Li Wei

Bio: Li Wei is an academic researcher from Jiangxi Normal University. The author has contributed to research in topics: Carbonylation & Palladium. The author has co-authored 2 publications.

Synthesis of novel aromatic polyamides containing cardo groups and triphenylphosphine oxide structures by a heterogeneous palladium-catalyzed carbonylation and condensation reaction

Abstract: New aromatic polyamides containing cardo groups and triphenylphosphine oxide structures were synthesized by a heterogeneous palladium-catalyzed carbonylation and condensation of bis(4-(3-iodophenoxy)phenyl)phenylphosphine oxide (BIPPO), aromatic diamines bearing cardo groups, and carbon monoxide. Polycondensations were carried out in N,N-dimethylacetamide under 1 atm of CO at 120 °C in the presence of a magnetically recyclable heterogeneous palladium catalyst and 1,8-diaza-bicyclo[5,4,0]-7-undecene (DBU) and afforded novel aromatic polyamides with inherent viscosities between 0.72 and 0.76 dL/g. All the polyamides were quite soluble in dipolar aprotic solvents and pyridine and could be converted into transparent, flexible, and tough polyamide films by casting from DMAc solutions. These polymers exhibited high thermal and thermooxidative stability with the glass transition temperatures of 237 °C–256 °C, the temperatures at 5% weight loss of 448 °C–465 °C in air. All the phosphorus-containing polyamides self-extinguished as soon as the flame was removed, and the limited oxygen indices (LOIs) of these polymers were in the range of 39%–44%. The polymer films also showed good mechanical properties and high optical transparency.

Recyclable palladium-catalyzed synthesis of new cardo poly(amide-imide)s from diiodo imides, aromatic diamines containing cardo groups, and carbon monoxide

Abstract: High molecular weight poly(amide-imide)s containing cardo structures were readily prepared by a supported palladium-catalyzed carbonylation polymerization of diiodo imide monomers, aromatic diamines containing cardo groups, and carbon monoxide. Polycondensation reaction proceeded effectively in N,N-dimethylacetamide (DMAc) at 100 °C in the presence of a bidentate phosphino-modified magnetic nanoparticles-anchored palladium complex [2P-Fe3O4@SiO2-PdCl2] as catalyst and 1,8-diazabicyclo[5,4,0]-7-undecene (DBU) as base under 1 atm of CO, yielding a series of new poly(amide-imide)s with inherent viscosities up to 0.95 dL/g. All the polymers obtained were easily soluble in some strong polar aprotic organic solvents and could be cast into transparent, flexible and tough films from their DMAc solutions. These cardo poly(amide-imide)s displayed high thermal stability with the glass transition temperatures ranging from 237 to 265 °C, the temperatures at 5% weight loss ranging from 433 to 475 °C in nitrogen. These PAI films also exhibited good mechanical behavior and high optical transparency. The present method provides the flexibility of incorporating different ratios of imide and amide groups in the polymer backbone in a controlled manner and eliminates the possibility of postpolymerization curing due to the imide moiety being preformed. Importantly, the supported palladium catalyst can be conveniently separated from the polymer by simply using an external magnetic field and recycled at least 8 times without apparent loss of catalytic efficiency.

Intrinsically Flame Retardant Polyamides: Research progress in the last 15 years

Abstract: Polyamides are essential thermoplastics whose current worldwide annual production exceeds 10 million tons. They are ubiquitous and easily ignitable polymeric materials that require addition of flame retardants to comply with fire safety requirements for various applications. Flame retardant additives can be incorporated into polymer matrix as fillers or at the molecular level, implying use of reactive additives. The latter approach is less developed, but usually offers several advantages over adding flame-retardant fillers: lower additive loading used to achieve specific level of fire performance, no flame-retardant migration with time, lower corrosiveness, better polymer stability etc. Rendering polyamides intrinsically flame retardant is therefore highly desirable. In this review we survey progress in inherently flame-resistant polyamides done over the period from 2004 to 2020. The polymers are grouped according to their chemical structures: aliphatic, semiaromatic and aromatic polyamides, polyamidoimides and hybrid siloxane-polyamides. Their monomer preparation, synthesis details, thermal properties and fire performance are discussed. The minimal inclusion criterion for this review was reported fire-resistance performance: either V-1/V-0 rating achieved in UL-94 burning tests or experimental or calculated LOI above 23%.