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Copolymerization of LA and CL has been extensively established [51–58]. Random copolymers of DLLA (r ₁ = 10.8) and CL (r ₂ = 0.37) were prepared by using lanthanide halides as initiators [55]. High molar mass copolymers of LLA and CL using Al and Zn compounds (e.g., Et₂AlOEt, aluminum acetyl acetonate) as catalysts and a variation in microstructure from random to diblock copolymers are also reported [51]. In the case of aluminum acetyl acetonate, the reactivity ratio of LLA was 44 and CL was 0.25. The microstructure depended on the temperature and the kind of initiator used. Also, magnesium complex with 4‐fluorophenol catalyst assisted as co‐catalyst system for sequential polymerization of LLA and CL to form poly(CL‐b‐LA) [120]. In the ligand‐assisted copolymerization, complexes with bulky substituents on the ligands yield a random arrangement, while less bulky substituents favor the formation of gradient copolymers, PLA‐gradual‐PCL. Alternating aluminum complexes bearing ligands containing electronegative atoms tends to favor CL polymerization rate selectively over LA [121, 122].

A series of copolymers of DLA and CL were synthesized by ROP using zinc lactate as a catalyst and carrying out the reaction at 145°C for 8 days. The formation of copolymers was confirmed by gel permeation chromatography (GPC), DSC and NMR. Interestingly, Kister et al. [53] used vibrational spectroscopy, particularly Raman spectroscopy, for determination of morphology, conformation, configuration, and composition of the copolymers. Raman spectroscopy thus appeared to be a suitable method for the identification of PDLA‐co‐PCL samples directly from solid samples without any special preparation.

Star‐shaped polymers consist of many linear polymers fused at a central point with many chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties, which are unattainable by simple linear polymers [123]. Adapting a dual reaction mode strategy, i.e., ROP with click reaction allowed formation of miktoarm star‐shaped and inverse star‐block copolymers of CL with LA to design novel structures [124]. Recently, synthesis of optically active poly(lactic‐alt‐caproic acid) by cross‐metathesis polymerization (CMP) followed by hydrogenation is adopted, which is seemingly an attractive synthetic approach for designing alternating aliphatic polyesters [125].