Thermal decomposition of polyimides containing phosphine-oxide units

Abstract

This work details analyses of the thermal decomposition behaviour of three phosphine-oxide containing aromatic processable polyimides. The polymers exhibited high thermal stability with initial decomposition temperatures in the range of 473-483°C and a char residue at 900°C in the domain of 48.6-58.4%. The values of non-isothermal decomposition kinetic parameters were determined using the Friedman isoconversional method, as recommended by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The data evidenced a complex decomposition process of the main chain, being probably initiated by the cleavage of the weaker P-C bonds, followed by the decomposition of the macromolecular backbone. The volatile products formed during the thermal decomposition of polyimides were analysed by TGA-FTIR. All spectra evidenced peaks associated with water, CO 2 , CO and aliphatic and aromatic decomposition products predominant from 500° to 800°C. By using Py-GC-MS studies the fragments originating from the thermal decomposition of the polyimides up to 600°C were identified. Based on these data, it was suggested that the thermal decomposition pathways of the three polyimides undergoes the same mechanism. Additionally, an oversimplified decomposition mechanism for the polyimides was proposed. The morphology of the char residue obtained after TGA experiments showed a continuous and dense structure. The EDX mapping identified the C, N, O and P atoms uniformly dispersed in the residual char surface.

Optical and Flame-Retardant Properties of a Series of Polyimides Containing Side Chained Bulky Phosphaphenanthrene Units

“…Also, in all three samples the presence of the NMP (RT = 11.175/10.082/9.255) from TIC may be attributed to the evaporation of the residual solvent encapsulated in the PI’s macromolecular chain. The presence of the 3-(trifluoromethyl)phenol was observed in the TIC of sample PI-3 at RT = 15.048 [ 36 ].…”

Synthesis of Phosphorus- and Fluorine-Containing Hyperbranched Imide Oligomers for Flame-Retardant Epoxy Thermosets

“…Based on the above results, it can be deduced that the nonflammability of the EP/HAPI-3 thermoset arises from the flame-retardant effect of DOPO and imide groups (Figure ). During combustion, imide radicals generated by the cleavage of carbon–nitrogen and carbon–carbon bonds in the imide rings can react with other pyrolysis products (e.g., aromatic hydrocarbons) to produce aromatic N-heterocyclic compounds via isomerization, rearrangement, and cyclization. , Meanwhile, the degradation of DOPO groups generates (poly)­phosphoric acid species. Notably, N-heterocyclic compounds and (poly)­phosphoric acid species not only promote the carbonization process but also enhance the char quality, and the resulting compact char residue has a good physical barrier effect that cuts off the supply of heat and air and protects the internal matrix from flame.…”

The Synergistic Effect of Triazine and Phosphaphenanthrene Units on the Physico-Chemical Behavior of Polyimides

“…The approaches that have been undertaken have mainly consisted of incorporating various moieties into the starting monomer’s structure (kink, spiro, cardo, cycloaliphatic, bulky, fluorinated, hetero, carbazole, perylene, chiral, nonlinear optical, or unsymmetrical units), copolymerization reactions, functionalization of the already obtained polyimides, or use of different fillers towards nanocomposite-based polyimide material development [ 5 , 7 , 9 , 10 , 11 , 12 , 13 , 14 ]. It has been proven that the incorporation of aromatic ether and isopropylidene units enables increased processability and lowered glass transition temperature of the corresponding polyimides, while maintaining increased thermal stability [ 15 , 16 , 17 , 18 ]. On the other hand, bulky hexafluoroisopropylidene moieties are known for their ability to enhance flame resistance properties and gas separation characteristics through increased free volume, as well as to improve the electrical insulation ability [ 16 , 19 ].…”

“…It has been proven that the incorporation of aromatic ether and isopropylidene units enables increased processability and lowered glass transition temperature of the corresponding polyimides, while maintaining increased thermal stability [ 15 , 16 , 17 , 18 ]. On the other hand, bulky hexafluoroisopropylidene moieties are known for their ability to enhance flame resistance properties and gas separation characteristics through increased free volume, as well as to improve the electrical insulation ability [ 16 , 19 ].…”

“…The thermal stability endowed by the incorporation of phosphinate linkage [–O–(O=)P–O–C] into a cyclic form is higher than that of a phosphonate type [–O–(O=)P–O–] based polymer [ 31 ]. Thus, recently, several phosphorus-containing polyimides have been reported with improved physico-chemical properties through monomer functionalization with flexible units [ 16 , 32 , 33 , 34 ] or by using copolymerization techniques [ 35 , 36 ]. Particular interest has been devoted to the development of phosphorus-based polyimides for use as proton exchange membranes [ 37 , 38 ], or polyimide composites with pristine or functionalized polyhedral oligomeric silsesquioxane for atomic oxygen resistance applications [ 39 , 40 , 41 ].…”