Polyester synthesis polymerization

The preceding discussions of the kinetics and molecular weight distributions in the step-growth polymerization of AB monomers are clearly exemplified by the esterification reactions of such monomers as glycolic acid or co-hydroxydecanoic acid. Therefore one method for polyester synthesis is the following ... 

The reaction between acid chlorides and aliphatic alcohols or phenolic compounds commonly takes place at low to moderate temperature (—10 to 100°C) in solution or by interfacial or dispersion polymerization techniques. It has been widely applied to polyester synthesis. Reviews and books are available on the polymerization techniques as well as on the chemistry of this reaction.2,207 294... 

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

The understanding of the SSP process is based on the mechanism of polyester synthesis. Polycondensation in the molten (melt) state (MPPC) is a chemical equilibrium reaction governed by classical kinetic and thermodynamic parameters. Rapid removal of volatile side products as well as the influence of temperature, time and catalysts are of essential importance. In the later stages of polycondensation, the increase in the degree of polymerization (DP) is restricted by the diffusion of volatile reaction products. Additionally, competing reactions such as inter- and intramolecular esterification and transesterification put a limit to the DP (Figure 5.1). 

Frechet and coworkers reported a first example of the synthesis of a hyperbranched aliphatic polyester by polymerization of an AB inimer, i.e., 4-(hydroxyethyl)-s-caprolactone [164]. It is worth noting that the synthesis of this inimer is quite long. Since this pioneering work, other teams have reported the polymerization of a series of AB [165-167] and AB2 [168] inimers, which are shown in Fig. 38. The polymerization of these inimers can be carried out in the absence or presence of a comonomer such as sCL [167]. 

M]0 = 5 M. A concentration of 5 M is fairly typical of a step polymerization that is often carried out with only the reactant(s) present (without solvent). The lowering of [H20] to achieve a particular Xn is less the more favorable the equilibrium (that is, the larger the K value). Thus the synthesis of polyamides (with typical K values > 102) is clearly easier from the equilibrium viewpoint than polyester synthesis (K 0.1-1). Polyesterification requires a greater lowering of [H20] than does polyamidation. It should be understood that simply to lower [H20] as much as possible is not the desired approach. One needs to control the [H20] so as to obtain the desired degree of polymerization. 

Lipase-catalyzed transesterification to prepare polyesters (replacing the traditional chemical polymerization at >200 °C) has received considerable attention in recent years. CaLB was found to mediate polyester synthesis in the ionic liquids [BMIm][BF4], [BMIm][PF6], and [BMIm][ Tf2N] at 60°C [110, 111, 112], but the molecular weight of the product was rather low compared with that in a solventless system [113], perhaps owing to the high viscosity of ionic liquid media. 

Lipase catalyzed esterifications were performed favorably solvent-free [21] and were applied also to bulk polymerization for polyester synthesis [22]. 

Lipase Transesterification and direct esterification (inch polyester synthesis) Ring-opening polymerization of 8-caprolactone Hydrolysis alcoholysis acetylation Higher stability of enzyme greater activity catalyst recyclable sometimes higher enantio- and regio-selectivity compared with VOCs... 

In the case of polyester synthesis from divinyl esters, hydrolysis of the vinyl end group partly took place, resulting in the limitation of the polymer growth.201 A mathematical model showing the kinetics of the polymerization predicts the product composition. On the basis of these data, a batch-stirred reactor was designed to minimize temperature and mass-transfer effects.202 The efficient enzymatic production of polyesters was achieved using this reactor poly(l,4-butylene adipate) with Mn 2 x 104 was synthesized in 1 h at 60 °C. 

Chain branches in stepwise polymerization may occur due to side reactions such as the addition of an -OH to a double bond in unsaturated polyester synthesis. Alternatively, chain branches can be a delibemte addition such as in polyurethane synthesis where a functionality greater than 2 is brought to bear (e.g. by using a triol chain extender) so that chain branching can occur. In systems of stepwise polymerization in which the reagents are polyftinctional these branches will lead to the occurrence of crosslinks and gelation. This is... 

Enzymatic polymerizations are a promising strategy under study by many groups throughout the world to develop environmental friendly processes for polyester synthesis. 

Okumara et al. [10] were the first to attempt the enzyme-catalyzed synthesis of oligoesters from a reaction between dicarboxylic acids and diols. Gutman et al. [11] reported the first study on polyester synthesis by enzyme-catalyzed polymerization of A-B type monomers. Two independent groups in 1993 [12, 13] were first to report enzyme-catalyzed ring-opening polymerization (ROP). Their studies focused on 7- and 6-membered unsubstituted cyclic esters, e-caprolactone (e-CL) and 8-valerolactone (8-VL), respectively. 

In the present chapter, the current status of enzymatic polyester synthesis is described. For information on the enzymatic synthesis of chiral polyesters and polyester block copolymers using enzymatic polymerizations please refer to Chapters 11 and 12 respectively. 

The in vitro polyester synthesis can proceed via two major polymerization modes (see Scheme 4.1) ... 

The most extensively studied enzymatic polymerization system is that of polyesters via polycondensations or ring-opening polymerizations. The state of the art of in vitro enzymatic polyester synthesis is reviewed in Chapter 4. 

There exist two main ways for the synthesis of polymers polycondensation and polymerization. A polycondensation is a series of chemical reactions between difunctional compounds thus the esterification of a diacid by a dialcohol produces a polyester. A polymerization is a chain reaction the polymers have at one extremity an active site, and they grow step by step by adjunction of monomers containing a double bond when a monomer clings to a chain, the double bond opens and the activity is transferred to the new extremity of the chain. Therefore, such a transformation requires an initiator able to create active sites. Industrially, the polymerization processes correspond to the largest tonnage and scientifically, for the preparation of good samples, they are also the most interesting. 

In recent years, the enzymatic synthesis of biodegradable polyesters was focused on the polycondensation method (22,23). Among the very few successful example of enzymatic ring-opening polymerization for polyesters synthesis, Novozyme-435 (immobilized lipase B from Candida antartica) has been proved an effective catalyst for polycaprolactone (PCL) synthesis in toluene (24). Considering the low cost and high recyclablity of IPPL, we also... 

Polyacrylic resins were employed to study how immobilization resin particle size influences Candida antarctica Lipase B (CALB) loading, fraction of active sites, and catalytic properties for polyester synthesis. CALB adsorbed more rapidly on smaller beads. Saturation occurred in less than 30 seconds and 48 h for beads with diameters 35 and 560-710 pm, respectively. Infrared microspectroscopy showed that CALB forms protein loading fronts for resins with particle sizes 560-710 and 120 pm while CALB appears evenly distributed throughout 35 pm resins. The fraction of active CALB molecules adsorbed onto resins not influenced by particle size was less than 50 %. At about 5% w/w CALB loading, decrease in the immobilization support diameter from 560-710 to 120,75 and 35 pm increased conversion of s-CL to polyester (20 to 36, 42 and 61%, respectively, at 80 min). Similar trends were observed for condensation polymerizations of 1,8-octanediol and adipic acid. 

Lipase-catalyzed polyester synthesis has received considerable interest [31] due to the harsh conditions used in traditional chemical polymerization (> 200 C), and has also been subjected to reaction in ILs. Both CaLB and PcL lipases have been found to catalyze polyester synthesis in [BMIM][BF4] and [BMIM][PF6], but this approach does not seem to offer any advantages over state-of-the-art lipase-mediated polyester synthesis [32, 33] [Eq. (3)]. Still, the polydispersity index of the polymers formed in ILs were remarkably affected, giving values close to 1, which indicate a very narrow molecular weight range compared to material prepared by conventional polymerization processes [33]. 

Finally, the preparation of nonaqueous polymer dispersions has been used as a technique for polymer production. Process advantages such as the use of lower temperatures for polyamide and polyester synthesis can be obtained [3.70]. Products such as synthetic elastomers can be obtained in powder form [3.104]. The fine particulate form of dispersions of water-soluble polymers (e.g., polyacrylamide) offers a convenient route to aqueous solutions of polymeric flocculants and thickeners [3.105]. 

Yang, Y., Yu, Y., Zhang, Y., Liu, C., Shi, W., Li, Q. Lipase/esterase-catalyzed ring-opening polymerization A green polyester synthesis technique. Process Biochem. 2011,46,1900-1908. 

---