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iiililiili^ @ EuroPean Patent Office ^-S Office europeen des brevets (fi) Publication number : 0 559 404 A1

@ EUROPEAN PATENT APPLICATION

@ Application number : 93301510.9 @ Int. CI.5 : C08K 5/14, C08K 5/1 1 , C08G 69/44, C08G 69/48, (§) Date of filing : 26.02.93 A61L 1 7/00, A61 L 27/00, //(C08K5/14, C08L77:00), (C08K5/27, C08L77:00)

(30) Priority : 06.03.92 US 847969 (72) Inventor : Holy, Norman Lee 901 Cherry Lane Penns Park, Pennsylvania 18943 (US) @ Date of publication of application : Inventor : Bortnick, Newman Mayer 08.09.93 Bulletin 93/36 509 Oreland Mill Road Oreland, Pennsylvania 19075 (US)

(S) Designated Contracting States : DE ES FR GB IE IT PT @ Representative : Angell, David Whilton et al ROHM AND HAAS (UK) LTD. European Operations Patent Department Lennig House © Applicant : ROHM AND HAAS COMPANY 2 Mason's Avenue Independence Mall West Croydon CR9 3NB (GB) Philadelphia Pennsylvania 19105 (US)

(S) Degradable polyamides.

(57) Compositions comprising polyamide rendered hydrolytically labile by the incorporation of certain esters therein are useful in or as articles intended for degradation by water. Certain of the hydrolytically labile polyamides are novel compounds.

O

10 10

LU Jouve, 18, rue Saint-Denis, 75001 PARIS EP 0 559 404 A1

This invention is concerned with biodegradable polymeric articles and certain useful therein. The polymers and articles become brittle after long exposure to water and are especially useful as biodegradable and netting, degradable dishware, and degradable films for packaging. Another use of interest is in biological implants. 5 Japanese Kokai No. 56 022324 describes the production of alternate block copolymers of low molecular weight aliphatic and low molecular weight aliphatic polyamides by ester-amide interchange which are useful for mulch films biodegradable via enzyme digestion (Rhizopus delemar lipase). In this , the to polyamide ratio is high in polyester, for example, 4 to 1 mole % polyester to 6. Japanese Kokai No. 54 119594 describes the production of a biodegradable low molecular weight aliphatic 10 polyester amide alternate block copolymer from polycaprolactone and in the presence of zinc acetate. The polyester to polyamide ratio is near 1 to 1 . Again, the product polymer is subject to enzymatic (lipase) deg- radation. Japanese Kokai No. 54 120727 describes polyester polyamide block copolymers, high in the polyester component, which are useful for production of biodegradable films orf ibers. There is no mention of marine uses 15 of the copolymers. US-A3,592,873 describes the preparation of polyamide esters as interpolymers to provide thermal stability in polyoxymethylenes. The polyamide esters are prepared by reacting lactams oralkyl substituted lactams with at least a four membered ring with lactones or alkyl substituted lactones, again with at least a four membered ring. 20 JAppl. Polymer Sci., 24(7), 1701-11 (1979) describes the synthesis of copolyamide-esters via amideester interchange of polycaprolactone with nylon 6, 66, 69, 11 , 12, or 612. It also describes degradation of the poly- mers by Rhizopus delemar lipase digestion or alcoholic alkali . The effect of nylon/polycaprolactone ratio on the biodegradability was examined and biodegradability was found to decrease as the polyamide con- tent increased and/or as the polyamide blocks shortened. 25 Eur. Polym. J., 529-557 (1984) describes the preparation of copolyesteramides by anionic ring opening copolymerization of s- with s-caprolactone. Alternating copolymers or random multiblock copoly- mers with amide to ester ratios of 90/1 0 to 1 0/90 were prepared. In addition, the reference describes cleavage by alkaline hydrolysis as well as tensile properties of films and fabricated from the copolymers. Chemtech, 21_, 26-30 (January, 1991) describes the biodegradability of a variety of commercial 30 and compares their utility for medical applications. Medical uses are related to mechanical and degradative properties of many of the commercial materials. The combination of properties which polyamides (or, more specifically, ) exhibit make them ideal for use in fibers. Furthermore, nylon fibers have many properties which make them ideal for use in netting, including strength, light weight, and resistance to degradation, However, some of these desirable properties 35 also result in a significant environmental problem. The lifetime for nylon netting in the ocean has been estimated as over ten years; and may be closer to thirty years. Netting which has been abandoned either intentionally or by accident continues to capture marine fish and mammals. These "ghost" nets account for enormous kills offish, seals, whales, and dolphins. Seal deaths alone are estimated to be about 40,000 annually off the coast of Alaska alone. A similar situation is found in abandoned lobster traps where any captured lobsters are unable 40 to free themselves from the trap's netting. Analogous situations exist in fresh water lakes, many being contam- inated with fishing line either lost or abandoned. Commercial nylons are also used in biological implants. However, because of their biological inertness, uses are limited to those in which the implant is permanent or in which it can be mechanically removed. Polymers of lactic acid are well-known for their degradability under microbial attack. Acopolyester of lactic and 45 glycolic acid is used as a biodegradable suture in repairing soft tissue wounds. These polymers have also been used to fabricate degradable bone plate which is used to reinforce a broken bone during its healing period. There is no record of lactic acid/nylon copolymers being used in a similar manner. Oxalate substitution for units in nylon 66, or similar units in other bi-directional polyamides for the purpose of rendering the material more degradable is not reported. Oxalate esters are highly reactive hydrol- 50 ytically. Thus, incorporation of oxalate units into nylon provides sites for attack and chain cleavage, whether biologically or by simple hydrolysis. We have now found amide polymers which will degrade at a controlled rate in fresh or ocean water and which can be used as degradable nylon useful for biological implants or as degradable nylon film. The invention also provides a process for the efficient production of the degradable nylon. 55 The invention involves incorporating into a nylon, or reacting with a nylon precursor, an appropriate ester, cyclic ester, or polyester such that the ester functionality is incorporated into the polymer backbone. Incorporation can be accomplished via three major routes; reaction of preformed polymers, for example, nylon 6 with poly- caprolactone; reaction of a prepolymer with a , for example, nylon 6 with dimethylglycolide; orcopo- 2 EP 0 559 404 A1

lymerization of two , for example, caprolactam with caprolactone. We have discovered that by con- trolling the extent of incorporation, the desirable properties of the nylon are largely maintained while at the same time the nylon becomes subject to hydrolysis by water, presumably (although we are not to be bound by such theoretical considerations) at the incorporated ester functionality. These ester functionalities, which 5 are hydrolytically unstable, act as weak links. The strength of the nondegradable nylon is preserved. However, as the ester functionalities are hydrolyzed, the chain falls apart. The hydrolysis may be uncatalyzed, catalyzed by acids or bases, or biologically catalyzed. Furthermore, since the hydrolysis results in creation of an acidic polymer end group, it can also be autocatalyzed. As the polymer chain length becomes shorter due to the hydrolytic degradation, the nylon becomes em- 10 brittled and, therefore, weaker. Thus, netting produced from ester modified nylon fibers becomes so weak over time that the struggles of a captured animal are sufficient to break the fiber, freeing the animal; biological im- plants degrade at a rate commensurate with their replacement by normal tissue; and films degrade at a pre- determined rate. Although some of the explanation in this disclosure refers to nylon as the polymer, the invention is appli- 15 cable generally to polyamides. Novel hydrolytically labile polyamides of this invention comprise: (a) from about 80 to about 99.99 weight percent of polyamide, such as nylon, including nylons 6, 6/6, 6/12, 6/9, 6/10, 11, 12, 4/12, 12/12, and the like; and (b) from about 0.01 to about 20 weight percent (based on (a) plus (b) ) of ester comprising oxalate of formula I (bidirectional esters) and/or dimethylglycolide of formula II (unidir- 20 ectional esters):

00 J I Ri0_lLU_OR2 0^o^R2 I II

wherein R1 and R2 are the same or different radicals selected from hydrogen and - C20 alkyl such as, for 30 example, dibutyl oxalate, dimethyl oxalate, lactic acid cyclic dimer, and the like. The oxalate ester can also be in the form of a polymer (that is where the R1 and R2 radicals form connecting links between oxalate units). Examples of these polymeric oxalates include those wherein R1 and R2 are derived from ethylene glycol, pro- pylene glycol, 1 ,4-butanediol, and the like. The oxalate, oxalate polymer, or glycolide dimer is randomly incor- porated into the polyamide chain as single, diad, triad, or oligomeric units. This invention also extends to the 35 use in biodegradable articles of the novel polyamides or of polyamides which have been made hydrolytically labile by randomly incorporating into the polymer chains of the polyamide, singularly or in combination, of from about 0.01 to about 20 weight percent of alkyl ester selected from compounds of the formula III, IV, V, or VI;

40 u II HO-(CR1R2)n-C-OR3 -[-(CR1R2)n-C-0-]x- III IV

45

� O 0 R30-C— (CR1R2)n-C-OR3

V VI

wherein R1 and R2 are the same or different radicals selected from H, or C^-C4 alkyl; R3 is selected from hy- drogen or CrC2o alkyl; n is 1 - 10; m is 2 - 6; and x varies with the polymer molecular weight range; such as, for example, 3-hydroxybutyric esters, polycaprolactone, caprolactone, adipic esters, and the like. Furthermore, 55 the invention includes the use of copolymers of amide and esterfunctionally such as, for example, caprolactam with caprolactone, caprolactam with dimethylglycolide, adipic ester and with dimethyl oxalate, and the like. The polyamides with which this invention is concerned include any of the materials typically referred to 3 EP 0 559 404 A1

as nylons, both bi-directional (produced from dibasic acids and diamines) and unidirectional (produced from amino-substituted acids or lactams). Lactam monomers can also be used. Similarly, the ester can be bi-direc- tional such as, for example, dimethyl adipate, dibutyl oxalate, oxalic acid polymers such as those with ethylene glycol, propylene glycol, or 1 ,4-butanediol, or the ester can be unidirectional, such as caprolactone or a poly- 5 ester, such as polycaprolactone, , polyglycolic acid, or poly-3-hydroxybutyrate. Acids, esters, or polymers of a-, p-, or higher, hydroxy-substituted carboxylic acids can also be used. The ester can also be in the form of a glycolide, such as dimethylglycolide. The ester can be incorporated at up to 20 weight percent without substantially and negatively affecting the desirable properties of the nylon. However, ester levels of one to ten weight percent are preferred depending upon the degradation time desired. 10 The ester-amide interchange or derivatization is readily accomplished in a melt. Melt temperatures can be in the range of about 180°C to about 300°C. Preferred melt temperatures vary with the ester to be incorporated. For example, from about 240°C to about 280°C is preferred for polycaprolactone while from about 200°C to about 220°C is preferred for dimethylglycolide. In the case of extrusion, ester incorporation is dependent on the extent of mixing and the residence time in the extruder. Twin-screw extruders are generally preferred over 15 single-screw extruders because of the greater extent of mixing. The reaction can be catalyzed by acidic cat- alysts, such as tin octoate or zirconium acetylacetonate, or the like; by base catalysts, such a lithium or sodium t-butoxide, sodium or lithium hydride, and the like; or, when lactam monomers are used, their sodium or po- tassium salts. Acidic catalysts are preferred. Most preferred is zirconium acetyl acetonate which we have found to be unexpectedly efficient in reducing the time required for incorporation of the ester into the polyamide. Cat- 20 alyst level of 0.0% to about 0.5% can be used. However, levels of about 0.05% to about 0.2% are preferred. Most preferred is a level of about 0.1 %. The final polymer compositions can include typical additives known in the art, for example; impact modi- fiers such as ABS (acrylonitrile/butadiene/styrene), MBS (methyl methacrylate/butadiene/styrene), all acrylic types, and the like; fillers such a hydrated alumina, glass or other fiber reinforcements, talc or other minerals, 25 metallic particles, and the like; colorants (e.g. pigments and dyes), toners, and color agents or concentrates such as those described in the Color Index (Society of Dyers and Colourists, U.S.A.), including Pigment Black 7, Pigment White 6, Pigment White 21, Pigment Green 7, Pigment Blue 15, Solvent Orange 60, Solvent Red 179, Solvent Green 28, Solvent Blue 45, Solvent Blue 101, Solvent Violet 14, Disperse Yellow 54, toner Irisol N™ (1-p-toluidino-4-hydroxyanthraquinone), and the like; lubricants such as high molecular weight alcohols 30 (such as those with 12-24 carbons), esters (especially long-chain alkyl esters of high molecular weight acids including butyl orstearyl stearate), monoesters of glycols (such as ethylene glycol monostearate), and the like; antioxidants such as organophosphites (such as tris(aryl)- or tris(alkylaryl)- or tris(alkyl)-phosphites), organo- phosphonites (such as trisaryl-, trisalkaryl-, or aryldialkaryl-phosphonites); thioesters (such a dilauryl thiodi- propionate, ditridecyl thiodipropionate, and distearyl thiodipropionate), and the like; and ultraviolet stabilizers 35 such as hydroxybenzophenones, salicylate esters, benzotriazoles, hindered [such as bis-(2,2,6,6-tet- ramethyl-4-piperidinyl) sebacate, 2,2,6,6-tetramethyl-4-piperdinyl benzoate, 1 ,2,3,4-tetrakis-(2,2,6,6-tetrame- thyl-4-piperdinyl) butane-tetracarboxylate, 1,2-bis-(2-oxo-3,3,5,5-tetramethyl-1-piperdinyl)ethane, 1-(3,5-di- tert-butyl-4-hydroxyphenyl)-2,2-bis-(2,2,6,6-tetramethyl-4-piperidinyloxycarbonyl)hexane, poly(1-oxyethy- lene-(2,2,6,6-tetramethyl-1,4-piperidinyl)-oxysuccinyl, N,N'-bis-(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexa- 40 nediamine, and bis-(4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyl)ethane, and the like; blowing agents; flatting agents; antistatic agents; conductive materials; odor control agents; and the like. In addition, for items discarded on land, a hydrolytic mechanism of degradation may not be entirely effective simply because of a lack of sufficient humidity or water to promote degradation at an appropriate rate. To en- hance degradation under these conditions, a photosensitizer may be added to the degradable nylon. Photo- 45 chemically active organic materials such as, for example, benzophenone, Rose Bengal, and the like, or inor- ganic salts, such as salts of iron, nickel, cobalt, and the like, may be added. The polyester-amide copolymer can be fabricated into monofilament fibers, netting, films, biological im- plants, disposable dinnerware and utensils, and similar articles using standard techniques practiced by those familiar with the specific area. This invention is not to be construed as limited to any particular method of pre- 50 paring the fibers, netting, film, or implants. In the following Examples, which are given for the purposes of illustration only, "parts" are "parts by weight".

Examples 1 to 6 - Unidirectional polymer. 55 Pellets of commercially available nylon 6(Capron®8207; Allied Chemical Co.) were combined with dime- thylglycolide (DMG) and extruded by means of a Leistritz twin-screw extruder. The mixtures were extruded in a single pass. The amounts of each component used are found in Table 1. 4 EP 0 559 404 A1

Table 1

Nylon 6 DMG Catalyst

5 Ex.No. g. % g. % g. % 1 1500 100 2 1485 99 15 1 -

10 3 1455 97 45 3 - 4 1410 94 90 6 - 5 1453.5 96.9 45 3 1.5 0.1

15 Catalyst = Zirconium acetylacetonate Extruded strands were pelletized and the pellets were then injection molded into notched Izod bars. The Izod bars were exposed to 60°C. sea water for periods of 7, 14, 21 , 35, or 60 days and then tested for brittleness (Izod). Test results are in Table 2.

,n Table 2 Notched Izod Behavior Units - ft. lbs./ in. of notch

Ex. No. Day

25 H/C 7 14 21 35 60

% % % % %

1 H 100 24.00 100 24.52 100 23.29 80 24.74 100 24.65

30 c ------20 3.49 2 H 100 22.97 100 24.07 100 23.64 20 23.38 20 23.70

C ------80 7.85 80 2.65 35 3 H 100 22.65 80 23.29 40 21.72 60 22.21 40 23.11

C - - 20 4.28 60 3.59 40 3.14 60 1.85

4 H 60 16.77 40 21.01 - 40 C 40 3.80 60 3.37 100 2.35 100 3.06 100 1.27

5 H 100 20.90 40 17.63 ------

C - - 60 5.07 100 3.54 100 2.80 100 3.68 45 H = hinged break C = clean break

Test Interpretation 50 Example 1, which is unmodified nylon 6, shows almost no change in notched Izod results over the course of 60 days immersion in 60°C. sea water. However, copolymers formed by incorporation of dimethylglycolide into nylon 6 shown switch from hinged to clean breaks in notched Izod tests. These results are consistent with a material which gradually becomes 55 embrittled.

5 EP 0 559 404 A1

Example 7 - Bidirectional polymer

Dimethyl adipate (1 part), 1,6-hexanediamine (1.1 parts), and dimethyl oxalate (0.1 parts) were combined in a round bottom flask and then heated to 100°C. The mixture was stirred while methanol formed during re- 5 action was allowed to distill off slowly. When methanol distillation ceased, the temperature of the mixture was increased to 125°C. Upon cooling a solid polymer was obtained.

Example 8 - Catalyst Effect on Ester Incorporation

10 Nylon 6 (9 parts), polycaprolactone (1 part), and a catalyst (0.01 parts), all parts by weight, were combined and heated rapidly to 270°C. The temperature was then held constant at 270°C. Samples were periodically withdrawn and analyzed by differential scanning calorimetry (DSC). Overtime, the peak in the DSC plot due to polycaprolactone diminished and finally disappeared, reflecting full incorporation of the polycaprolactone into the nylon 6 backbone. Time to full incorporation, that is, disappearance of the polycaprolactone peak, for 15 three different catalysts is in Table 3. The significant advantage of the zirconium acetylacetonate catalyst is apparent.

Table 3

Time to Full 20 Catalyst Incorporation Tin(ll) octoate > 4 hours Zinc acetate > 3 hours

25 Zirconium acetylacetonate 1.5-2 hours

Claims 30 1. The use, in or as an article intended for degradation by water of a composition comprising (a) polyamide and (b) from 0.01 to 20 weight percent, based on polyamide, of one or more alkyl esters effectively ran- domly incorporated into said polyamide such that said polyamide is hydrolytically labile; wherein the alkyl ester is selected from compounds of the formula;

40

O o ii 45 HO-(CR1R2)n— C-OR3 _r_(CR1R2)n-O0-]x- III IV

50 o o R30-C— (CR1R2)n-C-OR3

V VI

55 wherein R1 and R2 are the same or different radicals selected from hydrogen and - C4 alkyl; R3 is se- lected from hydrogen or - C20 alkyl; n is 1 - 10; m is 2 - 6; and x varies with the polymer molecular weight range. 6 EP 0 559 404 A1

The use of Claim 1 wherein the alkyl ester is incorporated into the polyamide in an amount of from 0.05 to 5 weight percent by weight.

The use of Claim 1 or 2 wherein either the polyamide comprises unidirectional nylon, preferably nylon 6, and the alkyl ester comprises one or more compounds of formula II, III, IV, or V, preferably polycaprolac- tone and/or poly-3-hydroxybutyrate, or the hydrolytically labile polyamide comprises a copolymer of cap- rolactam and one or more alkyl esters of formula III or V.

The use of Claim 1, 2 or 3 wherein the composition further comprises photochemically active material and/or impact modifier polymer.

A hydrolytically labile polyamide suitable for use according to Claim 1 comprising: a. from 80 to 99.99 weight percent of polyamide, and b. from 0.01 to 20 weight percent of ester selected from oxalates of formula I and glycolides of formula II

O O

II

wherein R1 and R2 are the same or different radicals selected from hydrogen and - C20 alkyl; wherein the oxalate or glycolide is incorporated into the polyamide chain.

A hydrolytically labile polyamide of Claim 5 wherein (A) the polyamide is symmetrical and the ester com- prises an oxalate, preferably dibutyl oxalate or (B) the polyamide is nylon 6/6 and the ester is selected from an oxalate or a polymer of an oxalate and an alkanediol, preferably dibutyl oxalate; or (C) the poly- amide is unidirectional, preferably comprising nylon 6, and the ester comprises a glycolide, preferably di- methylglycolide.

A hydrolytically labile polyamide according to Claim 5 comprising random copolymer of dimethyl oxalate, dimethyl adipate, and hexamethylenediamine, or random copolymer of: a. from 80 to 99.99 weight percent of a lactam, and b. fromO.01 to 20 weight percent of a glycolide of formula II wherein R1 and R2arethe same or different radicals selected from hydrogen and - C20 alkyl.

Fishing line, fibre netting, film, or biological implant embodying the use as claimed in any of Claims 1 to 4 or containing polyamide as claimed in any of Claims 5 to 7.

A method of preparing a composition suitable for use according to any of Claims 1 to 4, preferably a com- position according to any of Claims 5 to 7, comprising melt blending the components in the presence of zirconium acetylacetonate catalyst. EP 0 559 404 A1

European Patent EUROPEAN SEARCH REPORT Application Number Office

EP 93 30 1510 DOCUMENTS CONSIDERED TO BE RELEVAN category I citation ot document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION qnt. CI, 5) US-A-4 209 607 (S.W. SHALABY et al.) C 08 K 5/14 DATA BASE WPI/DERWENT, AN=79-78351B C 08 K 5/11 (43), Derwent Publications Ltd, London, C 08 G 69/44 GB; & JP-A-54 119 594 (AGENCY OF IND. C 08 G 69/48 SCI. TECH.) 17-09-1979 (Cat. D) A 61 L 17/00 A 61 L 27/00 , U,A JOURNAL OF APPLIED POLYMER SCIENCE, (C 08 K 5/14 C 08 L 77:00 vol. 24, no. 7, 1st October 1979, pages ) 1701-1711, John Wiley & Sons, Inc.: Y. (C 08 K 5/27 T0KIWA et al.: "Synthesis of C 08 L 77:00 ) copolyamide-esters and some aspects involved in their hydrolysis by lipase"

EP-A-0 245 840 (H0ECHST)

IECHNICAL FIELDS SEARCHED (Int. CI.5)

C 08 K C 08 G C 08 L A 61 L

1 he present search report has been drawn up for all claims Place of search Date of completion of the search Examiner THE HAGUE 17-06-1993 LER0Y A J CATEGORY OF CITED DOCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application document of the same category L : document cited for other reasons A : technological background O : non-written disclosure & : member of the same patent family, corresponding P : intermediate document document