JPH0617473B2 - Polyester polyol derivative and process for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester polyol derivative having at least one terminal amino group represented by the general formula [I].

(Prior Art) Japanese Patent Application Nos. 57-199384 and 57-165447, which are the prior applications of the present applicant.
58-75182, 59-66599, and 59-124019 describe polyether polyol derivatives having an amino group at the molecular end, a method for producing the same, a polymer by the reaction of the polyether polyol derivative with a polyisocyanate, and a method for producing the same. Is shown. The polyols used as starting materials in these inventions are all polyether polyols, and do not include polyester polyols.

In the reaction of a polyester polyol derivative having an amino group and a hydroxyl group as required at the molecular end and an aromatic amide group in the main chain with a polyisocyanate, a urea group,
Poly (urethane) ureaamide polymers containing aromatic amide groups are obtained and have many significant advantages compared to polyurethanes obtained from the corresponding polyester polyols and polyisocyanates.

In particular, the poly (urethane) ureaamide polymer obtained by the polyaddition reaction of the polyester polyol derivative having an amino group and optionally a hydroxyl group at the terminal of the present invention and having an aromatic amide group in the main chain with a polyisocyanate is ,
It has higher heat resistance and stronger mechanical strength compared to the structurally equivalent polyurethane.

U.S. Pat.No. 4,328,322 discloses a polyaddition reaction between a para-aminobenzoic acid ester of a polyol and a polyisocyanate obtained by reacting a polyol with para-nitrobenzoic acid chloride and then reducing the nitro group to convert all the terminal hydroxyl groups of the polyol into amino groups. The resulting polymer is disclosed. Also, polyamine was reacted with para-nitrobenzoic acid chloride or para-nitrobenzoic acid, and then the nitro group was reduced to convert all the terminal amino groups of the polyamine into amino groups of different species. Polyaddition of para-aminobenzoic acid amide with polyisocyanate Polymers obtained by the reaction are disclosed.

The present invention provides a poly (urethane) urea amide polymer by polyaddition reaction of a polyester polyol derivative in which a part or all of the terminals of the polyester polyol is substituted with an aromatic amino group, and the main chain has an aromatic amide group and a polyisocyanate. I will get it. Therefore, the polymers of the present invention are quite different in chemical structure from the polymers of US Pat. No. 4,328,322.

(Problems to be Solved by the Invention) An object of the present invention is to provide a polyester polyol derivative having an amino group at a terminal and, if necessary, a hydroxyl group and an aromatic amide group in the main chain, and a simple production method thereof. To do.

(Means for Solving Problems) The present invention relates to a polyester polyol derivative represented by the following general formula and a method for producing the same.

R ₁ is O (oxygen element) in the chain with a C _2-6 alkylene group.
R ₂ which may have: C _1-10 alkylene group, C _2-6 alkynylene group or phenylene group n: 2 x: a value indicating an average valence, and 0 ≦ x ≦ (n- Number of 1) p, r: average value showing the number of repeating structural units, 0 ≦
Number of p, r ≤ m q: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≤ q ≤ 10, not the number of repetitions.

m: positive number determined from molecular weight, p + r = m or R _3: an alkylene group of a straight-chain or branched _{C 3 to 6} R _4: a linear or branched divalent to tetravalent hydrocarbon group of _{C 2 to 6,} O in the chain of _{C 2 to 6} Removal of the terminal OH group from a polyester polyol or a divalent to tetravalent polyether group having a molecular weight of 3000 or less containing a linear or branched divalent to tetravalent hydrocarbon group having (oxygen element) as a repeating unit. The residue obtained by n: 2 x: a value showing an average valence, 0 ≦ x ≦ (n-1) number s, u, v: an average value showing the number of repeating structural units, 0
Number of ≦ s, u, v ≦ m t: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≦ t ≦ 10, not the number of repetitions.

m: a positive number determined from the molecular weight, s + u + v = m (wherein each segment represents a ratio, not an order of bonding, and represents a —NHC ₆ H ₄ CO— group in the main chain. Is not a block but is bonded at random and may or may not be bonded to the terminal aminobenzoyl group.) The polyester polyol derivative of the general formula [I] of the present invention partially or at the terminal of the polyester polyol. All are aromatically aminated and an aromatic amide group is contained in the main chain. The production is completed by substantially one-step reaction, the yield is high, and purification is not required.

The polyester polyol derivative of the present invention can be obtained by reacting a 2- to 4-valent polyester polyol having a molecular weight of 400 to 10000 with an aminobenzoic acid alkyl ester.

The polyester polyol used in the present invention may be either a condensed polyester polyol or a lactone polyester polyol obtained by a known method. Condensed polyester polyols include adipic acid, sebacic acid,
Saturated or unsaturated dibasic acids such as terephthalic acid, isophthalic acid, maleic acid and fumaric acid, maleic anhydride, acid anhydrides such as phthalic anhydride, dialkyl esters such as dimethyl terephthalate and ethylene glycol, propylene glycol, Butylene glycol, diethylene glycol, dipropylene glycol, neopentyl glycol, 1,6-hexylene glycol is a polyester polyol obtained by a condensation reaction with glycols such as, as a specific example, polyethylene adipate polyol, polybutylene adipate polyol, poly Adipate-based polyol consisting of one kind of acid and one kind of glycol such as hexylene adipate polyol, polyethylene butylene adipate polyol, polyethylene diethylene adipate polyol , Polyhexylene neopentylene adipate polyol and other adipate-based polyols consisting of one kind of acid and many kinds of glycol, aroma such as polyethylene adipate terephthalate polyol and polyethylene adipate isophthalate polyol consisting of many kinds of acid and one kind of glycol Group polyol etc. are mentioned.

Lactone-based polyester polyols are obtained by ring-opening polymerization of lactones such as ε-caprolactone and γ-butyrolactone. Depending on the type of initiator, various lactone polyester polyols are obtained. As the initiator, glycols such as ethylene glycol and butylene glycol, polyether polyols such as polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG), and condensation type polyester polyols such as adipate are selected. However, both are suitable for use in the present invention.

When the polyester polyol derivative of the present invention obtained from the above polyester polyol is used as a raw material for synthesizing an elastomer, a divalent polyester polyol having a molecular weight of 1000 to 4000 is suitable.

The aminobenzoic acid alkyl ester used in the present invention may be any of ortho, meta or para-aminobenzoic acid alkyl ester, but when the polyester polyol derivative of the present invention is used as a raw material for synthesizing an elastomer, the paraaminobenzoic acid alkyl ester is particularly preferable. It is suitable.

As the alkyl group of aminobenzoic acid alkyl ester, various ones can be exemplified, and preferable examples thereof include a chain having 1 to 8 carbon atoms such as methyl, ethyl, propyl, butyl, hexyl, octyl, cyclobutyl, cyclopentyl and cycloheptyl. Alternatively, cyclic alkyl can be mentioned. Further, 2-butoxyethyl, 2-ethoxyethyl and the like are also suitable.

Further, bis (aminobenzoic acid) alkyl esters can also be used. Bis (aminobenzoic acid) esters such as glycols having 2 to 8 carbon atoms such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, and peptylene glycol are preferable.

In the present invention, the aminobenzoic acid alkyl ester is 0.25n based on 1 mol of the n-valent polyester polyol.
Suitably, -10 nmoles, preferably 0.5-2 nmoles are reacted.

The polyester polyol derivative of the present invention can be obtained by carrying out dealcoholization by usually heating to 150 to 250 ° C. in the presence of a catalyst or a known esterification catalyst while passing an inert gas such as nitrogen gas. When a catalyst is used, it is preferable to use a weakly acidic or weakly basic catalyst that has little influence on the ester bond in the polyester polyol and is less likely to cause side reactions such as dehydration reaction of hydroxyl groups, for example, antimony trioxide, lead monoxide, etc. And organic titanium compounds such as tetraisopropyl titanate and tetrabutyl titanate, alkaline earth metal salts of weak acids such as calcium acetate, and the like, and organic titanium compounds are particularly preferable. The catalyst amount is usually 1000 ppm or less. Further, for the reaction, an inert solvent or a coloring inhibitor such as triphenyl phosphate can be used. The reaction is continued until the distillation of the aliphatic alcohol is completed, and the system is further depressurized to completely distill off the alcohol and excess aminobenzoic acid alkyl ester, if present. No purification is necessary.

It should be noted that points to be noted in the reaction between the polyester polyol and the aminobenzoic acid alkyl ester are the transesterification reaction between the ester bond in the molecular chain of the polyester polyol and the terminal OH group or the NH ₂ group of the aminobenzoic acid alkyl ester, or That is, the amide formation reaction proceeds simultaneously.

These two reactions are performed by adjusting the reaction temperature, the molar ratio of the polyester polyol and the aminobenzoic acid alkyl ester, and the time required for dealcoholization.
It is possible to control.

Therefore, the polyester polyol derivative obtained by the reaction of the polyester polyol of the present invention with the aminobenzoic acid alkyl ester has a molecular weight different from the calculated molecular weight of the charged polyester polyol and the charged amount of the aminobenzoic acid alkyl ester. In order to obtain a polyester polyol derivative having a desired molecular weight, the charged amount of raw materials should be taken into consideration. The content of amide groups is an important factor for achieving the object of the present invention to produce a polymer having higher heat resistance and higher mechanical strength.

The reaction for forming an aromatic amide group has not been fully clarified yet, but it can be inferred as follows.

Formula (1) is a reaction for terminal amination, and formula (2) is a reaction for forming an aromatic amide group adjacent to a terminal aminophenyl group.
Formula (3) is a reaction in which an aromatic amide group is inserted into the polyester main chain. Formula (4) is a reaction in which an aromatic amide group is further inserted into the polyester main chain having an aromatic amide group.

The aromatic amide group in the above polyester polyol derivative can be quantitatively confirmed by NMR analysis and nitrogen element analysis.

As a result of ¹³ C-NMR analysis, the number of amide groups in the polyester polyol derivative of the present invention when an aliphatic polyester polyol was used as a starting material was higher in the main chain than in the adjacent ends. From this result, the following can be estimated. Since the difference in the number of two kinds of ester groups, that is, the difference in the number of terminal aminobenzoic acid ester groups and the number of ester groups in the main chain is large, the probability that a reaction can occur is naturally greater in the main chain. Therefore, it is considered that the amide group formation reaction in the polyester main chain became dominant.

The polyester polyol derivative obtained by the method of the present invention is an esterified product in which all terminal hydroxyl groups are converted to amino groups, or a partially esterified product in which some unreacted hydroxyl groups remain, and an aromatic amide group in the main chain. Contains. The amination ratio (that is, the esterification ratio of the terminal hydroxyl group) and the degree of the amidation ratio can be varied over a wide range depending on the application, and at least one hydroxyl group of the polyester polyol is esterified on average. Is required, preferably the amination ratio is about 50 to 100%, and the amide group can be varied over a range of about 5 to 2000 mol% with respect to the terminal amino group, but about 5 to 100 mol% is preferable. . When the amide group is within this range, the viscosity of the polyester polyol derivative is appropriate and the moldability is excellent.

An example of the polyester polyol derivative of the general formula [I] when ethylene adipate is used as the raw material polyester in the present invention is given by the following formula. However where each of each segment represents the ratio does not indicate the order of binding, -NHC 6 _H 4 _CO- groups in the main chain is linked to a random rather than block, when attached to the terminal amino benzoyl group And may not be combined.

R ₁ : CH ₂ CH ₂ R ₂ : CH ₂ CH ₂ CH ₂ CH ₂ x: a value showing an average valence, and a number of 0 ≦ x ≦ 1 p, r: an average value showing the number of repeating structural units And 0 ≦
Number of p, r ≤ m q: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≤ q ≤ 10, not the number of repetitions.

m: a positive number determined from the molecular weight, p + r = m. Further, an example of the polyester polyol derivative of the general formula [I] when a diol obtained by ring-opening polymerization of ε-caprolactone is used as a raw material is It is given by the following formula.

R ₃ : CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ R ₄ : CH ₂ CH ₂ or an alkyl group such as CH ₂ CH ₂ CH ₂ CH ₂ x: a value showing an average valence, 0 ≦ x ≦ 1 S, u, v: the average value showing the number of repeating structural units, 0
Number of ≦ s, u, v ≦ m t: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≦ t ≦ 10, not the number of repetitions.

m: Positive number determined from molecular weight, s + u + v = m The above two examples are examples of using a bifunctional polyester polyol, and do not limit the structure of the polyester polyol derivative of the present invention. There is no.

(Effect of the Invention) The polyester polyol derivative of the present invention reacts with polyisocyanate to polycondense poly (urethane) ureaamide polymer and polycarboxylic acid to provide poly (ester) amide polymer.

The polyester polyol derivative of the present invention is also useful as a curing agent for epoxy resins.

(Example) Hereinafter, the present invention will be specifically described with reference to Examples and Reference Examples.

Example 1 (Synthesis of Polyester Polyol Derivative) Lactone-based polyester polyol [Plaxel-21
0, manufactured by Daicel Corporation, MW990, OH value 2.02 meq / g] 244
2 g (4.935 eq) was placed in a 4-necked flask equipped with a stirring rod, a cooling tube, a thermometer, and a nitrogen gas introducing tube, and dehydrated under reduced pressure at 100 ° C. for 1 hour under a nitrogen gas stream. Next, 570.5 g (3.46 mole) of ethyl paraaminobenzoate [first-grade reagent manufactured by Hanai Chemical Co., Ltd.] was added, and the temperature was raised to 88 ° C.

Next, add tetrabutyl titanate 1.025 g (340 ppm),
When the temperature was raised with stirring, the reaction system became a homogeneous solution at 110 ° C. and the wall surface of the four-necked flask began to get wet with the produced ethanol. The temperature was further raised, the reaction was carried out in the temperature range of 225 to 230 ° C. for 2 hours and 30 minutes, and ethanol was distilled off.

Then, the reaction system was cooled to 138 ° C., and then the pressure was reduced to 7 mmHg under a nitrogen gas stream. The temperature of the system was raised to 200 ° C., unreacted ethyl paraaminobenzoate was distilled off for 3 hours, and a reddish brown liquid having a viscosity at 30 ° C. of 11000 cps was obtained.
The yield was 2854g.

When this liquid was analyzed by gel permeation chromatography, free ethyl para-aminobenzoate was not detected. In addition, using the following analysis method for this liquid,
It was confirmed that a polyester polyol derivative having a terminal amino group was produced.

That is, the amine value was 0.998 meq / g by titration with perchloric acid in glacial acetic acid (Analytical Chemistry Handbook, Revised Edition, 3rd edition, p. 261). Also, the total number of hydroxyl groups and amino groups (active hydrogen group value)
According to the hydroxyl value measurement method (JIS K1557) that can measure 1.2,
It was 77 meq / g. These measured values are calculated from the charged amount of polyester polyol and ethyl para-aminobenzoate, which has an amine value of 1.213 meq / g and an active hydrogen group value of 1.728 m.
It did not match eq / g. Measured active hydrogen group value 1.277 meq / g
Therefore, the molecular weight of the polyester polyol derivative having a terminal amino group is 1566, and when this product is analyzed by gel permeation chromatography (GPC), the molecular weight distribution is higher on the polymer side than that of the starting polyester polyol. It was confirmed that there was a shift. or,
The ¹³ C-NMR analysis of this product confirmed the presence of an amide group, and the amide group was 20 mol% relative to the terminal amino group.
Were present. According to elemental analysis, nitrogen is 1.68%,
Consistent with the amount of amide calculated from this (total nitrogen-amine). From these results, the product polyester polyol derivative is a compound in which 78.2% of the terminal hydroxyl groups are converted to amino groups and the aromatic amide group in the molecular chain is contained in 20 mol% with respect to the terminal amino groups. It was The average structure of the product is estimated to be:

Example 2 Lactone-based polyester polyol [Plaxel-22
0, manufactured by Daicel Corp., MW2000, OH value 1.027 meq / g] 6
99 g (0.718 eq) was placed in a 4-necked flask and dehydrated under reduced pressure at 100 ° C. for 1 hour under a nitrogen gas stream. Next, 86.0 g (0.521 mole) of ethyl paraaminobenzoate was added to the 4-necked flask, and the temperature was raised to 200 ° C.

Next, add 0.195 g (248 ppm) of tetrabutyl titanate,
The temperature was raised to 240 ° C. Distillation of ethanol started, and then ethanol was distilled off for 8 hours in the temperature range of 235 to 240 ° C.

Then, the reaction system was cooled to 200 ° C., and then the pressure was reduced to 5 mmHg under a nitrogen gas stream. The temperature of the system was raised to 220 ° C., unreacted ethyl paraaminobenzoate was distilled off for 6 hours, and a reddish brown viscous liquid having a viscosity at 60 ° C. of 7,000 cps was obtained. The yield was 601 g.

The amine value measured by the same method as in Example 1 was 0.363 meq / g.
And the active hydrogen group value was 0.599 meq / g. According to elemental analysis, nitrogen was 0.94%. Therefore, the product polyester polyol derivative was a compound in which 61% of the terminal hydroxyl groups were converted into amino groups and 85% of the aromatic amide groups were contained in the molecular chain with respect to the terminal amino groups.

Example 3 Ethylene adipate polyester polyol (Nipporan N-4040, manufactured by Nippon Polyurethane Industry Co., Ltd., MW2014, O
645 g (0.640 eq) having an H value of 0.993 meq / g) was placed in a 4-necked flask and dehydrated under reduced pressure at 100 ° C. for 1 hour under a nitrogen gas stream.
Next, 106 g (0.640 mole) of ethyl paraaminobenzoate was added and the temperature was raised to 100 ° C. Next, tetrabutyl titanate 0.3
When 6 g (500 ppm) was added and the temperature was raised with stirring, ethanol began to distill at about 165 ° C. The temperature was further raised and the reaction was continued at 200 to 215 ° C for 10 hours. Then, the reaction system was cooled to 200 ° C. and the pressure was reduced to 5 mmHg under a nitrogen gas stream, and unreacted ethyl paraaminobenzoate was distilled off for 6 hours. Yield 660g, melting point 50 ℃
Of yellow solid was obtained.

The amine value measured by the same method as in Example 1 was 0.259 meq / g.
And the active hydrogen group value was 0.461 meq / g. The molecular weight calculated from the active hydrogen group number is 4330. The molecular weight was confirmed by GPC analysis. In addition, unreacted ethyl paraaminobenzoate was not detected. Elemental analysis showed 1.02% nitrogen. Therefore, in the product polyester polyol derivative, 56% of the terminal hydroxyl groups are converted to amino groups,
And an aromatic amide group in the molecular chain for the terminal amino group
The compound contained 182 mol%.

Reference Example 1 (Polyaddition Polymer of Polyester Polyol Derivative and MDI) 100 g of Polyester Polyol Derivative Obtained in Example 1
Is weighed into a 300 ml polypropylene cup and heated to 50 ° C. With the addition of 16.76 g of 4,4'-diphenylmethane diisocyanate [pure MDI, "Millionate MT" manufactured by Nippon Polyurethane Industry Co., Ltd.] melted at 50 ° C, with a propeller-type stirrer
Mix for 30 seconds. Then degas in a vacuum dessicator,
It was poured into an iron mold preheated to 100 ° C. The mold was placed in an oven at 110 ° C. and cured. Tack-free was 11 minutes. After 2 hours, the cured product was removed from the mold and subsequently post-cured at 110 ° C. for 16 hours. The 2 mm thick sheet thus obtained was a transparent, soft but strong elastomer. After curing at room temperature for 7 days, JI
The physical properties were measured according to S K6301 (hereinafter the same), and the results are shown in Table 1.

Reference Example 2 For comparison with the polymer of Reference Example 1, a polymer of the corresponding polyester polyol and MDI was synthesized. In order to match the molecular weight with that of the polyester polyol derivative used in Reference Example 1, two types of polycaprolactone polyol (PCL) having a molecular weight of about 2000 and about 1000 were blended and used as an average molecular weight of 1566. PCL 2000 (Daicel Chemical Industries'"Plaxel220", molecular weight 1959) 74.5 g and PCL
1000 ("Placcel 210" manufactured by Daicel Chemical Industries, molecular weight 9
88) Mixed polyol 100 with a liquid temperature of 50 ℃ blended with 25.5 g
A polymer was synthesized in the same manner as in Reference Example 1 using g and molten MDI (16.76 g) at 50 ° C. This reaction is slow to cure 1
There was a tack over time. After 2 hours, I tried to remove the mold, but it was too soft to remove, so I left it in the mold 110
Curing was continued for 16 hours at ℃, the mold was cooled, and then demolded. The sheet thus obtained was a transparent and soft elastomer. However, this sample is 3 at room temperature.
After 4 days it becomes opaque and after 7 days it has a hardness of 86 (JIS
A) has been reached. When this sample was heated at 50-60 ° C. for 20 minutes, it became transparent and soft again. When the hardness was measured after 1 hour at room temperature, it was found to be 56. This phenomenon is considered to be due to crystallization of the polyester component in the elastomer.

In the elastomer of Reference Example 1, no change in hardness due to such crystallization was observed. The physical properties of the sample of Reference Example 2 were measured after removing the crystal. The results are shown in Table 1.

Claims (2)

[Claims] 1. A polyester polyol derivative represented by the following general formula. R ₁ is O (oxygen element) in the chain with a C _2-6 alkylene group.
R ₂ which may have: C _1-10 alkylene group, C _2-6 alkynylene group or phenylene group n: 2 x: a value indicating an average valence, and 0 ≦ x ≦ (n- Number of 1) p, r: average value showing the number of repeating structural units, 0 ≦
Number of p, r ≤ m q: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≤ q ≤ 10, not the number of repetitions. m: positive number determined from molecular weight, p + r = m or R _3: an alkylene group of a straight-chain or branched _{C 3 to 6} R _4: a linear or branched divalent to tetravalent hydrocarbon group of _{C 2 to 6,} O in the chain of _{C 2 to 6} Removal of the terminal OH group from a polyester polyol or a divalent to tetravalent polyether group having a molecular weight of 3000 or less containing a linear or branched divalent to tetravalent hydrocarbon group having (oxygen element) as a repeating unit. The residue obtained by n: 2 x: a value showing an average valence, 0 ≦ x ≦ (n-1) number s, u, v: an average value showing the number of repeating structural units, 0
Number of ≦ s, u, v ≦ m t: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≦ t ≦ 10, not the number of repetitions. m: a positive number determined from the molecular weight, s + u + v = m (wherein each segment represents a ratio, not an order of bonding, and represents a —NHC ₆ H ₄ CO— group in the main chain. Is not a block but is bonded randomly, and may or may not be bonded to the terminal aminobenzoyl group). 2. Aminobenzoic acid alkyl ester based on 1 mol of an n-valent polyester polyol having a molecular weight of 400 to 10,000.
A method for producing a polyester polyol derivative represented by the following general formula, which comprises reacting 0.25n to 10nmol. R ₁ is O (oxygen element) in the chain with a C _2-6 alkylene group.
R ₂ which may have: C _1-10 alkylene group, C _2-6 alkynylene group or phenylene group n: 2 x: a value indicating an average valence, and 0 ≦ x ≦ (n- Number of 1) p, r: average value showing the number of repeating structural units, 0 ≦
Number of p, r ≤ m q: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≤ q ≤ 10, not the number of repetitions. m: positive number determined from molecular weight, p + r = m or R _3: an alkylene group of a straight-chain or branched _{C 3 to 6} R _4: a linear or branched divalent to tetravalent hydrocarbon group of _{C 2 to 6,} O in the chain of _{C 2 to 6} Removal of the terminal OH group from a polyester polyol or a divalent to tetravalent polyether group having a molecular weight of 3000 or less containing a linear or branched divalent to tetravalent hydrocarbon group having (oxygen element) as a repeating unit. The residue obtained by n: 2 x: a value showing an average valence, 0 ≦ x ≦ (n-1) number s, u, v: an average value showing the number of repeating structural units, 0
Number of ≦ s, u, v ≦ m t: Average value showing the number of structural units contained in one molecule, not the number of 0.05 ≦ t ≦ 10, not the number of repetitions. m: a positive number determined from the molecular weight, s + u + v = m (wherein each segment represents a ratio, not an order of bonding, and represents a —NHC ₆ H ₄ CO— group in the main chain. Is not a block but is bonded at random and may or may not be bonded to the terminal aminobenzoyl group.)