Two alpha-diimine monometallic Ni catalysts, catalyst 1 and catalyst 2, were studied in the copolymerization reaction of ethylene (E) with methyl methacrylate (MMA). The reaction products of these reactions were characterized using not only the usual techniques such as NMR, GPC and DSC but also the Langmuir balance and AFM. 1H and 13C NMR spectra revealed that both copolymers and mixtures of E and MMA (in a range of 20-70 mol% of MMA) could be obtained with these catalysts. A better insight of the products was possible with 1H DOSY NMR. Since p(E-MMA) copolymers comprising hydrophobic PE blocks and surface active PMMA blocks are amphiphilic, the Langmuir monolayer technique provided further information on the two-dimensional phase behavior of copolymer monolayers at the air-water interface. Additionally, AFM topographic images of the Langmuir-Blodgett (LB) monolayers deposited on mica substrates clearly showed that the morphology of the copolymer LB monolayer is quite different from the corresponding mixture of PE and PMMA homopolymers. These techniques together with molecular modeling calculations allowed us to conclude that with catalyst 2 it was possible to obtain a true block copolymer by a mechanism involving a cationic ester-enolate metal complex as the active species.
- Monolayer studies, AFM
- Polar monomers