Nanoporous polymers from interpenetrating polymeric networks

Prepletene polimerne mreže (ang. »interpenetrating polymer networks«, IPN) predstavljajo posebno vrsto vsestransko uporabnih večkomponentnih polimernih sistemov. Gre za preplet dveh polimernih mrež, ki med seboj nista kovalentno povezani. Tak material vsebuje mikro domene obeh polimernih komponent in tako deloma ohrani lastnosti obeh polimerov. Sinteza IPN običajno poteka v dveh zaporednih reakcijah, z ustreznim izborom monomerov pa je možna tudi sinteza v enem koraku. Pri tem je potrebno zagotoviti, da polimerizaciji posameznih monomerov potekata po ortogonalnih mehanizmih in se med seboj ne motita. Preverili smo, ali to velja za prosto radikalsko polimerizacijo stirena in polimerizacijo z odpiranjem obroča ε-kaprolaktona. Preučili smo kinetiko izbranih polimerizacij in določili pogoje, pri katerih oba izbrana monomera polimerizirata z enako hitrostjo, saj pričakujemo, da se s sočasno polimerizacijo verige temeljiteje prepletajo in s tem velikosti domen posameznih komponent manjšata. Nadalje smo IPN uporabili kot prekurzorje za pripravo poroznih polistirenskih ogrodij. Domene poli(ε-kaprolaktona) (PCL) smo selektivno odstranili s hidrolitsko razgradnjo, kar je vodilo do nastanka por v polistirenskem ogrodju. Preučili smo, kako na poroznost polistirenskega skeleta vplivajo način priprave, zamreženost, sočasnost obeh vrst polimerizacij in molska masa PCL. Porozno morfologijo skeleta smo preučevali z elektronsko vrstično mikroskopijo (SEM), iz adsorpcijskih izoterm pa smo določili specifične površine skeletov po Brunauer-Emmett-Teller metodi (BET). S sočasno sintezo IPN smo po nadaljnji obdelavi dobili mezo- in mikroporozne polimere s specifičnimi površinami do 89 m2/g, medtem ko smo po zaporedni pripravi dobili makroporozne polimere z zanemarljivo majhnimi specifičnimi površinami.Interpenetrating polymer networks (IPN) represent unique and versatile materials in the field of multicomponent polymer systems, composed of non-covalently linked chains. Such materials exhibit micro-sized domains of polymeric components and thus partly preserve characteristics of both polymers. A common procedure for the synthesis of IPN usually takes place in two sequential steps. Appropriate selection of monomers allows a one-step synthesis where the orthogonality of polymerization mechanisms is of cruical importance. Orthogonality of free radical polymerization of styrene and ring-opening polymerization of ε-caprolactone was investigated and confirmed. Under assumption that simultaneous conversions of monomers lead to smaller domains in IPN, the kinetics of such polymerizing system was also investigated. Further on, IPNs were used as the precursors for the preparation of porous polystyrene framework. For this purpose the domains of poly(ε-caprolactone) (PCL) were selectively hydrolized to produce the pores in the polystyrene framework. The effects of synthetic procedure used, cross-linking, simultaneity of orthogonal reactions and molar mass of PCL on the porosity of polystyrene framework were investigated. The porous morphology of polystyrene framework was studied using scanning electrone microscopy (SEM), whereas from the adsorption isotherms the specific surface areas were calculated using the Brunauer-Emmett-Teller method (BET). We have demonstrated that the simultaneously prepared IPNs offer an advantage over the sequentially prepared IPNs since the pore size decreased down to micropores and, subsequentely, the surface area increased from negligable values up to 89 m2/g

Chemiluminescence as source of photopolymerization

V tem diplomskem delu je raziskana možnost uporabe kemiluminiscence kot vira fotopolimerizacije. Pri fotopolimerizaciji sproži svetloba kemijsko, običajno radikalsko reakcijo, kar vodi v nastanek polimera. Za številna področja so zelo uporabni hiperzamreženi polimeri, pomembna metoda pri njihovi sintezi pa so emulzijske polimerizacije. Za pripravo takih materialov pri sobni temperaturi lahko uporabimo svetlobo kot iniciator, vendar le-ta težko prodre v emulzijo, zaradi česar je manj učinkovita. Zanimalo nas je, ali lahko za to uporabimo kemiluminiscenco, ki označuje proces, pri katerem pride zaradi kemijske transformacije do emisije svetlobe – na ta način bi in situ generirali svetlobo znotraj emulzije. Najbolj učinkovite so reakcije peroksalatnega tipa, kjer pri reakciji vodikovega peroksida in oksalata nastane visokoenergijski intermediat, energija pa se prenese na molekulo občutljivca, ki oddaja vidno svetlobo. V ta namen smo pripravili bis(2,4,6-triklorofenil) oksalat in poiskali najbolj učinkovito sintetsko pot s spreminjanjem topila, časa in temperature. Za reakcijo kemiluminiscence je potreben tudi občutljivec, od katerega je odvisna intenziteta in valovna dolžina izsevane svetlobe, zato smo preizkusili različne občutljivce in s pomočjo optičnega mikroskopa spremljali njihovo emisijo. Nadalje smo preizkusili tudi številne monomere in fotoiniciatorje ter poiskali ustrezen sistem, v katerem vidna svetloba sproži polimerizacijo. Sistem smo nadgradili s tvorbo stabilne emulzije za sintezo hiperzamreženih polimerov. Nazadnje smo stremeli k združitvi reakcije polimerizacije z reakcijo kemiluminiscence, pri čemer bi v emulziji generirana svetloba sprožila nastanek polimera.This thesis shows how chemiluminescence can be used as a source of photopolymerization. In photopolymerization it is light that activates a chemical, generally radical reaction that leads to formation of a polymer. Of great use nowadays are cross-linked polymers, and emulsions present an important method of their preparation. Polymerization of such materials at room temperature may occur by using light as an initiator, but as emulsions are rather opaque, the light cannot completely access the reaction mixture, consequently being less effective. Thus we have studied the prospect of using chemiluminescence as a light source from within the emulsion, as it is a reaction in which light is obtained as the product of chemical transformation. The most efficient are peroxyoxalate chemiluminiscence reactions, in which an electronically excited state is formed when hydrogen peroxide reacts with an oxalate. The energy may be transmitted to a fluorophore, causing it to emit light. For purpose of our study we have focused on the preparation of bis(2,4,6-trichlorophenyl) oxalate by changing time and solvents in already known synthesis, to find a reaction with the greatest yield. As the chemiluminescence depends significantly on the choice of the fluorophore, we have conducted various experiments to find a fluorophore with a suitable light intensity and wavelength for further analysis of photopolymerization. Moreover, many monomers and photoinitiators had to be tested to find an appropriate system that reacted only when activated by visible light. When such systems were found, we continued to make stable emulsions with them, suitable for synthesis of cross-linked polymers. Lastly the reactions of chemiluminescence and photopolymerization had to be merged into one system, one triggering another to provide an efficient way of photopolymerization in an emulsion

Porous polymers prepared by ring-opening polymerization in emulsions

V okviru doktorske disertacije smo s polimerizacijo z odpiranjem obroča (ROP) v zvezni fazi emulzij z visokim deležem interne faze (HIPE) polimerizirali heterociklične monomere. Prednost ROP neposredno v HIPE-u je v tem, da lahko pripravimo popolnoma razgradljiva poliHIPE-ogrodja specifične morfologije na osnovi poliestrov in sintetičnih polipeptidov. Za uspešno izvedbo ROP v HIPE-u smo pripravili brezvodne emulzije in uporabili organske katalizatorje, ki omogočajo izvedbo ROP pri relativno nizkih temperaturah in primerni hitrosti polimerizacije. Hitrost ROP v HIPE-u se je izkazala kot izredno pomemben parameter, saj mora zvezna faza emulzije želirati v času stabilne emulzije, obenem pa mora biti viskoznost emulzije primerna za zadovoljivo mešanje in prenos v primerne modele. V prvem delu doktorskega dela predstavljamo poliHIPE na osnovi semikristaliničnega poliestra, poli(ε-kaprolaktona) (PCL). S stopnjo zamreženosti smo vplivali na termomehanske lastnosti PCL poliHIPE-materiala, ki izkazuje oblikovni spomin. Oblikovni spomin smo raziskali s termomehanskimi cikličnimi testi in pokazali, da ga odlikujeta odlična fiksacija začasne oblike pri nizki temperaturi in odlična povrnitev v prvotno obliko med segrevanjem nad temperaturo tališča. Manj zamrežen poliHIPE ima višji temperaturi taljenja in kristalizacije in ga lahko fiksiramo že pri sobni temperaturi. Metodo ROP v HIPE-u smo razširili na različne vrste N-karboksianhidridov (NCA) α-aminokislin ter kot prvi pripravili poliHIPE-materiale iz sintetičnih polipeptidov. Hitrost polimerizacije se je izkazala kot izredno pomemben parameter za uspešno pripravo poliHIPE sintetičnih polipeptidov, saj mora omogočati nadzorovano izhajanje plinastega ogljikovega dioksida, ki se sprošča med ROP NCA. Sintezni postopek, ki smo ga razvili, omogoča sintezo poliHIPE-ogrodij na osnovi polipeptidov različne kemijske sestave, pri čemer je zaradi razlik v reaktivnosti NCA-monomerov za vsak sistem reaktantov potrebno prilagoditi eksperimentalne pogoje sinteze, kot so koncentracija monomerov, količina katalizatorja, količina surfaktanta, vrsta zamreževalca in topila. Vzpostavili smo relacije med sintezo, strukturo in lastnostmi sintetiziranih poliHIPE-ov ter postavili temelje za načrtovanje in pripravo različno funkcionaliziranih polipeptidnih poliHIPE-materialov. Pokazali smo, da lahko z deležem interne faze in količino surfaktanta prilagajamo morfologijo poliHIPE, ki igra pomembno vlogo pri uporabi materiala v namen gojenja celic. Na izbranem polipeptidnem poliHIPE-u smo potrdili, da material ni toksičen za celice ter da omogoča njihovo rast in proliferacijo. V nadaljevanju smo pokazali, da je razvita metoda primerna za pripravo poliHIPE-polimerov na osnovi različnih polipeptidov, kot tudi kopolipeptidov. Pokazali smo tudi, da lahko z odščito zaščitenih stranskih skupin polipeptidov pripravimo poliHIPE-hidrogele, ki omogočajo nadaljnje popolimerizacijske modifikacije. Opisan pristop k pripravi polipeptidnih poliHIPE-ov obeta načrtovanje in pripravo makroporoznih ogrodij na osnovi sintetičnih polipeptidov različne kemijske sestave, katerih funkcionalnost lahko enostavno prilagajamo z izborom NCA-monomerov.In this doctoral thesis, ring-opening polymerization (ROP) of heterocyclic monomers in a continuous phase of high internal phase emulsions (HIPEs) was performed. ROP directly in HIPE enables the preparation of fully degradable polyester and synthetic polypeptide polyHIPEs with specific porous morphology. For the successful implementation of ROP in HIPE, anhydrous HIPEs were prepared and organic catalysts were used to enable ROP at relatively low temperatures and suitable polymerization rate. It has been shown that the rate of ROP in HIPEs is an extremely important parameter, as the continuous phase of the emulsion must gel within the time-frame of emulsion stability, while at the same time the HIPE viscosity must be suitable for adequate stirring and transfer of emulsions into the molds. In the first part of the work, polyHIPEs based on a semi-crystalline polyester, poly(ε-caprolactone) (PCL), are presented. The thermomechanical properties of the prepared PCL polyHIPEs were investigated and found to be strongly dependent on the degree of PCL crosslinking. PCL polyHIPEs exhibit shape memory behavior with excellent fixation of the temporary shape at low temperatures and excellent recovery of the original shape when heated above the melting temperature, as demonstrated by cyclic thermomechanical tests. Less crosslinked polyHIPE shows higher melting and crystallization temperatures and as a result, its temporary shape can be fixed even at room temperature. The synthetic method was further extended to the polymerization of various types of α-amino acid N-carboxyanhydrides (NCAs) to prepare synthetic polypeptide polyHIPEs not previously reported. The polymerization rate has been shown to be an extremely important parameter for the successful preparation of polypeptide polyHIPEs, as it determines the rate of carbon dioxide release from HIPE during the ROP of NCA monomers. The synthetic process we developed allows the synthesis of polypeptide polyHIPE scaffolds with different chemical compositions. However, due to the different reactivity of NCA monomers, it is necessary to adjust the experimental conditions such as monomer concentration, catalyst amount, surfactant amount, type of crosslinker and type of solvent. Moreover, we have established relationships between the synthesis, structure and properties of the synthesized polyHIPE scaffolds and laid the foundation for the design and preparation of differently functionalized polypeptide polyHIPE scaffolds. We have shown that the morphology of the polyHIPEs, which plays an important role in the use of the material for cell culture, can be adjusted by the proportion of the internal phase in HIPE and the amount of surfactant. In the case of selected polypeptide polyHIPE, we have confirmed that the material is nontoxic to cells and that it allows good viability, migration and proliferation of cells throughout the polypeptide polyHIPE scaffold. Furthermore, the disclosed synthetic procedure is applicable for the preparation of polyHIPEs based on various polypeptides as well as copolypeptides. In addition, we have shown that we can prepare polyHIPE hydrogels by deprotecting the protected side groups of polypeptides. The unprotected functional groups allow further postpolymerization modifications of the polyHIPEs. The described approach to the preparation of polypeptide polyHIPEs promises the design and preparation of macroporous polypeptide scaffolds with different chemical compositions, whose functionality can be tuned simply by selecting the types of NCA monomers

Insight into chemical recycling of flexible polyurethane foams by acidolysis

[Image: see text] Acidolysis is emerging as a promising method for recycling polyurethane foam (PUF) waste. Here, we present highly efficient acidolysis of PUFs with adipic acid (AA) by heating the reaction mixtures with microwaves. The influence of experimental conditions, such as reaction temperature, time, and amount of the degradation reagent, on the polyol functionality, molecular weight characteristics, the presence of side products, and the degree of degradation of the remaining PUF hard segments was studied by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), nuclear magnetic resonance (NMR), size-exclusion chromatography (SEC) coupled to a multidetection system, and Fourier transform infrared (FT-IR) spectroscopy. The purified recycled polyols were used for the synthesis of flexible PUFs. The morphology and mechanical properties of the PUFs show that the degree of functionalization of the polyol by the carboxylic end groups, which is higher for larger amounts of AA used to degrade the PUFs, significantly affects the quality and performance of the flexible PUFs from the recycled polyols

Chemical recycling of flexible polyurethane foams by aminolysis to recover high-quality polyols

Polyurethane foams (PUFs) are widely used commodity materials, but most of them end up in landfills at the end of their life, which is not in line with the circular economy approach. Here, we introduce microwave-assisted aminolysis with amine reagents that contain primary and tertiary amino groups in the structure. These reagents enable complete degradation of the urethane groups in the structure of the flexible PUFs with a much lower amount of degradation reagent than is typically required for solvolysis reactions. The purified, recovered polyols are close equivalents to the corresponding virgin polyols in terms of their structural and molar mass characteristics. Therefore, they can be used for the production of high-quality PUFs without having to adapt the synthesis process. The flexible PUFs made from recovered polyols have comparable mechanical properties to those made from virgin polyols