The polymerization of cyclic dimethylsiloxanes in the presence of pigments was studied by an ampoule method at 50°C. The products were polydimethylsiloxanes (PDMS), whose molecular weight were 200,000 and 8,700 in the reaction with kaolinite and prussian blue, respectively.
The results of GC/MS measurement indicated that cyclic oligomers formed in the first step from D
4 by kaolinite were not D
8, D
12, and D
16, which were kinetically controlled species, but D
5, D
6, and D
7, which were thermodynamically controlled ones. The results of the reaction between cyclic siloxanes and kaolinite in the presence of hexane as a solvent indicated that the lower the concentration of cyclic siloxane was, the lower the molecular weight of product became. In, the case of 0.1% solution of D
3, D
4, and D
5, the final products had an identical composition, D
3 : D
4 : D
5 : D
6=4 : 80 : 15 : 1. These results show that the meeting of the two ends of a linear species is the main factor determining the distribution of cycle siloxanes, where a low monomer concentration leads to self-end-to-end ring closure, while polymerization among different molecules is encouraged at a high monomer concentration.
View full abstract