2 research outputs found
Simulation and Experiments To Identify Factors Allowing Synthetic Control of Structural Features of Polymeric Nanoparticles
To develop a detailed picture of
the microscopic structure of gelcore
star polymers and to elucidate parameters of the synthetic process
that might be exploited to control this structure, simulations of
their synthesis were performed that were based on a particular synthetic
approach. A range of results was observed from gelation at high reactant
concentrations to the formation of various sizes and compositions
of star polymers. Contrary to the prevailing experimental viewpoint,
the simulations always suggest the production of a broad distribution
of star polymer sizes. However, the GPC traces computed from simulation
results are in good qualitative agreement with experiment. Topologically,
the gelcore star polymers produced by simulation are not compact but,
rather, sparse blobs loosely connected by filaments of linker when
modeled in a good solvent. This is reflected in scaling relationships
that relate polymer size (e.g., radius of gyration) and degree of
polymerization. The arm–core composition is observed to be
stoichiometric, strongly reflecting relative reactant concentrations
during the synthesis. Reactions within star polymers that result in
greater intramolecular cross-linking compete with those between star
polymers that result in the production of larger star polymers from
the joining of smaller ones. The balance in this competition can be
controlled through the overall reactant concentration to limit and
control resulting star polymer size. Therefore, the mean size, as
well as the mean number of arms, can be controlled during synthesis
by careful tuning of the overall ratio of the arm and linker reactant
concentrations and the total reactant concentration
Structural transition of nanogel star polymers with pH by controlling PEGMA interactions with acid or base copolymers
<p>We use small angle X-ray scattering (SAXS) to characterise a class of star diblock polymers with a nanogel core on which the outer block arms are comprised of random copolymers of temperature sensitive PEGMA with pH sensitive basic (PDMAEMA) and acidic (PMAA) monomers. The acquired SAXS data show that many of the nanogel star polymers undergo a sharp structural transition over a narrow range of pH, but with unexpectedly large shifts in the apparent pKa with respect to that of the acidic or basic monomer unit, the linear polymer form or even an alternate star polymer with a tightly cross-linked core chemistry. We have demonstrated a distinct and quantifiable structural response for the nanogel star copolymers by altering the core or by pairing the monomers PDMAEMA–PEGMA and PMAA–PEGMA to achieve structural transitions that have typically been observed in stars through changes in arm length and number.</p> <p></p