4 research outputs found
UV induced reversible chain extension of 1-(2-anthryl)-1-phenylethylene functionalized polyisobutylene
<p>The synthesis of novel 1-(2-anthryl)-1-phenylethylene (APE) di-telechelic polyisobutylenes is described. Utilization of a difunctional cationic initiator and the <i>in situ</i> addition of the non-homopolymerizable APE lead to the formation of di-anthryl telechelic polyisobutylenes. Products were characterized by <sup>1</sup>H NMR spectroscopy and Size Exclusion Chromatography. The polymers were UV irradiated at 365 and 254Â nm and the reversible photocycloaddition of anthryl moieties was investigated. The chain extension of di-anthryl telechelic PIBs through photocoupling at 365Â nm produced higher molecular weight products from low molecular weight precursors. The effect of precursor polymer concentration on the degree of chain extension was investigated, and intermolecular interactions leading to the formation of tetramers was observed. The photocoupled products were UV irradiated at 254Â nm to induce the reversal of photocycloaddition of anthryl groups and to follow the consequent photoscission of polymers.</p
High Strength Bimodal Amphiphilic Conetworks for Immunoisolation Membranes: Synthesis, Characterization, and Properties
A strategy
for the synthesis of new cross-linkable bimodal amphiphilic grafts
(bAPGs) was developed. These grafts are of hydrophilic PDMAAm backbones
carrying low (<i>M</i><sub>n</sub> ∼ 17 200
g/mol) and high (<i>M</i><sub>n</sub> ∼ 117 000
g/mol) molecular weight hydrophobic PDMS branches, each branch carrying
a vinylsilyl end-group. The bAPGs were cross-linked by Karstedt catalyst
to bimodal amphiphilic conetworks (bAPCNs) by the use of polyhydrosiloxane-<i>co</i>-PDMS as the cross-linker. Membranes prepared from bAPCNs
exhibit mechanical properties surprisingly superior to earlier APCNs
prepared with APGs with monomodal low molecular weight branches. Membrane
bimodality controls surface morphology and topography by means of
elastic wrinkling instability during film formation. Semipermeable
bAPCN membranes with precisely controlled nanochannel dimensions were
prepared so as to allow rapid insulin diffusion and prevent passage
of IgG. bAPCN membranes were designed for immunoprotection of live
pancreatic islets and are thus key components for a bioartificial
pancreas
Real-Time Monitoring of Chemical and Topological Rearrangements in Solidifying Amphiphilic Polymer Co-Networks: Understanding Surface Demixing
Amphiphilic
polymer co-networks provide a unique route to integrating contrasting
attributes of otherwise immiscible components within a bicontinuous
percolating morphology and are anticipated to be valuable for applications
such as biocatalysis, sensing of metabolites, and dual dialysis membranes.
These co-networks are in essence chemically forced blends and have
been shown to selectively phase-separate at surfaces during film formation.
Here, we demonstrate that surface demixing at the air–film
interface in solidifying polymer co-networks is not a unidirectional
process; instead, a combination of kinetic and thermodynamic interactions
leads to dynamic molecular rearrangement during solidification. Time-resolved
gravimetry, low contact angles, and negative out-of-plane birefringence
provided strong experimental evidence of the transitory trapping of
thermodynamically unfavorable hydrophilic moieties at the air–film
interface due to fast asymmetric solvent depletion. We also find that
slow-drying hydrophobic elements progressively substitute hydrophilic
domains at the surface as the surface energy is minimized. These findings
are broadly applicable to common-solvent bicontinuous systems and
open the door for process-controlled performance improvements in diverse
applications. Similar observations could potentially be coupled with
controlled polymerization rates to maximize the intermingling of bicontinuous
phases at surfaces, thus generating true three-dimensional, bicontinuous,
and undisturbed percolation pathways throughout the material
Transport-Limited Adsorption of Plasma Proteins on Bimodal Amphiphilic Polymer Co-Networks: Real-Time Studies by Spectroscopic Ellipsometry
Traditional hydrogels
are commonly limited by poor mechanical properties
and low oxygen permeability. Bimodal amphiphilic co-networks (β-APCNs)
are a new class of materials that can overcome these limitations by
combining hydrophilic and hydrophobic polymer chains within a network
of co-continuous morphology. Applications that can benefit from these
improved properties include therapeutic contact lenses, enzymatic
catalysis supports, and immunoisolation membranes. The continuous
hydrophobic phase could potentially increase the adsorption of plasma
proteins in blood-contacting medical applications and compromise in
vivo material performance, so it is critical to understand the surface
characteristics of β-APCNs and adsorption of plasma proteins
on β-APCNs. From real-time spectroscopic visible (Vis) ellipsometry
measurements, plasma protein adsorption on β-APCNs is shown
to be transport-limited. The adsorption of proteins on the β-APCNs
is a multistep process with adsorption to the hydrophilic surface
initially, followed by diffusion into the material to the internal
hydrophilic/hydrophobic interfaces. Increasing the cross-linking of
the PDMS phase reduced the protein intake by limiting the transport
of large proteins. Moreover, the internalization of the proteins is
confirmed by the difference between the surface-adsorbed protein layer
determined from XPS and bulk thickness change from Vis ellipsometry,
which can differ up to 20-fold. Desorption kinetics depend on the
adsorption history with rapid desorption for slow adsorption rates
(i.e., slow-diffusing proteins within the network), whereas proteins
with fast adsorption kinetics do not readily desorb. This behavior
can be directly related to the ability of the protein to spread or
reorient, which affects the binding energy required to bind to the
internal hydrophobic interfaces