7 research outputs found
<i>Ring-and-Lock</i> Interactions in Self-Healable Styrenic Copolymers
Commodity
copolymers offer many useful applications,
and their
durability is critical in maintaining desired functions and retaining
sustainability. These studies show that primarily alternating styrene/n-butyl acrylate [p(Sty/nBA)] copolymers
self-heal without external intervention when monomer molar ratios
are within the 45:55â53:47 range. This behavior is attributed
to the favorable interchain interactions between aliphatic nBA side
groups being sandwiched by aromatic rings forming ring-and-lock associations driven by piâsigmaâpi (ÏâÏâÏ)
interactions. Guided by molecular dynamics (MD) simulations combined
with spectroscopic and thermomechanical analysis, the ring-and-lock interchain van der Waals forces between Ï orbitals of aromatic
rings and sigma components of aliphatic side groups are responsible
for self-healing. Despite the frequent occurrence of these interactions
in biological systems (proteins, nucleic acids, lipids, and polysaccharides),
these largely unexplored weak and ubiquitous molecular forces between
the soft acid aliphatic and soft base aromatic electrons may be valuable
assets in the development of polymeric materials with sustainable
properties
<i>Ring-and-Lock</i> Interactions in Self-Healable Styrenic Copolymers
Commodity
copolymers offer many useful applications,
and their
durability is critical in maintaining desired functions and retaining
sustainability. These studies show that primarily alternating styrene/n-butyl acrylate [p(Sty/nBA)] copolymers
self-heal without external intervention when monomer molar ratios
are within the 45:55â53:47 range. This behavior is attributed
to the favorable interchain interactions between aliphatic nBA side
groups being sandwiched by aromatic rings forming ring-and-lock associations driven by piâsigmaâpi (ÏâÏâÏ)
interactions. Guided by molecular dynamics (MD) simulations combined
with spectroscopic and thermomechanical analysis, the ring-and-lock interchain van der Waals forces between Ï orbitals of aromatic
rings and sigma components of aliphatic side groups are responsible
for self-healing. Despite the frequent occurrence of these interactions
in biological systems (proteins, nucleic acids, lipids, and polysaccharides),
these largely unexplored weak and ubiquitous molecular forces between
the soft acid aliphatic and soft base aromatic electrons may be valuable
assets in the development of polymeric materials with sustainable
properties
Instantaneous Directional Growth of Block Copolymer Nanowires During Heterogeneous Radical Polymerization (HRP)
Polymeric
nanowires that consist of ultrahigh molecular weight
block copolymers were instantaneously prepared via one-step surfactant-free
heterogeneous radical polymerization (HRP). Under heterogeneous reaction
and initiator-starvation conditions, the sequential copolymerization
of hydrophilic and hydrophobic monomers facilitates the formation
of amphiphilic ultrahigh molecular weight block copolymers, which
instantaneously assemble to polymeric nanowires. As polymerization
progresses, initially formed nanoparticles exhibit the directional
growth due to localized repulsive forces of hydrophilic blocks and
confinement of the hydrophobic blocks that adopt favorable high aspect
ratio nanowire morphologies. Using one-step synthetic approach that
requires only four ingredients (water as a solvent, two polymerizable
monomers (one hydrophilic and one hydrophobic), and water-soluble
initiator), block copolymer nanowires âŒ70 nm in diameter and
hundreds of microns in length are instantaneously grown. For example,
when 2-(<i>N</i>,<i>N</i>-dimethylamino)Âethyl
methacrylate (DMAEMA) and styrene (St) were copolymerized, high aspect
ratio nanowires consist of ultrahigh (>10<sup>6</sup> g/mol) molecular
weight pDMAEMA-<i>b</i>-St block copolymers and the presence
of temperature responsive pDMAEMA blocks facilitates nanowire diameter
changes as a function of temperature. These morphologies may serve
as structural components of the higher order biological constructs
at micro and larger length scales, ranging from single strand nanowires
to engineered biomolecular networks capable of responding to diverse
and transient environmental signals, and capable of dimensional changes
triggered by external stimuli
One-Step Synthesis of Amphiphilic Ultrahigh Molecular Weight Block Copolymers by Surfactant-Free Heterogeneous Radical Polymerization
Ultrahigh
molecular weight (>10<sup>6</sup> g/mol) amphiphilic
block copolymers were synthesized using one-step surfactant-free heterogeneous
radical polymerization (SFHRP). The polymerization initially involves
formation of water-soluble homopolymer blocks, followed by copolymerization
of a hydrophobic monomer, resulting in ultrahigh molecular weight
block copolymers. Facilitating heterogeneous reaction conditions and
continuous supply of an initiator controls the process. Using this
synthetic approach, we synthesized amphiphilic block copolymers of
polyÂ(2-(<i>N</i>,<i>N</i>-dimethylamino)Âethyl
methacrylate)-<i>block</i>-polyÂ(<i>n</i>-butyl
acrylate) (pDMAEMA-<i>b</i>-pnBA), pDMAEMA-<i>block</i>-pÂ(<i>tert</i>-butyl acrylate) (pDMAEMA-<i>b</i>-tBA), and pDMAEMA-<i>block</i>-polystyrene (pDMAEMA-<i>b</i>-pSt) with molecular weights of 1.98 Ă 10<sup>6</sup>, 1.18 Ă 10<sup>6</sup>, and 0.91 Ă 10<sup>6</sup> g/mol,
respectively. These ultrahigh molecular weight block copolymers can
self-assemble in nonpolar solvents to form thermochromic inverse polymeric
micelles as well as other shapes and exhibit many potential applications
Tri-Phasic Size- and Janus Balance-Tunable Colloidal Nanoparticles (JNPs)
These
studies show synthesis of triphasic size- and Janus balance
(JB)-tunable nanoparticles (JNPs) utilizing a two-step emulsion polymerization
of pentafluorostyrene (PFS) and 2-(dimethylamino)Âethyl methacrylate
(DMAEMA) and <i>n</i>-butyl acrylate (nBA) in the presence
of polyÂ(methyl methacrylate (MMA)/nBA) nanoparticle seeds. Each JNP
consists of three phase-separated copolymers: pÂ(MMA/nBA) core, temperature,
and pH-responsive (pÂ(DMAEMA/nBA)) phase capable of reversible size
and shape changes, and shape-adoptable (pÂ(PFS/nBA)) phase. Due to
built-in second-order lower critical solution temperature (II-LCST)
transition of pÂ(DMAEMA/nBA) copolymer, macromolecular segments collapse
when temperature increases from 30 to 45 °C, resulting in size
and shape changes. The pÂ(DMAEMA/nBA) and pÂ(MMA/nBA) phases within
each JNP assume concave, flat, or convex shapes, forcing pÂ(PFS/nBA)
phase to adopt convex, planar, or concave interfacial curvatures,
respectively. As a result, the JB can be tuned from 3.78 to 0.72.
The presence of pH-responsive DMAEMA component also facilitates the
size and JB changes due to protonation of the tertiary amine groups
of pÂ(DMAEMA/nBA) backbone. Synthesized in this manner, JNPs are capable
of stabilizing oil droplets in water at high pH to form Pickering
emulsions, which at lower pH values release oil phase. This process
is reversible and can be repeated many times
Expandable Temperature-Responsive Polymeric Nanotubes
Materials with the ability of dimensional changes on
demand exhibit
many potential applications ranging from adaptive composites that
mimic biological functions under extreme conditions to microfluidics
or neural implants to stimulate components of the nervous systems.
These studies show the synthesis of temperature-induced reversibly
expandable nanotubes that were prepared by polymerization of <i>N</i>-isopropylacrylamide (NIPAAM) in the presence of biologically
active 1,2-bisÂ(tricosa-10,12-diynoyl)-<i>sn</i>-glycero-3-phosphocholine
(DC<sub>8,9</sub>PC) diacetylenic phospholipids (PL). As a result,
thermally responsive poly-NIPAM-phospholipid nanotubes (PNNTs) were
prepared. Polymerization reactions occur within hydrophilic regions
of PL bilayers, whereas PL hydrophobic zones facilitate transport
and supply of the monomer for polymerization. The unique feature of
PNNTs is that, above 37 °C, the outer diameter (OD) as well as
the wall thickness (WT) shrink by 20 and 55%, respectively, whereas
the inner diameter (ID) increases by âŒ16%. This behavior is
attributed to the PNIPAM backbone buckling induced by local rearrangements
within PL bilayered morphologies. The presence of acetylenic moieties
along the PL bilayers in PNNTs provides an opportunity for irreversible
âlockingâ of designable dimensions, which is facilitated
by the formation of cross-linked PNNTs (CL-PNNTs)
Phage-Bacterium War on Polymeric Surfaces: Can Surface-Anchored Bacteriophages Eliminate Microbial Infections?
These studies illustrate synthetic
paths to covalently attach T1
and Ί11 bacteriophages (phages) to inert polymeric surfaces
while maintaining the bacteriophageâs biological activities
capable of killing deadly human pathogens. The first step involved
the formation of acid (COOH) groups on polyethylene (PE) and polytetrafluoroethylene
(PTFE) surfaces using microwave plasma reactions in the presence of
maleic anhydride, followed by covalent attachment of T1 and Ί11
species via primary amine groups. The phages effectively retain their
biological activity manifested by a rapid infection with their own
DNA and effective destruction of Escherichia coli and Staphylococcus aureus human pathogens.
These studies show that simultaneous covalent attachment of two biologically
active phages effectively destroy both bacterial colonies and eliminate
biofilm formation, thus offering an opportunity for an effective combat
against multibacterial colonies as well as surface detections of other
pathogens