STATISTICAL N-BUTYL ACRYLATE SULFOPROPYL BETAINE COPOLYMERS .3. DOMAIN SIZE DETERMINATION BY SOLID-STATE NMR-SPECTROSCOPY

The morphology of two statistical copolymers of n-butyl acrylate (A) and dimethyl(3-methacrylamidopropyl)(3-sulfopropyl)ammonium betaine(B) of B molar fraction 0.04 and 0.12 (copolymers AB-4.0 and AB-12) were analyzed through solid-state NMR spectroscopy (C-13 CP/DD/MAS) over a broad temperature range (160-360 K). In spite of the complexity of molecular motions and carbon line overlapping, the measurement of selective hydrogen rotating frame spin-lattice relaxation time T1rho, through C-13 detection clearly shows that spin diffusion actually occurs over rigid microdomains of about 1 and 2.2 nm for the unclustered AB-4 and clustered AB-12 copolymers, respectively. These minimum dimensions, corresponding to the shortest path for magnetization relaxation, are likely characteristic of the zwitterionic multiplets which are the primary dipolar aggregates in these heterogeneous materials and are compatible with literature models relying on antiparallel alignment of the dipoles in close-packed structures.