%0 Journal Article
%A Byard, Sarah
J.
%A Williams, Mark
%A McKenzie, Beulah E.
%A Blanazs, Adam
%A Armes, Steven P.
%D 2017
%T Preparation and Cross-Linking of All-Acrylamide Diblock
Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in
Aqueous Solution
%U https://acs.figshare.com/articles/journal_contribution/Preparation_and_Cross-Linking_of_All-Acrylamide_Diblock_Copolymer_Nano-Objects_via_Polymerization-Induced_Self-Assembly_in_Aqueous_Solution/4650157
%R 10.1021/acs.macromol.6b02643.s001
%2 https://acs.figshare.com/ndownloader/files/7580533
%K ADH
%K FT-IR
%K chain transfer agents
%K All-Acrylamide Diblock Copolymer Nano-Objects
%K DLS
%K PISA
%K TEM
%K PDMAC
%K solution pH
%K DP
%K ketone-functionalized PDAAM chains
%X Various carboxylic
acid-functionalized poly(N,N-dimethylacrylamide)
(PDMAC) macromolecular chain transfer agents (macro-CTAs) were chain-extended
with diacetone acrylamide (DAAM) by reversible addition–fragmentation
chain transfer (RAFT) aqueous dispersion polymerization at 70 °C
and 20% w/w solids to produce a series of PDMAC–PDAAM diblock
copolymer nano-objects via polymerization-induced self-assembly (PISA).
TEM studies indicate that a PDMAC macro-CTA with a mean degree of
polymerization (DP) of 68 or higher results in the formation of well-defined
spherical nanoparticles with mean diameters ranging from 40 to 150
nm. In contrast, either highly anisotropic worms or polydisperse vesicles
are formed when relatively short macro-CTAs (DP = 40–58) are
used. A phase diagram was constructed to enable accurate targeting
of pure copolymer morphologies. Dynamic light scattering (DLS) and
aqueous electrophoresis studies indicated that in most cases these
PDMAC–PDAAM nano-objects are surprisingly resistant to changes
in either solution pH or temperature. However, PDMAC40–PDAAM99 worms do undergo partial dissociation to form a mixture
of relatively short worms and spheres on adjusting the solution pH
from pH 2–3 to around pH 9 at 20 °C. Moreover, a change
in copolymer morphology from worms to a mixture of short worms and
vesicles was observed by DLS and TEM on heating this worm dispersion
to 50 °C. Postpolymerization cross-linking of concentrated aqueous
dispersions of PDMAC–PDAAM spheres, worms, or vesicles was
performed at ambient temperature using adipic acid dihydrazide (ADH),
which reacts with the hydrophobic ketone-functionalized PDAAM chains.
The formation of hydrazone groups was monitored by FT-IR spectroscopy
and afforded covalently stabilized nano-objects that remained intact
on exposure to methanol, which is a good solvent for both blocks.
Rheological studies indicated that the cross-linked worms formed a
stronger gel compared to linear precursor worms.
%I ACS Publications