Morphology of (methoxyethoxy/trifluoroethoxy)phosphazene copolymers

Block copolymers were synthesized by the anionically initiated copolymerization of (CH 3 OCH 2 CH 2 O)(CF 3 CH 2 O) 2 PNSi(CH 3 ) 3 , followed by the addition of (CF 3 CH 2 O) 3 PNSi(CH 3 ) 3 . Random copolymers were made by simultaneous polymerization of these monomers. These copolymers exhibit a linear dependency on the mole fraction “ m ” of the repeating units bearing a methoxyethoxy pendant side group as well as on molecular weights. The thermal and morphological characteristics of the block copolymers are different from those of the random copolymers of analogous “ m ” and molecular weight. All copolymers undergo a mesophase T (1) transition for a range of temperatures depending upon “ m ” and molecular weights of the copolymers. Morphological and structural features essentially resemble those of the low molecular weight (trifluoroethoxy)phosphazene homopolymer. Upon heating and cooling the solution cast copolymer specimens through T (1), most of them transform into an orthorhombic form with the unit cell dimensions a = 2,060 nm, b = 0,940 nm and c = 0,486 nm from their initial monoclinic form with a = 1,003 nm, b = 0,937 nm, c = 0,486 nm and γ γ 91°. These unit cell dimensions agree completely with those of the low molecular weight PBFP. Complicated morphologies comprised of square and globular shapes that depend upon the copolymer composition were obtained from dilute tetrahydrofuran/ p ‐xylene copolymer solutions. Electron microscopy directly reveals that chain extension occurs for the meltcrystallized copolymer specimen. The non‐crystallizable minor component in the block copolymers is rejected from the crystal lattice. In the random copolymers, the methoxyethoxy pendant side group enters into the crystal lattice and influences their morphological and structural features.