Biodegradable copolymers with succinimide and lactic acid units

Transcription

1 204 POLIMERY 2011, 56,n3 NITÃ TUDORAI, AURICA P. IRIAC ), RODICA LIPSA Petu Poni Institute of Macomolecula Chemisty Gigoe Ghica Voda Alley, No. 41A, Iasi, Romania Biodegadable copolymes with succinimide and lactic acid units Pat I. SYNTHESIS POSSIBILITIES Summay This pape pesent the possibility to achieve biodegadable copolymes with succinimide and lactic acid units via two diffeent outes of synthesis pocesses. The fist one (vaiant A) involves in situ copolyme synthesis using maleic anhydide, ammonium hydoxide and L(+)-lactic acid and the second (vaiant B) involves poly(succinimide) synthesis and then its modification with L(+)-lactic acid by mass polycondensation pocedue. The pepaed copolymes wee chaacteized by IR and 1 H NMR spectoscopy, molecula weights and paticle size distibution. The synthesized copolymes can be used as possible matix to achieve some matix/active pinciple systems with medical and phamaceutical applications, especially owing to thei biodegadability and biocompatibility. Keywods: poly(succinimide-co-lactic acid), amphiphilic copolymes, synthesis, chemical stuctue, paticles dimensions, molecula weight. BIODEGRADOWALNE KOPOLIMERY ZAWIERAJ CE JEDNOSTKI SUKCYNOIMIDU ORAZ JEDNOSTKI KWASU MLEKOWEGO. Cz. I. MO LIWOŒCI SYNTEZY Steszczenie Pzedstawiono dwa ó ne sposoby otzymywania kopolimeów zawieaj¹cych jednostki sukcynoimidu (SI) i kwasu mlekowego (LA) PSI-co-LA. Piewsza metoda (waiant A) polega na syntezie in situ z zastosowaniem bezwodnika maleinowego, amoniaku i LA(schemat A), a wg dugiej (waiant B) wykozystuje siê do tego celu otzymany wstêpnie polisukcynoimid i powadzi jego polikondensacjê w masie z LA (schemat B). Uzyskane kopolimey schaakteyzowano metodami spektoskopii IR (ys. 1 3, tabela 1) i NMR (ys. 4) oaz okeœlono ich ciê ay cz¹steczkowe (metoda GPC, tabela 2) a tak e wymiay cz¹stek i ozk³ad tych wymiaów (ys. 5, tabela 3). Opisane podukty mog¹ byæ zastosowane jako biodegadowalne i biokompatybilne noœniki substancji czynnych u ytkowanych w medycynie i famacji. S³owa kluczowe: amfifilowe kopolimey, sukcynoimid/kwas mlekowy, synteza, budowa chemiczna, wymiay cz¹stek, ciê a cz¹steczkowy. BIODEGRADABLE POLYMERIC MATERIALS GENERAL ARACTERISTICS Biodegadable polymes have gained impotance in phamaceutical and envionmental applications, as well as in packaging. Vaious featues, such as degadation ate, high mechanical popeties, biocompatibility, and safety ae desied fo biodegadable medical mateials. Plasticity and eactivity ae also euied fo extension of thei utilization. Among them, poly(l-lactide) (PLLA) is one of the most widely utilized classes of biodegadable and bioesobable polymes in the field of biomedical applications and has been used clinically in wound closue [1, 2] tissue epai and egeneation [3], and/o dug delivey [4]. Biodegadable polymes povide sustained o * ) Coesponding autho; achiiac1@yahoo.com contolled elease of encapsulated dugs and degade in the body into non-toxic and low-molecula-weight poducts that can be easily eliminated. Polymeic dug delivey systems have numeous advantages compaed to conventional dosage foms, such as impoved theapeutic effects and convenience, educed toxicity. In addition, a wide vaiety of polymes, pocessing and manufactuing techniues ae exploed fo incopoation of dug molecules into delivey vehicles of vaious geometical shapes. Paticulaly, sustained elease micosphees using biodegadable poducts such as: poly(lactic acid) (PLA), poly(lactide-co-glycolide) (PLGA), and poly(d,l-lactide)-poly(ethylene glycol) (PDLLA-PEG) have been investigated [5]. PLA has good biocompatibility and biodegadability, high mechanical stength, and excellent shaping and molding popeties. Howeve, the application scope of

2 POLIMERY 2011, 56, n3 205 PLA is limited, due to the difficulty of contolled degadation and poo compatibility with soft tissues (due to its high cystallinity) and induction of mateial defects (based on the lability of melt viscosity). To contol the cystallinity and degadation ate, many appoaches, fo example ing opening polymeization of lactides, chiality s contol, copolymeization with othe lactones and polyethes have been studied [6 10]. In pactice, to decease PLA cystallinity, synthesis of andom copolymes of L-lactide (LA) with depsipeptides consisting of glycolic acid (Glc) and -amino acids [Lysine (Lys) o aspatic acid (Asp)] having pendant amino o caboxyl goups poly[(glc-lys)-la] and poly[(glc-asp)-la] was epoted [11, 12]. Poly(glycolide) and its copolymes with lactide, due to thei biocompatibility and elative good mechanical popeties ae usually applied in medical pactice as vey good mateials fo biodegadable implants, employed both in bone sugey in the fom of scews, plates, sugical nails and in teating injuies of some intenal ogans in contolled dug elease as caies in the fom of micosphees [13, 14]. Also, PLA and its deivatives have been synthesized and investigated as andom copolymes, block copolymes and banched polymes [15 20]. Poly(succinimide) (PSI) and sodium poly(aspatate) (PAspNa) have a commecial impotance as buildes fo detegents, scale inhibitos, anticoosive agents, as they ae biodegadable and biocompatible. PSI was synthesized unde educed pessue by themal polycondensation of L-aspatic acid in dodecane, at 175 C with phosphoous acid as catalyst [21]. The polycondensation acceleating agents, pefeably phosphoic acid, diected to a polyme with aised biodegadability and sufficiently high aveage molecula weight (M w > ). Poly(aspatic acid) (PAS) and its salts can be achieved by eacting maleic anhydide, wate and ammonia. Maleic anhydide is hydolyzed to maleic acid and conveted to ammonium salt in the pesence of ammonium hydoxide solution. Then, ammonium salt is bulk polymeized at 170 C, to achieve PSI that is subseuently hydolyzed to obtain PAS [22]. Poly(aspatic acid) possesses caboxylic acid pendant goup in its stuctual unit and can be futhe used fo vaious modification puposes. Thus, high wate absobent gels wee poduced by themal cosslinking of feeze-died mixtue of patially neutalized poly(aspatic acid) and vaious amounts of low molecula weight PEG-diepoxide compounds in aueous medium. These poly(aspatic acid)-based hydogel mateials, possessing inheent biodegadability, potential non-toxicity and biocompatibility ae expected to be used as substates fo vaious biomedical applications and supeabsobent polymes [23]. In ode to apply succinimide and lactic acid based copolymes as novel mateials, we attempted to synthesize macomolecula chains with mentioned units in thei stuctue. In this study, we descibe the pepaation of copolymes based on succinimide and L(+)-lactic acid though two diffeent outes of synthesis and the chaacteization of the synthesized copolymes; we also eview the diffeences in thei popeties due to the two diffeent synthesis pocedues. Mateials EXPERIMENTAL L(+)-lactic acid (LA, 90 % aueous solution) and maleic anhydide (both Fluka), manganese acetate [( O) 2 Mn 4 H 2 O, Sigma-Aldich), sodium hydoxide (Oltchim SA Romania), acetone and ammonium hydoxide 25 wt. % aueous solution (Chemical Company SA, Romania) wee used as eceived. Synthesis The biodegadable copolyme compising succinimide and lactic acid units was synthesized using two diffeent pocedues. A fist one (vaiant A) involves in situ copolyme PSI-co-LA synthesis using maleic anhydide, ammonium hydoxide and L(+)-lactic acid while the second one (vaiant B) involves of poly(succinimide) synthesis and then its modification with L(+)-lactic acid by mass polycondensation pocedue. Vaiant A in situ synthesis (PSI-co-LA) The synthesis accoding to the eaction Scheme A illustates the fomation of the succinimide followed by its polycondensing pocess with L(+)-lactic acid. Pactically, fo copolyme synthesis 5.3 g (0.054 moles) maleic anhydide was used, dissolved unde stiing in 5.5 ml distilled wate, while taking cae that the solution tempeatue didn t exceed 40 C. Afte maleic anhydide complete dissolution, 7.75 ml NH 4 OH (25 wt. % aueous solution, moles) was gadually added at tempeatue maintained unde C. The obtained solution was cooled at oom tempeatue, then 30 g L(+)-lactic acid (90 wt. % aueous solution, 0.33 moles) and ( O) 2 Mn 4 H 2 O as catalyst (0.8 wt. % in popotional to lactic acid) wee intoduced. Futhemoe, the eaction mass was homogenized fo 30 minutes by stiing, then was put into a stainless steel autoclave and kept fo 5 h at 180 ± 10 C and ca Pa (3 atm) pessue. Afte cooling at oom tempeatue, a viscous yellow-bown solution was obtained. The eaction mass obtained in the autoclave was tansfeed into eaction vessel (V = 100 ml) euipped with stie, heating system and distillation-collecting device. Themal condition followed at C unde vacuum to distil and collect the seconday eaction poducts. The synthesized copolyme poly(succinimide-co-lactic acid) pesented high viscosity and was died in vacuum fo 48 h at 80 C, then lyophilized fo 48 h at -40 C and vacuum of 2 to (266 Pa).

3 206 POLIMERY 2011, 56,n3 O Maleic anhydide NH 4OH H 2 O NH Succinimide Tempeatue catalyst + n HO OH [Mn( O) 2 ] N N O OH 2 O Stuctue I (andom PSI-co-LA) +NH 3 OH H 2 N 2 N 2 N O OH 2 O OH H O NH p 2 N Scheme A. In situ synthesis of PSI-co-LA (vaiant A) 2 Stuctue II N O OH 2 O OH Vaiant B polysuccinimide polycondensation with L(+)-lactic acid The diffeence fom the peviously descibed vaiant A is that the copolyme with succinimide and lactic units is synthesized in two stages (see Scheme B). In the fist stage PSI was synthesized fom maleic anhydide and ammonia and in the second stage, the pepaed PSI was polycondensed with L(+)-lactic acid to get poly(succinimide-co-lactic acid) copolyme. In this stage it is possible to make an intemediay poduct (stuctue I) though the addition of the NH 3 molecules (obtained as a esult of the opening of the succinimide cycle) to the double bond fom the final stuctual units of succinimide. The NH 2 goup can also be used to paticipate at the condensing eaction of lactic acid poducing a new macomolecula chain. In the main, at fist (PSI synthesis), maleic anhydide 21.2 g (0.216 moles) was dissolved in 22 ml distilled wate, then 31 ml NH 4 OH (25 wt. %, 0.22 moles) aueous solution was added. The obtained solution was intoduced in the eaction autoclave and, as in vaiant A, was maintained 5 h at 180 ± 10 C and unde ca Pa (3 atm) pessue. Afte autoclave cooling, the esulted eaction mass was intoduced in a glass eaction vessel euipped with heating system and vacuum-distillation-collecting device of the seconday eaction poducts. The eaction mass was maintained fo 3 h unde eflux, then the tempeatue was aised to C to distil and collect the seconday poducts (appoximately 28 ml). The esulted PSI was highly viscous and had a ed-bown colou. 2.6 g of PSI (0.027 moles) wee submitted to mass polycondensation eaction with 15 g L(+)-lactic acid (0.166 moles) in the pesence of manganese acetate catalyst ( O) 2 Mn 4 H 2 O (0.8 wt. % in popotion to the eaction components). The eaction mixtue was maintained unde eflux fo 6 h at C, then the tempeatue was aised to C and maintained fo 3 h. The esulted poduct was pecipitated in acetone, eceived paticles vacuum died at 80 C fo 48 h and then vacuum (2 t = 266 Pa) lyophilized fo 48 h at -40 C. Analytical methods Fouie Tansfom Infaed Spectomete (FT-IR) Vetex 70 model (Buke, Gemany) fo specta ecoded on KB pellets (5 mg sample/500 mg KB), was used.

4 POLIMERY 2011, 56, n3 207 N N 2 PSI H + n HO n-1 OH Temp. cat. N N O OH 2 +NH 3 2 O OH Stuctue I H 2 N 2 N 2 N O OH 2 O OH H O NH N 2 N O OH 2 + H 2 O 2 O OH Stuctue II Poly(succinimide-co-lactic acid) Scheme B. Synthesis of PSI-co-LA by polysuccinimide polycondensation with L(+)-lactic acid (vaiant B) 1 H NMR specta of copolymes wee obtained on a Buke Avance DRX 400 NMR spectophotomete Rheinstetten (Gemany) with 16 scans and 0.1 Hz FID esolution. The samples wee dissolved in dimethyl sulfoxide (DMSO) with a concentation of about 5 wt. %. The analyses wee caied out at 25 C and chemical shifts wee epoted in ppm using tetamethylsilane (TMS) as the intenal efeence. Aveage molecula weight of the copolymes was detemined by gel pemeation chomatogaphy (GPC) techniue at ambient tempeatue. The system was euipped with an adjustable flow capacity and constant ate pump LC 1120 and an evapoative mass detecto PL-EMD 950 type. It was fitted also with columns PL-gel 5 m MIXED-D and PL-gel 5 m MIXED-C packed with styene/divinylbenzene copolyme. PL-polyme, polystyene standads 580 and dimethylfomamide (DMF) as the mobile phase wee employed at a flow ate of 0.7 ml/min (dimethylfomamide is a good solvent fo both PSI and copolymes). Measuements of the paticles dimensions wee done with a Mastesize 2000 system (vesion 5.31) Malven Instuments (England) in wate, using 0.5 mg copolyme paticles peviously lyophilized and ultasonicated in the dispesion unity of the device fo 10 seconds. The system device is constituted of an optical bank which uses lase light He-Ne 632 nm/2 mw, a dispesion unity of the sample Hydo 2000A type euipped with stie, eciculating pump, ultasonic and softwae to ecod and pocess esults on the compute. The measuements domain is between m. RESULT AND DISCUSSION The FT-IR specta of intemediay poducts and of synthesized copolymes ae pesented in Figs The copolymes achieved unde the two vaiants pesent simila stuctues, with IR absoption bands situated at close wavelengths (Table 1). Tansmittance Wavenumbe, cm -1 Fig. 1. FT-IR spectum of polysuccinimide

5 208 POLIMERY 2011, 56,n3 Tansmittance Wavenumbe, cm -1 Fig. 2. FT-IR spectum of L(+)-lactic acid Tansmittance T a b l e 1. The main FT-IR absoption bands* ) Sample Functional goups Wavelengths, cm -1 - ( ) OH lage band ( OH) L(+)-lactic acid -C-OH seconday alcohols 1128 ( C-OH) -OH ( C=O) 1732 PSI --NH-R seconday amides 1613 PSI-co-LA * ) See Figues OR ( C=O) --NH-R seconday amides ( C-N; NH amide band II) - ( ) -OH lage band ( OH) 1721 (va. B); 1738 (va. A) 1593 (va. B); 1590 (va. A) (va. B); 2944 (va. A) (va. B); 3400 (va. A). Based on othe infomation concening synthesis of copolymes with simila stuctues [24], two eaction mechanisms ae poposed (see Schemes A and B). By succinimide ing opening and eaction with L(+)-lactic acid two poly(lactic) acid chains ae fomed (Scheme A). In the pesence of manganese acetate catalyst the succinimide eacts though ing-opening polymeization with two hydoxyl goups fom diffeent L(+)-lactic acid molecules and eliminating ammonium molecules to give andom copolymes. The second possibility can be as follows: NH 3 molecules eleased by succinimide ing opening (stuctue I) can be added at -C=C- double bond foming an NH 2 goup that takes pat at an ammidation eaction with -OH goup fom lactic acid, developing a new PLA chain (Scheme B). The 1 H NMR specta of the copolymes pepaed accoding to mentioned pocedues ae pesented in the Fig. 4. Fom NMR specta the atio between succinimide (SI) and lactic acid (LA) units was detemined as SI / LA = 51.42/48.58 in case of vaiant A and SI / LA = 52.85/47.15 in case of vaiant B synthesis Wavenumbe, cm -1 Fig. 3. FT-IR specta of PSI-co-LA copolyme eceived accoding: a) vaiant A, b) vaiant B The aveage molecula weights of the synthesized copolymes ae pesented in Table 2. Table 2. Aveage molecula weights detemined by GPC Sample M n M w M w /M n PSI-co-LA synthesis vaiant A PSI-co-LA synthesis vaiant B PSI So, the molecula weight of copolyme fom vaiant B (M n = ), is highe than fom vaiant A (M n = 8254). In the fist case, the initial eaction components [maleic anhydide, ammonia and L(+)-lactic acid] wee put togethe fom the beginning, while in the second case the eaction components wee L(+)-lactic acid and poly(succinimide) pepolyme (M n = 3500), that paticipated with its molecula weight in the banched copolyme. The conditions of condensation wee the same in both cases (180 C, 3 atm, 5 h). It can be thus concluded that succinimide is less eactive then D,L-lactide [24]. Also, the educed molecula weights, egisteed fo the copolymes with the succinimide and lactic units synthesized though the above mentioned pocedues, compaed with the simila data fom the liteatue [25, 26], ae justified on the one side though the used catalyst 1042

6 POLIMERY 2011, 56, n3 209 N 2 n-1 N O OH 2 O OH H O NH 2 p N O OH n 2 O OH a) b) , ppm, ppm Fig. 4. NMR specta of PSI-co-LA copolyme eceived accoding: a) vaiant A, b) vaiant B Table 3. Paticles size distibution Sample d(0.1) 1), m d(0.5), m d(0.9), m Suface weighted mean 2), m Volume weighted mean 3), m Unifomity 4) Span 5) PSI-co-LA (vaiant A) PSI-co-LA (vaiant B) ) d(0.1), d(0.5), d(0.9) 10 %, 50 % and 90 % of the sample volume ae paticles with a smalle diamete than specified in the table. 2) Medium diamete fo the euivalent sphee of the same suface with that of the paticles, called also media Saute. 3) Medium diamete fo the volume. 4) Unifomity absolute deviation fom the median value. 5) Span epesents the width of the distibution. Span value is calculated with the fomula: [d(0.9) d(0.1)]/d(0.5). manganese acetate which pesents educed efficiency compaatively with stannous octoate o tin(ii) chloide which ae usually utilised, and, on the othe side, owing to the eaction conditions favouable fo multiple possibilities of competito eactions as, fo example, condensative o block copolymeization. The pepaed copolymes ae soluble in wate and cetain oganic solvents (DMF, DMSO, methanol etc.). The esults of measuements concening paticles size and dimensional distibution of paticles ae pesented in Table 3 and Fig. 5. We notice that 90 wt. % of the total paticle volume PSI-co-LA has diamete d(0.9) m (vaiant A), and d(0.9) m (vaiant B). Fo both vaiants of synthesis thee is an impotant deviation of Volume, % Paticle size, m Fig. 5. Paticle size distibution of PSI-co-LA copolyme eceived accoding: 1 vaiant A, 2 vaiant B medium value of paticles dimension and paticles ae heteogeneous in tems of thei size (Fig. 5). This fact is also evidenced by the data pesented, namely unifomity and span which have enough aised values (Table 3). The esults of these measuements ae in good ageement with the pepaation method. Thus, the copolyme paticles dimension in case of the vaiant A of synthesis, when the macomolecula chains can be egaded moe as andom and altenating copolyme with succinimide and lactic units obtained though polycondensing pocedue, ae smalle then those obtained though the vaiant B, when onto polysuccinimide ae gafted lactic acid units. NCLUSIONS This wok has poved the possibility to obtain biodegadable copolymes with succinimide and lactic acid units though two diffeent synthesis pocedues. In the fist case maleic anhydide, ammonia and L(+)-lactic acid wee used as eaction components (vaiant A of synthesis), and in the second case poly(succinimide) was peviously synthesized and subject to polycondensation with L(+)-lactic acid (vaiant B of synthesis). PSI-co-LA copolymes obtained though these two methods pesent simila popeties. The chaacteistics of the synthesized

7 210 POLIMERY 2011, 56,n3 copolymes suggest thei utilization as possible matix to achieve some matix/active pinciple systems with medical and phamaceutical applications, especially owing to thei biodegadability and biocompatibility. ACKNOWLEDGMENTS This eseach was suppoted by a CNCSIS-Idea Poject, No. 466 Reseaches in the field of polymeic matices design fo sensitive stuctues, Romania, Ministy of Education Reseach, REFERENCES 1. Fazza E. J., Schmitt E. E.: J. Biomed. Mate. Res. 1971, 1, Kobayashi H., Hyon S. H., Ikada Y.: J. Biomed. Mate. Res. 1991, 25, Daniels A. U., Chang M. K. D., Andiano K. P.: J. Appl. Biomate. 1990, 1, Chasin M., Lange R.: Biodegadable Polymes as Dug Delivey Systems, Macel Dekke, New Yok Kissel T., Li Y. X., Volland C., Goich S., Konebeg R.: J. Contolled Release 1996, 39, John G., Tsuda S., Moita M.: J. Polym. Sci., Pat A: Polym. Chem. 1997, 35, Nakayama A., Kawasaki N., Avanitoyannis I., Iyoda J., Yamamoto N.: Polyme 1995, 36, Kicheldof H. R., Boettche C.: Makomol. Chem. Macomol. Symp. 1993, 73, Li S. M., Rashkov I., Espateo J. L., Manolova N., Vet M.: Macomolecules 1996, 29, Benabdillah K. M., Coudane J., Boustta M., Engel R., Vet M.: Macomolecules 1999, 32, Ouchi T., Shiatani M., Jinno M., Hiao M., Ohya Y.: Makomol. Chem., Rapid Commun. 1993, 14, Ouchi T., Nozaki T., Ishikawa A., Fujimoto I., Ohya Y.: J. Polym. Sci., Pat A: Polym. Chem. 1997, 35, Kuciel S., Libe-Kneæ A., Zajchowski S.: Polimey 2009, 54, Piókowska E., Kuliñski Z., Gadzinowska K.: Polimey 2009, 54, Ouchi T., Hamada A., Ohya Y.: Macomol. Chem. Phys. 1993, 200, Stidsbeg K., Albetsson A. C.: Polyme 2000, 41, Deng X., Zhu Z., Xiong C., Zhang L.: J. Polym. Sci., Pat A: Polym. Chem. 1997, 35, Ouchi T., Miyazak H., Aimua H., Tasaka F., Hamada A.: J. Polym. Sci., Pat A: Polym. Chem. 2002, 40, Beitenbach A., Li Y. X., Kissel T.: J. Contolled Release 2000, 64, Tasaka F., Ohya Y., Ouchi T.: Macomolecules 2001, 34, Tomida M., Nakato T., Mayumi K., Shibata M., Matsunami S., Kakuchi T.: Polyme 1996, 37, US Pat (1994). 23. Pi¹tkowski M., Bogda³ D., Onduschka B.: Polimey 2009, 54, Feng Y., Klee D., Hocke H.: Macomol. Chem. Phys. 2002, 203, Biela T., Duda A., Penczek S.: Macomol. Symp. 2002, 183, Save M., Schappache M., Soum A.: Macomol. Chem. Phys. 2002, 203, 889. Received 15 II 2010.