Ring-opening polyaddition

Aromatic polyimides are most useful super engineering plastics which exhibit excellent thermal, electrical, and mechanical properties, and have been used widely in aerospace, electronics, and other industries over the past three decades [ 1 -4]. Aromatic polyimides are generally prepared through a two-step procedure by the ring-opening polyaddition of aromatic diamines to aromatic tet-racarboxylic dianhydrides in NMP (or DMAc) solution giving soluble polyamic acids, followed by thermal cyclodehydration (Eq. 1) [1-5]. 

Chitin is the most abundant biomacromolecule in the animal field, which is found normally in invertebrates as a structural component. This important polysaccharide was synthesized for the first time by the enzymatic polymerization using chitinase and a chitobiose oxazoline derivative (Scheme 14).131 The latter activated monomer has a distorted structure with an a configuration at Cl, which resembles a transition-state structure of substrate chitin at the active site during a hydrolysis process (Scheme 15).3b 131132 The ring-opening polyaddition of the chitobiose oxazoline derivative was exclusively promoted by chitinase at pH 10.6, where the hydrolytic activity of chitinase was very much lowered. 

Figure 7. Radical ring-opening polyaddition of bifunctional vinylcyclopropanes...

The complete ring-opening nature of the polymerization of a vinylcyclopropane stimulated us to apply it to radical ring-opening polyaddition... 

The poly(ether imide)s derived from ether-containing bis(ether anhydride)s (Scheme 2.8) or polyimides (Scheme 2.9) were prepared via a conventional two-stage procedure involving ring-opening polyaddition of the diamines (Tables... 

In 1995 the first in vitro synthesis of chitin was succeeded by a ring-opening polyaddition of a chitobiose oxazoline monomer, c.f.. 

Polycondensation is a typical method for polyimide syntheses, which need aromatic tetracarboxylic acids and aromatic diamines as monomers. Figure 10.1 shows that the polymerization process goes through two reactions The ring-opening polyaddition of aromatic diamines to aromatic tetracarboxylic dianhydrides in solution at room temperature gives soluble precursor polyamic acids, followed by solid-state thermal cyclodehydration to polyimides. 

Chitin is the most abimdant organic macromolecules in the animal field found in invertebrates (12). The in vitro ssmthesis of this important biomacromolecule has been achieved for the first time by enzymatic ring-opening polyaddition of a chitobiose oxazoline monomer (Fig. 3). Chitinase, a hydrolysis enzyme of chitin, regio- and stereoselectively induced the polymerization of the monomer in a basic buffer (38—41). It is postulated that the monomer is preferable as a... 

Wholly aromatic Pis like Kapton, insoluble in common organic solvents, are usually synthesized through a two-step method PI precursors, high molecular weight poly(amic acid)s (PAAs) are readily synthesized from ring-opening polyaddition of an extra-pure dianhydride and an equimolar diamine in aprotic amide solvents such as A,A-dimethylacetamide (DMAc) and A-methyl-2-pyrrolidone (NMP), then the as-cast dried PAA films are subjected to thermal or chemical imidization. The reaction scheme and the abbreviations of polymers and monomers are shown in Fig. 1. 

Synthesis of fluorinated chitin derivatives using chitinase from Bacillus sp. as a catalyst was carried out by Kobayashi and co-workers [227]. 6 -fluoro-, 6-fluoro-and 6,6 -difluoro-chitobiose oxazoline derivatives were newly prepared as TSAS monomers for chitinase. Ring-opening polyaddition of these monomers proceeded effectively at pH 8.0-9.0 and 30-40 C, giving rise to alternating 6-fluorinated chitin derivatives and fully 6-fluorinated chitin derivatives, under total control of region selectivity and stereoselectivity. 

It is known that the optimal pH for hydrolysis by chitinase is 7.8 [70]. The effects of pH on the ring-opening polyaddition of the monomer showed that the optimal value was around pH 10.6 in terms of the chitin yield (Table 3) at pH 8.0 the reaction time for the complete monomer conversion took 2.5 h however, the yield of synthetic chitin was 38%. At pH 10.6 it took 50 h and the... 

Table 3 Effect of pH on the ring-opening polyaddition of Chi-oxa monomer ...

The monomer was effectively recognized and consumed by HAase from ovine testes (OTH) at pH 7.5, giving rise to synthetic HA in good yields with high molecular weight values (Mn) via ring-opening polyaddition under total... 

Ring-opening Polyaddition of Optically Active Three Membered Rings... 

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