阅读说明：本技术 一种新型含希夫碱dopo磷氮阻燃剂及其合成方法和应用 (Novel Schiff base DOPO phosphorus nitrogen-containing flame retardant and synthesis method and application thereof ) 是由 李玉林 赖华 李薇 黄耿 萧丽芬 彭钢 于 2021-04-19 设计创作，主要内容包括：本发明公开了一种新型含希夫碱DOPO磷氮阻燃剂,其结构式如下：该阻燃剂以水杨醛、对氨基苯甲酸为原料合成相应的希夫碱,然后再与9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO)反应合成得到。该阻燃剂克服了添加型阻燃剂与基体相容性差、使用过程易流失、耐水性差等缺点,应用于环氧树脂(EP-51),成炭性好,能形成致密的炭层,能够显著提高树脂的极限氧指数LOI,当阻燃剂含量为3％(P含量仅为0.2035％)时,垂直燃烧UL-94达到V-0级,具有良好的阻燃效果。基于所述含希夫碱DOPO磷氮阻燃剂,本发明还提供一种含希夫碱DOPO磷氮阻燃剂的合成方法及应用。(The invention discloses a novel Schiff base DOPO phosphorus nitrogen-containing flame retardant, which has the following structural formula: the flame retardant is prepared by synthesizing corresponding Schiff base from salicylaldehyde and p-aminobenzoic acid, and then reacting with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The flame retardant overcomes the defects of poor compatibility of an additive flame retardant and a matrix, easy loss in the using process, poor water resistance and the like, is applied to epoxy resin (EP-51), has good char formation property, can form a compact char layer, can obviously improve the limiting oxygen index LOI of the resin, achieves V-0 level when the flame retardant content is 3 percent (the P content is only 0.2035 percent), and has good performanceAnd (4) flame retardant effect. Based on the Schiff base DOPO phosphorus nitrogen-containing flame retardant, the invention also provides a synthesis method and application of the Schiff base DOPO phosphorus nitrogen-containing flame retardant.)

1. A novel Schiff base DOPO phosphorus nitrogen-containing flame retardant is characterized by having a structure shown as the following formula (I):

2. a synthesis method of a novel Schiff base DOPO phosphorus nitrogen containing flame retardant is characterized by comprising the following steps:

step S1, mixing salicylaldehyde and p-aminobenzoic acid according to the molar ratio of (1-3): (1-2) dissolving in a solvent, adding a certain amount of an acid-binding agent to enable a reaction system to be in an alkaline environment, controlling the reaction temperature to be 0-50 ℃, stirring, reacting for 3-6 hours to obtain a large amount of yellow precipitates, performing suction filtration, washing and drying to obtain pure Schiff base;

step S2, synthesizing Schiff base and DOPO according to the molar ratio (1-3): (1-2) adding the mixture into a mixed solvent, stirring to obtain a yellow solution, heating and refluxing for 3-5 hours to obtain a large amount of white precipitates, and after complete reaction, performing suction filtration and recrystallization to obtain the Schiff base DOPO phosphorus nitrogen-containing flame retardant.

3. The method for synthesizing the novel Schiff base DOPO phosphorus nitrogen containing flame retardant according to claim 2, wherein in the step S1, the acid binding agent is at least one of sodium hydroxide, potassium hydroxide, triethylamine, potassium tert-butoxide, sodium methoxide, pyridine, sodium ethoxide and imidazole.

4. The method for synthesizing novel schiff base DOPO phosphorus-nitrogen containing flame retardant according to claim 2, wherein in the step S1, the solvent is one of methanol, ethanol, chloroform, tetrahydrofuran, dichloromethane, acetonitrile, dimethyl sulfoxide, 1, 4-dioxane, carbon tetrachloride, DMF and DMAC.

5. The method for synthesizing the novel Schiff base DOPO phosphorus nitrogen containing flame retardant according to claim 2, wherein in the step S1, the washing process adopts a solvent cooled by ice water for multiple times of leaching.

6. The method for synthesizing novel schiff base DOPO phosphorus-nitrogen containing flame retardant according to claim 2, wherein in the step S2, the mixed solvent is at least two of methanol, ethanol, chloroform, tetrahydrofuran, dichloromethane, acetonitrile, dimethyl sulfoxide, 1, 4-dioxane, carbon tetrachloride, DMF and DMAC.

7. The synthesis method of the novel Schiff base DOPO phosphorus nitrogen containing flame retardant as claimed in claim 2, wherein in the step S2, a mixed solvent of ethyl acetate and petroleum ether is adopted for recrystallization, wherein the volume ratio of ethyl acetate to petroleum ether is (1-5): (1-3).

8. The use of a novel schiff base-containing DOPO phosphorus nitrogen flame retardant as defined in claim 1 in the preparation of epoxy resins.

9. The use according to claim 8, wherein the amount of schiff base-containing DOPO phosphorus nitrogen flame retardant added is 3-7% of the total amount of epoxy resin.

Technical Field

The invention relates to the technical field of flame retardants, in particular to a novel flame retardant containing Schiff base DOPO phosphorus nitrogen, a synthesis method thereof and application of the flame retardant in an epoxy resin polymer matrix.

Background

The polymer material has rich source, easy processing, various varieties, excellent performance and low price, and is widely applied to the fields of aerospace, electronic information, household appliances, automobile industry and the like. However, most of the high molecular materials are flammable materials, which are prone to fire and cause serious loss of human life and property. Therefore, flame retardancy of polymer materials is a problem to be solved.

The widely adopted method for flame retarding of high molecular materials at present is to add a flame retardant in the processing process of polymers so as to improve the flame retarding performance of the polymers. The existing conventional flame retardant is generally an organic or inorganic additive, is usually added in a large amount, needs to be blended with a base material during construction, has the defects of poor compatibility with a matrix, easy loss in use, poor water resistance and the like, and is difficult to crosslink or seriously degraded into some high molecular resins, so that the reactive flame retardant capable of directly introducing a flame retardant group or element into a high molecular matrix chain segment is widely researched by numerous scholars at home and abroad due to good dispersibility and high flame retardant efficiency. The 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) type flame retardant is an organic phosphorus heterocyclic compound, has higher thermal stability, oxidation resistance and excellent water resistance, is a good reactive flame retardant and an additive flame retardant, is mainly used for flame retardance of polyester fibers, polyurethane foam plastics, thermosetting resins and adhesives, and has a derivative structure which is a hotspot for development of flame retardants due to excellent flame retardance.

Schiff base mainly refers to an imine or azomethine characteristic group compound containing carbon-nitrogen double bonds, and due to unique physical material properties such as light, electricity and magnetism, good coordination chemical properties and unique physiological activities such as antibiosis, anticancer and weeding, the Schiff base brings about extensive theoretical and application research of people. Schiff base has biological activities of bacteriostasis, sterilization, tumor resistance, virus resistance and the like and is applied to the medical field; schiff base and metal complexes thereof have important application in the fields of pharmacy, catalysis, analytical chemistry, corrosion and photochromism; in the field of catalysis, cobalt and nickel complexes of Schiff bases have been applied as catalysts; the Schiff base can also be used as a good ligand, and can be used for identifying and identifying metal ions and quantitatively analyzing the content of the metal ions, thereby gaining wide attention in the analysis field. In these application fields, the research on the antibacterial and bacteriostatic properties is the hot spot of the current research, and most of the researches are concentrated on the simple Schiff base complex, while the research on the flame retardant property of the polymer material applied with DOPO is less reported.

Accordingly, an object of the present invention is to provide a flame retardant having a small amount of addition, good compatibility with a substrate, and a good flame retardant effect, which solves the above-mentioned problems.

Disclosure of Invention

The invention aims to solve the technical problem of providing a novel flame retardant containing Schiff base DOPO phosphorus nitrogen, which has good compatibility with a substrate and good flame retardant effect and is less in addition when applied to a high polymer material.

In order to solve the problems, the technical scheme of the invention is as follows:

a novel Schiff base DOPO phosphorus nitrogen containing flame retardant has a structure shown as the following formula (I):

a synthesis method of a novel Schiff base DOPO phosphorus nitrogen-containing flame retardant comprises the following steps:

step S1, mixing salicylaldehyde and p-aminobenzoic acid according to the molar ratio of (1-3): (1-2) dissolving in a solvent, adding a certain amount of an acid-binding agent to enable a reaction system to be in an alkaline environment, controlling the reaction temperature to be 0-50 ℃, stirring, reacting for 3-6 hours to obtain a large amount of yellow precipitates, performing suction filtration, washing and drying to obtain pure Schiff base;

step S2, synthesizing Schiff base and DOPO according to the molar ratio (1-3): (1-2) adding the mixture into a mixed solvent, stirring to obtain a yellow solution, heating and refluxing for 3-5 hours to obtain a large amount of white precipitates, and after complete reaction, performing suction filtration and recrystallization to obtain the Schiff base DOPO phosphorus nitrogen-containing flame retardant.

Further, in step S1, the acid-binding agent is at least one of sodium hydroxide, potassium hydroxide, triethylamine, potassium tert-butoxide, sodium methoxide, pyridine, sodium ethoxide, and imidazole.

Further, in step S1, the solvent is one of methanol, ethanol, chloroform, tetrahydrofuran, dichloromethane, acetonitrile, dimethyl sulfoxide, 1, 4-dioxane, carbon tetrachloride, DMF, and DMAC.

Further, in step S1, the washing process uses ice water cooled solvent for multiple rinses.

Further, in step S2, the mixed solvent is at least two of methanol, ethanol, chloroform, tetrahydrofuran, dichloromethane, acetonitrile, dimethyl sulfoxide, 1, 4-dioxane, carbon tetrachloride, DMF, and DMAC.

Further, in step S2, a mixed solvent of ethyl acetate and petroleum ether is used for recrystallization, wherein the volume ratio of ethyl acetate to petroleum ether is (1-5): (1-3).

The invention also provides application of the novel Schiff base DOPO phosphorus nitrogen-containing flame retardant in the preparation process of epoxy resin.

Furthermore, the addition amount of the Schiff base DOPO phosphorus nitrogen-containing flame retardant is 3-7% of the total amount of the epoxy resin.

Compared with the prior art, the novel Schiff base DOPO phosphorus nitrogen-containing flame retardant, the synthesis method and the application thereof have the beneficial effects that:

the novel phosphorus-nitrogen flame retardant containing Schiff base DOPO provided by the invention is prepared by synthesizing corresponding Schiff base from salicylaldehyde and P-aminobenzoic acid, and then reacting with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to synthesize the phosphorus-nitrogen flame retardant containing the Schiff base DOPO, overcomes the defects of poor compatibility of an additive flame retardant and a matrix, easy loss in a using process, poor water resistance and the like, is applied to epoxy resin (EP-51), has good char formation property, can form a compact carbon layer, can obviously improve the limit oxygen index LOI of the resin, and has good flame retardant effect when the flame retardant content is 3 percent (the P content is only 0.2035 percent), and can reach V-0 level by vertically burning UL-94.

The novel Schiff base DOPO phosphorus nitrogen-containing flame retardant provided by the invention is simple in synthesis method, convenient to purify, high in yield, good in heating stability and convenient for industrial production.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is an infrared spectrum of a novel Schiff base DOPO phosphorus nitrogen-containing flame retardant synthesized by the invention;

FIG. 2 is a H-NMR chart of the novel Schiff base DOPO phosphorus nitrogen-containing flame retardant synthesized by the invention;

FIG. 3 is a TG diagram of the flame retardant of various embodiments of the present invention applied to epoxy resin and a blank epoxy resin;

FIG. 4 is a DSC chart of the novel Schiff base DOPO phosphorus nitrogen containing flame retardant applied to epoxy resin.

Detailed Description

In order to make the technical solutions in the embodiments of the present invention better understood and make the above objects, features and advantages of the present invention more comprehensible, specific embodiments of the present invention are described below.

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, combinations of values between the endpoints of each range, between the endpoints of each range and the individual values, and between the individual values can be used to obtain one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention discloses a method for synthesizing a novel Schiff base DOPO phosphorus nitrogen-containing flame retardant, which comprises the following steps:

step S1, mixing salicylaldehyde and p-aminobenzoic acid according to the molar ratio of (1-3): (1-2) dissolving in a solvent, adding a certain amount of an acid-binding agent to enable a reaction system to be in an alkaline environment, controlling the reaction temperature to be 0-50 ℃, stirring, reacting for 3-6 hours to obtain a large amount of yellow precipitates, performing suction filtration, rinsing with a solvent cooled by ice water for multiple times, and drying to obtain pure Schiff base;

wherein the acid-binding agent is at least one of sodium hydroxide, potassium hydroxide, triethylamine, potassium tert-butoxide, sodium methoxide, pyridine, sodium ethoxide and imidazole;

the solvent is one of methanol, ethanol, trichloromethane, tetrahydrofuran, dichloromethane, acetonitrile, dimethyl sulfoxide, 1, 4-dioxane, carbon tetrachloride, DMF and DMAC;

step S2, synthesizing Schiff base and DOPO according to the molar ratio (1-3): (1-2) adding the mixed solvent, stirring, heating and refluxing for 3-5 hours until a system solution is uniform and transparent yellow, generating a large amount of white precipitates, almost completely reacting one raw material of the dotting plates, cooling with ice water, performing suction filtration, recrystallizing with a mixed solvent of ethyl acetate and petroleum ether, wherein the volume ratio of the ethyl acetate to the petroleum ether is (1-5): (1-3), and obtaining the schiff base-containing DOPO phosphorus nitrogen flame retardant;

wherein the mixed solvent is at least two of methanol, ethanol, chloroform, tetrahydrofuran, dichloromethane, acetonitrile, dimethyl sulfoxide, 1, 4-dioxane, carbon tetrachloride, DMF and DMAC.

The novel schiff base-containing DOPO phosphorus-nitrogen flame retardant and the synthesis method thereof provided by the invention are explained in detail according to specific examples below.

Example 1

A synthesis method of a novel Schiff base DOPO phosphorus nitrogen containing flame retardant comprises the following reaction steps:

step S1, adding 0.1mol (12.2g) of salicylaldehyde and 0.1mol (13.6g) of p-aminobenzoic acid into a 125mL three-neck flask, adding 70mL of methanol, adding 0.2mol (11.2g) of potassium hydroxide as an acid binding agent, controlling a certain temperature to react at about 5 ℃, electrically stirring, reacting for 5 hours, generating a large amount of yellow precipitates, performing suction filtration, rinsing with a solvent cooled by ice water for multiple times, and drying to obtain 21.0g of Schiff base, wherein the yield is about 87.1%;

step S2, adding 0.05mol (12.0g) of synthesized Schiff base and 0.1mol (21.6g) of DOPO into a mixed solvent of THF and DMF, electrically stirring, heating to control the temperature to be 60-70 ℃, wherein the system is a yellow solution, the solution becomes colorless and transparent after 2 hours, then becomes a white milky solution, a new substance is generated on a spot plate, heating is continued, a white precipitate appears, after 3-5 hours of reaction, the raw materials almost completely react, cooling and filtering are carried out, and the mixed solvent of ethyl acetate and petroleum ether is used according to the volume ratio of 1: 1, recrystallizing to obtain 20.8g of pure flame retardant containing Schiff base DOPO, wherein the yield is 91.0%.

Referring to fig. 1 and fig. 2, fig. 1 is an infrared spectrum of the novel schiff base-containing DOPO phosphorus nitrogen flame retardant of the present invention; FIG. 2 is a diagram of H-NMR of the novel Schiff base DOPO phosphorus nitrogen-containing flame retardant synthesized by the invention.

The main absorption peaks of infrared absorption spectroscopy (IR) are: 3267(vs), 1655(vs),1605(vs),1413(m),1285(vs),1236(vs),1177(vs),1067(m),748(vs), 632(m),553(m),527 (m).

The results of the nuclear magnetic tests are as follows:¹H-NMR:δ3.9(1H)，6.60-6.89(4H)，(7.29-8.00)(8H)， 7.50(1H)，7.49(2H)，10.06(H)，12.71(1H)。

example 2

A synthesis method of a novel Schiff base DOPO phosphorus nitrogen containing flame retardant comprises the following reaction steps:

step S1, adding 0.2mol (24.4g) of salicylaldehyde and 0.2mol (27.2g) of p-aminobenzoic acid into a 150mL three-neck flask, adding 100mL of ethanol, adding 0.2mol (11.2g) of sodium hydroxide as an acid binding agent, controlling a certain temperature to react at about 20 ℃, magnetically stirring, reacting for 4 hours, generating a large amount of yellow precipitates, performing suction filtration, rinsing with a solvent cooled by ice water for multiple times, and drying to obtain 44.3g of Schiff base, wherein the yield is 91.9%;

step S2, adding 0.1mol (24.1g) of synthesized Schiff base and 0.1mol (21.6g) of DOPO into a DMF solvent, stirring, heating and refluxing, wherein the system is a yellow solution, the solution becomes colorless and transparent after 2 hours, then becomes a white milky solution, a new substance is generated when a spot plate is used, heating is continued, a white precipitate appears, after 3-5 hours of reaction, the raw materials almost completely react, cooling with ice water, performing suction filtration, and mixing the mixture with ethyl acetate and petroleum ether to obtain a solvent 1: 1, recrystallizing to obtain 42.0g of pure flame retardant containing Schiff base DOPO, wherein the yield is 92.0%.

Example 3

A synthesis method of a novel Schiff base DOPO phosphorus nitrogen containing flame retardant comprises the following reaction steps:

step S1, adding 0.2mol (24.4g) of salicylaldehyde and 0.2mol (27.2g) of p-aminobenzoic acid into a 150mL three-neck flask, adding 90mL of methanol, adding 0.2mol (11.2g) of sodium hydroxide as an acid binding agent, controlling a certain temperature to react at about 0 ℃, magnetically stirring, reacting for 5 hours, generating a large amount of yellow precipitates, performing suction filtration, rinsing with a solvent cooled by ice water for multiple times, and drying to obtain 45.0g of Schiff base, wherein the yield is 93.36%;

step S2, adding 0.1mol (24.1g) of synthesized Schiff base and 0.1mol (43.2g) of DOPO into a solvent of THF, stirring, heating to control the temperature to be 60-70 ℃, wherein the system is a yellow solution, the solution becomes colorless and transparent after 2h and then becomes a white milky solution, new substances are generated on a spot plate, heating is continued, white precipitation occurs, after 3-5 h of reaction, the raw materials almost completely react, the reaction is cooled by ice water, suction filtration is carried out, and recrystallization is carried out by using a mixed solvent of ethyl acetate and petroleum ether, so that 41.0g of relatively pure flame retardant containing Schiff base DOPO is obtained, and the yield is 89.71%.

Example 4

The Schiff base DOPO phosphorus nitrogen-containing flame retardant prepared in the embodiment 1-3 is applied to epoxy resin.

And (3) testing the combustion performance: weighing 25g of 4, 4-diaminodiphenylmethane in a 100mL beaker, heating and melting, cooling to about 100 ℃, adding 1%, 3%, 5% and 7% of flame retardants P1, P2 and P3 prepared in examples 1-3 with different mass contents, stirring and mixing uniformly, pouring 100g of epoxy resin which is weighed in a 75 ℃ water bath in advance into the beaker containing the curing agent and the flame retardants, stirring uniformly, quickly casting into a 130 x 6.5 x 3 national standard oxygen index sample strip and a 120 x 13 x 3.2 national standard vertical combustion sample strip mold, curing for 20 hours at room temperature, then curing for 3 hours at 100 ℃, then placing in a 160 ℃ vacuum drying oven for curing for 1 hour, naturally cooling to room temperature, and demolding to obtain a flame-retardant epoxy resin sample to be tested.

The limit oxygen index was measured by JF 3-oxygen index meter, and UL-94 vertical burning performance test was carried out by FZ-5401 vertical burning apparatus, the test results are shown in Table 1:

table 1: performance testing of flame-retardant epoxy resins

Wherein the weight percentage refers to the percentage of the additive relative to the total weight of the (epoxy resin Ep-51+ curing agent).

The determination of the limit oxygen index refers to a national standard method GB/T2406.2-2009, and the GB/T2408-2008 standard is adopted for UL-94 vertical combustion test.

The epoxy resin (EP-51) is selected from epoxy resins CYD-128 (EP-51) of Baling, China petrochemical Co., Ltd.).

As can be seen from Table 1, the flame retarding effect is markedly enhanced with increasing content of the flame retardant in EP, as compared with blank EP (LOI:28.0, T:28 s; not extinguished on burning).

Compared with other flame retardants of the same type (for example, in the technology of Chinese patent CN201310008589, LOI of blank EP is 21, flame retardants of 7 wt%, 10 wt% and 12 wt% are respectively added, and the LOI values of the flame-retardant epoxy resin measured by the flame-retardant epoxy resin are respectively 27, 28.5 and 29, and UL-94V-0 level), the flame-retardant effect is enhanced.

Compared with the technology of Chinese patent CN201610304553, when the content of the flame retardant is 3% and the content of P is only 0.2035% (W%), the flame retardant can reach V-0 grade, which shows that the flame retardant effect is good.

Example 5

TG tests were performed on the Schiff base DOPO phosphorus nitrogen containing flame retardant prepared in the embodiment 1-3 applied to epoxy resin, and the test method was as follows:

the TG tests were carried out in EP-51 using a thermogravimetric analyzer TGA (Q5000IR, TA instruments USA) with the same amount of flame retardant for the different examples: in the air atmosphere, the temperature is raised within the range of 0-900 ℃ at the speed of 20 ℃/min, and finally no polymer remains. Please refer to fig. 3, which is a TG diagram of the flame retardant applied to the epoxy resin and the blank epoxy resin according to various embodiments of the present invention. As can be seen from FIG. 3, the decomposition temperature of the flame retardant of blank EP is about 334 deg.C, while the decomposition temperatures of the epoxy resins corresponding to the flame retardants of P1, P2 and P3 (example 1, example 2 and example 3) are 322, 327 and 324 deg.C, respectively, which shows that the addition of the flame retardant has little influence on the thermal decomposition of the modified epoxy resin.

It should be noted that the epoxy resin (EP-51) in this example is also selected from epoxy resin CYD-128 (EP-51) from Baling, a limited chemical company in China.

Example 6

The Schiff base DOPO phosphorus nitrogen containing flame retardant prepared in the embodiments 1-3 is applied to epoxy resin for heat resistance performance test, flame retardants with different embodiments and the same content are applied to EP-51, and a temperature rise rate is measured by a differential scanning calorimeter (DSC Q20) of TA Instruments of America under nitrogen atmosphere: 10 ℃/min, temperature range: DSC test is carried out at 80-320 ℃. Referring to fig. 4, a DSC chart of the inventive schiff base-containing DOPO phosphorus nitrogen flame retardant applied to epoxy resin shows that the glass transition temperature Tg of pure EP without flame retardant is 118.3 ℃, while the glass transition temperature of the schiff base-containing DOPO phosphorus nitrogen flame retardant EP increases slightly with the increase of the content, from Tg at 5% to Tg 147 ℃ to Tg at 7% to Tg at 162.24 ℃, which indicates that the novel flame retardant has an accelerating effect on the increase of the EP glass transition temperature.

Compared with the prior art, the flame retardant containing Schiff base DOPO phosphorus nitrogen, the synthesis method and the application thereof have the beneficial effects that:

the phosphorus-nitrogen flame retardant containing Schiff base DOPO provided by the invention is prepared by synthesizing corresponding Schiff base from salicylaldehyde and P-aminobenzoic acid, and then reacting with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to synthesize the phosphorus-nitrogen flame retardant containing Schiff base DOPO.

The Schiff base DOPO phosphorus nitrogen-containing flame retardant provided by the invention is simple in synthesis method, convenient to purify, high in yield, good in heating stability and convenient for industrial production.

The embodiments of the present invention have been described in detail, but the present invention is not limited to the described embodiments. Various changes, modifications, substitutions and alterations to these embodiments will occur to those skilled in the art without departing from the spirit and scope of the present invention.