Iminocarbonic reactions with

This feature of the interfacial preparation of poIy(iminocarbon-ates) has an important consequence for the synthesis of copolymers if the dicyanate component is structurally different from the diphenol, partial hydrolysis of the dicyanate will lead to the presence of two structurally different diphenol components that will compete for the reaction with the remaining dicyanate. The interfacial copolymerization will therefore result in a random copolymer. On the other hand, during solution polymerization no hydrolysis can occur. Since the dicyanates can only react with diphenols and vice versa, solution polymerization results in the formation of a strictly alternating copolymer. 

Poly(amino acids) are insoluble in common solvents, are difficult to fabricate due to high melting point, and absorb a significant amount of water when their acid content reaches over 50 mol%. To solve these problems, polyesters derived from amino acids and lactic acids [e.g., poly (lactic acid-co-lysine) PLAL] are developed. The PLAL system is further modified by reaction with lysine A-carboxyanhydride derivatives. Another modification of poly(amino acids) includes poly(iminocarbon-ates), which are derived from the polymerization of desaminotyrosyl tyrosine alkyl esters. These polymers are easily processable and can be used as support materials for cell growth due to a high tissue compatibility. Mechanical properties of tyrosine-derived poly(carbonates) are in between those of poly(orthoesters) and poly(lactic acid) or poly(gly-colic acid). The rate of degradation of poly(iminocarbonates) is similar to that of poly (lactic acid). 

Illustrative Procedure 2 Poly(iminocarbonates) by Solution Polymerization (46) Under argon, 1 g of a diphenol and an exact stoichiometric equivalent of a dicyanate were dissolved in 5 ml of freshly distilled THF. 1 mol% of potassium tert-butoxide was added, and the reaction was stirred for 4 hr at room temperature. Thereafter, the poly(iminocarbonate) was precipitated as a gumUke material by the addition of acetone. The crude poly(iminocarbonate) can be purified by extensive washings with an excess of acetone. The molecular weight (in chloroform, relative to polystyrene standards by GPC) is typically in the range of 50,000-80,000. 

Friesen et al. reported that 2,3-allenols 340 can be converted to the corresponding carbamate derivatives 343, in which the terminal C=C bond of the allene moiety can be iodinated to afford diiodides 344. Under the catalysis by an Ag+ salt, compounds 344 react to give iminocarbonates 345 and oxazolindinones 346, leading to diols 347 and amino alcohols 348, respectively, after hydrolysis (Scheme 10.138) [160-162], A similar reaction was observed with trichloroacetimidates 350 [163],... 

In the palladium-catalyzed allylic amination reaction, primary and secondary amines can be used as nucleophiles, whereas ammonia does not react. Therefore, many ammonia synthons have been developed, and a variety of protected primary allyl amines can now be prepared using azide, sulphonamide, phthalimide, di-f-butyl iminocarbonate ((Boc)2NLi), and dialkyl A-(rerr-butoxycarbonyl)phosphoramide anions as the nucleophile [20], An example of the use of ((Boc)2NLi) 30 as the amine nucleophile in the palladium-catalyzed allylic amination reaction is shown in Eq. (9). This reaction also illustrates the problem with the regioselectivity in the reaction as a mixture of the products 31-33 are obtained [21]. 

CEs are known to react with phenols to form iminocarbonates which eventually lead to polycyanurates with the liberation of more acidic phenol moiety. This can be a method to alter the gel point of the resin, Tg, and thermal stability of the network by co-curing diphenol with CE. Thus, copolymerization of dicyanate with diphenols resulted in polycyanurates with altered network structure and diminished crosslink density [237]. However, an earlier report claims poly(imi-nocarbonate) by reaction of these two in equimolar quantities. The thermoplastic so formed was reported to retain the mechanical properties like a polycarbonate. This approach can produce strong, non-toxic, biodegradable films and molded plastics that are degradable at temperatures above 140 °C [169,238]. Except for a few very early reports [239], the reaction of CE with anhydrides to form poly(iminocarbamates) has not been explored much. 

Reaction of chloroformamidinium chloride (XXXVII) (cyanamide dihydrochloride) with diethyl iminocarbonate yields diethyl N-cyano-imidocarbonate (XXXVIII) ( ). 

The acylation of diethyl iminocarbonate, (EtO)2C=NH, with oxalyl chloride or phosgene, gave (Et0)2C=NC(0Et)=NC02Et, Et02CNC0, (Et02CNH)2CO, [CON=C(OEt)2]2, and (C0NHC02Et)2- The primary intermediates in the reactions... 

The cationic ROP of himethylene carbamate affords the corresponding polyurethanes with a regular microshucture [71-76]. The reaction is performed in the melt at 100 °C, and high conversions/yields are obtained. The mechanism and kinetics of the polymerizahon reaction, when studied in detail, was shown to proceed via an achve chain end with a protonated cyclic endo iminocarbonate as the active species and an absence of transfer reachons. In fact, the reaction involves... 

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