The production of elemental sulfur from petroleum refining has created atechnological opportunity to increase the valorization of elemental sulfur by the creation of highperformance sulfur based plastics with improved thermomechanical properties,elasticity and flame retardancy.W ereport on asynthetic polymerization methodology to prepare the first example of sulfur based segmented multi-block polyurethanes (SPUs) and thermoplastic elastomers that incorporate an appreciable amount of sulfur into the final target material. This approach applied both the inverse vulcanization of S 8 with olefinic alcohols and dynamic covalent polymerizations with dienes to prepare sulfur polyols and terpolyols that were used in polymerizations with aromatic diisocyanates and short chain diols.Using these methods,anew class of high molecular weight, soluble blockcopolymer polyurethanes were prepared as confirmed by SizeE xclusion Chromatography,N MR spectroscopy, thermal analysis,a nd microscopic imaging. These sulfur-based polyurethanes were readily solution processed into large area free standing films where both the tensile strength and elasticity of these materials were controlled by variation of the sulfur polyol composition. SPUs with both high tensile strength (13-24 MPa) and ductility (348 %strain at break) were prepared, along with SPU thermoplastic elastomers (578 %s train at break) which are comparable values to classical thermoplastic polyurethanes (TPUs). The incorporation of sulfur into these polyurethanes enhanced flame retardancy in comparison to classical TPUs,w hich points to the opportunity to impart new properties to polymeric materials as ac onsequence of using elemental sulfur.
Hydrolysis
and subsequent degradation of microcrystalline cellulose
in five ionic liquids (ILs) using metal salts and/or Brønsted
acids as catalysts allowed for the direct access to 5-hydroxymethylfurfural
(HMF), an important renewable biofuel precursor and a useful building
block. For each catalytic system, several reaction parameters (temperature,
reaction time, catalyst, and cellulose loading) have been selectively
changed. Four systems ([BMIM]Cl-CrCl3, [BMIM]Cl-FeCl3, [BMIM]Cl-[MIMC4SO3H][HSO4] and the not yet investigated [BMIM]Cl-TiOSO4) were found
to be effective for cellulose degradation into HMF. The extraction
of HMF from the reaction media represents however the weak point of
all these processes being able to affect negatively both HMF recovery
and IL recyclability. The critical step which causes the drastic decrease
in HMF yield starting from the first recycle has been clearly identified.
Furthermore, the possibility to use TiOSO4 as a sustainable
and robust catalyst for the conversion of saccharides (or polysaccharides)
in HMF has been shown. The present study could open new perspectives
for the one-pot synthesis of HMF starting from cellulose and/or other
sugars.
An
investigation of the copolymerization of cyclohexene sulfide
and carbon disulfide using salphen and salen Cr complexes as catalysts
and [PPN]+X– salts as cocatalysts, at
different temperatures and reaction times, is reported. Both catalytic
systems produce both polymer and cyclic products. For the first time,
poly(trithiocyclohexylcarbonates) (PCS) have been synthetized in high
yields and high molecular weights. Salphen-based catalysts, in comparison
with salen-based ones, show higher productivity and selectivity for
polymers with high molecular weight up to 18 kg/mol when the reaction
is carried out at 25 °C. At a higher temperature with (salphen)CrCl,
the maximum value of selectivity for copolymers (72%) was obtained
at a short reaction time (3 h). At long reaction times, great amounts
of cyclic by-product are observed, thus evidencing the tendency for
cyclohexene sulfide and CS2 to provide cyclic products
due to the stability of the trithiocyclohexylcarbonate. PCS possesses
high refractive index (n > 1.72), and antimicrobial
assays reveal that these materials are active against Escherichia coli and moderately active against Staphylococcus aureus. These properties along with
the T
g values of 80 °C make these
polymers suitable for interesting applications different from those
of poly(trithiopropylencarbonate).
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