GB1594024A - Polyamide block copolymers - Google Patents

Description

(54) POLYAMIDE BLOCK COPOLYMERS (71) We, SUNTECH INC., a Corporation organised under the laws of the Commonwealth of Pennsylvania, United States of America, of 1608 Walnut Street, Philadelphia, Pennsylvania 19103, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of forming polyamide block copolymers.

The process of forming a block copolymer is mainly directed to the forming of a block copolymer of two different polyamides which may be used, after further processing, for example, as a fiber. The copolymer comprises blocks of many monomeric repeating units of each of the different polyamides. By way of comparison, a copolymer may comprise random sequences of repeating units of each of the different polyamides. The latter can be referred to as random copolymers. Furthermore, a block copolymer and a random copolymer formed from the same two different polyamides are known to possess different properties.

Block copolymers of polyamides and methods for preparing such copolymers have been proposed, for example, in U.S. Patent No. 3,683,047 (British Patent No. 1,492,048). One disclosed method for producing a block copolymer involves mixing two different polyamide polymers at a temperature above the amide-interchange temperature of the mixed polyamides until the block copolymer is formed. Thus if the aforementioned mixing at the specified temperature is of further duration, the resulting product is a random copolymer.

The molecular weight of each of the polyamides used to make a block copolymer via an amide-interchange can be relatively high, for example 50,000-100,000. At above the amide-interchange temperature, the exchange can occur between the two different polyamide molecules at any location where the

linkage exists. Thus, with two different polyamides, each of 50,000 molecular weight, the amide-interchange may occur right in the middle of the two molecules. A copolymer may then be formed with one block having a molecular weight of 25,000 and the other block having an equal molecular weight while the the copolymer still has a molecular weight of 50,000. Equally, the amide-interchange may occur towards one end of a polyamide and thus a copolymer may result having one segment, of say, 49,800 molecular weight derived from one polyamide, attached to another segment, of say, 200 molecular weight derived from the other polyamide. Because of the apparent lack of control of where the amide interchange will occur other methods have been suggested.

The above U.S. Patent No. 3,683,047 suggests using two different low molecular weight, i.e. 1000-4000 polyamides. The polyamides are different. in part, in that one is an aminoterminated polyamide whereas the other is a carboxylic-terminated polyamide. The other difference resides in that the balance of the polyamides are copolymerised at a temperature at which amide-interchange or transamination is nominal while the reaction of the amino-terminated groups with carboxylic-terminated groups occurs almost completely.

The resulting product is a block copolymer wherein the blocks have essentially a molecular weight of the starting polyamide, i.e. 1000-4000.

The aforementioned methods require separate preparation of each of the starting components followed by remelting and mixing to make a block copolymer. This is a disadvantage.

Contrary to expectations based on the prior art, we have now found that a block polyamide copolymer can be formed from a blend of prepolyamide salt and melt spinnable polyamide as the starting component. Thus, the separate preparation of one of the starting polyamides can be by-passed as well as its remelting.

In one embodiment, the block polyamide copolymer can be formed from a dry blend of prepolyamide salt and particles of melt-spinnable polyamide. The premelting of the polyamide can then be by-passed, so that the heating requirements are kept at a minimum.

In another embodiment the block polyamide copolymer is formed from the prepolyamide salt and a molten melt-spinnable polyamide as the starting components.

The present process involves mixing the dry salt and the polyamide at a temperature in the range of from the melting point of the higher melting component to below the amide-interchange temperture of a blend of the melt-spinnable polyamide and the homopolymer which would result from the polymerization of the salt. The mixing at the elevated temperature continues until substantially all of the salt and the polyamide are converted into a block copolymer.

The resulting block copolymer can be converted into a fiber or monofilament which can be further converted to yarn or fabric, for example.

Reference is now made to the accompanying Figure which is a graph showing generalized curves for various kinds of polyamides that have been fractionally precipitated from formic acid. The curves represent approximately the data reported in the Examples. Generally, the curves demonstrate that different kinds of polyamides can be characterized by fractional precipitation from formic acid.

One of the components used as a starting material in this process is a salt consisting of a prepolyamide represented by the following formula:

wherein Rl, R2 and R3. which may be the same or different consist of H, Cl-ClO alkyls or C3-C10 isoalkyls: R4 consists of a C,-C", alkylene or C3-C", isoalkylene; and R5 consists of a C6-C14 arylene, C1-C1( alkylene, C3-C", isoalkylene or a single bond.

The foregoing solid salt can be referred to as a prepolyamide because, upon heating under suitable conditions, the salt loses water and forms an

linkage to form a polyamide.

The other component used as a starting material in this process is a melt-spinnable polyamide. The term "melt-spinnable polyamide" as used herein excludes the polyamide which may be formed bv the aforementioned prepolyamide salt. Melt-spinnable refers to a process wherein the polymer, a polyamide, is heated to above its melting temperature and, while molten, forced through a spinneret. The latter is a plate containing from one to many thousands of orifices, through which the molten polymer is forced under pressure. The molten polymer is a continuous filament and. depending on the number of orifices, many filaments can be formed at the same time. The molten filaments are cooled, solidified, converged and finally collected on a bobbin. This technique is described in greater detail in ENCYCLOPEDIA OF POLYMER SCIENCE AND TECHNOLOGY, Vol. 8, Man Made Fibers. Manufacture.

Polyamides which are crystallizable and have at least a 3()0C difference between melting point and the temperature at which the molten polymer undergoes decomposition can be melt spun. Examples of melt-spinnable polyamides are as follows: nylon-6.6 (also known as poly(hexamethylene adipamide); nylon-6. 10 (poly(hexamethylene sebacamide));nylon-6 (poly(pentamethylene carbonamide)); nylon-ll (poly(dexamethylene carbonamide)); MXD-6 (poly((metaxylylene adipamide)); PACM-9 (bis(paraminocyclohexyl) methane azelamide)); PACM-10 (bis(paraminocyclohexyl)methane sebacamide)): and PACM-12 (bis(paraminocyclohexyl)methane dodecanoamide)). Others are listed in ENCYC LOPEDIA OF POLYMER SCIENCE AND TECHNOLOGY, Vol. 10, Section Polyamide Fibers, table 12. Methods for preparing these polyamides are well known and described in numerous patents and trade journals.

The amount of salt present relative to the amount of the melt-spinnable polyamide can vary within a broad range. If, however, too much of either component is used, then the resulting copolymer is not a block copolymer but is a copolymer consisting of mostly long chains of the most prevalent component bridged together by relatively short segments of the lesser component arranged in a statistically random fashion. Differences between a random and a block copolymer can be demonstrated by comparing the physical properties of the two. For this invention, an operative range of the amount of salt relative to the total weight of the components is from about 10 weight % to about 75 weight %, with from about 20 weight % to about 40 weight % being preferred.

The process involves blending the dry prepolyamide salt with dry particles of the melt-spinnable polyamide. The resulting blend is then heated in an inert atmosphere. The temperature to which it is heated is in the range of from the melting point of the higher melting component of the blend to below about the amide-interchange temperature of a blend of melt-spinnable polyamide and the polyamide which would result from the polymerization of the salt. The lower temperature is defined by the melting point of either the melt-spinnable polyamide or the salt whichever is the higher.

Alternatively, the prepolyamide salt may be mixed with the molten melt-spinnable polyamide in an inert atmosphere of e.g. nitrogen or carbon dioxide. The molten polyamide is prepared by heating it to a temperature above its melting point but below its decomposition temperature. It too is heated in an inert atmosphere. The resulting mixture of the salt and the molten melt-spinnable polyamide is heated to a temperature in the range of from the melting point of the higher melting component to below the amide-interchange temperature of a blend of the melt-spinnable polyamide and the polyamide which would result from the polymerization of the salt. The lower temperature is defined by the melting point of either the melt-spinnable polyamide or the salt whichever is the higher.

The upper temperature for the process is an amide-interchange temperature. In this process, one of the polyamides which can have such an interchange is the melt-spinnable polyamide. The other material may be a polyamide formed from the prepolyamide salt.

Thus, if the latter polyamide is formed and mixed with the melt-spinnable polyamide there will be a temperature below which amide-interchange will not occur between the two or be so nominal as not to result in the formation of a block copolymer. Amide-interchange refers to the reaction in which an

in one polyamide (labelled A in the following illustration ) reacts with a polyamide (labelled B in the following illustration) so that the following is representative of fhe end result:

Amide-interchange is the mechanism by which a block copolymer is formed by a process known as melt blending.

The mixture of the salt and the melt-spinnable polyamide, which is either a dry blend or a mixture of the molten polyamide and the salt, is mixed within the aforementioned temperature range and under an inert atmosphere. The mixing at the elevated temperature continues until substantially all of the salt and the polyamide are converted to a block copolymer. Samples of the mixture can be taken during processing and tested to determine when the conversion is essentially completed. One of the testing methods is described in the Examples.

When substantially all of the salt and the polyamide are converted to a block copolymer, the resulting copolymer can be represented by the following structure:

(bivalent ) (radical ) of melt + (spinnable) (polyamide)m wherein the R groups are as heretofore defined, and the subscripts n and m refer to the relative amounts of each present.

Thus, the percentage. nnm (i00). is within the range of from 10 weight % to 75 weight % for the operative range. Nominal amounts of unreacted salt or melt-spinnable polyamide can remain; however, its effect on the resulting properties of the block copolymer would be negligible. Furthermore, any unreacted component can be converted during further processing of the block copolymer, for example, conversion to a fiber. On the other hand, it can be removed by various means.

As shown in the foregoing structure for the block copolymer, the melt-spinnable polyamide is present in its bivalent radical form. The bivalence results from the coupling of H

andior -N-groups within the melt-spinnable polyamide with the

and/or H -CH2-N-H of the salt.

The following exmaples describe how certain block polyamide copolymers were prepared using the present invention. Also described are comparisons with block copolymers of similar polyamides prepared by other methods. Also, comparisons are made with polyamides and random polyamide copolymers.

The invention is illustrated by the following examples.

EXAMPLES A salt having the following structure: + + [NH3(CH2)3-O-(CH2)2-O-(CH2)3NH3]

which can be referred to as a 30203-6 salt, was used as a component and prepared in the following manner. First 1,2-bis( -cyanoethoxyethane), having the following structure: NC-(CH)2-O-(CH),-O(CH)2-CN, was prepared. To prepare it, a 5 liter double wallled (for water cooling) glass reactor with a bottom drain and a stopcock was charged with 930 grams (15 moles) of ethylene glycol and 45.6 grams of 40% aqueous KOH solution. 1620 grams (30.6 moles) of acrylonitrile (NC-CH=CH2) were then added dropwise with stirring at such a rate that the temperature was kept below 35"C. After the addition had been completed, the mixture was stirred for an additional hour and allowed to stand overnight.

The mixture was neutralized to a pH of 7 by the addition of 6 molar HCI. After washing with a saturated NaCl solution three times, the product was separated from the aqueous layer, dried over CACTI and passed through an Al2O3 column to ensure that all basic materials had been removed. The yield was 90% of the theoretical value.

The next step was the preparation of 4,7-dioxadecamethylenediamine (NH2(CH2)3-O (CH2)2-O-(CH2)3NH2). Into an 800 milliliter hydrogenation reactor were charged 150 grams of 1,2-bis(P-cyanoethoxyethane), 230 milliliters of dioxane and 50 grams of Raney Co. After purging the air, the reactor was pressurized with hydrogen up to 2000 p.s.i. and heated to 110 C. As the hydrogen was consumed, additional hydrogen was added until the pressure remained constant. Upon cooling, the pressure was released and the catalyst was filtered. The dioxane was removed by atmospheric distillation. The remaining mixture was distilled using a 3-foot spinning band distillation unit. The diamine distilled at 123-124"C and 3.75 mm Hg. About 98 grams of 99.95% pure material were obtained. The resulting material can be referred to as a 30203 diamine.

The next step was the preparation of the salt. To a solution of 41.50 grams of adipic acid dissolved in a mixture of 250 milliliters of isopropanol and 50 milliliters of ethanol were added, with stirring, 50 grams of the 30203 diamine dissolved in 200 milliliters of isopropanol. An exothermic reaction occurred. Upon cooling, a polymer salt crystallized out of solution. The salt was collected on a Buchner funnel and subsequently recrystallized from a mixture of 400 milliliters of ethanol and 300 milliliters of isopropanol solution. The product, dried in vacuo overnight at 60"C, had a melting point of 127-128"C and the pH of a 1% solution was 6.9. 85 grams (92% yield of the thoretical) of the salt were obtained.

The block copolymer was prepared in the following manner. Seventeen and one tenth grams of dry 30203-6 salt and 40 grams of dry, ground nylon-6 were dry blended in a suitable container using a ball mill roller. After blending, the resulting blend was added to a vessel fitted with a stirrer. The vessel and its contents were purged with dry nitrogen. The vessel was inserted into a vapour bath maintained at 2450C and kept under a positive pressure of nitrogen. Once the mixture had become molten it was stirred for one hour.

After cooling, the resulting block copolymer was analysed as to its structure.

Alternatively, the block copolymer was prepared in the following manner. A suitable container was purged with dry nitrogen and while under nitrogen 40 grams of dry powdered nylon-6 were added to the container. The nylon-6 was a commercially available material.

The container and its contents were heated to 245"C by means of a vapour bath. The nylon-6 used had an onset melting point of 210 C. To the molten nylon-6 were added 17.1 grams of the 30203-6 salt which had.previously been prepared. While the addition of the salt was made, the container was kept under a positive pressure of nitrogen and, during and after the addition, the resulting mixture was constantly stirred. The container and its contents were maintained at a temperature of 245"C for one hour. After cooling, the resulting polymer was analysed as to its structure.

The method used to analyse the polymer structure involved the fractional precipitation of the polymer in formic acid. Generally, the method was as follows: One gram of dry polymer (copolymer, random or block or homo) was weighed to the nearest tenth of a milligram.

The one gram sample was dissolved in a standardized formic acid (i.e. 90% formic acid).

The resulting solution was diluted with distilled water to a given % of formic acid, e.g. 55% formic. The solution was allowed to stand at ambient temperature for three hours and then filtered. The collected precipitate was then washed with water, dried and weighed to give the % sample recovered at that particular formic acid concentration. A graph was the constructed by plotting the % of the sample recovered vs. the formic acid concentration.

The different polymers, i.e. random copolymer, block copolymer, homopolymer (e.g. nylon-6) each have different solubilities in formic acid. Thus, each gave a different characteristic curve as shown in the accompanying drawing.

Table I below contains the recovery data for nylon-6, polymerized 30203-6 salt, a physical mixture of equal amounts of nylon-6, polymerized 30203-6 salt, and block 30203-6/16 polymer prepared by melt blending; and random 30203-6/6 copolymer. Also shown for the mixture are calculated values based on what the expected values would be based on the recovery curves for the individual polymers.

TABLE I Precipitation of Various Polyamides in Formic Acid % Formic Acid % Recovered Nylon 6+ Polymerized Mixture of Random 30203-6+ 3 Polyamides 30203-6/6 1 2 1 2 Observed Calculated 60 0 0 - - 0 0 57 - 0 - - - 56 95.4 - - - - 55 - 92.2 - - 36.1 31.9 0 50 96.5 93.8 - - 39.3 32.2 0.2 47 - - - - - - 0.4 45 97.5 95.1 - - 53.7 44.0 44 - - - - - - 5.1 41 - - - - - - 11.7 40 - - - - 61.4 61.1 38 - - - - - - 23.8 35 - - - - 62.2 62.1 32 - - - - - - 62.2 30 98.4 96.4 0 0 - - 29 - - - - - - 71.1 26 - - - - - - 79.7 25 - - - - 63.8 62.8 23 - - - - - - 81.5 20 - - - 0.4 63.9 63.3 82.8 15 - - 0.7 0.7 67.5 64.2 10 - - ** 47.8 69.6 69.4 5 - - 86.7 83.6 86.5 80.6 2 - - ** 89.4 86.5 81.0 Notes + Sample 1 based on 2 grams whereas sample 2 is based on 1 gram * Mixture consists of 1 gram each of nylon 6, polymerized 30203-6 and block 32203-6//6 ** Sample taken but result was believed to be erroneous.

Both in the data in Table I and the representative curve (LINE A) in the drawing show that almost all of the nylon-6 is recovered when the % of formic acid is decreased to about 55-56%. In contrast with the polymerized 30203-6 salt, represented by line F, none of the polyamide precipitates until the formic acid concentration is down to about 15%. The data for the polymerized salt are given in Table I.

Both the data in the Table I and the representative curve (line D) in the Figure, also indicate that the precipitation of a random 30203-6/6 copolymer does not occur until about a 45% of concentration of formic acid is reached. Furthermore, in contrast to the nylon-6, which has an almost perpendicular recovery line (except for the top portion), the slope of the recovery curve for the random copolyamide is much more gradual.

The DCS (Differential Scanning Calorimeter) curves for the block copolymers, prepared by this process, showed the absence of endothermic peaks corresponding to the melting of either the 30203-6 salt or the 30203-6 polymer. Further, the block copolymer prepared by this process had endothermics which corresponded to those shown by the 30203-6//6 block copolymers prepared by melt blending. Finally, the block copolymers had melting points more than 40"C above that observed for a random copolymer of the same overall composition. Thus, this comparison indicates that block polyamide copolymers can be prepared by this invention.

Some of the foregoing polymers were also characterized by DSC melting points. In particular, melting points were obtained for nylon-6, random 30203-6/6 and the block 30203-6//6 copolymers prepared by the invention. The DSC values and inherent viscosities are given in the accompanying Table II.

TABLE II PHYSICAL CONSTANTS DSC "C Inherent Material Onset Peak Viscosity Nylon-6 210 222 1.03 Random 30203-6/6 138 161 0.81 Block 30203-6//6 Sample 7 186 207 0.86 Sample 8 193 208 0.78 Differences between polymers in melting temperatures reflect differences in block sizes whereas differences in viscosities reflect differences in molecular weights.

Recovery line E represents what happens when a mechanical blend of nylon-6, polymerized 30203-6 salt, and block 30203-6//6 is precipitated from a solution in formic acid. The actual recovery data for the blend are almost equal to a calculated recovery amount based on the actual recovery data for the individual polymers when taking into consideration the amount of each polymer used to make the mechanical blend. The actual recovery data and calculated values are shown in Table I above.

In general then, the foregoing comparison of the different recovery curves for the different polaymides indicates that the different polymers can be characterized in their solubility in formic acid.

Table III below contains recovery data for four different block 30203-6//6 copolymers.

The latter, samples 3, 4, 5 and 6, were prepared bv the melt blend of nylon-6 and 30203-6 polymer for various lengths of time. Table III also contains the recovery data for two block 30203-6//6 copolymers, samples 7 and 8, prepared by this invention.

Comparison of recovery lines for 30203-6//6 copolymers prepared by melt blending with those of the present invention indicates that the latter method results in a block copolymer.

The recovery lines are representative lines B and C in the drawing. Line B represents a composite recovery curve of 30203-6//6 block copolymer prepared by melt blending 30203-6 polyamide and nylon-6 at 282"C for about 2-3 hours. Line C represents the recovery curve of a block copolymer prepared by this invention. The small difference between lines B and C is believed to represent an experimental difference rather than a difference of structure.

Changes in processing for either or both of the block copolymers could change the % recovery. Support for this resides in the fact that other block copolymers prepared by this invention have recovery curves which are to the left of Line B.

Analogous results, as described heretofore, will be obtained when different salts, other than a 30203-6 salt, such as 30403-6, 30603-8 and 31003-14 are used. Similar results will be obtained when other temperatures are used. Also, similar results will be obtained when some other C 3Cl,, alkylene or a C3-Cl,, isoalkylene or a C6-C14 arylene is used instead of the tetramethylene (R5) used in the example. Examples of the heretofore mentioned Cl-ClO alkylenes and C3-C,n isoalkylenes include ethylene, trimethylene, isopropylidene, isobutylidene, and the like. Examples of the heretofore mentioned C6-C14 arylenes include napththylene, phenylene, tolylene, and the like. The previously mentioned Cl-ClO alkyls include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and ecyl, and the use of such groups, instead of the hydrogen used in R1, R2 and R3, in the example, together with isoalkyls will also yield similar results. Use of any one of the aforementioned alkylenes or the isoalkylenes instead of the ethylene used in R4 in the example will also yield similar results.

TABLE 111 PRECIPITATION OF VARIOUS BLOCK POLYAMIDES IN FORMIC ACID % Formic Acid % Recovered Melt Blend 30203-6fl6* By this invention 30203-6//6+ 3 4 5 6 7 8 55 58.5 0 0 0 0 0 50 73.2 53.1 0 0 2.7 0 47 82.9 69.9 24.7 0.9 39.1 35.3 44 86.5 84.7 58.7 6.7 64.3 70.7 41 87.9 ** 77.7 62.2 79.5 82.2 38 88.5 89.9 85.2 72.5 82.9 35 88.9 92.2 88.5 79.2 85.8 89.0 32 89.5 93.1 89.5 82.5 88.4 91.6 29 90.0 93.5 90.5 86.1 88.5 92.3 26 90.7 93.5 91.6 ** 90.1 93.0 23 89.3 94.0 $* 90.6 93.1 20 90.1 94.5 93.3 87.6 90.6 94.9 * Samples prepared by melt blends of 70% nylon-6 and 30%30203-6 polymer. Samples 3, 4, 5 and 6 were melt blended at 283 C. for 15, 60 and 180 and 360 minutes, respectively.

Indicates sample taken but result was believed to be erroneous.

+ Samples prepared using 70% nylon-6 and 30% 30203-6 salt.

Claims (10)

WHAT WE CLAIM IS:

1. A process for forming a block polyamide copolymer comprising: (a) blending a melt-spinnable polaymide and a salt consisting of a prepolyamide represented by the formula:

wherein R1, R2 and R3, which may be the same or different, consist of H, C1- C10 alkyls or C3-C10 isoalkyls; R4 consists of C1-C10 alkylenes or C3-C10 isoalkylenes; and R5 consists of C6-C14 arylenes, C1-C10 alkylenes, C3-C10 isoalkylenes or a single bond, the salt content amounting to a value within the range of from 10% to 75 weight % of the total weight; (b) heating in an inert atmosphere the resulting blend of the salt and the polyamide to a temperature in the range of from the melting point of the higher melting component to below the amide-interchange temperature of a mix of the melt spinnable polyamide and polyamide which would result from the polymerization of the salt; and (c) mixing the heated blend at the aforementioned temperature and in the inert atmosphere until substantially all of the salt and the polyamide are converted to the block polyamide copolymer.

2. A process for forming a block polyamide copolymer comprising: (a) blending dry particles of a melt-spinnable polyamide and a dry salt consisting of a prepolyamide represented by the formula:

wherein R1, R2 and R3, which may be the same or different, consist of H, C1-C10 alkyls or C3-C10 isoalkyls; R4 consists of C1-C10 alkylenes or C3-C10 isoalkylenes; and R5 consists of C6-C14 arylenes, C1-C10 alkylenes, C3-C11) isoalkylenes or a single bond, the salt content amounting to a value within the range of from 10 weight % to 75 weight % of the total weight; (b) heating in an inert atmosphere the resulting blend of the salt and the polyamide to a temperature in the range of from the melting point of the higher melting component to below the amide-interchange temperature of a mix of the melt spinnable polyamide and polyamide which would result from the polymerization of the salt; and (c) mixing the heated blend at the aforementioned temperature and in the inert atmosphere until substantially all of the salt and the polyamide are converted to the block polyamide copolymer.

3. A process for forming a block polyamide copolymer comprising: (a) mixing in an inert atmosphere a molten melt spinnable polyamide and a dry salt consisting of a prepolyamide represented by the formula:

wherein R1, R2 and R3, which may be the same or different consist of H, C1-C10 alkyls and C3-C10 isoalkyls; R4 consists if a C1-C10 alkylene or C3-C10 or C3-C10 isoalkylene; and R5 consists of C6-C14 arylene, C1-C10 alkylene or C3-C10 isoalkylene; the salt content amounting to from 10 weight % to 75 weight % of the total weight; (b) heating and mixing in inert atmosphere the resulting mixture of the salt and the polyamide to a temperature in the range of from the melting point of the higher melting component to below the amide-interchange temperature of the blend of the melt spinnable polyamide and polyamide which would result from the polymerization of the salt; and (c) continuing mixing at the aforementioned temperature and in the inert atmosphere until substantially all of the salt and the polyamide is converted to the block polyamide copolymer.

4. A process according to any of claims 1 to 3, wherein the salt content is in the range of from 20 weight % to 40 weight % of the total weight.

5. A process according to any of claims 1 to 3, wherein R1 and R2 and R3 are H.

6. A process according to claim 5, wherein R4 is a C2 alkylene.

7. A process according to any of claims 1 to 6, wherein R5 is a C6 arylene.

8. A process according to any of claims 1 to 7, wherein the temperature of mixing is substantially 245"C.

9. A process according to claim 1 substantially as herein defined with reference to the accompanying drawing and/or any of the specific examples.

10. A block polyamide copolymer formed by a process as claimed in any of claims 1 to 9.