Structure and properties of poly(4-methyl-2-pentyne) synthesized with NbBr5 and TaBr5-based catalytic systems

In this work, we used the concept of controlling the properties of poly(4-methyl-2-pentyne) [PMP] by changing the polymerization conditions. We synthesized PMP using novel NbBr5-and TaBr5-based catalytic systems. PMP obtained with TaBr5-based systems are characterized not only by greater resistance to dissolution, but also by significantly more limited swelling in organic solvents compared to PMP obtained with NbBr5-based catalysts. Solution and solid-state 13C NMR spectroscopy showed that synthesized PMP samples have a mixed ratio of cis-/trans-units. The X-ray diffraction indicated an increase in the polymer packing density with an increase in the dissolution selectivity, which can be associated not only with the ratio of cis-/trans-units in polymers, but also with the lengths of the sequences of units of the same geometry that influences the polymer conformation. According to the low-temperature argon sorption PMP demonstrates high Brunauer–Emmett–Teller (BET) surface area (up to 846 cm3/g). PMP film membranes exhibit a high level of permeability (PO2 = 1400–2100 barrer for polymers synthesized with NbBr5-based catalysts and PO2 ~ 1100 barrer for polymers synthesized with TaBr5-based catalysts). This study provides the opportunity of obtaining PMP, combining high permeability with high resistance to organic substances. [Display omitted] •A series of poly(4-methyl-2-pentyne) with high molecular masses were synthesized using Nb and Ta pentabromides catalysts.•The effect of catalysts on the structure and properties of poly(4-methyl-2-pentyne) was investigated.•The decrease of dissolution as well as swelling correlates with an increase in the polymer packing density.•TaBr5 catalysts gave polymers with high gas permeability and BET surface area along with resistance to organic solvents.