Ring-Opening Polymerization of ε-Caprolactone Initiated by Natural Amino Acids

Abstract

Introduction. Poly( -caprolactone) (PCL) is currently being investigated for use in medical devices and pharmaceutical controlled release systems because of its biocompatibility, biodegradability, and good drug penetrability. [1][2][3] PCL is usually synthesized by ringopening polymerization (ROP) of -caprolactone ( -CL), which is carried out in the presence of metal-contained 4-8 or metal-free compounds. [9][10][11][12][13] The ROP can be initiated by active hydrogen of amine and alcohol, [14][15][16] and the effect of active hydrogen on the polymerization is enhanced by an organic acid. Rozenberg obtained PCL with molecular weight over 8000 g/mol from the polymerization of -CL initiated by aniline in the presence of a protonic acid. 17 Xie et al. revealed that the polymerization of -CL in the presence of hydroxyl acid was a hydroxyl-initiated reaction, and the carboxyl group did not initiate but accelerated the polymerization. 18 Sanda et al. carried out the polymerization of -CL with alcohols as initiators and fumaric acid as an activator of the monomer. 19 Recently, we investigated the ROP of -CL in the presence of natural amino acids considering that they are essential components in human nutrition, and the biocompatibility and in vivo safety of thus-obtained PCL must be satisfying for medical and pharmaceutical purpose. The results, which are presented in this paper, indicate that polymerization of -CL was initiated by the amino group of amino acid (Scheme 1).Experimental Section. -CL (Aldrich) was dried over calcium hydride for 48 h and distilled under reduced pressure. 1,4-Dioxane was purified by distillation after drying with sodium. All other materials were analytical grade and used as received.1 H NMR spectra of PCL were recorded on a Mercury VX-300 (300 Hz) apparatus with tetramethylsilane (TMS) as internal standard and CDCl 3 as solvent. Number-average molecular weight by GPC (M n,GPC ) and polydispersity index (M w /M n ) of PCL were measured with a Waters high-performance liquid chromatography system equipped with a model 2690D separation module, a model 2410 refractive index detector, and Shodex K802.5 (pore size 60 Å) and Shodex K805 (pore size 500 Å) columns in series. The measurements were per-

Organophosphate-catalyzed bulk ring-opening polymerization as an environmentally benign route leading to block copolyesters, end-functionalized polyesters, and polyester-based polyurethane

“…7 Considerable effort has been directed toward the evaluation of various types of both organic acids/bases for the ROP of cyclic esters, 7-37 cyclic carbonates, [38][39][40][41][42][43] epoxides, [44][45][46][47] lactams, 48 cyclic (carbo)siloxanes, 49 cyclic phosphates, [50][51][52][53][54] etc. Regarding the ROP of cyclic esters, organic Brønsted acids, e.g., methane sulfonic acid (MSA) and triflimide, were found to be suited for the polymerization of lactones, [8][9][10][11][12][13][14][15][16][17][18][19] whereas organic bases, e.g., 1,8-diazadicyclo [5.4.0]undec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP), were effective for the ROP of the lactide (LA). 7,[20][21][22][23][24]26 In addition, the bifunctional catalytic system possessing two activation sites for the monomer and propagating chain end also turned out to be effective for the ROP of ε-caprolactone (ε-CL) and LA.…”

A Recoverable, Metal-Free Catalyst for the Green Polymerization of ε-Caprolactone

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Metal complexes are the most commonly explored catalysts for the production of polycaprolactone. Previous examples of metal complexes used as catalysts include tin, 2,6,[15][16][17][18][19][20][21] aluminum, 6,10,18,19,[22][23][24][25][26][27] iron, 6,18 scandium, 1,12,28 yttrium, 14,18,[29][30][31][32][33][34][35] zinc, [36][37][38][39] and other metals.…”

“…11 These reactions show characteristics of a controlled, living reaction (e.g., conversion shows a linear relationship to reaction time, molecular weight shows a linear dependence on conversion, and the resulting polymers show a low polydispersity). 3,11,46 Other purely organic systems that display catalytic activity include natural amino acids, 9 organic acids, 47 and acid/alcohol systems. 13 Unfortunately, these catalysts are all homogeneous species 48 that, while not contaminating the polymer with metal residue, are not easily recoverable from the reaction mixture, making catalyst recovery and recycle problematic.…”

Polymers in the Pharmaceutical Applications - Natural and Bioactive Initiators and Catalysts in the Synthesis of Biodegradable and Bioresorbable Polyesters and Polycarbonates

“…The studies performed by Liu and coworkers showed that they are also effective as initiators of ROP of CL (Liu & Liu, 2004). Authors found hat the number-average molecular weights of the obtained polymers did not exceed 5700 Da and that used amino acids were incorporated into macromolecule chain ( Figure 6).…”