Association and crystallization of poly(ethylene oxide)

Shimada, Taro; Okui, Norimasa; Kawai, T.

doi:10.1002/macp.1980.021811220

Cited by 20 publications

(9 citation statements)

References 16 publications

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“…1993 American Chemical Society involving hydroxy end groups is not expected in the IF crystal formation.20 Shimada et al found that low molecular weight PEO fractions with phenyl end groups do not show a stepwise increase in crystal lamellar thickness grown from the melt. 21 Similar behavior in PEOs with other bulkier end groups were also reported.22-24 Recently, we have investigated one PEO fraction with methoxy end groups (-OCH3) (MPEO) 25 and observed that the IF crystal was actually formed via a transformation of NIF crystals. The thickening and thinning processes in this transformation were faster compared to the PEO fraction with the same molecular weight and hydroxy end groups.…”

Section: Introductionsupporting

confidence: 63%

Isothermal thickening and thinning processes in low-molecular-weight poly(ethylene oxide) fractions crystallized from the melt. 4. End-group dependence

Cheng¹,

Wu²,

Chen³

et al. 1993

Macromolecules

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A series of low molecular weight poly(ethy1ene oxide) (PEO) fractions with different molecular weights (MW=3000 and7100) andendgroups (-OH,-OCH~,-OC(CH~)S, and-OC&) have beensystematically studied. The end-group effect on diffusional motion in the melt of these PEO fractions was characterized by self-diffusion coefficient measurements through nuclear magnetic resonance. Wide-angle X-ray diffraction experiments indicated that the crystal structures of the PEO fractions with different end groups were identical during and after crystallization. The existence of nonintegral folding chain (NIF) crystals in these PEO fractions in a wide undercooling region was observed by time-resolved synchrotron small-angle X-ray scattering, differential scanning calorimetry, and transmission electron microscopy experiments. The integral folding chain (IF) crystals were found to be formed through both thickening and thinning processes during and/or after the NIF crystallization. It was also found that, with increasing molecular weight and size of the end group, the thickening and thinning processes were increasingly hampered. Of additional interest, the fold length of initial NIF crystals not only increases with crystallization temperature (or decreasing undercooling) for each PEO fraction as commonly observed in polymer lamellar crystals but also changes with the size of the end group. The kinetics of transformation from NIF to IF crystals is explained through the chain sliding diffusional motion along the direction perpendicular to the lamellar surface, which is end-group size dependent. Linear crystal growth rate data measured via polarized light microscopy confirmed that the existence of bulky end groups reduces NIF crystal growth rates for PEO (MW = 3000) fractions. With increasing molecular weight, the end-group dependence gradually vanishes due to the introduction of chain entanglement.

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Section: Introductionsupporting

confidence: 63%

Isothermal thickening and thinning processes in low-molecular-weight poly(ethylene oxide) fractions crystallized from the melt. 4. End-group dependence

Cheng¹,

Wu²,

Chen³

et al. 1993

Macromolecules

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“…Figure illustrates the primary NIF chain crystallization of PEG6000 and the evolution of nearest IF chain crystals through thickening or thinning. The scheme is adapted to the model originally proposed by Ungar et al then modified by Cheng et al with the hydrogen bonding formation between hydroxyl end groups of polymer chains . It is known that the lamellar thickness is proportional to the crystal thermodynamic stability with the melting point obeying the Tamman equation.…”

Section: Discussionmentioning

confidence: 99%

Microstructure of Pharmaceutical Semicrystalline Dispersions: The Significance of Polymer Conformation

et al. 2018

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The microstructure of pharmaceutical semicrystalline solid dispersions has attracted extensive attention due to its complexity that might result in the diversity in physical stability, dissolution behavior, and pharmaceutical performance of the systems. Numerous factors have been reported that dictate the microstructure of semicrystalline dispersions. Nevertheless, the importance of the complicated conformation of the polymer has never been elucidated. In this study, we investigate the microstructure of dispersions of polyethylene glycol and active pharmaceutical ingredients by small-angle X-ray scattering and high performance differential scanning calorimetry. Polyethylene glycol with molecular weight of 2000 g/mol (PEG2000) and 6000 g/mol (PEG6000) exhibited remarkable discrepancy in the lamellar periodicity in dispersions with APIs which was attributed to the differences in their folding behavior. The long period of PEG2000 always decreased upon aging-induced exclusion of APIs from the interlamellar region of extended chain crystals whereas the periodicity of PEG6000 may decrease or increase during storage as a consequence of the competition between the drug segregation and the lamellar thickening from nonintegral-folded into integral-folded chain crystals. These processes were in turn significantly influenced by the crystallization tendency of the pharmaceutical compounds, drug-polymer interactions, as well as the dispersion composition and crystallization temperature. This study highlights the significance of the polymer conformation on the microstructure of semicrystalline systems that is critical for the preparation of solid dispersions with consistent and reproducible quality.

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“…It is obvious that regime II is not reasonable, since <re would be even higher than that for PE and would not agree with data from other sources.24-34 Kovacs has reported ae increasing with molecular weight in melt crystallization studies of PEO.24 Our values are comparable to those for this range of molecular weights (45 < <st < 60 erg cm-2 assuming a «10), obtained from growth rate data or from melting point measurements. [24][25][26][27][28][29][30][31][32][33][34] The work of chain folding, q, can be obtained from the surface free energy by q = 2abct, where the stem width a is taken as 0.467 nm. 2 The result, q = 3.5 ± 0.5 kcal mol-1, is close to but smaller than q for polyethylene,2 which is 5.06 kcal mol-1, and presumably this reflects the more flexible nature of PEO chains.…”

Section: Discussionmentioning

confidence: 99%

Kinetics of poly(ethylene oxide) crystallization from solution: temperature and molecular weight dependence

Ding¹,

Amis²

1991

Macromolecules

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The rate of crystal growth from dilute solutions of polyethylene oxide) (PEO) of high and intermediate molecular weight has been investigated by utilizing a new seeding technique in conjunction with dynamic light scattering. Crystallization of polymers in a dilute solution is initiated by the addition of seed crystals and the growth kinetics are monitored by repetitive measurements of diffusion coefficients of crystal particles. The crystal growth rate can be extracted from the linear plot of inverse decay constant of scattering particles vs time. It has been found that the temperature influence on crystal growth kinetics in terms of log G vs l/TAT depends on the choice of 7d°. Regardless of the exact values of Td°used for the range of molecular weight samples, it is found that for high PEO molecular weights (>3 X 10s) a transition could be recognized in the dependence of the growth rate on the extent of supercooling. No such transition is found for intermediate (<3 X 10s) molecular weight PEO. At constant supercooling, the growth rate generally increases with polymer molecular weight over the range from 5.63 X 104 to 7.7 X 10s.

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Association and crystallization of poly(ethylene oxide)

Cited by 20 publications

References 16 publications

Isothermal thickening and thinning processes in low-molecular-weight poly(ethylene oxide) fractions crystallized from the melt. 4. End-group dependence

Isothermal thickening and thinning processes in low-molecular-weight poly(ethylene oxide) fractions crystallized from the melt. 4. End-group dependence

Microstructure of Pharmaceutical Semicrystalline Dispersions: The Significance of Polymer Conformation

Kinetics of poly(ethylene oxide) crystallization from solution: temperature and molecular weight dependence

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