University of Groningen
Polymeric surfactants based on the chemical modification of alternating aliphatic polyketones
Araya Hermosilla, Esteban Alejand
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Araya Hermosilla, E. A. (2019). Polymeric surfactants based on the chemical modification of alternating aliphatic polyketones. University of Groningen.
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1
Chapter
Introduction
***
1.1 Supramolecular systems . . . 1 1.1.1 Supramolecular systems . . . 1 1.1.2 Self-Assembly . . . 2 1.1.3 Active molecules . . . 3 1.1.4 Antibiotics . . . 4 1.1.5 Dyes . . . 4 1.1.6 Redox-active molecules . . . 6 1.2 Polymeric surfactants . . . 7 1.3 Polyketones . . . 81.3.1 The Paal-Knorr reaction . . . 10
1.4 Aim of the thesis . . . 10
1.1
Supramolecular systems, self-assembly and active
molecules
1.1.1
Supramolecular systems
Supramolecular systems are complex architectures formed by molecular building blocks held together by noncovalent intermolecular forces such as hydrogen bond-ing, aromatic-aromatic interactions, hydrophobic interactions, metal-ligand coordi-nation, electrostatic interaction, and dispersion forces, among others. [1–7] There are two types of supramolecular systems: the so-called “supramolecular arrays”, which arise from the spontaneous organization of a large number of components, and the “supermolecules” formed by the intermolecular association of few components. [8] Supramolecular chemistry has been inspired and stimulated by living systems. [9,10]
Although biomolecules comprise essentially covalent bonds, they exhibit novel at-tributes and structures owing to the non-covalent interactions. The formation of the quaternary structure of proteins and the double helix of DNA are paradigmatic exam-ples of the noncovalent interactions value in biological systems. [11] Non-covalent interactions are considered to be labile and dynamic. Therefore, the linking of molecules via noncovalent intermolecular forces may result in self-assembled supra-molecular systems with adaptive response to diverse stimuli. [12–14] Indeed, these forces are necessary for the fabrication of stimuli-responsive materials with the po-tential of self-repair and rectification of defect as in living systems. For instance, supramolecular polymers are endowed with stimuli-responsive attributes. [1, 15] In addition, the reversibility in the supramolecular system is crucial for some function displayed such as chemical sensing [16, 17] and catalysis. [18, 19]
1.1.2
Self-Assembly
The creation of nanostructured materials with dynamic and refined functions is vital for nanoscience and nanotechnology. Nowadays the production of nanostructures can be performed by two strategies, i.e. “top-down” and “bottom-up” nanofabri-cation. [20] In reality, the significant progress in the fabrication of nanomaterials mainly stems from the improvement of top-down microfabrication techniques, since they allow designing extremely complex functional geometries and patterns with a high precision. [21, 22] Nevertheless, this approach encounter significant manu-facturing limitations due to the difficultness to reach geometries and patterns lower than 100 nm (for instance photolithography), it is a intrinsically two-dimension tech-nology, and their expensive fabrication process. [23, 24] Consequently, bottom-up process have become prominent and relevant alternative approaches. [25, 26] They rely strongly on self-assembly of functional molecules based on supramolecular chemistry principles. [27, 28] Supramolecular self-assembly, also called molecular self-assembly, consists in the spontaneous organization of a group of pre-designed molecules without human intervention, leading to the formation of complex supra-molecular entities and functional structures. [24, 26, 28–30] The self-assembly ap-proach has been used for the fabrication of polymeric micelles, [31] nanoreactors, [32] and self-assembled monolayers. [33] It is also important in life; many organelles, folded proteins, lipid membranes, nucleic acid are formed by self-assembly. This synthetic approach can be classified as static and dynamic. [24, 26, 34, 35] Static self-assembly occurs in absence of external influences and the spontaneous organi-sation of the building block in ordered systems is driven by the energy minimization, therefore, the system is at equilibrium and does not dissipate energy. [20, 24] For this type of self-assembly, it is very important to control the noncovalent interac-tion to form steady and well-defined structures. In other words, the molecules in a self-assembled aggregate must be connected by as many noncovalent interactions as possible in order to drive the system towards the most energetically favourable state, thus overcoming the competing interaction with the solvent. Moreover, they have to
1.1. SUPRAMOLECULAR SYSTEMS 3 overcome the favourable entropy that occurs when the aggregate is fragmented into a dissociate state. [28] Dynamic self-assembly (out-of-equilibrium systems) [36–39] is the less studied of the two self-assembly structures and is found mainly in living systems. It depends strongly on the dissipation of energy and on the presence of an external stimulus; the system is organized by reaching an energy minimum due to the influx of energy in the system, which is subsequently dissipated via an entropic pro-cess directly correlated with the interaction of the system building blocks. [40] Once the influx of energy disappears, the system may dissemble. [20] The best example of dynamic self-assembly can be found in a cell; it decreases the entropy by consuming energy from the environment (for instance in the form of food). However, stopping the source of energy (food) to the cell, it might dies. [24] An examples of dynamic self-assembled structures are magnetohydrodynamic self-assembly. [37] These dy-namic structures depend on a continuous energy supply and its dissipation to the environment, and therefore, when the flow of energy conclude they breakdown. [40] Static and dynamic self-assembly can be subdivided into hierarchical self-assembly, co-assembly and direct self-assembly. Hierarchical self-assembly systems, mainly found in nature, are constructed by the self-organization of molecular components in a first order assembly that becomes the foundation structure for a bigger assembly (second order), and so on, “growing up” in complex functional structures. [41–43] Co-assembly refers to the association process of different building blocks for the fabrication of a supramolecular system that it is not possible to produce by the self-assembly of an isolated molecule. In addition, this system may possess the prop-erties and/or functionalities of their constituents. [44–46] Direct self-assembly is a self-assembly process influenced by an external stimuli or a template. [47] For in-stance, a pre-patterned surface can be used to control the orientation and position of the building blocks in the fabrication process of a new nano-object. [48] Another self-assembly strategy, which is directly related to the noncovalent interactions, and used through this thesis, is the ionic self-assembly [49, 50] also called electrostatic self-assembly. [51–53] This is an interesting approach to produce supramolecular structures due to simplicity, cheapness, and flexibility. [54] This uses the electro-static interactions between charged molecules and it is accompanied by a coopera-tive binding mechanism. This means that the first bond stimulates the formation of the next one and this process is propagated towards the formation of a supramolecu-lar structure. [54, 55] In addition, other noncovalent interaction can be present such as aromatic-aromatic interaction, hydrogen bonding, and hydrophobic interaction, among others.
1.1.3
Active molecules
The main goal of supramolecular chemistry and self-assembly techniques is the design of systems with a desired structure and specific functionalities via the self-assembly of molecular building blocks in certain conditions. [56] To produce such systems, one often relies on the noncovalent interactions between molecules and in
their chemical properties. [20, 57, 58] Therefore, the first step of self-assembly is the synthesis of molecules (building blocks) with specific dimensions, forms, and chem-ical characteristics such as hydrophobicity, hydrophilicity, polarizability, charge and functionality. [11, 28] These “functional molecules” may possess photoactive, elec-troactive, ion-active or switching features. In this thesis, we made use mainly of bi-ological (antibiotic), redox, and photo (dye) organic active-molecules for the forma-tion of self-assembly structures with pH-sensitive polymer surfactants via the elec-trostatic self-assembly approach. These active molecules will be briefly discussed below.
1.1.4
Antibiotics
Antibiotics are biologically active molecules of natural origin or synthetics that are capable of inhibiting the growth (bacteriostatic) or kill bacteria (bactericidal). [59] They are still used to treat bacterial infections in human and veterinary medicine. [60] The action mechanisms of antibiotics are generally classified in inhibition of the cell wall synthesis, [61] DNA replication and repair, [62] and protein synthesis of bac-teria. [63] The over-utilization and misuse of antibiotics have created an environ-mental pressure for bacteria to evolve resistance, which is currently a global health problem. [64] Indeed, the discovery of new antibiotics for the resistant pathogens is of paramount interest. [65] The encapsulation of antibiotics may provide a solu-tion to this problem as it protects the drug from the environmental condisolu-tion while, at the same time, resulting in a controlled release and a targeted delivery. [66, 67] Therefore, this is an option to decrease the antibiotic dosage and, as a consequence, it would help to control bacterial resistance. Antibiotics have been encapsulated in liposomes, polymeric nanoparticles, solid lipid nanoparticles, dendrimers, and poly-mersomes. [68–71] The encapsulation of antibiotics can be accomplished by the electrostatic self-assembly method due to some antibiotics (for instance quinolones, antibiotics used in the second chapter of this thesis) are composed of ionic and aro-matic groups. In addition, the aroaro-matic planar architecture, the ionic character, and the hydrophobicity, which can be controlled externally by adjusting the solution pH due to the presence of weak acid groups, are essential characteristic that can be used for the encapsulation in polymeric nanostructures.
1.1.5
Dyes
Dyes are among the most import photoactive molecules for the humankind. They have been applied during our history mainly for imparting colour to fabrics. [72–74] In fact, they are described as “coloured substances, which are soluble or go into solution during the application process and impart colour by selective absorption of light”. [75] Nevertheless, with the recent technological advancements, they are being used in different areas either at the scientific or industrial level. Depending on the
1.1. SUPRAMOLECULAR SYSTEMS 5 N N HO Auxochrome Chromophore Chromogen
Figure 1.1: Schematic representation of the components of an organic dye molecule, 4-Hydroxyazobenzene. [75]
type of dye, namely its the molecular structure, aggregation attributes, solvent sol-ubility, absorption and fluorescence characteristics, application possibilities might involve photodynamic therapy, [76] solar cells, [77] biologic probes, [78, 79] ink-jet printing, [80] dermatology, [81] and photography, [82, 83] among others. Organic dyes molecules are constituted by a chromophore, a chromogen, and an auxochrome (Figure 1.1). [84] They also must possess a structure with alternating double and single bonds (conjugate system) and exhibit resonance of electrons, which is a sta-bilizing force since it lower the potential energy of the molecule. Overall, all the components and chemical characteristics provide to the dye the capacity of absorb-ing light in the visible range (400-700 nm); if one of them is missabsorb-ing the molecule loses the property of absorbing visible light (the colour is lost). [75] The components of the dye may play others important roles besides being responsible for the ability to absorb visible light. For instance, the auxochrome (so-called the colour helper since they can shift the colour of the chromogen) can be ionic groups such as carboxylic acid, hydroxyl, amino, and sulfonic acid groups, provide to the dye the solubility in water and the ability of interact with other molecules by means of electrostatic interactions.
Dyes have been used to form supramolecular structures. In fact, depending on the dye concentration and environmental conditions, dyes might self-assemble to-wards aggregates with different absorption and fluorescent characteristics in com-parison to their monomeric form. They can be aggregate either as J-aggregates or H-aggregates. The former is characterized by a new sharp absorption band, which is red shifted with respect to the long-wavelength absorption band of the monomer (bathochromically shifted) and with a high absorption coefficient, and resonance flu-orescence. [85–87] Conversely, aggregates with absorption bands blue shifted (hyp-sochromically shifted) in comparison to the monomer band and with small or no fluorescence are called H-aggregates. [88] Supramolecular structures have also been produced by the association of water-soluble polymers and dyes through the
electro-static self-assembly approach. [89] It has been found that polyelectrolytes enhance the aggregation of the dye since they induce a high local dye concentration by means of long-range electrostatic interactions. [90,91] In contrast, aromatic polyelectrolytes avoid the dye aggregation due to the specific short-range aromatic-aromatic interac-tions. [92, 93] The dye dispersion provided by these polymers rely on the linear aro-matic density and flexibility of the polymer, and the relative concentration between the polymeric charge aromatic group and the dye. [90, 94] Furthermore, the for-mation of polymer/dye supramolecular structures may improve the qualities of the dyes. For instance, the polyelectrolyte-porphyrin nano-assemblies display higher catalytic activity in comparison to the porphyrin not interacting with the polymer template. [53] Moreover, the improvement of phototoxic reactive oxygen species (ROS) production via the type I mechanism upon irradiation of the complex com-posed by an aromatic polyelectrolyte and methylene blue has also been reported. This is explained by the ability of the polymer to prevent the dye aggregation and enhance the dye-to-dye contact. [76]
1.1.6
Redox-active molecules
Oxidation-reduction reactions (redox) involve the transfer of electrons between atoms, ions, or molecules. These redox species can act as reducing or oxidizing agents; the former is a species that donates electrons and the latter accepts them. In this sense, active-redox molecules, also mentioned in the literature as electron donor-acceptor (D-A) molecules, can be described as molecules that are able to donate or receive electrons. Furthermore, these molecules possess the ability to adjust their molecu-lar conformation and physicochemical characteristics reversibly when they undergo redox reaction. [95–97] Redox-active molecules can be synthetic or present as such in nature. For instance, redox proteins, which are constituted of connected catalytic sites (defined as multi-electron redox centres or single-electron redox centres that in-teract with substrates and serve as reservoirs or sinks of electrons), perform essential functions in biological processes that request electrons transfer such as photosyn-thesis, respiration, and metabolism. [98] Other cases of natural D-A molecules are antioxidants or antiradicals (for instance carotenoids and flavonoids). [99, 100] Their function is to reduce free radicals by transferring electrons (becoming oxidized), and therefore, inhibits that other molecules endure an oxidation reaction with these free radicals. [101] In addition, antioxidants may also accept an unpaired electron from the free radical, becoming reduced and the free radical oxidized. [102] Synthetic D-A molecules have been used to produce redox-fluorescence switch molecules, [103] for the fabrication of batteries [104, 105] and memory devices. [106] In addition, there are synthetic redox-active molecules that can change their luminescent prop-erties when they experience a redox reaction. Due to the change from a colourless to coloured molecule after reduction, they have been used for the detection of bac-teria, [107] to quantify reducing carbonyl groups in cellulose, [108] to determine mammalian cell growth, [109] and for sensing metal ions. [110]
1.2. POLYMERIC SURFACTANTS 7 The synthesis of sub-micron or/and nanoparticles using redox-active molecules that can switch their solubility and luminescence properties in aqueous solution (i.e become hydrophobic and coloured reversibly) through their reduction/oxidation, and in addition, stabilized by ionic or anionic surfactants or polymeric surfactant, is a promising approach for the production of smart stimuli-responsive materials.
1.2
Polymeric surfactants
Polymers are macromolecules consisting of covalently bonded segments, referred to as monomers. They can be grouped in a general form as natural polymers (for in-stance polysaccharides, proteins and nucleic acids) and synthetic polymers, which include common plastics and adhesives. Other types of polymers are amphiphilic polymers [111, 112] also known as polymeric surfactants [113] (surface active poly-mers) or micellar polymers [114], which can be found in nature or synthesized through diverse polymerization reactions. Natural surfactants or biosurfactants (for example lipopolysaccharides) are abundant in nature and can be obtained either from the plant and animal kingdoms. These types of surfactant are utilized by the biolog-ical systems to overcome solubility problems, as emulsifiers and dispersants, and to modify surfaces. [115] They are biodegradable, available from renewable sources, and show low toxicity. [116, 117] Nevertheless, they exhibit separation problems from the natural source, as a result the separation and isolation cost exceeds the cost production of synthetic surfactant. [118] In view of this, the majority of scien-tific investigations and industrial applications have been focused on synthetic surfac-tants. Indeed, the latter have been used for the preparation of emulsions and suspen-sions, [119, 120] drug delivery systems, [121, 122], in photodynamic therapy, [123] and oil recovery. [124–126]
Polymeric surfactants are made of lyophilic and lyophobic segments (also named as hydrophilic and hydrophobic segments when the solvent is water) linked together by covalent bonds. Due to their amphiphilic properties, they are capable of:
- decreasing the surface tension of the solvent and the interfacial tension with another phase; [127]
- being absorbed by surfaces and interfaces such as dispersed solid or liquid phases; [128, 129]
- self-assembly as micelles when the polymer concentration reaches a certain value, called the “critical micelle concentration” (CMC).
In a micelle, the lipophilic segments are in the interior, constituting the hydropho-bic core, and the polar segments are directed to the solvent, making the hydrophilic corona. In the case that the solubility of the polymer in aqueous medium depends
on external stimuli such as pH and temperature, the polymer might show a stimuli-responsive behaviour. [130] For instance, pH-stimuli-responsive polymers contain acidic or basic groups, they can accept or release protons by adjusting the pH, resulting in an alteration of the hydrophilic-hydrophobic balance. [131] Thermosensitive polymers assume a water-soluble extent coil conformation at low temperatures. However, as the temperature increase, the water molecules are released in bulk, following the associative contact between the hydrophobic segments of the polymer. [132, 133]
The macromolecular nature of polymeric surfactants permits a diverse and com-plex distribution of hydrophilic and hydrophobic segments. [114] Indeed, the hy-drophobic pendant groups may be grafted onto a hydrophilic polymer backbone or, conversely, the hydrophilic pendant groups grafted onto a hydrophobic backbone. A different approach is the alternating arrangement of the hydrophobic and hydrophilic monomers. Besides, these methods to synthesize surface active polymers can be combined. [134] The diverse polymeric surfactant architectures have been classi-fied in different groups such as block copolymers, stars and graft copolymers, and amphiphilic dendrimers. All those polymers are identified by possessing large and well separated hydrophilic and hydrophobic monomers. [114] On the other hand, other polymeric surfactants exhibit an architecture where hydrophilic and hydropho-bic segments are scattered all over the macromolecule; these polymers are referred as polysoaps. They are defined as polymers that contain surfactant-like segments in the polymer repeating unit. [118]
A fundamental requirement for several applications is the precise control of the polymeric surfactant in terms of composition and polymer structure, molecular weight, and balance between the hydrophilic and hydrophobic segments. The best candidates to meet those criteria are the living radical polymerization approaches such as atom transfer radical polymerization (ATRP), [135, 136] reversible addition-fragmentation chain transfer polymerization (RAFT), [137, 138] and nitroxide-mediated polymerization (NMP). [139] Nonetheless, these polymerization methods are expensive in comparison with other approaches. In this thesis, we present the easy and cheap production of polymeric surfactants by the incorporation of hy-drophilic pendant groups onto a hydrophobic polyketone via the Paal-Knorr reac-tion. In addition, these amphiphilic polymers were used as building blocks for the production of smart colloids via the electrostatic self-assembly method, since they display pH stimuli-responsive properties (weak polyelectrolytes).
1.3
Polyketones
Aliphatic polyketones are a relatively new type of polymer. They can be synthesized in three different methods. In two of them, the copolymerization of CO with olefins is promoted by γ-rays or radicals. [140] They have not found widespread utilization owing to need harsh reaction conditions and display poor control of the structure and properties of the resultant polymers. For instance, the first attempted
copolymeriza-1.3. POLYKETONES 9 O O R R R = H, CH3 O O O R R
Figure 1.2: Scheme of aliphatic polyketone.
tion of CO with ethylene was achieved by Farbenfabriken Bayer using free-radical polymerization. It yields a random aliphatic polyketones by using extreme reaction conditions (230○C and 2000 atm). [141] On the other hand, a third approach, which uses a catalyst that is based on transition metal compounds, gives as result a copoly-mer with a precise alternating structure. The first alternating aliphatic polyketones was reported by Reppe and Magin by using milder condition (230○C and 200 atm) and K2[Ni(CN)4] as catalyst. [142] There was no technological breakthrough until a homogeneous palladium-based catalytic system was developed by Shell researchers of the 20thcentury. The economic requirements for industrial-scale production were achieved by using this system, which was 6 (kg of polymer) (g of Pd)-1h-1 under mild conditions (90○C, 4-5 MPa). [143]
The copolymerization of CO and ethylene using palladium derivatives as catalyst yield the synthesis of semicrystalline polyketones which are the simplest members of these type of polymers. They possess a relatively high melting point close to the thermal decomposition temperature. In addition, they are insoluble in common organic solvents and dissolve in highly polar and acid solvents. Overall, it makes their processing complicated. In order to improve the processability of polyketones, propylene is incorporated as a monomer at a desired molar ratio (Figure 1.2). The ter-polymerization brings disorder to the molecular packaging and, therefore, decreases the melting point of the polymer.
Polyketones exhibit important properties that make them interesting polymers. Their properties include:
- good chemical resistance towards solvent, acid and bases; - impermeability to hydrocarbons;
- low costs (e.g. carbon monoxide is a low-cost and easily accessible monomer); - relatively high reactivity, with the reactive carbonyl groups endowing the
poly-mer with photo-and biodegradability.
Due to the presence of the carbonyl groups, polyketones can be utilized as pre-cursors for the production of functional polymers via the chemical modification
ap-proach. Polyketones can readily be converted into a variety of polymers that contain functional groups such as bisphenols, [144] alcohols, [145] and ketals, [146] among others. Recently, the synthesis of pyrroles via the Paal-Knorr reaction has attracted special attention due to the absence of any catalysts and, more generally, of demand-ing reaction conditions.
1.3.1
The Paal-Knorr reaction
The Paal-Knorr condensation is a straightforward reaction for the synthesis of func-tional polymers. The mechanism of this reaction consists of the pyrrole ring forma-tion via the double condensaforma-tion reacforma-tion of a primary amine group with the polyke-tone 1,4 di-kepolyke-tone group (Figure 1.3). [147] Generally, the first step of the Paal-Knorr reaction is the addition of an amine to one of the carbonyl groups forming a hemiaminal (molecule number 2 in Figure 1.4). Afterwards, the second carbonyl is attacked by the nitrogen, resulting in the cyclization of the hemiaminal. Finally, the ring undergoes dehydration to yield the pyrrole ring (Figure 1.4). [148] In our research group, polyketones chemically functionalized via the Paal-Knorr reaction, have been applied to the production of self-healing materials, [149–151] emulsions with adhesive properties, [152, 153] coating materials, [154] and water-insoluble resins. [155, 156] This reaction shows several advantages such as the absence of solvent and catalysts, it is carried out in one-pot, it yields water as the single by-product, and it displays fast kinetics and relatively high yields. In particular, up to 80% carbonyl conversion (an upper limit due to the reversibility of the reaction and statistical reasons), the amine conversion is practically quantitative, thus avoiding also the need for any purification step of the final product. In addition, the reaction can readily be performed either in the laboratory or on larger scales. The num-ber of primary amines that may be used to functionalize polyketones is factually unlimited, making this easy synthesis a versatile method to prepare polymers with almost any desired pendant functional group. [147, 149, 150, 157] In this thesis, we proved that the Paal-Knorr reaction on a polyketone with different primary amines represents a simple, low cost, and straightforward method to produce polymeric sur-factants. The architecture of these amphiphilic polymers is based on a hydrophobic backbone consisting of aliphatic 1,4-dicarbonyl units and N-substituted pyrrole moi-eties. The hydrophilic pendant groups are provided by the primary amine chosen for the polyketone derivatization. In this thesis the pendant groups also display pH-responsive properties.
1.4
Aim of the thesis
This thesis is focused on the preparation of polymeric surfactants with pH-responsive properties by using an alternating aliphatic polyketone as starting materials and the Paal-Knorr condensation as synthetic route. These polyketones are used as building
1.4. AIM OF THE THESIS 11 O O R R R = H, CH3 + N R R O R O R x y Paal-Knorr reaction 100 0 C R' NH2 R' R': Functional group
Figure 1.3: Schematic representation of polyketones chemical modification via the Paal-Knorr reaction. RNH2 + O O H3C CH3 R R 1 O HN H3C CH3 R R 2 R OH N R R OH CH3 R HO H3C 3 - H2O N R R R HO H3C 4 N R R R 5 CH3 CH3 H3C - H2O
Figure 1.4: Schematic representation of the Paal-Knorr reaction (modify and simpli-fied from Amarnath. V and co-workers [148]).
blocks for the fabrication of supramolecular entities with applications in the encap-sulation of hydrophobic molecules, dispersion of dyes, and synthesis of redox-active nanoparticles.
Chapter 2 focusses in the encapsulation of two types of antibiotic (Oxolinic Acid and Flumequine), extensively used in Chilean salmoniculture, in polymeric micelles, using a pH-sensitive polyketone bearing imidazolium pendant groups. The encapsu-lation process was conducted in water, not using organic solvents, which is a valuable addition from a green chemistry perspective.
Chapter 3 describes the dispersion and aggregation of 5,10,15,20-tetrakis-(sulfonatophenyl)-porphyrin in an acid aqueous environment by using amphiphilic polyketone derivatives. Particularly, polymers with higher hydrophobicity (fewer functional groups) could prevent the aggregation of the dye at lower values of pH in comparison to polymers bearing higher incorporation of functional groups. Among several factors, the electrostatic interactions and preferential solvation of the dye by the polymer chain explain the stabilization and dispersion of the dye.
Chapter 4 describes the design of micro- and nano-polymeric complex micelles composed of polyketones bearing different pendant groups: a heteroaromatic amine, a heterocyclic aliphatic amine, and an aliphatic amine containing a hydroxyl group, and the dye 5,10,15,20-tetrakis-(sulfonatophenyl)porphyrin. In addition, it shows the control of the structure of supramolecular entities by changing the pH of the solutions.
Chapter 5 shows a simple, cheap and “green” method for the synthesis of nanopar-ticles of colored organic nanoparnanopar-ticles by the reduction of the tetrazolium salt (TTC) to the corresponding red formazan (TF) in the presence of aromatic polyketones. It demonstrates that aromatic-aromatic interactions between the functional groups of the polymers and the precursor molecule (TTC) are pivotal in the nanoprecipitation process.
Chapter 6 shows the flexibility of the Paal-Knorr reaction in the synthesis of func-tional polymers via the chemical modification of aliphatic polyketones. Two new applications are presented: the synthesis of polymer supported ionic liquids based on aliphatic polyketones and their utilization for the production of cyclic carbonates; and the application of two amphiphilic polymers, with a pH-responsive character, in the formation of water in oil emulsions.
