Aluminium and rare earths alkoxides as initiators for the heterogeneous anionic coordinated polymerisation of propylene oxide. A H-1 NMR approach of the regioselectivity and transfer ability of the catalytic system

In order to outline the placement of the monomer units during the heterogen eous anionic coordinated polymerization of propylene oxide, the regioselect ivity of the first monomer insertion at the initiator was examined by (HNMR )-H-1. To start, aluminium benzyl oxide chemically grafted onto a porous su pport was used as initiator. It was shown that the regioselectivity if the first insertion reflects the placements of the monomer units in the chain. Although there is no direct correlation between these two parameters, a kno wledge of the regioselectivity of this first insertion allowed us to compar e different catalytic systems. With aluminium alkoxides as initiators, both carbon atoms are are attacked at random in the first insertion step. Addin g triethylamine increases notably the regioselectivity electivity. The repl acement of aluminium by zirconium or a rare earth element gives about the s ame percentage of: regular insertion as that obtained with the complex alum inium alkoxide-NEt3. On the other hand, the allyl double bond content was m easured and the values of the transfer constant were deduced. Adding trieth ylamine to aluminium alkoxides or using Zr and rare earth based systems cau ses a decrease of the transfer constant. The more regular the PO insertion, is, the lower is the transfer constant.