Copolymerization Of L-lactide Research Articles

Molten ring-open copolymerization ofL-lactide and cyclic trimethylene carbonate

The biodegradable poly(L-lactide-co-trimethylene carbonate) [poly(LLA-co-TMC)] was synthesized by molten ring-open copolymerization and the structure and properties of the copolymer were investigated by GPC, NMR, FTIR, DSC, and Instron testing. The copolymer with a higher LLA content had a higher initial molecular weight (Mn), but a lower final Mn. In contrast, the copolymer with a higher TMC content had a lower initial Mn, but its Mn increased with increasing reaction time and TMC content. The glass transition temperature (Tg), the melting temperature (Tm) and the crystallinity of the copolymer decreased with increasing TMC content. The elongation of the copolymer significantly increased with increasing TMC content while the toughness passed through a maximum. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1429–1434, 1998

Synthesis and characteristics of polydepsipeptide with pendant thiol groups

To obtain water-soluble oligodepsipeptide with pendant thiol groups, the alternating co-oligomer [oligo(Glc-alt-Cys)], consisting of glycolic acid (Glc) and L-cysteine (Cys) residues as α-hydroxy acid and α-amino acid residues, respectively, was prepared by means of ring-opening homo-oligomerization of cyclo[Glc-Cys(MBzl)] and subsequent deprotection of methoxybenzyl groups. Moreover, to modify the properties of poly(lactic acid) [poly(LA)] and to introduce pendant thiol groups to poly(LA), the terpolymer of LA, Glc, and Cys {poly[LA-(Glc-Cys)]} was synthesized through ring-opening and copolymerization of L-lactide with the protected cyclodepsipeptide, cyclo[Glc-Cys(MBzl)] and subsequent deprotection of methoxybenzyl groups. By changing the mol fraction of (Glc-Cys) unit, the solubility, thermal transition, degradation behavior of the modified poly(LA), and the water contact angle of its film could be varied. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1283–1290, 1998

Polylactones, 39. Zn lactate-catalyzed copolymerization of L-lactide with glycolide or ɛ-caprolactone

Polylactones, 39. Zn lactate-catalyzed copolymerization of L-lactide with glycolide or ɛ-caprolactone

Meniscal tissue regeneration in porous 50/50 copoly(l-lactide/ε-caprolactone) implants

Porous materials of a high-molecular-weight 50/50 copolymer ofl-lactide and ɛ-caprolactone with different compression moduli were used for meniscal repair. In contrast to the previously used 4,4′-diphenylmethane and 1,4-trans-cyclohexane diisocyanates containing polyurethanes, degradation products of the copolymer are non-toxic. Two series of porous materials with compression moduli of 40 and 100 kPa respectively were implanted in the knees of dogs using a new, less traumatizing suturing technique. A porous aliphatic polyurethane series with compression modulus of 150 kPa was implanted for comparison. Adhesion of the implant to meniscal tissue was found to be essential for healing of the longitudinal lesion. Copolymer implants showed better adhesion, probably due to the higher degradation rate of the copolymer. Fibrocartilage formation was found to be affected by the compression modulus of the implant. Implants with a modulus of 40 kPa did not show ingrowth of fibrocartilage, whereas implants with compression moduli of 100 and 150 kPa yielded 50–70 and 80–100% fibrocartilage respectively. During degradation the copolymer phase separated into a crystalline phase containing mainlyl-lactide and an amorphous phase containing mainly ɛ-caprolactone. The copolymer degraded through bulk degradation.

Synthesis and Characterization of Biodegradable ε-Caprolactone/d,l-lactide Copolymer

Synthesis and Characterization of Biodegradable ε-Caprolactone/d,l-lactide Copolymer

Synthesis and Characterization of Biodegradable ε-Caprolactone/d,l-lactide Copolymer

Synthesis and Characterization of Biodegradable ε-Caprolactone/d,l-lactide Copolymer

Impact modification of lactic acid based poly(ester‐urethanes) by blending

Branched biodegradable poly(ester-urethane)(PEU) was blended with two elastic biodegradable copolymers in proportions 5, 10, 15, and 20 wt % to investigate their effect on this hard and brittle polymer. Copolymer of L-lactide and ϵ-caprolactone, P(L-LA50/CL50), was synthesized by ring-opening polymerization and the other elastic poly(L-lactic acid-co-ϵ-caprolactone)urethane, P(LA50/CL50)U, was prepared by direct polycondensation of L-lactic acid and ϵ-caprolactone, followed with urethane bonding. In addition, four elastic biodegradable copolymers, three of them P(L-LA/CL) and one P(LA/CL)U, were blended with linear PEU to investigate their modifying effect on PEU. These compositions studied were 10, 15, and 20 wt % of P(L-LA40/CL60), P(L-LA60/CL40), P(L-LA80/CL20), and P(LA40/CL60)U in PEU. Blending was done in a batch mixer. PEU became more ductile when blended with P(L-LA/CL) and P(LA/CL)U, and its impact resistance improved markedly. In general, an addition of 15 wt % of copolymer appeared to give the most desirable mechanical properties. Moreover, the more L-lactide in the P(L-LA/CL) copolymer, the better was the miscibility of the blends, as shown by dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). One P(L-LA/CL) was also blended with poly(DL-lactide) (PDLLA) to see if the dispersion of rubbery copolymer particles was the same in PDLLA and PEU. A well-known commercial nonbiodegradable rubber [styrene/ethylene/butylene copolymer (SEBS)] was blended with linear PEU to compare its effect on impact strength. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1335–1343, 1997

Impact modification of lactic acid based poly(ester-urethanes) by blending

Branched biodegradable poly(ester-urethane)(PEU) was blended with two elastic biodegradable copolymers in proportions 5, 10, 15, and 20 wt % to investigate their effect on this hard and brittle polymer. Copolymer of L-lactide and ϵ-caprolactone, P(L-LA50/CL50), was synthesized by ring-opening polymerization and the other elastic poly(L-lactic acid-co-ϵ-caprolactone)urethane, P(LA50/CL50)U, was prepared by direct polycondensation of L-lactic acid and ϵ-caprolactone, followed with urethane bonding. In addition, four elastic biodegradable copolymers, three of them P(L-LA/CL) and one P(LA/CL)U, were blended with linear PEU to investigate their modifying effect on PEU. These compositions studied were 10, 15, and 20 wt % of P(L-LA40/CL60), P(L-LA60/CL40), P(L-LA80/CL20), and P(LA40/CL60)U in PEU. Blending was done in a batch mixer. PEU became more ductile when blended with P(L-LA/CL) and P(LA/CL)U, and its impact resistance improved markedly. In general, an addition of 15 wt % of copolymer appeared to give the most desirable mechanical properties. Moreover, the more L-lactide in the P(L-LA/CL) copolymer, the better was the miscibility of the blends, as shown by dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). One P(L-LA/CL) was also blended with poly(DL-lactide) (PDLLA) to see if the dispersion of rubbery copolymer particles was the same in PDLLA and PEU. A well-known commercial nonbiodegradable rubber [styrene/ethylene/butylene copolymer (SEBS)] was blended with linear PEU to compare its effect on impact strength. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1335–1343, 1997

Structural characterization and hydrolytic degradation of a Zn metal initiated copolymer of L-lactide and ε-caprolactone

A bioresorbable aliphatic polyester was synthesized by bulk copolymerization of a 1/1 M/M L,L-lactide/ε-caprolactone mixture using zinc metal as initiator. The actual composition of the copolymer was found to be 1.5/1 as deduced from 1H NMR spectra obtained in DMSO-d6 solutions where higher resolution was obtained as compared with chlorinated solvents. Resonances due to L-lactyl units (L) exhibited triads stereosensitivity, ε-oxycaproyl units (C) being sensitive to dyads. Average lengths of both poly(lactic acid) and polycaprolactone sequences were evaluated and showed the presence of rather long PLA blocks. Furthermore, no CLC triad signal was found, suggesting the absence of transesterification rearrangements. 10 x 10 x 2 mm specimens made of the copolymer were allowed to age in isoosmolar pH = 7.4 phosphate buffer at 37°C. Degradation was monitored by various analytical techniques such as SEC, X-ray diffractometry, DSC, and 1H NMR. Data were compared with the behaviour of PCL and PLA homopolymers allowed to age under similar conditions. Crystallinity and composition changes arc discussed in terms of preferential degradation in L- and C-containing amorphous domains, crystallized long PLA blocks being much more resistant.

Synthesis and Properties of A–B–A Block Copoly(ester-ethers) Comprising Poly(l-lactide) (A) and Poly(oxypropylene-co-oxyethylene) (B) with Different Molecular Weights

Abstract An A–B–A triblock copoly(ester-ether) comprising poly(l-lactide) (A) and poly(oxyethylene-co-oxypropylene) (B) was prepared by copolymerization of l-lactide and a commercially available telechelic copolyether, Pluronic® (PN), with different molecular weights by the catalysis of tin(II) octanoate. The low molecular weight PN gave the copolymers having a low or medium molecular weight and a unit composition slightly different from the feed ratio. With PN whose molecular weight was around 10000, high molecular weight copolymers were obtained in high yield. For the PN with molecular weight of 8400, the block copolymerization was examined at different feed ratios, in which the molecular weight and the unit composition were successfully controlled by changing the l-lactide/PN ratio in feed. The copolymer containing 10 wt% of this PN was melt-spun into a filament, which was drawn to various draw ratios at 40 and 60 °C. The tensile modulus and strength of the filament increased with the draw ratio increasing at 60 °C, while at 40 °C they reached a plateau above the draw ratio of 5.0. It was found that the copolymer filaments showed an improved flexibility due to the incorporation of the soft PN segments. The in vitro hydrolysis test of the drawn filaments showed that the block copolymer has much higher degradability than the homo poly-l-lactide.

The influence of basic filler materials on the degradation of amorphous D- and L-lactide copolymer

Composite films made of poly L/D copolymer and hydroxylapatite (HA) as filler material were made in two different volume percentages. As references pure copolymer films and composite films with magnesium oxide (MgO) were prepared to serve as strongly basic model filler material. All these materials were immersed in phosphate buffered saline to study the effect of filler materials on the degradation rate of the copolymer. Filled films showed less molecular weight decrease than the unfilled films, while lactate release was higher for the filled films than for the unfilled films. This effect implies that the filler materials influence the degradation mechanism by preventing the occurrence of the autocatalytic effect of the acidic endgroups, resulting from hydrolysis of the polymer chains. The polymer chains at the surface of the material are less protected by the filler materials, which causes a more rapid degradation of these chains and a higher lactate release. At the same time composites seem to show an erosion type of degradation rather than bulk degradation in unfilled materials.

Properties and Degradability of the Fibers of Block Copoly(ester-ether) Comprising Poly(L-lactide) and Poly(oxyethylene-co-oxypropylene).

The A-B-A tribloc copoly (ester-ether) comprising poly (L-lactide) (A) and poly(oxyethylene-co-oxypropylene) (B) was prepared by copolymerization of L-lactide and a commercially available telechelic copolyether, PluronicrTM (PN) by the catalysis of tin octanoate. The copolymers were melt-spun by the conventional method. Then, the as-spun filament obtained was drawn to 2.5-12.5 times at 40 and 60°C. At a constant draw ratio the tensile modulus of the filament decreased with increasing composition of PN in the copolymer and with increasing draw ratio. Upon immersion in a phosphate buffer (pH=7.4), the filaments showed a time-dependent decrease in tensile strength with accompanying surface erosion. The degradability of the filaments with the same identical copolymer compositions was found to decrease with increasing draw ratio, because of the increased orientational crystallization of PLLA. The block copolymers comprising PLLA and PN, therefore, were shown to have high potentiality as the biodegradable polymers with improved flexibility and biodegradability.

Effects of preparation conditions of cisplatin-loaded microspheres on the in vitro release

Microspheres from glycolide- l-lactide copolymers (PGLA) incorporating cis-diammine dichloroplatinum (II) (CDDP) were prepared with an O/O-type emulsion method to study the effects of the preparation conditions on the in vitro release of CDDP. PGLA was virtually immiscible with CDDP. Homogeneous dimethyl formamide (DMF) solutions of CDDP and PGLA were poured into liquid paraffin containing Span 80 as a surfactant, followed by solvent evaporation at elevated temperatures. DMF was used as the common solvent of PGLA and CDDP because it had the lowest boiling point of their conventional common solvents. The influencing factors studied in this work include rate of temperature rise, operating temperature for solvent evaporation, Span 80 concentration, the molecular weight of PGLA, CDDP loading and PGLA concentration. The effect of these preparation conditions on CDDP release was evaluated based on the observation of the resulting microspheres by scanning electron microscopy (SEM) and the plot of the amount of CDDP released against time. It was found that the operating temperature for the solvent evaporation and the rate of temperature rise to the operating temperature had a large effect on the release profile of CDDP. SEM observation of the cross-section of the microspheres revealed that the microsphere inside had a hole, although any significant deposit of micro-crystals of CDDP on the microsphere surface was not noticed.

Processing and characterization of absorbable polylactide polymers for use in surgical implants.

Absorbable fibers of linear poly-alpha-hydroxy acids have been used successfully in providing temporary scaffolds for tissue regeneration. In some surgical applications, degradation rates for poly(glycolide) (PGA) are too high, but implants of poly(L-lactide) (PLLA) fibers may degrade too slowly for optimal function. Polymers produced by copolymerization of L-lactide with varying amounts of D-lactide may offer an alternative choice for absorbable fiber based implants. Poly(L/D-lactide) stereocopolymers with L/D lactide molar ratios of 95/5, 90/10, and 85/15 were considered. Melt-spun/hot-drawn fibers with L/D molar ratios of 90/10 and 85/15 and draw ratios ranging from 3.0 to 8.9 were further evaluated by mechanical testing, differential scanning calorimetry, birefringence, x-ray diffraction, and in vitro exposure to pH 7.4 phosphate buffered saline at 37 degrees C. Fabrication was reproducible and results indicated that tensile strength, modulus, an birefringence all increased with increasing draw ratio up to a draw ratio of 6.7 and declined thereafter; elongation to failure decreased for the entire range studied. For fibers with a draw ratio of 6.7, there was a 10% relative difference in crystallinity between the 90/10 and 85/15 lactide fibers (90/10 was higher). Wet strength retention after 12 weeks in vitro exposure was approximately 10% for the 90/10 fibers and 30% for the 85/15 fibers. The intermediate wet strength retention of lactide stereocopolymer fibers when compared to reported values for PGA and PLLA fibers, suggests these materials may be useful in absorbable surgical implants for tissue repair and regeneration.

Preparation of a new nerve guide from a poly( l-lactide-co-6-caprolactone)

A copolymer of l-lactide and 6-caprolactone (50:50, w/w) was synthesized and characterized. The thermal behaviour of this material did not show any crystallinity for several months; only after more than 1 yr of aging at room temperature and, particularly, in the in vitro degradation tests did it partially crystallize. The values of tensile strength, percent elongation at break and elastic modulus were, respectively, 25 MPa, 490% and 3 MPa. Transparent, elastic nerve guides having inner diameter of 1.3 mm and wall thickness of 175 μm were prepared.

Block copolymers of L-lactide and poly(ethylene glycol) for biomedical applications

Block copolymers of L-lactide and poly(ethylene glycol) for biomedical applications

Preparation and properties of absorbable fibres from l-lactide copolymers

Absorbable fibres have been prepared from various copolymers of l-lactide with either d-lactide or ϵ-caprolactone. The lower crystallinity of these copolymers, compared with the homopolymer, is desirable in the light of their potential use as an absorbable suture material and has a pronounced effect on both preparation procedure and mechanical properties of these fibres. Due to the low crystallinity of the fibres, their mechanical properties are related to the structure of the amorphous phase, as is reflected by the effect of the glass transition temperature and molecular weight on tensile properties. By means of a dry spinning/hot drawing process, low crystalline fibres having strengths of 1 GPa could be prepared, whereas fibres prepared by melt spinning/hot drawing have strengths ranging from 0.19 for a completely amorphous copolymer to 0.53 GPa for the poly( l-lactide) homopolymer.

High molecular weight copolymers of l-lactide and ?-caprolactone as biodegradable elastomeric implant materials

High molecular weight copolymers of L-lactide and e-caprolactone have been synthesized by ring opening copolymerization with stannous octoate as catalyst. The good mechanical properties of the 50/50 copolymers make it a suitable material for biomedical applications such as nerve guides etc., where degradation of the elastomeric implant is required. In contrast to the frequently used MDI containing polyurethanes, degradation products of the P(LLA-e-CL) are non toxic. The use of such a material is therefore preferable.

Synthesis and hydrolytic degradation behaviour of high-molecular-weight l-lactide and glycolide copolymers

High-molecular-weight copolymers of l-lactide and glycolide have been synthesized. The influence of the glycolide content on the mechanical and thermal properties of the as-polymerized copolymer was studied. Excellent mechanical properties and a large melting-point depression were observed. The dyad splitting of the carbonyl carbon atoms in the 13C nuclear magnetic resonance spectrum was used to determine the average length of the monomer sequences. It was found that the synthesized copolymers did not reveal a truly random monomer distribution. Hydrolytic degradation of a copolymer containing 27 mol% glycolide showed that large amounts of highly crystalline material were still present after 140 days, and that 10 mol% glycolide has been incorporated in the poly( l-lactide) lattice.

Two-ply biodegradable nerve guide: basic aspects of design, construction and biological performance

A synthetic biodegradable nerve guide was constructed of two polymeric layers: an inner microporous layer prepared from a copolymer of l-lactide and ϵ-caprolactone (pore size range 0.5–1μm) and an outer microporous layer prepared from a polyurethane/poly( l-lactide) mixture (pore size range 30–70 μm). This nerve guide was used to bridge a 7 mm gap in the right sciatic nerve of rats. It enabled the sciatic nerve to regenerate across the gap, forming a new, well-defined nerve that effectively re-established the contact between the proximial and distal nerve end, as effective as an autograft.