ТHE RADICAL POLYMERIZATION OF METHYL METHACRYLATE IN THE PRESENCE OF MANGANESE (II) 5-METHYL-5-HEXEN-2,4-DIONATE

Abstract

presence of unsaturated β-diketonate - manganese (II) 5-methyl-5-hexene-2,4-dionate (Mn(m‑d)2·2Н2О) were investigated. It is shown that the presence of vinyl fragments in ligand structure leads to a significant decrease in the initiating activity in comparison with the saturated manganese (II) acetylacetonate (Mn(асас)2·2Н2О). In contrast to Mn(acac)2×2H2O, the rate of radical polymerization is an order of magnitude lower than in the case of Mn(mgd)2·2Н2О. In this case, large induction periods are observed during which the transition Mn (II)→ Mn (III) occurs. Varying the concentration of Mn(mgd)2·2Н2О results in an insignificant change in the rate of the process. The content of manganese in polymers obtained under the action of Mn(mgd)2·2Н2О increases directly proportional to the chelate concentration in the initial polymerizable mixture and is 0.02-1.20% by weight. In the case of using the limiting analogue, the amount of metal in the polymers does not depend on the initial concentration of Mn(acac)2×2H2O and is 0.11 wt. %. Polymethyl methacrylates obtained with Mn(mgd)2·2Н2О have [η] values 2-3 times lower than polymeric products isolated from the system with Mn(acac)2×2H2O. Such features of the unsaturated chelate behavior are related to its simultaneous participation in the radical polymerization of MMA as an initiator, monomer and inhibitor. The inhibitory effect of Mn(mgd)2·2Н2О is associated with formation of stable tertiary radicals in which the unpaired electron is delocalized in a chelate cycle. In addition, growing MMA radicals can form stable complexes with manganese atom, which leads to its oxidation to the trivalent state and chain termination. The monomer function facilitates the copolymerization of Mn(mgd)2·2Н2О with MMA, insertion of b-diketonate fragments into the polymer chain and formation of branched polymethyl methacrylates. The inhibiting function makes it possible to regulate the molecular masses of the products. The resulting metal polymers based on MMA and manganese (II) vinyl-b-diketonate may be of potential interest as catalysts or initiators of various reactions.

Keywords

• вініл-b-дикетонати, ініціатор, радикальна полімеризація, метилмета- крилат, інгібірування