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Several acrylic esters were polymerized with radical and anionic initiators and the stereoregularity of the polymers was determined. The radical polymerization of tert-butyl acrylate gave syndiotactic-rich polymers at low temperatures as did isopropyl and trimethylsilyl acrylates. A radically obtained polymer of triphenylmethyl acrylate was atactic in contrast to poly(triphenylmethy1 methacrylate). In the anionic polymerization with phenylmagnesium bromide or butyllithium as catalyst, the stereoregularity of the polymers was governed by the coordination of the catalyst which depends on the polarity and bulkiness of ester groups, the polarity of solvents, and the temperature in the polymerization. ZUSAMMENFASSUNG:Die Mikrotaktizitat einiger radikalisch bzw. anionisch hergestellter Polyacrylate wurde bestimmt. Die radikalische Polymerisation von tert-Butylacrylat ergabebenso wie die des Isopropyl-bzw. Trimethylsilylacrylatesbei niedrigen Temperaturen Polymere mit hohem Gehalt an syndiotaktischen Dyaden. Ein radikalisch hergestelltes Poly(triphenylmethylacrylat) war, im Gegensatz zu Poly(triphenylmethyImethacrylat), ataktisch. Bei der anionischen Polymerisation mit Phenylmagnesiumbromid bzw. Butyllithium wird die Mikrotaktizitat des Polymeren von der Koordination des Katalysators bestimmt. Es wurde gefunden, da13 die Art der Koordination abhangt von der Polaritat und Raumerfiillung der Estergruppen, der Polaritat des Losungsmittels sowie von der Reaktionstemperatur. d, 1 M solution in heptane, 0,7 ml. e, 1 M solution in heptane, 2 ml. f, 1 M solution in heptane, 0,6 ml. g, Not determined. h, 2,3 M solution in diethyl ether, 0,3 ml. Dibenzo-18-crown-6, mole ratio [Crown]/[catalyst] = 1.

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SynopsisNuclear magnetic resonance (NMR) spectroscopy was used to determine the stereoregularity of radically polymerized poly(ethy1 acrylates), poly(trimethylsily1 acrylates), and poly(isopropy1 acrylate-a,p-dz). The ethyl acrylate polymers consisted of a random configuration having about 50% of isotactic diads, and their stereoregularities were independent of the polymerization temperature (40 to -78°C). Poly(trimethylsily1 acrylates) and poly(isopropy1 acrylate-a,p-dz) prepared a t low temperatures had a syiidiotactic configuration. Syndiotactic poly(methy1 acrylate) was derived from syndiotactic poly(trimethylsily1 acrylate). For poly(methy1 acrylate), an approximate estimation of the stereoregularity by infrared spectroscopy was proposed. 2335 0

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