Polymerizations of malealdehyde were carried out with alkalimetal alkoxides, A1Et3, pyridine, AlEt3-TiC14 and BF30Et2 as catalysts. All the polymers obtained with other catalysts than AlEt3 and AlEt3-TiC14 were composed only of the cyclized unit (dialkoxydihydrofuran ring) (> 95 yo) and the 1.2-addition structure (< 5 Yo). I R spectra of the polymers obtained with AlEt3 and AIEt3-TiC14 catalysts were suggestive of the presence of five-membered lactone rings which may occur as a result of termination by hydride transfer. The steric structure (cis us. trans) of the dialkoxydihydrofuran ring in polymer was inferred from the comparison of the I R spectra of the polymer with those of the isomeric dialkoxydihydrofurans in the 800 cm-' region. Anionic catalysts gave higher contents of the cis configuration, while coordinated anionic catalysts gave comparable amounts of the cis and trans structures. ZUSAMMENFASSUNG:Die Polymerisation von Maleindialdehyd wurde mit Alkali:ilkoholaten, Al(CeH5)3, Pyridin, AI(CzH5)3-TiC14 und BF30(CzHs)z als Katalysatoren durchgefiihrt. Alle Polymeren, die mit anderen Katalysatoren als iU(CZH5)3 und AI(CzH5)3-TiC14 erhalten wurden, waren nur aus Ring-Einheiten (Dialkoxydihydrofuranring) (> 95 yo) und der 1.2-Additions-Struktur (< 5 yo) zusammengesetzt. IR-Spektren der mit Al(CzH5)3 und Al(CeH5)3-TiC14

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