Molecular Mobility and Phase Composition in ... - ACS Publications

Chapter 11

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Molecular Mobility and Phase Composition in Polyolefins: From Fundamental to Applied Research V. M. Litvinov* DSM Resolve, P.O. Box 18, 6160 MD Geleen, The Netherlands *E-mail: [email protected]

Molecular mobility, phase composition and morphology of polyethylenes (PE), polypropylenes (PP) and random poly(ethylene-co-propylene) (PPR) were studied by solid-state low-field 1H NMR, X-ray, DSC and microscopy methods. Influence of the following factors on the phase composition and molecular mobility is discussed: (1) the effect of the amount and the type of comonomers in PE and PP chains, (2) thermal aging, and (3) deformation. Small changes in the chemical composition, thermal history and mechanical load can significantly influence molecular mobility in the amorphous phase. A series of studies by the author shows that solid-state NMR provides a unique and complementary tool to traditional methods in obtaining information about physical structures and local dynamics in polyolefins. This information is useful to achieve a better understanding of deformation behavior of this class of polymers.

Introduction The physical and mechanical properties of semi-crystalline polymers are significantly influenced by morphology, phase composition and molecular mobility in different phases. Therefore, a quantitative characterization of these meso-/nano-scopic characteristics of semi-crystalline polymers is of great importance to advance our understanding of their properties. In this respect, the phase composition is probably one of the most important morphological parameters, mainly because the amorphous and crystalline phases exhibit vastly © 2011 American Chemical Society In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

different behavior and their relative contributions to the material properties should be accurately known. Numerous 1H, 2H and 13C solid-state NMR studies of polyolefins have provided detailed information on phase structure and morphology, especially with respect to crystalline polymorphs, phase composition, chain conformation, and molecular motions. In this paper, a series of studies of polyolefins using low-field 1H NMR is reviewed. Several examples of methods and applications are provided, which help improve our understanding of the physical structures of polyolefins and the role of the physical structures in the different applications.


Results and Discussion Methods for Crystallinity Determination The most common methods for crystallinity determination are X-ray diffraction, density measurement, and differential scanning calorimetry. Each of these methods is based on a different physical property and gives rise to a different definition of the crystalline phase. In general, crystallinity determination using different methods does not always yield the same result on even the same sample (1) because of the following reasons: (i) The complex morphology of semi-crystalline polymers requires different sets of assumptions for the analysis of the data recorded by different techniques. (ii) The discrimination of the crystalline and amorphous phases is made on the basis of different characteristics, such as the enthalpy of melting (DSC), long range periodicity (WAXD), and the specific volume (density analysis). (iii) The two-phase model, which is traditionally used for determining crystallinity, is rather simplified for the description of semi-crystalline polymers due to the presence of a crystal-amorphous interface or rigid amorphous fraction, which can be detected either as crystalline or amorphous fraction depending on the method used. In other words, the borderline is difficult to draw between crystalline and amorphous phases for different methods. Several experimental methods, such as neutron scattering, dielectric relaxation, calorimetry, and solid-state NMR, have shown that an intermediate layer separates crystalline and amorphous phases, and the properties of this layer, i.e., crystal-amorphous interface (1, 4, 5) or rigid amorphous fraction (6, 7), are intermediate between those for crystalline and amorphous phases. A three-phase model, in which the interface is taken into account, could provide better description of the experimental data. Therefore, the term “phase composition” is perhaps more appropriate than simply “crystallinity” to emphasize the multi-phase nature of semi-crystalline polymers. The interfacial layer is usually thought to be a transitional region located in between the crystals and the mobile amorphous regions. The interface has distinct chain dynamic and is characterized by a degree of order perpendicular to the lamellae surface but disorder in the lateral direction (8). Solid-state NMR is one of the most informative techniques for the characterization of molecular mobility and molecular scale heterogeneity in materials. Over the years, different solid-state NMR methods with relatively basic or sophisticated features were used for the investigation of morphology 180 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


and molecular mobility in polyolefins. 13C NMR spectroscopic methods provide detailed information about molecular mobility in the different phases of PE because of high phase selectivity, which exploits differences in chemical shifts for crystalline and amorphous phases (9–12). However, quantitative studies of phase composition, domain sizes, and molecular mobility in PE by 13C NMR could suffer from a lack of accuracy due to very long 13C T1 value for PE crystals. For the characterization of a large series of samples, one should choose the most robust, convenient and accurate NMR method. 1H NMR T2 relaxometry was widely used for this purpose. The high sensitivity of 1H NMR makes this method very attractive for the characterization of crystallization kinetics (13), premelting behavior (14), and quality control (15). Wide-line 1H NMR and relaxation experiments were frequently applied to study the effect of the chemical structure, molar mass and temperature on the phase composition and molecular mobility (16–20). Phase Composition Analysis by NMR T2 Relaxometry When the term crystallinity is used in connection with low-resolution NMR technique, this refers to the rigid fraction at temperatures well above Tg, i.e., the fraction of material possessing the lowest molecular mobility; this term is also distinguished from semi-rigid (interfacial) and soft non-crystalline phases (either oriented or non oriented) in a material. Characterization of the three-phase structure is important from a theoretical viewpoint, and it is a key factor in determining the overall crystalline structure, the morphology and (thus) the mechanical properties.

Optimum Analysis Temperature for Phase Composition by NMR T2 Relaxometry At room temperature, a significant fraction of the amorphous phase in i-PP and HDPE is rigid. With increasing temperature, molecular mobility begins to increase in the inner/softer part of the amorphous phase towards the lamellae surface resulting in decrease in the amount of the rigid fraction, which is composed of the crystalline phase and the rigid fraction of the amorphous phase (Figure 1). To observe distinct differences in molecular mobility of the crystalline and amorphous phases, and consequently in the T2 relaxation, the temperature of the sample should substantially exceed the dynamic glass transition temperature (Tgd) at the time scale of the NMR experiment, i.e., in the range of 10-4 - 10-5 sec. Since the T2 relaxation experiments should be performed at temperatures well above Tg, the sample exposure to elevated temperatures can cause irreversible changes in the phase composition and in molecular mobility. Therefore, the temperature for the experiments should not be too high to prevent annealing of the sample during the NMR experiment. The amount of the rigid fraction in HDPE (21) and i-PP (22) is almost constant in the temperature range from ~70°C to 100 °C, and its value is close to the crystallinity measured by DSC and X-ray. In this temperature range, the difference in molecular mobility in rigid, semi-rigid and soft fractions is high enough for (i) 181 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

accurate deconvolution of the decay of the transverse magnetization relaxation (T2 decay) into the relaxation components originating from different phases, and (ii) annealing can be avoided during NMR experiments at these temperatures. Therefore, this temperature range is optimal for phase composition analysis in HDPE and i-PP.


Analysis of the Decay of the Transverse Magnetization Relaxation Precautions should be taken for accurate measurements of the T2 relaxation function of materials which are composed of rigid and soft phases, like semicrystalline polymers above Tg of the amorphous phase (23–26). The T2 decay – the time dependence of the Mxy component of the macroscopic magnetization vector - is a weighted sum of T2 decays from phases with distinct difference in molecular mobility. The relative fraction of the T2 relaxation components is proportional to the content of hydrogen in these phases. The T2 relaxation time of these relaxation components allows the determination of relative difference in molecular mobility in different phases and in a series of samples of the same chemical origin. The longer the T2 relaxation time, the larger the frequency (and/or the amplitude) of molecular motions is.

Figure 1. Schematic drawing of the effect of temperature on the amount of rigid, semi-rigid ands soft fractions of melt-crystallized PE, and molecular mobility in these fractions as determined by the analysis of T2 decay.

182 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


Analysis of the phase composition in complex polymeric materials using T2 relaxation data is usually complicated due to several reasons: (a) multiphase/component composition; (b) morphological heterogeneities of materials, such as distribution of domain sizes resulting in a distribution of frequency of molecular motions; (c) spatial heterogeneity of materials on the micrometer scale, which is formed during processing, i.e., heterogeneous distribution of components, differences in morphology through the sample volume because of variation in temperature gradient and flow induced orientation in different parts of a sample, for example in skin layer versus core part; (d) molecular-scale and morphological heterogeneity, which is caused by the chemical heterogeneity, such as molar mass distribution and a variation in the chain composition, chain sequences and tacticity along a single chain; (e) complexity of molecular motions causing a complex shape of the decay of the transverse magnetization relaxation. Because of these reasons, a thorough study of the T2 relaxation as a function of temperature both for a polymeric material and for the separate components that were used for its preparation, is desired for reliable data analysis. The theoretical description of the T2 decay shape for semicrystalline polymers above the Tgd is still under debate and a purely phenomenological analysis of the decay shape with two- or more components is commonly used. Different functions were used for describing the T2 decay for semicrystalline polyolefins (20, 26–31). The shape of the relaxation component for the crystalline phase was described either by an Abragamian or a Gaussian function. A Gaussian, Weibull or an exponential function was used to describe the T2 relaxation of the crystal-amorphous interface. The relaxation of the soft amorphous fraction was described either with a single exponential or a sum of two exponential functions. It should be noted that the phase composition, as characterized by the NMR method, is affected to some extent by the temperature of the experiment (25), and by a fitting function used for the deconvolution of the T2 decay into the separate components (13, 20, 30, 32). Nevertheless, the amount of rigid phase, which is determined from the T2 relaxation analysis, corresponds rather well with crystallinity values obtained by other methods.

Temperature Dependence of Phase Composition and Molecular Mobility in Polyolefins

1. HDPE, Ethylene-Octene Copolymer (m-PE) and i-PP The three-phase model provides the most appropriate description of the phase composition in HDPE (21) and i-PP (22) at temperatures of ~70 - 100 °C. Above these temperatures, the phase composition is affected by annealing and partial melting. Crystallinity values, as determined by the NMR method, are in good agreement with those determined for the same samples using SAXS. Crystallinity of m-PE is significantly lower than that of HDPE (33). Above room temperature, 183 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

crystallinity of m-PE with 30 wt% octane chain units gradually decreases with increasing temperature and approaches zero at 70°C.


2. Random Poly(Ethylene-co- propylene) (PPR) The phase structure of PPR is more complex than that of i-PP due to the presence of small amount of ethylene chain units in the main chain, as well as atactic propylene chain units. Four different phases/fractions with different molecular mobility are determined at 110°C by the T2 relaxation method (26): (i) crystalline phase, (ii) semi-rigid crystal-amorphous interface, (iii) soft fraction of the amorphous phase, and (iv) small amount of the amorphous fraction, which has molecular mobility similar to that of rubbers.

3. Thermoplastic Vulcanizates (TPV) Composed of i-PP, EPDM, and Paraffinic Oil TPV’s are rubbery materials, which are processable as thermoplastics but exhibits properties similar to those of vulcanized rubbers at usage temperatures. TPV’s are produced by dynamic vulcanization of blends containing a thermoplast and an elastomer. At 110 °C, the NMR relaxation method allows us to perform a rather accurate determination of the amount of different phases/components of TPV – namely, crystalline and amorphous phases of PP, EPDM and paraffinic oil – and molecular mobility in these phases (34). Crystallinity of PP is hardly affected by the TPV’s composition and is close to 70 wt %. A small fraction of oil molecules plasticizes the amorphous phase of PP and the plasticization effect is proportional to oil : PP mass ratio in the TPV composition. Results suggest that a thin interfacial layer is formed by propylene-rich chain fragments of EPDM of EPDM/oil rubbery phase and by PP chains of the PP phase. The interface is the source of physical junctions, which are formed at the shell of EPDM rubber particles and at the surface of PP particles occluded in the EPDM phase. NMR allows quantitative determination of the network density in the rubbery phase of the TPV’s (34). The network structure is formed by chemical crosslinks, physical junctions at the EPDM/PP interface, temporary and trapped chain entanglements. The total network density in EPDM rubbery phase is affected by the following changes in the TPV composition: (i) the network density increases with increasing amount of the crosslinker per weight unit of EPDM; (ii) decreases with increasing oil content because of chain disentanglements; and (iii) increases with increasing PP/EPDM weight ratio due to an increase in the density of physical junctions at the EPDM/PP interface. The EPDM network density largely influences the translational and rotational mobility of oil molecules; i.e. the higher the crosslink density, the more the mobility of oil molecules is hindered. Some relationships between the TPV composition, network density and mechanical properties are established (34).



Domain Size Determination by NMR Spin-Diffusion Experiments Traditionally, transmission electron micrograph (TEM) and small-angle X-ray scattering (SAXS) are two major techniques used to determine the lamellar thickness. The former offers the advantage of direct access to the morphology. SAXS is a well-developed method to quantitatively determine the thicknesses of alternating layers of the crystalline and amorphous regions of the lamellae morphology. The NMR experiments permit unambiguous identification of the three-phase morphology due to a large difference in the relaxation behavior of the chain units in mobile amorphous fraction, semi-rigid crystal-amorphous interface and crystalline phase (21, 22). The domain thickness in HDPE and i-PP, which is determined by NMR in the temperature range from ~70 to 100°C, is in good agreement to those measured by SAXS and TEM on the same sample. The thickness of the interface is nearly constant in the studied temperature range and equals 1.1 – 1.3 nm. This value is in the same range as previously estimated for PE value by Monte Carlo simulations (35). It should be noted that the interface thickness is close to the length of the statistical segment of PE and i-PP chains, which consists of 6 – 7 carbon–carbon bonds and equals to ~0.8 nm for fully extended polyolefinic chain. Therefore, distinct differences in molecular mobility in different fractions of HDPE are apparently caused by short-range correlations of chain motion due to the short length of the statistical segment.

The Effect of Annealing on Phase Composition, Molecular Mobility, and Domain Sizes Annealing at Temperatures Close to Melting Temperature Range Chain rearrangements upon prolonged annealing of HDPE and i-PP at elevated temperatures result in an increase in the lamellar thickness at the expense of the interfacial layer and the soft amorphous phase (21, 22). Annealing also causes a decrease in molecular mobility in the crystalline phase due to perfecting of the crystalline order. Lamellae thickening and a slight increase in the crystallinity would cause additional slippage of chain entanglements towards the inner part of inter-lamellar amorphous regions causing additional immobilization of the soft fraction of the amorphous phase. The following mechanism of morphological changes during annealing at elevated temperatures is suggested. Upon approaching the melting temperature, molecular mobility increases both in the amorphous phase, the crystal-amorphous interface, and in the crystalline phase. An increase in molecular mobility is accompanied by partial melting of small crystals and less ordered fragments of lamellae. An increased mobility in the amorphous phase and chain diffusion in and out of the crystals (αc-relaxation) facilitates structural reorganizations, which occur in the amorphous layer adjacent to the lamella surface, causing a continuous shift of the interface towards the inner part of the amorphous regions and thus reducing the thickness of the amorphous layer and increasing the lamellae thickness. The thickness of rigid (crystalline) domains increases linearly as a function of the logarithm of the annealing time, 185 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

which is in good agreement with theoretical predictions and experimental results for other polymers (36, 37).


Aging of i-PP at Temperatures Slightly Exceeding Tg A significant change in impact strength, flexural modulus and dimensions of injection molded part, which are made from i-PP, occurs upon prolonged aging at ambient temperature (38). The exact origin of these changes is not well understood. NMR T2 relaxation experiments has helped in understanding this phenomenon (38). Molecular mobility of the rigid fractions, which at 28°C is composed of crystalline phase and rigid amorphous fraction, is hardly affected by aging for 1000 hours. The amount of the rigid fraction increases by ~1–2 wt%. Aging causes a significant decrease in molecular mobility in the soft amorphous fraction. This decrease can be caused by two different phenomena: (i) the formation of small crystals in inter-spherolitic amorphous domains during the secondary crystallization, and (ii) an increase in the density of the amorphous phase due to relaxation of residual stresses. The results obtained suggest that aging-induced changes in the macroscopic properties of injection molded articles largely originate from a decrease in molecular mobility in the amorphous phase.

Long Term Aging at Elevated Temperatures and Hydrostatic Pressure One of the important applications of random propylene copolymers (PPR) is the production of hot water pipes. The pipes can be used under hydrostatic pressure and at elevated temperatures up to 70°C continuously for 50 years and for a short time at 80°C. Breakage of pipes can occur if aging time at a certain temperature exceeds that of the specification. It has been shown that 1H NMR T2 relaxation analysis is the most sensitive tool for determining changes in PPR samples that are caused by storage of PPR pipes at these conditions (26). The long term aging causes the following changes in the phase composition and molecular mobility. The crystallinity increases by ≤5% with increasing storage temperature. The amount of semi-rigid and soft amorphous fractions slightly decreases upon storage at the expense of the highly mobile chain fragments in the amorphous phase, which have a higher concentration of ethylene comonomer units than chain fragments in the soft amorphous fraction. The following processes, which occur in PPR due to exposure to hydrostatic pressure at elevated temperatures, are suggested (26). (i) Creep upon hydrostatic pressure causing chain elongation in the amorphous phase. (ii) The increase in crystallinity, which can occur due to the attachment of chain fragments in the amorphous phase to existing crystals and/or due to the formation of new crystals. In both cases, mobility in the amorphous phase decreases due to a decrease in the chain length between adjacent crystals, i.e., the length of tie molecules. (iii) A better phase separation of ethylene-rich chain fragments from the PP matrix. The better phase separation results in an additional decrease in molecular mobility in the PPR matrix, since more mobile chain fragments with ethylene chain units, 186 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

if they are mixed on the molecular scale with PP chain fragments, cause some increase in molecular mobility of the PP matrix due to intermolecular coupling of chain motions. All these changes cause embrittlement of pipes followed by their breakage. It was shown that the combination of DSC and NMR relaxometry is a powerful tool for the investigation of the molecular origin of damages in broken PPR pipes and fittings, and for estimating their usage temperature and time.

The Effect of Deformation on Phase Composition, Molecular Mobility, and Domain Sizes


Ethylene Copolymers Changes in phase composition and molecular mobility were studied for vulcanized semi-crystalline ethylene-octene copolymer (m-PE) and amorphous EPDM rubber using a specially designed device, which made it possible to perform NMR experiments under fixed uniaxial compression and to record applied force (33). These two samples differ as regards network structure, i.e., EPDM has a larger density of chemical crosslinks, whereas the total network density in m-PE is significantly larger because small crystallites act as physical network junctions. These differences in the network structure largely influence the elastic properties. Despite the larger total network density in m-PE, strain-induced orientation of EPDM chains in compressed sample is significantly greater, suggesting that the density of chemical crosslinks largely determines the elastic behavior. Crystallinity of m-PE does not increase upon compression. It appears that compression causes rearrangements of crystallites due to chain detachment from the crystal surface and its attachment to neighboring crystals. It can be concluded that physical network junctions, which originate from chains anchoring to crystallites, would not be efficient in bearing the force, and the applied force is mainly carried by chemical crosslinks and trapped chain entanglements. Thus, an increase in the density of chemical crosslinks is required for improvement the elastic recovery (the compression set) of m-PE. It has been demonstrated that 1H NMR T2 relaxation experiments under uniaxial compression can provide useful information to help in a better understanding the viscoelastic behavior of heterogeneous elastomeric materials, such as semi-crystalline polymers, filled elastomers, thermoplastic elastomers and thermoplastic vulcanizates.

Isotactic Polypropylene Changes in phase composition, molecular mobility and domain thickness in uniaxially stretched i-PP have been investigated as a function of temperature, draw ratio (λ), drawing temperature and drawing rate (39). The NMR experiments have been performed on samples after strain recovery. For the drawing temperature range between 25 and 110°C, typical ductile deformation behavior with a yield point, neck formation and propagation, and strain hardening have been found. 187 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

The Effect of Drawing Rate Deformation-induced changes in the phase composition and molecular mobility are hardly affected by changes in drawing speed which is varied from 1 to 100 mm/min. This suggests that chain rearrangements, which lead to changes in morphology and physical structures upon drawing, are fast as compared to the total time scale of deformation used, or the effect of drawing speed diminishes during strain recovery.


The Effect of Drawing Ratio Drawing to λ = 7, which corresponds to beginning of the strain hardening, causes a small increase in the amount of the rigid fraction, which indicates the presence of highly strained tie molecules in the amorphous phase. Upon increase in λ from 10 to 16, a further increase in the amount of the rigid fraction is observed. This increase can be attributed to strain-induced crystallization and/or large immobilization of chains in the amorphous phase. At λ = 7, molecular mobility in the semi-rigid and soft fractions is already largely decreased, and it continues to decrease up to the highest draw ratio.

The Effect of Drawing Temperature Drawing temperature has a large effect on the strain-induced transformation of the spherulitic morphology of i-PP to fibrillar morphology. The amount of the rigid fraction increases with increasing drawing temperature for all draw ratios. Molecular mobility in crystalline and amorphous phases is lower at higher deformation temperatures. Relative differences in imperfections in the crystalline structure can be identified by comparing T2 relaxation time for the rigid fraction T2r. At the same λ, T2r is longer at lower deformation temperatures. This indicates larger imperfections in the crystalline phase of i-PP, which is stretched at 25°C, as compared to the undeformed sample. At drawing temperature of 25°C, the long period and the thickness of the rigid domains slightly decrease at the expense of the thickness of the semi-rigid and soft domains, which suggests defragmentation and disordering of crystals. At higher drawing temperatures, an increase in the long period and lamellae thickness is observed upon increasing the draw ratio and drawing temperature, whereas the thickness of amorphous layer, which separate adjacent crystals, slightly decreases. As far as molecular mobility is concerned, it decreases with increasing draw ratio both in the rigid and soft phases. The decrease is more pronounced at higher deformation temperatures, which points out a more perfect structure organization due to partial melting followed by recrystallization at higher deformation temperatures. The observed changes in the phase composition and molecular mobility suggest that faster rate of chain motions in the crystalline phase (αc-relaxation) facilitates transformation of the spherulitic morphology to a fibrillar one. Moreover, partial melting followed by strain-induced crystallization can possibly occur at higher temperatures. 188 In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.

Conclusions


A series of studies of polyolefins shows that solid-state low-field 1H NMR provides a powerful and complementary tool to traditional methods to obtain information about physical structures, the phase composition, molecular mobility in different phases. Even small changes in the chemical composition, thermal history and a mechanical load can significantly influence molecular mobility in the amorphous phase. This information is useful to achieve a better understanding of yield and deformation behavior of polyolefins. If more detailed information about physical phases and their chemical origin is required, high-field 13C NMR spectroscopy should be used .

Acknowledgments The studies of the author were sponsored by DSM and SABIC-Europe. The author thanks D. Demco, C. Hedesiu, K. Remerie, M. Soliman, G. Vanden Poel, R. Kleppinger, R. Deblieck, W. Gijsbers, B. Blümich and V. Mathot for collaboration on topics presented in this paper.

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Isasi, J. R.; Mandelkern, L.; Galante, M. J.; Alamo, R. G. J. Polym. Sci., Polym. Phys. 1999, 37, 323. Baker, A. M. E.; Windle, A. H. Polymer 2001, 42, 667. Hiss, R.; Hobeika, S.; Lynn, C.; Strobl, G. Macromolecules 1999, 32, 4390. Iwata, K. Polymer 2002, 43, 6609. Sajkiewicz, P.; Hashimoto, T.; Saijo, K.; Gradys, A. Polymer 2005, 46, 513. Schick, C.; Wurm, A.; Mohammed, A. Thermochim. Acta 2003, 396, 119. Androsch, R.; Wunderlich, B. Polymer 2005, 46, 12556. Gautman, S.; Balijepalli, S.; Rutledge, G. C. Macromolecules 2000, 33, 9136. Schmidt-Rohr, K.; Spiess, H. W. Macromolecules 1991, 24, 5288. Hillebrand, L.; Schmidt, A.; Bolz, A.; Hess, M.; Veeman, W.; Meier, R. J.; Van der Velden, G. Macromolecules 1998, 31, 5010. Kuwabara, K.; Kaji, H.; Tsuji, M.; Horii, F. Macromolecules 2000, 33, 7093. Litvinov, V. M.; Mathot, V. B. F. Solid State Nucl. Magn. Reson. 2002, 22, 218. Kristiansen, P. E.; Hansen, E. W.; Pedersen, B. J. Phys. Chem. B 1999, 103, 3552. Kristiansen, P. E.; Hansen, E. W.; Pedersen, B. Polymer 2000, 41, 311. Tanzer, C. I.; Roy, A. K. Proc. SPE ANTEC ’95: Boston, MA, USA 1995, 2, 2700. Bergmann, K. J. Polym. Sci., Polym. Phys. 1978, 16, 1611. Fedotov, V. D.; Abdrashitiva, N. A. Polym. Sci. USSR 1985, 27, 287. Kakudate, T.; Kakizaki, M.; Hideshima, T. J. Polym. Sci.: Polym. Phys. 1985, 23, 787. Eckman, R. R.; Henrichs, P. M.; Peacock, A. J. Macromolecules 1997, 30, 2474. 189

In NMR Spectroscopy of Polymers: Innovative Strategies for Complex Macromolecules; Cheng, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2011.


20. Hansen, E. W.; Kristiansen, P. E.; Pedersen, B. J. Phys. Chem. B 1998, 102, 5444. 21. Hedesiu, C.; Kleppinger, R.; Demco, D. E.; Buda, A.; Blümich, B.; Remerie, K.; Litvinov, V. M. Polymer 2007, 48, 763. 22. Hedesiu, C.; Demco, D. E.; Kleppinger, R.; Vanden Poel, G.; Gijsbers, W.; Blümich, B.; Remerie, K.; Litvinov, V. M. Macromolecules 2007, 40, 3977. 23. Zhang, L.; Hansen, E. W.; Helland, I.; Hinrichsen, E.; Larsen, A.; Roots, J. Macromolecules 2009, 42, 5189. 24. Mauri, M.; Thomann, Y.; Schneider, H.; Saalwächter, K. Solid State Nucl. Magn. Reson. 2008, 34, 125. 25. Litvinov, V. M.; Penning, J. P. Macromol. Chem. Phys. 2004, 205, 1721. 26. Litvinov, V. M.; Soliman, M. Polymer 2005, 46, 3077. 27. Tanaka, H.; Inoue, Y. Polym. International. 1993, 31, 9. 28. Dadauli, D.; Harris, R. K.; Kenwright, A. M.; Say, B. J.; Sünnetçioĝlu, M. M. Polymer 1994, 35, 4083. 29. Dujourdy, L.; Bazile, J. P.; Cohen-Addad, J. P. Polym. Int. 1999, 48, 558. 30. Schreurs, S.; François, J. P.; Adriaensens, P.; Gelan, J. J. Phys. Chem. B 1999, 103, 1393. 31. Weglarz, W. P.; Peemoeller, H.; Rudin, A. J. Polym. Sci., Part B: Polym. Phys. 2000, 38, 2487. 32. Kenwright, A. M.; Say, B. J. In NMR Spectroscopy of Polymers; Ibbett, R. N., Ed.; Blackie Academic & Professional: London, 1993; p. 231. 33. Litvinov, V. M. Macromolecules 2001, 34, 8468. 34. Litvinov, V. M. Macromolecules 2006, 39, 8727. 35. In’t Veld, P. J.; Hütter, M.; Rutledge, G. C. Macromolecules 2006, 39, 439. 36. Peterlin, A. Polymer 1967, 6, 25. 37. Sanchez, I. C.; Peterlin, A.; Egy, R. K.; McCrackin, F. L. J. Appl. Phys. 1974, 45, 4216. 38. Hedesiu, C.; Demco, D. E.; Kleppinger, R.; Vanden Poel, G.; Remerie, K.; Litvinov, V. M.; Blümich, B.; Steenbakkers, R. Macromol. Mater. Eng. 2008, 293, 847. 39. Hedesiu, C.; Demco, D. E.; Remerie, K.; Blümich, B.; Litvinov, V. M. Macromol. Chem. Phys. 2008, 2009, 734.


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