Letter Cite This: ACS Macro Lett. 2017, 6, 1207-1211
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Chain Tilt and Crystallization of Ethylene Oxide Oligomers with Midchain Defects Martin Pulst,† Christian Schneemann,† Paweł Ruda,† Yury Golitsyn,† Ann-Kathrin Grefe,‡ Bernd Stühn,‡ Karsten Busse,† Detlef Reichert,† and Jörg Kressler*,† †
Faculty of Natural Sciences II, Martin Luther University Halle-Wittenberg, D-06099 Halle (Saale), Germany Institute of Condensed Matter Physics, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
‡
S Supporting Information *
ABSTRACT: Many text books and publications do not focus on the necessity of chain tilting in crystalline lamellae of oligomers and polymers, a fundamental aspect of their crystallization already discussed by Flory. Herein we investigate the chain tilt of ethylene oxide oligomers (EOs) containing various midchain defects by WAXS, SAXS and solid state 13C MAS NMR spectroscopy. At low temperatures, one out of the two EO chains of EO9-meta-EO9 and EO11-TR-EO11 containing a 1,3disubstituted benzene or a 1,4-disubstituted 1,2,3-triazole defect in central position of the oligomer chain forms crystals and the other EO chain as well as the defect remain in the amorphous phase. The aromatic midchain defect of these two oligomers can be incorporated into the crystalline lamella upon heating below Tm. Then, the adjoining amorphous EO chain crosses from the lamellae to the amorphous regions at an angle ξ, which is preordained by the substitution pattern of the aromatic defect, revealing that the chain tilt angle ranges between 36° ≤ ϕ ≤ 60°.
U
chain,9−13 a regular insertion of defects is necessary to modify the solid-state properties of polymers with larger molar mass (so-called precision polymers).14−16 However, chain tilting in these defect containing oligomers or polymers has not yet been addressed properly. Obviously, the oligo or polymer chains are bent at the defect at a preordained bend angle ξ, which can deliberately be varied with both the type of the defect as well as its substitution pattern.9−11 Thus, the bend angle of the defect might have a significant influence to the chain tilt angle ϕ, and it might pave the path for a new method in addition to the conventional scattering6,7 and spectroscopic17 techniques for determination of chain tilt angles. In this study we propose the introduction of designed defects coupling two ethylene oxide oligomer (EO) chains to study the chain tilt angle ϕ in the crystals. This concept is also based on our previous result11,12 that a 1,4-disubstituted 1,2,3-triazole (TR) midchain defect (EO11-TR-EO11, cf. Figure 1c) can be
nderstanding of crystallization processes is of fundamental importance for a plethora of applications of oligomers and semicrystalline polymers.1−3 While most traditional schematic models1−5 show the crystalline oligomer or polymer chains aligned parallel to the lamella thickness Lc (cf. Figure 1a), recent sophisticated experimental and computational studies on oligomeric n-alkanes,6 as well as polyethylene,7,8 establish that the crystalline oligomer and polymer chains are tilted at an angle ϕ to the lamella thickness (see Figure 1b), a necessity already discussed by Flory.5 The chain tilt in the lamellae decreases the density of the amorphous chains leaving the crystals at its surface, and thus, the amorphous chains have a much lower density than the chains within the crystalline lamellae. The chain tilt angle depends on the crystal surface, which is optimized by the packing of end groups and the chains crossing from the crystals to the amorphous regions.6 Obviously, there is an additional contribution of chain folds when present.5,7 However, the crystallization behavior of macromolecules can be deliberately influenced by the insertion of defects into their chains. While a single defect can significantly influence the crystallization of an oligomer © XXXX American Chemical Society
Received: September 26, 2017 Accepted: October 12, 2017
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DOI: 10.1021/acsmacrolett.7b00757 ACS Macro Lett. 2017, 6, 1207−1211
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Figure 1. (a) Schematic model of a defect free oligomer lamella without chain tilt in the crystalline regions (ϕ = 0°) and (b) corresponding model where the crystalline chains are tilted at an angle ϕ to the lamella thickness Lc. (c−f) Structures of the oligomers under investigation containing either 1,2,3-traizole or benzene midchain defects with their respective bend angles ξ.
Figure 2. EO9-meta-EO9 (a) WAXS diffraction pattern after crystallization at T = −20 °C and during reheating in steps of ΔT = 5 °C. The inset is a zoom of the diffraction pattern at T = 0 °C. The two prominent EO reflections are marked by their Miller indices and the arrows indicate the appearing reflections. (b) 13C MAS CP NMR spectra obtained after crystallization at T = −20 °C and during reheating in steps of ΔT = 5 °C. The inset shows a comparison of the CP spectrum at T = 0 °C (blue line) and the corresponding SP spectrum (gray line) of the molten sample at T = 15 °C.
incorporated into the EO crystal close to its surface since its size is similar to the diameter of an EO 72 helix. In contrast, it has been known that benzene rings in the middle of EO chains are completely excluded from the EO crystal when disubstituted in ortho (1,2-), meta (1,3-), or para (1,4-) position and linked via ester bonds to the oligomer chains.10 Thus, we choose to introduce differently disubstituted benzene rings to the EO chains via ether bonds (cf. Figure 1d−f) with reduced space requirement compared to the ester bonds. However, because of their different substitution patterns, the benzene defects might also govern the direction of the chains leaving the crystals when located close to the crystal surface. Thus, the influence of these aromatic midchain defects and the corresponding bend angles on the crystallization behavior of EO with respect to the chain tilt in the lamellae is investigated by wide and small-angle X-ray scattering (WAXS and SAXS) as well as solid state 13C magic angle spinning (MAS) crosspolarization (CP) and single pulse (SP) NMR spectroscopy. There is EO9-meta-EO9 (cf. Figure 1e) containing a 1,3disubstituted benzene ring in the middle of the oligomer chain, which is synthesized by coupling of two EO monomethyl ether chains (having an average of 9 EO monomer units each) with α,α′-dibromo-m-xylene (details of synthesis and characterization are given in the Supporting Information, pages S-2−S8). A bend angle of ξ = 120° results from the substitution pattern of EO9-meta-EO9. Temperature-dependent WAXS diffractograms (see page S-9 in the Supporting Information for experimental details) are shown in Figure 2a. After crystallization at T = −20 °C, two prominent Bragg reflections appear at 2θ = 19.5° and 23.5°, which belong to the (120) and (032)* ((032)* means an overlapping of (032), (13̅ 2), (112), (2̅12), (1̅24), (2̅04), and (004) reflections18,19) Miller planes of the monoclinic unit cell of EO20 constituted of four 72 helices. However, the intensity ratio of these two reflections is unusual since the (120) reflection has normally a lower intensity compared to the (032)* reflection. Simulation results (described in the Supporting Information, Figure S9) show that this is explainable by a translational motion of the EO chains within the unit cell caused by the defect, which has no significant influence on the chain tilt. The crystallinity X is calculated by comparing the integral intensity of the total diffraction pattern with the integral intensities of all Bragg reflections after subtraction of the amorphous halo using X’Pert
HighScore software. X is marginally lower than 50% indicating that one EO9 chain belongs to the crystal (extended chain due to low molar mass21) and the other EO9 chain as well as the benzene ring are excluded from the crystal. However, two additional Bragg reflections are observed at 2θ = 16.6° and 20.8° (marked by black arrows in Figure 2a), whose intensities are increasing upon heating until final melting at Tm = 14.2 °C (see Table S2). The new reflections do neither belong to the diffractions patterns of crystals containing 72 helices20 nor to crystals formed by planar zigzag conformations22 of EO chains. Thus, further studies are necessary for an adequate explanation of the crystallization behavior of EO9-meta-EO9. 13 C MAS CP and SP NMR spectroscopy experiments are performed to investigate the origin of the new Bragg reflections and shown in Figures 2b and S11 (for experimental details and line assignment see Figures S12−S14, Supporting Information). After crystallization at T = −20 °C, the typical resonances of EO (δ = 72.6 ppm (methylene groups) and δ = 59.1 ppm (methoxy end groups)) appear in the CP spectrum where almost exclusively the carbons with a slow molecular dynamics are detected. Since these resonances are also found in the SP spectrum (cf. Figure S11), which is sensitive to mobile (usually amorphous or liquid above the glass transition temperature) species, the NMR data confirm that one EO9 chain is crystalline and the other one remains amorphous at this temperature. Furthermore, a complex line shape is detected for the CP NMR signals of the benzene rings (125 ppm ≤ δ ≤ 140 ppm) at T = −20 °C consisting of broad components and some small sharp resonances. The broad signal belongs to the disordered benzene rings in the amorphous regions on the lamella surface while the sharp peaks indicate that a few benzene rings are already part of the crystals at this temperature. When comparing the CP spectrum at T = −10 °C with an almost quantitative fully relaxed single-pulse MAS experiment at the same temperature (see Figure S15), it turns out that the broad components actually are remains of well resolved lines at the positions of the benzene rings in the mobile amorphous state, indicating a substantial amount of mobility of these benzene rings, which are not included in the crystals. The mobility of these rings suppresses their appearance in the CP spectra and 1208
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Figure 3. (a) Schematic model of the incorporation of the benzene rings (green hexagons) into the tilted lamellae of EO9-meta-EO9 upon heating below Tm. The arrangement of the unit cells within the lamellae is indicated by the pink lines and the schematic relation between the bend angle ξ and the chain tilt angle ϕ (ξ + ϕ = 180°) is included. (b) Monoclinic unit cell of the crystalline part of the oligomer. The carbon atoms of the benzene rings are highlighted in green color and the directions of the adjoining amorphous EO chain are shown as orange lines. The pink unit cell axes are highlighted to indicate the position of the unit cell in the schematic model. (c) Relation between bend angle ξ of the midchain defects and the possible chain tilt angle ϕ for the four oligomers under investigation (see text for details). The range of ϕ for defect free EO proposed by Schmidt-Rohr et al.7 is shown in red color. (d) Background corrected SAXS traces of EO9-meta-EO9 after crystallization at T = −20 °C and during reheating in steps of ΔT = 5 °C.
leaves only the observed broad features. During heating, the resonances of EO remain unchanged but the resonances of the benzene ring undergo a transformation, that is, the proportion of the broad NMR signals decreases and, simultaneously, the intensities of the sharp resonances increase. Though this is qualitatively well apparent from Figure 2b, we present a quantitative line-shape analysis of the CP spectra in the Supporting Information (Figure S16). This indicates the transfer of the benzene rings of EO9-meta-EO9 from the amorphous phase to the crystalline lamellae upon heating (see the schematic model in Figure 3a). It is additionally supported by the different chemical shift of the sharp benzene resonances in the CP spectrum at T = 0 °C compared to the values of molten EO9-meta-EO9 in the SP spectrum at T = 15 °C (see inset of Figure 2b), emphasizing π−π interactions23 between the benzene rings within the crystals. Thus, the incorporation of the aromatic midchain defects is also the explanation for the appearance of the new WAXS reflections in the same temperature range (cf. Figure 2a) and might pave the path for a quantitative calculation of chain tilt angle. We construct the structural model for benzene-containing crystals of EO9-meta-EO9 in order to gain details of the arrangement of the aromatic rings and, thus, also on the chain tilt angle in the lamellae. The calculations using BIOVIA Materials Studio Reflex software result in a monoclinic unit cell with the space group P21/a and the cell parameters of a = 8.09 Å, b = 12.83 Å, c = 39.98 Å, and β = 125.45° (all details of a similar procedure are described in our recent work11 and in the Supporting Information on pages S-17−S-18). Then, the positions of the aromatic benzene rings within the unit cell of EO9-meta-EO9 are refined and the obtained unit cell and the simulated WAXS diffraction pattern are shown in Figures 3b and S17a, respectively. Furthermore, the two appearing reflections at 2θ = 16.6° and 20.7° can be assigned to the (111) and (113) Miller planes and their symmetry analogues, respectively, which represent intermolecular distances between the benzene rings (cf. Figures S18 and S19). Thus, the chain defects have fixed positions within the unit cell close to the crystal surface. The amorphous EO chains leave the unit cell
(orange lines in Figure 3b) with a predetermined angle as defined by the substitution pattern of the midchain defect, that is, by the bend angle ξ between the crystalline and the adjoining amorphous chain. According to the schematic model and under consideration of the arrangement of the unit cell within the lamellae (mauve lines in Figure 3a), the chain tilt angle ϕ in the crystalline lamellae can be approximated from the bend angle ξ since the sum of both angles is 180° as schematically depicted in Figure 3a. A value of ϕ = 60° is obtained for EO9-meta-EO9 (ξ = 120°) and it is slightly larger than the values estimated by Schmidt-Rohr et al.7 who proposed a chain tilt angle range between 41° ≤ ϕ ≤ 52° (see Figure 3c) for defect free low molar mass EO. Additional SAXS measurements depicted in Figure 3d support the proposed structure model (experimental details can be found in the Supporting Information). A scattering peak is observed at q* = 0.097 Å−1 in the SAXS trace recorded at T = −20 °C corresponding to a long period (d = 2π/q*) of d = 64.5 Å together with its weak second order maximum at 2q*, indicating a lamellar structure. Analysis of data with the correlation function method allows to determine thicknesses of crystalline and amorphous layers separately. At T = −20 °C, Lc is found to be 23.6 Å. It increases upon heating to 0 °C by about ΔLc = 4.7 Å, which is comparable to the size of a disubstituted benzene ring (≈ 4.9 Å24). Upon melting (T ≥ 0 °C), a more complicated behavior is observed, i.e. a broad scattering peak appears at q′ = 0.05 Å−1 (d = 116 Å), indicating that structures with larger distances are formed upon melting. In our recent work,11,12 the crystallization behavior of EO11TR-EO11 (cf. Figure 1c) was investigated, and the corresponding structure model is rather similar to this of EO9-meta-EO9 (cf. Figure S22). Thus, the crystalline chains of EO11-TR-EO11 are tilted at an angle of ϕ = 36° (ϕ = 180° − ξ, with ξ = 144°), which is in perfect agreement with the chain tilt determined from the monoclinic angle of the unit cell11 (ϕ = β − 90°) of ϕ = 35.4°, revealing that the structural model is excellently suitable for the calculation of ϕ from the bend angle of the midchain defect. Furthermore, the calculated chain tilt angle of EO11-TR-EO11 confirms that also these small tilt angles (marginally lower than the values for defect free EO 1209
DOI: 10.1021/acsmacrolett.7b00757 ACS Macro Lett. 2017, 6, 1207−1211
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ACS Macro Letters determined by Schmidt-Rohr et al.,7, see Figure 3c) can be realized in EO lamellae. For analysis of the validity of the traditional crystalline− amorphous model without chain tilt (ϕ = 0°, cf. Figure 1a), a linear unbent EO (ξ = 180°) containing a 1,4-disubstituted benzene ring (EO9-para-EO9, cf. Figure 1f) was studied. Figure 4a,b shows the WAXS diffraction patterns and NMR spectra,
but neither a peak shift nor additional resonances occur indicating that the midchain defect of EO9-para-EO9 cannot incorporate into the crystals upon heating. As in all other oligomers, the crystallization at T = −20 °C starts with the packing of EO helices into the monoclinic unit cell and the formation of lamellae with tilted chains. SAXS measurements reveal a tilt angle of ϕ = 38° at this temperature (cf. Figure S21a), which indicates that the ab plane of the unit cell is the lamella surface.17,25,26 The incorporation of the 1,4-disubstituted benzene ring and the second EO9 chain into the crystal is prohibited for two reasons: (i) The crystal surface is in average formed by equal amounts of benzene rings and −OCH3 end groups, which stops further EO crystallization at low temperatures due to density arguments. (ii) The chain tilt prevents the incorporation of the defect upon heating since a 1,4disubstituted benzene ring would require lamellae where the chains are aligned parallel to the lamella thickness (ϕ = 0°, cf. Figure 3c). Thus, the prevented incorporation of the 1,4disubstituted benzene defect confirms the chain tilt governed by the monoclinic angle of the unit cell. The traditional model where the oligomer chains are aligned parallel to the lamella thickness (Figure 1a) is not applicable for this linear unbent EO9-para-EO9. EO9-ortho-EO9 containing a 1,2-disubstituted benzene ring in central position of the oligomer chain was studied as a control experiment and the corresponding WAXS diffraction patterns and solid state NMR spectra are shown in Figure 4c,d, respectively. The bend angle of ξ = 60° (see Figure 3c) is not in the range of an adequate value for an incorporation into the lamellae with tilted EO chains (ϕ = 27°, cf. Figure S21b), that is, the second oligomer chain would interfere with the crystal structure. Thus, it is not surprising that only EO chains can crystallize and neither additional reflections are detected by WAXS (Figure 4c) nor additional sharp resonances of the midchain defect are observed in the 13C MAS CP NMR spectra upon heating below Tm (Figure 4d). This perfectly verifies the results of the other three samples under investigation in context of the discussed chain tilt. In conclusion, we investigated the chain tilt of ethylene oxide oligomers employing midchain defects using WAXS, SAXS and solid-state 13C MAS NMR spectroscopy. EO9-meta-EO9 and EO11-TR-EO11 form lamella crystals at low temperatures, where one EO chain crystallizes and the defects as well as the other EO chain are widely excluded from the crystals. The midchain defects incorporate upon heating below Tm into the lamellae, which allows direct calculation of the chain tilt angle from the substitution pattern of the aromatic midchain junctions, that is, the chains in the crystalline lamellae are tilted at an angle ranging between 36° ≤ ϕ ≤ 60°. In contrast, the midchain defects of EO9-para-EO9 and EO9-ortho-EO9 cannot be incorporated into the crystalline lamellae upon heating, which is prevented by packing constrains caused by the respective substitution pattern of these midchain defects. Particularly, the prevented incorporation of the 1,4-disubstituted midchain defect of EO9-para-EO9 indicates that also this linear unbent EO forms tilted lamellae, as confirmed by SAXS measurements.
Figure 4. (a, c) WAXS diffraction patterns of EO9-para-EO9 and EO9ortho-EO9, respectively, after crystallization at T = −20 °C and during reheating in steps of ΔT = 5 °C. (b,d) 13C MAS CP NMR spectra of EO9-para-EO9 and EO9-ortho-EO9, respectively, obtained after crystallization at T = −20 °C and during reheating in steps of ΔT = 5 °C. The insets show the comparisons of the CP spectra at T = 0 °C (blue lines) and the corresponding SP spectra (gray lines) of the molten oligomers at T = 15 °C.
respectively. After crystallization at T = −20 °C, the characteristic (120) and (032)* reflections are observed by WAXS and the determined degree of crystallinity is close to 50%, indicating that in complete analogy to EO9-meta-EO9, one EO9 chain belongs to the crystal and the other one as well as the aromatic defect remain in the amorphous phase. During heating, the diffraction patterns do not change significantly, that is, only a slight shift of the reflections with increasing temperature is noticed caused by thermal expansion, but additional reflections do not appear until final melting at Tm = 14.5 °C. The WAXS data are supported by the corresponding 13 C MAS CP NMR spectra (cf. Figure 4b) since the CP spectrum at T = −20 °C shows only sharp resonances for the crystalline EO chains and the NMR signals of the amorphous benzene rings are broad (slightly less broad than the corresponding CP NMR spectra of EO9-meta-EO9, since all four protonated carbons have an identical chemical shift as a result of the different substitution pattern, cf. Figures S12− S14). This is also not changing during heating, only a slight temperature-related sharpening of all resonances is detected,
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.7b00757. 1210
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Containing a Well-Defined Point Defect in the Middle of the Polymer Chain. J. Phys. Chem. B 2017, 121, 4620−4630. (13) Ahamed, B. N.; Van Velthem, P.; Robeyns, K.; Fustin, C.-A. Influence of a Single Catenane on the Solid-State Properties of Mechanically Linked Polymers. ACS Macro Lett. 2017, 6, 468−472. (14) Song, S.-F.; Guo, Y.-T.; Wang, R.-Y.; Fu, Z.-S.; Xu, J.-T.; Fan, Z.Q. Synthesis and Crystallization Behavior of Equisequential ADMET Polyethylene Containing Arylene Ether Defects: Remarkable Effects of Substitution Position and Arylene Size. Macromolecules 2016, 49, 6001−6011. (15) Zheng, Y.-R.; Tee, H. T.; Wei, Y.; Wu, X.-L.; Mezger, M.; Yan, S.; Landfester, K.; Wagener, K.; Wurm, F. R.; Lieberwirth, I. Morphology and Thermal Properties of Precision Polymers: The Crystallization of Butyl Branched Polyethylene and Polyphosphoesters. Macromolecules 2016, 49, 1321−1330. (16) Mudraboyina, B. P.; Obadia, M. M.; Allaoua, I.; Sood, R.; Serghei, A.; Drockenmuller, E. 1,2,3-Triazolium-Based Poly(ionic liquid)s with Enhanced Ion Conducting Properties Obtained through a Click Chemistry Polyaddition Strategy. Chem. Mater. 2014, 26, 1720−1726. (17) Kim, I.; Krimm, S. Tilted-Chain Lamellar Morphology in Initially Crystallized Low Molecular Weight Poly(ethylene oxide) from Raman Longitudinal Acoustic Mode Spectra. Macromolecules 1994, 27, 5232−5234. (18) Lai, C.-Y.; Hiltner, A.; Baer, E.; Korley, L. T. J. Deformation of Confined Poly(ethylene oxide) in Multilayer Films. ACS Appl. Mater. Interfaces 2012, 4, 2218−2227. (19) Zhu, L.; Cheng, S. Z. D.; Calhoun, B. H.; Ge, Q.; Quirk, R. P.; Thomas, E. L.; Hsiao, B. S.; Yeh, F.; Lotz, B. Crystallization Temperature-Dependent Crystal Orientations within Nanoscale Confined Lamellae of a Self-Assembled Crystalline-Amorphous Diblock Copolymer. J. Am. Chem. Soc. 2000, 122, 5957−5967. (20) Takahashi, Y.; Tadokoro, H. Structural Studies of Polyethers, (-(CH2)m-O-)n. X. Crystal Structure of Poly(ethylene oxide). Macromolecules 1973, 6, 672−675. (21) Buckley, C. P.; Kovacs, A. J. Melting Behaviour of Low Molecular Weight Poly (ethylene-oxide) Fractions I. Extended Chain Crystals. Prog. Colloid Polym. Sci. 1975, 58, 44−52. (22) Takahashi, Y.; Sumita, I.; Tadokoro, H. Structural Studies of Polyethers. IX. Planar Zigzag Modification of Poly(ethylene oxide). J. Polym. Sci. Polym. Phys. Ed. 1973, 11, 2113−2122. (23) Shen, X.; Hu, W.; Russell, T. P. Measuring the Degree of Crystallinity in Semicrystalline Regioregular Poly(3-hexylthiophene). Macromolecules 2016, 49, 4501−4509. (24) Cox, E. G. Crystal Structure of Benzene. Rev. Mod. Phys. 1958, 30, 159−162. (25) Brubach, J. B.; Ollivon, M.; Jannin, V.; Mahler, B.; Bourgaux, C.; Lesieur, P.; Roy, P. Structural and Thermal Characterization of Monoand Diacyl Polyoxyethylene Glycol by Infrared Spectroscopy and XRay Diffraction Coupled to Differential Calorimetry. J. Phys. Chem. B 2004, 108, 17721−17729. (26) Baltá Calleja, F. J.; Hay, I. L.; Keller, A. Diffraction Effects in Single Crystals and Spherulites of Poly(ethylene oxide). Kolloid Z. Z. Polym. 1966, 209, 128−135.
Details of synthesis and characterization, as well as additional WAXS, SAXS, DSC, and solid state NMR spectroscopy data (PDF).
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Martin Pulst: 0000-0001-5957-9895 Detlef Reichert: 0000-0002-6876-1901 Jörg Kressler: 0000-0001-8571-5985 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank the SFB TRR 102, Project B07, as well as Deutsche Forschungsgemeinschaft (DFG), Projects KR 1714/ 9-1 (J.K.) and RE 1025/19-1 (D.R.) for financial support. We acknowledge also Wolfgang H. Binder and S. Tanner for the support with the MALDI-ToF measurements within the cooperation of SFB TRR 102.
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REFERENCES
(1) De Rosa, C.; Auriemma, F. Crystals and Crystallinity in Polymers: Diffraction Analysis of Ordered and Disordered Crystals; Wiley: Hoboken, NJ, 2014. (2) Strobl, G. The Physics of Polymers; 3rd ed.; Springer: Berlin; Heidelberg, 2007. (3) Strobl, G. From the Melt via Mesomorphic and Granular Crystalline Layers to Lamellar Crystallites: A Major Route Followed in Polymer Crystallization? Eur. Phys. J. E: Soft Matter Biol. Phys. 2000, 3, 165−183. (4) Wunderlich, B. Macromolecular Physics - Crystal Structure, Morphology, Defects; Academic Press: New York; London, 1973. (5) Flory, P. J. On the Morphology of the Crystalline State in Polymers. J. Am. Chem. Soc. 1962, 84, 2857−2867. (6) Hoffman, J. D.; Miller, R. L. Kinetics of Crystallization from the Melt and Chain Folding in Polyethylene Fractions Revisited: Theory and Experiment. Polymer 1997, 38, 3151−3212. (7) Fritzsching, K. J.; Mao, K.; Schmidt-Rohr, K. Avoidance of Density Anomalies as a Structural Principle for Semicrystalline Polymers: The Importance of Chain Ends and Chain Tilt. Macromolecules 2017, 50, 1521−1540. (8) Yeh, I.-C.; Lenhart, J. L.; Rutledge, G. C.; Andzelm, J. W. Molecular Dynamics Simulation of the Effects of Layer Thickness and Chain Tilt on Tensile Deformation Mechanisms of Semicrystalline Polyethylene. Macromolecules 2017, 50, 1700−1712. (9) Lee, S.-W.; Chen, E.; Zhang, A.; Yoon, Y.; Moon, B. S.; Lee, S.; Harris, F. W.; Cheng, S. Z. D.; van Meerwall, E. D.; Hsiao, B. S.; et al. Isothermal Thickening and Thinning Processes in Low Molecular Weight Poly(ethylene oxide) Fractions Crystallized from the Melt. 5. Effect of Chain Defects. Macromolecules 1996, 29, 8816−8823. (10) Chen, E.-Q.; Lee, S.-W.; Zhang, A.; Moon, B.-S.; Honigfort, P. S.; Mann, I.; Lin, H.-M.; Harris, F. W.; Cheng, S. Z. D.; Hsiao, B. S.; et al. Isothermal Thickening and Thinning Processes in Low Molecular Weight Poly(ethylene oxide) Fractions Crystallized from the Melt 6. Configurational Defects in Molecules. Polymer 1999, 40, 4543−4551. (11) Pulst, M.; Samiullah, M. H.; Baumeister, U.; Prehm, M.; Balko, J.; Thurn-Albrecht, T.; Busse, K.; Golitsyn, Y.; Reichert, D.; Kressler, J. Crystallization of Poly(ethylene oxide) with a Well-Defined Point Defect in the Middle of the Polymer Chain. Macromolecules 2016, 49, 6609−6620. (12) Golitsyn, Y.; Pulst, M.; Kressler, J.; Reichert, D. Molecular Dynamics in the Crystalline Regions of Poly(ethylene oxide) 1211
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