Synthesis, Charactaerization and Computer Simulations of Stereoregular
Poly-(methylphenylsiloxane)
Author
AHN, HYEON WOO
Degree
PhD, University of Cincinnati, Engineering : Materials Science , 2002.
Pages
221p.
Abstract
The synthesis of stereoregular siloxane polymers may revolutionize the
siloxane industry. In the past, the preparation of stereoregular siloxane
polymers was hindered by the unavailability of appropriate organosilicon
monomers, the lack of efficient synthetic methods suitable for the
stereoselective polymerization, and difficulties in the evaluation of the
stereoregulartity of the resulting polymers. Thus, in this dissertation, the
synthesis of stereoregular poly(methylphenylsiloxane) (PMPS) was pursued using
cis-trimethyltriphenylcyclotrisiloxane (cis-P3) as the monomer. In addition, a
new concept of stereoregular polymer, which was named ‘Ahn-Clarson’s
Stereoregular Polymer’ was proposed and its significance was studied by
computer simulations. The result of the simulations indicate the possibility
that we would obtain PMPS with extended linear behavior in its conformation by
placing the same number of pendant groups on both sides of the chain in an
alternating fashion. For the synthesis of stereoregular PMPS, detailed
information on the preparation and separation of the monomer was determined.
Using pure cis-P3, when cyclohexane was used as solvent in an anionic
ring-opening polymerization, an equilibrium reaction was observed. In this
reaction, it was found that
2,4’,6,8’-tetramethyl-2’,4,6’,8-tetraphenylcylcotetrasiloxane (trans-P4[IV])
was hardly formed and its mechanism was proven by 1H-NMR. Also, a totally
non-equilibrium anionic ring-opening polymerization was accomplished when
tetrahydrofuran was used as solvent and the condition to achieve the
non-equilibrium reaction was determined. Using a non-equilibrium anionic
ring-opening polymerization, stereoregular PMPS with 80% isotacticity was
prepared and was proven by both 1H-NMR and DSC. Current contradictions of the
assignment of the triad peaks of PMPS were explained and it was proven that
the meso-meso triad peak was seen upfield. Finally, the rotational isomeric
state theory was employed to calculate the characteristic ratio of different
types of stereoregular PMPS and it is proposed here that the current
structural parameters of PMPS must be revised for more accurate calculations.