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Title: Conformation and Phase Separation of Oligo (ethylene glycol) Grafted Polystyrene in Dilute Aqueous Solutions

Abstract

Temperature induced conformational changes of poly(p-oligo(ethylene glycol) styrene) (POEGS) in aqueous solutions were investigated by small angle neutron scattering (SANS), neutron transmission and dynamic light scattering (DLS). The molecular weight of the polymer studied was 9400 g/mol with a polydispersity index of 1.18 and each repeat unit of the polymer had four ethylene glycol monomer segments. The polymer was water soluble due to the hydrophilicity of the OEG side chains and these solutions showed lower critical solution temperature (LCST) depending on the concentration of the polymer. Measurements of solution behavior were made as a function of temperature in the range of 25-55 C for three polymer concentrations (0.1 wt%, 0.3 wt%, and 1.8 wt%). Neutron transmission measurements were used to monitor the amount of polymer which precipitated or remained in solution above the cloud point temperature (T{sub CP}). DLS revealed the presence of large clusters in all solutions both below and above T{sub CP} while SANS provided information on the structure and interactions between individual chains. It was found that in the homogeneous region below T{sub CP} the shape of individual polymers in solution was close to ellipsoidal with the dimensions R{sub a} = 37 Angstroms and R{sub b} =more » 14 Angstroms and was virtually independent of temperature. The SANS data taken for the most concentrated solution studied (1.8 wt%) were fit to the ellipsoidal model with attractive interactions which were approximated by the Ornstein-Zernike function with a temperature-dependent correlation length in the range of 24-49 Angstroms. The collapse of individual polymers to spherical globules with the radius of 15 Angstroms above TCP was observed.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Center for Nanophase Materials Sciences
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
931735
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Polymer; Journal Volume: 48
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AQUEOUS SOLUTIONS; CONFORMATIONAL CHANGES; GLYCOLS; MOLECULAR WEIGHT; POLYSTYRENE; TEMPERATURE DEPENDENCE

Citation Formats

Cheng, Gang, Melnichenko, Yuri B, Wignall, George D, Hua, Fengjun, Hong, Kunlun, and Mays, Jimmy. Conformation and Phase Separation of Oligo (ethylene glycol) Grafted Polystyrene in Dilute Aqueous Solutions. United States: N. p., 2007. Web. doi:10.1016/j.polymer.2007.05.016.
Cheng, Gang, Melnichenko, Yuri B, Wignall, George D, Hua, Fengjun, Hong, Kunlun, & Mays, Jimmy. Conformation and Phase Separation of Oligo (ethylene glycol) Grafted Polystyrene in Dilute Aqueous Solutions. United States. doi:10.1016/j.polymer.2007.05.016.
Cheng, Gang, Melnichenko, Yuri B, Wignall, George D, Hua, Fengjun, Hong, Kunlun, and Mays, Jimmy. Mon . "Conformation and Phase Separation of Oligo (ethylene glycol) Grafted Polystyrene in Dilute Aqueous Solutions". United States. doi:10.1016/j.polymer.2007.05.016.
@article{osti_931735,
title = {Conformation and Phase Separation of Oligo (ethylene glycol) Grafted Polystyrene in Dilute Aqueous Solutions},
author = {Cheng, Gang and Melnichenko, Yuri B and Wignall, George D and Hua, Fengjun and Hong, Kunlun and Mays, Jimmy},
abstractNote = {Temperature induced conformational changes of poly(p-oligo(ethylene glycol) styrene) (POEGS) in aqueous solutions were investigated by small angle neutron scattering (SANS), neutron transmission and dynamic light scattering (DLS). The molecular weight of the polymer studied was 9400 g/mol with a polydispersity index of 1.18 and each repeat unit of the polymer had four ethylene glycol monomer segments. The polymer was water soluble due to the hydrophilicity of the OEG side chains and these solutions showed lower critical solution temperature (LCST) depending on the concentration of the polymer. Measurements of solution behavior were made as a function of temperature in the range of 25-55 C for three polymer concentrations (0.1 wt%, 0.3 wt%, and 1.8 wt%). Neutron transmission measurements were used to monitor the amount of polymer which precipitated or remained in solution above the cloud point temperature (T{sub CP}). DLS revealed the presence of large clusters in all solutions both below and above T{sub CP} while SANS provided information on the structure and interactions between individual chains. It was found that in the homogeneous region below T{sub CP} the shape of individual polymers in solution was close to ellipsoidal with the dimensions R{sub a} = 37 Angstroms and R{sub b} = 14 Angstroms and was virtually independent of temperature. The SANS data taken for the most concentrated solution studied (1.8 wt%) were fit to the ellipsoidal model with attractive interactions which were approximated by the Ornstein-Zernike function with a temperature-dependent correlation length in the range of 24-49 Angstroms. The collapse of individual polymers to spherical globules with the radius of 15 Angstroms above TCP was observed.},
doi = {10.1016/j.polymer.2007.05.016},
journal = {Polymer},
number = ,
volume = 48,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The conformation and clusterization of comb like polymers of polystyrene densely grafted with oligo(ethylene glycol) (OEG) side chains in 1.0 wt% solutions of D2O, toluene-d8 and methanol-d4 was investigated as a function of the degree of polymerization (DP) of the backbone by small angle neutron scattering (SANS). Each side chain had four EG repeat units and the DP of the polystyrene backbone was varied from 8 to 85. The global conformation of the polymers in toluene and methanol was shown to assume ellipsoidal, cylindrical or worm-like chain morphologies with increasing DP of the polystyrene backbone. At the same time, inmore » D2O, the polymer conformation was described by the form factor of rigid cylinders. The second viral coefficient was measured for the polymer with a DP of 85 in all three solvents and the solvent quality of toluene, methanol and D2O was identified as good, marginal and poor for this polymer. Due to a poor solvent quality, the PS backbone (DP = 85) is partially collapsed in D2O whereas it is moderately expanded in toluene and methanol. Polymers with the DP of 8 were found to aggregate into clusters in all three solvents, with the characteristic size between 100 and 200 ?and a fractal dimension of 2. With increase of the DP, the clusters diminished in D2O and completely disappeared in toluene and methanol. This observation suggests that the clusterization of these short side-chain polymers is caused by end group and hydrogen bonding interactions between different chains.« less
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  • The crystal structure of silica sodalite, including possible locations for encapsulated ethylene glycol, was determined at room temperature by using a combined single-crystal X-ray and powder neutron diffraction analysis. Unit cell composition: Si/sub 12/O/sub 24/ x 2C/sub 2/H/sub 4/(OH)/sub 2/, M/sub r/ = 845, cubic, Im3m, a = 8.830 (1) A (X-ray), a = 8.8273 (1) A (neutron). These refinements reveal that the correct space group for silica sodalite is Im3m (rather than I43m) and, therefore, that the sodalite framework is fully expanded. At room temperature, each sodalite cage contains one ethylene glycol molecule which has a range of geometricalmore » positions. Intramolecular distances for the ethylene glycol molecule are (X-ray) C-C 1.78 (4), C-O 1.30 (6) A, (neutron) C-C 1.70 (3), C-O 1.25 (3) A. The shortest distances (3.4 A) between oxygens of the framework and molecule are consistent with weak hydrogen bonding. From the neutron diffraction data it was found that a sluggish phase change from cubic to lower symmetry occurs upon cooling below 200 K. At 10 K, silica sodalite appears to be monoclinic with approximate cell parameters a = 12.250 (8) A, b = 12.471 (8) A, c = 8.512 (6) A, ..beta.. = 91.37 (6)/sup 0/, based on an indexing of 12 peaks, but the precise symmetry is as yet unknown.« less