CAMPHORQUINONE AS A PHOTOINITIATOR IN THE POLYMERIZATION OF 2-HYDROXYETHYL METHACRYLATE IN AQUEOUS SOLUTION: A KINETIC STUDY

Abstract

The photoinitiated polymerization of 2-hydroxyethyl methacrylate (HEMA) (1-3 M) using camphorquinone (CQ) \ triethanolamine (TEOHA) system has been studied in the pH range 6.0-9.0. The kinetics of the reaction has been evaluated during the initial stages causing about 5% HEMA conversion to avoid the effects of any variation in the volume of the solution. The change in the concentration of HEMA during polymerization has been determined by a UV spectrometric method at 208 nm with a precision of 3%. The apparent first-order rate constants (kobs) for the polymerization of HEMA by CQ in the presence of 0.01 M TEOHA, carried out up to 100 s, range from 3.35-7.78 (1 M), 2.72-6.78 (2 M) and 2.33`5.89x104 s-1(3 M). The second-order rate constants for the interaction of TEOHA radicals with HEMA (1-3 M) range from 2.33-7.78x10-2 M 1 s-lat pH 6.0-9.0 indicating an increase in the reactivity of TEOHA radicals with an increase in the pH of the solution. There is a linear relation between kobs (1-3 M HEMA) and inverse of solution viscosity suggesting the quenching of CQ excited state with an increase in the viscosity of the medium.

Keywords

• Camphorquinone
• 2-hydroxyethyl methacrylate
• pH effect
• polymerization
• viscosity effect.