the polymer relative viscosity is measured by the ratio of the downflow time for a 1 % solution of the polymer in 97 . 5 % sulfuric acid to the downflow time for said sulfuric acid per se . a ubbelhode viscosimeter is used for the measurements . free amino groups are determined by acidimetric titration of a solution of the polymer in a phenolmethanol solution . as an end point indicator use can be made of thynol blue or of a conductimeter . total amino groups are determined dissolving the polymer in phenol , precipitating it by the addition of a water - acetone mixture , drying the precipitated polymer and titrating total amino groups as specified for free amino groups . carboxy groups are determined by alkalimetric titration on the polymer dissolved in benzyl alcohol . phenolphthalein is used as an indicator . polyethylene glycol content is determined by a thiosulfate titration of the iodine set free when the polymer is dissolved with warning in phoshoric acid and and sodium iodide . poise viscosity is determined with a melt indexer apparatus as described on astm d1238 - s7t at 260 ° c ., with a 0 . 1035 cm radius and 2 cm length capillary , at a speed gradient at the walls ( γ ) ≦ 10 sec - 1 . the amount of dyeing matter absorbed onto the fiber is determined using a ph 4 , with a 2 % solution of orange ii ( sandoz ). a sample of previously dried filament is kept in a conditioned ( t = 20 ° c ., relative moisture = 95 %) surrounding until it reaches a constant weight . saturation moisture content is determined by weight difference . preparation of a hydrophilic copolyamide having orderly ( a - b - a ) groups according to the invention . the formed thread properties are comparable to those of a regular polyamide thread , except that it shows a higher moisture sorption . 113 parts caprolactam , 3 . 39 parts water , 0 . 44 parts of acetic acid , 1 . 07 parts benzenesulfonic acid , 0 . 11 parts of 1 , 3 , 5 - trimethyl - 2 , 4 , 6 - tris -[ 3 , 5 - di - tert - butyl - 4 - hydroxybenzyl ] benzene , are warmed to 240 ° c . in a closed vessel provided with stirrer ; the autogeneous pressure is of at least 3 atm ., and such conditions are maintained for 2 hours . subsequently , the pressure is progressively decreased reaching a 250 mmhg residual pressure within 3 hours . the produced ( precursor ) polymer shows the following data : η r = 1 . 9 ; carboxy groups = 110 eq / 10 6 g ; m n ( average number molecular weight )= 10 , 000 . 10 . 27 parts polyethylene glycol of average m . w .= 2 , 000 , 0 . 23 parts potassium titanoxide oxalate dihydrate and 0 . 17 parts 1 , 3 , 5 - trimethyl - 2 , 4 , 6 - tris [ 3 , 5 - di - tert - butyl - hydroxybenzyl ] benzene are added to the reaction vessel . subsequently , pressure is progressively decreased to 0 . 3 mm hg and kept at this value for 3 hours . the cooled and granulated polymer is washed 4 times with 95 ° c . water ; after drying it shows the following data : ______________________________________relative moisture 0 . 02 % η . sub . rel 2 . 30η . sub . poise 3 , 700free amino groups 4 eq / 10 . sup . 6 gtotal amino groups 35 eq / 10 . sup . 6 gacid groups 33 eq / 10 . sup . 6 gpolyethylene glycol content 7 . 0 % conversion to ( a -- b -- a --) structure 70 %( calculated from the differencebetween polymer cooh and precursorcooh ) ______________________________________ the copolyamide was spun and stretched for comparison to polyamide 6 . the filaments show the following properties : ______________________________________ hydrophilic fiber made of the poly - polyamide 6 fiber &# 39 ; mer according tomeasures = 40 nh . sub . 2 this invention______________________________________titer d tex 77 . 7 76 . 1strength cn / tex 44 . 8 42 . 0modulus cn / tex 248 218elongation % 31 . 9 40 . 6shrinking in 100 ° c . water , % 12 . 6 12 . 8tinctorial absorp - tion to saturation % 2 2moisture % when satu - rated in a condition 8 . 7 15 . 4surrounding - 20 ° c .- rel . moist . 95 % ______________________________________ preparation of a hydrophylic copolyamide wherein amino groups - terminated peg is directly treated with adipic acid and water . the polymer obtained by reaction of diaminic peg and dicarboxylic polyamide shows random block distribution within the macromolecular chains : the properties ( modulus , % shrinkage ) of the filament are decidedly lower than for a comparable polyamide filament or ( a - b - a ) copolyamide filament of example 1 . 113 parts caprolactam , 3 . 39 parts water , 0 . 91 parts adipic acid , 10 . 27 parts terminal - amino - groups - modified - peg , 0 . 28 parts 1 , 3 , 5 - trimethyl - 2 , 4 , 6 ,- tris [ 3 , 5 - di - tert - butyl - 4 - hydroxybenzyl ] benzene are warmed to 240 ° c . in a closed vessel under stirring ; autogenous pressure is at least 3 atm . and such conditions are maintained for 2 hours . subsequently , pressure is steadily decreased in the vessel to reach a 250 mm hg residual pressure within 3 hours , and at this value it is maintained for 4 hours . the polymer is cooled and granulated , washed 4 times with 95 ° c . water ; after drying it shows the following characteristics : ______________________________________relative moisture 0 . 02 % η . sub . rel 2 . 40η . sub . poise 4 , 300amino groups 31 eq / 10 . sup . 6 gacid groups 37 eq / 10 . sup . 6 gpolyethylene glycol content 6 . 8 % ______________________________________ ______________________________________ hydrophilic fiber made of the polymer polyamide according to thismeasures 6 fiber example______________________________________titer d tex 77 . 7 76 . 2strength cn / tex 44 . 8 30 . 8modulus cn / tex 248 152elongation % 31 . 9 46 . 5shrinkage in h . sub . 2 o 12 . 6 16 . 4at 100 ° c . tinctorial absorp - tion to satura - 2 1 . 9tion % moisture % when sa - turated in a condi - tion surrounding - 8 . 7 14 . 7t 20 ° c .- rel . moisture 95 % ______________________________________ preparation of random block copolyamide , obtained adding polyethylene glycol 2 , 000 and esterification catalyst directly together with caprolactam : the obtained filament has mechanical and textile properties inferior to filament according to claim 1 . 113 parts caprolactam , 3 . 39 parts water , 0 . 44 parts acetic acid , 1 . 07 part benzenesulfonic acid , 0 . 28 parts 1 , 3 , 5 - trimethyl - 2 , 4 , 6 - tris [ 3 , 5 - di - tert - butyl - 4 - hydroxybenzyl ] benzene , 10 . 27parts polyethyleneglycol of 2 , 000 average molecular weight , 0 . 23 parts potassium titanoxide oxalate dihydrate are heated to 240 ° c . in a closed , stirred reaction vessel ; autogenous pressure is at least 3 atm , and such conditions are maintained for 2 hours . subsequently , pressure is steadily decreased in the vessel to reach 0 . 3 mm hg residual pressure within 5 hours and it is maintained at this level for 3 hours . the cooled and granulated polymer is washed 4 times with 95 ° c . water ; after drying it shows the following characteristics : ______________________________________relative moisture 0 . 02 % η . sub . rel 2 . 30η . sub . poise 4 , 500free amino groups 3 eq / 10 . sup . 6 gtotal amino groups 35 eq / 10 . sup . 6 gcarboxy groups 34 eq / 10 . sup . 6 gpeg content 7 . 1 % ______________________________________ the polymer was spun for comparison to polyamide 6 , and the obtained filament had the following characteristics : ______________________________________ hydrophilic fiber made of the polymer polyamide according to thismeasures 6 fiber example______________________________________titer d tex 77 . 7 76 . 0strength cn / tex 44 . 8 31 . 5modulus cn / tex 248 148elongation % 31 . 9 44 . 0shrinkage inh . sub . 2 o at 110 ° c . 12 . 6 17 . 2tinctorial ab - sorption to sa - 2 1 . 9turation % moisture % whensaturated in aconditioned sur - 8 . 7 14 . 5rounding - t 20 ° c . - rel . moist . 95 % ______________________________________ preparation of hydrophilic block copolyamide ( a - b - a ) with the use of tetravalent ti or zr catalyst . the polymer shows a high viscosity in the molten state and is unsuitable to be worked into filament . the procedure of example 1 is used , but employing titanium tetrabutoxide ( 0 . 22 parts ) and a zirconium tetraderivative ( 0 . 21 parts ). ______________________________________measures ti - derivative zr - derivative______________________________________relative moisture % 0 . 030 0 . 027η . sub . rel 2 . 37 2 . 35η . sub . poise 8 , 700 7 , 900free terminal amino groups 3 eq / 10 . sup . 6 g 3 eq / 10 . sup . 6 gtotal terminal aminogroups 35 eq / 10 . sup . 6 g 35 eq / 10 . sup . 6 gterminal acid groups 39 eq / 10 . sup . 6 g 40 eq / 10 . sup . 6 gpolyethylene glycol 7 . 2 % 7 . 4 % content______________________________________ the polymer was fed to the spinning machine . at 260 ° c . formining the polymer in a thread ( spinning test ) is impossible ; at 280 ° c . extrusion is feasible , but picking up the thread is impossible . preparation of hydrophilic ( a - b - a ) block copolyamide through coploycondensation of peg with polamide precursor having carboxy terminal groups : the filament has amino groups in an amount insufficient for dyeing . 100 parts of the obtained polyamide 6 terminating with dicarboxy groups as described in example 2 are reacted with 10 . 27 parts of m . w . 2 , 000 polyethylene glycol . the vessel , at 250 ° c . and under stirring , is smoothly brought down to a 0 . 3 mm hg residual pressure and kept under such conditions for 3 hours . once cooled and granulated , the polymer is washed 4 times with 95 ° c . water ; after drying it shows the following characteristics : ______________________________________ η . sub . rel 2 . 32 nh . sub . 2 2 eq / 10 . sup . 6 g cooh 45 eq / 10 . sup . 6 g peg % 7 . 3______________________________________ preparation of a hydrophilic polymer according to this invention but using a monocarboxy acid only ( ka of between 10 - 5 and 10 - 4 ): the produced thread is undyeable when using conventional methods adopted for polyamide fibers , evidencing that additional use of an acid of ka ≧ 10 - 1 as a m . w . regulator is necessary . 113 parts caprolactum , 3 . 39 parts water , 0 . 68 parts acetic acid , 0 . 11 parts of 1 , 3 , 5 - trimethyl - 2 , 4 , 6 - tris [ 3 , 5 - di - tert - butyl - 4 - hydroxybenzyl ] benzene are reacted according to the process of the invention as described in example 1 . the granulated polymer , after washing 4 times with 95 ° c . water and subsequent drying , shows the following characteristics : ______________________________________relative moisture % 0 . 03η . sub . rel in h . sub . 2 so . sub . 4 2 . 30η . sub . poise at 260 ° c . ( γ = 11 ) 1 , 900amino groups 9 eq / 10 . sup . 6 gacid groups 37 eq / 10 . sup . 6 gpolyethylene glycol content 7 . 4 % conversion to ( a -- b -- a --) structure ˜ 70 % ______________________________________ the polymer was spun and stretched as in example 1 and compared to polyamide 6 . the thread shows the same properties as thread of example 1 , but the obtained stocking is undyeable . evidence is seen that a reaction between carboxyterminated peg and hydrophilic amino - terminated copolyamide is hindered by thermal instability of the former ; the reation does not take place . 113 parts caprolactam , 3 . 39 parts water , 1 . 03 parts benzylamine , 0 . 11 parts of 1 , 3 , 5 - trimethyl - 2 , 4 , 6 - tris [ 3 , 5 - di - tert - butyl - 4 - hydroxybenzyl ] benzene are subjected to the process of example 1 , but with the use of carboxy - terminated polyethylene glycol in the same amount as for polyethylene glycol in example 1 . ______________________________________relative moisture 0 . 03 % η . sub . rel 2 . 07η . sub . poise 800amino groups 99 . 8 eq / 10 . sup . 6 gcarboxy groups 14 . 5 eq / 10 . sup . 6 gpeg content 7 . 4 % ______________________________________