## 2 Materials and Methods
### Gas Permeability Measurements  
The experimental unit scheme is presented in Figure 3. The polymer film was hermetically fixed in the membrane cell, which was located in a thermocryostat (Huber CC-410) that allowed the experiment to be carried out in the temperature range -20 to 140 \({}^{\circ}\)C. The membrane (film) divided the volume of the cell into two cavities: the reservoir (feed side) and the receiver (permeate side). The gas to be studied was supplied on the feed side at 1 atmosphere at a flow rate of 1-2 mL/s. The carrier gas (helium or argon) was supplied on the permeate side with the same flow rate for the experiments without evacuation (experiments with PMPentene). For the experiments with significant amounts of condensable components (butane) and all the experiments with PMPentyne, continuous evacuation of the permeate side by a flow vacuum pump (ASF Thomas) was applied (stage cut did not exceed 0.1). The partial pressure drop across the membrane in both cases was kept at -1 atmosphere. For the second case, further dilution of the permeate sample with carrier gas was applied. Chromatographic analysis of a permeate sample diluted with helium was conducted on a Shimadzu GC-17 chromatograph (Kyoto, Japan) with a thermal conductivity detector (TCD 1) and capillary column (GS-Tek 8253-5015) allowing for the analysis of mixtures of C\({}_{1}\)-C\({}_{5}\) hydrocarbons (saturated, unsaturated, isomers) with helium as carrier gas. As PMPentyne is a highly permeable polymer with low time-lag values (\(\theta\approx\) 0.01-0.1 s), it was possible to carry out gas permeation measurements under slow linear heating of the membrane cell (0.3 \({}^{\circ}\)C/min) [15].  
Figure 2: Repeating unit of PMPentyne.  
The gas permeability coefficient (\(p\)) was calculated according to the equation:  
\[P_{i}=\frac{Vc_{i}^{\prime}l}{A\Big{(}p_{1}c_{i}-p_{2}c_{i}^{\prime}\Big{)}}, \tag{1}\]  
where \(V\) is the flow rate of the gas carrier with the penetrant, cm\({}^{3}\) (STP) s\({}^{-1}\); \(A\) is the membrane area, cm\({}^{2}\); \(p_{1}\) is the feed pressure, cmHg; \(p_{2}\) is the permeate pressure, cmHg; \(c_{i}\) is the concentration of the penetrant in the feed flow, vol%; \(c_{i}^{\prime}\) is the concentration of the penetrant in the gas carrier stream in the permeate, vol%; and \(l\) is the membrane (film) thickness, cm.  
It is known that the gas separation selectivity \(\alpha_{P_{g}}\) (\(\alpha_{P_{g}}=P_{g}/P_{g}\)) includes \(\alpha_{D_{g}}\) (selectivity of diffusion, \(\alpha_{D_{g}}=D_{g}/D_{g}\)) and \(\alpha_{S_{g}}\) (selectivity of gas solubility, \(\alpha_{S_{g}}=S_{g}/S_{g}\)), which depends on temperature. For this reason, we needed to determine all key permeability parameters at the required temperatures.  
The diffusion coefficients (\(D\)) were determined by the differential permeability method. In this method, the time dependence of the unsteady penetrant flow through the membrane, with a stepwise change in concentration on the upstream side of the membrane, was registered online. The aim of the method is to obtain the differential permeability curve by TCD 2 and to carry out its subsequent processing by using the functional scale method [16].  
The experimental gas transport parameter measurements were carried out in the temperature range \(-20\) to \(80\)\({}^{\circ}\)C for PMPentene and \(-20\) to \(40\)\({}^{\circ}\)C for PMPentyne (from \(0\)\({}^{\circ}\)C for butane). In the case of PMPentyne the data for \(80\)\({}^{\circ}\)C were extrapolated from the experimental data.