Amines initiation

With amine initiators the so-called self-catalysed polyols are obtained, which are used in the formulation of rigid spray foam systems. The rigidity or stiffness of a foam is increased by aromatic initiators, such as Mannich bases derived from phenol, phenoHc resins, toluenediamine, or methylenedianiline... 

Since amines initiate cyanoacrylate polymerization, the monomer cannot be isolated directly, because a polymer is generated immediately after formation of the monomer. An acid is then added to the polymer, and heat (140-180°C) is applied to the reaction mixture. Because of the relatively low ceiling temperature of the polymer, the pure monomer can be isolated, in greater than 80% yield, by the thermal reversion of the polymer back to the free monomer [4,5]. 

Table 1 Rp and Ea of MMA Bulk Polymerization Using Diacylperoxide-Amine Initiation System...

We have also investigated [15,16] the following novel BPO-amine initiation systems ... 

Rate Equations of MMA Polymerization Using Peroxide-Amine Initiation Systems... 

The mechanism of amide formation is a source of insight into the properties of carboxylic acids and amines. Initially, we might expect an amine to act as a base and simply accept a proton from the carboxylic acid. Indeed, that does happen, and a quaternary ammonium salt is formed when the reagents are mixed in the absence of a solvent. For example,... 

The authors concluded that the side reactions normally observed in amine-initiated NCA polymerizations are simply a consequence of impurities. Since the main side reactions in these polymerizations do not involve reaction with adventitious impurities such as water, but instead reactions with monomer, solvent, or polymer (i.e., termination by reaction of the amine-end with an ester side chain, attack of DMF by the amine-end, or chain transfer to monomer) [11, 12], this conclusion does not seem to be well justified. It is likely that the role of impurities (e.g., water) in these polymerizations is very complex. A possible explanation for the polymerization control observed under high vacuum is that the impurities act to catalyze side reactions with monomer, polymer, or solvent. In this scenario, it is reasonable to speculate that polar species such as water can bind to monomers or the propagating chain-end and thus influence their reactivity. 

Another innovative approach to controlling amine-initiated NCA polymerizations was reported in 2003 by Schlaad and coworkers [20]. Their strategy was to avoid formation of NCA anions, which cause significant chain termination after rearranging to isocyanocarboxylates [11, 12], through use of primary amine hydrochloride salts as initiators. The reactivity of amine hydrochlorides with NCAs was first explored by the group of Knobler, who found that they could react... 

A new approach of controlling NCA polymerization was reported by the Cheng group in 2007 [22]. hr a screen of amine initiators for the polymerization of Bn-Glu NCA, they found that hexamethyldisilazane (HMDS) showed remarkable control of polymerizations and led to formation of PBLG with excellent chain length control, with less than 22% deviation from the expected molecular weights, and narrow molecular weight distributions < 1.2) (Scheme 13). The NCA polymer-... 

R Glu = -(CH2)2COOCH2CeH5 Lys = -(CH2)4NHC(0)0CH2C6Hs Scheme 15 Polypeptide synthesis using TMS-amine initiators... 

Decarboxylative polymerisation of the N-carboxyanhydride can be brought about in two ways, the first being the use of a humidity cabinet [15] and the second involving the use of a suitable amine initiator, (Scheme 5). 

Amine initiated polymerisation is achieved by stirring the NCA with an appropriate amount of initiator in a suitable solvent, such as tetrahydrofuran. Over a period of time, the polymer precipitates and can be isolated by filtration. 

Most enamines, unfortunately, are sensitive to hydrolysis. The parent enamine, iV,iV-dimethylvinylamine, has in fact been prepared [3], but appears to be unstable. Enamines of cyclic ketones and many aldehydes can readily be isolated, however [4-7]. The instability of enamines might at first appear to diminish the utility of enamines as nucleophiles, but actually this property can be viewed as an added benefit enamines can be readily and rapidly generated catalytically by using a suitable amine and a carbonyl compound. The condensation of aldehydes or ketones with amines initially affords an imine or iminium ion, which then rapidly loses a proton to afford the corresponding enamine (Scheme 1). 

Schulte PA, Ringen K, Hemstreet GP, et al Risk assessment of a cohort exposed to aromatic amines. Initial results. 7 Occup Med 27 115-121, 1985... 

Kricheldorf HR, Garaleh M, Schwarz G (2005) Tertiary amine-initiated zwitterionic polymerization of pivalolactone - a reinvestigation by means of MALDI-TOF mass spectrometry. J Macromol Sci, Part A Pure Appl Chem 42 139-148... 

The course of the amination reaction is strongly dependent upon the nature of the amine used. With secondary amines, initial oxidation of the amine occurs to form an enamine attack of this intermediate at C-4 leads to a species such as 30 (Scheme 12), which ring-closes to form a pyrrole isomeric with that already described <2001TL5981>. 

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl ethers, the related naphthalene compounds, and even sufficiently reactive aromatic hydrocarbons. Generally, the coupling must be carried out in media which are neutral or slightly basic or which are buffered in the appropriate pH range. The reaction may also be carried out in nonaqueous media. While some primary and secondary aromatic amines initially form an A-azoamine, which may rearrange to the more usual amino-C-azo compound, tertiary amines couple in a normal manner. 

Tertiary amines initiate polymerization by zwitter-ion formation [13.14]. 

A detailed examination of the kinetics of amine-initiated polymerisation of sarcosine led Waley and Watson (14) to postulate a reversible addition of amines to NCA, viz. 

Table 3. Rates of amine-initiated polymerisations of NCA s in solution...

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