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Tesi etd-02022009-232550

Thesis type
Tesi di dottorato di ricerca
Bioinspired plastics through molecular recognition and self-replication
Settore scientifico disciplinare
Corso di studi
Relatore Prof. Giusti, Paolo
Relatore Prof. Ciardelli, Francesco
Parole chiave
  • Template polymerization
  • self-replication
  • NMR
  • nanoparticles
Data inizio appello
Data di rilascio
Riassunto analitico
Self-replication through radicalic template polymerization was studied and realized. Kinetic studies of template polymerizations were carried out in order to determine the kind of mechanism involved and the relative stoichiometry of polymers in the formation of complexes. Different replicating couples were taken under consideration in order to investigate also the diverse applicability of the system. In particular the replicating couples acrylic acid (AA) with polyacrylic acid (PAA), vinyl pyrrolidone (VP) with polyvinyl pyrrolidone (PVP) and N-isopropyl acrylamide (NIPAAm) with poly-N-isopropyl acrylamide (PNIPAAm) were used. Synthetic procedures were optimized. The first step only of the bicycle of replication was achieved with the double couple AA/PAA-VP/PVP through water polymerization initiated by the radicalic initiator potassium persulfate (K2S2O8). The second step, the one related to the closure of the bicycle of replication, was not achieved because of the intrinsic instability of the monomer VP in acidic environment. Conversely, the entire bicycle of replication was achieved with the double couple AA/PAA-NIPAAm/PNIPAAm through water polymerization initiated by the redox pair ammonium persulfate ((NH4)2S2O8) and sodium metabisulfite (Na2S2O5). Before molecular weight determinations, complexes PAA-PNIPAAm and PAA-PVP were successfully separated and two different separation procedures relative to the two different complexes obtained, were optimized. The PAA/PVP complex was separated through esterification of the acrylic portion of the complex and successive selective precipitation of the ester while the PAA/PNIPAAm complex was separated via dissolution of the complex in basic water solution (NaOH); the resulting polyacrylic sodium salt was precipitated in methanol and hence separated from solution, the PNIPAAm portion was recovered by vacuum drying. GPC analyses of molecular weights of polymers derived from the complexes, were carried out in order to investigate the transfer of molecular information between molecules participating in the self-replicating cycle.
Interesting results arose from GPC determinations of molecular weights of the daughter polymers (i.e. the polymer deriving from polymerization on the preformed template) proving the role of the template molecule as an internal control towards the definition of the characteristics owned by the nascent polymer. A complete characterization of the products obtained in all steps was carried out through calorimetric, chromatographic, spectrophotometric and morphologic analyses. Information about the reaction mechanism and the kinetic were obtained via different technologies and methodologies: HPLC, conductivity and NMR. In this way the kind of mechanism of the template polymerization was determined. A complete NMR characterization of the system was realized with particular interest on the intermolecular interactions and the kinetic behaviours of the formation of the complex between PAA and PNIPAAm. Stoichiometry of the complex was also determined via NMR.
Synthesis of nanoparticle systems from templated complexes was achieved. A new synthetic procedure for nanoparticles was achieved and a complete characterization of the new material was performed. Swelling and deswelling experiments have been carried out at different temperatures and pH in order to obtain more information about the material behavior exposed to different external stimuli. Drug delivery applications of the nanoparticle system were investigated using ascorbic acid as drug model. Nanoparticles were loaded in two different ways: via adsorption from preformed nanoparticles in water solution added with ascorbic acid and loaded by reaction, adding ascorbic acid during the formation of nanoparticles by template polymerization. Tests of release from nanoparticles loaded in both ways were carried out in different pH and temperature conditions with good results. Temperature and pH both have a great influence in the release of drug and very good results have been obtained for temperature and pH near to the corporeal ones. Obviously nanoparticles loaded by adsorption release more than the other but it surely depends on the different and weaker force of binding of ascorbic acid to the polymeric complex.