sodium bicarbonate solution and potassium carbonate solution, and the concentration of the neutralizer is 10-25%.
The invention has the beneficial effects that:
(1) the aromatic and aliphatic chain co-brominated high molecular polymer has the advantages of simple reaction path, good product quality, high yield, low impurity content, simple and easy product post-treatment method, obviously improved product performance, high thermal stability, easy storage, convenient use, environmental protection and energy conservation, and suitability for industrial production.
(2) The preparation method of the aromatic and aliphatic chain co-brominated high molecular polymer changes the original production process, adopts two-stage bromination reaction, uses a self-made mild brominating agent, adopts combination of bromine and quaternary ammonium salt to convert bromine into a mild brominating agent in the first stage of aliphatic chain bromination, and realizes bromination reaction of the styrene butadiene polymer aliphatic chain at a lower temperature; the method has advanced process, avoids bromine substitution reaction of methyl and methylene on an aliphatic chain structure by reducing the reaction activity of bromine, can realize recovery of quaternary ammonium salt used in the first stage of bromination by simple water washing, has high raw material utilization rate, convenient post-treatment, high product purity and less side reaction, and does not need to consume a large amount of organic solvent. The thermal stability of the product is obviously improved, and the comprehensive utilization rate of bromine is high; greatly improves the thermal stability of the product and is suitable for industrial production.
(3) The invention relates to a method for preparing a high molecular polymer brominated by aromatic and aliphatic chains together, which aims to reduce the dosage of a flame retardant, improve the compatibility of a high molecular flame retardant material and a base material, maintain the specific ductility and other mechanical properties of the base material, improve the bromine content of the high molecular material, realize the bromination of a benzene ring structural unit under the condition that a styrene butadiene polymer has been partially brominated, particularly a linear chain double bond has been brominated, and provide two benzene ring bromination schemes by selecting a specific catalyst and a brominating agent to provide the high molecular polymer with different aromatic bromine contents, wherein the bromine content of the product can reach 60-80 percent, the product has excellent thermal stability, the relative molecular weight of the product is higher, the addition of the flame retardant is less, the compatibility with the base material is good, and the flame retardant property is obviously improved, environment protection, energy saving and easy large-scale production.
Detailed Description
The invention will be better understood from the following examples. However, those skilled in the art will readily appreciate that the description of the embodiments is only for illustrating the present invention and should not be taken as limiting the invention as described in the claims.
Example 1
A high molecular polymer with aromatic and aliphatic chains co-brominated, which has a structural formula as follows:
the preparation method comprises the following steps in sequence:
(1) bromination of aliphatic chains: a1000 ml four-necked flask was charged with 240g of methylene chloride and 30g of styrene-butadiene polymer, and the mixture was dissolved with stirring for further use. A500 ml four-necked flask was charged with 60g of methylene chloride, 70g of liquid bromine, and 90g of tetraethylammonium bromide to prepare a tetraethylammonium tribromide methylene chloride solution for use. The reaction temperature of a 1000ml four-mouth bottle is controlled at 10 ℃, and a pre-prepared tetraethylammonium tribromide dichloromethane solution is poured into a styrene butadiene polymer solution to perform bromination reaction for 10 hours. And after the reaction is finished, adding 100ml of water, washing with water to recover tetraethylammonium bromide, mechanically preparing the tetraethylammonium tribromide, adding a proper amount of anhydrous sodium sulfate into the organic layer, stirring until the water content is 200ppm, and keeping the organic layer for later use.
(2) Aromatic bromination: adding 1g of azobisisobutyronitrile, 1g of benzoyl peroxide and 15g of N-bromosuccinimide into the organic layer which is brominated in the step (1), and controlling the reaction temperature to be 30 ℃; the bromination reaction was carried out for 10 hours. And adding 100g of water into the reaction solution, washing with water to recover the succinimide, mechanically applying to prepare the N-bromosuccinimide, and keeping an organic layer for later use.
3) And (3) post-treatment: and (3) adding a sodium sulfite aqueous solution with the mass concentration of 15% into the high molecular polymer system prepared in the step (2) to remove residual bromine, adding a sodium carbonate solution with the mass concentration of 15% to adjust the pH to 7, recovering the organic solvent through steam stripping, and separating to obtain a powdery high molecular polymer product.
Example 2
A polymer formed by co-brominating aromatic and aliphatic chains, having the structural formula:
the preparation method comprises the following steps in sequence:
(1) bromination of aliphatic chains: a1000 ml four-necked flask was charged with 210g of dichloroethane and 30g of styrene-butadiene polymer, and the mixture was dissolved by stirring for further use. A tetrabutylammonium tribromide dichloroethane solution was prepared by charging 50g of dichloroethane, 70g of liquid bromine, and 100g of tetrabutylammonium bromide to a 500ml four-necked flask and prepared for use. A1000 ml four-necked flask was set to a reaction temperature of 15 ℃ and a prepared tetrabutylammonium tribromide dichloroethane solution was poured into a styrene butadiene polymer solution to conduct bromination for 13 hours. And after the reaction is finished, adding 100ml of water, washing with water to recover tetrabutylammonium bromide, mechanically preparing tetrabutylammonium tribromide, adding a proper amount of calcium oxide into an organic layer, stirring until the water content is 200ppm, and keeping the organic layer for later use.
(2) Aromatic bromination: adding 1.5g of azobisisoheptonitrile, 1.5g of dicumyl peroxide and 18g of dibromohydantoin into the organic layer which is brominated in the step (1), and controlling the reaction temperature to be 39 ℃; the bromination reaction was carried out for 13 hours. 100g of water is added into the reaction solution, the hydantoin is recovered by washing, the dibromohydantoin is prepared by applying mechanically, and the organic layer is reserved for use.
(3) And (3) post-treatment: adding 20% hydrazine hydrate aqueous solution to the high molecular polymer system prepared in the step (2) to remove residual bromine, adding 20% sodium hydroxide solution to adjust the pH value to 7, recovering the organic solvent through steam stripping, and separating to obtain a powdery high molecular polymer product.
Example 3
A high molecular polymer with aromatic and aliphatic chains co-brominated, which has a structural formula as follows:
the preparation method comprises the following steps in sequence:
(1) bromination of aliphatic chains: 150g of chlorobenzene and 30g of styrene-butadiene polymer were added to a 1000ml four-necked flask and dissolved by stirring for further use. 50g of chlorobenzene, 70g of liquid bromine and 53g of benzyltrimethylammonium bromide are added into a 500ml four-mouth bottle to prepare a benzyltrimethylammonium tribromide chlorobenzene solution for later use. The reaction temperature of a 1000ml four-mouth bottle is controlled at 17 ℃, and a prepared benzyl trimethyl ammonium tribromide chlorobenzene solution is poured into a styrene butadiene polymer solution for bromination reaction for 13 hours. And after the reaction is finished, adding 100ml of water, washing with water to recover benzyltrimethylammonium bromide, mechanically using the benzyltrimethylammonium bromide to prepare benzyltrimethylammonium tribromide, adding a proper amount of 5A molecular sieve into the organic layer, stirring until the water content is 150ppm, and keeping the organic layer for later use.
(2) Aromatic bromination: adding 2g of iron powder into the organic layer after the bromination in the section 1, controlling the reaction temperature to be 35 ℃, and dropwise adding 25g of liquid bromine; bromination was carried out for 15 hours and the organic layer was kept aside.
(3) And (3) post-treatment: adding a sodium bisulfite solution with the mass concentration of 20% into the high molecular polymer system prepared in the step 2) to remove residual bromine, adding a sodium bicarbonate solution with the mass concentration of 20% to adjust the pH value to 7, recovering the organic solvent through steam stripping, and separating to obtain a powdery high molecular polymer product.
Example 4
A high molecular polymer with aromatic and aliphatic chains co-brominated, which has a structural formula as follows:
the preparation method comprises the following steps in sequence:
(1) bromination of aliphatic chains: 250g of carbon tetrachloride and 30g of styrene butadiene polymer are added into a 1000ml four-mouth bottle, and stirred and dissolved for later use. 50g of carbon tetrachloride, 70g of liquid bromine and 96g of hexadecyl trimethyl ammonium bromide are added into a 500ml four-mouth bottle to prepare a hexadecyl trimethyl ammonium tribromide carbon tetrachloride solution for later use. The reaction temperature of a 1000ml four-mouth bottle is controlled at 15 ℃, and a prepared cetyl trimethyl ammonium tribromide carbon tetrachloride solution is poured into a styrene butadiene polymer solution for bromination reaction for 15 hours. After the reaction is finished, 150ml of water is added, cetyl trimethyl ammonium bromide is recovered by water washing, the cetyl trimethyl ammonium tribromide is prepared by mechanical application, a proper amount of anhydrous barium sulfate is added into the organic layer, the mixture is stirred until the water content is 170ppm, and the organic layer is reserved.
(2) Aromatic bromination: adding 3g of aluminum trichloride into the organic layer which is brominated in the step (1), controlling the reaction temperature to be 35 ℃, and dropwise adding 17g of liquid bromine; bromination was carried out for 15 hours and the organic layer was kept aside.
(3) And (3) post-treatment: and (3) adding a sodium thiosulfate solution with the mass concentration of 20% into the high molecular polymer system prepared in the step (2) to remove residual bromine, adding a 20% potassium carbonate solution to adjust the pH value to 7, recovering the organic solvent through steam stripping, and separating to obtain a powdery high molecular polymer product.
Example 5
A high molecular polymer with aromatic and aliphatic chains co-brominated, which has a structural formula as follows:
the preparation method comprises the following steps in sequence:
(1) bromination of aliphatic chains: a1000 ml four-necked flask was charged with 250g of methylene chloride and 30g of styrene-butadiene polymer, and the mixture was dissolved with stirring for further use. 50g of dichloromethane, 70g of liquid bromine and 80g of benzyltriethylammonium chloride are added into a 500ml four-mouth bottle to prepare a dichlorobenzyltriethylammonium chloride dibromide solution for later use. Controlling the reaction temperature of a 1000ml four-mouth bottle to be 20 ℃, pouring the prepared dibrominated benzyl triethyl ammonium chloride dichloromethane solution into the styrene butadiene polymer solution for bromination reaction for 15 hours. After the reaction is finished, 150ml of water is added, benzyltriethylammonium chloride is recovered by water washing, the benzyltriethylammonium chloride dibromide is prepared indiscriminately, a proper amount of anhydrous sodium sulfate is added into the organic layer, the mixture is stirred until the water content is 250ppm, and the organic layer is reserved.
(2) Aromatic bromination: adding 1g of stannic chloride and 1g of antimony trichloride into the organic layer which is brominated in the step (1), controlling the reaction temperature to be 35 ℃, and dripping 25g of liquid bromine chloride; bromination was carried out for 13 hours and the organic layer was kept aside.
(3) And (3) post-treatment: and (3) adding a sodium thiosulfate solution with the mass concentration of 20% into the high molecular polymer system prepared in the step (2) to remove residual bromine, adding a 20% potassium carbonate solution to adjust the pH value to 7, recovering the organic solvent through steam stripping, and separating to obtain a powdery high molecular polymer product.
TABLE 1 bromine content and thermal Properties of the high molecular weight polymers of examples 1 to 5
The following is a summary of further analysis of the experimental data and bromine content statistics of examples 1-5 above.
The invention provides a high molecular polymer with aromatic and aliphatic chains co-brominated, wherein aliphatic bromine and aromatic bromine exist in the molecular structure at the same time, styrene butadiene polymer is taken as a raw material, a combined catalyst and a brominating agent are added to realize the co-bromination of the aliphatic chains and the aromatic chains, then a reducing agent and a neutralizing agent are added to respectively remove residual bromine and adjust PH, water vapor stripping is carried out to recover an organic solvent, and a powdery high molecular polymer product with high bromine content is prepared by separation.
The invention relates to the bromination of aliphatic chains and aromatic chains of styrene butadiene, wherein two stages of bromination both use a combination of a catalyst and a brominating agent, so that the combination of the catalyst and the brominating agent is the most key raw material in the invention. Specifically, the first stage is aliphatic chain bromination, the combination of the catalyst and the brominating agent used in the invention improves the thermal stability of the product, the comprehensive utilization rate of bromine is high, and the preparation method has the advantages of small harm to the environment, high product yield and good product quality, and can be suitable for industrial production.
The good homogeneous reaction system is the basic condition for realizing complete bromination and rapid bromination, styrene butadiene is easy to dissolve in halogenated alkane organic solvent, and the subsequent procedures can also be carried out by water washing and other steps, so that the selection of an organic solvent which is not miscible with water is extremely beneficial to the subsequent product treatment. Preferably, in the implementation of the invention, the organic solvent is one or more of dichloromethane, dichloroethane, trichloromethane, carbon tetrachloride and chlorobenzene, and the mass ratio of the organic solvent to the styrene butadiene polymer is (5-10): 1.
Under the conditions of normal temperature and no catalyst, the double bond on the butadiene and liquid bromine can generate electrophilic addition reaction, but liquid bromine is a strong brominating reagent, when the amount of the liquid bromine is large, the bromine substitution reaction of methyl and methylene on the fat chain structure can occur, and the bromine substitution reaction of the methyl and the methylene on the fat chain can easily cause chain breakage of a high molecular polymer, so that the flame retardant and the thermal stability of the product are reduced in the processing process of the product and a base material; when the liquid bromine amount is insufficient, the bromine addition reaction on the aliphatic chain can not be completed, and the product yield is low. In the preparation method of the aromatic and aliphatic chain co-brominated high molecular polymer, a special mild bromination system is prepared according to the requirement, so that the full reaction of raw materials can be ensured, the generation of byproducts can be inhibited, and the excellent thermal stability of the product can be ensured. The quaternary ammonium salt can be combined with liquid bromine to form a mild bromination reagent, and after bromine is transferred to double bonds to realize addition reaction, the quaternary ammonium salt is formed again, does not participate in main reaction and only serves as a transfer medium of the bromine. Preferably, the quaternary ammonium salt is one or more of tetraethylammonium bromide, tetrabutylammonium bromide, hexadecyltrimethylammonium bromide and benzyltriethylammonium chloride.
On one hand, the invention comprehensively considers the medium effect of the quaternary ammonium salt from the chemical kinetics point of view, and optimally selects the proportion of the quaternary ammonium salt, the liquid bromine and the styrene butadiene in order to avoid the bromine substitution reaction of the liquid bromine and methyl and methylene on an aliphatic chain structure in the reaction process. Preferably, the molar ratio of the liquid bromine to the quaternary ammonium salt is (1:0.5) to 1, and the mass ratio of the liquid bromine to the styrene butadiene polymer is (6.5-8.5): 3.
on the other hand, in the prior art, the required reaction temperature of the styrene butadiene in the bromination process by the brominating agent is higher, generally 40-80 ℃, but in the specific implementation process of the invention, the bromination reaction is carried out by the mild brominating agent, so that the reaction activity of bromine is reduced, the styrene butadiene polymer can be brominated at a lower temperature, and in order to ensure that the complete bromination of the aliphatic chain is realized, the preferable reaction temperature is 10-20 ℃, and the reaction time is 10-15 hours.
The quaternary ammonium salt is used as a relatively expensive catalyst, can be recovered by simple water washing without any change before and after the reaction, and is almost insoluble in the halogenated alkane. Therefore, the quaternary ammonium salt is preferably recycled and reused in a water washing mode, the recovery rate is 90% -98%, the method is environment-friendly and energy-saving, the cost is remarkably saved, the method is suitable for production of modern industry, the green energy-saving and environment-friendly concept pursued by the modern society is met, and sustainable development is facilitated.
In order to reduce the dosage of a flame retardant, improve the compatibility of a high-molecular flame-retardant material and a base material, simultaneously keep the specific ductility and other mechanical properties of the base material, and improve the bromine element content of the high-molecular material, under the condition that a styrene butadiene polymer has been partially brominated, particularly under the condition that a linear chain double bond has been brominated, the bromination of a benzene ring structure unit in high-molecular polymerization is difficult to realize due to the influence of steric hindrance, the invention provides a specific catalyst and brominating agent combination to realize the bromination of a benzene ring structure, and the combination of the catalyst and the brominating agent is divided into two types, wherein the catalyst is a composite catalyst. Specifically, one is a combination of an organic composite catalyst and an organic brominating agent, namely a combination of a catalyst of an azo compound and a peroxide compound and an organic brominating agent, and the other is a combination of an inorganic composite catalyst and an inorganic brominating agent, namely a combination of a catalyst of a Lewis acid and a metal simple substance catalyst and an inorganic brominating agent. As can be seen from the above-mentioned composition, in order to carry out the next bromination of the benzene ring structure, the water content of the system needs to be controlled within 300ppm, otherwise, the too high water content may affect the catalyst, thereby affecting the bromination of the benzene ring structure, and preferably, the drying agent is one or more of anhydrous sodium sulfate, anhydrous barium sulfate, calcium oxide, and 5A molecular sieve.
Generally, azo-based compounds and peroxy-based compounds are used as initiators for addition polymerization between monomers to link a plurality of monomers to form macromolecules. And due to the influence of steric hindrance, bromine can only replace hydrogen ions in a fatty chain on the premise of no catalyst. Therefore, in the two-stage bromination of the invention, a combination of a self-made organic composite catalyst and an organic brominating agent is utilized, wherein the azo compound and the peroxide compound form a binary composite catalyst system, and the binary composite catalyst system and the brominating agent perform a synergistic effect to brominate a benzene ring structure in the styrene butadiene polymer. Specifically, the peroxide compound can improve the heat resistance of a final product, but when the peroxide compound is used as an initiator alone, the peroxide compound can be induced and decomposed, so that the efficiency of the initiator is reduced, therefore, the azo initiator and the peroxide initiator form a binary composite catalyst, the generation of induced decomposition is avoided, the utilization rate is improved, the binary composite catalyst can be fully utilized in different half-life periods, and the using amount of the catalyst is effectively saved. The binary composite catalyst and the organic brominating agent generate a synergistic effect, when the binary composite catalyst initiates a benzene ring in styrene butadiene to open an unsaturated double bond, bromine in the brominating agent and the benzene ring generate an addition reaction, and the bromination of the benzene ring structure is realized. Preferably, the organic brominating agent is one or more of N-bromosuccinimide, dibromohydantoin and tetrabromocycloketone.
The invention also defines another self-made composite catalyst and brominating agent combination, the composite catalyst is a Lewis acid catalyst, but Lewis acid as the catalyst often has the defects of low initiation efficiency and incapability of obtaining polymers with high molecular weight and narrow molecular weight distribution at the same time, so the invention provides a Lewis acid and metal simple substance composite catalyst system, the metal simple substance is used as a carrier, the Lewis acid and the metal simple substance form a solid-liquid phase system, the catalytic activity is high, and after the reaction, the composite catalyst can be easily separated and recovered for recycling, and the activity of the catalyst is not reduced. When the composite catalyst acts with pi bond in benzene ring, inorganic brominating agent produces bromination reaction with benzene ring. Preferably, the inorganic brominating agent is liquid bromine or bromine chloride.
On one hand, in order to improve the bromine content and the thermal stability of a final product, the use amounts of a combined catalyst and a brominating agent are required to be controlled, the content of the brominating agent is too high, so that the bromination of methyl and methylene in an aliphatic chain is generated after the bromination of a benzene ring is finished, the thermal stability of the final product is influenced, and a plurality of benzene ring structures are realized, therefore, the use amounts of the composite catalyst and the brominating agent are limited, preferably, the use amount of the composite catalyst is 5-10% of that of a styrene butadiene polymer, and the mass ratio of the brominating agent to the styrene butadiene polymer is (0.5-1): 1.
On the other hand, on the basis of controlling the use amounts of the composite catalyst and the brominating agent, complete bromination of the aromatic is guaranteed, preferably, the reaction temperature is 30-50 ℃, and the reaction time is 10-15 hours.
In conclusion, the invention provides a preparation method of a high molecular polymer with aromatic and aliphatic chains brominated together, which is scientific, reasonable and simple, has low synthesis cost and can meet the requirement of industrial production. As can be seen from the data of the examples 1-5 in the table 1, the bromine content of the product can reach 78.5% at most, the relative molecular mass of the product is high and can be 113000 at most, the thermal stability of the product is excellent, the temperature of 5% thermal weight loss is 250-270 ℃, the softening point is 120-130 ℃, the addition amount of the flame retardant is small, the compatibility with the base material is good, the flame retardant performance is obviously improved, the environment is protected, the energy is saved, and the large-scale production is easy to realize.
However, the above description is only an embodiment of the present invention, and the scope of the present invention should not be limited by this, and all equivalent changes and modifications made in the claims of the present invention should be covered by the present invention.