## 2 Materials and Methods  
Small-angle neutron scattering (SANS) experiments were performed using the KWS-2 instrument at the JCNS at MLZ in Garching, Germany [1]. The measurements were typically performed using sample-to-detector distances of 1.5, 8, and 20 m, and neutron \(\lambda\) of 5 and 10 A (\(\Delta\lambda/\lambda=10\%\)), to achieve a maximum dynamic \(q\)-range of \(1\times 10^{-3}\)-0.7 A\({}^{-1}\). Scattering data was collected in static and real-time modes. Each raw scattering data set was corrected for detector sensitivity, electronics background, and empty cell contribution and converted to scattering cross-section data using instrument software QtiKWS [15]. Data was then converted to the absolute scale (cm\({}^{-1}\)) through reference to the scattering from a secondary standard sample (Plexiglass). Hydrogenated polyethylene glycol dimethyl ether (hPEGMB, M\({}_{\text{W}}\) = 20,000 g mol\({}^{-1}\) with a polydispersity of D = 1.01) that was synthesized in house [16] was dissolved in deuterated tetrahydrofuran (dTHF, Sigma-Aldrich Chemie GmbH, Munich, Germany) by weighing the components in appropriate amounts to ensure a polymer volume fraction (vol/vol%) \(\phi_{\text{pol}}\) = 2% in the final solution. The solution was first heated to 50 \({}^{\circ}\)C under stirring, to achieve a homogeneous distribution of polymer chains in solution and then transferred into a sample container with ZnSe windows (Laser components GmbH, Olchting, Germany), which is appropriate for simultaneous FTIR and SANS measurements. The sealed sample container with a beam path length of 1 mm was installed in a Peltier-controlled holder of own production that can enable the variation of temperature on the sample between 5 \({}^{\circ}\)C and 130 \({}^{\circ}\)C in a controlled way. To determine the crystallization temperature of PEGDME from the dTHF solution in decreasing temperature, the system was investigated by differential scanning calorimetry (DSC) using a DSC131 EVO Calorimeter (SETARAM Instrumentation, KEP Technologies EMEA, Kirchheim unter Teck, Germany) prior to the simultaneous FTIR and SANS analysis. Uniaxially oriented amorphous deuterated syndiotactic polystyrene (d-sPS) films, about 50 \(\upmu\)m thick, were prepared by quenching a melt of d-sPS in an ice water bath, drawing the melt-quenched film four times at 373 K, and clipping well-oriented portions from the drawn films [17]. d-sPS co-crystal films containing protonated toluene as guest (d-sPS/hTol) were obtained by exposing the oriented amorphous films to a vapor of hTol (Sigma-Aldrich Chemie GmbH, Munich, Germany). The d-sPS/hTol co-crystalline films were transferred into the sample container with ZnSe windows for simultaneous FTIR and SANS analysis at room temperature. In situ FTIR investigations were carried out during the SANS measurements with a JASCO VIR-200 spectrometer (JASCO Deutschland GmbH, Pfungstadt, Germany) installed at the sample position of the KWS-2 in an appropriate geometry that enabled a simultaneous irradiation of the sample using IR and neutron coaxial beams. Polarized IR beams were obtained by using a precision automated PIKE polarizer KRS-5 (PIKE Technologies, Madison, WI, USA). For the in situ DLS measurements, a 15 mg/mL solution of apomyoglobin (apoMb) molten globule was prepared. ApoMb was obtained from horse heart myoglobin (Sigma-Aldrich Chemie GmbH, Munich, Germany) by the butanone method (as performed in [18]) and then refolded by dialysis in 20 mM NaH\({}_{2}\)PO\({}_{4}\)/Na\({}_{2}\)HPO\({}_{4}\) (Sigma-Aldrich Chemie GmbH, Munich, Germany) pH 7 buffer. Before storage in the freezer at \(-\)20 \({}^{\circ}\)C, the solution was lyophilized. To replace the exchangeable protons by deuterium, the freeze-dried apoMb powder was dissolved in heavy water (D\({}_{2}\)O, 99.9% D, Sigma-Aldrich Chemie GmbH, Munich, Germany), incubated for 1 day, and lyophilized again. To obtain the molten globule state of apoMb the powder was dissolved in D\({}_{2}\)O and centrifuged to remove the large aggregates.