The effect of amines on the polymerization of methyl methacrylate N. Arsu*, M. Aydın Yıldız Technical University, Chemistry Department, 80270 Istanbul, Turkey (Received 4 January 1999) SUMMARY: Different amines, namely N-isopropylmorpholine, N-isopropylpyrrolidine, N-isopropylpiperi- dine, and 1,3-dimorpholinopropane were synthesised and they were used with type I and type II photoinitia- tors in the polymerization of methyl methacrylate. Their efficiency was compared with that of N-methyldie- thanolamine (NMDEA), which is a well known synergist, and it was found that 1,3-dimorpholinopropane worked as well as NMDEA. High concentrations of N-isopropylpyrrolidine and 1,3-dimorpholinopropane lead to an increase in the rate of polymerization of methyl methacrylate. ZUSAMMENFASSUNG: Verschiedene Amine (N-Isopropylmorpholin, N-Isopropylpyrrolidine, N-Isopro- pylpiperidin und 1,3-Dimorpholinopropan) wurden hergestellt und mit Typ-I- und Typ-II-Photoinitiatoren fu¨r die Polymerisation von Methylmethacrylat verwendet. Ein Vergeich ihrer Wirksamkeit mit der von N- Methyldiethanolamin (NMDEA) ergab, daß 1,3-Dimorpholinopropan genauso wirksam ist wie NMDEA. Hohe Konzentrationen von N-Isopropylpyrrolidin und 1,3-Dimorpholinopropan fu¨hren zu einer Erho¨hung der Polymerisationsgeschwindigkeit von Methylmethacrylat. Introduction Tertiary amines are added to UV-curing formulations in order to ameliorate the inhibiting action of atmospheric oxygen, and in the case of type II photoinitiator to gener- ate initiating radicals. Tertiary amines are invaluable in reducing the concentration of oxygen in films, thereby enabling the polymerization process to take place effi- ciently 1) . Type II photoinitiators are commonly used in the presence of an amine synergist 2) . The function of the carbonyl compound is to generate an a-aminoalkyl radi- cal which acts as the photoinitiating species 3) , as shown in Scheme 1. It has been found that there is a correlation between the acidity of the a-CH bonds and the ability of the amine to act as a synergist, a feature of great importance is the ease with which in either the exciplex or in the reaction of the solvated radical ions hydrogen transfer from the amine to the sensitizer can take place (Eq. (1)). This process involves the transfer of a proton and, therefore, the acidity of the C1H bond should be of importance and this would dictate that the order of reac- tivity of alkyl groups attached to nitrogen is primary A secondary A tertiary. Although this trend has been generally observed, exceptions have been found 4 – 7) . Fundamental work was established by Cohen 8) on ali- phatic tertiary amines and by Davidson 9, 10) on aromatic tertiary amines, to show that these compounds are poten- tial reducing agents for carbonyl compounds in their tri- plet state. Most of the frequently used type II photoinitiators, e. g. benzophenones, thioxanthones and benzil, are readily reduced by amines 11 – 13) . In this study, the photoinduced free radical polymeriza- tion of methyl methacrylate (MMA) in the presence of various amines, namely N-isopropylpiperidine (1), N-iso- * Correspondence author. Die Angewandte Makromolekulare Chemie 266 i WILEY-VCH Verlag GmbH,D-69451 Weinheim 1999 0003-3146/99/0305–0070$17.50+.50/0 Scheme 1. 70 Die Angewandte Makromolekulare Chemie 266 (1999) 70–74 (Nr. 4645)