Perfluorinated linear hetero-oligomers and polymer electrolytes

Abstract

A poly(PEG-co-PFPE) or poly(PPG-co-PFPE) copolymer or hetero-oligomer capable of dissolving > 5% (m / m) of a sodium salt, such as NaTFSI. When mixed with a sodium salt, a polymer electrolyte (PE) is formed. The hetero-oligomer is formed by mixing PEG or PPG with PEPE in the presence of a Candida antarctica lipase enzymatic catalyst and heating the mixture and isolating the resulting hetero-oligomer from the lipase catalyst.

Description

PERFLUORINATED LINEAR HETERO-OLIGOMERS AND POLYMER ELECTROLYTESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and is a n on-provision al of, US Patent Application 63 / 742,961 (filed January 8, 2025), the entirety of which is incorporated herein by reference.BACKGROUND OF THE INVENTION

[0002] The combustion of fossil fuels, while remaining the main enabler of industrialization, is associated with environmental pollution which causes undesirable effects to the population, the climate, and natural ecosystems worldwide. Since the ensuing multifaceted problems have become a global emergency, there is an increasing need for efficient energy storage systems capable of capturing intermittent but sustainable forms of energy As the demand for lithium-ion batteries has been climbing sharply, sodium-ion batteries are becoming a viable energy storage solution, alternative to the leading technology.

[0003] Sodium is abundant, affordable, and has an appropriate redox potential (Na⁺ / Na — “2.71 V vs. SHE, 0.3 V more positive than that of Li). Replacement of conventional liquid electrolytes with solid polymer electrolytes (SPEs) would improve Na-polymer batteries, especially in view of sodium’s high reactivity and its elevated tendency to dendrifi cation. Polymer electrolytes (PEs) are very promising because they are highly flexible, can be easily processed, and offer favorable interfacial contacts with the electrodes.

[0004] Conventional linear perfluropolyether diols (PFPE-diols) are characterized by very low glass transition temperatures (-89°C to -117°C), which decrease with the molar mass of the polymer between 1000 and 4000 g / mol. These PFPEs are very effective indissolving lithium salts, such as LiTFSI because the CF2 units interact preferentially with the anion (TFSI ), while CO groups of the PEG fragments within PFPE interact more with Li+cations.

[0005] This same solubility did not translate to sodium salts. Conventional PFPEs 800-1100 g / mol) can dissolve only 4.8 % (m / m) of NaTFSI, resulting in a PE with no measurable conductivity. When 20 % (m / m) dimethyl sulfoxide (DMSO) is added as a plasticizer, up to 12,47 % (m / m) of NaTFSI could be dissolved with good conductivities. The formation of polymer electrolytes (PEs) based on PFPEs with good solubility of sodium salts, such as NaTFSI, without using plasticizers would be desirable. Unfortunately, straightforward synthesis of such PEs remains a technical problem to be solved.

[0006] The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.SUMMARY

[0007] This disclosure provides a poly(PEG-co-PFPE) copolymer capable of dissolving > 5% (m / m) of a sodium salt, such as NaTFSI. When mixed with a salt, a polymer electrolyte (PE) is formed. An advantage that may be realized in the practice of some disclosed embodiments is that the polymer electrolyte can contain substantially larger amounts of sodium ions than conventional PEs without using a plasticizer.

[0008] In a first embodiment, a method for forming a hetero-oligomer is provided. The method comprising: mixing a polyethylene glycol diester (PEG) and a perfluoropolyether oligomer (PFPE) having a formula of PEG-PFPE-PEG, the mixing occurring in the presence of a Candida antarctica lipase enzymatic catalyst, thereby forming a mixture; heating the mixture to polymerize the PFPE and the PEG, therebyforming a hetero-oligomer (PFPE-PEG-PFPE); and isolating the hetero-oligomer from the lipase enzymatic catalyst.

[0009] In a second embodiment, a polymer electrolyte is provided. The polymer electrolyte comprising: the hetero-oligomer produced by an enzymatic copolymerization of (1) a polyethylene glycol di ester (PEG), (2) a perfluoropoly ether oligomer (PFPE) and (3) a Candida antarctica lipase enzymatic catalyst, thereby forming a mixture:, the hetero-oligomer being further mixed with a sodium salt at > 5% by mass.

[0010] In a third embodiment, a method for forming a hetero-oligomer is provided. The method comprising: mixing a polypropylene glycol (PPG) and a perfluoropolyether oligomer (PFPE) having a formula of PPG-PFPE-PPG, the mixing occurring in the presence of a Candida antarctica lipase enzymatic catalyst, thereby forming a mixture; heating the mixture to polymerize the PFPE and the PPG, thereby forming a hetero- oligomer (PFPE-PPG-PFPE), and isolating the hetero-oligomer from the lipase enzymatic catalyst.

[0011] This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define or limit the scope of the invention, which is defined only by the appended claims. This brief description is provided to introduce an illustrative selection of concepts in a simplified form that are further described below in the detailed description. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which:

[0013] FIG. 1A is a synthetic scheme of PEG 600 diester produced from PEG 600 di acid.

[0014] FIG. 1B is a schematic scheme showing enzymatic synthesis of Poly(PEG-co- PFPE) from PFPE and PEG 600 diester. In the case of PFPE-PEG-PFPE the subscript indices take the following values: q=1.80, m=4,57, n=1.76, r=11.71 and s=1.03.

[0015] FIG. 2 displays profiles of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes between -150 to 100 °C.

[0016] FIG. 3 shows FT-IR spectra of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes

[0017] FIG. 4A and FIG. 4B show Gaussian decomposition of FT-IR spectra of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes in the region 525- 1910 cm’1. The bands related to the salt are shown as black continuous lines, the other bands as dotted red lines (see Table 2B). The fit is given as a continuous line, the original spectrum in comprised of dotted lines.

[0018] FIG. 5 depicts graphs showing the relationship between the percentage fractional area of most peak intensities of the FT-IR bands between 975 and 1380 cm’1(within Region I) of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes, as a function of the molar ratio nNa / npolym.

[0019] FIG. 6 depicts graphs showing dependence of the direct current conductivity σ3vs reciprocal temperature of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes. The red dotted lines show the fitting of the curves by using the VTF equation. The black dotted lines are guidelines for the eye.

[0020] FIG. 7 depicts graphs showing dependence of the VTF parameters vs the molar ratio nNa / npolymused in fitting the direct current conductivity σ3vs reciprocal temperature (see FIG. 6) of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes. The dotted lines are meant as guidelines for the eye.

[0021] FIG. 8 depicts graphs showing dependence of the equivalent conductivity Λ3vs the square root of the molalityof the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes. Data is fitted using equation 2.

[0022] FIG. 9 is a graph of Na+transport number of select PFPE-PEG-PFPE / (NaTFSI)x (0.000 < x < 2.160) polymer electrolytes as a function of the mole-to¬ rn ole ratio x.DETAILED DESCRIPTION OF THE INVENTION

[0023] This disclosure provides a method for the enzymatic synthesis of a linear polymer based on perfluropolyether (PFPE) and polyethylene glycol methyl diester ( PEG) units, which cannot be achieved by conventional organic chemistry methods. This disclosure also provides a polymer electrolyte resulting from the method. The polymer is suitable to dissolve sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) up to 20.0 % by mass yielding a polymer electrolyte (PE). In some embodiments, the resulting PE has >5%, > 6%, > 7%, > 8%, > 9%, > 10%, > 11%, > 12%, > 13%, > 14%, > 15%, > 16%, > 17%, > 18%, > 19%, or > 20% by mass of a sodium salt, such as NaTFSI.

[0024] By way of illustration, a series of seven polymer PEs with formula PFPE- PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) were produced from a PFPE-PEG-PFPE copolymer (CP, x=0) as examples without the need of a plasticizer, such as DMSO (i.e. the polymer electrolyte is DMSO-free). The polymer electrolytes had glass transition temperatures which increase in the range from -77°C to -49 °C with salt concentration. The PEs were thermally stable up to at least 270 °C and the CP was thermally stable up to at least 350 °C (in a closed pan). The representative macromolecular structure is that of an α,ω-OH-terminated hetero-oligomer bridged by ester functional groups The calculated average numerical molecular weight was 2619 g / mol with a poly dispersity of 1.475. The thermal stability of the copolymer (CP) was at least 350 °C, significantly higher than pure PEG and PEG / PFPE blends. For example, blends based on PEG 400 and PFPE1000-diol were stable only up to 150 °C. In some embodiments, a polypropylene glycol (PPG) or a polypropylene glycol diester is used instead of the PEG.

[0025] No studies have been conducted on polyester copolymers combining PEG and PFPE in the main chain. The lack of investigations in this area of research can be attributed to the novelty of the field but also to synthetic difficulties in modulating the structure of desirable polymer targets. The copolymer could only be successfully synthesized by means of enzymatic catalysis. Enzymatic polymerization of oligomeric PEG diester and PEG-PFPE-PEG was carried out using NOVOZYME®-435 as an enzymatic catalyst, yielding a copolymer designated as PFPE-PEG-PFPE. The resulting copolymer was doped with NaTFSI resulting in a series of eight solvent-free PEs with formula PFPE-PEG-PFPE / (NaTFSI) (0.000 < x < 2.160).

[0026] Conductivity and equivalent conductivity studies revealed that there are two main salt-doped phases in the system, providing two concomitant pathways for long-range ionic migration. The first is represented by PEG, the second by PFPE / PEG. Thehighest conductivity at 25 °C in the PEG phase was observed for sample P6 with a value of 3.6 ■ IO-5S ■ cm"1. Similarly, a conductivity of 6.6 ■ 10~5S ■ cm"1was observed for sample P7 in the PFPE / PEG phase. For the sake of comparison, the conductivity of PFPE1000-DMCdoped with LiTFSI was 2.0 ■ IO”5S ■ cm”1at 25°C. The cationic transport numbers were as high as 0.94 and 0.80 in the two domains, respectively, exhibiting values much higher than PEO-based PEs. The VTF behavior of the direct current conductivity and the Onsager parameters vs reciprocal temperature indicate the role of the segmental motions of the copolymer in determining the conductivity mechanism. The biphasic properties of the PEs based on the copolymer, at least from a conductivity standpoint, contrast with the blends of PEG / PFPE-diol doped with LiTFSI, perhaps due to the use of Li as opposed to Na cations.

[0027] Taken together, the synthesized copolymer enhances the properties of pristine PEG due to the assistance of PFPE both in terms of thermal and chemical stability but also in terms of cationic conductivity. This material may be of interest beyond the field of energy storage, with potential application as lubricant and refrigerating fluid.

[0028] Referring to FIG. 1A, the reaction protocol was started by converting commercially available PEG 600 carboxylic diacid to PEG 600 methyl diester (known also as PEG 600 dimethyl carbonate). Thin layer chromatography examination (TLC, solvent mixture methanol: chloroform, 1:9) provided support for the completion of the reaction. The structure of the PEG diester was confirmed from its1H- and13C-NMR spectra. Further confirmation came from the expected shifts in the carbonyl vibrations of PEG di ester with respect to the PEG di acid as shown by FT-IR analysis.

[0029] Referring to FIG. 1B, the PEG diester was then reacted with PFPE in the presence of the biocatalyst, NOVOZYME®-435, yielding the copolymer poly(PEG-co-PFPE), referred to herein as PFPE-PEG-PFPE, NOVOZYME®-435 is a lipase B enzyme from Candida antarctica that is immobilized on a macroporous support formed by poly(methyl methacrylate) crosslinked with divinylbenzene.

[0030] If PEG is represented with “A” and PFPE with “B”, the most likely structure of the copolymer was found to be the hetero-oligomer BAB. Referring again to FIG. 1B, the subscript indices for PFPE are q=1.80, m=4.57, n=1.76. The subscript index for the PEG 600 methyl diester units is r=11.71, this value is calculated from the equivalent weight of PEG 600 diacid (300-350 g / mol) provided by the manufacturer. The basic BA (or AB) pattern is repeated s number of times. A value of s=1.03 was used accurately reproduce the percentages of the experimental CHN analysis (C 33.50+0.16 %; H 3.41+0.11 %). The calculated percent composition corresponding to the BAB structure is the following: C 33.41 %; H 3.52 %. In one embodiment, q is about 1.80, m is about 4.57, n is about 1.76, r is about 11.71 and s is about 1.03 The structures (AB)Sand A(BA)s cannot be used by themselves to explain the results of the CHN analysis. In fact, their calculated elemental percentages systematically exceed the experimental values. These alternative structures are expected to be present in smaller amounts given that methyl ester terminal groups would readily react with PFPE-diol in the presence of NOVOZYME®-435, as the copolymer is increasing in length. The calculated molecular weight for the BAB structure is 2619 g / mol. This value can be compared with the experimental Mnvalue measured by Gel Permeation Chromatography (GPC): Mn= 3881 g / mol (see Table 1A). Both the PFPE-diol and the copolymer exhibit a negative refractive index. The observed discrepancy between the calculated and experimental value of the molecular weight is consistent with typical errors routinely observed in GPC measurements of polymeric systems. The calculated molecular weight value was used in the determination of the ratio between the moles of Na and the moles of copolymer: x = nNa / npolym(see Table IB).

[0031] The PEG-PFPE-PEG copolymer (CP) was used to dissolve NaTFSI yielding a series of PEs with the formula, PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160). The composition parameters are given in Table IB. The dissolution proceeded smoothly by¬ simple mixing, as expected. The materials appear to be highly viscous, light yellow, and cloudy liquids. Up to 20.0 % (m / m) of salt could be dissolved. This latter observationconfirms that the presence of PEG significantly increases the solubilization properties of the copolymer in comparison with pristine PFPE.Table 1 A: Molecular weight distribution parameters determined by Gel Permeation Chromatography for the co-polymer poly(PEG-co-PFPE).Parameter Value3,881 g / molMwb)5,725 g / molc)7,648 g / molMz+1d)9,254 g / molMv5.725 g / mol6,633 g / molMz / Mw1.336Mw / Mn^ 1.475Mz+1 / Mw1.617a) Number average molecular weight.b) Weight average molecular weight.c) Z average or size average molecular weight.d) Z+ l average molecular weight.e) Viscosity average molecular weight.f) Peak molecular weight.g) Poly dispersity index.Table IB: Composition of the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes.Sample %polym %NaTFSI b) x = nNa / npolyma),b)CP 100% 0% 0Pl 99.6 0.4 0.035P2 99.2 0.8 0.070P3 98.4 1.6 0.141P4 96.8 3.2 0.286P5 93.6 6.4 0.591P6 87.2 12.8 1.268P7 80.0 20.0 2.160a) %polym, npolymare the mass percentages and number of moles of PFPE-PEG-PFPE, respectively, determined from the measured experimental masses of the copolymer. b)%NaTFSI and nNaare the mass percentage of NaTFSI and the number of moles of Na, respectively, within the PFPE-PEG-PFPE / (NaTFSI)x (0.000 < x < 2.160) polymer electrolytes, determined on the basis of the stoichiometric amount of salt with respect tototal mass.

[0032] The fact that the BAB structure captures the main characteristics of the data set pertaining to this system does not exclude that longer chain copolymers were formed. As shown in Table 1 A, the weight average molecular weightis equal to 5,725 g / mol and the polydispersity Mw / Mnis equal to 1.475. The values of the Z and Z+l average molecular weights Mzand Mz+1are equal to 7,648 and 9,254 g / mol, respectively. These molecular weight distribution parameters signify that higher-order embodiments of the structure BA)sB, (AB)s, and A(BA)s, with s taking values up to at least 5, were successfully synthesized albeit in significantly smaller amounts. Herein, the copolymer preferably labeled as PFPE-PEG-PFPE, as opposed to poly(PEG-co-PFPE), given that the hetero-oligomeric structure is the dominant macromolecular chain in the system.

[0033] ’ll NMR: Within the ’H-NMR spectra, close inspection of the ratio of the integral of the CEE peak to that of the outermost CFfcpeak of the ethylene oxide units of the PEG diester, when compared to the ratio of the integrals of the same peaks in thecopolymer provided useful information. This comparison indicates that the methyl groups have decreased in going from the precursor to the copolymer, given that said ratio decreases from 0.88 to 0.52. More reliable information is obtained from the13C-NMR spectra. The carbonyl carbon peaks were detected as a single peak at 170.9 and a pseudo¬ doublet at 170.4 and 170.3 ppm in the13C NMR spectrum of the copolymer. The first peak is attributed to the unreacted methyl ester groups while the latter two peaks are assigned to the methyl ester groups which have undergone transesterification. The qualitative comparison of the corresponding integrals shows that if the first peak is taken to be 1.00, the sum of the second two peaks is 2.18. This suggests that about two third of the methyl ester moieties did react, while one third did not. This constitutes a further confirmation of the successful synthesis of the linear copolymer. At the same time, the prevalent structure BAB does not completely account for the observed spectrum without the concession that other structures are also possible [(AB)Sand A(BA)S],

[0034] 19F NMR: The19F-NMR spectra of the PFPE-diol and of the copolymer reveal that the m / n ratios are equal to 2.60 and 2.54, respectively. These findings underline that the integrity of PFPE is conserved following enzymatic polymerization.

[0035] Thermal Analysis of the Copolymer and Polymer Electrolytes

[0036] The thermal analysis of the copolymer (CP) and the PEs (Pl to P7) was conducted by means of DSC measurements in the temperature interval of — 150 °C to 100 °C and between 30 °C to 350 °C. The DSC profiles are shown in FIG. 2. The glass transition temperature Tgincreases from -76.7 °C to -49.2 °C with increasing concentration of the salt. There is an apparent small inversion of the overall linear trend between samples CP and Pl; given that the standard deviation is 2.5 °C, such inversion is non-significant. Endothermic events are observed for samples CP, Pl to P5 between 22.3 and 15 °C. These events are attributed to melting temperatures (7'm) occurring in the samples, mainly involving the copolymer. The copolymer units can interact in different ways (beside hydrogen-bonding interactions): either A with A or B with B or A with B.Since A and B are expected to be soluble in each other and with themselves, a singlephase melting was observed. The values of Tmdecrease with the concentration of dopant. This event is absent in P6 and P7 at the highest concentrations of the salt.Exothermic events take place for samples P4 and P5 at -40.2 °C and -28.9 °C, respectively. Smaller peaks for P6 and P7 were detected at -1.6 °C and -1.3 °C, respectively, that were attributed to the same type of events. These events were ascribed to crystallization of the NaTFSI salt. Without wishing to be bound to any particular theory, dissolution of the salt is believed to occur first within the PEG moieties.Dissolution in PFPE opens the backbone chains. Therefore, partial crystallization occurs for the stoichiometries corresponding to P4 and P5, with some residual crystallization occurring with P6 and P7. Samples P4 and P5 are associated with compositions in which about 4 and 2 PFPE-PEG-PFPE chains are present for every NaTFSI unit, respectively. These compositions lead to electrolytic complexes particularly prone to crystallization, with P5 understandably crystallizing at higher temperature than P4. No other significant events were observed between 30 °C to 350 °C for the copolymer and the PEs, except at about 320 °C. where leakage from the Al pan occurred only in the case of the PEs.Instead, the host copolymer is stable up to at least 350 °C, while the PEs are less and less stable with increasing concentration of the salt. Nonetheless, the PEs are stable up to at least 270 °C boding well for their applications in energy storage devices. These results are remarkable considering that blends based on PEG 400 and PFPE1000— diol were stable only up to 150 °C.

[0037] FT-IR of the Copolymer and Polymer Electrolytes

[0038] The vibrational study of the hetero-oligomer PFPE-PEG-PFPE copolymer and the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x <2.160) PEs was carried out by FT-IR ATR spectroscopy in the mid-infrared region, as shown in FIG. 3. Gaussian decomposition was performed in the spectral intervals 525-1910 cm’1(Region I) and 2500-3800 cm'1(Region II). See FIG. 4 A and FIG. 4B. The full assignment is given in Table 2 A and Table 2B. The spectra did not require normalization, as they arespontaneously normalized with respect to the stretching CH peaks measured between 2500 and 3100 cm’1. A cursory observation of the stacked spectra shows that there are clear similarities across all samples from the pure copolymer to the sample with the highest concentration of salt (P7). A closer look reveals that the vibrations of NaTFSI become more and more visible on the envelope of the spectra between 526 and 1380 cm’ \ as the concentration of the salt increases. Additional salt vibrations appear in the interval 975 to 1380 cm’1. Other bands not evident from the spectral profiles were confirmed to be present by difference spectroscopy, by subtracting the Pl spectrum from the P2 to P7 spectra. Salt vibrations are much more intense than observed in PFPE / (NaTFSI)x(DMSO)y (0.004 < x < 0.610, 3.205 < y < 3.794). This phenomenon is most likely due to the dampening effect of the DMSO plasticizer, which was not used in the present case.

[0039] PEG 600 diacid is characterized by a more intense peak at 1093 cm’1with a smaller right-shoulder peak at 1043 cm’1. The difference in wavenumber is Aw — 50 cm”1. Similarly, PEG 600 diester exhibits a more intense peak at 1097 cm’1with a smaller right-shoulder peak at 1142 cm’1(dw — 50 cm”1). In both cases these peaks were attributed to the stretching of internal CO in conjunction with stretching CC (vP£'c(C0), vPPG(CC)) and to the stretching CO (yPEG(CO)) of terminal groups(-OCH2COOH and OCH2COOCH3), respectively. These assignments should be compared to similar bands of PEG oligomers (PEG 400), where a less intense left¬ shoulder at 1078 cm-1was attributed to vPfiG(CO) while a more intense peak at 1123 cm’1was attributed to vPEG(CO) in conjunction with vPEG(CC). The value of Aw was45 cm”1. The peaks appear to be inverted with respect to each other in terms of intensity and consequent assignments due the carbonyl-containing groups as opposed to the hydroxyl groups. These assignments should be compared to those of the bands measured at 1129 cm’1(right shoulder) and at 1199 cm’1(more intense peak) in the case of PFPE diol. The first peak was assigned to yPFPE(CO), VPFPE(CF) due to CO and CF near the OH terminal groups, respectively, while the second peak was assigned to vPFPG(CO), vPFPE(CF) due to internal CO and CF bonds, respectively. There may be an additionalcontribution due to vPPPE(CC). The value of Aw is 70 cm”1. Given the information above, it is possible to infer the position of the CO, CF, and CC vibrations in PFPE terminated by an OH on one side and an organic carbonate on the other (-CH2COOCH2-) as is the case on PFPE-PEG-PFPE. Similarly, it is possible to infer the position of the same stretching bands in PEG terminated on both sides by PFPE units, linked by organic carbonates In PFPE-PEG-PFPE, the stretching vibrations vP£G(CO), vPEC'( CO ■■■ HO — ), vPEG(CC) are believed to be due to internal CO of PEG coordinated or not by OH terminal groups of PFPE, appear at 1097 cm-1. The stretching i'pgpg(CO), vpppg(CF), vPEPE(CC) and vpgpg(CO — HO — ), vPEPE(CF), vpppg(CC) due to CO and CF near the OH terminal groups of PFPE will appear at 1129 cm”1. The stretching vPEG(CO) or vpgG(CO ■■■ Na+) associated with internal CO coordinated or not with sodium cations will be found at 1142 cm”1. This band will also include a contribution fromv(C — (C — 0) — PC) not coordinated by Na+. This latter contribution is expected to be matched by a band at 1189 cm”1corresponding to v(C — (C ~ 0) — PC) and v(C — (C = 0) — OCC) due to the organic carbonates coordinated or not with Na+. The stretching vPFPE(C0), vPEPE(CF) and vPFPE(C0 Na+), vpppg(CF •■■■ TaFSI”) are believed to be due to CO and CF moieties, coordinated or not with Na+and appear at 1199 cm”1(actual value is about 1210 cm”1). These beliefs were the basis of the Gaussian decomposition in Region I. These specific bands were assumed to be fixed in frequency. Due to the complexity of the fingerprinting region, frequency changes of these bands could not be allowed to take place, even if all other bands were allowed to change, but the fitting was satisfactory, nonetheless. Spectral data also showed that the barycenter of the carbonyl groups between 1700 and 1760 cm-1shifts higher in going from the PEG diacid (1705, 1729, 1756 cm”1) to the PEG diester (1719, 1731, 1754 cm-1). There is also a noticeable peak at 1209 cm-1with a higher intensity in the PEG diester as opposed to the PEG diacid that can be attributed to the symmetric CH3 deformation in the PEG diester. Both these observations confirm that PEG diacid was successfully converted to the PEG diester.

[0040] The success of the decomposition in Region I is confirmed by the semi-quantitative analysis of the fractional percentage areas of most bands between 975 to 1380 cm’1, as shown in FIG. 5. The bands at 1097 and 1129 cm'1decrease in intensity with the value of x (nNa / npoiym), while the bands at 1142 and 1210 cm’1increase in intensity. This observation indicates that the CO and CF groups in terminal positions are initially uncoordinated or, in the case of CO, are coordinated with the terminal OH groups of PFPE-PEG-PFPE. As the salt is introduced, the CO moi eties tend to coordinate the Na4cations, while CF moieties coordinate the TFS1’ anion.

[0041] The bands measured at 1052, 1133, and 1178 cm’1corresponding to vibrations of the salt, increase in intensity with the value of x, as expected (Table 2B). The band at 1062 cm’1was attributed to the stretching CF (vPFPE(CF)). This band increases in intensity with the value of x, suggesting that the interaction with TFS1’, through the partially positive carbon atoms of the CF, groups, ultimately increases the electronic charge density of the CF groups. This effect is caused by the negative charge delocalization in the TFSI’ anion and the accumulation of negative charges on the surface of PFPE helixes. The band measured at 1283 cm’1, which is associated with the twisting CH2 of PEG (TP£G(CH2)), decrease in intensity with the value of x. The band detected at 954 cm-1, which is attributed to the rocking CH2 of the copolymer and CF2 of PFPE mixed with stretching vibrations of CO and CC of the copolymer (pol-vm(CH2), vpol-vm(CC), v^o / ym(C0), pPPPE(CF2)), decreases in intensity as well. These observations points to the higher rigidity of the PEs at the higher concentrations of salt. The band at 1189 cm-1which is linked to the organic carbonates (vide supra and Table 2B) decreases in intensity as the result of increasing coordination by Na+cations of the CO groups next to the carbonyl moieties. The behavior of this peak correlates with the carbonyl peaks measured at 1699 and 1748 cm'1The first of the latter bands is attributed to carbonyl coordinated with OH groups and Na+cations, the second is attributed to carbonyl coordinated with Na+cations. The peak at 1748 cm”1dominates at the highest concentration of salt.

[0042] The Gaussian decomposition in Region II (Table 2 A) was conducted in a similar manner as for Region I. However, the intensities are much lower, and a vibrational semi-quantitative analysis was not equally reliable. The decomposed spectra indicate that the peak at 3299 cm-1decreases in intensity with increasing salt concentration. This peak was attributed to hydrogen bonding interactions between OH groups and the organic carbonates (vPEG(OH)). The peaks detected at 3504 and 3708 cm’1slightly decrease in intensity as well. The first peak was attributed to the stretching of OH group interacting intrachain with oxygen atoms of the copolymer (vP£G(OH)), while the second peak to isolated or “free” OH groups(OH)). The absence of a solvent / plasticizer pushes the frequencies of all these peaks to higher values than in PFPE / (NaTFSI)x(DMSO)y.

[0043] Impedance Spectroscopy and Transference Number Studies of the Polymer Electrolytes

[0044] The Impedance Spectroscopy investigation of the PFPE-PEG- PFPE / (NaTFSI)x(0.000 < x < 2.160) PEs was carried out in the range 100 mHz - 1 MHz, between 10 °C and 80 °C. The Nyquist plots are characterized by a well-defined semicircle followed by a lofty sloping branch. The simulation of these traces used the following equivalent circuits: Q1+ R2 / Q2+ R3 / Q3and R1 / Q1+ R2 / Q2+ R3 / Q3. Q1+ R2 / Q2or R1 / Q1+ R2 / Q2account for the sloping branch, while R3 / Q3 accounts for the semicircle. Ru(u = 1,2,3) and Qv(v = 1,2,3) represent resistances and constant phase elements (CPEs), respectively. The impedance of a CPE (ZCPE) is e 2'“ and,depending on the value of n, it can represent an ideal capacitor C for n = 1, a pure resistance R for n = 0, or a Warburg diffusion element W for n = 0.5. Qxhas the character of a capacitor C (since n~l) and is attributed to the electric double layer established in proximity of the Pt electrodes of the conductivity cell. Q2has the character of a Warbug diffusion element W (since 0.5 < n < 0.75), and Q3has the character of a capacitor C (since n > 0.8) R1swhen present, exhibits high values of resistance (R1>IO6fl) and is associated with a resistance in parallel with the electrical double layer. Such resistance may be caused by a very small reduction of terminal -CH2OH groups to terminal -CH3 groups, which would appear to become more important at higher temperatures and at higher concentrations of salt. NaTFSI would effectively become a supporting electrolyte for such side reaction. R2 / Q2 which behaves as a parallel RW is attributed to a salt-doped PEG phase. R3 / Q3 which behaves as a parallel RC is associated with a salt-doped phase comprised of PFPE alternating to PEG. The BAB copolymer can close pack with other BAB copolymers in two ways. B can be in direct contact with B, and A with A. Otherwise, one can have A in contact with B and B in contact with A. A with A (PEG with PEG) give rise to a salt-doped PEG phase. B with B (PFPE with PFPE) give rise to a salt-doped PFPE phase. Such phase does not conduct ions as mentioned above. A with B (PEG with PFPE) give rise to a salt-doped PFPE / PEG phase. Such phase is expected to conduct ions, albeit less than the salt-doped PEG phase. The first circuit is suitable for the fitting of the lower-concentration PE (x — 0.035) up to the highest temperature (80 °C) The highest-concentration PE (x — 2.160) used the second circuit for most temperatures, with the exception of the trace at 10 °C. In other words, as the concentration and temperature increase the more complex circuit becomes progressively necessary as opposed to the simpler circuit for a satisfactory fitting of the Nyquist plots.

[0045] The comparison between R2 / Q2and R3 / Q3 suggests that the most conductive phase is represented by the PEG domains as opposed to the PFPE / PEG domains. The latter domains will allow for a lower level of conductivity but will also act as capacitive charge storage region due to the presence of PFPE. In other words, R2and R3(R2< R3)canbe used to determine the conductivities in the PEG and PFPE / PEG regions, respectively. The derived conductivity contributions σ2and σ3are shown in FIG. 6 as a function of reciprocal absolute temperature, respectively (σ2> σ3). Theσ2is systematically higher in value but less resolved than σ3. The lower resolution is not attributed to a physical phenomenon. This is due to the fact that the fitting of the branch is more challenging than that of the semicircle being a composite phenomenon. PFPE inthe copolymer is believed to be much more free in assisting the ionic conductivity when in contact with PEG, as opposed to PFPE by itself. The room temperature (25 °C) conductivities are 3.6 ■ 10~5S ■ cm’1within PEG for sample P6 and 6.6 ■ IO-5S ■ cm’1in PFPE / PEG for sample P7.

[0046] The profiles of σ3(FIG. 6) are amenable to fitting by using the Vogel-Tamman-Fulcher (VTF) equation:σVTF(T) = Aσ / √T · exp(-Eaσ / (R(T-T0σ)))

[0047] The parameters in eq. (1) have the following meaning: 1) Aarepresents the concentration of ionic charge carriers, 2) Eaais proportional to the activation energy for conductivity, and 3) To ais the thermodynamic ideal glass transition temperature. T0σcorresponds to the temperature at which the configurational entropy is null or the “free volume” becomes zero. Initial values for Towere chosen in this interval based on the experimental values of the glass transition temperature: (Tg,σ- 55) < T0,σ< (Tg,σ- 40). The VTF fitting for P1-P3 (0.035 < x < 0.141) is possible only above 25 °C, while a fullrange fitting is successful for P4-P7 (0.286 < x < 2.160). The former observation can be related to the DSC results. The melting temperatures Tmobserved between 22.3 and 15 °C for the samples from CP to P5 indicate that the solidification of the electrolytes from Pl to P3 is an obstacle for long range ionic migration. This is true especially at lower concentration of salt where the ionic reservoir is insufficient to sustain optimum conductivity in the entire temperature range.

[0048] The VTF fitting parameters as a function of x are shown in FIG. 7. The profile of Aσmonotonically increase with x. This observation reveals that addition of salt results in an augmented concentration of effective ionic carriers. T0,σ3increases in the same way, contrary to what happened for PEG400 / (LiCl)xwhen adding more LiCl salt. The average values of the pseudo-activation energy Ea,σ3remain relatively constant andwithin the interval 7-8 kJ / mol. These values are higher than observed in PFPE-diol doped with LiTFSI (0.47 kJ / mol) but display as similar concentration-independence.

[0049] The equivalent conductivity Λ3(calculated from σ3) vs. the square root of the 1 / 2molality cNawas investigated, as shown in FIG. 8. Interestingly, no clear exponential decay is present in A3, contrary to what is typically observed. This phenomenon was attributed to the strong salt dissociation enabled by the copolymer, preventing significant changes in ion-pairing and further accumulation of neutral species with higher values of x. The profiles of A3can be fitted with the following equation:A3= Ho + A1exp(-a1c^2) + K2e~a^cNa ~^)2(2)1 / 2

[0050] There is a single maximum at about cNa1 / 2≈ 0.3. This is attributed to the presence of triple ions Na+••• TFSI~ ••• Na+and TFSI~ ■■■ Na+••• TFSI~ in the1 / 2PFPE / PEG phase. In the limit of cNa0, equation 2 reduces to the Onsager equation, under the conditions that Λo= Ko+ K1+ K2and A = -2K1a1+ 2K2a2A~ Aj) ~ A ■ (3)

[0051] exhibits negative values, unlike all other parameters, which is quite surprising. However, this can be explained considering that the salt dissolves first in PEG and then in PFPE, Additional salt does not cause a baseline decrease in ion-pairing but an increase in ionic dissociation due to the interactions of the anion with the CF2 moieties. In spite of negative K1values, the Onsager parameters Λoand A exhibits satisfactory profiles as a function of the reciprocal absolute temperature. The parameters can be fitted with the following VTF-like equation:Λ0,i(T) = A'0,0 / √T · exp(-EaΛ / (R(T-T0Λ)))VT \R(T-T^J (4)where the parameters A‘OtO,and T0Eare a pre-exponential constant, the pseudoactivation energy for conduction at infinite dilution, and the thermodynamic ideal glasstransition temperature for conduction at infinite dilution, respectively. The index i identifies the fitting region (i = II, III). Equation 4 can be used, with obvious alterations, for the fitting of both / l0and A. The shift between region II and region III occurs in the temperature interval 45-50 °C, similarly to what previously observed in the case of PFPE / (NaTFSI)x(DMSO)y. Why this change occurs at about 50 °C is unclear, when there is no corresponding thermal event occurring at this temperature (vide supra). The biphasic character of PFPE (more specifically PEG-PFPE-PEG) and PFPE / PEG may be the root causes of the observed change. The ideal glass transition temperature (190 K) falls within the interval measured in the case of σ3(see FIG. 8), Also, the activation energies and Ea’Aare similar to Ea<j3(4-5 kJ / mol as opposed to 7-8 kJ / mol). In region I the VTF fitting is not possible. This is due to the thermal events (Tm) occurring between 15 °C and 22.3 °C.

[0052] The conductivity Λ2was calculated from σ2. The scarce quality and paucity of data points with respect to the multiplicity of features did not permit a proper fitting. However, there are two maxima at about cNa1 / 2≈ 0.3and cNa1 / 2≈ 0.7. These two events are related to the same triple ions described above in the salt-doped PFPE / PEG phase The first and second event pertain to the PEG and PFPE subphases, respectively. This is consistent with the expectation that PEG is filled first and then PFPE.

[0053] Transport numbers of Na+are shown in FIG. 9. PFPE-PEG copolymers have substantially higher Na+transport numbers compared to PEG polymers. The AC impedance and chronoamperometric data were used to determine tNa+. Three parallels RQ were needed to simulate the symmetric cell assembly (Na|PE|separator|Na) which is associated with a small semicircle followed by a big one. The first semicircle can be reproduced by the parallel Ri / Qi which accounts for the bulk resistance of the electrolyte within the PFPE / PEG phase. The bigger semicircle can be fitted by R2 / Q2inseries with R3 / Q3. R2 / Q2 represents a smaller contribution with respect to R3 / Q3 and is attributed to the PEG phase. R3 / Q3 is attributed to a solid electrolyte interphase (SEI). The transport numbers determined on the basis of R1before and after polarization, changebetween 0.81 and 0.94 with increasing salt concentration (PFPE / PEG phase). Similarly, on the basis of R2, before and after polarization, the transport numbers are systematically lower and change between 0.56 and 0.80 going through a minimum (PEG phase). The latter value interval is higher than what normally observed for PEO-based PEs (ti a+ = 0.1-0.5). The fact that the cationic transport number is higher in PFPE / PEG as opposed to PEG, can be explained considering that the proximity of PFPE decreases the residence time of Na+cations within PEG. The cations are most likely delocalized amongst the ethylenoxide units of an individual PEG chain with the possibility of interchain hopping between PEG chains. When PFPE is present it disrupts the cationic coordination to the oxygen atoms and facilitates interchain hopping. Remarkably, two distinct ionconducting pathways are available for Na+in the disclosed system, further confirming the biphasic properties of the PEs.Table 2A: FT-IR band assignments for the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes in the spectral region between 2500 and 3800 cm’1(Region II).Observed wavenumbers (cm-1)PFPE-PEG- PFPE-PEG-PFPE / Assignmentc'dPFPEab(NaTFSI)xa’b3708 (vvw) 3708 (vvw)v;^e(OH)3504 (vvw) 3504 (vvw) vPEG(OH)3299 (vvw) 3299 (vvw) v^c(0H)3014 (vw) 3014 (vvw) v££G(CH2 ” (C = 0) - CF2)2939 (vw) 2940 (vw) VaEG(CH2) (EJ2902 (vw) 2904 (vw) (CH2 - cc- - GF2)2869 (vw) 2871 (vw) vfFG(CH2) (42)2829 (vvw,2830 (vw, sh)sh)v.rG(CH2) (Et)2779 (vvw,2781 (vvw, sh)sh)2608 (vvw, sh) 2603 (vw, sh) vPFPE(HO - CH2)a) Relative intensities of observed bands are reported in parentheses: vs: very strong; s: strong; m: medium; w: weak; vw: very weak; sh: shoulder.b) v: stretching; 8: bending; p: rocking; ©: wagging; T: twisting; 8sr: scissoring; a: antisymmetric, s: symmetric.c) Free: isolated OH group; polym: PEG-PFPE-PEG; Hy: hydrogen bonding cage of OH groups with TFST.d) The assignment is based on literature references.Table 2B: FT-IR band assignments for the PFPE-PEG-PFPE / (NaTFSI)x(0.000 < x < 2.160) polymer electrolytes in the spectral region between 525 and 1910 cm'1(Region I).Observed wavenumbers (cm"1)PFPE-PEG- PFPE-PEG-PFPE / Assignmentc dPFPEa’b(NaTFSI)xa,bv(C = 0) or1756 (w) 1748 (w)v(C = 0 - Na+)1732 (vw) 1699 (vvw) v(C = 0 - HO -) orv(C = 0 - (HO—) ■■■ Na+)1476 (vvw)1453 (vw) 1458 (vvw) <Pf?(CF2), CPG(CH2) (Et)1450 (vw)1403 (vvw)1388 (vw) & / FP£(CF2), toPBG(CH2) (£))1377 (vw)1352 (vw) 1353 (w) v™(SO2)^^p-(CH2) (E))1333 (vw, sh) <4™(SO2)1269 (m, sh) 1283 (m, sh) TP£G(CH2) (EJvPPPF(CO), vPPP£(CF) or 1209 (s) 1210 (s) vPFPft'(CO --- Na+), vPPP£'(CF ---- TFSr)v(C - (C = O) - OC), v(c - (C = 0) - OCC) or 1 189 (m) 1189 (w)v(C - (C = O - Na+) - OC), v(C - (C = 0 - Na+) - OCC)1178 (m) VaaTFSi(CF3)1142 (m) 1142 (m)VPEG (CO)orV^«(CO - Na+)v(C - (c = o) - oc)1133 (vw) vJS^(SO2)vPPPE(CO), vPPP7?(CF), vPPPF(CC)* or 1129 (s) 1129 (m)vPFPE(CO - HO -), VPFPE(CF"), vPFPE(CC)*vPEG(CO), vPEG(CO - HO -), 1097 (m) 1097 (m)vP£G(CC)*1060 (vs) 1062 (vs) vPFP£(CF)1052 (m) <'aTra(SNS)94 (m, sh) 954 (m, sh)9 (vw, sh) pVolym^Q^y Vpoiym(CC), 947 (m) 949 (m) vpolym(CO), pPPPE(CF2) (£\)07 (w, sh) 916 (w, sh)3 (vw, sh) 899 (w)866 (vw, sh) pPoJv^(CH2), vP°lym(CO\ 849 (m) 848 (w, sh) pPPPi(CF2) (EJ832 (vw)(w, sh) 813 (vw, sh)787 (vw) vWarra(CS)5Poi>’m(CC0), d'P°^m(COC), (vw) 760 (vvw)pP0iym(CH2), pPFPE(CE2) (Ej739 (vw) 3^aTFSI(CF3)(vw) 718 (vw)Spoiym^CCG^ 8polym(CQC), (vw)684 (vw) p^^(CH2), p™'(CF2) (£J (vw)(w, sh) 654 (w)653 (w) 5WO7TS / (SNS)5P°iym(CC0), 5P^y^(C0C)5633 (vvw)pPo«y^(CH2), pPFPE(CF2) (ET)616 (m)600 (m)5^°^m(CCO), (S?™o™(coc), (vw) 575 (w)pp°lym(CH2\ pPFPE(CF2) (EJ570 (m) <aTFS / (CP3)^poiym^CCO)*, ^'^(COC)*, 543 (vw) 537 (vw)pP°^m(CH2)*, pPFP£(CF2)* (EJ)a) Relative intensities of observed bands are reported in parentheses: vs: very strong; s: strong: m: medium; w: weak; vw: very weak, sh: shoulder.b) v: stretching; 5: bending; p: rocking, co: wagging; T: twisting, 5sr: scissoring; a: antisymmetric; s: symmetricc) Free: isolated OH group; polym: PEG-PFPE-PEG; Hy: hydrogen bonding cage of OH groups with TFSL.d) The assignment is based on literature references* assignment made in this work

[0054] Reagents

[0055] NOVOZYME®-435, polyethylene glycol) 600 carboxylic diacid (PEG di acid), anhydrous Fluorolink E 10-H (PFPE), and analytical grade methanol were obtained from Strem Chemicals Inc., Sigma Aldrich, Fisher Scientific, and Spectrum Chemicals, respectively. NOVOZYME®-435 was dried for a week in a vacuum oven (10‘2mbar at room temperature), whereas poly(ethylene glycol) 600 diacid and PFPE were dried under turbomolecular vacuum (10'4mbar at room temperature) for two weeks prior to use Dialysis membranes were acquired from Spectrum Laboratories Inc.

[0056] Synthesis of poly(ethylene glycol) 600 diester

[0057] Methanol was added to PEG 600 diacid, a transparent colorless liquid, followed by addition of 3-4 drops of concentrated H2SO4 (37 % v / v) in a round bottom flask. The reaction mixture was stirred at room temperature under inert atmosphere of argon for 24 h. Complete conversion of diacid groups to methyl diester was confirmed by TLC (data not shown). After completion of the reaction, methanol was removed on a rotavapor. The PEG diester was dissolved in chloroform and washed with saturated sodium bicarbonate, followed by water in a separatory funnel to remove the unreacted PEG diacid. The solvent was then removed on a rotavapor PEG diester, also a colorless liquid, was stored in a glove box under argon atmosphere.

[0058] Synthesis of PFPE-PEG-PFPE hetero-oligomer

[0059] PEG diester and PFPE oligomers (both are clear light yellow) were added in a round bottom flask in the ratio of 1: 1 mol / mol, followed by addition of NOVOZYME®-435 (10 wt % with respect to the total mass of the oligomers). The reaction was solvent-free. The reaction mixture was heated in oil bath at 90 °C under vacuum (10‘2mbar) with stirring for 60 h. After completion of the reaction, the copolymer was dissolved in chloroform and NOVOZYME®-435 was removed by filtration The filtrate was concentrated and dialyzed against deionized water (18.2 MQ-cm) using a MWCO 2000 membrane. Dialysis was completed in 24 hours and the deionized water was replaced every' 3-4 hours to maintain a high dialysis rate. The final product was a cloudy, highly viscous liquid, light yellow in color. The CHN elemental analysis performed by Galbraith Laboratories (TN) revealed the following percentages: C 33.50+0.16 %; H 3.41+0.11 %; N <0.5%.

[0060] Synthesis of PFPE-PEG-PFPE / (NaTFSl)x Polymer Electrolytes

[0061] A series of PEs were prepared by dissolving different amounts of NaTFSI (0.1 to 1.21 g) in PFPE-PEG-PFPE (11.00 g) in 100-mL Pyrex bottles. Mixtures were stirred for 24 to 48 h to completely dissolve the salt. Higher salt concentrations used longer stirring time for complete dissolution. See Table IB for the elemental composition of the PEs, mixtures were labelled from Pl to P7, in order of increasing salt concentration. The PEs were light-yellow, cloudy, highly viscous liquids.

[0062] Instruments and Methods

[0063] Nuclear Magnetic Resonance

[0064] NMR spectroscopy was used to characterize the synthesized copolymers and precursor oligomers Perdeuterated methanol (MeOH-d4) was used as solvent to dissolve the samples. Perdeuterated methanol (MeOH-d4) was used as solvent for1H- andl9F-NMR spectral recordings, while deuterated chloroform (CDCh) was used as solvent for thel3C-NMR spectrum recordings.

[0065] Thel9F-NMR spectra were recorded at room temperature using a Bruker Avance III 400 MHz spectrometer, equipped with a 5-mm broadband probe tuned to19F at 376.54 MHz and inverse-gated proton decoupling (400.18 MHz) was applied with the following parameters: a 75 kHz spectral window, a 12-microsecond 90° pulse, 64k data points, a 55-ms acquisition time, a 1,0-s relaxation delay, and 1024 scans. Each spectrum was processed with line broadening.19F chemical shifts were referenced to pure CFCI3. The1H NMR spectra were recorded on a Bruker Avance III 600 MHz with the following parameters: a 12 kHz spectral window, a 30° pulse lasting 3.0 ps, 64k data points, a 2.73- s acquisition time, a 1.0-s relaxation delay, and 16 scans. The spectra were referenced to TMS and processed with 0.3 Hz line broadening.

[0066] The13C NMR spectra were recorded at room temperature using a Bruker Avance III 600 MHz spectrometer with a 5-mm inverse probe tuned tol3C at 150.92 MHz. Power-gated proton decoupling (600.13 MHz) was applied with these settings: a 36 kHz spectral window, a 30° pulse lasting 4.5 microseconds, 64k data points, a 909-millisecond acquisition time, a 2.0-second relaxation delay, and 8192 scans. The spectra were referenced to TMS and processed with 1 Hz line broadening.

[0067] Gel Permeation Chromatography

[0068] Gel permeation chromatography (GPC) experiments were conducted using a TOSOH HLC8320 GPC EcoSEC system equipped with both ultraviolet (UV) and refractive index (RI) detectors to determine the molecular weight distribution parameters of the copolymer. The analysis was performed with a TSKgel SuperHZ column.Tetrahydrofuran (THF) was used as solvent and as the mobile phase with a flow rate set at 0.35 mL / min. The GPC data were calibrated using polystyrene standards.

[0069] Differential Scanning Calorimetry

[0070] The DSC profiles of the copolymer, PEs, and precursor materials were recorded by means of a Shimadzu DSC 60 Differential Scanning Calorimeter equipped with a liquid N2 cooling system. Each sample (about 15-17 mg) was sealed in an Aluminum hermetic pan under Argon atmosphere. The samples were heated at a rate of 10 °C min-’1from ~150 to 100 °C, cooled at the same rate to —150 °C, and then reheated to 100 °C. The samples were kept at ~ 150 and 100 °C for 5 min. Each glass transition temperature (Tg) value was measured based on the second heating cycle as the midpoint temperature of the stepwise change in heat flow (W / g) following linear interpolation. The samples were also heated at a rate of 10 °C min-1from 30 to 350 °C

[0071] Fourier-Transform Infrared Spectroscopy

[0072] A Thermo Scientific Nicolet 6700 FT-IR spectrometer equipped with a Specac MKII Golden Gate ATR cell was used to record spectra of the hetero-oligomer, PEs, and precursor materials in the medium infrared range. Samples were sealed in the A R cell under Argon atmosphere. Every spectrum was obtained by averaging 1024 scans, with a resolution of 4 cm'1, utilizing a TGS detector. The spectra were background-corrected using the OMNIC Spectra software in conjunction with the software IGOR Pro 8. The spectra were decomposed using Gaussian functions by means of a custom-macro in IGOR Pro 8.

[0073] Impedance Spectroscopy

[0074] Impedance Spectroscopy measurements of the PEs were performed using a BioLogic LISA VSP Potentiostat-Galvanostat in the frequency range 100 mHz - 1 MHz. Impedance spectra of the PEs were measured using an Amel 192 conductivity cell within a thermostatically controlled environment, from 10 to 80 °C. Temperature deviations were less than 0.05 °C. Data were obtained in the form of complex impedance—+ iZ"(m) and the equivalent circuit analysis was performed with EC-Lab software.

[0075] Transport Numbers

[0076] The transport numbers of Na+cations within selected PEs were measured using a symmetric assembly consisting of Na| PE | separatorNa packed in a 2032 coin cell. The cell was compressed using a MSK-110 hydraulic crimper in an Argon filled glove box. Using a pellet press die, a disc with a diameter of 16 mm was formed by pressing 30 mg of Na metal onto the surface of a Pt current collector. Pt-supported Na electrodes were used to sandwich a Celgard PTFE separator soaked in 20 pL PE. An electrochemical impedance analyzer (BioLogic USA VSP) was used to measure the chronoamperometric and AC impedance profiles.

[0077] Definitions

[0078] Approximately or about: As used herein, the term “approximately” or “about,” as applied to one or more values of interest, refers to a value that is similar to a stated reference value. In certain embodiments, the term “approximately” or “about” refers to a range of values that fall within 25%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less in either direction (greater than or less than) of the stated reference value unless otherwise stated or otherwise evident from the context (except where such number would exceed 100% of a possible value).

[0079] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they ha ve structural elements that do notdiffer from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

What is claimed is:

1. A method for forming a hetero-oligomer, the method comprising:mixing a polyethylene glycol diester (PEG) and a perfluoropolyether oligomer (PFPE) having a formula of PEG-PFPE-PEG, the mixing occurring in the presence of a Candida antarctica lipase enzymatic catalyst, thereby forming a mixture;heating the mixture to polymerize the PFPE and the PEG, thereby forming a hetero- oligomer (PFPE-PEG-PFPE), andisolating the hetero-oligomer from the lipase enzymatic catalyst.

2. The method as recited in claim 1, wherein the PEG is a polyethylene glycol methyl diester.

3. The method as recited in claim 1, wherein the PEG has an average molecular weight of about 600 g / mol,4. The method as recited in claim 1, wherein the hetero-oligomer has a molecular weight of3881 + 10 g per mol.

5. The method as recited in claim 1, wherein the hetero-oligomer has a molecular weight of between 1,000 and 10,000 g per mol6. The method as recited in claim 1, wherein the hetero-oligomer has a molecular weight of between 1,000 and 5,000 g per mol.

7. The method as recited in claim 1, wherein the hetero-oligomer has a molecular weight of between 2,000 and 4,000 g per mol.

8. The method as recited in claim 1, wherein the hetero-oligomer has a molecular weight of between 3,000 and 4,000 g per mol9. The method as recited in claim 1, further comprising dissolving a sodium salt in the hetero-oligomer such that the sodium salt is present at > 5% by mass.

10. The method as recited in claim 1, further comprising dissolving a sodium salt in the hetero-oligomer such that the sodium salt is present at > 10% by mass.

11. The method as recited in claim 1, further comprising dissolving a sodium salt in the hetero-oligomer such that the sodium salt is present at > 15% by mass.

12. A polymer electrolyte comprising:the hetero-oligomer produced by an enzymatic copolymerization of (1) a polyethylene glycol diester (PEG), (2) a perfluoropolyether oligomer (PFPE) and (3) a Candida antarctica lipase enzymatic catalyst, thereby forming a mixture;, the hetero-oligomer being further mixed with a sodium salt at > 5% by mass.

13. The polymer electrolyte as recited in claim 12, wherein the a NaTFSI is bis(trifluoromethane)sulfonimide sodium salt such that the polymer electrolyte has a formula of PFPE-PEG-PFPE / (NaTFSI)xwherein(0000 < x < 2.160).

14. The polymer electrolyte as recited in claim 13, wherein the NaTFSI is present at > 10% by mass.

15. The polymer electrolyte as recited in claim 13, wherein the NaTFSI is present at > 15% by mass.

16. A method for forming a hetero-oligomer, the method comprising:mixing a polypropylene glycol (PPG) and a perfluoropoly ether oligomer (PFPE) having a formula of PPG-PFPE-PPG, the mixing occurring in the presence of a Candida antarctica lipase enzymatic catalyst, thereby forming a mixture; heating the mixture to polymerize the PFPE and the PPG, thereby forming a hetero- oligomer (PFPE-PPG-PFPE); andisolating the hetero-oligomer from the lipase enzymatic catalyst.

17. The method as recited in claim 16, wherein the PPG is a polypropylene glycol diester.

18. A polymer electrolyte comprising:the hetero-oligomer produced as recited in claim 17;a NaTFSI is bis(trifluoromethane)sulfonimide sodium salt,the resulting polymer electrolyte having a formula of PFPE-PEG-PFPE / (NaTFSI)xwherein(0000 < x < 2.160)

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