5 research outputs found
Molecularly Designed Interfacial Viscoelasticity by Dendronized Polymers: From Flexible Macromolecules to Colloidal Objects
ISSN:1936-0851ISSN:1936-086
Dendronized Polymers with Ureidopyrimidinone Groups: An Efficient Strategy To Tailor Intermolecular Interactions, Rheology, and Fracture
A library of polyÂ(methyl
methacrylate)-based dendronized polymers
with generation numbers <i>g</i> = 1â3 was prepared,
which contain different degrees of dendritic substitution (0â50%)
with strongly hydrogen bonding 2-ureido-4Â[1<i>H</i>]Âpyrimidinone
(UPy) moieties at their respective <i>g</i> = 1 levels.
Our rheological and thermal studies demonstrate that the strong intermolecular
UPy interactions are suppressed for <i>g</i> = 2 and essentially
eliminated for <i>g</i> = 3. Focusing on samples with short
backbone degrees of polymerization (<i>P</i><sub>n</sub> â 40), the linear viscoelastic response alters from liquid-like
in the absence of UPy to gel-like with ever increasing moduli as the
UPy content increases. Nonlinear rheological measurements indicate
a transition from ductile to brittle behavior and, in parallel, a
transition from shear strain thinning to shear strain hardening. This
unique behavior makes UPy-DPs promising candidates for the design
of new functional materials
Design, synthesis and cytotoxic activity of water-soluble quinones with dibromo-p-benzoquinone cores and amino oligo(ethylene glycol) side chains against MCF-7 breast cancer cells
ISSN:2040-2503ISSN:2040-251
Rheology and Packing of Dendronized Polymers
A series
of homologous dendronized polymers (DPs) with generations
(<i>g</i>) 1â3 and backbone nominal degrees of polymerization
(<i>P</i><sub><i>n</i></sub>) in the range 50â3000
have been synthesized and characterized in order to investigate the <i>g</i>- and <i>P</i><sub><i>n</i></sub>-dependent
viscoelastic properties and packing of this class of densely grafted,
associating and effectively âthickâ macromolecules in
their molten state. Rheological measurements reveal an unusually long
thermal equilibration time, attributed to (i) the tendency of DPs
to minimize local density gradients, as realized via their mutual
weak interpenetration, and (ii) the intermolecular DPâDP correlations
and inter- and intramolecular hydrogen bonding and ÏâÏ
stacking interactions. With the help of simulations and X-ray scattering
measurements, a scenario emerges, according to which DPs interact
via local cooperative rearrangements of the dendrons, akin to a Velcro
fastening process. In this picture, neighboring bonds accelerate the
local interpenetration process. Results from X-ray scattering show
increased lateral backboneâbackbone correlations with a columnar
arrangement of backbones and a liquid crystalline underlying order.
Linear viscoelasticity is characterized by plateau moduli which originate
from intermolecular bonding and whose extent in frequency and absolute
value depends on <i>P</i><sub><i>n</i></sub> and <i>g</i> and can be lower than or comparable to that of the backbone.
Very long relaxation times can be probed (sometimes via creep measurements)
and attributed to the lifetime of the bonds. The nonlinear shear rheology
data suggest a resemblance in behavior to unentangled linear chains
with finite extensibility and point to reduced deformability of the
DPs in flow. These findings indicate that DPs constitute a promising
class of functional macromolecules with tunable properties