Rigid-rod thermosets based on 1,3,5-triazine-linked aromatic ester segments

First use of grape waste-derived building blocks to yield antimicrobial materials

Grape marc is an underutilised waste material that poses significant environmental issues. This study offers the first proof-of-concept investigation into the polymerisation of both crude and purified Sauvignon blanc grape marc extracts using the diacyl chlorides terephthaloyl chloride, succinyl chloride, adipoyl chloride, sebacoyl chloride, and the tartaric acid derivative (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbonyl dichloride to obtain new materials, in what to the best of our knowledge is the first reported example of a direct polymerisation of an agricultural waste extract. A total of 26 novel materials were prepared. It has also shown that quercetin, a phenolic monomer found in grape marc extracts, can be polymerised with (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbonyl dichloride to give a polymer that shows activity towards S. aureus.

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.

Recent Technological Developments in Cyanate Ester Resins

Although they are relative newcomers to the composites industry, cyanate ester (CE) resins are enjoying unprecedented success in certain applications. Several major space and radome manufacturers have qualified CE resins despite the extensive database on epoxies and the inherently conservative nature of the industry. Increasing demands on the materials used in these areas have stimulated the use of CE resins over other more conventional polymers. The aim of this review is to bring to the reader’s attention the more recent developments in the processing, toughening, properties and applications of cyanate esters, an exciting, versatile and important class of resins.

Synthesis and Properties of a Liquid Crystalline Thermoset Epoxy Resin Containing 1,3,4-Oxadiazole Groups

A new liquid crystalline thermoset (LCT) based on 1,3,4-oxadiazole was prepared from liquid crystalline epoxy resin containing oxadiazole and diaminodiphenyl methane. The LCT was characterized and compared with the conventional thermoset. The Time—Temperature Transformation diagram was constructed to determine an appropriate set of cure cycles. The goal of this paper was centered on the evaluation of the mechanical performances of this new class of thermoset. In the case of LC thermoset, a higher Tg and good fracture resistance were noticed than that of the conventional thermoset. The LC thermoset exhibited higher thermal stability when compared with the conventional non-LC thermosets. The results tempted to consider the LCT materials as potential candidates for advanced composites.

Magnetic Field Orientation of Liquid Crystalline Epoxy Thermosets

The effect of magnetic fields on the orientation and properties of 4,4'-bis(2,3-epoxypropoxy)-alpha-methylstilbene cured with sulfanilamide has been studied. This epoxy system is initially isotropic and forms a smectic A phase upon curing. A magnetic field was applied during the cure reaction, resulting in alignment of the molecules along the direction of the applied field. Measurement of the orientation parameter of the fully cured material by wide-angle X-ray scattering (WAXS) showed that orientation improved with an increase in field strength. The orientation parameters of the smectic layer normals calculated from the inner reflection of the WAXS pattern attained a maximum level of approximately 0.8 at a field strength of approximately 12 T. The orientation parameters calculated from the outer reflection of the WAXS pattern were considerably lower, possibly due to the presence of amorphous regions associated with domain boundaries or the loss of molecular alignment within the smectic layers due to topological restrictions of the cross-linking sites. Orientation resulted in an anisotropic linear thermal expansion coefficient after curing, although the overall volumetric expansion was constant. The elastic tensile modulus increased with the square of the orientation parameter, attaining a maximum value of 8.1 GPa, compared to 3.1 GPa for the unoriented material. The change in modulus with orientation could be fit with a simple model for the modulus of anisotropic materials.