doktorska disertacija
Patricija Hriberšek (Avtor), Ksenija Kogej (Mentor), Marija Bešter-Rogač (Član komisije za zagovor), Jurij Reščič (Član komisije za zagovor), Ema Žagar (Član komisije za zagovor)

Povzetek

V tem delu smo z različnimi tehnikami proučevali vpliv valence dodanega protiiona ter ionske jakosti raztopine (I) na asociacijske pojave v vodnih raztopinah poli(α-alkilkarboksilnih kislin) pri sobni temperaturi in med segrevanjem ter ohlajanjem. Z dinamičnim (DLS) in statičnim sipanjem svetlobe (SLS) smo v vodnih raztopinah dveh stereoizomerov poli(metakrilne kisline) (PMA); ataktične (aPMA) in izotaktične (iPMA) v prisotnosti anorganskih kovinskih večvalentnih (NaCl, MgCl2, CaCl2 in LaCl3) ter organskih hidrofobnih enovalentnih (tetrametilamonijevega (TMACl), tetraetilamonijevega (TEACl) in tetrapropilamonijevega (TPACl)) kloridov raziskovali tvorbo nanodelcev. Asociati iPMA so stabilni pri višji stopnji nevtralizacije (αN) karboksilnih kislin (αN≈ 0,20) kot asociati aPMA (αN = 0), kar kaže na močnejšo medmolekulsko asociacijo med verigami iPMA. Nastali asociati PMA v prisotnosti anorganskih kovinskih protiionov imajo značilnosti mikrogelskih delcev z gostejšim jedrom in nabreklo korono. Glede na izračunani parameter oblike (ρ) (ρ≈ 0,90), se oba izomera v prisotnosti Mg2+obnašata drugače kot v prisotnosti Na+, Ca2+ in La3+, za katere so značilne nižje vrednosti (ρ≈ 0,70⎯0,80). Asociati, ki nastanejo v prisotnosti Mg2+, imajo enakomernejšo porazdelitev mase (brez jasno izoblikovane strukture jedro-korona) v primerjavi z asociati v prisotnosti Na+, Ca2+ in La3+. To smo pripisali močni hidrataciji Mg2+ ionov, zaradi česar Mg2+ ioni favorizirajo monodentatno vezavo s karboksilnimi (COOH)/karboksilatnimi (COO⎯) skupinami. Ca2+ in La3+ ioni pa se vežejo nanje na bidentatni način, ki je močnejši od monodentatnega. Na razlike v strukturi asociatov v prisotnosti različno valentnih kationov kažejo tudi izrazito različne odvisnosti ionizacijskih enatlpij (ΔHion) od αN in rezultati fluorimetričnih ter pH meritev. Strukturo, podobno mikrogelskim delcem, tvorita tudi oba izomera v prisotnosti TMA+, ki s COOH/COO⎯ skupinami interagira direktno preko elektrostatskih interakcij, medtem ko pri vezavi večjih in bolj hidrofobnih TEA+ in TPA+ na verige aPMA prevladujejo interakcije hidrofobnega značaja, zato so ti delci bolj nabrekli in zrahljani (ρ≈ 0,90). Asociati iPMA pa imajo bolj iztegnjeno strukturo, ker TEA+ in TPA+, ki sta sterično bolj zahtevna, ločita izotaktične verige v raztopini, zato se lahko slednje med sabo povezujejo s H-vezmi preko COOH in COO⎯ skupin. Z več eksperimentalnimi tehnikami (vizualni eksperiment, UV-Vis spektroskopija, DLS in SLS, kalorimetrija, fluorimetrija, NMR) smo v nadaljevanju jasno dokazali nasproten vpliv temperature na medmolekulsko asociacijo v razredčenih vodnih raztopinah a- in iPMA v prisotnosti vseh proučevanih anorganskih kovinskih večvalentnih in organskih hidrofobnih enovalentnih protiionov. Med segrevanjem pride v primeru raztopin aPMA do asociacije verig aPMA in posledično do obarjanja ter ločitve faz (LCST obnašanje; angl. lower critical solution temperature). Nastala oborina aPMA se v prisotnosti Na+, Mg2+ in Ca2+ med ohlajanjem raztopi, v prisotnosti La3+ pa je agregacija ireverzibilna. Nasprotno od aPMA pa se med segrevanjem asociati iPMA popolnoma ali delno razgradijo (UCST obnašanje; angl. upper critical solution temperature) brez makroskopske ločitve faz. De-asociacija je popolnoma reverzibilna. Višanje valence kationa znižuje LCST za raztopine aPMA in zvišuje UCST za raztopine iPMA. Ugotovili smo tudi, da višanje I raztopin NaCl, MgCl2 in CaCl2 vodi do znižanja temperature, pri kateri pride do ločitve faz, medtem ko v primeru LaCl3 višanje I nima bistvenega vpliva na LCST. Tudi raztopine aPMA v prisotnosti hidrofobnih kationov se obnašajo kot LCST polimerne mešanice. V primeru prisotnosti TMA+ se med segrevanjem nastala oborina med ohlajanjem raztopi, medtem ko oborine v raztopinah TEACl in TPACl ostanejo prisotne. S povečevanjem dolžine na dušik vezanih alkilnih verig in s tem naršačajočo hidrofobnostjo kationa, vrednosti LCST za raztopine aPMA padajo. Asociati iPMA tudi v raztopinah soli organskih kationov med višanjem temperature razpadejo, vendar se med ohlajanjem ne tvorijo več nazaj, kot je to značilno za asociate izotaktične oblike v prisotnosti anorganskih protiionov. Hidrofobnejša analoga poli(α-alkilkarboksilnih kislin), poli(etakrilna kislina) (PEA) in poli(propilakrilna kislina) (PPA), tvorita v prisotnosti anorganskih kovinskih večvalentnih kationov Na+, Mg2+, Ca2+ in La3+ asociate z bolj nabreklo strukturo in enakomerno porazdeljeno maso po celotnem delcu kot jih tvorita a- in iPMA zaradi daljših in sterično zahtevnejših hidrofobnih etilnih in propilnih stranskih skupin, ki se nahajajo v notranjosti delcev. Tem ugotovitvam v prid govorijo DLS in SLS rezultati (ρ≈ 1,0) in fluorimetrične meritve. Tako kot aPMA tudi PEA in PPA sodita med LCST polimerne mešanice. Asociacija PEA in PPA v prisotnosti anorganskih kationov Na+, Mg2+, Ca2+ in La3+ je ireverzibilna. Do ločitve faz pride tako na makroskopskem nivoju (v prisotnosti dvovalentnih Mg2+ in Ca2+) v obliki oborine podobne gelu, kot tudi na mezoskopskem nivoju (v prisotnosti Na+ in La3+), ko raztopine postanejo zgolj motne ali pa izpade fina oborina. To je posledica tvorbe močnih vodikovih vezi COOH···COO⎯ med polimernimi verigami, ki postajajo med segrevanjem čedalje bolj favorizirane zaradi slabšanja kakovosti topila in se med ohlajanjem še ojačijo. Daljšanje hidrofobne stranske skupine preiskovanih aPMA, PEA in PPA močno vpliva na njihovo obnašanje v vodnih raztopinah. Daljša in bolj hidrofobna kot je stranska skupina (metilna < etilna < propilna), šibkejša je polikislina in tvori močnejše vodikove vezi COOH···COO⎯ zaradi izrazitejšega pozitivnega induktivnega efekta. H-vezi v kombinaciji COOH···COO⎯, ki se tvorijo v raztopinah PEA in PPA, so močnejše kot H-vezi v kombinaciji COOH···COOH v raztopinah aPMA, in zagotavljajo stabilnost asociatov, ki se tvorijo med segrevanjem.

Ključne besede

polimeri;polielektroliti;polimerne kisline;protiioni;interakcije;sipanje svetlobe;spektroskopija;izotermna titracijska kalorimetrija;doktorske disertacije;

Podatki

Jezik: Slovenski jezik
Leto izida:
Tipologija: 2.08 - Doktorska disertacija
Organizacija: UL FKKT - Fakulteta za kemijo in kemijsko tehnologijo
Založnik: [P. Hriberšek]
UDK: 544.6.018.47-036.5(043.3)
COBISS: 41312771 Povezava se bo odprla v novem oknu
Št. ogledov: 348
Št. prenosov: 86
Ocena: 0 (0 glasov)
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Ostali podatki

Sekundarni jezik: Angleški jezik
Sekundarni naslov: Association processes in aqueous solutions of poly([alpha]-alkylcarboxylic acids)
Sekundarni povzetek: In the present work, the effect of counterion valency and the ionic strength of the solution (I) on the association phenomena in aqueous solutions of poly (α-alkylcarboxylic acids) at room temperature and during heating and cooling was studied by various techniques. By dynamic (DLS) and static light scattering (SLS) the formation of nanoparticles of two poly(methacrylic acid) (PMA) isomers, atactic (aPMA) and isotactic (iPMA), was investigated in aqueous solutions of inorganic metal multivalent (NaCl, MgCl2, CaCl2, and LaCl3) and organic hydrophobic monovalent (tetramethylammonium (TMACl), tetraethylammonium (TEACl) and tetrapropylammonium (TPACl)) chlorides. iPMA associates are stable at a much higher degree of neutralization (αN) of carboxylic groups (αN≈ 0,20) than aPMA associates (αN = 0), indicating a stronger intermolecular association between iPMA chains. The PMA associates in the presence of inorganic metal counterions have the characteristics of microgel particles with a denser core and a swollen corona. According to the values of shape parameter (ρ) (ρ≈ 0,90), both isomers behave differently in the presence of Mg2+ than in the presence of Na+, Ca2+ and La3+. Associates formed in the presence of Mg2+ thus have a more even mass distribution (without a clear formation of a core-shell structure) in comparison with those in the presence of Na+, Ca2+ and La3+, which are characterized by lower values of ρ(≈ 0,70⎯0,80). This was attributed to the strong hydration of Mg2+ ions, resulting in Mg2+ ions favoring monodentate binding to carboxylic (COOH)/carboxylate (COO⎯) groups. Ca2+ and La3+ ions, on the other hand, bind more strongly and in a bidentate manner. Differences in the structure of associates in the presence of multivalent cations are also reflected in different dependences of ionistaion enthalpies (ΔHion) on αN, and also in different results of fluorimetric and pH measurements. Microgel-like particles are also formed by both PMA isomers in the presence of TMA+. These organic cations interact with COOH/COO⎯ groups directly through electrostatic interactions, while the binding of larger and more hydrophobic TEA+ and TPA+ to PMA chains is dominated by hydrophobic type of interactions. As a result, these particles are more swollen and loosened (ρ≈ 0,90). Meanwhile, the structure of iPMA associates is more elongated in the presence of larger counterions TEA+ and TPA+ due to their ability to hinder iPMA main chains from getting into contact with one another, thus preventing the more extensive aggregation of polyions. By several experimental techniques (visual experiment, UV-Vis spectroscopy, DLS and SLS, calorimetry, fluorimetry, NMR), it was clearly shown that the temperature-induced intermolecular association of a- an iPMA in aqueous solutions in the presence of inorganic metallic multivalent and organic hydrophobic monovalent counterions displays an opposite thermoresponsiveness. In the case of aPMA, association and phase separation take place during heating (so-called lower critical solution temperature behaviour; LCST). The resulting aPMA precipitate dissolves in the presence of Na+, Mg2+ and Ca2+ during cooling, while the aggregation is irreversible in the presence of La3+. In contrast to aPMA, iPMA associates disintegrate completely or partially upon heating the solutions without macroscopic phase separation (so-called upper critical solution temperature behaviour; UCST). De-association is completely reversible. Increase in the I of NaCl, MgCl2, and CaCl2 solutions leads to a decrease in the LCST values, whereas in the case of LaCl3, an increase in I has no significant effect on LCST. aPMA solutions in the presence of hydrophobic cations also display a LCST behaviour. When TMA+ cations are present in the solution, the aPMA precipitate formed during heating dissolves upon cooling, while this is not the case in TEACl and TPACl solutions. With increasing length of the nitrogen-bound alkyl chains, and thus the hydrophobicity of the cation, the LCST values for aPMA solutions decrease. Meanwhile, organic cations induce ireversible disintegration of iPMA associates in aqueous solutions during heating. A more hydrophobic analogues of poly (α-alkylcarboxylic acids), poly (ethacrylic acid) (PEA) and poly (propylacrylic acid) (PPA), in the presence of inorganic metal multivalent cations Na+, Mg2+, Ca2+, and La3+ form associates with a more swollen structure and evenly distributed mass throughout the particle in comparison with the ones formed by a- and iPMA due to longer and sterically more demanding hydrophobic ethyl and propyl side groups located inside the particles. These findings were also supported by DLS and SLS results (ρ≈ 1,0) and fluorimetric measurements. Like aPMA, also PEA and PPA display LCST behaviour. The association of PEA and PPA in the presence of Na+, Mg2+, Ca2+ and La3+ is irreversible. Phase separation occurs on both, the macroscopic level (in the presence of divalent Mg2+ and Ca2+) in the form of a gel-like precipitate, as well as on the mesoscopic level (in the presence of Na+ and La3+), when solutions become merely opaque or fine precipitate is formed. This is due to the formation of strong hydrogen bonds COOH···COO⎯ on different polymer chains. Because the solvent quality is worsened during heating, these COOH···COO⎯ bonds become more and more favored and get in addition even stronger during cooling. As a result, stable associates of PEA and PPA are formed. The lengthening of hydrophobic alkyl side groups of the investigated aPMA, PEA, and PPA strongly influences their behaviour in aqueous solutions. Weaker polyacid has longer and more hydrophobic side group (methyl < ethyl < propyl) and forms stronger hydrogen bonds COOH···COO⎯ due to a more pronounced positive inductive effect. The hydrogen bonds in the pair COOH···COO⎯ that form between PEA and PPA chains are thus stronger than the hydrogen bonds in the pair COOH···COOH that form between aPMA chains and ensure the stability of the associates formed during heating.
Sekundarne ključne besede: -;
Vrsta dela (COBISS): Doktorsko delo/naloga
Študijski program: 1000381
Konec prepovedi (OpenAIRE): 1970-01-01
Komentar na gradivo: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo
Strani: XVI f., 224 str.
ID: 12109512