Lamellar thickness of crystallizable ethene runs in ethene-propene copolymers by solid state NMR

Crystallizable runs of ethene in ethene-propene copolymers can be identified in ¹³C CPMAS NMR spectra as a resonance at 33 ppm. In the absence of spin diffusion, the variation in intensity of this resonance with a ¹H spin lock will reflect the intrinsic T^H_1ρ. Spin diffusion leads to a more complex relaxation decay, which reflects the local polymer morphology. Simulations of the spin diffusion process have been carried out for a simplified two-phase model for the morphology with the aim of determining whether the lamellar thickness of the crystalline and amorphous regions can be found from the T^H_1ρ observed via the ¹³C NMR spectrum. Calculations covering the expected range of the input parameters, namely the spin diffusion coefficients, domain lengths, and intrinsic relaxation times, show that, providing the intrinsic relaxation time in the amorphous phase is known, an accurate estimate of the crystalline and amorphous lamellar thicknesses can be made. Analysis of simulated T^H_1ρ decays indicate that, in general, the time constant of the fastest decaying component can be identified with the intrinsic relaxation time of the amorphous phase. © 1994 John Wiley & Sons, Inc.     

Rotating frame proton spin-lattice relaxation measurements of poly(ethylene oxides)

Measurements of T_1ρ as a function of temperature have been made on three polyethylene oxides (PEO) with molecular weights of 550, 6000, and 2.8 × 10⁶ in order to try to elucidate various problems arising in the interpretation of previous T₁ measurements on PEO. In contrast to the T₁ measurements, the T_1ρ measurements show discontinuities at the melting or softening points of the respective polymers concerned, and also show nonexponential magnetization decay in the case of PEO 6000 and 2.8 × 10⁶, which is presumbly due to the existence of “mobile” and “crystalline” regions, in qualitative agreement with NMR studies and x-ray measurements. Motional correlation frequencies and activation energies have been derived where possible by using the BPP theory adapted to the rotating frame and also the strong collision Slichter-Ailion theory. There is reasonable correlation with other data on motional frequencies where it is available, although the overall situation for the so-called α transition in PEO 6000 and 2.8 × 10⁶ is still not clear. It is suggested that spin-diffusion is an important mechanism for all three polymers; for PEO 550 because it contains CH₃ endgroups which act as sinks, and for the other two polymers where the mobile fraction performs the same function.     

Correlation between local mobility and mechanical properties of high‐speed melt‐spun nylon‐6 fibers

This article establishes the processing–microstructure–motion–property relationship of high‐speed melt‐spun nylon‐6 fibers. From solid‐state ¹H NMR T_1ρ (spin–lattice relaxation time in the rotating frame) relaxation studies, all nylon‐6 fibers spun at 4500–6100 m/min showed three‐component exponential decay with the time constants T_1ρ,I, T_1ρ,II, and T_1ρ,III, indicating that there existed three different motional phases. These phases were assigned to immobile crystalline, intermediate rigid amorphous, and mobile amorphous regions. The determination of the correlation time (τ_c) of the respective phases provided information about the local molecular mobility of each phase with respect to the spinning speed. As the spinning speed increased, τ_c of the crystalline region increased (4500–5200 m/min) and then reached a plateau. However, τ_c for the rigid amorphous region increased from 5200 m/min onward, indicating that the rigid amorphous chains were more oriented and constrained in the spinning speed range of 5500–6100 m/min. The drastic increase of the maximum thermal stress for all fibers from 5500 to 6100 m/min was coincident with the τ_c characteristics of the rigid amorphous region. The significant increase in tenacity and Young's modulus and the large decrease in elongation at break at 5500–6100 m/min were also in good agreement with the local molecular motion of the intermediate rigid amorphous phase in the nylon‐6 fibers. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 993–1000, 2001     

Molecular dynamics in polyethylene and ethylene-1-butene copolymer investigated by NMR methods

1H and 13C NMR spectra and 1H spin-lattice relaxation times T₁ and T_1ρ have been employed to study the structure and molecular dynamics in polyethylene and ethylene-1-butene copolymer in the temperature range from 100 to 370 K. Results are interpreted in terms of α, β and γ -relaxation, as well as methyl group rotation. The activation energies for all motions were established. The incorporation of 1-butene into ethylene chain leads to an increase of mobility in amorphous and crystalline phases as well as appearance the 13C resonance characteristic to the monoclinic structure in addition to the orthorhombic observed in both polymers. The crystallinity degree derived from T_1ρ in studied polymers is close to that determined using DSC method.     

聚环氧乙烷(PE0)与聚双酚A羟基醚(PBHE)共混体系的研究

 用偏光显微镜(PLM)、扭辫(TBA)、IR及WAXD对PEO/PBHE共混体系结晶形态进行了研究。结果表明,PEO含量在50％以上的共混体系,几乎完全被PEO球晶充满,非晶态PBHE作为微区分散在大球晶之间或球晶之中。PEO含量为40％和30％的照片上呈现树枝晶。PEO含量为20％以下时照片中不再看到结晶出现,PEO与PBHE形成单一非晶相。PEO/PBHE共混体系的组分之间存在着氢键相互作用,这种作用强于PBHE分子间的氢键作用。共混体系的结晶度及T_g随PBHE组分含量的增加,前者减小后者增加并符合FOX方程揭示的规律。PEO与PBHE具有很好的相容性。     

Nuclear magnetic relaxation and molecular motion in poly(vinylidine fluoride)

Pulsed NMR T₁, T₂, and T_1ρ measurements are reported for poly(vinylidine fluoride) (PVF₂). The results demonstrate clearly the presence of four relaxation processes, three amorphous and one crystalline. The α relaxation is undoubtedly a crystalline one, while β and γ are both amorphous, in agreement with earlier conclusions from dielectric and dynamic mechanical measurements. The fourth relaxation (β′) observed initially in the mechanical measurements of Kakutani, but undetected in dielectric experiments, has been confirmed in our results and the process is described by an activation energy of 15.1 kcl/mole. Motion of folds on the surface of crystal lamellae is deemed to be the responsible mechanism for the β′ relaxation. Two models have been considered in the interpretation of the α process; rotation of crystalline chains in the vicinity of defects and rotational oscillation of restricted amplitude of all crystalline chains about the main chain axes. Rotation of amorphous chains is a possible mechanism for the γ process while motions of a general nature are responsible for the β relaxation. Our experimental results again indicate that spin diffusion plays an important role in the overall NMR response of the polymer.     

Phase transitions in chlorobenzene-cis-decalin mixtures

The dielectric constant ?' and loss tangent tan δ of chlorobenzene-cis-decalin mixtures have been measured in the temperature range 77 K to 330 K and frequency range 0.1 to 100 kHz. On cooling, ?' increases with decreasing temperature upto about 135 K, after which it drops rapidly with decreasing T followed by a slow decrease. This indicates that the liquid mixture goes to an amorphous phase which transforms to a glass phase of restricted dipole rotation below T_g; however, the peak in ?' is due to relaxation in the amorphous phase (α relaxation) and does not give an exact T_g. On heating, the behaviour of the cooling curve is retraced upto 160 K, after which ?' drops suddenly to a value lower than that at 77 K in the glass phase. This indicates the transition to a crystalline phase in which dipole rotational freedom is completely lost. The crystalline phase changes to a eutectic liquid phase of high ?' at a temperature (200 K) lower than the melting point of chlorobenzene and cis-decalin. Dielectric dispersion is observed only in the glass and amorphous phases. The dielectric relaxation time is independent of the concentration of chlorobenzene.     

Solid-state 13C-NMR studies of the aging of poly(vinylidene fluoride)/poly(methyl methacrylate) blends

Solid state ¹³C-NMR was used to investigate the miscibility and subsequent separation of solution-cast blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) (PMMA) with aging for a range of compositions. It was found that one amorphous phase and intimate mixing of the polymer chains in this phase existed for all compositions of the blends, even after 2 months of aging at room temperature as determined by the proton spin lattice relaxation time T_1ρH in the rotating frame, and the time constant T_CH for transfer of magnetization. The T_1ρH is sensitive to the spatial homogeneity of the blend via spin diffusion and would indicate the presence of phases or domains in the amorphous component of the blend larger than approximately 19 Å. The T_CH is proportional to the inverse sixth power of the interatomic distances needed for transfer of magnetization from proton to carbon and would be sensitive to a separation of polymer chains in the amorphous phase with aging on the order of 4–5 Å. There was an increase of the T_1ρH and T_CH values with aging, indicating that a subtle separation between unlike chains in the amorphous phase was occurring although a single amorphous phase was present.     

1H NMR studies of molecular relaxations of poly-1-butene

The temperature dependance of the proton NMR line shape, T₁ and T_1ρ of isotactic poly-1-butene forms I, I′, II, and III have been studied between 100 and 400 K (up to melting). The usual line shape decompositions concerning rigid vs. crystalline and mobile vs. amorphous phases are discussed. The rigid-lattice second moments were calculated introducing a fast rotation of the methyl group. Complex spin-lattice decays were analyzed as a continuous distribution of rates. Relaxation behavior was analyzed in terms of a Williams-Watt correlation function. Motions in the crystalline parts of samples in forms II and III very similar to the amorphous one were revealed, leading us to compare form II to a condis crystal during the crystal form transformation. © 1995 John Wiley & Sons, Inc.     

Electrical and differential scanning calorimetry studies of poly(ethylene oxide) complexed with alkaline-earth thiocyanates

Audio-frequency dielectric relaxation measurements and differential scanning calorimetry studies have been performed on poly(ethylene oxide) (PEO) complexed with calcium and barium thiocyanate. The measurements were performed over the temperature range 5.5-300 K. The relaxation spectrum for the complexed material consists of two peaks. The activation enthalpy for the peak corresponding to the γ relaxation of pure PEO depends upon the size of the dopant cation. The activation enthalpy for the second peak is independent of the nature of the dopant cation and is very similar to that observed for the α_c relaxation observed in pure PEO. Furthermore, the room-temperature electrical conductivity of the complexed materials is much smaller than that for pure PEO and hence very much less than for PEO-complexed with alkali-metal salts. However, above T_g the conductivity rises rapidly and is larger for the barium-thiocyanate-complexed PEO than for the calcium-complexed material. Finally, the DSC studies show that one effect of the ions is to shift the glass transition to higher temperatures.     

Poly-1-oxy-2-phenyltrimethylene as studied by 1H pulsed low resolution NMR: a possible oxygen scavenger

Aromatic polymers can adsorb a large amount of oxygen on their aromatic rings. In semicrystalline aromatic polymers, the amount of adsorbed oxygen is much larger in the amorphous phase than in the crystalline counterpart. As a consequence, fully amorphous aromatic polymers are more suitable as oxygen scavengers than semicrystalline polymers.A pulsed low resolution ¹H-NMR relaxation study on semicrystalline and fully amorphous poly-1-oxy-2-phenyltrimethylene (St–CO), deuteriated and not deuteriated on the backbone, is reported. T₁ relaxation values were measured at 30 and 57 MHz and compared with the values of two aromatic polymers previously studied, syndiotactic polystyrene (s-PS) and polyphenyleneoxide (PPO), both patented as oxygen scavengers. For all these polymers, using a set of equations, at each temperature, the amount of adsorbed oxygen was calculated.Very short T₁ values are observed at the low temperature point of PPO which is the best oxygen scavenger at low temperature, while St–CO adsorbs oxygen efficiently at room temperature. Thus, St–CO might be suitable to be used as an oxygen scavenger.In St–CO, a ¹H T_1ρ relaxation study on the rotating frame has also been performed. In the atactic copolymer, in the temperature range 150–160 K, a sharp transition was observed only in the presence of oxygen. In agreement with a previously given interpretation for analogous data, the observed transition might be related to low frequency motions present in low molecular weight components.     

A three-phase microstructural model to explain the mechanical relaxations of branched polyethylene: a DSC,WAXD and DMTA combined study

The thermal transitions of well-characterised single-site catalysed polyethylenes having various degrees of short chain branching have been studied by differential scanning calorimetry, X-ray diffraction and dynamic mechanical thermal analysis. A critical discussion based on the results obtained by means of the different techniques is presented. The results suggest that the γ transition is independent of the branching content and degree of crystallinity, pointing towards a sub-glass local relaxation mechanism related to both amorphous and crystalline fractions. The temperature of the β transition, T _β from dynamic mechanical measurements, is in agreement with the glass transition temperature obtained by calorimetry, T _g. Moreover, T _γ, and also T _β are directly related to a change in the thermal expansion coefficient of the amorphous phase observed by X-ray scattering. It is found that the corresponding scattering distance of the amorphous halo depends on crystallinity. In addition, the calorimetric heat capacity values at T _β do not account for the total amorphous fraction determined for each material. The relaxation motions assigned to the amorphous phase glass transition seems to parallel the subsequent melting of the crystalline structure, suggesting a hierarchical motion of different structures as temperature increases. Dynamic mechanical thermal analysis supports these observations, showing a broad transition in the phase angle involving first the relaxation of amorphous phase, then the (presumable) more rigid intermediate phase, and finally the crystalline phase, as the temperature increases.     

Lactone polymers. I. Glass transition temperature of poly-ε-caprolactone by means on compatible polymer mixtures

Dynamic mechanical properties determined with a torsion pendulum were used to ascertain the glass transition temperature T_g of poly-ε-caprolactone. By measurements on compatible blends of poly-ε-caprolactone and poly(vinyl chloride), the T_g of amorphous poly-ε-caprolactone was shown to be 202°K at about 1 cps. This is 16°K lower than the T_g of annealed, crystalline polymer. The blend transition data were well fitted by both the Fox and the Gordon-Taylor expressions. The Fox expression was also used to describe the decrease from 233°K of the secondary low-temperature relaxation due to poly(vinyl chloride) by assuming the low temperature relaxation of poly-ε-caprolactone, 138°K, was responsible for the decrease in the blends. The 138°K relaxation due to poly-ε-caprolactone was decreased when more than 50% poly(vinyl chloride) was present.     

A 13C NMR study of the effect of γ-irradiation on the chain dynamics of poly(ethylene oxide)

A comparison of solid-state ¹³C nuclear magnetic resonance (NMR) spectra of virgin and vacuum γ-irradiated poly (ethylene oxide) (PEO) evidences marked differences. The unirradiated PEO shows a well-resolved amorphous resonance and a weak, broad envelope of crystalline resonances, while the irradiated PEO presents well-resolved resonances for both the crystalline and amorphous carbons. Upon recrystallization from the melt both PEO samples yield solid-state ¹³C NMR spectra that are closely similar to that of the virgin, unheated sample. Observation of both melt-recrystallized samples at ?60°C yields similar spectra with well-resolved crystalline resonances. Crosslinking is the predominant chemical change occurring during the γ-irradiation of PEO under vacuum and produces a change in the motional character of the crystalline phase. This change is not the result of a reduction in crystallinity as evidenced by differential scanning calorimetry (DSC) observations. The most probable explanation is that the crosslinks are concentrated at the surface of the crystalline lamellae with a resultant change in the low frequency molecular motions of the crystalline chains. This motional change shifts the T_1p^H such that the crystalline carbon nuclei can now be cross-polarized at room temperature and the resonance linewidth is reduced. Following melting and recrystallization the motional characteristics of the irradiated PEO are nearly identical to those of the unirradiated sample, probably as a result of a redistribution of the crosslinks throughout the amorphous phase during recrystallization.     

Novel Biodegradable Poly(pentadecalactone-co-oxo-crown ether) Studied with Solid-State 1H and 13C NMR

Two grades of a novel biodegradable copolymer of ω-pentadecalactone (PDL) and 2-oxo-12-crown-4 (OC), with respective molar compositions of 77/23 and 52/48, were characterized with 1D and 2D MAS ¹H and ¹³C NMR spectroscopy. The results indicate that both copolymers are semi-crystalline with PDL divided over the crystalline and amorphous phase, and OC exclusively located in the amorphous phase. Proton T₂ and T_1ρ relaxation confirm the existence of small crystalline domains.     

STUDIES OF THE CRYSTALLIZATION BEHAVIOR IN THE CRYSTALLINE/AMORPHOUS POLYMER BLENDS: POLY(ETHYLENE OXIDE)/POLY(METHYL METHACRYLATE) AND POLY(ETHYLENE OXIDE)/POLY(VINYL ACETATE)

The crystallization process of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA)and PEO/poly(vinyl acetate) (PVAc) blends has been characterized by Fourier Transform Infrared(FTIR) spectra in conjunction with Differential Scanning Calorimeter (DSC) measurements. Thecrystallinity of PEO varies consistently with PEO content in PEO/PVAc blends and the PEO/PMMAblends containing 50 wt% or less PMMA. For the PEO/PMMA blends containing 60 wt% ormore PMMA, the crystallinity of PEO decreases more than PEO content but develops with crystal-lization time. These results can be explained in terms of difference between the crystallization tem-perature (T_c) and glass transition temperature (T_g) of the blends as a function of content of amorphouscomponent.     

Conductance and relaxations in the glassy and rubber states of aqueous poly( vinyl pyrrolidone): A cryofixation medium

The dielectric permittivity and loss of poly(vinyl pyrrolidone), molecular weight 40,000, containing 40% (by weight) water have been measured over the temperature range 77–325 K and frequency range 12 Hz to 0.1 MHz. A prominent relaxation due to rotational diffusion of water molecules in a hydrogen-bonded structure occurs at T < T_g (237 K). The half-width of the dipolar relaxation spectra is 2.27 decades and is temperature independent, which is strikingly different from the corresponding features of pure polymers. It is concluded that H-bonded amorphous solid water persists in the glassy polymer matrix and that the H-bonded structure contains the pyrrolidone side groups of the randomly oriented chain. The relaxation peak at T near T_g is masked by a large dc conductivity which, when expressed in terms of electric modulus, has a spectrum of half-width 1.37 instead of 1.14 decades expected for dc conductivity alone. The contribution from dipolar reorientation in the glass-rubber range of the PVP-H₂O solution is smaller than that in its sub-T_g relaxation.     

Properties of polyethylene modified with phosphonate side groups. II. Dynamic mechanical behavior

The viscoelastic behavior of phosphonate derivatives of phosphonylated low-density polyethylene (LDPE) was studied by dynamic mechanical techniques. The polymers investigated contained from 0.2 to 9.1 phosphonate groups per 100 carbon atoms and included the dimethyl phosphonate derivative and two derivatives for which the phosphonate ester group was an oligomer of poly(ethylene oxide) (PEO). The temperature dependences of the storage and loss moduli of the dimethyl phosphonate derivatives were qualitatively similar to those of LDPE. At low phosphonate concentrations, the α, β, and γ dispersion regions characteristic of PE were observed, while at concentrations greater than 0.5 pendent groups per 100 carbons atoms, only the β and α relaxations could be discerned. At low degrees of substitution, the temperature of the β relaxation T_β decreased from that of PE, but above a degree of substitution of 0.1, T_β increased. This behavior was attributed to the competing influences of steric effects which tend to decrease T_β and dipolar interactions between the phosphonate groups which increase T_β. For the phosphonate containing PEO, a new dispersion region designated as the β′ relaxation was observed as a low-temperature shoulder of the β relaxation. The temperature of the β′ loss was consistent with T_g(U) of the PEO oligomers as determined by differential scanning calorimetry, and it is suggested that the β′-loss process results from the relaxation of PEO domains which constitute a discrete phase within the PE matrix.     

Investigation on the dynamics of aromatic polyesters by means of high resolution solid state CPMAS 13C NMR

The dynamics of amorphous aromatic polyesters consisting of poly(ethylene terephthalate) (PET), poly(ethylene isophthalate) (PEI), and poly(ethylene 2,6-naphthalenedicarboxylate) (PEN) has been investigated by means of solid state CPMAS ¹³C NMR. Proton T₂, ¹³C T_1ρ, and proton T_1ρ decays have been measured in particular, and the experimental data fitted to suitable model functions to determine best relaxation parameters. The fitting results show for proton T₂ and ¹³C T_1ρ measurements the presence of two components with different relaxation times and intensities, arising from different motional domains. The proton T_1ρ, on the contrary, shows a single component which limits the dimensions of the two regions to less than 20 Angstroms. The dependence of ¹³C T_1ρ values on two different irradiating field strengths (H₁ = 38 KHz, H₁ = 60 KHz) allowed the assignment of each component to relatively rigid and mobile regions. By comparing the three polymers we observe that PEN and PEI have a similar relaxation behavior, while a higher fraction of mobile components was found for PET. These differences are believed to arise mainly from local motions of the aromatic rings. The relaxation measurements have been evaluated to suggest a correspondence to O₂ and CO₂ gas permeabilities in PET, PEI, and PEN. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1557–1566, 1998     

Nuclear relaxation in atactic polystyrenes: T1 and T1ρ measurements

Measurements have been made on a series of linear atactic polystyrenes whose molecular weights range from 900 to 1.8 × 10⁶, where M _w/M _n ? 1.2. Spin lattice relaxation times have been measured in the laboratory frame (T₁) and in the rotating frame (T_1ρ) in the temperature range 90–500°K. Two major relaxation minima were observed in both sets of measurements. The high temperature process corresponds to the glass transition (α process), the position of the minimum depending on the chain length. The low temperature process appears to originate from the n-butyl endgroups in the polymer, its position being independent of chain length while its intensity is inversely proportional to molecular weight. No other minima were observed, in contrast to some other observations made by broadline and pulsed NMR techniques. Relaxation was exponential in all cases except in the region of the high temperature T_1ρ minimum and above. This nonexponential behavior is possibly connected with the transition at T > T_g observed by a number of other techniques and which is thought to correspond to a transition between two types of liquid state. A correlation frequency diagram has been drawn for all the processes observed in polystyrene by other techniques, (α, β, αβ, γ, and δ) which shows that the T₁ and T_1ρ minimum positions correlate well with the α process and that there is a possible contribution to the relaxation due to the γ process on the low temperature side of the α process. At these measurement frequencies the α and β processes are merged into an αβ process. There is no evidence for a contribution from the mechanical δ process. The effect of the endgroups is observed to very high molecular weights (4.98 × 10⁵), and it seems that a three-dimensional diffusion model would be more adequate than the one-dimensional model used to interpret similar behavior of paraffins and polyethylenes. Measurements of T₁ in the low-temperature region would constitute a method for a rough measurement of the molecular weight of these polymers.