Supramolecular Hydrogels And Macromolecular Self-assembly Based On The Inclusion Complexation Interactions

Our research group studied the interpolymer complexation and miscibility enhancement by hydrogen bonding in the 1990s. It was found that immiscibility-miscibility-complexation transitions occur upon progressive increase in the density of hydrogen bonding. Later on, we proposed and developed a new concept of "Non-Covalent Connected Micelles" (NCCMs). Recently, we constructed a new kind of NCCMs using host-guest recognition, which is widely used in supramolecular chemistry, as the driving force for macromolecular self-assembly. Based on the previous research work in our group, the present thesis is mainly focusing on realizing photoresponsibility of pseudopolyrotaxane (PPR) hydrogel, preparation of hydrogel hybridized with clay, and self-assembly of poly(acrylic acid) (PAA) induced by azobenzene pyridinium with different alkyl chains, using inclusion complexation between cyclodextrin (CD) and guest molecules as the driving force. The content of this thesis is as follows:1. Photoreversible pseudopolyrotaxane hydrogels based on competitions of host-guest interactionsPhotoreversible pseudopolyrotaxane (PPR) hydrogels were simply achieved via competitions of three host-guest interactions. Our studies proved that the strength of the interactions is in the sequence of turans-Azo-C1-N+/?-CD> PEG/a-CD> cis-Azo-C1-N+/a-CD. PEG10K and?-CD form PPR hydrogel in water. The hydrogel can be transfered into sol by simply adding competitive guest trans-Azo-C1-N+, which replaces PEG units forming complexes with a-CD. After UV irradiation, PPR hydrogel regenerates because Azo-C1-N+ in cis form looses its ability to complex with a-CD and then the latter is threaded by PEG chain again. Following irradiation of the regenerated hydrogel by visible light converts it to sol again. The photocontrollable processes of gel-to-sol and sol-to-gel can be repeated cyclically. Thus the widely investigated PEG/a-CD PPR hydrogel is proved'active'in supramolecular chemistry, and the reversible nature of the supramolecular materials is fully materialized.2. Pseudopolyrotaxane(PPR) on clay nanoplatelets:demonstration and forming hydrogels wherefromClay is efficient in fabricating new polymeric hydrogels with outstanding properties. However, up to now, no reports on introducing clay nanostructures into supramolecular hydrogel, e.g. pseudopolyrotaxane (PPR) hydrogels, appeared. The PPR hydrogels, though usually are mechanically weak, are promising as biomedical materials because of their shear-thinning properties. Introducing clay nanostructures into PPR hydrogels are very attractive as it is reasonable to expect to improve the mechanical properties as well as to reduce the organic contents. However, in practice this target is difficult to reach, as PEG chains possess strong interactions with clay nano-platelets so may tightly adhere to the platelet surfaces, which makes the PEG chains threading into CD cavities impossible.Herein, we report a very simple way of modifying PEG chain by capping with a pyridinium group (PEG-N+), which can anchor to clay surface via electrostatic interaction and thus make the chains to form brushes. Such chains are then able to thread into CDs and thus form hybrid PPR hydrogel. These hydrogels with homogeneously dispersed clay nanoplatelets display dynamic modulus one order of magnitude higher than the native hydrogel of PEG and a-CD. Furthermore, the resultant PPR hydrogel can perform photo-switchable sol-gel transitions fully based on the above discussed competitive host-guest interaction.3. Hybrid supramolecular hydrogel using clay nanosheet as supra-cross-linkers via inclusion complexationA derivative of azobenzene Azo-C4-N+ and?-cyclodextrin monomer GMA-CD was firstly synthesized and inclusion complex N+-(Azo-CD)-GMA formed between them. This inclusion complex was ion exchanged with Na+of clay to obtain double bond functionalized clay (C-GMA) as "supramolecular-cross-linker" (SCL). Adding a co-monomer and performing the polymerization will lead to the formation of hybrid supramolecular hydrogel.4. Self assembly of poly(acrylic acid) (PAA) induced by azobenzene pyridinium with different alkyl chainsAzobenzene pyridinium with different alkyl chains Azo-R-N+, named Azo-C1-N+, Azo-C4-N+ and Azo-C10-N+were synthesized. The self assembly of poly(acrylic acid) (PAA) induced by these azobenzene pyridinium and azobenzene/a-CD, and their pH sensitivity and light responsibility were studied. The results are as follows:(1) PAA/Azo-C4-N+ can self assemble into rods while PAA/Azo-C1-N+and PAA/Azo-C10-N+ self assemble into spheres;(2) PAA/Azo-Cl-N+/a-CD can self assemble into vesicles, while PAA/Azo-C4-N+/a-CD gives spheres and PAA/Azo-C 10-N+/a-CD gives rods;(3) PAA/Azo-R-N+ is pH sensitive. The morphology of PAA/Azo-C4-N+ can transfer from rods to spheres with increasing pH.(4) PAA/Azo-R-N+/a-CD is pH sensitive as well. The morphology of PAA/Azo-C4-N+/a-CD can transfer from aggregated spheres to separated spheres, and finally disappeared while the pH was increased.(5) PAA/Azo-R-N+/a-CD is light responsive. After UV irradiation, the morphology of PAA/Azo-C4-N+/a-CD can transfer from spheres to rods, similar to that of PAA/Azo-C4-N+...