Polydispersity index Polyester

See also PBT degradation structure and properties of, 44-46 synthesis of, 106, 191 Polycaprolactam (PCA), 530, 541 Poly(e-caprolactone) (CAPA, PCL), 28, 42, 86. See also PCL degradation OH-terminated, 98-99 Polycaprolactones, 213 Poly(carbo[dimethyl]silane)s, 450, 451 Polycarbonate glycols, 207 Polycarbonate-polysulfone block copolymer, 360 Polycarbonates, 213 chemical structure of, 5 Polycarbosilanes, 450-456 Poly(chlorocarbosilanes), 454 Polycondensations, 57, 100 Poly(l,4-cyclohexylenedimethylene terephthalate) (PCT), 25 Polydimethyl siloxanes, 4 Poly(dioxanone) (PDO), 27 Poly (4,4 -dipheny lpheny lpho sphine oxide) (PAPO), 347 Polydispersity, 57 Polydispersity index, 444 Poly(D-lactic acid) (PDLA), 41 Poly(DL-lactic acid) (PDLLA), 42 Polyester amides, 18 Polyester-based networks, 58-60 Polyester carbonates, 18 Polyester-ether block copolymers, 20 Polyester-ethers, 26... 

Controversial results are reported in the literature regarding the polydispersity of polyesters produced by SSP, associated with the side reactions in the later stages of the reaction. These are not only dependent on the concentrations of the reactive groups but also on their intramolecular distances [11], Additionally, it has been found that cyclization leads to a different polydispersity. According to theoretical considerations, the polydispersity index of an SSP polymer is generally higher than that of prepolymer produced in the melt phase, which should, in an ideal case have a value of 2 [21-24, 59],... 

All these limitations were overcome by implementing a third approach based on the ROP of lactones [7, 8]. Indeed, many examples of living or/and controlled polymerization with fast initiation are reported using this technique. High molar mass aliphatic polyesters with low polydispersity indexes can be thus be synthesized. In terms of the availability of the monomers, this approach occupies... 

The Novozym 435-catalyzed ring-opening polymerization of e-caprolactone shown in Figure 6.2 was also performed in the presence of methyl or ethyl gluco-pyranosides. In this way, polyesters with low polydispersity index (PDI) values and initiated by alkyl glucopyranosides (acylated at their primary OH) could be prepared [48]. 

Table 1 Average molecular weights, polydispersity index, mole-percent branching agent, branching frequency, Mark-Houwink-a value, and melting temperature for the synthesized polyesters. L = linear PBA, TMP = trimethylol propane was used as a branching agent, BT = 1,2,4-butanetriol was used as branching agent ...

The molecular weight distribution (MWD) of polyester polyols is broader than that of polyether polyols. The polydispersity index (PDI) of high MW polyester polyols (e.g., 2000 daltons) is around 2.8. 

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]. 

Lipase-catalyzed synthesis of PBS is a recently developed method, which is fulfilled at milder conditions without remnant metal salt. In 2006, Azim et al. (2006) reported Candida antarctica lipase B catalyzed synthesis of PBS from the monophasic reaction mixtures of diethyl succinate and 1,4-butanediol. The reaction temperature played an important role in determining the molecular weight of PBS. After polymerization for 24 h in diphenyl ether, PBS with of 2,000,4,000, 8,000, and 7,000 was produced at 60, 70, 80, and 90°C, respectively. The low molecular weight was due to precipitation after polymerization for 5-10 h, limiting the growth of the polyester chain length. Increasing the polymerization temperature from 80 to 95°C can result in the maintenance of a monophasic reaction mixture after 21 h, which led to production of PBS with of 38,000 and polydispersity index of 1.39. 

If the termination reaction in chain polymerization is by disproportionation, then the polydispersity index, MJM , is 2. Termination by combination yields a polydispersity index of 1.5. Stepwise polymerizations, such as polyester formation, yield a value of 2. Anionic polymerizations yield surprisingly narrow distribution, with values sometimes less than 1.05. 

Some of the earliest work on the use of imidazolium-derived NHCs as catalysts focused on their ability to serve as initiators for polymerization reaction. Pioneers of this area, Waymouth and Hedrick extensively investigated the synthesis of polyesters under the influence of an NHC catalyst. Their results have been summarized in a number of excellent accounts. In 2002, Hedrick first investigated catalytic living polymerization using NHCs for cyclic esters (Scheme 14.27). Then, Waymouth and Hedrick studied polymerization of lactides and a-caprolactones and explored the chemical and mechanical properties of the resulting polymers. Also, the use of multifunctional alcohol initiators, such as ethylene glycol or pentaerythritol, produced star polymers with good conversion and low PDI (polydispersity index). ... 

Finally, the catalytic activity of DMCs in esterification reactions can be readily combined with their catalytic activity in epoxide ring-opening polymerizations, as was reported by Suh et al. [35]. This study showed that the copolymerization of propylene oxide with cyclic acid anhydrides such as succinic, maleic, or phthalic anhydride, catalyzed by a Zn-Co-DMC, afforded polyester polyols characterized by a moderate molecular weight and narrow polydispersity index. 

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