  In this work, linear polystyrene-poly(2-vinylpyridine) (PS-b-P2VP) and
heteroarm star PS_22P2VP_22 ionizable block copolymers were used as dispersing
agents for the liquid-phase exfoliation of pristine graphene. Various
strategies such as direct exfoliation, film hydration and phase transfer have
been employed and compared. The best strategy involved a two-step process,
namely, pre-exfoliation of graphite in polymer/CHCl3 solutions followed by
phase transfer to acidified water. High concentrations of stable aqueous
suspensions of graphene flakes, highly enriched in monolayer structures, were
then obtained by using the star-shaped copolymers as stabilizers. The
as-prepared graphene/copolymer hybrids were used as a filler material in order
to prepare functional polymer composites for mechanical reinforcement. Such
copolymer-modified graphene sheets have proven to be efficient reinforcing
agents of PVA, as a significant increase of storage modulus (145% higher than
that of neat PVA) was achieved even at a low graphene weight fraction of 0.1
wt%.
