Synthesis, characterization and computer simulations of stereoregular poly(methylphenylsiloxane)

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-P 3, 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.