Synthesis Of Hyperbranched Polyamidoamines And Their Modifications

Hyperbranched polymers are a novel kind of three dimensional torispherical irregular macromolecules possessing highly branched architectures, many inner cavities and a large amount of terminal functional groups. Due to their unique molecular structures and properties, hyperbranched polymers have become the hot topics in many R&D fields. Up to date, the great progress has been made in the synthesis, characterization, modification, and application of hyperbranched polymers. Especially, various synthesis methodologies have been developed during the past two decades, which provide the promising chance for their applications. However, many problems still need to be resolved, such as how to perfect the theories, how to explore the unknown features, how to explain new phenomena and spread the application fields. In this dissertation, the previous studies of hyperbranched polymers are summarized firstly, including their synthesis, properties and applications. Based on them, some creative investigations are conducted in the synthesis and modification of hyperbranched polymers to obtain various functional materials. A novel kind of functional hyperbranched polyamidoamins are designed and synthesized via the A2+BB'2 strategy. Several interesting functional materials are further generated by the modification of the resulting hyperbranched polymers. In our research works, (1) the first hyperbranched polymer gelator, i.e., the amine-terminated hyperbranched polyamidoamine is investigated systematically. (2) The hyperbranched polyamidoamine is successfully used to form the hollow spheres (i.e., vesicles) via complex self-assembly, and the hollow spheres are further stabilized by chemical cross-linking. (3) Besides, the hyperbranched polyamidoamines are served as both reductants and stabilizers to prepare the stable colloid metal nanoparticles with highly antimicrobial activities. (4) In addition, the multifunctional polymer films with enough mechanical strength are prepared from modification of the hyperbranched polyamidoamines. The films show promising proton-conductive behavior and effective binding abilities to various guest molecules. The details and key conclusions are described as follows: 1. Synthesis of the Amino-terminated Hyperbranched Polyamidoamine Gelator and the Formation of Physical GelA novel kind of hyperbranched polymer gelator, i.e., the amino-terminated hyperbranched polyamidoamine, is obtainted successfully. It is synthesized by the Michael addition polymerization of N,N'-methylene bisacrylamide (MBA) and 1-(2-aminoethyl)piperazine (AEPZ). The unequal reactivity of the various amines in AEPZ leads to the formation of the hyperbranched structure in the polymerization. The degree of branching (DB) is characterized with the assistance of 2D NMR. The resulting polymer can self-assemble into the thermo-reversible physical gel in DMF, DMAC, pyridine, DMSO or NMP. Its gelation ability to DMF is the strongest among them, with the critical gelation concentration (CGC) being as low as 2.5 mg/mL. The microstructure of the gel consists of continuous and open network on the nano scale revealed by cryo-TEM. It is further revealed that the driving force of the gelation is ascribed to the hydrogen bonds among amide and amine groups in the highly branched macromolecules. Besides, the gels also exhibit the typical dynamic mechanical behavior of physical gels.2. Hollow Spheres Based on Complex Self-assembly of Hyperbranched PAMAM/Linear PAA Polymer Pair and Their FunctionizationA novel kind of polymer hollow spheres are prepared successfully based on the complex self-assembly of the hyperbranched PAMAM/linear PAA (h-PAMAM/l-PAA) polymer pair in aqueous solution. By adjusting the solution pH, the assembled aggregates of nanoparticles or vesicles are formed When the pH is lower than 2.1, the assembled aggregates are nanoparticles with l-PAA as the core and the prontonated h-PAMAM as the shell. On the contrary, when the pH is upper than 7.5, the resulting nanoparticles consist of the inner h-PAMAM and outer layer of the solvated l-PAA. When the pH is in the range from 2.1 to 7.3, the aggregates become into vesicles and exhibit the typical hollow structure. Interestingly, at ca. pH 4.6, the vesicle conversion happens. The optical microscopy, UV-vis spectrometer, TEM and zeta potential are adopted to investigate the behaviour and mechanism of the complex self-assembly. The driving forces of the complex self-assembly are ascribed to hydrophilic-hydrophobic balance and the specific interactions between the carboxylic acid groups of l-PAA and various amine units of h-PAMAM. Since the self-assembled vesicles are sensitive to the environment changes, we try to use glutaric dialdyde (GDA) as a cross-linker to stabilize their hollow structures. The resulting cross-linked hollow spheres are very stable and they can be used to encapsulate various noble metallic cations and reduce them into nanoparticles in situ. In the resulting hybrid hollow spheres, the content of Au, Ag or Pd reaches 15.2 wt%, 12.3 wt%, or 8.0 wt% respectively. Such hybrid materials may be suitable for the potential applications in metal catalysis.3. Hyperbranched Polyamidoamines as Both Reducing and Stabilizing Agents to Form Colloid Metal Nanoparticles Facilely and Their Highly Antimicrobial ActivityA facile and green method is described to prepare the stable colloid silver nanoparticles in aqueous solution by utilizing the amine-terminated hyperbranched poly(amidoamine) (HPAMAM-NH2) both as stabilizer and reductant. The formation of silver nanoparticles is verified by FTIR, UV-vis, TEM, EDS and XRD measurements. The well-dispersed colloid silver nanoparticles with small particle sizes are obtained. And the average particle size can be controlled effectively from ca. 15 to 4 nm by simply adjusting the molar ratio of N/Ag in feed. The antibacterial activity of the HPAMAM-NH2/Ag nanocomposites is also investigated against Gram-positive and Gram-negative bacteria. They are able to inhibit the growth and multiplication of several kinds of bacteria efficiently, such as Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Klebsiella mobilis. The bacterial inhibition ratio reaches up to 95% at a low silver concentration of 2.7μg/mL. This method can also be extended to other derivative systems. Typically, a series of colloid silver or gold nanoparticles (AgNPs or AuNPs) are also successfully prepared by in situ reduction and stabilization of hyperbranched poly(amidoamine) with terminal dimethylamine groups (HPAMAM-N(CH3)2) in water, and they all exhibit highly antimicrobial activity. The particle size can be adjustable from ca. 8.5 and 1.0 nm. The bacterial inhibition ratio reaches up to ca. 98% at the low silver (or gold) content of 2.0μg/mL (or 2.8μg/mL). The resulting metal NPs with smaller particle size can provide much more effective contact surface with the bacteria, thus enhancing their antimicrobial efficiency. Besides, the cationic nature of the hyperbranched PAMAMs can also do some contribution to the antimicrobial activity. The coexistence of the amide moieties, piperazine rings and tertiary amine groups in the hyperbranched structure is important to their effective reducing and stabilizing abilities. Besides, it is note worthy that many terminal functional groups in the hyperbranched PAMAMs can be modified to fabricate series of promising antibacterial materials.4. The Polymer Electrolyte Film with Proton Conductive Properties by Modification of Hyperbranched PolyamidoamineA series of novel crosslinked polymer electrolyte membranes are successfully prepared based on the modification of a hyperbranched poly(amidoamine) with terminal vinyl groups. The membranes possess the different contents of proton-generating sites (i.e., protonated tertiary amine groups) and triflate (Tf2N-) in the crosslinked network. They show good mechanical and thermal stability. The water uptakes of them are ca. 8.4-24.5%. Their proton conductivity is in the order of ca. 10-5-10-2 S/cm from 30 to 80 oC, and it increase with improving the protonation ratio. AFM results disclose the micro-phase separation of the hydrophilic proton-generating sites and the hydrophobic domains of Tf2N- ions. The resulting locally continuous hydrophilic clusters provide proton transport channels to produce the high proton conductivity. This kind of polymer electrolyte membranes may have potential applications in PEFCs and other electrochemical fields.5. A Robust Film Generated from Hyperbranched Polyamidoamine as Host Material and Its Efficient Binding AbilitiesA functional film (named as c-HP) with enough mechanical strength is prepared by the modification of the hyperbranched polyamidoamine and it shows effective binding properties to dyes and metal cations. On the one hand, the film c-HP can encapsulate various water-soluble dyes efficiently, and it can be regenerated and used repeatedly without decreasing its binding efficiency. The effective dye encapsulation ability is attributed to its unique molecular structure, i.e., three dimensional cross-linked networks, the numerous cavities in the branched microstructure, the coexistence of the hydrophilic protonated tertiary amine groups and the hydrophobic assembly of triflate (Tf2N-). On the other hand, the base-treated film c-HP is also able to absorb silver cations (Ag+) from silver nitrate (AgNO3) aqueous solution and reduce Ag+ into Ag0 in situ, producing the hybrid films containing Ag nanoparticles. In this process, the film c-HP exhibits the self-reduction and stabilization role due to the numerous amino groups in the branched points. Furthermore, its binding properties can be extended to some other noble metals like gold (Au), palladium (Pd) and platinum (Pt). As a result, this kind of polymer film material may have promising applications in the fields of dye wastewater treatment and metal catalysis.In one word, the facile preparation of hyperbranched polyamdioamines pays the way for their large-scale production and wide applications. The modification exploring and studies on such kind of hyperbranched polymers to obtain various functional materials provide some important information for the academic researches and the applied fields.