Polymer Networks Assembled In Aqueous Solution Based On Cyclodextrin Complexation

The basic tenet that interactions at the molecular level control characteristics at the macroscopic level is increasingly exploited in the design of new materials. This is much in evidence in the design of biocompatible polymer hydrogels by macromolecular assembly which have potential applications in biodegradable drug-delivery systems and chemical sensors. A versatile approach to construct the polymer network is using the cyclodextrin (CD) inclusion complexes to form inter-polymer strand cross-links. This thesis focuses on three kinds of biocompatible reversible polymer networks:substituent binary host-guest interaction cross-linked networks generated by mixing P-CD and hydrophobic guest (alkyl, adamantyl or dansyl) substituted poly(acrylate), CD dimer cross-linked networks formed by mixingβ-or y-CD dimer and guest substituted poly(acrylate) and polymer networks generated by crystallization of poly(ethylene glycol) threaded cc-CD.Steady and dynamic rheological studies showed that the alkyl (octadecyl, hexadecyl or dodecyl) substituted poly(acrylate) (HMPAA) forms polymer networks by itself or its mixture with 6A-(1-(2-aminoethyl)amino)-6A-deoxy-β-cyclodextrin substituted poly(acrylate) (PAAβCDen) due to the strong hydrophobic or inclusive associations. The viscosity of the networks can be controlled by changing alkyl chain length, host-guest molar ratio, polymer concentration, salt concentration, pH value, temperature, and addition of nativeβ-CD. The complexation between alkyl andβ-CD substituent obeys a restrict 1-to-1 stoichiometry regardless of the alkyl chain length. A viscosity maximum as a function of ionic strength and pH value was observed due to the competition between electrostatic repulsions and hydrophobic or inclusive associations. The storage modulus and the loss modulus of hydrophobic HMPAA and inclusive HMPAA+PAAβCDen solutions obey time-temperature superposition. The horizontal and vertical temperature shift factors obey a simple-exponential Arrhenius relationship, where the activation energies for hydrophobic association system are found to be Ea= 3.4 kJ/mol and Eb= 12.1 kJ/mol, and for inclusive association system Ea= 53.9 kJ/mol and Eb= 2.9 kJ/mol, respectively.Model binary associating polymer networks have been constructed through the substituent host-guest interactions between 1-(2-aminoethyl)amidoadamantyl substituted poly(acrylate) (PAAADen) and 6A-amino-6A-deoxy-β-cyclodextrin substituted poly(acrylate) (PAAβCD) or PAAβCDen. The rheological properties of the networks are tunable through either adjustment of theβ-CD/AD mole ratio, adding nativeβ-CD, temperature, the degree of PAA substitution or ionic strength. The host-guest inclusions of the AD substituents by the P-CD substituents and by nativeβ-CD were studied by 2D1H NMR NOESY spectroscopy. The association constant, K1=3020±60 mol-1 dm3, between theβ-CD and AD substituents in PAAβCDen/PAAADen network is determined by isothermal titration microcalorimetry (ITC). A series of polymer networks were prepared by P-CD and AD randomly substituted poly(acrylate)s in which the short amide tethers (PAAPCD and PAAAD), and the intermediate length diacylamino-1,6-hexyl tether incorporating six methylenes (PAAβCDhn and PAAADhn) and the longer diacylamino-1,12-dodecyl tether incorporating twelve methylenes (PAAβCDddn and PAAADddn) are employed. A1H NMR and rheological study shows how polymer backbone steric effects, competitive complexation betweenβ-CD and AD substituted poly(acrylate)s and the length of the polymer backbone to substituent tether control the construction of polymer networks through host-guest interactions between p-CD and AD substituents.Rheological and 1H NMR studies showed that linked CD dimers (N,N-bis(6A-deoxy-6A-β-cyclodextrin)-urea,66βCD2ur, N,N-bis(6A-deoxy-6A-p-cyclodextrin)-succinamide,66βCD2su, N,N-bis(6A-deoxy-6A-y-cyclodextrin)-urea,66yCD2ur and N,N-bis(6A-deoxy-6A-γ-cyclodextrin)-succinamide,66yCD2su) and guest substituted poly(acrylate)s (PAAAD, PAAADen, PAAADhn, PAAADddn, octadecyl substituted poly(acrylate) (PAAC18) and dodecyl substituted poly(acrylate) (PAAC12)) can form novel polymer networks based on CD host-guest interactions. The rheological properties of the networks are tailed by the linked CD dimer linker length, AD substituted poly(acrylate) tether length, alkyl substituent length and CD annular size.A series of three fluorophore (N-(2-aminoethyl)-, N-(6-aminohexyl)-and N-(12-aminododecyl)-5-dansyl-sulfonamide) substituted poly(acrylate)s (PAADSen, PAADShn and PAADSddn) were synthesized. In order to advance the understanding of aqueous supramolecular assembly based on the substituent interaction, the dansyl substituents mobilty, dimerization and complexation byβ-CD have been studied by steady-state and time dependent fluorescence and UV-vis spectroscopy. The host-guest interaction between dansyl andβ-CD substituent or nativeβ-CD is characterized by 2D 1H NOESY NMR. The complexation constant betweenβ-CD and either of PAADSen, PAADShn, and PAADSddn is determined by fluorescence titration (K=87,105 and 52 dm3 mol-1 as the tether length increases). For each polymer (PAADSen, PAADShn or PAADSddn), the dansyl group shows three fluorescence relaxation times corresponding to the free (τ1= 4.0,6.5 and 6.6 ns), dimeric (τ2= 1.6,1.8 and 2.9 ns) and P-CD complexed dansyl states (τ3= 9.3,13.5 and 10.2 ns) where the order of the values in parentheses corresponds to progressive increases in tether length. The rheological properties of the fluorescence polymer networks assembled by dansyl substituted poly(acrylate)s and PAAβCDen or 66βCD2ur are studied.The sol-gel transition induced by the assembly of inclusive complexes between a-CD and poly (ethylene glycol) (PEG) was observed by rheological method. Rheology is a powerful tool to distinguish the polymeric hydrogel structure from a gel-like aggregation. The effect of PEG molecular weight, the storage time, and the sonication on the network formation were systematically investigated. The thermal properties and crystalline structure of the polymer networks formed between a-CD and high molecular weight PEG were characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD).