the polymers used in the preferred embodiments of the present invention are prepared by the polycondensation of dimethyl terephthalate , dimer acid , or preferably its diisopropyl ester and a polymethylene diol ( n = 4 to 8 , and preferably 4 ). ## str7 ## the preferred parent dimer acid of the diisopropyl ester utilized in the polymerizations is derived from high purity oleic acid and is formed by a clay catalyzed high pressure dimerization of the oleic acid in the presence of water . the mechanism of formation of the dimer acid is probably free radical in nature and the product is believed to consist of a mixture of acyclic unsaturated c 36 acids . the unsaturated materials are then hydrogenated and the dimer ester used in the present polymerizations possesses a slight degree of unsaturation as evidenced by an iodine number of 5 . in addition to the c 36 acids that make up the dimer acid there is present some monofunctional acid ( iso - stearic ) and a certain quantity of trifunctionality in terms of a &# 34 ; trimer ( c 54 ) acid .&# 34 ; the former may act as a chain terminator and the latter as crosslinking agent . detailed structures of the c 36 components of the dimer acid have not been elucidated as yet and the diacid is sometimes represented graphically as shown below ( with four almost equal branches ). ## str8 ## the reaction may be run in the absence or preferably in the presence of stabilizers taken from the types of hindered phenols or secondary aromatic amines . an example of the former is irganox 1098 sold by ciba - geigy [ n , n &# 39 ;- hexamethylene bis ( 3 , 5 - ditert - butyl - 4 - hydroxy hydrocinnamide )] and an example of the latter is naugard 445 sold by uniroyal [ 4 , 4 &# 39 ;- bis ( α , α - dimethylbenzyl ) diphenyl amine )]. oxides and alkoxides of numerous polyvalent metals may be employed as catalysts . a preferred catalyst for the polymerization is a mixture of 0 . 1 % tetrabutyl orthotitanate and 0 . 005 % magnesium acetate ( percentages based on total charge weight ). if a dyed end product is desired a compatible dye such as , for instance , d & amp ; c green # 6 can be added in suitable concentrations based on expected polymer yield . the polymerization is run in two stages . in the first stage , run under nitrogen at temperatures ranging from 160 ° to 250 ° c ., polycondensation via transesterification and esterification occurs resulting in oligomeric chains . these are converted to materials having a high degree of polymerization in the subsequent step run at 240 ° to 255 ° c ., at pressures of less than 1 mm of mercury . the resulting polymers exhibit inherent viscosities ( measured in hexafluoroisopropyl alcohol ) of 0 . 6 to 1 . 3 . the tm of the polymers , depending on composition , varies from 190 ° to 210 ° c . apparent viscosities at suitable extrusion temperatures vary from 2 × 10 3 to 9 × 10 3 poise . a summary of polymer properties is given in table i . the polymers may readily be extruded in a ram type extruder , such as , an instron capillary rheometer , at temperatures usually exceeding the polymer tm by 10 ° to 50 ° c . the resulting extrudate may be drawn , usually in a two - stage process using either two consecutive heated glycerine baths or a hot shoe followed by a subsequent glycerine bath . the draw ratio may vary from about 400 to 700 %. the oriented fibers exhibit properties that are quite unexpected . size 3 / 0 strands possess knot tensiles in the 35 - 40 × 10 3 psi range , straight tensiles in the 60 - 80 × 10 3 psi range and a young &# 39 ; s modulus of less than 150 × 10 3 psi . elongations range from 35 to 50 %. in summary , the polymers described lend themselves to ready extrusion and drawing to strong and supple fibers which are useful as flexible monofilament sutures . both stabilized and unstabilized fibers , upon co 60 sterilization ( 2 . 5 megarads ) suffer practically no losses in physical properties as judged by a comparison of inherent viscosities and tensile strength before and after sterilization . the unexpected retention of physical properties revealed by the unstabilized fibers presents a distinct advantage of the present invention over prior art . the desired amounts of dimethyl terephthalate , diisopropyl dimerate ( obtained from emery industries as emerest 2349 ), a 1 . 3 to 2 . 0 molar excess of a polymethylene diol and a given stabilizer are placed under nitrogen into a dry reactor fitted with an efficient mechanical stirrer , a gas inlet tube and a takeoff head for distillation . the system is heated under nitrogen to 160 ° and stirring is begun . to the homogeneous stirred solution the required amount of catalyst is added . the mixture is stirred and heated under nitrogen for given time periods at 190 ° c . ( 2 - 4 hours ) and 220 ° c . ( 1 - 3 hours ). the temperature is subsequently raised to 250 ° to 255 ° c . and over a period of 0 . 4 - 0 . 7 hours , the pressure is reduced in the system to below 1 mm / hg ( preferably in the range of 0 . 05 mm to 0 . 1 mm ). stirring and heating under the above conditions is continued to the completion of the polymerization . the endpoint is determined by either ( a ) estimating visually the attainment of maximum melt viscosity , ( b ) measuring inherent viscosity or melt indices of samples removed from the reaction vessel at intermediate time periods , and ( c ) using a calibrated torquemeter immersed into the mixture . in practice , depending on the terephthalate / dimerate ratio , in vacuo reaction times vary from 2 to 13 hours . at the end of the polymerization cycle the hot mixture is equilibrated with nitrogen and allowed to cool slowly . the reaction product is isolated , chilled in liquid nitrogen and ground . the ground chips are dried at 80 ° to 110 ° c . for 8 to 16 hours under vacuum of 1 mm or less and subsequently submitted for extrusion . extrusion through the instron rheometer is geared towards producing an extrudate which upon drawing ( 5 × to 7 × ratio ) yields a fiber in the 8 - 10 mil diameter range ( size 3 / 0 suture ). the polymers are packed at 110 ° to 130 ° c . in the extrusion chamber and extruded after a dwell time of 9 to 15 minutes through a 40 mil die . the ram speed is 2 cm / minute . extrusion temperatures depends both on the polymer tm and on the melt viscosity of the material at a given temperature ; usually extrusion proceeds at temperatures of 10 ° to 50 ° c . above the tm . die swells of up to 40 % are experienced by usually are much smaller ( 5 - 20 %); the extrudate is taken up at a speed of 18 feet per minute . the extrudate ( diameter range , 19 - 22 mm ) is passed through rollers at an input speed of four feet per minute onto a hot shoe or into a draw bath varied from 50 ° to 100 ° c . draw ratio in this first stage of operation vary from 5 × to 6 ×. the drawn fibers are placed over another set of rollers into a glycerine annealing bath ( second stage ) kept at temperatures ranging from 70 ° to 95 ° c . draw ratios for the second stage operation vary from 1 . 1 × to 1 . 25 ×. finally , the fiber is passed through a water wash bath and taken up on a spool . in the following examples inherent viscosity ( ninh ) is obtained for polymer solutions in hexafluoro - 2 - propanol ( hfip ) ( 1 g ./ 1 ). the infrared spectra are obtained for polymer films cast from chcl 3 or hfip . the nmr spectra are recorded for polymer samples in solution in 60 / 40 hexafluoroacetone sesquideuterium oxide . the glass transition ( tg ), crystallization ( tc ) and melting ( tm ) temperatures of the polymers in nitrogen are recorded , using a d . s . c . ( differential scanning calorimetry ) apparatus . the percent crystallinity is determined by x - ray . a hot - stage microscope is used to determine the melting behaviour of the polymers . fiber tensile properties are measured on an instron , model no . 1122 . steel faced jaws are used throughout . for the measurement of the young &# 39 ; s modulus , line contact jaws are applied . for straight tensile and moduli measurements a speed of 100 mm / min ., a chart speed of 200 mm / min . and a gauge length of 12 cm is employed . for knot tensiles the above parameters are 100 mm / min ., 100 mm / min . and 5 cm , respectively . the following materials are placed in a nitrogen glove box into a flamed , vacuum dried two - necked round bottom flask fitted with a stainless steel paddle shaped stirrer : the open neck is fitted with a rubber septum , the flask and stirrer assembly is removed from the glove box , attached to an efficient mechanical stirrer and placed into an oil bath heated at 160 ° c . after several minutes , the reaction mixture liquifies and mechanical stirring is started . the catalyst ( 1 . 0 ml ) consisting of 0 . 1 % tetrabutyl orthotitanate and 0 . 005 % magnesium acetate ( percentages based on total charge weight ) dissolved in a mixture of methanol and butanol is added through the septum to the reaction via a syringe . the septum is replaced by a short distilling head fitted with a receiver and a nitrogen inlet nozzle . the reaction mixture is heated under nitrogen at 190 ° c . for 3 hours and at 220 ° c . for 2 hours . as the methanol distillation ceases , the reaction temperature is increased to 250 ° c ., the receiver containing the distillate is replaced by an empty flask and gradually , over a period of 30 minutes , the pressure in the reaction setup is reduced to 0 . 08 mm . the mixture is heated at this pressure and at 250 ° c . for 4 hours . the hot viscous mass is equilibrated with nitrogen and allowed to cool to room temperature . the polymer is isolated , chilled and then ground . the polymer chips are dried for 8 hours under a good vacuum and a temperature of 80 ° c . properties of the polymer and of others prepared by similar reaction schemes are shown in table i ( see sample # 6 for above - described polymer ). the procedure of example i is followed , in all respects with the one exception that a like quantity of dimethyl isophthalate is substituted in place of the dimethyl terephthalate used in the initial reaction mixture . the final product is a poly ( tetramethylene dimerate coisophthalate ) polymer . the procedure of example i is followed in all respects , with the one exception that 52 . 4 g . of dimethyl cyclohexane - 1 , 4 - dicarboxylate is substituted in place of the 50 . 8 g . of the dimethyl terephthalate used in the initial reaction mixture . the final product is a poly ( tetramethylene dimerate co - cyclohexane - 1 , 4 - dicarboxylate ) polymer . ten grams of the copolymer described in example i are packed at 150 ° c . into the extrusion chamber of an instron rheometer and after 15 minutes of dwell time the sample is extruded at a ram speed of 2 cm / min ., a shear rate of 212 . 6 sec - 1 and a temperature of 250 ° c . the resulting melt viscosity is found to be 6178 poise . the takeup speed of the extrudate is 18 ft / min . and the extrudate is quenched in ice water . the diameter of extrudate is 21 . 0 mils . the extrudate is drawn at 5 × over a hot shoe held at a temperature of 99 ° c . and at 1 . 2 × through a glycerine bath kept at 95 ° c . the fiber is pulled through a water bath ( room temperature ) to remove the glycerine and taken up on a spool . the draw tension for both the first drawing stage is 420 g . and for the second stage 380 g . ; the total draw ratio is 6 . 0 ×. tensile data for fibers obtained in this and other runs are shown in table ii . fibers prepared from polymer # 9 ( table i ) are strung under a tension of 50 g . on an adjustable annealing rack . the adjustable bar is lowered about 10 % to allow the fibers to relax freely . after 16 hours the adjustable bar is raised to a height which is sufficient to straighten the fibers without imparting any tension ( 0 % relaxation ). the fibers are subjected to one hour of heating at 110 ° c . and then cut off the annealing rack . fibers annealed in this manner , upon exposure to free shrinkage ( 60 ° c ./ 2 . 5 hours ) shrink 2 . 3 % as opposed to 15 . 6 % for unannealed strands . copolymer x , which is the poly ( tetramethylene dimerate - co - terephthalate ) of example i of the hoeschele u . s . pat . no . 3 , 954 , 689 was prepared , the molar monomer ratio [ dimerate / terephthalate ] being 15 : 725 / 84 : 275 and the poly . ninh at 25 ° c . in hfip being 1 . 32 . in addition , homopolymer y , which comprises poly ( tetramethylene terephthalate ) [ pbt ] was prepared , the polyninh at 25 ° c . in hfip being 1 . 52 . polymers x and y were subjected to extrusion in the same manner as indicated in example iv , but the extrusion and orientation conditions were as follows : a 40 mil . die was used and the shear rate was 212 . 6 sec - 1 ______________________________________ copolymer x homopolymer y______________________________________1 . extrusion conditions temperature 240 ° c . 250 ° c . αapp ., sec . sup .- 1 212 . 6 212 . 6 ηapp ., poise 10 , 207 8 , 2732 . draw ratio 4 × at 72 ° c . 4 × at 71 ° c . 1 . 2 × at 90 ° c . 1 . 25 at 90 ° c . 3 . tensile properties tensile strength 71 , 657 psi 70 , 011 psi knot strength 28 , 427 psi 64 , 958 psi elongation 62 % 32 % young &# 39 ; s modulus 36 , 266 psi 398 , 953 psi______________________________________ table i__________________________________________________________________________synthesisand properties of poly ( tetramethylene dimerate co terephthalate ) polymers polymerizationmonomer % d & amp ; c reaction scheme poly . ηinhsample ratio * stabilizer green # 6 temp . pressure time at 25 ° c . m . p . ° c . no . d / t type ** ( by wt .) ° c . mm hg hours in hfip ( microscopy ) tm ° c . __________________________________________________________________________1 13 / 87 naugard 445 0 160 atm . n . sub . 2 0 . 2 0 . 90 not not ( 1 %) 190 &# 34 ; 3 . 0 available available 220 &# 34 ; 2 . 5 250 &# 34 ; 1 . 5 250 0 . 05 5 . 02 13 / 87 naugard 445 0 160 atm . n . sub . 2 0 . 2 0 . 98 195 - 197 196 ( 1 %) 190 &# 34 ; 3 . 0 220 &# 34 ; 2 . 5 250 &# 34 ; 1 . 5 250 0 . 05 2 . 03 13 / 87 naugard 445 0 160 atm . n . sub . 2 0 . 2 0 . 90 195 - 196 195 ( 1 %) 190 &# 34 ; 3 . 0 220 &# 34 ; 2 . 5 250 &# 34 ; 1 . 5 250 0 . 05 2 . 04 13 / 87 naugard 445 0 . 3 160 atm . n . sub . 2 0 . 2 1 . 17 197 - 199 194 ( 1 %) 190 &# 34 ; 3 . 0 220 &# 34 ; 2 . 5 250 &# 34 ; 1 . 5 250 0 . 05 4 . 05 12 / 88 naugard 445 0 . 3 160 atm . n . sub . 2 0 . 2 0 . 96 197 - 198 199 ( 1 %) 190 &# 34 ; 3 . 0 220 &# 34 ; 2 . 0 250 0 . 05 13 . 06 12 / 88 naugard 445 0 . 3 160 atm . n . sub . 2 0 . 2 1 . 21 197 - 198 199 ( 1 %) 190 &# 34 ; 3 . 0 220 &# 34 ; 2 . 0 250 0 . 05 4 . 07 12 / 88 naugard 445 0 160 atm . n . sub . 2 0 . 2 1 . 00 198 - 200 203 ( 1 %) 190 &# 34 ; 2 . 5 220 &# 34 ; 3 . 0 250 0 . 05 8 . 08 11 / 89 naugard 445 0 160 atm . n . sub . 2 0 . 2 0 . 63 203 - 208 204 ( 1 %) 190 &# 34 ; 3 . 5 220 &# 34 ; 1 . 8 250 &# 34 ; 1 . 5 250 0 . 05 5 . 39 10 / 90 naugard 445 0 160 atm . n . sub . 2 0 . 2 1 . 15 not not ( 1 %) 190 &# 34 ; 3 . 0 available available 220 &# 34 ; 2 . 0 250 0 . 05 7 . 510 10 / 90 naugard 445 0 . 3 160 atm . n . sub . 2 0 . 2 1 . 06 202 203 ( 1 %) 190 &# 34 ; 3 . 0 200 &# 34 ; 2 . 0 250 0 . 05 5 . 011 10 / 90 none 0 . 3 160 atm . n . sub . 2 0 . 2 1 . 08 202 - 203 202 190 &# 34 ; 3 . 0 220 &# 34 ; 2 . 0 250 0 . 08 4 . 012 10 / 90 irganox 1098 0 . 3 conditions same as in 1 . 24 202 - 203 205 ( 0 . 25 %) sample 11 . __________________________________________________________________________ * d = dimerate moiety ; t = terephthalate moiety . ** naugard 445 : 4 , 4 &# 39 ; bis ( α , dimethylbenzyl ) diphenyl amine irganox 1098 n , n &# 39 ;-- hexamethylene bis ( 3 , 5ditert - butyl - 4 - hydroxyhydrocinnamide ) table ii__________________________________________________________________________extrusion and drawing conditions andultimate tensile properties for fiber derived from dimerate co terephthalate ) polymersextrusion drawing conditions tensile propertiesconditions ratio t ° c . knot straight % y . m . sample ηapp 1st 2nd 1st 2nd dia . ( psi × ( psi × elong - ( psi × no . t ° c . ( poise ) stage stage stage stage ( mil ) 10 . sup .- 3 ) 10 . sup .- 3 ) ation 10 . sup .- 3 ) __________________________________________________________________________1 215 5587 5 × 1 . 3 × 52 75 9 . 2 35 . 1 69 . 8 49 79 . 62 210 5050 6 × 1 . 08 × 85 92 8 . 6 32 . 5 74 . 0 47 79 . 23 210 5050 6 × 1 . 08 × 85 92 8 . 6 35 . 3 67 . 0 42 82 . 34 230 7682 5 × 1 . 1 × 96 95 9 . 5 36 . 3 75 . 8 43 108 . 55 225 6124 5 × 1 . 2 × 99 95 9 . 7 35 . 5 71 . 2 55 60 . 06 250 6178 5 × 1 . 2 × 99 95 9 . 0 40 . 6 81 . 4 41 117 . 27 215 7198 5 × 1 . 15 × 85 92 9 . 1 41 . 2 70 . 9 40 134 . 28 215 1128 6 × 1 . 17 × 52 72 8 . 2 37 . 3 66 . 7 35 141 . 29 220 9616 5 × 1 . 2 × 85 90 9 . 1 38 . 7 82 . 1 42 147 . 710 215 6285 5 × 1 . 25 × 79 79 9 . 2 43 . 8 70 . 3 40 162 . 211 210 7735 5 × 1 . 25 × 82 79 9 . 4 39 . 9 57 . 3 37 125 . 812 235 8541 5 × -- 91 -- 9 . 8 41 . 1 62 . 6 48 138 . 9__________________________________________________________________________ the poly ( polymethylene terephthalate , isophthalate or cyclohexane - 1 , 4 - dicarboxylate - co - dimerate ) used in accordance with the present invention may be spun as multifilament yarn and woven or knitted to form sponges or gauze , ( or nonwoven sheets may be prepared ) or used in conjunction with other compressive structures as prosthetic devices within the body of a human or animal where it is desirable that the structure have high tensile strength and desirable levels of compliance and / or ductility . useful embodiments include tubes , including branched tubes , for artery , vein or intestinal repair , nerve splicing , tendon splicing , sheets for tying up and supporting damaged kidney , liver and other abdominal organs , protecting damaged surface areas such as abrasions , particularly major abrasions , or areas where the skin and underlying tissues are damaged or surgically removed . in more detail , the surgical and medical uses of the filaments of the present invention include , but are not necessarily limited to :
a flexible monofilament surgical suture having unique handling and knot tying characteristics . said suture comprises a drawn and oriented monofilament of a poly , having the following combination of mechanical properties : tensile strength -- at least about 60 , 000 psi knot strength -- at least about 35 , 000 psi young &# 39 ; s modulus -- between about 80 , 000 and 280 , 000 psi elongation -- from about 20 % to 80 %.