Poly(D,L-lactide) synthesis using tin(II) 2-ethylhexanoate initiated ring-opening polymerization (ROP) takes over 30 hours in bulk at 120 °C. The use of microwave makes the same bulk polymerization process with the same initiator much faster and energy saving, with a reaction time of about 30 minutes at 100 °C. Here, the poly(lactide) synthesis was done in a microwave reactor, using frequency of 2.45 GHz and maximal power of 150 W. The reaction temperature was controlled via infra-red system for in-bulk-measuring, and was maintained at 100 °C. Different molar ratios of monomer and initiator, [M]/[I], of 1,000, 5,000 and 10,000 were used. The achieved average molar masses for the obtained polymers (determined by gel permeation chromatography) were in the interval from 26,700 to 112,500 g/mol. The polydispersion index was from 2.436 to 3.425. For applicative purposes, the obtained material was purified during the procedure of microsphere preparation. Microspheres were obtained by spraying a fine fog of polymer (D,L-lactide) solution in tetrahydrofuran into the water solution of poly(vinyl alcohol) with intensive stirring.
References
[1]
Gilding, D.K.; Reed, A.M. Biodegradable polymers for use in surgery-polyglicolic/poly(lactic acid) homo-and copolymers. Polymer？1979, 20, 1459–1464, doi:10.1016/0032-3861(79)90009-0.
[2]
Tomihata, K.; Suzuki, M.; Oka, T.; Ikada, Y. A new resorbable monofilament suture. Polymer Degrad. Stability？1998, 59, 13–18, doi:10.1016/S0141-3910(97)00183-3.
[3]
Leenslag, J.W.; Pennings, A.J. High-strength poly(L-Lactide) fibers by a dry-spinning hot-drawing Process. Polymer？1987, 28, 1695–1702, doi:10.1016/0032-3861(87)90012-7.
[4]
M？kel？, P.; Pohjonen, T.; T？rm？l？, P.; Waris, T.; Ashammakhi, N. Strength retention properties of self-reinforced poly L-lactide (SR-PLLA) sutures compared with polyglyconate (MaxonR) and polydioxanone (PDS) sutures. An in vitro study. Biomaterials？2002, 23, 2587–2592, doi:10.1016/S0142-9612(01)00396-9. 12033607
[5]
Channuan, W.; Siripitayananon, J.; Molloy, R.; Mitchell, G.R. Defining the physical structure and properties in novel monofilaments with potential for use as absorbable surgical sutures based on a lactide containing block terpolymer. Polymer？2008, 49, 4433–4445, doi:10.1016/j.polymer.2008.07.058.
[6]
Penning, J.P.; Dijkstra, H.; Pennings, A.J. Preparation and properties of absorbable fibres from L-lactide copolymers. Polymer？1993, 34, 942–951, doi:10.1016/0032-3861(93)90212-S.
[7]
Leenslag, W.J.; Pennings, A.J.; Bos, R.M.; Rozema, F.R.; Boering, G. Resorbable materials of poly(L-lactide): VII In vivo and in vitro degradation. Biomaterials？1987, 8, 311–314, doi:10.1016/0142-9612(87)90121-9. 3663810
[8]
Winet, H.; Bao, J.Y. Fibroblast growth factor-2 alters the effect of eroding polylactide-polyglycolide on osteogenesis in the bone chamber. J. Biomed. Mater. Res？1998, 40, 567–576, doi:10.1002/(SICI)1097-4636(19980615)40:4<567::AID-JBM8>3.0.CO;2-D. 9599033
[9]
Lunt, J. Large-scale production, properties, and commercial applications of polylactic acid polymers. Polym. Degrad. Stab？1998, 59, 145–152, doi:10.1016/S0141-3910(97)00148-1.
[10]
Sodergard, A.; Stolt, M. Properties of lactic acid based polymers and their correlation with composition. Prog. Polym. Sci？2002, 27, 1123–1163, doi:10.1016/S0079-6700(02)00012-6.
Herrmann, J.; Bodmeier, R. The effect of particle microstructure on the somatostatin release from poly(lactide) microspheres prepared by a W/O/W solvent evaporation method. J. Control. Release？1995, 36, 63–71, doi:10.1016/0168-3659(95)00051-9.
[13]
Miyajima, M.; Koshika, A.; Okada, J.; Ikeda, M. Effect of polymer/basic drug interactions on the two-stage diffusion-controlled release from a poly(L-lactic acid) matrix. J. Control. Release？1999, 61, 295–304, doi:10.1016/S0168-3659(99)00149-2. 10477802
[14]
Aso, Y.; Yoshioka, S.; Po, A.L.W.; Terao, T. Effect of temperature on mechanisms of drug release and matrix degradation of poly(D,L-lactide) microspheres. J. Control. Release？1994, 31, 33–39, doi:10.1016/0168-3659(94)90248-8.
[15]
Yoshioka, S.; Aso, Y.; Kojima, S. Drug release from poly(D,L-lactide) microspheres controlled by γ-irradiation. J. Control. Release？1995, 37, 263–267, doi:10.1016/0168-3659(95)00083-6.
[16]
Pradhan, R.S.; Vasavada, R.C. Formulation and in vitro release study on poly (D,L-lactide) microspheres containing hydrophilic compounds: glycine homopeptides. J. Control. Release？1994, 30, 143–154, doi:10.1016/0168-3659(94)90261-5.
[17]
Izumikawa, S.; Yoshioka, S.; Aso, Y.; Takeda, Y. Preparation of poly(L-lactide) microspheres of different crystalline morphology and effect of crystalline morphology on drug release rate. J. Control. Release？1991, 15, 133–140, doi:10.1016/0168-3659(91)90071-K.
[18]
Zhang, X.; Wyss, U.P.; Pichora, D.; Goosen, M.F.A. A mechanistic study of antibiotic release from biodegradable poly(D,L-lactide) cylinders. J. Control. Release？1994, 31, 129–144, doi:10.1016/0168-3659(94)00011-5.
[19]
Uhrich, K.; Cannizzaro, S.; Langer, R.; Shakesheff, K. Polymeric systems for controlled drug release. Chem. Rev？1999, 99, 3181–3198, doi:10.1021/cr940351u. 11749514
[20]
Jacoby, M. Custom-made biomaterials. Chem. Eng. News？2001, 79, 30–35.
[21]
Hyon, S.H.; Jamshidi, K.; Ikada, Y. Synthesis of polylactides with different molecular weights. Biomaterials？1997, 18, 1503–1508, doi:10.1016/S0142-9612(97)00076-8. 9426180
[22]
Bendix, D. Chemical synthesis of poly(lactide) and its copolymers for medical applications. Polymer Degrad. Stability？1998, 59, 129–135, doi:10.1016/S0141-3910(97)00149-3.
[23]
Leenslag, J.W.; Pennings, A.J. Synthesis of high-molecular-weight poly(L-lactide) initiated with tin 2-ethylhexanoate. Makromol. Chem？1987, 188, 1809–1814, doi:10.1002/macp.1987.021880804.
[24]
Nijenhuis, A.J.; Grijpma, D.W.; Pennings, A.J. Lewis acid catalyzed polymerization of L-Lactide. Kinetics and mechanism of the bulk polymerization. Macromolecules？1992, 25, 6419–6424, doi:10.1021/ma00050a006.
[25]
Du, Y.J.; Lemstra, P.J.; Nijenhuis, A.J.; van Aert, H.A.M.; Bastiaansen, C. ABA type copolymers of lactide with poly(ethylene glycol). Kinetic, mechanistic and model studies. Macromolecules？1995, 28, 2124–2132, doi:10.1021/ma00111a004.
[26]
Schwach, G.; Coudane, J.; Engel, R.; Vert, M. More about the polymerization of lactides in the presence of stannous octoate. J. Polym. Sci. Part A: Polym. Chem？1997, 35, 3431–3440, doi:10.1002/(SICI)1099-0518(19971130)35:16<3431::AID-POLA10>3.0.CO;2-G.
[27]
Kricheldorf, H.R.; Kreiser-Saunders, I.; Boettcher, C. Polylactones: 31. Sn(II)octoate-initiated polymerization of L-lactide: a mechanistic study. Polymer？1995, 36, 1253–1259, doi:10.1016/0032-3861(95)93928-F.
[28]
Zhang, X.; McDonald, D.A.; Goosen, M.F.; McAuley, K.B. Mechanism of lactide polymerization in the presence of stannous octoate: The effect of hydroxy and carboxylic acid substances. J. Polym. Sci. Part A: Polym. Chem？1994, 32, 2965–2970, doi:10.1002/pola.1994.080321519.
[29]
In’t Veld, P.J.A.; Velner, E.M.; van de Witte, P.; Hamhuis, J.; Dijkstra, P.J.; Feijen, J. Melt block copolymerization of ε-caprolactone and L-lactide. J. Polym. Sci. Part A: Polym. Chem？1997, 35, 219–226, doi:10.1002/(SICI)1099-0518(19970130)35:2<219::AID-POLA3>3.0.CO;2-N.
[30]
Tong, Z.; Peng, W.; Zhiqian, Z.; Baoxiu, Z. Microwave irradiation copolymerization of superabsorbents from cornstarch and sodium acrylate. J. Appl. Polym. Sci？2005, 95, 264–269, doi:10.1002/app.21265.
[31]
Li, H.; Liao, L.; Liu, L. Kinetic investigation into the non-thermal microwave effect on the ring-opening polymerization of ε-caprolactone. Macromol. Rapid Commun？2007, 28, 411–416, doi:10.1002/marc.200600648.
