Molecular Dynamics in the Crystalline Regions of Poly(ethylene oxide

Article pubs.acs.org/JPCB

Molecular Dynamics in the Crystalline Regions of Poly(ethylene oxide) Containing a Well-Defined Point Defect in the Middle of the Polymer Chain Yury Golitsyn, Martin Pulst, Jörg Kressler, and Detlef Reichert* Faculty of Natural Sciences II, Martin Luther University HalleWittenberg, D-06099 Halle (Saale), Germany S Supporting Information *

ABSTRACT: The chain mobility in crystals of a homopolymer of poly(ethylene oxide) (PEO) with 22 monomer units (PEO22) is compared with that of a PEO having the identical number of monomer units but additionally a 1,4-disubstituted 1,2,3-triazole (TR) point defect in the middle of the chain (PEO11−TR−PEO11). In crystals of PEO22, the characteristic αc-relaxation (helix jumps) is detected and the activation energy of this process is calculated from the pure crystalline 1H FIDs to 67 kJ/mol. PEO11− TR−PEO11 exhibits a more complex behavior, i.e. a transition into the high temperature phase HTPh is noticed during heating in the temperature range between −5 and 10 °C which is attributed to the incorporation of the TR ring into the crystalline lamellae. The crystal mobility of the low temperature phase LTPh of PEO11−TR−PEO11 is in good agreement with PEO22 since helical jump motions could also be detected by analysis of the 1H FIDs and the corresponding values of their second moments M2. In contrast, the high temperature phase of PEO11−TR−PEO11 shows a completely different behavior of the crystal mobility. The crystalline PEO chains are rigid in this HTPh on the time scale of both, the 1H time-domain technique and in 13C MAS CODEX NMR spectroscopy, i.e. the αc-mobility of PEO in the HTPh of PEO11−TR−PEO11 is completely suppressed and the PEO11 chains are converted into a crystal-fixed polymer due to the incorporation of the TR rings into the crystal structure. However, the TR defect of PEO11−TR−PEO11 shows in the HTPh characteristic π-flip motions with an Arrhenius type activation energy of 223 kJ/mol measured by dielectric relaxation spectroscopy. This motion cannot be observed by corresponding 13C MAS CODEX NMR measurements due to an interfering spin-dynamic effect.

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groups,6 amide groups,7 and rigid aromatic8,9 and flexible aliphatic rings,10 which were introduced via acyclic diene methatesis (ADMET) polymerization at specific positions along the PE chains. However, the structural effect of two different types of well-defined point defects on the crystallization behavior of poly(ethylene oxide) (PEO) was also studied: (i) Benzene units were introduced into the PEO chain by reaction of terephthalic acid, phthalic acid, or isophthalic acid with hydroxyl end-caped PEO11,12 under formation of ester bonds and (ii) 1,2,3-triazole (TR) defects were achieved by reaction of azide- and alkyne modified PEO via Cu(I)catalyzed Huisgen-type 1,3-dipolar cycloaddition (CuAAC, “click” reaction).13,14 It should also be noted that there is a report on the influence of TR point defects to the

INTRODUCTION Point defects in polymer chains received some attention in the past. On the one hand, they might be introduced on purpose to control the properties of polymer materials. On the other hand, chain defects might be a result of attempts to create specific chain architectures, as connecting precursors to form welldefined branches, stars or networks. Thus, their effect on crystallinity and crystal size is the object of interest in particular in semicrystalline polymers. Generally, two types of defects can be distinguished: (i) randomly distributed defects which were introduced by random copolymerization of two or more monomers 1,2 or by defects of the stereoregularity in homopolymers;3 (ii) well-defined chain defects which can be introduced by special polymerization techniques. The most prominent polymer under investigation was poly(ethylene) (PE) where both types of defects were studied, i.e., random defects, e.g., obtained by copolymerization of ethylene and propylene2 as well as a plethora of well-defined chain defects, e.g., alkyl groups,4,5 phosphate groups,4 hydrophilic pendant © XXXX American Chemical Society

Received: February 28, 2017 Revised: April 10, 2017 Published: April 11, 2017 A

DOI: 10.1021/acs.jpcb.7b01949 J. Phys. Chem. B XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry B

Figure 1. Structures of (a) PEO22 and (b) PEO11−TR−PEO11. (c) Schematic model for the structural transformation of PEO11−TR−PEO11. This transition from the low temperature phase (LTPh) into the high temperature phase (HTPh) is attributed to the incorporation of the TR rings into the crystal lamellae which occurs upon heating in the temperature range between −5 and +10 °C.

resolution, 13C MAS experiments allow for investigation of motional characteristics of almost every atom of the molecule. Line shape investigations are sensitive to molecular processes on the order of the invers interaction strength of the dominant NMR interaction, which is for 1H about some tens of kilohertz while in 2H experiments, it shifts to fast motions on the order of some 100 kHz. Special 13C MAS experiments can observe even slower motions on the order of some kilohertz.32−34 Motions with characteristic jump rates in the range of 10 Hz to some kilohertz (so-called “slow motions”) can be studied by NMR exchange techniques.35 While the basic concept of the exchange experiment is that of a 2D experiment,36 time saving 1D methods have been developed31,37−40 and successfully applied to a number of polymer applications.41−51 While there are a number of NMR investigations on polyethylene18,24,52−59 and other semicrystalline polymers,31,46,47,60,61 there are, to the best of our knowledge, only few investigations of the αcdynamics in PEO28,62 and these focus on the effect of crystal thickness on chain dynamics. The physical properties of PEO do not only depend on the molar mass of the polymer chains but also on their architecture, e.g., star-PEO,63 branched-PEO,64,65 and PEO networks.66 One convenient synthesis approach to create these topologies, the CuAAC (“click” reaction),66−68 results in the formation of a 1,4-disubstituted 1,2,3-triazole (TR) ring in the polymer chains. In a recent paper,14 we introduced a TR ring as a well-defined point defect in the middle of the linear polymer chain (PEO11− TR−PEO11) and studied its effect on the crystallization behavior. Here, we apply a number of dynamic NMR methods, ranging from improved 1H line shape investigations69 to 13C CODEX experiments.31 The aim is to check if and how the TR ring participates or affects the αc-mobility of the PEO chain segments. Basically, the 13C MAS CODEX method provides enough spectral resolution in order to address the dynamics of different carbon atoms, as in the CH2 groups of the EO monomer units and the two C atoms in the TR ring. However, since the carbon atoms in the TR ring are in direct neighborhood to 14N atoms, a competing spin exchange70 process exists which is called RIDER and which completely masks its molecular dynamics process. Since the TR rings possess a dipole moment which is not aligned in the chain direction, it permits using DR spectroscopy71 to study the reorientation of the TR ring separately. We will demonstrate that the combination of the different methods results in a comprehensive picture of the effect of the well-defined point defect on the αc-relaxation in crystals of PEO11−TR−PEO11.

crystallization of poly(ε-caprolacton) (PCL) at different positions of the polyester chain.15 Most of the investigations focused on structural properties like crystallinity and chain packing. However, there are also a few reports of the influence of crystal defects on the chain mobility of the polymers.16,17 These studies seem to be important since molecular dynamics play also an important role for the properties of semicrystalline polymers.18 For example, it has been shown that the so-called αc-mobility, i.e., the local reorientation of chain segments in the crystallites, is directly related to mechanical properties like flexibility, brittleness, creep,19 and drawability.18 The αc-relaxation is a molecular dynamics process of simultaneous local rotations, resulting in translations of monomeric units of the chains in the crystalline stems and thus in chain diffusion.20 This process is not a translation of the whole chain but it occurs as diffusion of chain defects like kinks along the chain and thus, through the crystal.21−23 A kink at a certain site in the polymer chain propagates by local jump motions along the chain and results in a translation of the chain. While PE is the best investigated polymer with respect to the αc-relaxation,24 PEO also exhibits a relatively fast αc-relaxation which originates from helical-jump motions along the 72 helix.25,26 It should be mentioned that the characteristic helix jump process of PEO can be attributed to a rotation of the helix by an angle of 360° × 2/7 ≈ 102.9° with simultaneous translation of the length of an EO monomer unit in this 72 helix conformation of 2.78 Å since the crystallographic positions have to be unchanged after a helix jump motion.18 Thus, it is an interesting object to study, due to the numerous applications of this polymer. Dielectric relaxation (DR) spectroscopy would be a convenient experimental technique to study the αc-relaxation due to its relative ease and the wide frequency range which can be covered.27 However, because the basic reorientation step of a chain segment in the PEO helix (helical jump) does not change the dipole moment of the EO chain,28 DR spectroscopy is not applicable to study the local molecular chain dynamic in crystalline PEO, leaving solid-state NMR spectroscopy as the most widely used dynamic method that provides a molecular picture of dynamic processes on relevant time scales. The toolbox of dynamic solid-state NMR spectroscopy provides a variety of methods, ranging from simple line-shape investigations29,30 all the way up to sophisticated magic-angle spinning (MAS) exchange techniques.31 The different methods can be distinguished from each other based on their spectral resolution and characteristic time scales which are covered. While 1H experiments provide only a poor or no spectral B


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EXPERIMENTAL SECTION Polymers. Two linear PEO samples with and without, respectively, well-defined point defect in the middle of the chain were employed (see Figure 1, parts a and b). The defect free, methoxy-terminated PEO22 homopolymer had an average of 22 monomer units and was obtained from Sigma-Aldrich. PEO22 has a rather low polydispersity (Mw/Mn) of Đ = 1.03 but crystallizes in two fractions of extended chain crystals.14 Thus, two melting endotherms are observed for the two fractions in the DSC heating trace at 37.8 and 41.3 °C, respectively (see Figure S1, Supporting Information). The PEO sample with a 1,4-disubstituted 1,2,3-triazole (TR) ring in the middle of the polymer chain had 11 monomer units on each side of the TR ring and is named PEO11−TR−PEO11. The polydispersity of this sample is Đ = 1.01. All details of polymer synthesis and characterization are given in ref 14. As also described there, the PEO11−TR−PEO11 sample undergoes a structural transformation at temperatures between −5 and +10 °C upon heating. In the low temperature phase (LTPh), one PEO11 chain is crystalline (72 helix conformation) and the TR rings are excluded from the crystals (cf. Figure 1c). In contrast, the TR rings are part of the crystals in the high temperature phase (HTPh) which is also schematically depicted in Figure 1c. The high temperature phase is additionally stabilized by attractive C−H···π interactions of the aromatic TR rings and thus, the HTPh crystals have also different lattice parameters as compared to the crystals in the LTPh. The melting temperature Tm of the HTPh of PEO11− TR−PEO11 is 22.8 °C. It should also be noted that the phase transition is irreversible, i.e. the HTPh persists even when the sample is cooled from 10 °C again to lower temperatures.14 NMR Spectroscopy. The 1H NMR free-induction decays (FIDs) were measured on a 200 MHz Bruker Avance III spectrometer, equipped with a custom-made static 5 mm probehead. The temperature was controlled with a BVT-3000 heating-device with an accuracy of ±1 °C. The low temperatures have been achieved by means of an AirJet forced air chiller. To estimate the fraction of the crystalline part, singlepulse experiments were applied. The duration of the π/2 pulse was 3.0 μs. In order to detect the fast-decaying signal part arising from the crystalline part of the sample, the probehead has a very short dead-time of 2.5 μs. The recycle delay was chosen such to meet the condition of 5T1 to allow complete restoration of the initial signal. The corresponding relaxation times at every temperature step were estimated by means of the saturation-recovery pulse sequence.72 In total, 32 scans were acquired for each experiment. The samples were melted and then gradually cooled to −40 °C with a cooling rate of about 1−2 K/min in the spectrometer to induce crystallization. After the temperature equilibration process was completed, the 1H NMR FIDs were measured at different temperatures in the range from −40 °C to the melting point of the respective sample. We waited 30 min for temperature stabilization at each temperature step. Additionally, the HTPh of PEO11−TR− PEO11 was investigated over a broad temperature range since the structural transformation was irreversible during recooling from 10 °C as mentioned above. Thus, the applied temperature program for this measurement consisted of the following steps: (i) heating of the sample to 30 °C until complete melting; (ii) cooling to −20 °C (with a cooling rate of 2 K/min) and waiting for 30 min to allow crystallization in the LTPh;

(iii) increasing of the temperature (with a rate of 1−2 K/ min) to 10 °C to transform PEO11−TR−PEO11 crystals into the HTPh modification; (iv) further recooling of the HTPh to −10 °C. The corresponding FIDs were recorded during rereheating from −10 °C until melting of the HTPh phase of PEO11−TR− PEO11 in steps of 5 °C. 13 C-MAS CODEX NMR experiments were performed on a Bruker Avance 400 spectrometer, operating at a 13C Larmor frequency of 100 MHz. A 4 mm double-resonance probehead was used and a MAS spinning frequency of 10 kHz was applied in all experiments. To enhance the weak carbon signal, we employed cross-polarization transfer with a contact time of 0.5−1.0 ms, depending on the actual temperature. The 13C π/2 pulse length varied between 2.5 and 3.0 μs. Recycle delays lasted for 5−7 s at the different temperatures. At least 1024 accumulations were acquired to obtain a reasonable signal-tonoise ratio of the weak TR resonances. Temperatures lower than −20 °C were hardly achievable in the MAS experiments because of the fast sample rotation, which leads to a frictioncaused temperature increase. Thus, we concentrated with these CODEX measurements on the high temperature phase of PEO11−TR−PEO11 and the temperature program described for the 1H FIDs was used to transform PEO11−TR−PEO11 into the HTPh modification (steps i to iv). Then, the CODEX NMR data were acquired during rereheating of this HTPh from −10 °C until final melting. Dielectric Relaxation Spectroscopy. DR spectroscopy was performed with a broadband dielectric spectrometer alpha series from Novocontrol GmbH equipped with a Quatro Cryosystem temperature controller. The PEO11−TR−PEO11 sample was placed between two gold plated electrodes which were separated by 100 μm and the diameter of the electrodes was 20 mm. The applied temperature program was chosen identical to the crystallization studies of PEO11−TR−PEO11 as described in ref 14: after cooling the sample from +30 to −4 °C, the spectra were recorded during reheating in steps of 2 °C under a nitrogen atmosphere. The measurements were taken in the frequency range of 10−1 Hz ≤ ν ≤ 107 Hz.

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RESULTS AND DISCUSSION Component Analysis. In order to determine the phase composition of the samples, i.e., the ratio of crystalline to amorphous chains, single-pulse 1H NMR experiments were performed in the temperature range between −40 °C and the melting temperature Tm. The absolute intensities of the temperature dependent free-induction decays (FID) as a function of time t and temperature Texp are Curie-corrected (FIDnorm) according to FIDnorm(t , Texp) = FID(t , Texp)

melt

FID

Texp 1 (t = 0, Tmelt ) Tmelt (1)

where FIDmelt is the FID at the temperature of the molten material Tmelt. Figure 2a shows the FIDnorm values of PEO11− TR−PEO11 at different temperatures. The 1H NMR experiments distinguish between the different phases by their different mobility in the temperature range Tg < Texp < Tm where Tg is the glass transition temperature. The chains in the amorphous phase are highly mobile, leading to a relatively long FID, while these in the crystalline phase are much less dynamic and have a very specific FID shape. As reported previously,28,73 C


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interphase and amorphous phase, respectively, and are explained in detail below. We now briefly discuss the three different components. The first component is the crystalline phase with low chain mobility and it has a fast decay due to the strong dipole−dipole interaction. Because of the short dead-time of the custom-made probe head, it is possible to detect this fraction of the FIDs almost completely and no elaborate comparison with echo experiments is necessary.74 This component can be fitted by the so-called Abragam function, from which parameters a and b are estimated. The second moment of the line shape of M2 is a quantitative measure of the homonuclear dipolar interaction between protons and is calculated by75 1 M 2 = a 2 + b2 (3) 3 The value of M2 is determined by the intracrystalline structure, e.g. the structural parameters of the helix or the lattice, and its reduction from this value at very low temperatures is the result of the molecular dynamics 69 (ΔMdyn However, as can be seen from Figure 3, the form 2 ).

Figure 2. (a) Curie-corrected 1H FIDs of the PEO11−TR−PEO11 sample at different temperatures. (b) Decomposition of 1H FID at T = 15 °C into different signal fractions according to eq 2.

the semicrystalline polymer PEO can be characterized at temperatures between −50 °C and Tm by even three phases: (i) the immobile crystalline phase, (ii) the interphase between rigid and amorphous fractions, and (iii) the mobile amorphous phase (see Figure 2b). The necessity of taking into consideration a three phase model is provided in the Supporting Information, Figure S2. It is evident that the FIDnorm cannot be fitted with a two phase model in the semicrystalline state demonstrated for the example at 15 °C. The basic idea behind our approach is that the homonuclear dipolar interaction between neighboring protons is determined by the mutual distances but is additionally affected by molecular reorientation. If the internuclear vectors reorient on a time scale which is comparable or shorter than the inverse of the dipolar coupling, the value of the decay time T2* increases and eventually the socalled second moment of the dipolar interaction M2 which is a quantitative measure of its strength, decreases. The three phases in the 1H FID of PEO differ in the mobility of the chain segments which influences the decay time of the FID. The mobile amorphous component decays slower with T2a* whereas the more rigid molecules in the crystal have a shorter decay time T2cr*. The rigid-amorphous interphase has an intermediate decay time T2i*. Thus, the fitting function for the FID signal consists of three distinct components:

Figure 3. Normalized crystalline FIDs of PEO22 for different temperatures. The inset shows the corresponding second moment M2. The straight line represents the static value of M2 for PEO (see text for details).

of the signal changes significantly with increasing temperature and the Abragam function cannot anymore describe the data precisely. For those FIDs which reveale complex behavior, a stretched exponential function is used with a stretching factor for the crystalline phase ranging from 1.6 to 2 (i.e., being close to a Gaussian function). Then the second moment of the line shape is defined from the decay time T2cr* according to 2 M2 = (T2cr*)2 (4)

sin(bt ) + fi bt βi ⎫ ⎧ ⎧ ⎫ ⎞ βa ⎪ ⎪ ⎛ t ⎞ ⎪ ⎪ ⎛ t exp⎨−⎜ ⎟ ⎬ + fa exp⎨−⎜ ⎟ ⎬ ⎪ ⎪ ⎪ ⎪ ⎩ ⎝ T2i* ⎠ ⎭ ⎩ ⎝ T2a* ⎠ ⎭

FIDnorm(t ) = fcr exp{− 0.5(at )2 }

The second component corresponds to the rigid-amorphous phase or interphase. It represents a transition region between solid crystalline and pure amorphous state in terms of dynamics. As shown by spin diffusion measurements,76 the interphase is less ordered and has an irregular shape. A stretched exponential function is used to fit the interphase and amorphous components. The stretching exponents are allowed to vary in the ranges from 1.6 to 2 and from 1 to 1.3 for βi and

(2)

where fcr, f i, and fa are the fractions of the crystalline phase, interphase, and amorphous phase, respectively (fcr + f i + fa = 1). βi and βa are the shape parameters of the decay of the D


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The Journal of Physical Chemistry B βa, respectively. These restrictions stabilize the fitting procedure and for further reliability, the fitting window is limited to 200 μs. At longer times, the inhomogeneity of the B0 field contributes to the shape of the FID signal and might overlay the effect of molecular dynamics. In summary, the fitting is accomplished with three different components of the fitting function and in total, nine fitting parameters are varied. We like to note that there are more robust and simultaneously more time-consuming methods for elucidation of the shape parameter T2* and β. These so-called filtered MNR experiments employ DQ-filtered or MAPE filter with subsequent fixed parameter FID fitting.77 We also applied this technique to selected data sets, however, the results, i.e., the relative phase content and T2* of both procedures, are almost identical, and thus, it is concluded to use the more robust and less elaborate single-pulse experiments. It should be noted that in some systems, e.g., polymer-based nanocomposites, the interface or the rigid-amorphous component is not found in the experimental data, and a two-component fit is applicable.78 Phase Composition as a Function of Temperature. As already mentioned in the previous section, three components of the FID could be identified at temperatures above −50 °C. Because of the significantly different mobility of the molecules belonging to the different phases, the fitting procedure provides reliable and accurate results. When the temperature decreases, the dynamics of the chains in the intermediate areas become more and more restricted, such that at T ≤ −50 °C it is not possible to distinguish between crystalline and “frozen” intermediate phases anymore. As a result, it is only possible to detect an apparent degree of crystallinity by means of NMR FID analyses, to which both the “neat” crystalline phase and the “frozen” intermediate phase contribute. Figure 4a shows the result of the FID decomposition for both samples under investigation. It is obvious that the inclusion of TR ring into the chain resulted in a lower degree of crystallinity. The data show that the apparent crystalline

fraction of PEO11−TR−PEO11 obtained from NMR measurements is about 0.8 while in PEO22 it reached almost 0.9. In addition, the insertion of the TR ring changed the temperature dependence of the crystalline fraction significantly. The crystallinity of PEO22 remains constant up to the melting point while for the PEO11−TR−PEO11 sample, a gradual decrease of the immobile fraction starts already at −5 °C. This can be assigned to the partial melting of the small crystallites, which has also been observed in the DSC experiments.14 The PEO11−TR−PEO11 sample is molten at 25 °C, while PEO22 retained a large degree of crystallinity even at 35 °C. Figure 4b shows the temperature dependence of the relaxation time T2* for PEO22 and PEO11−TR−PEO11. For the crystalline and the interface component, the dynamics is slow and outside the dynamic window of the method and thus, the molecules appear to be static on the experiments time scale and the T2cr* values depend only weakly on temperature. In contract, the dynamics of the molecules of the amorphous fraction is fast enough to affect the T2a* values and thus, a continuous increase of T2a* with temperature is observed, indicating a shortening of the motional correlation time with increasing temperature. Chain Dynamics in Crystalline Domains of PEO22 and PEO11−TR−PEO11. Information on the dynamics of the crystalline phase can conveniently be obtained from the temperature dependence of the 1H free induction decay.69 The experimentally measured FIDs are a superposition of contributions from the different phases. In order to discuss the crystalline signal, the FIDs were decomposed according to eq 2, yielding the signal of the crystalline PEO22 signal separately which is shown for different temperatures in Figure 3. A significant increase of the T2* values with temperature is obvious, however, only the second moment M2 values provide a real quantitative measure of the kinetics. At low temperature (T ≤ −50 °C), the low-temperature value of M2 combines information on the distance between neighboring protons and on small-amplitude motions of the CH2 groups.69 The temperature-induced reduction of its value can be associated with the change of mutual distances by the lattice expansion. In this regime, the behavior of the M2 is described by the equation M2stat(T) = (13500 − 20T/°C) kHz2, which is shown as a line in the inset of Figure 3. At higher temperatures, our measured temperature dependence of M2 cannot be explained by this equation; it deviates substantially from the straight line Mstat 2 . Considering that PEO is a crystal-mobile polymer with αcrelaxation, the accelerated reduction of the M2 values with increasing temperature indicates the onset of the temperature induced motions of the polymer backbone and the averaging of the dipolar interaction by molecular reorientations. “Onset of motion“ means that the characteristic time of the molecular jumps become comparable with the characteristic time scale of the NMR experiment which is roughly the inverse of the static dipolar coupling in a CH2 group, i.e., about some 10 ms. The crystalline signals were fitted simultaneously at all temperatures as described in ref 69, the correlation times τc of the jump motion were determined, and from their temperature dependency (cf. Figure 5), an activation energy of about 67 kJ/mol was calculated. In summary, the dynamics of the crystalline regions of the PEO22 sample is dominated by the αc-relaxation process which is detectable by 1H FID experiments in the temperature range from −40 to +40 °C. The sample PEO11−TR−PEO11 exhibits a more complex dynamic behavior. As shown in Figure 6, the 1H FID second moment M2 does not decrease uniformly with increasing

Figure 4. (a) Phase fractions and (b) T2* values from 1H line-shape experiments for the three phases as defined in eq 2 for the samples PEO22 and PEO11−TR−PEO11. E


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temperature (HTPh) phases. At low temperatures, the TR ring is excludes from the crystal, the crystalline dynamics is similar to that in PEO22 (see Figure 3) and its M2 values decrease with increasing temperature. Between −5 and +10 °C, a new phase (HTPh) appears in which the TR ring is now part of the crystal. If we assume that this insertion hinders the mobility of the polymer chain such that the crystallites appear in the experiment as rigid. Assuming that the fractions of the two phases change between −5 and +10 °C continuously in favor of the HTPh (as suggested by 13C CP MAS NMR spectroscopy data14), the temperature dependence of the M2 values as shown in Figure 6a becomes obvious. With further heating of the sample, the crystalline structure of the HTPh is stabilized, most likely due to attractive C−H···π interactions. This leads to a tighter chain packing and consequently to a larger M2 value at T = 20 °C, as compared to the low-temperature value. Chain Dynamics in Crystals of the High-Temperature Phase of PEO11−TR−PEO11. As reported previously,14 the structural changes occurring in the PEO11−TR−PEO11 crystals are irreversible. As seen by 13C CP MAS NMR spectroscopy14 and the 1H NMR data from Figure 6b, the HTPh remains even after cooling down from +5 to −10 °C. This permits us to investigate the dynamics of the HTPh in the wider temperature range and to describe the effect on the molecular dynamics of the incorporation of the TR ring into the crystal. Figure 6b displays the renormalized FID signals of crystalline component of the HTPh obtained at different temperatures. In contrast to the PEO22 sample, the T2cr* and M2 values of the HTPh of PEO11−TR−PEO11 remain almost unaffected until the melting point is reached. The weak temperature dependence is due to thermal expansion of the crystalline lattice and can be described by M2HTPh(T) = (12200 − 5.4T/°C) kHz2. It implies that the molecular dynamics in the PEO11−TR−PEO11 crystals is heavily restricted and that the helical jumps are now much slower and are not detectable in the dynamic window of the 1H FID. Since the dynamic range of 1H FID experiment is on the order of some tens of kilohertz, the necessity of a dynamic method with a slower dynamic window is apparent. Also, the 1 H FID signal of the crystalline fraction is a superposition of protons of the EO chain segments as well as of the TR ring. The latter contributes only about 1% to the overall 1H signal and the results are thus dominated by the EO segments. Any dynamic signature of the TR rings, differently from the EO chains, is almost impossible to detect in the 1H NMR experiments and thus, a method with a better spectral resolution is needed. The 13C MAS exchange method CODEX serves both purposes well. This dynamic 13C MAS experiment provides a spectral resolution similar to a 13C MAS spectrum and it detects molecular reorientations and provides kinetic parameters as correlation times of motion and jump angles in a range between some hundred microseconds up to some hundreds of milliseconds. The correlation time can be read-off from the so-called τm dependence, where τm is the length of the mixing period which is the period during which the molecular process may happen. The molecular reorientation is detected by the CODEX experiment via the different orientations of the chemical-shift anisotropy (CSA) tensors of a carbon atom before and after.79 After normalization and taking care of spin dynamic effects, the CODEX signal intensity (S/ S0) shows a decay in dependence of τm, and the time constant of this decay is in good approximation equal to the correlation

Figure 5. Comparison of the jump process in the crystalline domain of PEO22 obtained from NMR data and the π-flip motion of the TR ring in the HTPh of PEO11−TR−PEO11 calculated from DR spectroscopy data.

Figure 6. Normalized crystalline FIDs of PEO11−TR−PEO11: (a) complete signal (LTPh and HTPh); (b) signal from HTPh only. The insets show the corresponding second moment M2.

temperature. From about 0 °C, it increases again which is on first glance completely counterintuitive since it would indicate that the mobility becomes slower on increasing the temperature. It can only be explained by the existence of different phases within the crystalline phase. These phases must have a different dynamic behavior and the relative amount of the phases must be temperature dependent. From the 13C MAS data in ref 14, we concluded that the crystalline component includes a mixture of low-temperature (LTPh) and highF


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The Journal of Physical Chemistry B time of motion, τc. This means in turn that, in case no decay is observed, there is no molecular reorientation on the time scale of τm. Figure 7a shows the CODEX signals of all resolved

molecular reorientation. It is due to dipolar coupling between the carbons and a closely neighbored quadrupolar nucleus (in this case the 14N of the TR ring) and the experimentally determined time constant is governed by the T1 of the 14N nucleus. This process completely masks a possibly underlying decay due to a molecular reorientation and thus, no conclusion on the dynamics of the TR ring can be drawn from these data. On the other hand, the 13C CODEX NMR data of the EO units (carbons C5) do not show a decay at all and thus, it must be concluded that these carbons appear rigid up to a time scale of some hundreds milliseconds. Temperature depended CODEX data (Figure 7b) confirm these conclusions: the decay time of the 14N coupled carbons C2 remain approximately constant, resulting from the weak temperature dependence of the 14N T1. The decay of the 13C CODEX NMR signal of carbon C5 does not change either, indicating that up to 10 °C, the EO chains are rigid up to a time scale of about 1 s. It should be noted that the small decay of the 13C CODEX NMR signal of carbons C5−C7 is due to proton-driven spin diffusion,80,81 a spin dynamic process that does not report on molecular reorientation either. It must be concluded from the combined 1H and 13C NMR data that the PEO22 crystals perform in the temperature range between −40 and 30 °C helical jumps with a correlation time on the order of 10 μs to 10 ms while in the HTPh of PEO11− TR−PEO11 crystals, the EO units are rigid or perform jumps which are slower than a second and therefore are not detectable by the CODEX experiment. Obviously, the incorporation of the TR ring into the crystal strongly hinders the reorientation of the EO chains. The question remains whether the TR rings themselves have some molecular dynamic. This question cannot be answered from the NMR data: nor form the 1H data, because the signal of the TR ring is only about 1% of the entire signal and thus undetectable, and neither from the 13C CODEX data, because the RIDER effect completely masks a possible molecular dynamic process. Replacement of the 14N by

Figure 7. (a) 13C CODEX decay curves of different carbons for the HTPh of PEO11−TR−PEO11 at T = 0 °C. (b) 13C CODEX decay curves of the C2 carbon in the TR ring and of the EO groups (C5) in the HTPh of PEO11−TR−PEO11 at different temperatures.

carbon atoms (the line assignment is given as inset in Figure 7, and the spectrum is depicted in Figure S3, Supporting Information). It is obvious that most of the EO segments do not exhibit a decay up to a τm of about 1s, while those carbons in the TR ring and in the EO units adjacent to the ring clearly show a decay with a decay time on the order of some ten milliseconds. The latter might indicate to a molecular reorientation, however, in this case, the decay is due to a spin dynamic process called RIDER70 which does not report on

Figure 8. (a) Derivative imaginary part of the complex dielectric function of PEO11−TR−PEO11 as a function of temperature and angular frequency. The observed relaxation process of the TR rings (π-flips) in the HTPh (8 °C ≤ T ≤ 20 °C) is indicated by an arrow. (b) Derivative imaginary part of the complex dielectric function of PEO11−TR−PEO11 at 20 °C as a function of the angular frequency. The red curve is the fit with the derivative expression of the HN function, eqs 6 and 7, and the decomposed contributions of electrode polarization (green line) and the π-flipping relaxation process (blue curve with the characteristic inverse relaxation time at the peak maximum) are also included. (c) Chain of the crystalline part of PEO11−TR−PEO11 in the HTPh. The dipole moment of the TR ring is shown as orange arrow (drawn according to ref 84). (d) Arrangement of the TR rings in the unit cell of the HTPh of PEO11−TR−PEO11 (top left) as well as their rotations by angles of ≈90°, 180°, and ≈270° as possible relaxations motions (see text for details). The (122) and (122̅ ) Miller planes are shown in brown and green colors, respectively. G


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The Journal of Physical Chemistry B 15

7), the relaxation of the TR rings has to be independent from PEO. Relaxation processes of aromatic rings are called π-flips and are well studied for polymers containing an aromatic ring in the repetitive unit (e.g., poly(ethylene terephthalate) (PET), poly(p-phenyleneterephtalamide) (PPTA) or poly(2-hydroxypropyl ether of bisphenol A) (PHR))85−87 and also for low molecular weight molecules with aromatic groups.88,89 The relaxation time τTR of PEO11−TR−PEO11 at a certain temperature is obtained by fitting of the εder″(ω) data with the derivative expression of the Havriliak−Negami (HN) function82 which is given by

N would be useful; however, this is practically not feasible. Instead, the existence of an electrical dipolar movement in the TR ring paved the path for the application of DR spectroscopy. Because a helical jump does not change the dipole moment of the EO chain,28 these experiments report only on the molecular reorientations of the TR ring. π-Flips in Crystals of the HTPh of PEO11−TR−PEO11. The crystal mobility of PEO11−TR−PEO11 was further investigated by dielectric relaxation spectroscopy. The measured complex dielectric function ε*, also called permittivity, is separated into its real part ε′ and its imaginary part ε″ (ε* = ε′ + iε″ with i = −1 ). Since the data are strongly influenced by electrode polarization in the low frequency range, the onedimensional derivative technique of Wübbenhorst and van Turnhout82 is applied for quantitative data evaluation. The derivative imaginary part of the complex dielectric function εder″ is calculated from the real part of the complex permittivity by εder ″(ω) = −

π ∂ε′ 2 ∂[ln ω]

εder ″(ω) = −

(

π

Δεβγ(ωτTR )β cos β 2 − (1 + γ )θHN

(1 + 2(ωτ

TR )

β

( π)

cos β 2 + (ωτTR )2β

)

(1 + γ )/2

)

(6)

with π ⎛ sin β 2 ⎜ θHN = arctan⎜ π −β ⎝ (ωτTR ) + cos β 2

(5)

( )

where ω is the angular frequency (ω = 2πν) and εder″ is shown as a function of angular frequency and temperature in Figure 8a. This 3D plot can be divided into three major temperature regions, i.e. two transitions appear. The first transition is observed at about 8 °C and is in perfect agreement with the temperature of the structural changes in PEO11−TR−PEO11 where the TR ring is incorporated in the PEO crystal, as already mentioned. The second transition corresponds to the final melting at 22.8 °C.14 However, the curve shapes of εder″(ω) in molten PEO11−TR−PEO11 (T ≥ 24 °C) and of its LTPh (T ≤ 6 °C) are rather identical. Only a strong decrease of εder″(ω) is observed with increasing angular frequency, caused by electrode polarization but no relaxation process is noticed in the measured frequency range. This is typical for a dielectric measurement of PEO since the relaxation processes of amorphous and molten PEO could be detected exclusively in the gigahertz range83 which will not be discussed in this study. However, the helix jumps of crystalline PEO usually have relaxation times in the micro- to millisecond range (see Figure 5 and ref 62) but they cannot be detected by this method since the dipole moment of the 72 helix of PEO is not changing during a helix jump motion process28 which would be necessary for the detection of a relaxation process by dielectric spectroscopy. However, the permittivity curves of the HTPh of PEO11− TR−PEO11 (8 °C ≤ T ≤ 20 °C) are obviously different. An additional relaxation process is noticed at intermediate frequencies (marked by an arrow in Figure 8a). As already mentioned, the difference of this LTPh is that the TR ring is incorporated into the crystal structure. 1,4-disubstituted TR rings have a strong dipole moment (μTR ≈ 4.3 D)84 which is aligned almost perpendicular (cf. Figure 8c) to the lengths axis of the PEO chains according to the postulated structure model of PEO11−TR−PEO11.14 Thus, it might be possible to detect relaxation processes by dielectric spectroscopy and two different opportunities are conceivable: (i) observation of the crystalline αc-relaxation process of PEO where the TR rings act as dipole labels and/or (ii) an independent relaxation process of the crystalline TR rings. Since helix jumps of PEO are ruled out by the temperature dependence of 1H M2 and 13C CODEX NMR experiments (see the discussion above and Figures 6 and

( )

⎞ ⎟ ⎟ ⎠

(7)

where Δε is the dielectric strength (Δε = εs − ε∞), β and γ are shape parameters (0 ≤ β ≤ 1 and β · γ ≤ 1), and εs and ε∞ are the low and high frequency limits of the permittivity, respectively. It should be mentioned that all observed relaxation processes can be fitted with a symmetric derivative expression of the HN function (γ = 1, then also known as derivative expression of the Cole−Cole function27). Since the low frequency region is influenced by electrode polarization effects, this contribution is additionally considered by the term Aω−σ (the shape parameters A and σ are obtained from the low frequency data).71 An example of the fit with the derivative expression of the NH fit to the data at 20 °C is depicted in Figure 8b. It should be noted that the applied method of the one-dimensional derivative technique has no influence of the value of τTR, only the line width of the relaxation peaks is remarkably decreased (peak sharpening). However, by means of a control experiment, the raw data of ε′(ω) and ε″(ω) are additionally fitted by the Cole−Cole function27 and the obtained relaxation times are in good agreement with the data calculated by the derivative technique (cf. Supporting Information, Figure S4). The temperature dependent relaxation times are plotted in Figure 5 and follow an Arrhenius type behavior. Thus, the activation energy Ea is calculated from the slope of the Arrhenius plot multiplied with the gas constant R yielding a value of Ea = 223 kJ/mol. This value is in the typical order of magnitude for activation energies of π-flipping motions of semicrystalline polymers, e.g., in PPTA (Ea = 167 kJ/mol)86 or in a polyimide (Ea = 182 kJ/mol)90 and is much larger than the value obtained for the αc-relaxation of PEO (Ea = 67 kJ/ mol, see Figure 5). This additionally confirms that the observed π-flips of the TR rings are independent from the helix jumps of PEO. A qualitative specification of the π-flip motion by NMR spectroscopy not possible from experimental data, since the 13C CODEX NMR data are strongly influenced by the RIDER effect as discussed above (cf. Figure 7). However, a qualitative estimation could be done from the crystal symmetry since the most important requirement for relaxation processes in polymers is that the crystal symmetry is not changed during H


Article

The Journal of Physical Chemistry B this process.18 The unit cell of the proposed structure model of the HTPh of PEO11−TR−PEO11 has the symmetry group P21/ a;14 i.e., one set of TR rings are arranged in the (122) Miller planes and the other TR rings in the symmetry equivalent (12̅2) Miller planes (cf. Figure 8d). This is an indication that the π-flip motions could be assigned to an rotation of the TR rings around the bond axis by an angle of 180° within the (122) Miller plane or by an angle of ≈90° or ≈270°, respectively into the symmetry equivalent (12̅2) Miller plane as also shown in this figure. It should be mentioned that only a rotation by an angle of ≈90° (right upper image section of Figure 8d) is compatible with the C−H···π interactions of the TR rings. The other two rotations (180° and ≈270°) yield a structure where these interactions are lost. Thus, most probable relaxation movement of the π-flip motions of the aromatic TR rings is a rotation by an angle of ≈90° into the symmetry equivalent Miller plane.

Jörg Kressler: 0000-0001-8571-5985 Detlef Reichert: 0000-0002-6876-1901 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS J.K. and D.R. thank the Deutsche Forschungsgemeinschaft (DFG) for financial support (KR 1714/9-1 and DR 1025/191). Within the cooperation of SFB/TR 102, the authors thank also T. Thurn-Albrecht for providing the broadband dielectric spectrometer and K. Saalwächter for very helpful discussions and suggestions.

■

■

CONCLUSIONS We investigated the influence of a 1,2,3-triazole point-defect in the PEO chain on NMR crystallinity and intracrystalline mobility. 1H FID analyses revealed a lower crystallinity in PEO11−TR−PEO11 as well as a different temperature dependence of the crystallinity, as compared to the homopolymer PEO22. The latter was characterized by a gradual speeding up of the molecular mobility of the crystalline phase (as observed from the decay time T2cr* of the 1H FIDs and the corresponding values of the second moment M2), while the TR containing sample showed a partial melting of crystals and a gradual decrease of the crystallinity. The analyses of the pure crystalline FIDs confirmed for the PEO22 sample the existence of the well-known αc-relaxation process with an activation energy of about 67 kJ/mol. The PEO11−TR−PEO11 sample exhibited a polymorphism with a transition region between −5 and +10 °C. The two phases differed in the location of the TR ring: while in the LTPh, die TR ring was pushed out of the crystal, it was incorporated into the crystal in the HTPh.14 Our data confirmed that the LTPh had similar dynamic behavior as compared to the neat PEO22 while in the HTPh, the EO chains were rigid on the NMR time scale. Since the transition between the phases was irreversible, the HTPh could be studied over a wider temperature range by undercooling. DR spectroscopy proved that the rigid EO chains do not hinder the TR ring in the HTPh from undergoing a π-flip motion with an activation energy of about 223 kJ/mol. This work might also contribute to an understanding of molecular dynamics of poly(ethylene oxide)s where more complicated polymer architectures (e.g., PEO networks) are constructed with junction points of 1,4disubstituted 1,2,3-triazoles.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcb.7b01949. Additional DSC, NMR, and DR spectroscopy data (PDF)

■

REFERENCES

(1) De Rosa, C.; Auriemma, F.; de Ballesteros, O. R.; Resconi, L.; Camurati, I. Crystallization Behavior of Isotactic Propylene-Ethylene and Propylene-Butene Copolymers: Effect of Comonomers Versus Stereodefects on Crystallization Properties of Isotactic Polypropylene. Macromolecules 2007, 40, 6600−6616. (2) Alamo, R. G.; VanderHart, D. L.; Nyden, M. R.; Mandelkern, L. Morphological Partitioning of Ethylene Defects in Random PropyleneEthylene Copolymers. Macromolecules 2000, 33, 6094−6105. (3) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger, B.; Waymouth, R. M. Stereospecific Olefin Polymerization With Chiral Metallocene Catalysts. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143− 1170. (4) 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. (5) Rojas, G.; Berda, E. B.; Wagener, K. B. Precision Polyolefin Structure: Modeling Polyethylene Containing Alkyl Branches. Polymer 2008, 49, 2985−2995. (6) Berda, E. B.; Wagener, K. B. Probing the Effects of Hydrophilic Branch Size, Distribution, and Connectivity in Amphiphilic Polyethylene. Macromol. Chem. Phys. 2008, 209, 1601−1611. (7) Ortmann, P.; Lemke, T. A.; Mecking, S. Long-Spaced Polyamides: Elucidating the Gap between Polyethylene Crystallinity and Hydrogen Bonding. Macromolecules 2015, 48, 1463−1472. (8) Song, S. F.; Miao, W. J.; Wang, Z. B.; Gong, D. R.; Chen, Z. R. Synthesis and Characterization of Precisely-Defined Ethylene-co-Aryl ether Polymers via ADMET Polymerization. Polymer 2015, 64, 76−83. (9) 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. (10) Song, S. F.; Guo, W. Q.; Zou, S. F.; Fu, Z. S.; Xu, J. T.; Fan, Z. Q. Polyethylene Containing Aiphatic Ring and Aromatic Ring Defects in the Main Chain: Synthesis via ADMET and Comparisons of Thermal Properties and Crystalline Structure. Polymer 2016, 107, 113−121. (11) 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. (12) Lee, S. W.; Chen, E. Q.; Zhang, A. Q.; Yoon, Y.; Moon, B. S.; Lee, S.; Harris, F. W.; Cheng, S. Z. D.; vonMeerwall, 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. (13) Mudraboyina, B. P.; Obadia, M. M.; Allaoua, I.; Sood, R.; Serghei, A.; Drockenmuller, E. 1,2,3-Triazolium-Based Poly(ionic

AUTHOR INFORMATION

Corresponding Author

*(D.R.) E-mail: [email protected]. ORCID

Martin Pulst: 0000-0001-5957-9895 I


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(34) Takegoshi, K.; Hikichi, K. Effects of Blending on Local Chain Dynamics and Glass-Transition - Polystyrene Poly(Vinyl MethylEther) Blends as Studied by High-Resolution Solid-State C-13 Nuclear-Magnetic-Resonance Spectroscopy. J. Chem. Phys. 1991, 94, 3200−3206. (35) Hagemeyer, A.; Schmidt-Rohr, K.; Spiess, H. W. 2D-NMR Experiments for Studying Molecular Order and Dynamics in Static and Rotating Solids. Adv. Magn. Opt. Reson. 1989, 13, 85−130. (36) Jeener, J.; Meier, B. H.; Bachmann, P.; Ernst, R. R. Investigation of Exchange Processes by 2-Dimensional NMR- Spectroscopy. J. Chem. Phys. 1979, 71, 4546−4553. (37) Yang, Y.; Schuster, M.; Blumich, B.; Spiess, H. W. Dynamic Magic-Angle Spinning NMR-Spectroscopy - Exchange-Induced SideBand. Chem. Phys. Lett. 1987, 139, 239−243. (38) GerardyMontouillout, V.; Malveau, C.; Tekely, P.; Olender, Z.; Luz, Z. ODESSA, a New 1D NMR Exchange Experiment for Chemically Equivalent Nuclei in Rotating Solids. J. Magn. Reson., Ser. A 1996, 123, 7−15. (39) Reichert, D.; Zimmermann, H.; Tekely, P.; Poupko, R.; Luz, Z. Time-Reverse ODESSA. A 1D Exchange Experiment for Rotating Solids with Several Groups of Equivalent Nuclei. J. Magn. Reson. 1997, 125, 245−258. (40) Luz, Z.; Tekely, P.; Reichert, D. Slow Exchange Involving Equivalent Sites in Solids by One- Dimensional MAS NMR Techniques. Prog. Nucl. Magn. Reson. Spectrosc. 2002, 41, 83−113. (41) Bonagamba, T. J.; Becker-Guedes, F.; deAzevedo, E. R.; Schmidt-Rohr, K. Slow Ester Side-Group Flips in Glassy Poly(alkyl methacrylate)s Characterized by Centerband-Only Detection of Exchange Nuclear Magnetic Resonance. J. Polym. Sci., Part B: Polym. Phys. 2001, 39, 2444−2453. (42) deAzevedo, E. R.; Franco, R. W. A.; Marletta, A.; Faria, R. M.; Bonagamba, T. J. Conformational Dynamics of Phenylene Rings in Poly(p-phenylene vinylene) as Revealed by C-13 Magic-AngleSpinning Exchange Nuclear Magnetic Resonance Experiments. J. Chem. Phys. 2003, 119, 2923−2934. (43) Becker-Guedes, F.; deAzevedo, E. R.; Bonagamba, T. J.; Schmidt-Rohr, K. Solid-State Exchange NMR Characterization of Segmental Dynamics in Glassy Poly(alkyl methacrylate)s. Appl. Magn. Reson. 2004, 27, 383−400. (44) Cossiello, R. F.; Kowalski, E.; Rodrigues, P. C.; Akcelrud, L.; Bloise, A. C.; deAzevedo, E. R.; Bonagamba, T. J.; Atvars, T. D. Z. Photoluminescence and Relaxation Processes in MEH-PPV. Macromolecules 2005, 38, 925−932. (45) Miyoshi, T.; Pascui, O.; Reichert, D. Slow Chain Dynamics in Isotactic-Poly(4-methyl-1-pentene) Crystallites Near the Glass Transition Temperature Characterized by Solid-State C-13 MAS Exchange NMR. Macromolecules 2004, 37, 6460−6471. (46) Miyoshi, T.; Mamun, A.; Hu, W. Molecular Ordering and Molecular Dynamics in Isotactic-Polypropylene Characterized by Solid State NMR. J. Phys. Chem. B 2010, 114, 92−100. (47) Chen, W.; Reichert, D.; Miyoshi, T. Helical Jump Motions of Poly(L-Lactic Acid) Chains in the alpha Phase As Revealed by SolidState NMR. J. Phys. Chem. B 2015, 119, 4552−4563. (48) Wachowicz, M.; White, J. L. Miscible Blend Dynamics and Thermodynamics: Quantitatively Untangling Slow Conformational Events in Amorphous Polymer Mixtures. Macromolecules 2007, 40, 5433−5440. (49) Wachowicz, M.; Gill, L.; Wolak, J.; White, J. L. Polypropylene and Polyethylene-Copolymer Blend Miscibility: Slow Chain Dynamics in Individual Blend Components Near the Glass Transition. Macromolecules 2008, 41, 2832−2838. (50) Wachowicz, M.; Gill, L.; White, J. L. Polyolefin Blend Miscibility: Polarization Transfer versus Direct Excitation Exchange NMR. Macromolecules 2009, 42, 553−555. (51) Gill, L.; Damron, J.; Wachowicz, M.; White, J. L. Glass Transitions, Segmental Dynamics, and Friction Coefficients for Individual Polymers in Multicomponent Polymer Systems by ChainLevel Experiments. Macromolecules 2010, 43, 3903−3910.

liquid)s with Enhanced Ion Conducting Properties Obtained through a Click Chemistry Polyaddition Strategy. Chem. Mater. 2014, 26, 1720−1726. (14) 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. (15) Atanase, L. I.; Glaied, O.; Riess, G. Crystallization Kinetics of PCL Tagged with Well-Defined Positional Triazole Defects Generated by Click Chemistry. Polymer 2011, 52, 3074−3081. (16) Chhajer, M.; Chen, E. Q.; Cheng, S. Z. D. Self-Diffusion Coefficients of Flexible Linear Polymers With Local Inhomogeneities at the Center of Each Chain. J. Macromol. Sci., Part B: Phys. 2001, 40, 615−624. (17) Chen, E.-Q.; Lee, S.-W.; Zhang, A.; Moon, B.-S.; Mann, I.; Harris, F. W.; Cheng, S. Z. D.; Hsiao, B. S.; Yeh, F.; von Meerwall, E. D. Isothermal Thickening and Thinning Processes in Low Molecular Weight Poly(ethylene oxide) Fractions Crystallized from the Melt. Effects of Molecular Configurational Defects on Crystallization, Melting, and Annealing. In Scattering from Polymers. Characterization by X-rays, Neutrons, and Light; Cebe, P., Hsiao, B. S., Lohse, D. J., Eds.; American Chemical Society: 1999; pp 118−139. (18) Hu, W. G.; Schmidt-Rohr, K. Polymer Ultradrawability: The Cucial Role of Alpha-Relaxation Chain Mobility in the Crystallites. Acta Polym. 1999, 50, 271−285. (19) Mansfield, M.; Boyd, R. H. Molecular Motions, AlphaRelaxation, and CHain Transport in Polyethylene Crystals. J. Polym. Sci., Polym. Phys. Ed. 1978, 16, 1227−1252. (20) Boyd, R. H. Relaxation Processes in Crystalline Polymers Experimental Behavior - A Review. Polymer 1985, 26, 323−347. (21) Reneker, D. H. Point Dislocations in Crystals of High Polymer Molecules. J. Polym. Sci. 1962, 59, S39−S42. (22) Reneker, D. H.; Fanconi, B. M.; Mazur, J. Energetics of Defect Motion which Transports Polyethylene Molecules along their Axis. J. Appl. Phys. 1977, 48, 4032−4042. (23) Ewen, B.; Strobl, G. R.; Richter, D. Phase-Transitions in Crystals of Chain Molecules - Relation Between Defect Structures and Molecular-Motion in the 4 Modifications of N-C33h68. Faraday Discuss. Chem. Soc. 1980, 69, 19−31. (24) Hu, W. G.; Boeffel, C.; Schmidt-Rohr, K. Chain Flips in Polyethylene Crystallites and Fibers Characterized by Dipolar C-13 NMR (vol 32, pg 1611, 1999). Macromolecules 1999, 32, 1714−1714. (25) Arlie, J. P.; Spegt, P.; Skoulios, A. Etude de la Cristallisation des Polymeres. 2. Structure Lamellaire et Repliement des Chaines du Polyoxyethylene. Makromol. Chem. 1967, 104, 212−229. (26) Schmidt-Rohr, K.; Spiess, H. W. Multidimensional Solid-State NMR and Polymers; Academic Press: London, 1994. (27) Schönhals, A.; Kremer, F. Analysis of Dielectric Spectra. In Broadband Dielectric Spectroscopy; Springer: Berlin and Heidelberg, Germany, 2003; pp 59−98. (28) Hikichi, K.; Furuichi, J. Molecular Motions of Polymers having Helical Conformation.1. Poly(ethylene glycol) and Polyoxymethylene. J. Polym. Sci., Part A: Gen. Pap. 1965, 3, 3003−3013. (29) Anderson, P. W.; Weiss, P. R. Exchange Narrowing in Paramagnetic Resonance. Rev. Mod. Phys. 1953, 25, 269−276. (30) Baram, A.; Luz, Z.; Alexander, S. Powder Magnetic-Resonance Spectra in Presence of Planar Rotational Jumps. J. Chem. Phys. 1976, 64, 4321−4328. (31) deAzevedo, E. R.; Hu, W. G.; Bonagamba, T. J.; Schmidt-Rohr, K. Principles of Centerband-Only Detection of Exchange in SolidState Nuclear Magnetic Resonance, and Extension to Four-Time Centerband-Only Detection of Exchange. J. Chem. Phys. 2000, 112, 8988−9001. (32) Schmidt, A.; Smith, S. O.; Raleigh, D. P.; Roberts, J. E.; Griffin, R. G.; Vega, S. Chemical-Exchange Effects in the NMR-Spectra of Rotating Solids. J. Chem. Phys. 1986, 85, 4248−4253. (33) Schmidt, A.; Vega, S. NMR Line-Shape Analysis for 2-Site Exchange in Rotating Solids. J. Chem. Phys. 1987, 87, 6895−6907. J


Article

The Journal of Physical Chemistry B (52) McCall, D. W.; Douglass, D. C. Molecular Motion in Polyethylene.V. Appl. Phys. Lett. 1965, 7, 12−14. (53) Olf, H. G.; Peterlin, A. NMR Study of Molecular Motion in Polethylene. Colloid Polym. Sci. 1967, 215, 97−111. (54) Olf, H. G.; Peterlin, A. NMR Study of Molecular Motion in Oriented Long-Chain Alkanes. 2. Oriented Mats of Polyethylene Single Crystals. J. Polym. Sci. B Polym. Phys. 1970, 8, 771−789. (55) Schmidt-Rohr, K.; Spiess, H. W. Chain Diffusion Between Crystalline and Amorphous Regions in Polyethylene Detected by 2D Exchange C-13 NMR. Macromolecules 1991, 24, 5288−5293. (56) Hu, W. G.; Boeffel, C.; Schmidt-Rohr, K. Chain Fips in Polyethylene Crystallites and Fibers Characterized by Dipolar C-13 NMR. Macromolecules 1999, 32, 1611−1619. (57) Kuwabara, K.; Kaji, H.; Horii, F. Solid-State C-13 NMR Analyses for the Structure and Molecular Motion in the Alpha Relaxation Temperature Region for Metallocene-Catalyzed Linear Low-Density Polyethylene. Macromolecules 2000, 33, 4453−4462. (58) Yao, Y. F.; Graf, R.; Spiess, H. W.; Lippits, D. R.; Rastogi, S. Morphological Differences in Semicrystalline Polymers: Implications for Local Dynamics and Chain Diffusion. Phys. Rev. E 2007, 76, 060801. (59) Yao, Y. F.; Graf, R.; Spiess, H.; Rastogi, S. Influence of Crystal Thickness and Topological Constraints on Chain Diffusion in Linear Polyethylene. Macromol. Rapid Commun. 2009, 30, 1123−1127. (60) Miyoshi, T.; Pascui, O.; Reichert, D. Helical Jump Motions in Isotactic Poly(4-methyl-1-pentene) Crystallites Revealed by 1D MAS Exchange NMR Spectroscopy. Macromolecules 2002, 35, 7178−7181. (61) Miyoshi, T.; Hu, W.; Li, Y. J. Dynamic Geometry and Kinetics of Polymer Confined in Self-Assembly via Cooperative Hydrogen Bonding: A Solid-State NMR Study under Paramagnetic Doping. Macromolecules 2010, 43, 4435−4437. (62) Johansson, A.; Tegenfeldt, J. NMR-Study of Crystalline and Amorphous Poly(ethylene oxide). Macromolecules 1992, 25, 4712− 4715. (63) Stowe, M. K.; Liu, P.; Baker, G. L. Star Poly(ethylene oxide) as a Low Temperature Electrolyte and Crystallization Inhibitor. Chem. Mater. 2005, 17, 6555−6559. (64) Hawker, C. J.; Chu, F. K.; Pomery, P. J.; Hill, D. J. T. Hyperbranched Poly(ethylene glycol)s: A New Class of IonConducting Materials. Macromolecules 1996, 29, 3831−3838. (65) Pfefferkorn, D.; Pulst, M.; Naolou, T.; Busse, K.; Balko, J.; Kressler, J. Crystallization and Melting of Poly(glycerol adipate)-Based Graft Copolymers With Single and Double Crystallizable side Chains. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1581−1591. (66) Samiullah, M. H.; Reichert, D.; Zinkevich, T.; Kressler, J. NMR Characterization of PEG Networks Synthesized by CuAAC Using Reactive Oligomers. Macromolecules 2013, 46, 6922−6930. (67) Huisgen, R. Kinetik und Mechanismus 1.3-Dipolarer Cycloadditionen. Angew. Chem. 1963, 75, 742−754. (68) Binder, W. H.; Sachsenhofer, R. ’Click’ Chemistry in Polymer and Materials Science. Macromol. Rapid Commun. 2007, 28, 15−54. (69) Bärenwald, R.; Champouret, Y.; Saalwächter, K.; Schäler, K. Determination of Chain Flip Rates in Poly(ethylene) Crystallites by Solid-State Low-Field H-1 NMR for Two Different Sample Morphologies. J. Phys. Chem. B 2012, 116, 13089−13097. (70) Saalwachter, K.; Schmidt-Rohr, K. Relaxation-Induced Dipolar Exchange With Recoupling - An MAS NMR Method for Determining Heteronuclear Distances Without Irradiating the Second Spin. J. Magn. Reson. 2000, 145, 161−172. (71) Schonhals, A.; Schlosser, E.; Carius, H. E. Dielectric-Relaxtion in Polymer Solids. Acta Polym. 1990, 41, 412−417. (72) Vangeet, A. L.; Hume, D. N. Measurement of Proton Relaxation Times with a High Resolution Nuclear Magnetic Resonance Spectrometer - Direct Method. Anal. Chem. 1965, 37, 983−988. (73) Faucher, J. A.; Koleske, J. V.; Santee, E. R.; Stratta, J. J.; Wilson, C. W. Glass Transitions of Ethylene Oxide Polymers. J. Appl. Phys. 1966, 37, 3962−3964. (74) Schäler, K.; Roos, M.; Micke, P.; Golitsyn, Y.; Seidlitz, A.; Thurn-Albrecht, T.; Schneider, H.; Hempel, G.; Saalwächter, K. Basic

Principles of Static Proton Low-Resolution Spin Diffusion NMR in Nanophase-Separated Materials With Mobility Contrast. Solid State Nucl. Magn. Reson. 2015, 72, 50−63. (75) Fedotov, V.; Schneider, H. Structure and Dynamics of Bulk Polymers by NMR-Methods. NMR Basic Principles Prog. 1989, 21, 1− 176. (76) Roos, M.; Schäler, K.; Seidlitz, A.; Thurn-Albrecht, T.; Saalwächter, K. NMR Study of Interphase Structure in Layered Polymer Morphologies With Mobility Contrast: Disorder and Confinement Effects vs. Dynamic Heterogeneities. Colloid Polym. Sci. 2014, 292, 1825−1839. (77) Kim, S. Y.; Meyer, H. W.; Saalwachter, K.; Zukoski, C. F. Polymer Dynamics in PEG-Silica Nanocomposites: Effects of Polymer Molecular Weight, Temperature and Solvent Dilution. Macromolecules 2012, 45, 4225−4237. (78) Mujtaba, A.; Keller, M.; Ilisch, S.; Radusch, H. J.; ThurnAlbrecht, T.; Saalwachter, K.; Beiner, M. Mechanical Properties and Cross-Link Density of Styrene-Butadiene Model Composites Containing Fillers with Bimodal Particle Size Distribution. Macromolecules 2012, 45, 6504−6515. (79) deAzevedo, E. R.; Hu, W. G.; Bonagamba, T. J.; Schmidt-Rohr, K. Centerband-Only Detection of Exchange: Efficient Analysis of Dynamics in Solids by NMR. J. Am. Chem. Soc. 1999, 121, 8411−8412. (80) Bronniman, C. E.; Szeverenyi, N. M.; Maciel, G. E. C-13 Spin Diffusion of Adamantane. J. Chem. Phys. 1983, 79, 3694−3700. (81) Meier, B. H. Polarization Transfer and Spin Diffusion in SolidState NMR. Adv. Magn. Opt. Reson. 1994, 18, 1−116. (82) Wubbenhorst, M.; van Turnhout, J. Analysis of Complex Dielectric Spectra. I. One-Dimensional Derivative Techniques and Three-Dimensional Modelling. J. Non-Cryst. Solids 2002, 305, 40−49. (83) Sengwa, R. J.; Kaur, K.; Chaudhary, R. Dielectric Properties of Low Molecular Weight Poly(ethylene glycol)s. Polym. Int. 2000, 49, 599−608. (84) Schulze, B.; Schubert, U. S. Beyond Click Chemistry Supramolecular Interactions of 1,2,3-Triazoles. Chem. Soc. Rev. 2014, 43, 2522−2571. (85) Kawaguchi, T.; Mamada, A.; Hosokawa, Y.; Horii, F. H-2 NMR Analysis of the Phenylene Motion in Different Poly(ethylene terephthalate) Samples. Polymer 1998, 39, 2725−2732. (86) Schadt, R. J.; Gardner, K. H.; Gabara, V.; Allen, S. R.; Chase, D. B.; English, A. D. Dynamic Structure of Poly(p-Phenyleneterephthalamide). Macromolecules 1993, 26, 6509−6516. (87) Kaji, H.; Fuke, K.; Horii, F. Two-Dimensional C-13 Magic Angle Turning NMR Analyses of Dynamics in Poly(2-hydroxypropyl ether of bisphenol A). Macromolecules 2003, 36, 4414−4423. (88) Calucci, L.; Zamir, S.; Singer, D.; Zimmermann, H.; Wachtel, E. J.; Poupko, R.; Luz, Z. A Deuterium NMR Investigation of Polymorphism in Benzene Pizzanes. Liq. Cryst. 1997, 22, 1−9. (89) Reichert, D.; Hempel, G.; Zimmermann, H.; Schneider, H.; Luz, Z. Dynamic Carbon-13 MAS NMR: Application to Benzene Ring Flips in Polyaryl Ethers. Solid State Nucl. Magn. Reson. 2000, 18, 17−36. (90) Cheng, S. Z. D.; Chalmers, T. M.; Gu, Y.; Yoon, Y.; Harris, F. W.; Cheng, J. L.; Fone, M.; Koenig, J. L. Relaxation Processes and Molecular-Motion in a New Semicrystalline Polyimide. Macromol. Chem. Phys. 1995, 196, 1439−1451.

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Molecular Dynamics in the Crystalline Regions of Poly(ethylene oxide

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