Isomorphism in the poly(3,3-bis-hydroxymethyloxetane) family and copolymers: Poly (3,3-bis-hydroxymethyloxetane-co-3-methyl-3-hydroxymethyloxetane)

Copolymers of 3,3-bis-hydroxymethyloxetane, BHMO, 3-metyl-3-hydroxymethyloxetane, MHMO, or with 3-ethyl-3-hydroxymethyloxetane, EHMO, monomer units were characterized by x-ray fiber diffraction, differential scanning calorimetry and ¹³C solid-state nuclear magnetic resonance (NMR). The copolymers are statistically random and crystalline throughout the range of compositions. Both P(BHMO) and P(MHMO) appear to crystallize in the same crystal form. The fiber repeat indicates a planar zigzag backbone conformation, c(fiber axis) = 4.77 ± 0.03 Å. Similarities in the x-ray fiber diagrams as well as a linear dependence of T_m with composition of copolymer with no change in fiber diagrams indicates isomorphism, a phenomenon in which the random substitution of MHMO monomeric units into the crystalline lattice of P(BHMO) occurs without hindering crystallization of the resulting copolymer. © 1994 John Wiley & Sons, Inc.