Dehydration polycondensation

Generally, PAs are produced by the dehydrating polycondensation of a diamine monomer and a dicarboxylic acid monomer. 

Lim et al. used a palladium complex for the cationic polymerization of TH F and the ROMP of NB [10]. The same group also showed that even condensation and chain polymerization could be performed simultaneously in one step (Scheme 11.45). This was achieved by the use of unimolecular compounds which can simultaneously act both as an initiator for chain polymerization, and as an end-capper for condensation polymerization. The method provides a simple means of combining NMRP with a condensation polymerization to yield interesting and useful block copolymers [207]. Another interesting new system for the combination of chain (AROP of CL) and step (dehydration polycondensation) polymerizations for polyester-based new material, in which scandium trifluoromethane sulfonate catalyzed both polymerization modes, was reported by Takasu et al. (Scheme 11.46) [208]. 

A process of subjecting a mixture of lactic acid, an aliphatic dihydric alcohol and an aliphatic dibasic acid directly to dehydration polycondensation (9)... 

A process of producing a polyester by subjecting lactic acid to dehydration polycondensation in the presence of a catalyst, in which solid-phase polymerization is carried out at least in part of the steps... 

No one had believed that direct polycondensation of L-lactic acid can give a high molecular weight of PLLA, until 1995 when Mitsui Chemical Co. first succeeded in synthesizing such a PLLA by using a special solution polycondensation technique. With this epoch-making success, many researchers including the present authors made efforts to establish the direct polycondensation of L-lactic acid. As shown in Scheme 1.22, two equilibria exist in the dehydrative polycondensation of L-lactic acid one is hydration/... 

Keywords synthesis, PLA, polycondensation, azeotropic dehydrative polycondensation, ring-opening polymerization, enzyme-catalyzed polymerization, molecular weight, kinetics, mechanism... 

Takasu et al. [24] reported that scandium trifluoromethanesulfonate [Sc(OTQ3] and scandium trifluoromethanesulfonimide [Sc(NTf2)s] are effective for one-step dehydration polycondensation of L-lactic acid. Bulk polycondensation of L-lactic acid was carried out at 130-170°C to give PLLA with Mn of 5.1 xlO -7.3xl0 (yield 32%-60%). However, the solution polycondensation was... 

Figure 3.3 Flow diagram of the azeotropic dehydrative polycondensation of LA...

Ajioka et al. [26] have synthesized PLA with a higher than 300 000 by azeotropic dehydrative polycondensation of LA in the presence of a catalyst and an organic solvent. These polymers have good mechanical properties and can be processed into products such as cups, film, and fiber, which can be used as compostable materials. 

Ricinoleic acid was polymerised via dehydration with an immobilised poly(e-caprolactone) (PCL) catalyst to give a polymer with MW up to 8,500 Da [14]. Immobilised CALB was efficient as a catalyst for the dehydration polycondensation of cis-9,10 epoxy-18-hydroxyoctadecanoic acid (from the outer birch bark) in toluene, in the presence of molecular sieves at 75 C, to give a polyester with the highest MW of 2.0 X lO Da after 68 h [15]. 

Various combinations of dicarboxylic acid and their activated derivatives with glycols have been reacted enzymatically to generate biodegradable polyesters under mild reaction conditions (Table 12.2), in accordance with the following general scheme of dehydration polycondensation mode (Scheme 12.3) [7]. 

A regioselective direct dehydration polycondensation between a polyol sugar component, sorbitol, and an adipic acid was carried out with a CALB catalyst at 90 °C for 48 h. The product, polysorbityl adipate, was water-soluble the Mn and MW values were 10,880 and 17,030 Da, respectively. Sorbitol was esterified at the primary alcohol group of 1-and 6-positions with high regioselectivity (85 5%). To obtain a water-insoluble sorbitol polyester, sorbitol, adipic acid and 1,8-octanediol (molar ratio 15 50 35) were terpolymerised at 90 °C for 42 h. The methanol-insoluble portion (80%) had an MW of 1.17 x 10 [30]. 

As described by Hunsen and co-workers [31], cutinase HiC (cutin hydrolase from Humicola insolens) catalysed a dehydration polycondensation between a glycol and a diacid at 70 °C for 48 h under vacuum, containing 1 % w/w enzyme. With the adipic acid component fixed, polyesters with M values up to 12,000 Da were obtained from diols. With the 1,4-cyclohexanedimethanol component fixed, polyesters obtained from succinic acid, adipic acid, suberic acid and sebacic acid had Mn values of 900, 4,000, 5,000 and 19,000 Da, respectively. 

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