posted on 2014-03-11, 00:00authored bySansanee Srichan, Navaphun Kayunkid, Laurence Oswald, Bernard Lotz, Jean-François Lutz
Sequence-controlled semicrystalline
copolymers were prepared by
nitroxide-mediated copolymerization of a large excess of octadecylstyrene
with small amounts of functional N-substituted maleimides (i.e., N-(n-propyl)maleimide, N-benzylmaleimide, pentafluorophenyl
4-maleimidobenzoate, 4-(N-maleimido)azobenzene, N-(1-pyrenyl)maleimide, and N-(2-(amino-BOC)ethylene)maleimide).
These copolymers were prepared in bulk at 110 °C using the commercial
alkoxyamine BlocBuilder MA as initiator and control agent. Time-controlled
additions protocols were used to place the N-substituted maleimides
at precise chain location along the poly(octadecylstyrene) backbones.
Size exclusion chromatography and 1H NMR studies indicated
that well-defined copolymers with controlled monomer sequences, composition,
chain length, and molecular weight distribution were formed in all
cases. Although possessing an atactic backbone, these polymers exhibit
a semicrystalline behavior. The electron diffraction method indicated
that the octadecyl side chains form lamellar phases. Moreover, differential
scanning calorimetry studies evidenced a melting temperature in the
range 40–45 °C and a crystallization temperature around
30–35 °C. It was observed that melting is influenced by
the composition and sequence distribution of the copolymers. Thus,
small microstructural variations allow a precise control over order–disorder
transitions.