Browsing by discipline "Polymer Chemistry"

The aim of the thesis is to identify and test anionic biopolymer derivatives in flocculation application. Several potential polysaccharides are listed in literature, but chemical modification is often needed to improve their performance in the selected application. Totally 28 polysaccharide derivatives were received from varying suppliers and screened by rheology and charge. The most potential biobased products in addition to synthetic polyacrylamide references were purified by dialysis and characterized by charge density, apparent viscosity in water and brine and intrinsic viscosity in brine. Xanthan gum, carboxymethyl cellulose and guar gum appeared to have the best combination of high viscosity and charge density. Xanthan gum revealed exceptional behavior in brine as its viscosity increases upon salt addition due to helix formation. This phenomenon opens numerous possibilities in brine applications. In the application testing 9 biopolymer derivatives representing 6 different types of polysaccharides in addition to two reference polyacrylamides were studied by flocculating bentonite. The evolution of flocs was monitored online with focused beam reflectance measurement. Xanthan gum, carboxymethyl cellulose and guar gum have the best performance in flocculation as expected based on the characterization results supporting the statement that size and charge are key parameters in flocculation performance. The biobased products fall behind in flocculation efficiency compared to polyacrylamides, but their performance can be improved by chemical modification. A quick thermal stability screening was also performed, and xanthan gum appeared to be even more thermally stable compared to the polyacrylamide reference in the selected environment. As a conclusion it is justified to claim that in the future the biobased products have a great potential to offer alternative solutions in the applications where synthetic fossil-based polymers are currently used. The recommended path forward is to find suitable modification mechanisms to increase the flocculation performance of xanthan gum, carboxymethyl cellulose and guar gum. Nucleophilic reaction of the saccharide oxygen is a typical example of chain modification for polysaccharide chemistry. Based on the results presented in this thesis, the future of biobased products from renewable resources looks promising.

Hydrogels are promising biomaterials for tissue engineering. Concerning hydrogels chemical structures, the hydrogen bonding towards water makes them hydrophilic compounds. Hydrogels contain 95% ~ 99% water as the swelling agent and have the characteristics of extracellular matrix. Therefore, they are suitable for cell growth and appropriate for forming cell culture. Hydrogels can mimic the cell microenvironments and promote cell differentiation by interactions with cells. Cells can get oxygen, nutrients exchange as well as removal of metabolic waste to live. Hydrogels can be categorized into natural hydrogels, synthetic hydrogels and hybrid hydrogels by sources. Agarose, Collagen and Calcium alginate are the most popular natural hydrogels. Polyethylene (glycol) and its derivative Polyethylene (glycol) Diacrylate (PEGDA) are indispensable synthetic hydrogels. In this thesis, hydrogels are studied for their chemical structure, physical and mechanical properties and gel formation. Typical hydrogels, i.e. agarose, polyethylene (glycol) diacrylate (PEGDA), collagen and calcium alginate, are reviewed for their methodology of formation, mechanical properties and applications. Since hydrogel is a solid containing a given amount of water, it has viscoelasticity. Rheology test mechanism is described for viscoelastic materials. Micropatterning methods of hydrogels are investigated in variety of approaches. How the patterned surfaces affect cell behaviour is discussed in our literature review. From the experimental results, agarose and polyethylene (glycol) diacrylate are successfully fabricated and their micropatterned hydrogels show promising properties. In addition, impact of mechanical properties, such as water diffusion in hydrogels, how temperatures influence hydrogel structures and durability of the structures storage are investigated. Hydrogel viscoelasticities are measured by rheometer. Hydrogels are also tested in chips and cell wells for future cell growth study. Finally, this research has successfully fabricated the 3D micropatterned hydrogels for cell culture.

Työssä valmistettiin poly(N-isopropyyliakryyliamidia) vesipohjaisissa liuoksissa atominsiirtoradikaalipolymeroinnilla. Valmistettuja polymeerejä liitettiin kemiallisilla sidoksilla poly(bentsimidatsobentsofenantroliiniin), minkä huomattiin parantavan jälkimmäisen kolloidista stabiiliutta vesidispersiossa. Poly(N-isopropyyliakryyliamidi) on huoneen lämpötilassa vesiliukoinen, mutta kun liuosta lämmitetään yli polymeerin alemman kriittisen liuoslämpötilan, joka on noin 32 °C, saostuu se ulos liuoksesta. Työssä pyrittiin valmistamaan hallitusti moolimassaltaan pieni ja iso homopolymeeri, missä myös onnistuttiin. Samalla saatiin tietoa erilaisten initiaattorien soveltuvuudesta ja niiden rakenteen vaikutuksesta poly(N-isopropyyliakryyliamidin) vesipohjaisiin liuospolymerointeihin. Initiaattorin valinnassa painotettiin nopeaa radikaalinmuodostusta ja soveltuvuutta liitosryhmäksi kahden polymeerin välille. Poly(bentsimidatsobentsofenantroliini) on täysin konjugoitu rengasrakenteinen polymeeri. Rakenteensa takia se soveltuu hyvin esimerkiksi n-tyypin puolijohteeksi, mutta on rakenteeltaan erittäin jäykkä. Tästä johtuen se on niukkaliukoinen yleisimpiin neutraaleihin liuottimiin. Poly(bentsimidatsobentsofenantroliini) syntetisoitiin polyfosforihapossa ja muodostuneeseen polymeeriin liitettiin karboksyylihappo- ja amiinipääteryhmien muodostamalla amidisidoksella poly(N-isopropyyliakryyliamidi) in situ. Valmistettuja homopolymeerejä ja lohkokopolymeerejä karakterisoitiin erilaisin menetelmin. Poly(N-isopropyyliakryyliamidin) moolimassoja ja moolimassajakaumia tutkittiin kokoekskluusiokromatografialla, sekä MALDI-TOF -spektroskopialla. NMR-mittauksia käytettiin polymeerien rakenteiden selvittämiseen ja polymerointikinetiikan tutkimiseen. Rakenteita tutkittiin myös UV-Vis - ja infrapunaspektroskopialla, sekä alkuaine- ja termogravimetrisellä analyysillä. Dispersioiden stabiilisuutta tutkittiin visuaalisesti. Mahdollisissa jatkotutkimuksissa voitaisiin keskittyä N-isopropyyliakryyliamidin propagaationopeuden hallintaan ja lohkokopolymeerin muodostamien partikkeleiden pintavarausten tutkimiseen esimerkiksi zeta-potentiaalimittauksilla. Synteesiä voitaisiin yrittää muokata poly(N-isopropyyliakryyliamidin) tehokkaamman kiinnittämisen saavuttamiseksi.

Solutions of thermoresponsive polymers exhibit a drastic and discontinuous change in their properties with temperature. A thermoresponsive polymer that is soluble at low temperatures but undergoes reversible phase transition in a solvent with rising temperature resulting in precipitation or cloud formation is said to exhibit Lower Critical Solution Temperature (LCST)-type behaviour. On the other hand, polymers that exhibit Upper Critical Solution Temperature (UCST)-type behaviour are soluble in water at temperatures above UCST and become reversible insoluble when temperature decreases below upper critical solution temperature. This work deals with the synthesis of novel upper critical solution temperature block copolymers and the effect of pH and electrolyte on their cloud point temperatures. The polymers poly(N-acryloylglycinamide) (PNAGA), poly(ethyleneoxide)-b-poly(N-acryloylglycinamide) (PEO-b-PNAGA), poly(N-isopropyl acrylamide)-b-poly(N-acryloylglycinamide) (PNIPAAm-b-PNAGA) and poly(ethyleneoxide)-b-poly(N-acryloylglycinamide)-b-poly(N-isopropyl acrylamide) (PEO-b-PNAGA-b-PNIPAAm) were synthesized by Reversible Addition-Fragmentation chain-Transfer polymerization in dimethyl sulphoxide. PEO-b-PNAGA and PEO-b-PNAGA-b-PNIPAAm exhibited UCST-type behaviour both in pure water (studied by NMR) and 0.1M NaCl solutions (studied by turbidimetry). Poly (ethyleneoxide) (PEO) block played an important role in enhancing the UCST behaviour of PNAGA by improving the polymers solubility. Yet, higher cloud points in 0.1M NaCl were observed than for PNAGA due to the presence of hydrophobic dodecyl end group. Measuring the particle size between 10-50 °C by dynamic light scattering proved that the polymers phase separated on cooling below the UCST. PEO-b-PNAGA-b-PNIPAAm showed multiresponsive behaviour both in pure water and electrolyte solution exhibiting both LCST and UCST. Change in pH had a dramatic effect on the UCST of PNAGA owing to the carboxylic acid end group shifting the cloud points to higher temperatures with increase in pH. The cloud points were lower for the PNAGA block copolymers in pH 4 buffer solutions compared to that of PNAGA itself due to high solubility of poly (ethylene oxide) block in aqueous solutions.

Preparation of polymer nanoparticles has become of great interest to polymer scientists due to their wide range of applications. Block copolymer nano-objects have been studied for decades, however new production methods are still needed to achieve better commercial viability and thus a wider use of the materials. Polymerization-induced self-assembly (PISA) is a new approach to preparing block copolymer nanoparticles, in which the polymerization of the second block and the self-assembly of the particles are achieved in one step. The method exploits the growing insolubility of the propagating chain to induce the self-assembly already during the polymerization, yielding nano-objects of various morphologies. The approach has gained significant attention in the last few years, and its popularity is expected to grow in the future. This thesis presents the fundamentals of PISA, while offering insight into both the benefits and challenges of the method. The focus of the work is on aqueous emulsion RAFT PISA formulations. Additionally, a new method for the preparation of poly(ethylene glycol)-block-poly(N-vinylcaprolactam) nanoparticles through PISA was developed. The synthesis exploited the lower critical solution temperature behaviour of poly(N-vinylcaprolactam) by conducting the polymerization of said block above its phase transition temperature in water. The polymerizations were carried out as RAFT reactions in emulsion and the resulting particles were characterized by dynamic light scattering. The method yielded particles of 200 nm in diameter that dissolved in water upon cooling to room temperature. Moreover, the purified and dried polymers were analysed using size-exclusion chromatography, NMR spectroscopy and turbidimetry. Preliminary tests showed that the stable particles can be physically crosslinked with salicylic acid to prevent dissolution upon cooling.

Pro Gradussa käsitellään vuorottelevan lisäys-irrotusketjunsiirto- eli RAFT-menetelmän soveltamista alkydi-akrylaattikopolymeerien miniemulsiopolymeroinnissa. Tavoitteena oli valmistaa tuotteita, joilla on kapeampi kokojakauma kuin alkydi-akrylaattikopolymeereilla, jotka on valmistettu perinteisellä miniemulsiopolymeroinnilla. Tiettävästi RAFT-menetelmää ei ole käytetty aiemmin alkydi-akrylaattikopolymeerien miniemulsiopolymeroinnissa. Kokeellisessa osassa alkydista valmistettiin makroketjunsiirtäjä liittämällä alkydiin esterisidoksella ketjunsiirtäjäryhmiä. Liitettävä ketjunsiirtäjä oli joko 3- (bentsyylisulfanyylitiokarbonyylisulfanyyli)-propaanihappo (CTA2) tai 2-(dodekyylisulfanyylitiokarbonyylisulfanyyli)-2-metyylipropaanihappo (DDMAT). Makroketjunsiirtäjiä valmistettiin kolmea eri synteesireittiä, joista jokaisella onnistuttiin liittämään ketjunsiirtäjäryhmiä alkydiin. Liittyneiden ketjunsiirtäjäryhmien määrää ei kyetty määritettämään, ainoastaan vertaamaan ketjunsiirtäjiä toisiinsa. CTA2-pohjaisia alkydimakroketjunsiirtäjiä käytettiin alkydi-butyyliakrylaatti(BA)-kopolymeerien valmistamisessa miniemulsio- ja massapolymerointina. Massapolymeroinnit tehtiin auttamaan miniemulsiopolymerointituotteiden analysoinnissa. Ketjunsiirtäjäryhmien läsnäolon havaittiin vaikuttavan massapolymeroinnissa muodostuvan tuotteen lukukeskimääräiseen moolimassaan (Mn) ja polydisperisteetti-indeksiin (PDI). Kun ketjunsiirtäjäryhmien määrä kasvoi, pieneni muodostuvan tuotteen Mn sekä PDI. Valitettavasti miniemulsiopolymeroinneissa ei havaittu vastaavaa vaikutusta, mikä viittaa siihen, että CTA2-pohjainen alkydimakroketjunsiirtäjä ei kykene kontrolloimaan BA:n miniemulsiopolymerointia. CTA2:ta käytettiin myös vapaana ketjunsiirtäjänä (ilman alkydia) BA:n miniemulsio- ja massapolymeroinnissa. Massapolymeroinneissa onnistuttiin valmistamaan BA-polymeereja, joiden Mn oli 27 000 g/mol ja PDI alle 1,2. Miniemulsiopolymeroinneissa onnituttiin valmistamaan BA-polymeereja, joiden Mn oli 69 000 g/mol ja PDI noin 1,8.

Dually thermoresponsive poly(sulfobetaine methacylate)-graft-(poly(poly(ethylene glycol) methyl ether methacrylate)-co-poly(di(ethylene glycol) methyl ether methacrylate) were synthesized via single electron transfer living radical polymerization (SET-LRP). Two different such graft copolymers S70-g-P25D25 and S70-g-P70D280 with different side chain lengths were prepared and studied. These polymers showed 'schezophrenic' self-assembly behavior in response to temperature and ionic strength in aqeuous solution in water. S70-g-P25D25 formed nanostructures at temperatures both above the lower critical solution temperature (LCST) and below the upper critical solution temperature (UCST) with inversed core-shell nature in aqueous solution. Under saline condition no nano structure could be observed at temperatures below the UCST. For S70-g-P70D280, LCST type self-assembly was observed with the formation of similar nanostructures, but at temperatures below UCST, instead of intermolecular aggregation, unimolecular self-assembly was obsverved due to the much more crowded side chains.

Recent years have seen an increasing interest in green chemistry and an emphasis on renewable resources. New methods for more efficient fractioning and processing of biomass have been explored as a potential replacement for the current pulping industry. It was found that a number of imidazolium based ionic liquids are capable of dissolving cellulose, lignin and even wood as a whole. Although many ionic liquids have been studied for their dissolution properties, the exact dissolution mechanism is not yet fully understood. In the current research, solid state NMR was applied to study the dissolution process of woodpulp in an ionic liquid. A set of spectral techniques, 13C CPMAS, HETCOR, 1H HRMAS and NOESY, was applied to partly dissolved softwood dissolving pulp. The ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc) was used as a solvent. The used samples were 66 wt%, 50 wt%, 33 wt% and 25 wt% pulp in EMIMAc. The CPMAS spectra proved useful in studying the breakdown of the cellulose crystalline structure. Cellulose fibril surfaces were effected already in the 66 wt% pulp sample. The in core crystallinity remained mainly intact up to 33 wt% pulp and then almost completely disappeared for the 25 wt% sample. The HETCOR experiments yielded no information on specific interactions between cellulose and EMIMAc because of too low signal intensities. The HRMAS spectra showed large changes in chemical shifts between the samples for EMIMAc and cellulose protons. The largest changes 0.3-0.7 ppm, were observed for the acidic EMIMAc protons and water. This means a change in hydrogen bonding interactions is taking place for both EMIMAc and cellulose upon increasing the EMIMAc concentration. The NOESY spectra showed that in the 50 wt% sample cellulose mainly interacts with water. In the 25 wt% sample water is largely replaced by acetate anions at the cellulose chains.

Hyaluronic acid (HA) hydrogels are interesting biomaterials for drug delivery and tissue engineering applications. Glycidyl ether derivatives have gained much interests due to their thermo-responsive properties. Thermo-responsive random copolymers of glycidyl methyl ether (GME) and epoxyhexane (EH) were synthesized. Once their properties were studied, they were grafted onto hyaluronic acid to obtain gelation at temperatures above the phase transition temperature of poly (GME-EH). PGME is a water-soluble polymer at low temperatures, but phase separates at 57.3oC. The transition temperature of PGME is too high to be utilized in medical applications. Thus a hydrophobic monomer EH was used to decrease the transition temperature of PGME via copolymerization. Several samples of random copolymers poly (GME-EH) were successfully synthesized by anionic ring opening polymerization (AROP). The transition temperature of copolymers was characterized by NMR, turbidimetry and micro-calorimetry respectively to study the phase transition behavior. Tetraoctylammonium bromide was used as initiator resulting with a bromide as the end group. Bromide was substituted by azide group to be used in click chemistry reaction with alkyne-functional HA. The reaction of the azide group on the end of copolymer chain was detected by FT-IR spectroscopy. Grafting was achieved by click chemistry following copper-catalyzed azide-alkyne cycloaddition (CuAAC) procedure. Rheology was used to study the gelation of the final product: thermo-responsive hyaluronic acid hydrogel. However, for different reasons the final product failed to form a gel.

In this master's thesis research reversible addition-fragmentation chain-transfer polymerization (RAFT) was utilized to synthesize primary and tertiary amine-based cationic copolymers to be utilised as micelles for gene transfer. Materials that were synthesized included 2-aminoethyl methacrylamide hydrochloride (AEMA.HCl) monomer, homopolymers such as polymethyl methacrylate (PMMA) and poly (N,N-dimethylamino ethyl methacrylate) (PDAMEMA), and copolymers such as polymethyl methacrylate-block-poly (2-dimethylamino) ethyl methacrylate (PMMA-b-PDMAEMA), polymethylmethacrylate-block-poly(dimethylamino ethyl methylcrylate-statistical-2-aminoethyl methacrylamide hydrochloride) (PMMA-b-P[DMAEMA-co-AEMA.HCl]) and poly (dimethylamino ethyl methylcrylate-statistical-2-aminoethyl methacrylamide hydrochloride) (P[DMAEMA-co-AEMA.HCl]). Prepared polymers were characterized using nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC) methods. Also, via dialysis method aqueous micelles of PMMA-b-PDMAEMA block copolymer were prepared, and charaterized using dynamic light scattering (DLS). AEMA-hydrochloride monomer was synthesized via amidation process using methacrylic anhydride, and purified by recrystallization in isopropanol. Proton Neutron Magnetic Resonance (1HNMR) results revealed successful synthesis and production of a highly pure monomer. PMMA and PDMAEMA homopolymers of narrow molecular weight distribution were synthesized via RAFT using azobisisobutyronitrile (AIBN) initiator and 4-cyano-4-(phenylcarbonothioylthio) pentanoic acid (CPA) as chain transfer agent (CTA). With PMMA as a macro-CTA and AIBN initator DMAEMA was polymerized resulting in the formation of PMMA-b-PDMAEMA cationic block copolymer. 1HNMR analysis revealed a polymer consisting of PMMA and PDMAEMA blocks, and size exclusion chromatography (SEC) results also indicated production of a polymer with narrow molecular weight distribution. Results from dynamic light scattering (DLS) study showed PMMA-b-PDMAEMA (Mn=~23000 g/mol) diblock copolymer forms micelles with hydrodynamic radius in the range of 10-100 nm when THF-based copolymer solution was dialyzed in water. The size of micelle decreased at higher pH values. With respect to size PMMA-b-PDMAEMA copolymer micelles could be considered suitable for DNA transfer. Also, with AIBN initiator CPA and PMMA were used as CTA and a macro-CTA in two separate reactions to polymerize DMAEMA and AEMA-hydrochloride monomers simultaneously leading to formation of P(DMAEMA-co-AEMA.HCl) and PMMA-b-P(DMAEMA-co-AEMA.HCl) copolymers respectively. It was observed through SEC polymerization occured in both cases and resulting polymers exhibit very narrow molecular weight distribution. However, the molecular nature and composition of both copolymers cannot be reliably predicted based on 1HNMR results due to complications as a result of polymers poor solubility in various NMR solvents.