Design, Synthesis And Properties Of Functionalized Silicon-containing Dendrimers

Dendrimers are a family of monodisperse polymers with well-defined compositions and three-dimensional geometry based on a hyperbrached, tree-like architecture emanating from a central core.They have been the subjects of intense study due to interesting and potentially useful properties that derive from their unique structural characteristics which different from the conventional linear polymers, such as precise molecular structure, high geometric symmetry, a large number of functional groups, cavities within the molecular, controllable molecular weight, nano-size molecular shape and highly branched topology, etc.The special properties make them promising candidate for a wide variety of applications that include supramolecular chemistry, catalysis, biomedical, and environmental protection, and so on. Organosilicon materials exhibit unique properties such as good thermal stability, low glass transitions temperature and excellent biocompatibility, which made them important and essential polymer materials.In this dissertation, a series of experimental and theoretical investigation have been carried out focusing on the design, synthesis, and properties of functionalized silicon-containing dendrimers.The main contents are as follows:1.The 0.5-2th generations of siloxane-based PAMAM dendrimers with disiloxane as a core unit were synthesized by two different methods:the divergent and the double-stage method. Luminescent properties of the complexes of siloxane-based PAMAM dendrimers with lanthanide ions were investigated. Results show that the double-stage method is more suitable as the synthetic procedure is simple and provides higher yield than the divergent method. DSC analysis indicates that the introduction of the siloxane into the interior of the dendrimers has significant effect on the flexibility of the dendrimer structures.The luminescent properties investigation shows that narrow-width emissions were observed from the complexes of GO.5,G1.5, and G2.0 with lanthanide ions, indicating intramolecular energy transfer process takes place between the lanthanide ions and the dendrimer ligands. Also, the energy transfer efficiency was increased with the increasing of the dendrimers generation number. The introduction of the siloxane as a core unit has significant effect on the flexibility of the dendrimer structures, and hence reduces the steric hindrance at the periphery of higher generation dendrimers.Furthermore, the increased flexibility provides the possibility to obtain well-defined structures by modifying the dendrimer with larger functional group and increases the binding abilities of dendrimers for metal ions by making it easy for meatl ions to diffuse into the interiors of dendrimer structures.2.A series of PAMAM dendrimers functionalized polysiloxane (PHMS-PAMAM) were synthesized. Ester groups were first introduced to the side chian of polysiloxane by the hydrosilylation reaction of poly(methylhydrosiloxane) with unsaturated compound DMAA which containing ester group.Then a series of PAMAM dendrimers-graft-polysiloxane were synthesized followed the divergent method, by using the amidation and Michael addition reactions.FTIR spectral was employed to monitor the reaction to determine the optimum reaction time.A series of A-B-A type PAMAM dendrimers-polysiloxane block copolymers (PAMAM-PDMS-PAMAM) were synthesized using methylacrylate, ethylenediamine, and a,ω-bis(y-aminopropyl)polydimethylsiloxane as starting materials. The synthesis was carried out following the divergent method by using the amidation and Michael addition reactions.FTIR spectral was employed to monitor the reaction, results show that during the synthesis of PAMAM-PDMS-PAMAM-G0.5,G1.0, and G1.5,the using of toluene/methanol (v:v=3:1)mixture as solvent can effectively reduce the reaction time.3.The interactions between PAMAM dendrimers-graft-polysiloxane with ionic surfactant sodium dodecyl sulfate (SDS), Dodecyltrimethylammonium bromide (DTAB), and 1-Hexadecylpyridinium chloride (HPyCl) were investigated. The effects of polymer concentration and temperature on the aggregation were considered. Transmission electron microscopy (TEM) was employed to analyse the morphology of the aggregates. Results indicate that the interactions between amino-terminated PAMAM dendrimers-graft-polysiloxane with SDS and HPyCl are stronger than the ester-terminated product, and can efficiently reduce the CMC values of SDS and HPyCl. But the ester-terminated PAMAM dendrimers-graft-polysiloxane exhibit stronger interactions toward DTAB than the amino-terminated product. The CAC values of the PHMS-PAMAM/SDS systems and ester-terminated PHMS-PAMAM with DTAB systems were firstly decreased and then increased with the increasing of polymer concentration in the solution, while it has little effect on the CAC values of other systems.The effect of temperature on the CAC shows with the increasing of temperature the CAC values of the systems was first decreased and then raised. Expect for PHMS-PAMAM-G1.0/SDS and PHMS-PAMAM-G1.0/DTAB systems, the minimum value of CAC is around 35℃.Thermodynamic results indicate that formation of aggregates in PHMS-PAMAM/SDS systems were the entropy driven progress, while they were enthalpy driven progress in PHMS-PAMAM/DTAB systems. As for PHMS-PAMAM/HPyCl systems, the formations of aggregates were entropy driven progress at low temperature and enthalpy driven progress at high temperature. The morphology of the aggregates was analysed taking PHMS-PAMAM-G3.0/SDS and PHMS-PAMAM-G2.5/DTAB systems as examples, results show that irregular aggregates with core-shell structure occur in the system, with the increasing of surfactant concentration, the particle sizes of aggregates were also increased and the association between different aggregates occurs.Compared with pure surfactant systems, the PAMAM dendrimers-graft-polysiloxane/surfactant systems have lower CMC value. Meanwhile the core-shell structure aggregates can be used as template for nanomaterials and carriers for medicines. These properties make them being potential candidate for appilications in oil production, textiles, cosmetics, household chemicals, nanomaterials, pharmaceutical, biomedical, and so on.4. A series of carbosilane dendrimers were synthesized by the divergent method, and ester functionalized dendrimers were obtained by peripherally modification with ester groups. As the ester group has higher reactivity, whichs provide a new way for the further functionalization.5.The interactions between metal ions and the functional groups of dendriemrs were investigated using the B3LYP functional of the density functional theory. The complex structures and interactions of sulfur and oxygen containing functional groups PVBS,PVBSO, PVBSO2 with divalent metal chlorides (Cu(II), Ni(II), Zn(II), Cd(II), and Pd(II))were investigated theoretically. Results indicate that PVBS tends to coordinate with metal ions by sulfur and oxygen atoms forming five-membered ring chelating complexes;while PVBSO and PVBSO2 prefer to interact with metal ions by the oxygen atom of the sulfoxide or sulfone and hydroxyl group to form six-membered ring chelating compounds. Theoretical calculations reveal that sulfur atoms of PVBS are the main contributor when coordinate with metal ions, while oxygen atoms also take part in the coordination with Cu(II),Zn(II), and Cd(II).As for PVBSO,the oxygen atoms of sulfoxide group play a key role in the coordination, but sulfur and hydroxyl oxygen also participate in the coordination. Similarly, sulfone group oxygen atoms of PVBSO2 dominate the coordination of Ni(II), Cu(II), and Pd(II), while the affinities of Zn(II) and Cd(II) are mainly attributed to the hydroxyl oxygen atoms.The geometries and energetics of complexes of Hg(II) and Pb(II) with sulfur-and aminopyridine-containing functional groups PVBS-AP, PVBSO-AP, and PVBSO2-AP have also been investigated theoreticall. The interactions of the metal ions with chelating resins were evaluated. The results indicate that PVBS-AP behaves as a tridentate ligand to coordinate with the metal ions by S and two N atoms to form chelating compounds while PVBSO2-AP interact with metal cations in a tricoordinate manner by 0 and two N atoms forming chelating complexes.Hg(II) complexes exhibit larger binding energies than the corresponding Pb(II) complexes, implying the chelating resins exhibit higher affinity toward Hg(II), which is consistent with the experimental results as the adsorption capacities of PVBS-AP, PVBSO-AP, and PVBSO2-AP for Hg(II) are higher than those of Pb(II) and can selectively adsorb Hg(II) from binary ion systems in the presence of the coexistent Pb(II). Natural bond orbital analysis suggest that the charge transfer from the chelating resins to metal ions is mainly dominated by the interactions of lone pair of electrons of the donor atoms with the unoccupied orbitals of metal ions. Second-order perturbation analyses suggest that S atom in PVBS-AP playing a dominant role in the coordination, whereas 0 and N2 atoms of PVBSO-AP are the main contributor of coordination to Hg(II), and N2 atom of PVBSO2-AP is mainly responsible for the coordination to Hg(Ⅱ).For PVBSO-AP-Pb2+ and PVBSO2-AP-Pb2+ complex, the coordination is dominated by the synergetic effect of N1,N2,and 0 atoms.These investigations on the interactions between metal ions and the functional groups well elucidate the structures of the complexes and the coordination modes, as well as the chelating mechanism, which provide a basis for the design of dendrimers with ions adsorption selectivity.