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Low-Temperature Relaxations In Polyurethans, William Macknight, T. Kajiyama Dec 1967

Low-Temperature Relaxations In Polyurethans, William Macknight, T. Kajiyama

William MacKnight

A study has been made of the relaxation phenomena in three series of glassy polyurethans in the temperature range from -190 to 100° and at various frequencies up to 110 Hz using dynamic mechanical and dielectric relaxation. The structures of the repeat units of the three series are given in eq 1-3. Several overlapping relaxation peaks are discernible in the temperature and frequency region investigated. All of these relaxations arise largely from motion in the amorphous phase. The following assignments of the various relaxation peaks to specific molecular motions have been made on the basis of comparisons both within and …

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Viscous And Elastic Behavior Attributed To Polymer Entanglements, William Macknight, Roger S. Porter, Julian F. Johnson Dec 1967

Viscous And Elastic Behavior Attributed To Polymer Entanglements, William Macknight, Roger S. Porter, Julian F. Johnson

William MacKnight

No abstract provided.

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Properties Of Ethylene - Methacrylic Acid Copolymers And Their Sodium Salts: Infrared Studies, William Macknight, L. W. Mckenna, B. E. Read Dec 1966

Properties Of Ethylene - Methacrylic Acid Copolymers And Their Sodium Salts: Infrared Studies, William Macknight, L. W. Mckenna, B. E. Read

William MacKnight

An infrared spectroscopic investigation of ethylene-methacrylic acid copolymers and their sodium salts has been carried out. All the copolymers studied were based on a parent copolymer containing 4.1 mol % of methacrylic acid groups. This was then neutralized to various e;d;ents (from O to 78%) with sodium hydroxide. The per cent ionization was determined from the integrated absorbance of the 1700 cm -1 un-ionized carbonyl stretching band. Temperature-dependent infrared studies showed that the behavior of the un-ionized acid groups over the entire range of ionization is quantitatively comparable to that of low molecular weight car­boxylic acids in nonpolar solvents. A …

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Effect Of S(Pi) On The Polymerization Of Liquid Sulfur And The Nature Of S(Pi), William Macknight, J. A. Poulis, C. H. Massen Dec 1966

Effect Of S(Pi) On The Polymerization Of Liquid Sulfur And The Nature Of S(Pi), William Macknight, J. A. Poulis, C. H. Massen

William MacKnight

The Tobolsky-Eisenberg theory serves to explain the equilibrium polym­erization of sulfur in terms of the dependence of S8 (ring) concentration on temperature and the dependence of number-average degree of polymeri­zation on temperature. The predictions of the theory are completely in accord with experiment. In this paper it is shown that it is possible to take the presence of another component in the melt, S,,, into account, using a slightly modified version of the Tobolsky-Eisenberg theory. When this is done it is found that the earlier conclusions remain valid. The molecular complexity and structure of Sw is also discussed.

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Chemical Stress Relaxation, William Macknight Dec 1966

Chemical Stress Relaxation, William Macknight

William MacKnight

No abstract provided.

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Volume Changes Accompanying The Extension Of Rubber-Like Materials, William Macknight Dec 1965

Volume Changes Accompanying The Extension Of Rubber-Like Materials, William Macknight

William MacKnight

No abstract provided.

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Properties Of Polymeric Sulfur, William Macknight, A. V. Tobolsky Dec 1964

Properties Of Polymeric Sulfur, William Macknight, A. V. Tobolsky

William MacKnight

No abstract provided.

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Relaxation Of Disulfide And Tetrasulfide Polymers, William Macknight, A. V. Tobolsky, M. Takahashi Dec 1963

Relaxation Of Disulfide And Tetrasulfide Polymers, William Macknight, A. V. Tobolsky, M. Takahashi

William MacKnight

The chemorheology of cross-linked polyethylene disulfide, polyethylene tetrasulfide, and mixtures of these polymers with elemental sulfur is investigated. It is shown that stress decay in the disulfide polymer occurs by scission of the small quantities of higher poly­sulfide linkages present in the network. It is also shown that elemental sulfur decreases the chemical relaxation time in cross-linked polyethylene disulfide in a predictable manner.

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Cleavage Reactions In Crosslinked Urethane Elastomers, William Macknight, A. V. Tobolsky Dec 1963

Cleavage Reactions In Crosslinked Urethane Elastomers, William Macknight, A. V. Tobolsky

William MacKnight

A study of network cleavage in a crosslinked poJ.yurethane elastomer was ma.de using the technique of stress relaxation. 
It was found that the data could be well represented by a sum 
of two exponential decay terms, and a theoretical explanation for this is presented. stress relaxation in the. polyurethane sample investigated is discussed in terms of the reversible cleavage 
of various linkages formed by isocyanate reactions. It is possible to identify two different decay processes and obtain activation energies for these processes. These are identified with cleavage of two different linkages. It is not possible at present to give a …

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Physical Chemistry Of Crosslinked Polysulfide Elastomers, William Macknight, G. E. Leroi, A. V. Tobolsky Dec 1963

Physical Chemistry Of Crosslinked Polysulfide Elastomers, William Macknight, G. E. Leroi, A. V. Tobolsky

William MacKnight

No abstract provided.

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Urethane Elastomers Containing Disulfide And Tetrasulfide Linkages, William Macknight, G. D. T. Owens, A. V. Tobolsky Dec 1962

Urethane Elastomers Containing Disulfide And Tetrasulfide Linkages, William Macknight, G. D. T. Owens, A. V. Tobolsky

William MacKnight

The chemorheology of two cross-linked polyurethane elastomers containing (1) disulfide groups and (2) tetrasulfide groups was investigated by stress relaxation experiments. It was found that the tetrasulfide-containing elastomer underwent stress decay at a rate 10 times faster than the disulfide-containing elastomer, showing that the tetrasulfide linkage undergoes bond interchange much more rapidly than the disulfide linkage. Spectroscopic evidence is cited tending to confirm the greater stability of the disulfide linkage. The behavior of a cross-linked polyurethane elastomer without polysulfide linkages is presented for comparison. 

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The Glass Transition Temperature Of Polymeric Sulfur, William Macknight, A. V. Tobolsky, R. B. Beevers, V. D. Gupia Dec 1962

The Glass Transition Temperature Of Polymeric Sulfur, William Macknight, A. V. Tobolsky, R. B. Beevers, V. D. Gupia

William MacKnight

No abstract provided.

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