No abstract

A low-molecular lignin fraction (L) was extracted for the preparation of bio-based epoxy resins. Various compositions with the "green" 1,3-glycerol diglycidyl ether (1) and the co-component pyrogallol (2) were tested. In a first series of experiments, thermosets consisting of 1 and L, were studied with respect to variable lignin contents between 20 and 50%. The best thermoset has a tensile strength of 37 MPa and a Young's modulus of 2.2 GPa at 40% lignin input. Secondly, lignin-free compositions of 1 and 2 were prepared. For a molar fraction of the functional groups (n(OH) n(Epoxy)(-1)) of 130%, the tensile strength could be enhanced to 93 MPa and the modulus reached 3.7 GPa. Finally, systems with all three components were examined. The best mechanical performance of the corresponding neat thermosets was reached at n(OH) n(Epoxy)(-1) of 130%. Tensile strength decreases slightly to 86 MPa and Young's modulus remains nearly unchanged at 3.2 GPa. Two resin compositions, L+ 1 and L+ 1+ 2, were tested for the preparation of unidirectional composites reinforced with man-made cellulosic fibers (50% by vol.). The bending strength was 208 MPa in combination with a bending modulus of 12.5 GPa

Radical cations of a series of a-methyl-substituted bi-, ter-and quaterthiophenes were investigated by EPR and, in part, ENDOR spectroscopy. In the case of terthiophenes, the electronic and steric effects of methyl substituents were studied. The experimentally determined spin density distributions were rationalized by means of semiempirical quantum-mechanical calculations (MNDO, PM3, RHF-INDO/SP). Sterically noo-hindered oligothiop hene radical cations are planar and form mixtures of cis and trans conformers, whereas uniform species were observed in the case of sterically hindered, non-planar radical cations.

Various functionalized polythiophene films on electrode surfaces were produced by electropolymerization. Starting from 3-(2-hydroxyethyl)thiophene (1) different ether and ester derivatives were synthesized:  3-(2-(benzyloxy)ethyl)thiophene (2), 3-[2-((triphenylmethyl)oxy)ethyl]thiophene (3), 3-[2-((trimethylsilyl)oxy)ethyl]thiophene (4), 3-[2-((dimethyl-tert-butylsilyl)oxy)ethyl]thiophene (5), 3-(2-acetoxyethyl)thiophene (6), 3-(2-(benzoyloxy)ethyl)thiophene (7), 3-[2-((p-nitrobenzoyl)oxy)ethyl]thiophene (8), and 3-[2-((3,5-dinitrobenzoyl)oxy)ethyl]thiophene (9). Cyclovoltammetric analyses in acetonitrile with tetrabutylammonium perchlorate (TBAP) as supporting electrolyte gave the characteristic peak potentials (E p's) of the electrochemical oxidation of these monomers. Under our standard conditions homopolymerization of the monomers 2−9 could not be achieved, whereas copolymerization of 2−9 with 3-methylthiophene (10) was successful. The resulting polymeric films were characterized by FT IR spectroscopy and chemical reactions.

SUMMARY By the protection of the carboxyl group of 3-thiopheneacetic acid with differently substituted benzyl groups a series of new thiophene derivatives were synthesized. While 3-thiopheneacetic acid is not electropolymerizable, the new obtained monomers can be easily electrooxidized to form stable electroactive polymers. The electrochemical characterizations show that the substitution of the benzyl groups exerts little effect on the electropolymerization process and that the obtained polymers exhibit the typical properties of polythiophene derivatives, e. g., redox behavior and electrochromism. SEM studies show that all synthesized monomers possess a very good film formability and the resulting polymers exhibit a rather compact and homogeneous morphology on the Pt electrodes also containing scattered particles. Using p-nitrobenzyl-protected polymer as an illustrative example, it was demonstrated that the used protecting group can be easily split off in the solid state and the desired reactive carboxyl group can be produced on the polymer surface. Therefore, through the protection of the carboxyl group, the electropolymerization and the following removal of the protecting group, a new type of polymer matrix material with reactive carboxyl groups was simply prepared by using commercially available 3-thiopheneacetic acid monomer.