Nn. Volkova et al., NMR-STUDIES OF SOL-GEL TRANSITION AND MOL ECULAR-DYNAMICS IN SYSTEMS BASED ON METHYL-METHACRYLATE METHACRYLIC-ACID COPOLYMER, Vysokomolekularnye soedinenia. Seria A, 38(4), 1996, pp. 608-614
The NMR measurements showed that the sol-gel transition in systems bas
ed on methyl methacrylate-methacrylic acid copolymer proceeds via thre
e stages. In the first stage, the diffusion of plasticizer causes devi
trification of the polymer; simultaneously, the aggregates of latex pa
rticles disassemble on the macroscopic scale. The second stage feature
s the formation of a gel having non-equilibrium structure, which exper
iences final rearrangement in the third stage. The ratio of the relaxa
tion rates at these stages depends on the plasticizer content. Upon co
mpletion of the sol-gel transition, the system becomes multiphase: it
contains elastomeric domains, crystalline (or glassy) phase, and inter
mediate regions. NMR spectroscopy provides a means for determining the
ultimate compatibility of polymer and plasticizer using small samples
. The macromolecules exhibit higher mobility at lower temperatures, wh
ile molecules of plasticizer are more mobile at high temperatures. The
inversion of mobility occurs approximately at the melting temperature
of the plasticizer.