Preferred reinforcement promoters include those chemicals having the following structure: ##STR1## wherein R1 is an organic group free of olefinic or acetylenic unsaturation having a valence of n; R2 ; R3 and R4 are hydrogen, carboxy or monovalent organic groups free of olefinic or acetylenic unsaturation; X is: ##STR2## m has a value of 0 or 1; and n has a value of at least two, and preferably fr