Bioinspirierte Titin-analoge Polymere

Abstract

Bioinspired polymers imitating the multiple domain structure of the muscular protein Titin on the basis of hydrogen bond bearing cyclic precursor polymers have been synthezised and their mechanical properties have been examined. Prior to this the Ring Expansion Polymerization (REP) for the synthesis of cyclic polymers based on the living-like Acyl Group Transfer Polymerization of thiiranes by Nishikubo et al. was investigated in detail. For this purpose a system consisting of thiirane monomer 2-(phenoxymethyl)thiirane (PMT), 2-methylthiirane (MT), 2-tert-butoxymethyl)thiirane (TBMT) or 2-((o-methylphenoxy)methyl)thiirane (MPMT), cyclic initiator 2,4-thiazolidindione (TZD) and derivatives thereof and catalyst tetrabutylammonium chloride (TBAC) in N-methylpyrrolidin-2-one (NMP) was investigated. Insertion of MT, TBMT and MPMT in TZD proceeded under good control of degree of polymerization and dispersity although a ring merging reaction under formation of polymer rings in doubled size, in case of PMT even up to quadrupled size was observed. In case of PMT the degree of ring merging decreased with increasing monomer concentration, reaction temperature and molar monomer-to-initiator-ratio, whereas the other monomers did not show such a dependance. By fitting of the molar mass distribution curves of PMT-based polymers obtained by SEC measurements via multiple Gaussian functions the time-dependent relative molar concentration of each ring species was observed. Thus the rate coefficients for the merging reaction at polymer concentrations between 14 and 52 wt-% could be obtained in a range of several orders of magnitude between 10^(−2) and 10^(−6) L/mol/s. Switching the initiator to TZD substituted in 3-position a huge increase of ring merging up to degrees of seven was observed. The cyclic structures of the polymers were verified via mass spectrometry and atomic force microscopy. In addition to homopolymerization cyclic (AB)n-multiblock copolymers consisting of MT and PMT with up to eight blocks formed via ring merging could be synthezised and were put to tensile-testing. In comparison to linear diblock copolymers with similar composition they exhibited a clearly different behaviour in terms of elongation at break and toughness. Bioinspired polymers were synthezised by combination of linear and cyclic segments and tested on their mechanical properties as well. For this purpose cyclic (ABC)n-multiblock copolymers with an additional monomer block made from ethyl-2-(4-(thiirane-2-ylmethoxy)-benzamido)acetate (ETBAA) able to form self-complementary hydrogen bonds were synthezised. The cyclic precursor polymers were coupled via 1,3-dipolar cycloaddition according to Huisgen with a bifunctional linker or with monofunctional poly(n-butyl acrylate) (PBA) or poly(methyl acrylate) (PMA) prepared via RAFT-Polymerization. According to this procedure in the first case polymer with polycyclic topology was obtained whereas in the second case macromolecules with a chain–ring–chain-topology were synthezised. Tensile-testing of the metioned chain–ring–chain-polymer did not show improved material properties compared to linear PMA except a noticably higher elasticity. However, the poly(ring polymers) revealed a unique stress-strain behavior, a good elasticity behavior and a higher applicable tension compared to unaltered ring polymers due to formation of intra and intermolecular physical hydrogen bonds. One of the polymers even formed a physical network by reversible crosslinking between hydrogen bonding motifs and exhibited a shape memory and the ability of partial self-healing.