DEGRADABLE CYCLOOCTADIENE ACETAL COPOLYMERS - VERSATILE PRECURSORS TO1,4-HYDROXYTELECHELIC POLYBUTADIENE AND HYDROXYTELECHELIC POLYETHYLENE

In addition to environmental issues associated with polymers possessin g easily cleavable links, the selective degradation of copolymers at o ne of the monomer units is a convenient route to telechelic polymers. Ring-opening metathesis polymerization (ROMP) initiated by (Cy(3)P)(2) Cl2Ru=CHR (Cy = cyclohexyl; Ph = phenyl; R = CHCPh(2) or Ph) was used for the synthesis of cyclooctadiene (COD)/4,7-dihydro-1,3-dioxepin cop olymers. 1,4-Hydroxytelechelic polybutadiene (HTPBD) is obtained upon fragmentation of a copolymer of COD and 4,7-dihydro-2-phenyl-1,3-dioxe pin at the benzylidene acetal functionalities by stirring with acids ( aqueous HCl/MeOH, aqueous H2SO4, or trifluoroacetic acid (TFAA)/MeOH i n CH2Cl2). For the benzylidene acetal the copolymerization reaction ma y be run in neat monomer with no additional solvent. Reaction quenchin g, and polymer cleavage, precipitation, and purification may be effect ed in one step by stirring the viscous reaction product in MeOH contai ning 10% HCl. A two-step procedure using trifluoroacetic anhydride (TF AA)/acetic acid (AcOH) in CH2Cl2 followed by NaOMe/MeOH in THF was emp loyed for the degradation of a COD/4,7-dihydro-1,3-dioxepin copolymer. Acetal incorporation and thus the molecular weights of the resulting telechelics are dependent upon the feed ratios. The percent methylene acetal incorporated into the COD/acetal copolymer is similar to 60% of the amount of acetal in the feed (e.g., for COD/acetal feed = 2:1, CO D/acetal incorporation = similar to 4:1). For the less reactive benzyl idene acetal, incorporation is similar to 40% of the amount of acetal in the feed. Polydispersities for 1,4-HTPBD prepared from the COD/benz ylidene acetal copolymer are typically narrow (similar to 1.1-1.3). It was also demonstrated that the COD/benzylidene acetal copolymer may b e simultaneously hydrogenated and degraded in one step using p-toluene sulfonohydrazide to produce hydroxytelechelic polyethylene (HTPE).