Lactides copolymerization

The stereocopolymers of lactic acid, prepared by the polymerization of various stereoisomers, are discussed in a subsequent section in this book and will not be discussed here. Typical comonomers that have been used for lactic acid or lactide copolymerization are glycolic acid or glycolide (GA) [11-17], poly (ethylene glycol) (PEG) or poly(ethylene oxide) (PEG) [15 3], poly(propylene oxide) (PPO) [16-18], (7 )- 3-butyrolactone (BL), 6-valerolactone (VL) [44-46], E-caprolactone (CL) [47-54], 1,5-dioxepan-2-one (DXO) [55-60], trimethylene carbonate (TMC) [61],... 

The comparative results of Rxns 6 and 10 show that Sn(Oct)2 did not inhibit PDL polymerization. Comparison of Rxns 1 and 2 as well as 3 and 4 showed that high molecular weight copolymers could be formed by first polymerizing PDL with Novozyme 435 in the absence of L-lactide and Sn(Oct)2. Since Sn(Oct>2 did not inhibit Novozyme-435 catalyzed PDL polymerization, we believe L-lactide inhibits Novozyme-435 catalyzed PDL polymerization. In other words, the formation of low molar mass copolymers in Rxns. 1 and 3 and relatively higher molar mass copolymers in Rxns. 2 and 4 is directly related to the presence or absence of L-lactide in the reactions. Hence, the strategy of first performing Novozyme-435 catalyzed PDL polymerization and, subsequently, adding L-lactide to the reaction, is a way to circumvent L-lactide inhibition. Reactions 7 and 9 show that when Novozyme-435 is absent from the two-catalyst system, Sn(Oct)2 alone at 70°C was ineffective for PDL/L-lactide copolymerization and L-lactide homopolymerization, respectively. 

Diiminatc zinc complexes are highly active catalysts in the copolymerization of epoxides and C02. Complexes that are catalytic are of the form ZnLX, where X is alkoxide, acetate, or bis(tri-methylsilyl)amide. Changing the ligand geometries of the complexes allows variation in the catalytic behavior and activity.941 The polymerization of lactide with diiminate zinc has also been studied.942... 

These representative aliphatic polyesters are often used in copolymerized form in various combinations, for example, poly(lactide-co-glycolide) (PLGA) [66-68] and poly(lactide-co-caprolactone) [69-73], to improve degradation rates, mechanical properties, processability, and solubility by reducing crystallinity. Other monomers such as 1,4-dioxepan-5-one (DXO) [74—76], 1,4-dioxane-2-one [77], and trimethylene carbonate (TMC) [28] (Fig. 2) have also been used as comonomers to improve the hydrophobicity of the aliphatic polyesters as well as their degradability and mechanical properties. 

Basko M, Kubisa P (2006) Cationic copolymerization of E-caprolactone and L,L-lactide by an activated monomer mechanism. J Polym Sci A Polym Chem 44 7071-7081... 

Tasaka F, Ohya Y, Ouchi T (2001) One-pot synthesis of novel branched polylactide through the copolymerization of lactide with mevalolactone. Macromol Rapid Commun 22 820-824... 

Table 10 Comparison of the copolymerization of lactide and glycolide in bulk by SnOct2 and BiHexs...

Polymerization and copolymerization of the two l,4-dioxane-2,5-diones (dilactones), glyco-lide and lactide (XLIX with R = H and CH3, respectively) proceeds using anionic initiators ... 

Scheme 13 Synthesis of a m-hydroxygluconic acid from a protected glucono-1,5-lactone derivative and further copolymerization with L-lactide...

Scheme 2 Copolymerization of a sugar-lactone with L-lactide...

To produce biodegradable poly(lactic acid-co-lysine) copolymers (for cell adhesion), it was first necessary to synthesize the monomer 3-[4-(A-benzyloxycarbonyl)aminobutyl]-6-methylmorpholine-2,5-dione (4, Scheme 4). During the final ring-closure step, a minor amount of epimerization occurs. However, the diastereomeric purity of 4 is in excess of 95%. The monomer 4 is copolymerized with L,L-lactide (3,6-dimethyl-l,4-dioxane-2,5-dione, 5) (Scheme 5) in tin(II) 2-ethylhexanoate at 100 °C for 24 hours. 

Due to the lack of vinyl monomers giving rise to crystalline segment by cationic polymerization, amorphous/crystalline block copolymers have not been prepared by living cationic sequential block copolymerization. Although site-transformation has been utilized extensively for the synthesis of block copolymers, only a few PIB/crystalline block copolymers such as poly(L-lactide-fc-IB-fc-L-lactide) [92], poly(IB-fr- -caprolactone( -CL)) [93] diblock and poly( -CL-fr-IB-fr- -CL) [94] triblock copolymers with relatively short PIB block segment (Mn< 10,000 g/mol) were reported. This is most likely due to difficulties in quantitative end-functionalization of high molecular weight PIB. 

Fig. 48 Formation of poly(lactide-co-glycolide) by copolymerization of lactide and glycol-ide...

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