Andreas Gerken

New polymer syntheses, 101. Liquid‐crystalline hyperbranched and potentially biodegradable polyesters based on phloretic acid and gallic acid

Three series of randomly branched copolyesters were prepared from mixtures of acetylated trimethylsilylesters of non-toxic natural hydroxy acids. The first series is based on 1 : 1 molar ratio of β-(4-hydroxyphenyl)propionic acid (HPPA, phloretic acid) and 4-hydroxybenzoic acid (4-HBA). The second series was prepared from HPPA, 4-HBA and vanillic acid (VA, molar ratio 1 : 1 : 1), and in the third series VA was replaced by 4-hydroxycinnamic acid (HCA). The branching density was varied via the feed ratio of triacetylgallic acid. The stability of the nematic phase increases with decreasing branching density, but a partial LC-character was found even at relatively short length of the linear chain segments. Finally, two star-shaped and hyperbranched copolyesters were prepared. The incorporation of a star center type molecule allowed the control of the molecular weight, but eliminated the liquid-crystalline character almost completely. The ternary copolyesters and the quaternary copolyesters of VA were characterized by dynamic rheological measurements, and in the latter case also a few stress-strain measurements were conducted.

New Polymer Syntheses 87. Thermosetting Nematic or Cholesteric Diesters Having Propargyl Endgroups

4-Propargyloxy benzoic acid, 6-propargyloxy-2-naphthoic acid and 4′-propargyloxybiphenyl-4-carboxylic acid were synthesized from the corresponding hydroxy acids and converted into the acid chlorides. Diesters were then prepared by the reaction of these acid chlorides with diphenols such as hydroquinone, methylhydroquinone n-octylthiohydroquinone and phenylhydroquinone. Most of these diesters form an enantiotropic nematic melt but some diesters form a monotropic liquid crystal phase. Cholesteric phases were observed for diesters of (S)-2-methylbutylthiohydroquinone. Diesters derived from 6-propargyloxy-2-naphthoic acid begin to crosslink above 200 °C with an optimum cure temperature of 240–250 °C. The crosslinking of the 4′-propargyloxybiphenyl-4-carboxylic acid derivatives occurs at a temperature 60 °C higher. Several diesters crosslink in the nematic state, but most of them undergo isotropization before completion of the crosslinking process. Numerous cholesteric blends of nematic diesters and chiral diesters of isosorbide were studied and Grandjean textures with bright colours were found. Thermal crosslinking in the cholesteric phase was feasible in several cases.

LC-polyimides XXXIV. Noncrystalline thermotropic copoly(ester-imide)s based on PET

Four series of copoly(ester-imide)s (co-PEIs) were prepared by transesterification of poly(ethylene terephthalate), PET, with N-(4-carboxyphenyl)trimellitimide and an acetylated diphenol. Methylhydroquinone, tert. butylhydroquinone, phenylhydroquinone, and 2,7-dihydroxynaphthalene were used as diphenols. The chemical structures of these co-PEIs were characterized by chemical analyses, 1H-, and 13C-NMR spectra. A low degree of crystallinity was observed when the PET content was above 85% mol %. Between 60 and 80 mol % PET all co-PEIs are biphasic, whereas below 60 mol % the co-PEIs form a homogeneous nematic melt and below the glass transition temperature (Tg) a nematic glass. The Tgs vary continously with the molar composition but the mechanical properties drop sharply when the nematic phase changes to an isotropic one.

New polymer syntheses. 102. Aspirin‐modified LC polyesters based on PET and 4‐hydroxybenzoic acid

Four series of liquid-crystalline copolyesters were prepared by the transesterification of poly(ethylene terephthalate) (PET) with 4-acetoxybenzoic acid (4-ABA) or mixtures of 4-ABA and acetylsalicylic acid (ASA). Two series consisted of 30 mol % PET, and the other two series consisted of 40 mol % PET. The molar ratio of 4-HBA and ASA was varied in all four series from 0 to 25 mol %. One 30% PET series and one 40% PET series were prepared with the addition of acetic acid, which caused a more perfect randomization of the sequence but yielded slightly lower molecular weights. The incorporation of ASA reduced the crystallinity, which vanished completely at a salicylic acid (SA) content greater than 10 mol %. SA also reduced the stability of the nematic phase, but all the copolyesters were thermotropic up to a 20 mol % SA content. Furthermore, the molecular weights decreased with the increasing incorporation of ASA. Despite this negative trend, the melt viscosity and the storage and loss moduli passed a maximum between 5 and 10% SA. Obviously, the incorporation of SA favored the formation of entanglements.

New polymer syntheses. 89. Thermosetting cholesteric oligoesters having propargyl endgroups

Abstract Three series of cholesteric oligoesters containing propargyl endgroups were prepared by polycondensations of three different dicarboxylic acid dichlorides with mixtures of diols and monofunctional propargyl derivatives in pyridine. These three series are based on terephthaloylchloride, naphthalene-2,6-dicarbonylchloride, and biphenyl-4,4′-dicarbonylchloride. tert-Butylhydroquinone, phenylhydroquinone, and isosorbide were the diols, and propargyl alcohol, 4-propargylthiophenol, and 6-propargyloxynaphthaloyl chloride served as chain stoppers. All isolated oligoesters were thermotropic, but only a few of them were capable of forming a Grandjean texture upon shearing of the cholesteric melt. The thermal crosslinking of the propargyl endgroups was monitored by an exothermic process in the DSC measurements. The lowest cure temperatures (200–240°C) were observed for the 6-propargyloxy-2-naphthoic acid endgroups. Thermal crosslinking in the cholesteric phase was observed for four samples.