University of Groningen Polymeric surfactants based on the chemical modification of alternating aliphatic polyketones Araya Hermosilla, Esteban Alejand

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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3

Chapter

Amphiphilic modified

polyketones as stabilizers of the

tetra-anionic form of

5,10,15,20-Tetrakis-(4-sulfonatophenyl)porphyrin in

aqueous acid conditions

1

***

3.1 Introduction . . . 28

3.2 Experimental . . . 30

3.3 Results and discussion . . . 32

3.4 Conclusions . . . 41

Abstract. In this work, we present the synthesis of amphiphilic polymers, bearing secondary amines and hydroxyl groups as pendant ones. The approach to the syn-thesis is the modification of polyketone with N-(2-hydroxyethyl)ethylenediamine via the Paal-Knorr reaction. Four polymers were synthesized at different carbonyl con-version (x) values (0.19, 0.35, 0.51, and 0.63). These polymers were used to stabilize

1_{This chapter is based on: Araya-Hermosilla, E., M. Roscam Abbing, J. Cataln-Toledo, F.} Oyarzun-Ampuero, A. Pucci, P. Raffa, F. Picchioni & I. Moreno-Villoslada (2019). Synthesis of tuneable amphiphilic-modified polyketone polymers, their complexes with 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin, and their role in the photooxidation of 1,3,5-triphenylformazan confined in polymeric nanoparticles. Polymer 167: 215-223.

the non-self-aggregated tetra-anionic form of 5,10,15,20-tetrakis-(4-sulfonatophenyl) porphyrin at acidic conditions. A correlation between the carbonyl conversion de-gree and the shift on the transition pH value between the tetra-anionic and di-anionic forms of the dye can be clearly detected. For TPPS in the presence of polyke-tones with a 0.63 degree of carbonyl conversion (polykepolyke-tones modified with N-(2-hydroxyethyl)ethylenediamine PK50-HEDA80) the transition pH was found to be 2.75, 1.6 units lower than the pristine dye (4.35). On the other hand, following the same procedure, the transition pH was found at lower values (1.86 and 1.73) for HEDA60 (polyketone with a 0.51 degree of carbonyl conversion) and PK50-HEDA40 (polyketone with a 0.35 degree of carbonyl conversion), respectively. Elec-trostatic interactions and preferential solvation of the dye by the polymer chain can be used to explain the obtained data.

Keywords. Paal-Knorr chemical modification, polyketone derivatives, amphiphilic properties, TPPS, porphyrin dispersion, hydrophobic interaction.

3.1

Introduction

Polyketones constitute an interesting class of polymeric materials. They can be eas-ily functionalized by a reaction with primary amines via the Paal-Knorr approach. [147] This reaction possesses three main attributes: it is a solvent and catalysts free reaction that can be carried out in one-pot, and yields water as the only by-product. The number of primary amines that may be used to functionalize polyketones is fac-tually unlimited, making this easy synthesis a versatile method to prepare polymers with almost any desired pendant functional group. [147, 149, 150, 157] Therefore, the Paal-Knorr reaction on polyketones represents a simple, low cost, and straight-forward way to prepare amphiphilic polymers. The architecture of these polymers is based on a hydrophobic backbone consisting of aliphatic 1,4-dicarbonyl units and N-substituted pyrrole moieties, and hydrophilic pendant groups, provided by the pri-mary amine chosen for the polyketone derivatization.

Porphyrins are a vital class of natural macrocyclic compounds that play a sig-nificant role in the metabolism of living organisms. Some of the outstanding ex-amples are heme, an iron-containing porphyrin, found in hemoglobin, myoglobin, hemoproteins, and chlorin, a magnesium-containing reduced porphyrin found in chlorophyll. [191, 192] The porphyrin skeleton comprises four pyrrole rings linked by four methylene bridges, [193, 194] which can accept up to two protons at low values of pH. [191, 192, 195] Porphyrins have been used in photodynamic therapy (PDT), [196, 197] catalysis, [198] in sensors, [199–201] light-harvesting materi-als [202] etc. 5,10,15,20-Tetrakis-(sulfonatophenyl)porphyrin (TPPS) (Figure 3.1) is a water-soluble porphyrin meso-substituted by four hydrophilic sulfophenyl sub-stituents. This molecule has been extensively investigated for its ability to self-aggregate, which is due to a flat, wide, and electron-rich surface, charge-transfer

3.1. INTRODUCTION 29 interactions, dispersion forces, and aromatic-aromatic interactions. Its aggregation in water depends on the pH, [203] ionic concentration, [204] and dye concentra-tion. [157] It can be enhanced by interaction with polyelectrolytes, [205] dendrimers, [206, 207] micelles, [208] vesicles, [209] or any other positively charged molecule and surface. However, aggregation may be an unwanted feature that jeopardizes the molecule performance for some applications.

NH HN N N -_O 3S SO3 -SO3 --_O 3S NH HN NH+ NH+ -_O 3S SO3 -SO3 --_O 3S H4TPPS2- H2TPPS 4-pKa = 4.9

Figure 3.1: Acid and basic forms of TPPS.

As a consequence, the ability to control the aggregation of porphyrins such as TPPS is of paramount interest. Previous works have demonstrated that the use of aromatic-aromatic interactions between positively charged aromatic polymers and the negatively charged TPPS allows the stabilization of the tetra-anionic form of the dye at low pH, preventing its self-aggregation. [157] Likewise, amphiphilic copoly-mers possessing positively charged aromatic moieties together with pyrrolidone pen-dant groups showed the importance of the amphiphilic structures in the control of dye aggregation and stabilization of its basic form. [175] It remains the question whether aliphatic amphiphilic cationic polymers based on polyketones are able to disperse the photosensitizer TPPS, or enhance the dye self-aggregation as other polycations do. In this context, the present work reports the preparation of pH-sensitive sur-factant polymers for the stabilization of TPPS in an aqueous environment, via the functionalization of polyketones with N-(2-hydroxyethyl)ethylenediamine (HEDA) (Figure 3.2) through the Paal-Knorr reaction. Four polymers were synthetized at different degrees of carbonyl conversion, therefore displaying a different balance of hydrophilic/hydrophobic moieties. These polymers were used to stabilize the non-aggregated tetra-anionic form of TPPS in water.

O O R R R = H (50 mol%), CH3 (50 mol%) + N R R O R O R x y Paal-Knorr reaction 100 0 _C H2N HN OH HN OH

Figure 3.2: Schematic representation of the chemical modification of polyketone 50 via Paal-Knorr reaction with N-(2-hydroxyethyl)ethylenediamine (HEDA).

3.2

Experimental

Reagents

HEDA (Sigma-Aldrich 99%) and 2,5-hexanedione (Sigma- Aldrich 98%) were com-mercially available and used as received. 5,10,15,20-Tetrakis(4-sulfophenyl) porphyrin TPPS (TCI) was used without further purification for the interaction stud-ies. Polyketones made of ethylene, propylene, and carbon monoxide were synthe-sized according to reported procedures. [190, 210] In particular, a polyketone com-prised of 50% ethylene and 50% propylene (PK50, Mw 3636) was used. Distilled water, 1-propanol (Sigma-Aldrich), and CDCl3 (Sigma-Aldrich) were used as sol-vents. The pH was adjusted with minimum amounts of HCl (Sigma-Aldrich) and NaOH (Sigma-Aldrich).

Equipment

Water was deionized in Arium 611 Sartorius deionizer. The pH was controlled on a Seven2GoTM pH meter. Surface tension measurements on the polymer solutions were performed using a Lauda drop volume tensiometer TVT 1. UV-vis measure-ments were performed in a Cary 100 Bio Uv-visible spectrophotometer. Fluores-cence measurements were done in a Fluorolog Jovin Yvon fluorimeter. 1H-NMR measurements were made in a Varian Mercury Plus 400 MHz spectrometer. The polymer synthesis was performed in a microwave CEM Discover. ATR-FT-IR spec-tra were recorded using a Thermo Nicolet NEXUS 670 FT-IR. Elemental analysis measurements were performed with a Euro EA elemental analyzer.

Procedures

Paal-Knorr reaction. A model compound was synthesized as a reference for the characterization of the polymers after the Paal-Knorr reaction. The reaction between

3.2. EXPERIMENTAL 31 stoichiometric amounts of HEDA and 2,5-hexadione was performed in a round-bottom flask equipped with a magnetic stirrer and a reflux condenser. 0.46 g of 2,5-hexadione (0.004 mol) and 0.42 g of HEDA (0.004 mol) were dissolved in 1-propanol (30 mL) and moved to a microwave oven. The reaction was carried out during 150 minutes at 100○_{C (100 W) based on a reported procedure. [211] In order}

to fully evaporate the solvent, the sample was placed in an oven for 48 h at 50 0C. The product was analyzed by1_{H-NMR in CDCl}

3. Functionalization of PK50 with

HEDA was carried out at different 1,4-dicarbonyl/primary amine molar ratios by changing the amount of the primary amine (see Table 3.1). Around 20 g of PK50 and variable amounts of HEDA were placed in a 100 mL round bottom flask equipped with a magnetic stirrer and a reflux condenser. The reaction mixture was moved to the microwave apparatus. The microwave power was kept at 100 W and the tem-perature was set up at 100○_{C. After 2.5 hours, microwave heating was ceased and}

the products were further purified by solvent extraction technique, using brine and chloroform as solvents. Chloroform was evaporated in a vacuum oven at 50○_{C for}

48 hours. The polymers were characterized by1H-NMR in CDCl3 and ATR-FT-IR. The carbonyl conversion is defined as the molar fraction of converted 1,4-dicarbonyl units (x) and was calculated by elemental analysis by the following formula [157]:

x = N Mc

nMN+N M_c−M_p

(3.1)

where N is the nitrogen content in g per g of polymer, MNrepresents the atomic

mass of nitrogen (14 g/mol), n is the number of nitrogen atoms of the converted 1,4-dicarbonyl segment (2 units), Mpis the molecular weight of the converted

1,4-dicarbonyl segment (194 g/mol), and Mcis the molecular weight of the non-converted

1,4-dicarbonyl segment (126 g/mol) of PK50. Mp and Mcwere calculated taking

into account the incorporation of ethylene and propylene in the copolymers at ra-tio of 1:1. In order to adjust the stoichiometry of charged groups when using the polyketone derivatives, we consider a polymeric molecular weight (Table 3.1) given in g/mol of basic groups (M+) following [157]:

M+=

xMp+yM_c

xz (3.2)

where y is the fraction of non-converted 1,4-dicarbonyl groups, provided that x + y = 1, and z is the number of atoms susceptible to protonate in the converted repetitive unit, in this case 1, provided that the di-carbonyl moieties are not suscep-tible to protonation.

Polyketone derivative PK50 (g) Moles of di-carbonyl group HEDA (g) Moles of HEDA N (%) x M+

(g/mol of basic groups) PK50-HEDA20 19.65 0.031 3.25 0.031 3.79 0.19 731 PK50-HEDA40 19.05 0.061 6.30 0.061 6.54 0.35 428 PK50-HEDA60 19.56 0.093 9.70 0.093 8.88 0.51 315 PK50-HEDA80 19.24 0.130 12.72 0.130 10.32 0.63 268

Table 3.1: Amounts in the feed and carbonyl conversion (x) in the Paal-Knorr reac-tion between PK50 and HEDA.

Surface tension studies. Aqueous stock solutions of the polymers were prepared at a concentration of 5 ⋅ 10−4 _{M of functional groups. The surface tension test was}

conducted diluting the polymer stock solutions to 1 ⋅ 10−4 _{M of functional groups,}

and increasing the pH with aqueous sodium hydroxide. The solutions were allowed to equilibrate overnight. A 1 mL-plastic syringe was attached to a needle with a capillary radius of 1.65 mm. The temperature was set at 20○_{C during the period of}

measurement and the water density was set to 0.997 g/mL.

Interaction studies between the polymers and TPPS. Aqueous samples were prepared from stock solutions of the reactants. The pH was adjusted between 3.4 and 1.1 with minimum amounts of NaOH and HCl with a concentration of 1 M. The samples were allowed to equilibrate overnight. Absorption UV-vis analyzes were performed in a quartz cell of 1 cm path length. The obtained data were plotted with the OriginPro 8 software, and sigmoidal fitting was done using the Boltzman function to analyse the transition pH change of TPPS. Fluorescence quartz cells of 1 cm of path length were used for fluorescence measurements and three-dimensional spectra were recorded.

3.3

Results and discussion

Model compound synthesis. A model compound using 2,5-hexanedione and HEDA was synthesized as a reference to help identifying the signals in1_H-NMR

spectroscopy. The resulting product after the Paal-Knorr reaction (pyrrol-HEDA model compound) shows the signal corresponding to the pyrrole group at 5.8 ppm (protons 1), as can be seen in Figure 3.3. The methylene protons of the amine com-pound appear at 3.9, 3.6, 2.9, 2.7 ppm, which are assigned to protons 3, 6, 4, and 5, respectively, based on multiplicity and chemical shift. [212] Finally, the methyl protons (protons 2) appear at 2.2 ppm.

3.3. RESULTS AND DISCUSSION 33

Figure 3.3:1_{H-NMR spectra of pyrrole-HEDA model compound.}

Polyketones 50 modified with HEDA. The modification of PK50 with HEDA dis-plays carbonyl conversion (x) values close to the expected when taking into account the molar ratio of reactants in the feed (see Table 3.1). The success of the PK50 mod-ification can be confirmed by ATR-FT-IR and1_{H-NMR spectroscopies. Figure 3.4}

shows the1_{H-NMR spectra of PK50-HEDA at different conversion values (x). The}

polymeric nature of the molecules, together with a statistical distribution of ethy-lene and propyethy-lene monomers in PK50, as well as the statistical distribution of the converted 1,4-dicarbonyl units, are responsible for the appearance of broad peaks. However, using the information obtained from the model compound it was possible to assign the signals. PK50-HEDA 20, 40, 60 and 80 display their pyrrole rings with proton signals between 5.5 and 6 ppm corresponding to protons 1 and 2 from the ethylene and propylene 1,4-dicarbonyl segments, respectively. When the Paal-Knorr reaction is carried out on the propylene 1,4-dicarbonyl segment, a peak appears at around 2 ppm corresponding to the methyl groups (proton 3). Methylene protons 4 and 7 can be clearly assigned at 3.8 and 3.6 ppm, respectively due to their expected chemical shift. On the other hand, methylene protons 5 and 6 can be assigned to the peaks at 2.8 and 2.7 ppm, respectively, that overlap with the peaks of the residual 1,4-dicarbonyl units. That can be corroborated by comparison to the spectrum of the pristine PK50.

Figure 3.4: 1H-NMR spectra of PK50 modified with HEDA at different x: 0.63, PK50-HEDA80 (a); 0.51, PK50-HEDA60 (b); 0.35, PK50-HEDA40 (c); 0.19, PK50-HEDA20 (d); 0.0, PK50 (e).

Figure 3.5 shows the ATR-FT-IR spectrum of PK50-HEDA at different x values normalized with respect to the CH3peak at 2963 cm−1. As conversion increases, the

intensity of the carbonyl group (1700 cm−1_{) decreases, due to the disappearance of}

the 1,4-dicarbonyl moieties. In the range of 1399-1350 cm−1_{three medium intensity}

peaks appear which may be attributed to the scissoring bending vibration of the CH2

next to the carbonyl group, and the symmetrical bending vibration of the CH3. The

intensity of those peaks decreases as the conversion increases. On the other hand, for the four modified polyketones a peak at 750 cm−1appears which can be assigned to the CH2 rocking vibration (rocking in phase) of the pendant group. Overall, the

decrease in intensity of the carbonyl and CH2 scissoring bending vibration peaks,

and the increase in intensity of the CH2 rocking vibration, indicate the successful

achievement of the polyketones modification. In the range of 3700-3000 cm−1 _a

broad peak appears which correspond to the hydrogen bonding occurring with ex-changeable protons in the pendant group. In the range of 1650-1500 cm−1_{a series}

of weak peaks appear which can be assigned to stretching of C=N and C=C in the pyrrole ring. The asymmetrical and symmetrical stretching bands of aliphatic C-H of PK50 appearing between 2969 and 2873 cm−1_{broaden as x increases, including}

3.3. RESULTS AND DISCUSSION 35

Figure 3.5: FT-IR spectra of PK50 modified with HEDA at different x: 0.63, HEDA80 (a); 0.51, HEDA60 (b); 0.35, HEDA40 (c); 0.19, PK50-HEDA20 (d); 0.0, PK50 (e).

Surface tension study of PK50-HEDA80. Polyketone modified with HEDA has an amphipathic structure. The amine pendant groups provide the hydrophilic and the backbone the hydrophobic segments (Figure 3.2). Therefore, this polymer can be classified as pH-responsive surfactant polymer. It is water-soluble at low pH values, due to the protonation of the amine. However, the solubility of the polymer is altered by increasing the pH. [131, 213] In other words, the polymer becomes less positively charged and the hydrophilic/hydrophobic polymeric balance changes in favour to hydrophobicity. This phenomenon can be studied by surface tension experiments; the polymer loses the charge as the pH increases and the deprotonated hydrophobic blocks begin to be absorbed at the water/air interface. As a result, the polymer low-ers the surface tension of the solution. [214, 215] Figure 3.6 shows the reduction of the surface tension of the polymer solution as a function of the pH and concentra-tion. The polymer exhibit higher surface activity as the pH increases. This can be observed clearly when the experiments performed at pH 3 and 7 are compared. This was expected, since the increase of the polymer hydrophobicity results in higher sur-face excess. [216] In addition, it is well known that incrementing the concentration of the polymeric surfactants causes a continuous increase in surface activity. It was observed at each value of pH, the surface tension decreases as the polymer concen-tration increases (Figure 3.6). Polymeric surfactants may self-assembly as polymeric micelles. [217, 218] This can be monitored through surface tension measurements; the surface tension reaches a plateau at a certain polymer concentration, indicating the micelles formation. The experiments performed at pH 5, 6 and 7 displayed a plateau when the concentration reached 15 mg/mL. On the other hand, the polymer

solutions did not exhibit a plateau at pH 3 and 4. Therefore, if the concentration increases, it is expected that the surface tension continues decreasing.

Figure 3.6: Surface tension graph of PK50-HEDA80 as a functions of pH and con-centration. () pH 3.0 ( ) pH 4.0 (N) pH 5.0 (H) pH 6.0 (_) pH 7.0.

Stabilization of H2TPPS4−by PK50 modified with HEDA. The changes on the

acid-base properties of TPPS at dilute conditions were studied in the presence of the different PK50 derivatives. Pristine TPPS presents a transition pH between the tetra-anionic (H2TPPS4−) and the di-anionic forms (H4TPPS2−) of around 4.9 at a

concentration of 1 ⋅ 10−6 _{M. [157, 175] In this investigation, the absorbance of the}

TPPS band at 434 nm was used in order to estimate the transition pH in a range of pH from 1 to 9, since it reveals the protonation of the pyrrole groups (Figure 3.7, left side). By fitting the data with a Boltzmann sigmoidal curve and further derivation allowed to find the transition pH of TPPS at 4.35 (Figure 3.7, right side).

3.3. RESULTS AND DISCUSSION 37

Figure 3.7: Transition pH of TPPS at a concentration of 1 ⋅ 10−6M. The di-anionic form displays a Soret band at 434 nm in the absorbance spectra and two Q bands at 594 and 646 nm. On the other hand, the tetra-anionic form displays a Soret band at 414 nm and four Q bands appearing 634, 578, 552 and 516 nm (Figure 3.8). [157, 206, 219]

Figure 3.8: Normalized UV-vis spectra of 1 ⋅ 10−6_{M TTPS at pH 1.04 (a), 1.87 (b),}

2.97 (c), 3.95 (d), 5.10 (e), 6.28 (f), 7.21 (g), 7.86 (h) and 9.03 (i).

At this concentration, the tendency of the dye to undergo self-aggregation is very low at both its tetra-anionic and di-anionic forms. More concentrated solutions of the dye induce the formation of aggregates, typically H-aggregates for H2TPPS4−

with a Soret band shift to around 400 nm, and J-aggregates for H4TPPS2−with the

Figure 3.9: Schematic structure of J-aggregates (right) and H-aggregates (left) formed by TPPS. [220]

Figure 3.10 shows the absorbance spectrum of TPPS at a concentration of 1⋅10−6

M in the presence of PK50-HEDA80 at a concentration of 1 ⋅ 10−4 _{M of functional}

groups at different pHs. At pH 3.4 and 2.8 TPPS is found as H2TPPS4−with a Soret

centered at 421 nm and four Q bands centered at 518, 553, 590, 646 nm. These peaks are red shifted comparing to the pristine H2TPPS4−, which present a Soret

centered at 414 and four Q bands centered at 634, 578, 552 and 516 nm. The red shift of the bands is caused by the decrease in the energy gap between the HOMO and LUMO orbitals due to the interaction with polymers. This red shift is generally a consequence of water molecules leaving the hydration sphere of the dye and being replaced by organic, less polar moieties such as organic solvents. [175, 221] In the present case this is probably due to presence of polymeric hydrophobic segments. This tendency of the dye to be solvated by organic residues and the stabilization of the negative charges furnished by the charged amino group of PK50-HEDA80 are responsible for the stabilization of the tetra-anionic form of the dye. Indeed, even if the net charge of the tetra-anionic form is higher than in the di-anionic form, the latter is more hydrophilic, since it consists of 4 peripheral negative charges and 2 positive charges in the center of the porphyrin group. Further decrease of the pH results in the appearance of a band centered at 490 nm at the expense of the monomeric Soret band at 421 nm. This new band corresponds to J-aggregates of the di-anionic H4TPPS2−. A Q-band centered on 705 nm appears at the expense of the

Q-bands of the tetra-anionic form, consistent with a change of symmetry form D2h

to D4h. [207, 208] In addition, the residual monomeric band at 421 nm increasingly

shifts to higher energies, up to 426, by decreasing the pH up to 1.0. This is due to the coexistence of both the monomeric tetra-anionic and di-anionic forms of the dye at different ratios. These observations have their correlation in 3D-fluorescence observations. At pH 2.8 and 3.4 a maximum is observed at 420 nm of excitation and 652 and 715 nm of emission wavelengths (Figure 3.11). This corresponds to the tetra-anionic form of the dye based on the shape and number of bands. [206, 222] However, there is a shifting of the emission maxima to lower energies, since for the pristine dye the emission maxima appear at 642 and 705 nm upon excitation

3.3. RESULTS AND DISCUSSION 39 at 414 nm. [157] For lower values of pH the main contribution to the fluorescence comes from the residual monomeric di-anionic species (H4TPPS2−), because the

corresponding excitation wavelengths appear in the range of 430-440 nm and the corresponding emission band is single, and appears centered at 670, shifted 10 nm from the fluorescence band of the pristine di-anionic species, that appears at 680 nm. [157, 175]

Figure 3.10: Normalized UV-vis spectra of 1⋅10−6M TTPS in the presence of PK50-HEDA80 1 ⋅ 10−4M at pH 1.0 (a), 1.6 (b), 1.94 (c), 2.4 (d), 2.8 (e), and 3.4 (f).

The absorbance of the TPPS band at 490 nm, in the presence of the polymers, was tested at different values of pH (Figure 3.12, left side) in order to estimate the transition pH. The band at 490 was used for these experiments, since it reveals the formation of J-aggregates of the di-anionic H4TPPS2−. In other words, it shows the

protonation of the TPPS pyrrole groups. By fitting the data with a Boltzmann sig-moidal curve and further derivation allows to find the shift of the transition pH of TPPS (Figure 3.12 right side). For TPPS in the presence of PK50-HEDA80 the tran-sition pH was found to be 2.75; 1.6 units lower than the pristine dye (Figure 3.12a, right side). This polymer is the most hydrophilic polymer of the studied series. Therefore, it is hypothesized that being the hydrophobic interaction the strongest driving force for the stabilization of the tetra-anionic form of the dye, the transi-tion pH should be at lower values for the rest of the polymers. Note that the molar mass of the polymers is given in g/mole of protonable polymeric units. Therefore, the same amount of polymeric charges are present in the experiments, thus an in-creasing amount of the residual 1,4-dicarbonyl units is present in the system as x decreases. Indeed, following the same procedures the transition pH were found at lower pH, with values of 1.86 and 1.73 for PK50-HEDA60 and 40 (Figure 3.12b, c right side), respectively.

Figure 3.11: Fluorescence spectra of 1⋅10−6TTPS in the presence of PK50-HEDA80 1 ⋅ 10−4at different pHs. pH 1.0 (a), pH 1.6 (b), pH 1.94 (c), pH 2.4 (d), pH 2.8 (e), pH 3.4 (f).

3.4. CONCLUSIONS 41

Figure 3.12: Transition pH shift of TPPS at1 ⋅ 10−6 _{in presence of the polymer at}

1 ⋅ 10−4_{. (a) PK50-HEDA80. (b) PK50-HEDA60. (c) PK50-HEDA40}

3.4

Conclusions

The functionalization of polyketone with N-(2-Hydroxyethyl)ethylenediamine was successfully achieved by Paal-Knorr reaction. Their structures were studied by ele-mental analysis, ATR-IR and 1H-NMR spectroscopies. The interaction of the

poly-mers with TPPS was studied with respect to shifts of the absorption bands and shift of the transition pH between the di-anionic and tetra-anionic form of the dye. The three polymers were able to stabilize the tetra-anionic form of TPPS at low values of pH and the more hydrophobic polymer changed the dye transition pH more than two units lower than the pristine dye. Indeed, PK50-HEDA40 with the lowest car-bonyl conversion degree, therefore with a higher hydrophobic character, stabilized the tetra-anionic form of the dye at lower values of pH with a shift of the transition pH to 1.73, 2.6 units lower than the pristine dye. The electrostatic and hydropho-bic interactions of the dye with the polymer chains explain the stabilization of the tetra-anionic form of TPPS. Herein, it has been demonstrated systematically the im-portance of the hydrophobic interaction in the dispersion of TPPS in water at acid conditions. In addition, this polymer/dye system is a promising material that can be incorporated into aerogels and, therefore, used in the photo-oxidation of pollutants.

Supporting information

Figure 3.13: Normalized visible spectra of 1 ⋅ 10−6 _{M TTPS in presence of}

PK50-HEDA60 (A). pH 1.1 (a), pH 1.6 (b), pH 1.82 (c), pH 2.0 (d), pH 2.5 (e), pH 2.8 (f), pH 3.4 (g). Normalized visible spectra of 1 ⋅ 10−6_{M TTPS in presence of}

PK50-HEDA40 (B). pH 1.2 (a), pH 1.5 (b), pH 1.83 (c) pH 2.0 (d), pH 2.6 (e), pH 2.8 (f), pH 3.1 (g).

3.4. CONCLUSIONS 43

Figure 3.14: Fluorescence spectra of 1⋅10−6M TTPS in presence of PK50-HEDA60. pH 1.1 (a), pH 1.6 (b), pH 2.0 (c), pH 2.5 (d), pH 2.8 (e), pH 3.4 (f).

Figure 3.15: Fluorescence spectra of 1⋅10−6_{M TPPS in presence of PK50-HEDA40.}