Bicyclic acetals polymerization

The understanding of the stereochemistry of bicyclic acetal polymerization has recently been advanced by the synthesis of optically active DBO enantiomers by the following procedure 41 A2) ... 

Sumitomo, H. and Okada, M. Ring-Opering Polymerization of Bicyclic Acetals, Oxalactone, and Oxalactam. Vol. 28, pp. 47—82. 

Ring-Opening Polymerization of Bicyclic Acetals, Oxalactone, and Oxalactam... 

In connection with studies on the ring-opening polymerization of cyclic acetals, we have undertaken investigations on the polymerization of bicyclic acetals, bicyclic oxalactone, and bicyclic oxalactam, which yield polysaccharide analogs, macrocyclic oligoesters, and a hydrophilic polyamide, respectively, some of which can be expected to be useful as novel speciality polymers. The monomers employed in the studies were prepared via synthetic routes presented in Scheme 1, starting from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer) I. 

Polymerization of 6,8-dioxabicyclo[3.2.1]octane, 2, has been most extensively studied among bicyclic acetals. This monomer is readily prepared from 3,4-dihydro-2H-pyran-2-carbaldehyde 1 by reduction with sodium borohydride followed by add-... 

The difference in behavior of the cis- and trans-isomers 43 and 45 is ascribed mainly to the greater ring strain in the trans-isomer which results in a more favorable free energy change for its polymerization. This result is similar to that reported for the polymerization of cis- and frans-8-oxabicyclo[4.3. OJnonane 48 and 4936. The molecular weights of the polymers of the bicyclic ether 49 were, however, much higher than those of the polymers of the bicyclic acetal 45. 

The bicyclic acetals 43 and 45 can be regarded as 4,5-disubstituted-l,3-dioxolanes. In connection with their pdymerizabilities, it is interesting to note here that cis-4,5-dimethyl-l,3-dioxolane has a slightly greater tendency to polymerize than its trans-counterpart22, 37. The polymerization of 45 is an equilibrium reaction and the system is completely reversible. From the temperature dependence of the equilibrium... 

Other cyclic acetals that have been studied are 1,3,5-trioxane, 1,3,5-trioxepane, 1,3,6,9-tetraoxacycloundecane, and 1,3,5,7-tetroxocane (also referred to as 1,3,5,7-tetroxane) [Kawakami and Yamashita, 1979 Munoz-Escalona, 1978 Schulz et al., 1984 Szwarc and Perrin, 1979]. Polymerization of bicyclic acetals has been of interest for synthesizing polysaccharides [Good and Schuerch, 1985 Hirasawa et al., 1988 Okada, 1991 Okada et al., 1989 Sumitomo and Okada, 1984]. 

Sumitomo, H. and M. Okada, Sugar Anhydrides and Related Bicyclic Acetals, Chap. 5 in Ring-Opening Polymerization, Vol. 1, K. J. Ivin and T. Saegusa, eds., Elsevier, London, 1984. 

Heterobicyclic compounds often display specific behavior in their ring-opening polymerization. This is attributed to their rigid and bulky structures which contain, in most cases, two or more asymmetric carbon atoms. Sometimes, stereoelectronic effects involving heteroatoms also play an important role in regulating polymerization processes. For example, racemic bicyclic acetals such as 6,8-dioxabicy-clo[3.2.1]octane and its derivatives often undergo stereospecific polymerization even in the presence of conventional Lewis acid initiators. 

Similar enantiomer selection at the growing chain end is commonly observed in the cationic polymerizations of bicyclic acetals having bicyclo[3.2.1]octane skeletons. [24]... 

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