The conformations and dipole moments of polymethacrylate molecules

Abstract

The local conformations of stereoregular polymethacrylate (PMA) chains have been examined. The mean square dipole moment <μ 2> and the correlation parameter g=< μ 2>/ nm 2 for n→ α ( n is the degree of polymerization; m-dipole moment of the monomer unit) has been calculated for these and the stereoirregular chains. The isotactic PMA chains are mainly in the tg (or gt) conformation (60–80% of the monomer units), but a noticeable proportion (40-20%) have a tt conformation which serves as contact between them. The monomer units of the syndiotactic PMA chains have mainly the tt conformation (75–80%) with a participation of (about 20%) gg conformations. Up to 7% of the monomer units take on a gt and tg conformation. Values of g are greater than 1 over the whole range of admissible energy parameters where the chains are stereo-regular. The value is near the experimental in the case of all other chains and is obtained only by assuming strong hindrance to rotation of the pendant side group.