Lactic acid condensation polymerization

Previously, PLAs were obtained via condensation of lactic acid by heating and driving off water, which produced a gummy polymeric material of ill-dehned molecular weight and microstmcture [6]. Ring-opening polymerization (ROP) of dilactones, pioneered by Carothers in 1932 [7], was the hrst initiative for an... 

The synthesis of PLA is a multistep process which starts from the production of lactic acid and ends with its polymerization [2-4, 6-7]. An intermediate step is often the formation of the lactide. Figure 21.2 shows that the synthesis of PLA can follow three main routes. Lactic acid is condensation polymerized to yield a low molecular weight, brittle polymer, which, for the most part, is unusable, unless external coupling agents are employed to increase its chains length. Second route is the azeotropic dehydrative condensation of lactic acid. It can yield high... 

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

Polylactide is a degradable polyester, formed by the ring-opening polymerization of lactide or the condensation polymerization of lactic acid. Lactide is produced from lactic acid, which derives from the fermentation of D-glucose, which is usually harvested from high-starch-content crops, such as com or sugar beet (Fig. 1). 

PLA was first produced by Pelouze (2), in 1845, through condensation polymerization of lactic acid. Although PLA was first synthesized more than 160 years ago, its commercial feasibility and usefulness has not been prominent until recently, when an economical way of manufacturing the monomer for PLA was discovered and commercialized (3). 

The second method is azeotropic condensation polymerization of lactic acid, which produces high-molecular weight PLA without using chain-extenders or esterification-promoting adjuvants. This type of polymerization needs high reaction rates and thus uses catalysts however, due to the use of catalysts, the PLA produced by this method is not suitable for some applications, such as medical, since any residual catalyst offers toxicity within the polymer, which is harmful for medical applications. In addition to toxicity, residual catalyst degrades PLA in further processing (39). On the other hand, the level of residual catalyst can be reduced with the use of sulphuric acid (55,56). 

Ajioka, K. Enomoto, K. Suzuki, and A. Yamaguchi, The Basic Properties of Poly Lactic Acid Produced by The Direct Condensation Polymerization of Lactic Acid, Journal of Environmental Polymer Degradation, Vol. 3 (8), p. 225-234,1995. 

Azeotropic dehydration and condensation polymerization (route 2 in Figure 8.2) yields directly high molar mass polymers. The procedure, patented by Mitsui Toatsu Chemicals [13, 14], consists of the removal of condensation water via a reduced pressure distillation of lactic acid for 2-3h at 130°C. The catalyst (in high amounts) and diphenyl ester are added and the mixture is heated up to reflux for 30-40 h at 103°C. Polycondensated PLA is purified to reduce residual catalyst content to the ppm range [5,10,15]. 

Ajioka, M., Enomoto, K., Suzuki, K., Yamaguchi, A. The basic properties of polyQactic acid) produced by the direct condensation polymerization of lactic acid. I. Environ. Polvm. Dearad.. 1995, 3, 225-234. 

Polylactic acid (PEA) is probably the best-known biobased polymer. It is made from glucose by fermentation to its monomer lactic acid. Two molecules of lactic acid are then condensed into the dimer lactide, which is subsequently ring-opened and polymerized to PLA in the presence of a catalyst. 

The DPC process dehydrates lactic acid into ohgomers, which are then further polymerized to PLA with simultaneous dehydration. However, removal of water generated from the condensation of lactic add is very difficult during the final stage of polymerization because the diffusion of moisture in the highly viscous polymeric... 

Ajioka M, Inomoto K, Susuld K, Yamaguchi A (1995) Basic properties of polylactic add produced by the direct condensation polymerization of lactic acid. Bull Chem Soc Jpn 68 2125-2131... 

These types of chiral Schiff bases can be obtained by the condensation of 2,2 -diamino-l,l -binaphthalene with saUcyl aldehydes. 1,2-Diaminocyclohexane can be also used as base material (13). In addition, methods for polymerization and copolymerization of lactic acid compounds have been reported by Hiltunen in a series of papers (14 16). 

Synthesis PL A is a thermoplastic aliphatic polyester which is formed by condensation polymerization of lactic acid, as mentioned in the preceding. Lactic acid is isolated from tapioca, corn and other plant root starches, sugarcanes, or other resources. Bacterial fermentation is normally used to produce lactic acid... 

Lactic acid through condensation polymerization to produce lower-molecular-weight PLA (degree of polymerization (DP) is normally less than 100). 

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