A process of preparing a reaction product enriched in (i) monoadduct, (ii) a mixture of adducts, (iii) a mixture of adducts and one or more oligomers, or (iv) a mixture of adducts, oligomers, and low molecular weight polymers, wherein the adducts are discrete molecules formed from addition of 1 to 7 vinylaromatic units to a monomethylaromatic compound, the oligomers are vinylaromatic addition product(s) having a degree of polymerization in the range of 8 to 25, and low molecular weight polymers are vinylaromatic addition product(s) having a degree of polymerization in the range of 26 to 80, which process comprises: 1) bringing together components A), B), C), and D) hereinafter described, by feeding at least component B) to a mixture formed at least from components A), C), and D), or to a mixture that is being formed by the feeding of at least components A), C), and D), in each case where components C) and D) are fed separately from each other and/or are fed as a complex formed or being formed from each other; 2) correlating the pseudo steady-state concentration of component B) in the reaction mixture during the feeding, the molar ratio of component A):component B) and maintaining the temperature or temperatures of the reaction mixture at one or more temperatures in the range of 80°C to 130°C to produce said reaction product, wherein the pseudo steady-state concentration is a concentration of a kinetically active reactant or component, which concentration remains constant or substantially constant during the course of a reaction other than startup and termination; and 3) terminating the feed of component B) and then terminating the reaction; wherein: -- component A) is at least one aromatic hydrocarbon in which there is one and only one methyl group in the molecule, which methyl group is bonded to an aromatic ring, and in which at least one position on the aromatic ring bearing the methyl group is unsubstituted; -- component B) is at least one monovinylaromatic hydrocarbon; -- component C) consists of n-butyllithium, sec-butyllithium, phenyllithium, benzyllithium, 1-hexyl-1-phenyllithium or polystyryllithium; and -- component D) is at least one aliphatic poly(tertiary amine) ligand that complexes with component C). 1) bringing together components A), B), C), and D) hereinafter described, by feeding at least component B) to a mixture formed at least from components A), C), and D), or to a mixture that is being formed by the feeding of at least components A), C), and D), in each case where components C) and D) are fed separately from each other and/or are fed as a complex formed or being formed from each other; 2) correlating the pseudo steady-state concentration of component B) in the reaction mixture during the feeding, the molar ratio of component A):component B) and maintaining the temperature or temperatures of the reaction mixture at one or more temperatures in the range of 80°C to 130°C to produce said reaction product, wherein the pseudo steady-state concentration is a concentration of a kinetically active reactant or component, which concentration remains constant or substantially constant during the course of a reaction other than startup and termination; and 3) terminating the feed of component B) and then terminating the reaction; -- component A) is at least one aromatic hydrocarbon in which there is one and only one methyl group in the molecule, which methyl group is bonded to an aromatic ring, and in which at least one position on the aromatic ring bearing the methyl group is unsubstituted; -- component B) is at least one monovinylaromatic hydrocarbon; -- component C) consists of n-butyllithium, sec-butyllithium, phenyllithium, benzyllithium, 1-hexyl-1-phenyllithium or polystyryllithium; and -- component D) is at least one aliphatic poly(tertiary amine) ligand that complexes with component C).