Synthese und Charakterisierung von Poly(tert-butylacrylat)- und Polyacrylsäure-Sternpolymeren

Sternpolymere aus Poly(tert.-butylacrylat)-Armen und einem Mikrogel-Core aus Ethylenglykoldimethacrylat wurden nach der arm-first Strategie hergestellt. Diese weisen eine enge Armzahlverteilung auf. Mit sinkender Precursorlänge, mit steigendem Verhältnis [bifunktionelles Monomer]/[Initiator], sowie mit zunehmender Reaktionszeit und Gesamtkonzentration nimmt die mittlere Armzahl fn zu. Die Sternbildung verläuft ähnlich einer Polykondensation. Die Molekulargewichte wurden mittels GPC gekoppelt mit einem online-Viskosimeter und einem online-Vielwinkellichtstreudetektor (MALLS) bestimmt.Die intrinsischen Viskositäten der Sternpolymere sind sehr niedrig. Für Armzahlen f ca. 8 erhält man ein Maximum in der doppellogarithmischen Auftragung der intrinsischen Viskosität und des Molekulargewichts. Die Trägheitsradien nehmen nur wenig mit dem Molekulargewicht zu. Die erhaltenen Koeffizienten liegen im von Daoud und Cotton vorhergesagten Bereich. Die Schrumpfungsfaktoren sinken auf g ca. 0,2 bzw. g' ca. 0,25. Aus den Poly(tert.-butylacrylat)-Sternpolymeren wurden durch Verseifung mit HBr in Methanol Polyacrylsäure-Sternpolymere hergestellt, welche ebenfalls mittels GPC-Viskosimetrie und GPC-MALLS charakterisiert wurden. Für die ionischen Sternpolymere findet man deutlich höhere Schrumpfungsfaktoren, kein Maximum in der intrinsischen Viskosität und höhere Exponenten als von Daoud und Cotton vorhergesagt. Erklärt wurde dies mit der hohen Segmentdichte in Sternpolymeren, die bei den ionischen Sternpolymeren zu einer hohen Ladungsdichte führt. Dadurch müssen sich die Arme stärker strecken als bei nicht-ionischen Sternen und es resultieren größere Moleküldimensionen.

Synthesis and characterization of polyelectrolyte brushes

On the pathway to synthesizing synthetic model systems for human cartilage, macroinitiators for the ATRP of styrene sulfonate esters with different chain lengths and initiation site densities from 10 % to 100 % were synthesized. Polymer brushes from styrene sulfonate ethyl ester and styrene sulfonate dodecyl ester with varying grafting density, backbone length and side chain length were synthesized and characterized by 1H-NMR, AUC, AFM, TEM, and in the case of the ethyl esters, GPC-MALLS. Polyelectrolyte brushes from styrene sulfonate were synthesized from the corresponding esters. These brushes were characterized in solution (GPC-MALLS, static and dynamic light scattering, SANS, 1H-NMR) and on solid interfaces (AFM and TEM). It was shown that these brushes may form extended aggregates in solution. The aggregation behavior and the size and shape of the aggregates depend on the side chain length and the degree of saponification. For samples with identical backbone and side chain length, but varying degrees of ester hydrolysis, marked differences in the aggregation behavior were observed. A functionalized ATRP macroinitiator with a positively charged head group was synthesized and employed for the synthesis of a functionalized polyelectrolyte brush. These brushes were found to form complexes with negatively charged latex particles and are thus suitable as proteoglycan models in the proteoglycan-hyaluronic acid complex.

From amphiphilic block copolymers to ferrocenyl-functionalized polymers for biosensoric applications

The present thesis can be divided in three main parts. In all parts new polymer architecturesrnwere synthesized and characterized concerning their special features.rnThe first part will emphasize the advantage of a polystyrene-block-(hyperbranchedrnpolyglycerol) copolymer in comparison to an analogue polystyrene-block-(linear polyglycerol)rncopolymer. Therefore a synthethic route to prepare linear block copolymersrnhas been developed. Two strategies were examined. One strategy was based on thernclassic, sequential anionic polymerization; the second strategy was based on arn“Click-Chemistry” coupling reaction. In a following step glycidol was hypergraftedrnfrom these block copolymers by applying a hypergrafting reaction with glycidol. Thernbehavior of the amphiphilic block copolymers synthesized was studied in differentrnsolvents. Furthermore the polarity of the solvent was changed to form the correspondingrninverse micelles. DLS, SLS, SEC-MALLS-VISCO, AFM and Cyro TEMrnmeasurements were performed to obtain a visual image from the appearance of thernaggregates. It was found that a linear-hyperbranched architecture is necessary, ifrnwell defined, monodisperse aggregates are required, e.g. for the preparation of orderedrnnanoarrays. Linear-linear block copolymers formed only polydisperse aggregates.rnAdditionally it was found that size distribution could be improved dramaticallyrnby passing the aggregates through a SEC column with large pores. The SEC columnsrnacted like a template in which the aggregates adopt a more stable conformation.rnIn the second part anionic polymerization was employed to synthesize silaneendfunctionalizedrnmacromonomers with different molecular weights based on polybutadienernand polyisoprene. These were polymerized by a hydrosilylation reaction inrnbulk to obtain branched polymers, using Karstedt’s catalyst. Surprisingly the additionrnof monofunctional silanes during the polymerization had only a minimal effect concerningrnthe degree of polymerization. It was possible to introduce silanes without increasingrnthe overall number of reaction steps by a very convenient “pseudo-copolymerization”rnmethod. All branched polymers were analyzed by SEC, SEC-MALLS,rnSEC-viscometry, 1H-NMR-spectroscopy and DSC concerning their branching ratio.rnThe branching parameters for the branched polymers exhibited similar characteristicsrnas hyperbranched polymers based on AB2 monomers. Detailed kinetic study showedrnthat the polymerization occurred very rapidly in comparison to the hydrosilylation polymerizationrnof classical AB2 type carbosilanes monomers.rnThe last part will deal with ferrocenyl-functionalized polymers. On the one hand,rnferrocenyl-functionalized polyglycerols (PG) were studied. Esterification of PGs withrndifferent molecular weight using ferrocenemonocarboxylic acid gave the ferrocenylrnfuntionalized polymers in high yields. On the other hand three different block copolymersrnwere prepared with different ratios of styrene to butadiene units (10:1, 4:1, 2:1).rnThe double bonds of the 1,2-PB block were hydrosilylated using silanes bearing onern(HSiMe2Fc) or two (HSiMeFc2) ferrocene units. High degrees of functionalizationrnwere obtained (up to 83 %). In this manner, six different ferrocenyl-rich block copolymersrnwith different fractions of ferrocene were prepared and analyzed, employingrnNMR-spectroscopy, SEC, SEC/MALLS/viscometry, DLS and cyclic voltammetry. Thernredox properties of the studied polymers varied primarily with the nature of the silanernunit attached. Additionally, the redox properties in solution of the studied polymersrnwere influenced by the block length ratio of the block copolymers. Unexpectedly, withrnincreasing block length of the ferrocenyl block the fraction of active ferrocenes decreased.rnNevertheless, in case of thin monolayer films this behaviour was not observed.rnAll polymers (PG and PS-b-PB based) exhibited good electrochemical propertiesrnin a wide range of solvents, which rendered them very interesting for biosensoricrnapplications.