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OPTICALLY ACTIVE POLYMERS PREPARED FROM HALOACETALDEHYDES
Abstract
Optically active polychloral was prepared where the optical activity arose exclusively from molecular asymmetry (i.e., helical conformation). Molecular asymmetry requires isotacticity, a high conformational energy barrier for the polymer backbone, and an asymmetric initiator to induce a predominance of one helical screw-sense. Polychloral meets the first two criteria. Asymmetric initiators used to obtain optically active polychloral include tetramethylammonium (+)- or (-)-O-acetylmandelate (TMAAc), tetramethylammonium (+)- or (-)-(alpha)-methoxymandelate (TMA(alpha)M), lithium methyl (+)- or (-)-hydroxidemandelate (LiMM), and lithium cholesteroxide (LiC). Using the above initiators at 0.5 mole % the following maximum specific rotations were obtained for polychloral: TMA(+)Ac initiated {(alpha)}(,D)('25) = -1860, TMA(-) M initiated {(alpha)}(,D)('25) = +210, and Li(-)MM initiated {(alpha)}(,D)('25) = -4760. Optical activity measurements were made in the solid-state due to polychloral's insolubility. Errors in specific rotation were typically 7%. Polychloral initiated by LiC was used as a chromatographic support to obtain 17% resolution of racemic poly((alpha)-methylbenzyl methacrylate). These initiators were mixed with chloral at a temperature greater than pure chloral's ceiling temperature (T(,c) = 58(DEGREES)C). It was generally observed that with either increasing holding times or with higher holding temperatures, prior to cryotachensic polymerization, that polychloral's specific rotation increased. This increase was attributed to the formation of oligomers above T(,c) which help prevent errors in the conformational dyad sequences required for helicity (i.e., g('+)t or g('-)t). Between TMAAc and TMA(alpha)M initiated polychloral there was a nine-fold difference in maximum specific rotation. TMAAc polymer's higher optical activity was attributed to the greater size and polarity of the acetyl group versus the methoxy group in TMA(alpha)M. This resulted in stronger, second order nonbonded interactions between the acetyl group and the polymer's trichloromethyl group, resulting in a greater probability for one helical screw-sense. LiMM initiated polychloral had a specific rotation two times greater than TMAAc initiated polychloral. This increase was attributed to LiMM's asymmetric center being closer to the first trichloromethyl group in the polymer than the TMAAc's asymmetric center resulting in even stronger second order non-bonded interactions to induce molecular asymmetry.
Subject Area
Polymers
Recommended Citation
HARRIS, WILLIAM JAMES, "OPTICALLY ACTIVE POLYMERS PREPARED FROM HALOACETALDEHYDES" (1982). Doctoral Dissertations Available from Proquest. AAI8229559.
https://scholarworks.umass.edu/dissertations/AAI8229559