Preparation, Supramolecular Encapsulation, and Self-assembly of Hyperbranched Polymers
|School||Shanghai Jiaotong University|
|Keywords||hyperbranched polymer hyperbranched poly(amido amine) hyperbranched poly(sulfone-amine) couple-monomer methodology diethylenetriamine methyl acrylate palmitoyl chloride acidylation amphiphilic supramolecular chemistry|
Hyperbranched polymers are a kind of highly branched/dendritic macromolecules with three-dimensional architecture. The past 15 years witnessed the remarkable developments of hyperbranched polymers in the aspects of synthesis methods, functionalization and applications. Nevertheless, there are still many problems to be resolved, new phenomena to be found and new directions to be inaugurated in this field. On the basis of the previous works, this thesis aims at solving some of the problems, especially the facile synthesis of water-soluble hyperbranched polymers, representing new research approaches, and finding new phenomena based on the as-prepared hyperbranched polymers. The water soluble hyperbranched poly(amido amine)s (PAMAMs) are readily synthesized by the“couple-monomer methodology”(CMM). The supramolecular encapsulation and self-assembly behaviors of hyperbranched PAMAMs and other water-soluble hyperbranched polymers are investigated in details. The synergistic encapsulation phenomenon is found in the multi-dye encapsulations of hyperbranched polymers. Regular honeycomb-patterned porous films are fabricated by solvent evaporation-induced self-assembly of hyperbranched polymer on solid substrates, including silicon wafer, quartz, glass slide and mica. Encapsulation and self-assembly behavior of hyperbranched polymer are combined and photoluminescent porous films are obtained from the self-assembly of dye-loaded hyperbranched polymer. The details of research methods and results are described as follows.1 Synthesis, modification and characterization of hyperbranched PAMAMs.A series of water soluble aliphatic hyperbranched PAMAMs with similar chemical structure of poly(amido amine) dendrimer were successfully synthesized from commercially available AB and Cn type monomers by one-pot polymerization via the couple-monomer methodology (CMM). The AB type monomer used is methyl acrylate, and Cn are multi-amino compounds such as ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and pentaethylenehexamine (PEHA). The reaction conditions, such as the reaction time, temperature, and pressure, were investigated and feasible conditions were indicated for the synthesis of hyperbranched PAMAM by CMM. Hyperbranched polymers with different terminal groups and properties can be obtained by adjusting the feed ratio of AB to Cn (Rfeed). FTIR, NMR, DSC, and TGA were used to characterize the polymers. It was found that the polymers’properties such as solubility, thermal behavior and encapsulation capability vary with changing the feed molar ratio of AB to Cn. According to the NMR spectra, when the molar ratio of MA to Cn is low, the end groups of the products are amine groups, while when the ratio is high, the end groups are methoxyl groups. The larger the feed molar ratio of MA to Cn, the more are the methoxyl groups and the less the amine groups residual in the polymer. The solubility of hyperbranched PAMAMs is good in chloroform and some polar solvents, including N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl dulfoxide, water, methanol and ethanol, while poor in apolar solvents, such as acetone, tetrahydrofuran and ether. What’s more, the solubility of the products in apolar solvents increases with increasing the molar ratio of MA to Cn. In addition, the products formed from the monomers with different Cn have different solubility in apolar solvents. The products formed from EDA show worse solubility in acetone, THF and ether than those formed from TEPA and PEHA. When the chain length of the Cn type monomer rises, the solubility of its products in apolar solvents gets better. With increasing the Rfeed, Tg will rise gradually and reach the maximum, then will decrease. The products with amine groups as end groups can’t encapsulate dye molecular, while that with methoxyl groups as end groups can encapsulate some dyes molecules.Amphiphilic core-shell hyperbranched PAMAMs with benzoyl or palmitoyl groups were prepared by acidylation of amine groups in hyperbranched PAMAMs with benzoyl chloride or palmitoyl chloride. Modification of amine groups changes the solubility, thermal behaviour, fluorescence, and encapsulation capability of hyperbranched PAMAMs. All acylating products turn insoluble in water. The products end-capped with benzoyl groups display better solubility in apolar solvent, such as acetone and THF, than those without end-capped, and those end-capped with palmitoyl groups become insoluble in polar solvents such as DMF, DMSO, DMAC, and methanol, while soluble in chloroform and THF and partial soluble in ether. The Tgs of the benzoyl end-capped products become much higher than those before modification. The introduction of long chain alkyls endows the palmitoyl end-capped products with crystallization ability. All the PAMAMs without end-capping lost weight less than 5% till 200 oC. The products end-capped with benzoyl or palmitoyl groups showed greater thermal stability, losing no more than 5% weight even up to 300 oC. The hyperbranched PAMAMs were fluorescent and the fluorescence performances were changed after modification. The emitting wavelength can be changed by varying the concentration of the polymer solutions. The encapsulation capability was improved obviously by modification the amine groups by benzoyl or palmitoyl groups.It is expected that the hyperbranched PAMAMs can play an important role in the industrial application fields such as phase-transferring agents, coatings, sewage treatment agents, drug carrier, surfactant, catalyzer, self-assembly building blocks because of their versatility and availability.2 Supramolecular Encapsulation of Amphiphilic Hyperbranched PAMAMs to Dyes.Dye-encapsulation properties of amphiphilic hyperbranched PAMAMs, especially of HP(DETA-MA)1.2P, which was prepared from methyl acrylate and diethylenetriamine (molar ratio feed is 1.2 ) and modification with palmitoyl chloride, were investigated. The amphiphilic hyperbranched PAMAMs can carry water-soluble dyes, including Congo red (CR), methyl orange (MO), methyl blue (MB), fluorescein sodium (FSS), eosin Y (EY), Phloxine B (PB), and rose Bengal (RB), from aqueous solution into chloroform. The loading capacity (Cload) of HP(DETA-MA)1.2P is different to various dyes. Each HP(DETA-MA)1.2P macromolecule can encapsulate about 22.4 Congo red molecules on average, while only 0.63 methyl blue molecules.The loading capacity of HP(DETA-MA)1.2P is dependable on pH value to some extent. Multi-times single-dye encapsulation will help HP(DETA-MA)1.2P load more dye molecules. A part of loaded-dye molecules in the HP(DETA-MA)1.2P macromolecules can be released by reducing concentration of dye aqueous solution of upper layer and the HP(DETA-MA)1.2P chloroform solution can encapsulate dye again when mixed with high concentration dye solution. Such a liberation and encapsulation process is feasible and reversible for HP(DETA-MA)1.2P.The selectivity of host to guests and the influence of interaction between different dyes on loading capacity were investigated by performing comparable single-dye and double-dye experiments. It’s found that there are two kinds of encapsulation cases, synergistic encapsulation or selective encapsulation, when an aqueous solution containing two kinds of dyes is mixed with a chloroform solution of HP(DETA-MA)1.2P. Gradually double-dye encapsulation experiments were carried out to prove the synergistic or competitive interaction between different pair of dyes. There is synergistic interaction between MO and MB molecules and the Cload of HP(DETA-MA)1.2P to MO (Cload(MO)) in the double-dye encapsulations increased about 72% with the cooperation of MB. The synergistic encapsulation phenomenon was confirmed by the measurements of UV/vis, 1HNMR, DSC and TGA on the dye-encapsulated hyperbranched polymers. Investigations on the guest-host supramolecular systems with different pH indicated that the pH value has certain influence on the synergistic encapsulation Cload, but it was not the dominating factor for the synergistic encapsulation. The MB molecules did improve the Cload(MO).There is competitive interaction between MO and RB(or PB, EY, FSS) molecules. MO molecules can’t be encapsulated by the HP(DETA-MA)1.2P with the existence of RB or PB, while the presence of MO molecules almost have no influence on the encapsulation of HP(DETA-MA)1.2P to RB or PB. When MO and EY exist at the same time, both of Cload(MO) and Cload(EY) decrease. When MO and FSS exist at the same time, no FSS molecules can be encapsulated and the Cload(MO) decreases.The results of DSC, TGA and dynamic light scattering (DLS) measurements verify that the transferred dyes were not localized at the space among the macromolecules, but inside the cavity of individual hyperbranched macromolecules.3 Synthesis of Amphiphilic Hyperbranched Poly(sulfone-amine)s and Their Supramolecular Encapsulation Behavior to Dyes.In order to justify the generality of the encapsulation of hyperbranched polymer to dye molecules, hyperbranched poly(sulfone-amine) was prepared from A2 type monomer, divinyl sulfone, and BB’2 type monomer, 1-(2-aminoethyl) piperazine, and three samples of core-shell amphiphilic hyperbranched poly(sulfone-amine) (HPSA), which were synthesized by end-capping of hyperbranched poly(sulfone-amine) with valeryl chloride, nonanoyl chloride and palmitoyl chloride, were used as hosts to encapsulate dyes. They exhibit high capabilities to load water soluble dyes, such as CR, MO and RB. It is found that the longer the terminal hydrophobic chain is, the higher the loading capability would be for the same dye. For the palmitoyl-terminated HPSA, the average number of dye molecules trapped by per macromolecule achieves 41.8 of CR, 19.4 of MO, and 3.0 of RB, respectively. Such high loading capability is considered to attribute to the high water-solubility of the hyperbranched poly(sulfone-amine) core and the large polarity difference between the hydrophilic core and hydrophobic shell. Similar to HP(DETA-MA)1.2P, the loaded dyes can be released from the amphiphilic hyperbranched poly(sulfone-amine) macromolecules by mixing its chloroform solution with pure water. The high loading capability associated with the reversible releasing property would pave the way for the molecular vessels in the application of drug transfer/delivery, selective molecular recognition and separation, nanocatalysis and nanocoating.Double-dye encapsulation experiments also were carried out to investigate the generality of the synergistic and competitive encapsulation phenomena of hyperbranched polymers. Five pairs of dye, including MO/MB, MO/RB, MO/PB, MO/EY and MO/FSS, were also chosen as dyes pair in the double-dye encapsulation experiments. It’s found that the phenomena of synergistic and selective encapsulation also exist when an aqueous solution containing two kinds of dyes is mixed with a chloroform solution of HPSAP. There is also synergistic interaction between MO and MB molecules and Cload of MB can be raised to a 40 folds level of single-dye encapsulation without loss of MO. The interaction between MO and RB(or PB, EY, FSS) molecules is the same as the case when HP(DETA-MA)1.2P was chosen as host.4 Self-assembly of Amphiphilic Hyperbranched PAMAMs and dye-loaded Amphiphilic Hyperbranched PAMAMs.Regular honeycomb-patterned porous films were prepared from solvent evaporation-induced molecular self-assembly of the amphiphilic hyperbranched poly(amido amine), HP(DETA-MA)1.2P, on solid substrates. The organized structure was confirmed by SEM, AFM, and TEM. The honeycomb structure holes are several microns and have special double layer structure. The morphology of the films was described in details and the corresponding self-assembly mechanism was discussed. Such method to fabricate the honeycomb films was convenient and showed good reproducibility on various substrates, such as silicon wafer, quartz, glass slide, freshly cleaved mica. The ordered porous films may have potential applications in the filed of biology (biomaterials), photonics, electronics, and patterned templates.The similar films have also been prepared from dye-loaded amphiphilic hyperbranched PAMAM. What’s more, the films were fluorescent. The fluorescence of the assembled functional films can be adjusted by the encapsulated dyes, and the emission peak can be tuned by the excitation wavelength. This novel strategy greatly enlarges the assembling diversity, makes versatile complex patterned film easily accessible, paves the way for multi-substance non-molecular self-assembly that allows one or more substance disperse and distribute in another one at the molecular level, and opens a straightforward route to functionalization of self-assembly structures. This is the first time to combine the supramolecular encapsulation behavior with self-assembly of the amphiphilic hyperbranched polymers and make self-assembly films functionalized by encapsulation.The facile and large-scale synthesis of hyperbranched PAMAMs paves the way for their academic research in a deeper level and wide range of applications. The findings of synergestic encapsulation and substrate-supported self-assembly of amphiphilic hyperbranched polymers promise the fascinating future of this field and enlighten us to discovery more new phenomena based on hyperbranched polymers.