Ring-opening Polymerisation of Lactide

Figure 2.14 Organocatalytic ring-opening polymerisation of lactide with a hydroxyethyl functionalised NhIC compound as catalyst.

Regardless of the methods used to synthesise lactic acid-based polymers, the monomers must be purified [34]. The ring-opening polymerisation of lactides can be initiated or catalysed by many compounds acting via different general mechanisms. Protic acids (hydrobromic acid (HBr), hydrochloric acid (HCl), triflic acid and so on). 

PLA is synthesised by the ring-opening polymerisation of lactide [10, 11, 24], the cyclic dimer of lactic acid, which is produced on a large scale via fermentation. 

M. D., Mahon, M. F. Robust chiral zirconium alkoxide initiators for the room-temperature stereoselective ring-opening polymerisation of rac-lactide. 2008,21,1437-1443. 

The polymers are synthesised via two routes direct polycondensation of lactic and glycolic acids or ring-opening polymerisation of the cyclic lactide and glycolide dimers.The nomenclature for polymers prepared by different routes is full of contradictions, but polymers prepared from lactic acid by polycondensation are strictly referred to by the acid, as in poly(lactic acid), and those prepared by ring-opening polymerisation by the dimer, as in polylactide (PLA). ... 

Addition of L-lactide monomer to preformed active PCL chains gave 98% conversion of lactide monomer and formation of block copolymer. That is, the PCL end groups initiated the ring-opening polymerisation of L-lactide. It was also demonstrated that there was no transesterification reaction during the polymerisation the end groups of the propagating lactide chain did not attack the preformed PCL chain. 

It was also shown that lactide ends would not initiate ring-opening polymerisation of 8-caprolactone in the presence of aluminium triiospropoxide caprol-actone ends 10 would open L-lactide rings [117]. 

Jugdaohsingh R, Anderson SH, Tucker KL, Elliott H, Kiel DP, Thompson RP, Powell JJ (2002) Dietary silicon intake and absorption. Am J Clin Nutr 75(5) 887-893 Li HL, Zhu Y, Xu D, Wan Y, Xia L, Zhao X (2009) Vapour-phase silanization of oxidised porous silicon for stabilizing composition and photoluminescence. J Appl Phys 105 114-307 Mclnnes SJP, Thissen H, Choudbury NR, Voelcker NH (2009) New biodegradable materials produced by ring opening polymerisation of poly(L-lactide) on porous silicon substrates. J Coll Interf Sci 332 336-344... 

Mclimes SJ, Thissen H, Choudhury NR, Voelcker NHJ (2009) New biodegradable materials produced by ring opening polymerisation of poly(L-lactide) on porous silicon substrates. Colloid Interf Sci 332... 

However, ring-opening polymerisation of the lactide, as practised by Cargill, appears more advantageous. The latter is polymerised in the presence of tin/zirconium or titanium catalysts (this technique is also used to polymerise lactones, e.g. caprolactone on the large scale). Lactide, rather like lactic acid, but now possessing two asymmetric carbon atoms within its structure can exist as three stereoisomers L-lactide, D-lactide, and the meso-lactide (see Figure 10.9). 

RING-OPENING POLYMERISATION OF LACTONES, LACTIDES CABOXYANHYDRIDES AND SIMILAR MONOMERS... 

The second process, ring-opening polymerisation of lactones, lactides and glycolide (Fig. 4.3), is free from these limitations. High molecular weight polyesters can be easily prepared under mild conditions from lactones of different ring size, substituted or not by functional groups (Lou et al, 2003). 

Ring-opening polymerisation of lactones, lactides and glycolide. 

Supercritical carbon dioxide as a medium for the ring-opening polymerisation of lactones and lactides and a processing aid for aliphatic polyesters... 

The gold(I) complexes of the hydroxycyclohexyl functionalised carbene ligands were tested for their ability in the ring opening polymerisation (ROP) of L-lactide under solvent-free melt conditions [177,178]. 

A methoxy-terminated PEG-/>-PLA copolymer (CHsO-PEG-fo-PLA) was synthesised using the anionic ring-opening polymerisation (ROP) of both ethylene oxide and D,L-lactide in anhydrous tetrahydrofuran (THE). A typical experimental procedure for the synthesis of CHsO-PEG-f -PLA is described below. 

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