Neutral amino acid ester accelerators

Neutral amino acid ester accelerators should yield monomer formulations having better shelf-life than the corresponding amino acids. This has been established experimentally (39). 

There is much evidence that the amines including polyamines accelerate hydrolyses of phosphoras acid esters via the general basic catalysis. In the unbuffered solution, a small amount of protonated amino groups are present in the PEI molecnles (<0.5-5.0% depending on the PEI molecular mass PEI with the molecular mass from 800 (PEI-800) to 60000 (PEI-60) were studied). This means that under these conditions PEIs behave as neutral polymers rather than polyelectrolytes. The pH kinetic profile danonstrates that up to pH 9.2 the observed rate constant of hydrolyses of 1 and 3 in 0.05M solution of PEI-50 does not exceed the limits of 5 x 10 s, while a further increase in the pH results in a ca. tenfold increase in the hydrolysis rate of both phosphonates. This pH dependence is rather typical and reflects the growth of the rate constant in the field of accumulation of catalytic species, namely nonprotonated amino groups, hi addition, the contribution of basic hydrolysis to kobs values at high pH should also be taken into account. 

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