CA1123984A

CA1123984A - Block copolymers of lactide and glycolide and surgical prosthesis therefrom

Info

Publication number: CA1123984A
Application number: CA314,425A
Authority: CA
Inventors: Yuzi Okuzumi
Original assignee: Ethicon Inc
Current assignee: Ethicon Inc
Priority date: 1977-11-16
Filing date: 1978-10-26
Publication date: 1982-05-18
Also published as: FR2409278A1; GB2008135B; FR2409278B1; DE2849785C2; GB2008135A; DE2849785A1

Abstract

ABSTRACT

High molecular weight block copolymers of L(-)-lactide and glycolide are prepared by reacting a high glycolide-low L(-)-lactide copolymer with a high L(-)-lactide-low glycolide copolymer in the presence of an ester interlinking agent. The block coploymer so obtained may be extruded to form filaments useful in the preparation of absorbable sutures.

Description

~ .23~

BACKGROUND OF THE INVENTION
Field of the Invention This invention relates to absorbable polymers of lactide and glycolide, and more particularly, to block co-polymers of lactide and glycolide wherein polymeric units are joined by an ester interlinking agent.
Descri~ption of the Prior Art Homopolymers and copolymers of lactide and glycolide are well-known in the preparation of synthetic absorbable sutures as disclosed, for example, in U.S. Patents Nos.
3,636,956, January 25, 1972, Allan K. Schneider, 2,703,316, March 1, 1955, Allan K. Schneider, and 3,468,853, Septen~er 23, 1969, E. E. Schmitt. Preferred polymers are polyglycolide or copolymers of glycolide with L(-)-lactide which are highly crystalline, fiber-forming materials that can be extruded into fibers and have good physical properties and reasonable absorption times when implanted in living animal tissue.
Copolymers of lactide and glycolide for use in the preparation of surgical sutures are presently limited to a narrow range of compositions, namely, those copolymers which - contain about 80 percent by weight of units derived from glycolide. Random copolymers containing less than about 80 percent of units derived from glycolide to about 40 percent of units derived from glycolide are found to be of low crystal-linity, and sutures prepared from such polymers are character-ized by low tensile strength and poor strength retention in living animal tissue. Polymers containing les,s than about 40 percent by weight of units derived from glycolide and up to 100 percent of units derived from lactide are fiber-forming and result in strong suture

-2-.

~L23~

materials, but tensile strength retention and/or the rate o absorption of such sutures in living animal tissue is typically less than preferred.
It is an object of the present invention to provide co-polymers of lactide and glycolide having from about 50 to 75 per-cent by weight of units derived from glycolide which are never-theless highly crystalline, fiber-orming materials. It is another object of this invention to provide absorbable sutures comprised of a copolymer of lactide and glycolide containing from about 50 to 75 percent of units derived from glycolide. It is a further object of thls invention to provide a method for preparing highly crystalline block polymers o lactide and glycolide containing from about 50 to 75 percent by weight o~
units derived from glycolide~

SUMMAR~

In accordance with the present invention, highly crys-talline, fiber-forming block copolymers of lactide and glycolide having from about 50 to 75 percent by weight of units derived from glycolide are obtained by admixing in a polymerization 2~ reactor and in the presence o an ester interlinking agent a polylactide or random copolymer of lactide/glycolide containing at least about 60 percent of lactide derived units, and a poly-glycolide or a random copolymer of lactide/glycolide containing at least about 80 percent of glycolide derived units. These polymer reactants are sometimes referred to hereinafter as ~'~ 239~3~

"prepolymers". The ratio of lactide to glycolide derived lmits in the prepolymers are selected to provide a final polymer prod- -uct having the desired overall composition of from about 50 to 75 percent glycolide derived units. ~he prepolymers and ester interlinking ayent are heated with agitation to a temperaturé
above the melting points of the two prepolymers and undér a dry, inert atmosphere until the ester interlinking reaction is com-plete.
m e resulting interlinked lactide/glycolide block co-polymers are characterizéd by having an inherent viscosity of atleast about 1.0 determined on a 0~1 g/dl solution in hexafluoro-isopropanol (~FIP) at 25C, a melting point of at least about 160C, and a crystallinity of at least about 15 percent. The block copolymers are melt extrudable to form continuous filaments useful in the preparation of surgical sutures. Such sutures are characterized by having a crystallinity of at least about 15 per-cent and inherent viscosity of at least 1.0, straight tensile and knot strengths of at least 40,000 psi and 30,000 psi, respec-tively; straight tensile strength retention in vivo of at least 30 percent after 14 days; and substantially complete absorption in vivo within about 180 days or less.
More specifically, the invention relates to a block copolymer of lactide and glycolide containing from 50 to 75 wt percent of units derived from glycolide which comprises a first polymer of polylactide or a copolymer of lactide and glycolide containing at least about 60 percent by weight of units derived from lactide, a second polymer of polyglycolide or a copolymer of lactide and glycolide containing at least about ~0 percent by weight of units derived from glycolide, and an ester inter-linking unit joining said first and second polymers, said interlinking unit having the formula O O
-- C --X --C --~ - 4 -wherein X is an alkylene or arylene radical, said block copolymer having an inherent viscosity determined as a 0.1 percent solution in hexafluoroisopropanol at 25C of at least about 1.0, a melt-ing point of at least about 160C and a crystallinity of at least about 15 percent.

~ESCRIPTIO~ OF DRAWINGS_ FIGURE 1 is a perspective view of a needle-suture combination, FIGURE 2 is a perspective view of a needle-suture combination within a hermetically sealed container;

; -4a -~, ~:1239~3~ ETH-436 FIGURE 3 illustrates a screw machined from the polymer of the present invention;
FIGURE 4 is a cross-sectional view of a composite yarn containing filaments of different composition; and FIGURE S is a plan view of a surgical fabric knitted from fibers of the present invention.

In the following description and examples, all parts and percentages are by weight unless otherwise specified.
The method of the present invention comprises a multistep polymerization process. In the first step there is prepared as a first prepolymer, a polylactide or a high lactide random co-polymer of optically active lactide and glycolide with the lac-tide derived component comprising at least about 60 percent and most preferably from about 60 to 80 percen~ of the composition.
The polymerization is carried out in a conventional manner using - a polymerization reactor equipped with heating and stirring means and in the presence o a polymerization catalyst such as stannous octoate. The polymerization is conducted with pure and dry re-actants and under an atmosphere of dry nitrogen at temE erature sufficient to maintain the reaction mixture in a molten state until the polymerization is complete. The preparation of random copolymers of lactide and glycolide is described in U.S. Patent~
~os. 3,636,956, January 25, 1972, Allan K. Schneider and

3,792,010, February 12, 1974, David Wasserman, particularly Ex-am~les XVII and VIII thereof respectively.

~3~

The second step of the polymerization method of the pre-sent invention consists of preparing as a second prepolymer a polyglycolide or high glycolide random copolymer of lactide and glycolide with the glycolide derived component comprising at least about 80 percent and most preferably from about 80 to 95 percent of the composition~ The polymerization is carried out in a conventional manner as described above.
The high lactide and high glycolide prepolymers from the.
first and second steps are then combined with an ester interlink-ing agent in a polymerization reactor equipped with heating andstirring means, and the interl.inkiny reaction is carried out under conditions whichare basically identical to those followed .in the preparation of the prepolymers. The temperature of the reactor is controlled to maintain the reactants in a molten state, and the reaction is conducted under a dry nitrogen atmosphere~
Following ompletion of the polymerization reaction, the block copolymer product is discharged, solidified by cooling, ground into a powder, and dried under vacuum.
As a permissible alternative, the high lactide prepolymer may be comprised of optically active L(-)-lactide or D(~-lactide with optically inactive d,l-lactide. For purposes OL clarity, the ensuing description and examplesrefer primarily to the poly-merization of I,(-)-lactide and glycolide in the first step, but it is understood that D(+)-lactide may be used in place of L(-)-lactide, and d,l-lactide may be used in place of glycolide.

~3~

The final block copolymer products of the present invention are generally extractable with chlorofoxm only to the extent of less than about 5 percent by weight. The poly-mers are thereby distinguished from simple mixtures of high lactide and high glycolide random copolymers having the same relative lactide~glycolide composition since, in such mixtures, the entire high lactide copol~mer portion is extractableO
The low level of extractables in the polymers of the present invention suggest that only a minor proportion of the individ-ual random prepolymer survive the ester interchange reactionO
The ester interlinking agents useful in the presentinvention include those selected from the group consisting of N-acylimide, ~-acyllactam of polycarboxylic acid such as ~,N'-terephthaloyl bis-phthalimide, ~,N-isophthaloyl bis-phthalimide~
N,M-terephthaloyl bis-succinimide, ~-N'-terephthaloyl bis-caprolactam and ~,N-terephthaloyl his-caprolactam and N,~t-isophthaloyl bis-caprolactam.
The preparation of N,N'-terephthaloyl bis-caprolactam is disclosed in U.S. Patent ~o. 2,682,526, June 29, 1954, Flory. The preparation of compounds such as N,~'-iso.phthaloyl bis-succinimide and ~, ~t -sebacyl phthàlimide is disclosed in U. S. Patent No.. 2,558,67$, June 26, 1951, Flory.
The amount of ester interlinking agent required for the reaction is generally from 0.01 to 5 percent by weight, and most generally from 0.1 to 5 percent by weight depending upon the relative molecular weights of the interlinkirlg agent and the two prepolymers.

~7~

~i23~ 4 ETH-436 The mechanism of the ester interlinking reaction is il-lustrated by the following general reaction whichl for purposes of clarity, utilizes polylactide and polyglycolide as the pre-polymers, it being understood that for purposes of the present invention, copolym~rs of lactide and glycolide as aforedescribed may be employed in place of these homopolymers.

O O
l~3 /C~
HO(COCHO)mH + H(OCH2CO)nOH + Y N - C - X - C - N Y
C O O C
O O
Polylactide Polyglycolide Interlinking Agent o H3 / ~
)m C X - C (OCE2CO) OH ~ 2Y NM
O O C

Lactide/Glycolide Block Copolymer wherein Y is an organic divalent radical such as arylene, alkylene, and alicyclic; X is an alkylene or arylene radical; and m and n are integers representing the degree of polymerization of the re-spective prepolymers.
As a specific example of the present invention, ~lock co-polymers are formed from prepolymers comprising random copolymers of lactide and glycolide using N,N'-isophthaloyl bis-phthalimide as the interlinking agent according to the following reaction, 1~23984 ETH-436 where "polymer A" is polylactide or a lactide/glycolide random copolymer containing at least about 60 percent units derived from lactide, and "polymer B" is a polyglycolide or a glycolide/lactide random copolymer containing at least about 80 percent units de rived from glycolide~

HO(polymer A)H + H(polymer B)OH
@-co ~ c l~ c 2~-co-~ t HO(polymer A) - C- ~ -C - ~polymer B)OH
O O

The reaction of the interlinking agent with the prepolyme.rs is extended if the normal carboxyl end groups of the prepolymers are first converted to hydroxy end groups to obtain bifunction-ally hydroxy terminated polymers. This can be accomplished by the use of a diol such as ethylene glycol, diethylene glycol, 1,3-propane diol, or glycerine as a chain transfer agent during the preparation of the prepolymers. ~his reaction is illus-trated with respect to polyglycolide as follows:

~23~

o ' ~2C o I ¦ ~ HO - C~2 - C~12 - 0~ -O-C~ ~o .

H(ocH2co)nocH2cH2oH

The bifunctionally terminated polyesters undergo reaction ; with the ester interlinking agent, according to the following s general equation;

H(polymer A)mOROH ~ H(polymer s)nOROH

O O
~, 11 11 C~ / C~
Y N - C - X - C ~ N Y
11 ~1 C O O C
1~ 11 O O

HOE~polymer A)mORO - C - X - C - ~polymer B)nORO - C - X - C -]z-(polymer A)O~
O O O O

+ Y NH
C
O

~z3~ 4 ETH-436 wherein R is a di~alent alkylene or alicyclic radical derived from the diol chain transfer agent, m and n are as defined above, and z is an integer indicating the degree of polymeriza-tion resulting from the ester interchange reaction. In the above equation, it is understood that polymers "A" and "B" do not necessarily alternate in the polymer chain but may appear in any random sequence. It is further understood that not all the carboxyl end groups of all the prepolymers are necessarily con-verted to hydroxyl groups, and that the nonconverted prepolymers may act as chain terminating groups as indicated in the above equation.
The method and block copolymer compositions of the pre-sent invention are further illustrated by the following examples.
In the examples, inherent viscosity (~inh) was determined at 25C on 0.1 g/dl solutions of polymer in hexafluoroisopropanol ~HFIP). Melting tamperature (Tm) was determined with a DuPont 990 DSC apparatus using 4 mg samples and a heating rate of lO~C/min. Crystallinity was determined by the method of Hermans and Weidinger.

3~

9.58 g of L(-)-lactidel 68.7 ~ glycolide, 0.07 g di-ethylene glycol and 0.4 ml of 0.033 molar solution of stannous octoate catalyst in toluene were placed in a reactor. The mix-ture was heated to 200C under a nitrogen atmosphere with con-stant agitation and maintained at 200C for one-half hour, then raised to 235C. A viscous random copolymer of 10 mole percent L(-)-lactide and 90 mole percent glycolide was formed. To this high glycolide copolymer, 72.8 g of poly~L(-)-lactide-co-glycolide] copolymer prepared from 65 mole percent of L(-)-lactide and 35 mole percent of glycolide was added. After the copolymers were completely molten, 2.26 g (1.5 wt percent) of N,N'-isophthaloyl bis-phthalimide was added. The reaction mixture was stixred for 25 minutes at 235C, and the product discharged from the reactor. ~he thus obtained block copolymer consisted of about 40 w~ percent of u~its deri~ed from L(-)-lactide and 60 wt percent of units derived from glycolide and possessed an inherent viscosity of 1.56 and a melting temperature of 195C.
The block copolymer was dried and extruded as a monofila-ment employing an Instron Rheometer at 235C. The monofilamentwas drawn 6 times at 70C. The drawn filament possessed a dia-meter of 8 mils, straight break strength of 71,000 psi, elonga-tion at break of 37 percent, and knot break strength of 37,000psi.
The drawn fila~ent was annealed at 90C for 6 hours under a nitrogen atmosphere~ and sterili~ed with ethylene oxide gas.
Short lengths of the sterile filament were subcutaneously im-planted in rats to determine in vivo, the tensile strength reten-tion and absorption. The results are set forth in the following:

* Trademark . i ~

1~2398~ ETH-436 Original Break Strength Remaining ~fter:
7 days 14 days 21 days 78% 42% 9~

Absorption: Percent of Filament Mass Remaining After:
8 weeks 12 weeks 16 weeks 40~ 4% 0%

EXAMPLES 2 to 13 Block copolymerization, extrusion, drawing, annealing, sterilization, and implantat~ons in rats were carried out under similar conditions as described in Example 1, except the high ; lactide copolymer composition, high glycolide copolymer composi-tion, the overall lactide to glycolide ratios and the amount and kind of interlinking agent were varied or changed. Results are summarized in the following Tables I to III. Table I pertains to the block copolymer and the composition thereof. Table II summa-rixes the monofilament properties while Table ITI deals with the n vivo tests with rats.

A block copolymer was prepared in the same mannex as de-scribed in Example 1, except 1.0 percent by weight of N-N'~
terephthaloyl bis-caprolactam was used as the ester interlinking agent. The inal product possessed an inherent viscosity of 1.47.

~3~84 _ __ __ _ _ _ __ '~ a~ a~ ~~ ~1 L~ ~~ Ln l r- In CO
__ ~ _ ..__ _ _ _ 8 ~ ~ c~. ~ ~ ~ ~ ~ ~ ~ u~
.~ __ __ __ ___ ~1 ~ ~0 ~) ~'1 ~n N ~ l l t'`l 1--l ~ el~
j~_ ~i _ N _ N ~ _ _ _ _ _ _ ~`i ~ ~ ~ ~ t~ ~ ~ N ~ ~ N
.~ . - - - - - -_ ___ ~ _~ __ P~ H _ ~ __ ~ _ '~ ~ NN ~ N 11~ O ~ O ;~ O ~ ~

o ~N 1~ ~ U ~ O r~ 117 3 o I ~ o ~ ~ ~
~ & _ _ _ _ _ ~ ~

O ~ ~ ~ o o o o o o o o ~ ~ o ~
~ ;~ ~ :~
O __ _ _ _ _ ;~
O I ~ ~ ~ ~ f~) N O ~`J 10 rt lD ~ eS~ ~ ~D r~ _ _ m & _ _ __ _ __ _ ~ z z ~ ~' ~ ~ O ~ ~ ~ ~ ~ In U~ ~ ~0 .~
.~ ~ t`
_ _ _ _ __ .. ~ ~ ~r u~ ~ ~ _ _ ~ ~1 ~z3~ ~ ETH-436 TAB~E II

Example ~onofilament Properties No. _ _ _ _ __ ._ _ Dia- DrawStraigh~ Elonga- Knot meter ratiobreak tion break mils stxength ~ strength3 psi 103 pSi 10 ; 4 8 6 106 58 74 7 ~ 5 53 63 34 . 5 76 75 42 11 10 5 7~ 37 36 13 . 8 6 10~ ~1 77 _ _ _ _ ~ 39 ~ 4 ETH-436 TABLE III

Example Subcutaneous Implantation in Rats No. _ _ _ _ _ _ _ _ _ Percent original break Percent original ilament strength remaining remaining unabsorbed 7 1~ 21 8 12 16 20 days daysdays wks wks wks wks

4 ~9 49 0 19 0 h 74 30 0 12Trace 0 :7 78 42 9 40 ~ 0 8 8~ 64 5 58 21 - 0 ; :~ 9 77 43 5 Trace 0 11 49 8 0 92 32 - Trace ~ 39~ ETH-436 It is to be understood that inert additives such as coloring materials and plasticizers can be incorporated with the polymers of the present invention. As used herein, the term "inert" means materials that are chemically inert to the polymer, S and biologically inert to living tissue, i.e., do not cause any of the adverse effects previously discussed~ Any of a variety of plasticizers such as, for instance, glyceryl triacetate, ethyl benzoate, diethyl phthalate~ dibutyl phthalate, and bis-2-methoxyethyl phthalate can be used if desired. The amount of plasticizer may vary from 1 to about 2~ percent or more based on the weight of the polymer. Not only does the plasticizer render the filaments of the present invention even more pliable, it also serves as a processing aid in extrusion and thread preparation.
In addition, mixtures of the block copolymers o the present in-vention with up to about 50 percent by weight of other compat-ible nontoxic and absorbable polymers are also useful in the preparation o absorbable sutures and other medical devices in accordance with the present invention.
Block copolymers of the present invention are ad~ersely affected by moisture, and filaments and sutures prepared rom these polymers are accordingly preferably dried to a substantial-ly moisture-free condition and stored in dry, hermetically sealed packages, a preferred form o~ which is shown in the drawing as FIGURE 2. In FIGURE 2/ there is shown a suture package 14 having ~ ~3~ ETH-436 disposed therein a coil of suture 12, one end of which is at-tached to needle 13. The needle and suture are positioned within a cavity 16 that is evacuated or filled with a dry a~mosphere of air or nitrogen. The illustrated packa~e is fabricated of two S sheets of aluminum foil or an aluminum foil-plastic laminate and heat sealed or bonded with adhesive at the skirt 16 to hermeti-cally seal the cavity and isolate ~he contents of the package from the external atmosphere.
Filaments of the present invention may be used as mono-filament or multifilamen~ sutu~es, or may be woven, braided, orknitted either alone or in combination with othex absorbable fibers such as poly(alkylene oxalate), polyglycolide or poly(lactide-co-glycolide), or with nonabsorbable fibers such as nylon, polypropylene, polyethyleneterephthalate, or polytetra-fluoroethylene to form surgical nets, fabrics and tubular struc-tures having use in the repair of or~ans, arteries, veins, ducts, esophagi and the like.
FIGURES 3 and 5 show various types of prosthesis that might be made with the filaments of the present invention. In FigurP 3 there is shown a screw 11 and in Figure 5 there is shown a knitted ~abric 21.
~ ultifilament yarns that contain the absorbable lactide-co-glycolide filaments of the present invention together with nonabsorbable filaments are illustrated in FIGU~E 4 wherein the nonabsorbable fiber is represented by the hatched fiber cross section 19. In FIGURE 4, the fibers 20 are Pxtruded from poly-mer compositions of the present invention as described above.
The relative proportions of absorbable filaments 20 and nonab-sorbable filaments 19 may be varied to obtain the absorption characteristic desired in the woven fabric or tubular implants.
.

Composite fabrics of absorbable and nonabsorbable mate-rials fashioned by textile processes including weaving, knitting, and nonwoven felting are described in U.S. Patent Nos. 3,108,357, October 29, 1963, W. J. Liebig, and 3,463,158, August 26, 1969, E. E. Schmitt. Methods of weaving and crimping tubular vascular prostheses are described in U.S. Patent ~o. 3,096,560, July 9, 1963, W. J. Liebig. Similar techniques may be used in the manufacture of surgical aids wherein nonabsorbable fibers are combined with absorbable fibers composed of the polymers of 10 this invention. The surgical utility of `'bicomponent filaments'`
containing absorbable and nonabsorbable components is described in U.S. Patent No. 3,463,158. Monofilamerlts 21 of the poly-mers of -the present invention may be woven or l~nitted to form an absorbable fabric having the structure illustrated in FIGURE

5, useful surgically in hernia repair and in supporting damaged liver, kidney and other internal organs The polymers of the present invention are also useful in the manufacture of cast films and other solid surgical aids such as scleral buckling prostheses. Thus, cylindrical pins, 20 screws 11 as illustrated in FIGURE 3, reinforcing plates, etc., may be machined from the cast polymer having in vivo absorption characteristics depending upon the polymer composition and molecular weight.
Many different emhodiments of this invention will be apparent to those skilled in the art and may be made without departing from the spirit and scope thereof. It is accordingly understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims

The embodiments of the invention in whcih an exclusive property or privilege is claimed are defined as follows:

1. A block copolymer of lactide and glycolide contain-ing from 50 to 75 wt percent of units derived from glycolide which comprises a first polymer of polylactide or a copolymer of lactide and glycolide containing at least about 60 percent by weight of units derived from lactide, a second polymer of poly-glycolide or a copolymer of lactide and glycolide containing at least about 80 percent by weight of units derived from glycolide, and an ester interlinking unit joining said first and second polymers, said interlinking unit having the formula wherein X is an alkylene or arylene radical, said block copolymer having an inherent viscosity determined as a 0.1 percent solution in hexafluoroisopropanol at 25°C of at least about 1.0, a melt-ing point of at least about 160°C and a crystallinity of at least about 15 percent.

2. The polymer of Claim 1 wherein said first polymer comprises a copolymer having from 60 to 80 wt percent of units derived from L(-)-lactide and from 20 to 40 wt percent units de-rived from glycolide.

3. The polymer of Claim 1 wherein the second polymer comprises a copolymer having from 5 to 20 wt percent of units de-rived from L(-)-lactide and from 80 to 95 wt percent of units de-rived from glycolide.

4. The polymer of Claim 1 wherein the interlinking unit has the formula

5. A synthetic absorbable suture comprising at least one drawn and oriented filament of the block copolymer of Claim 1.

6. A polymer of Claim 1 wherein the normal carboxyl end groups of said first and second polymers are converted to hydroxyl end groups and said first and second polymers are joined to said interlinking unit through said hydroxyl end groups.

7. A polymer of Claim 6 wherein said hydroxyl end groups are derived from an alkylene or alicyclic diol.

8. A polymer of Claim 7 wherein said diol is selected from the group consisting of ethylene diol, diethylene diol, 1,3-propane diol, glycolic acid and glycerine.

9. A surgical prosthesis comprising a fabric manufac-tured at least in part from synthetic absorbable fibers compris-ing drawn and oriented filaments of a block copolymer of Claim 1.

10. A surgical prosthesis comprising a solid surgical aid cast or machined from an absorbable polymer comprising a block copolymer of Claim 1.

11. An absorbable surgical suture of Claim 5, comprising at least one drawn and oriented filament of a crystalline co-polymer of lactide and glycolide containing from about 50 to 75 percent of units derived from glycolide, said suture having a crystallinity of at least 15 percent, an inherent viscosity of at least 1.0 as determined on a 0.1 percent solution in hexa-fluoroisopropanol at 25°C, a straight tensile and knot strength of at least 40,000 psi and 30,000 psi respectively, straight tensile strength retention in vivo of at least 30 percent after 14 days, and substantially complete absorption in vivo within about 180 days.

12. A block copolymer of lactide and glycolide contain-ing from 50 to 75 wt percent of units derived from glycolide which comprises a first copolymer of an optically active lactide and an optically inactive lactide containing from about 60 to 80 percent by weight of units derived from optically active lactide, a second copolymer of lactide and glycolide containing from about 80 to 95 percent by weight of units derived fxom glycolide, and an ester interlinking unit joining said first and second copolymers, said interlinking unit having the formula wherein X is an alkylene or arylene radical, said block copolymer having an inherent viscosity determined as a 0.1 percent solution in hexafluoroisopropanol at 25°C of at least about 1,0, a melt-ing point of at least about 160°C and a crystallinity of at least about 15 percent.

13. The polymer of Claim 12 wherein the optically active lactide is L(-)-lactide or D(+)-lactide and the optically inac-tive lactide is d,l-lactide.

14. The polymer of Claim 12 wherein the second copolymer comprises from 5 to 20 wt percent of units derived from L(-)-lactide and from 80 to 95 wt percent of units derived from glycolide.

15. The polymer of Claim 12 wherein the interlinking unit has the formula

16. A polymer of Claim 12 wherein the normal carboxyl end groups of said first and second polymers are converted to hydroxyl end groups and said first and second polymers are joined to said interlinking unit through said hydroxyl end groups.

17. A polymer of Claim 16 wherein said hydroxyl end groups are derived from an alkylene or alicyclic diol.

18. A polymer of Claim 17 wherein said diol is selected from the group consisting of ethylene diol, diethylene diol, 1,3-propane diol, glycolic acid and glycerine.

19. A synthetic absorbable suture comprising at least one drawn and oriented filament of the block copolymer of Claim 12.

20. A surgical prosthesis comprising a fabric manufac-tured at least in part from synthetic absorbable fibers compris-ing drawn and oriented filaments of a block copolymer of Claim 12.

21. A surgical prosthesis comprising a solid surgical aid cast or machined from an absorbable polymer comprising a block copolymer of Claim 12.

22. An absorbable surgical suture of Claim 19, compris-ing at least one drawn and oriented filament of a crystalline co-polymer of lactide and glycolide containing from about 50 to 75 percent of units derived from glycolide, said suture having a crystallinity of at least 15 percent, an inherent viscosity of at least l.0 as determined on a 0.1 percent solution in hexafluoro-isopropanol at 25°C, a straight tensile and knot strength of at least 40,000 psi and 30,000 psi, respectively, straight tensile strength retention in vivo of at least 30 percent after 14 days, and substantially complete absorption in vivo within about 180 days.