## 1 Introduction  
Poly(\(\varepsilon\)-caprolactone) (PCL) and polylactide (PLA) are two of the most commonly used polyesters for biomedical applications due to their good biocompatibility and lack of toxicity [1; 2]. These polymers are very attractive because they degrade in vivo by hydrolytic deesterification during the carboxylic acid cycle and are subsequently excreted as carbon dioxide and water. PCL is known to be a semicrystalline, linear, aliphatic polyester with a slow degradation rate [3]. In the case of PLA, it is possible to obtain polymers with various crystallinities depending on the type of monomer used in the synthesis of polymer. PLA can be obtained by polycondensation from lactic acid or by ring-opening polymerization (ROP) of a lactide (LA) which is a cyclic dimer of lactic acid. LA monomers exist in three different stereoisomer forms: d-lactide (d-LA), l-lactide (l-LA) and _meso_ d,l-lactide (d,l-LA). A racemic mixture of d- and l-lactide is referred to as _rac_-lactide (_rac_-LA) [4]. Due to the significantly different properties (and thus rate of degradation) of PCL and PLA, biomaterials based on the LA and \(\varepsilon\)-caprolactone (CL) copolymers have attracted more attention in the fields of surgery, drug delivery systems and tissue engineering [5]. Improved copolymer properties strongly depend both on chemical composition and the chain microstructure. ROP is the most common method of synthesizing polyesters for biomedical applications due to ability to control polymer properties and architecture during this process. The ROP of a cyclic ester can be performed in the presence of cationic/anionic initiators, metal coordinate and enzymatic catalysts [6]. Enzyme catalysis has provided an environmentally friendly, synthetic strategy for a variety of polyester-based biomaterials [7; 8; 9]. Several lipases have been tested as catalysts for the ROP of different polyesters [10; 11; 12], among which _Candia antarctica_ lipase B (CALB) is the most promising biocatalyst. The enantioselectivity of the CALB is referred to as enabling a selective polymerization of d-LA and no polymerization of l-LA and its _meso_ form [13; 14]. Probably, the first monomer units during l-LA homopolymerization catalyzed by the immobilized form of CALB are opened. The resulting \(S\)-configuration of the secondary alcohol cannot undergo further monomer addition and causes the inhibition of the reaction. In contrast, \(R\)-configured secondary alcohol obtained from d-LA is able to react with another enzyme activated monomer and thus to propagate the chain [15]. [PERSON] et al. [16] reported that CALB immobilized on acrylic resin is more active for the ROP of d-LA than for l-LA when reaction was conducted in toluene. Interestingly, CALB seems to catalyze the ROP of l-LA in ionic liquids (ILs). ILs are attracting more attention as non-aqueous, green solvents for biocatalysis polymer synthesis [17; 18]. Enzymes in ILs may have higher activity, enantioselectivity, regioselectivity and stability than in conventional organic solvents [17]. [PERSON] et al. conducted the first ROP of l-LA in ILs using free form of CALB. The polymers were obtained with a number-average molecular weight (\(M_{n}\)) 54,600 g/mol and 43,800 g/mol with respect to the 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF\({}_{4}\)]) and 1-butyl-3-methylimidazolium bis((trifluoromethylsulfonyl))imide ([bmim][NT\({}_{2}\)]) at 110 \({}^{\circ}\)C after 24 h [19]. [PERSON] et al. [20] also obtained poly(l-lactide) (PLLA) with high \(M_{n}\) (37,800 g/mol) in 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF\({}_{6}\)]) at 90 \({}^{\circ}\)C using the immobilized form of CALB. On the other hand, [PERSON] et al. [21] obtained a low molecular weight PLLA with \(M_{n}\) = 581 g/mol after 11 days of polymerization at 65 \({}^{\circ}\)C using immobilized form of CALB and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF\({}_{6}\)]) as a solvent.