| Photochemistry of Bisphenol-A-Based Polycarbonate: The Effect of the Matrix and Early Detection of Photo-Fries Product Formation |
31 MAY 91 |
32 pages |
| Authors:
Charles E. Hoyle; Himanshu Shah; Gordon L. Nelson; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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 | The effect of polymer matrices on a photo-induced rearrangement process has been shown to be dependent upon whether the photoreactive group is attached to a polymer backbone, or free. If diphenylcarbonate is simply embedded in a polymer matrix, the rearrangement process is independent of whether the host film is above or below its glass transition. However, if the diphenylcarbonate group is incorporated as part of a polycarbonate backbone, the Fries ... |
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| Photodegradation of Polyimides. 3. The Effect of Chemical Composition, Radiation Source, Atmosphere, and Processing |
31 MAY 91 |
44 pages |
| Authors:
Charles E. Hoyle; Edgardo T. Anzures; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Polyimide films made from diarylanhydrides with oxygen, carbonyl, and hexafluoroisopropylidene 6F bridging groups are photolabile when irradiated with unfiltered light from a medium pressure mercury lamp. The presence of oxygen is necessary to the photolytic degradation process, which results in the ultimate oxidative ablation of thin polyimide films. Films based on the 6F dianhydride containing a hexafluoroisopropylidene hinge group are the most unstable. However, photolysis of 6F dianhydride based polyimides ... |
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| Photodegradation of Polyimides. 4. Mechanism for the Photooxidation Process Based on a Model Compound |
31 MAY 91 |
37 pages |
| Authors:
Charles E. Hoyle; D. Creed; R. Nagarajan; P. Subramanian; Edgardo T. Anzures; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Based on analysis of the photochemistry of a model compound, N- phenylphthalimide, the photolysis of polyimide derived from 4,'-oxydianiline (ODA) and a diarylanhydride with a hexafluorinated isopropylidene bridging group (6F) is proposed to proceed via formation from a phthalic anhydride type photoproduct. The quantum yield for product formation of N-phenylphthalimide is quite low (<10 to the -3rd power) indicating a rather inefficient first step in the overall oxidative degradation process. ... |
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| An Investigation of the Degradation and Stabilization of Polymer Systems |
14 JUL 89 |
6 pages |
| Authors:
Charles E. Hoyle; Gordon L. Nelson; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| The project on Investigation of the Degradation and Stabilization of Polymer Systems concentrated primarily on a detailed study of the factors which effect the photolytic decomposition of polyurethanes based on aromatic diisocyanates. An extensive investigation of the photophysics of 1,5-naphthalene diisocyanate based polyurethanes in solution was also conducted. In addition, ground work was laid to initiate studies on the photodegradation of polycarbonate, polyureas, and polymides. Employing both steady and time ... |
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| Photooxidation of an MDI (Methylene 4,4'-Diphenyl Diisocyanate) Based Polyurethane Elastomer |
29 JUL 87 |
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| Authors:
Charles E. Hoyle; Y. G. No; G. L. Nelson; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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 | The photolysis of a polyurethane elastomer based on methylene 4,4'- diphenyl diisocyanate (MDI) in air and under vacuum results in the oxidation of primary photoproducts at relatively short irradiation times. The degree of crosslinked gel and the ultraviolet absorption spectra are both dependent on the presence of oxygen during the photolysis. Apparently, photolysis of the primary photoproducts (probably photo-Fries type) contributes to the degree of crosslinking generated upon photolysis. These ... |
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| Fluorescence of Polyureas Based on 1,5-Naphthalene Diisocyanate |
29 JUL 87 |
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| Authors:
Charles E. Hoyle; C. H. Chang; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Polyureas based on 1,5-naphthalene diisocyanate (NDI) form intramolecular excimers in dilute solution. The excimer formation is enhanced in benzene which is a relatively poor solvent for NDI based polyureas. Photolysis in dimethyl formamide solution results in a decrease in the overall intensity and a shift to the red, due most likely to photo-Fries product formation. Excimer fluorescence in the polyurea films is directly dependent on the nature of the diamine ... |
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| The Effect of Flexibility on the Photodegradation of Aromatic Diisocyanate Based Polyurethanes |
29 JUL 87 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| The photolytic degradation of 2, 4-TDI/aliphatic diol polyurethanes is directly dependent on the flexibility of the polymer backbone. The extent of photodegradation is accelerated above the glass transition temperature indicating the role of chain flexibility and/or oxygen diffusion in the decomposition process. Photolysis of the model compound ethyl N-phenylcarbamate (EPC) in neutral host polymer matrices indicates that the para photo-Fries to ortho photo-Fries product ratio experiences an accelerated increase with ... |
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| Excimer Formation of a Naphthalene Diisocyanate Based Polyurethane in Solution |
29 JUL 87 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Naphthyl carbamates are shown to form excimers which are stabilized by hydrogen bonding inherent in the participating species. Substitution of a methyl group on the central nitrogen atom of the carbamate moiety severely limits excimer formation. A polyurethane based on 1,5-naphthalene diisocyanate forms intramolecular excimers in dilute solutions of both good and poor solvents; however, excimer formation is significantly enhanced in poor solvents where intramolecular contact between naphthyl carbamate groups ... |
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| The Effect of Crystallinity and Flexibility on the Photodegradation of Polyurethanes |
24 SEP 86 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Using fluorescence spectroscopy and gel content measurements, the photolysis of simple polyurethanes based on methylene 4,4'-diphenyl diisocyanate (MDI) is shown to depend on both the flexibility and crystallinity of the polymer. Polyurethane films based on MDI and 1,2-dodecanediol (MDI-12) can be either annealed or quenched to yield a semi-crystalline (as measured by DSC and X-ray diffraction) or amorphous film, respectively. In the case of the quenched (amorphous) films, photolysis yields ... |
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| Photolysis of Segmented Polyurethanes. The Role of Hard-Segment Content and Hydrogen Bonding |
24 SEP 86 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; Y. G. No; G. L. Nelson; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| The photodegradation of segmented polyurethanes based on methylene 4, 4' -diphenyl diisocyanate (MDI) is shown to be dependent on the physical structure of the polymer. As the hard segment content of the polyurethane is increased, the photodegradation efficiency is lowered. In particular, the extent of the photolytic decomposition is inversely dependent on the degree of hydrogen bonding in the aryl carbamate groups in the polyurethane backbone. Utilizing appropriate model compounds ... |
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| Photophysics of Polyurethanes Based on 1,5-Naphthalene Diisocyanate in Solution and Film |
24 SEP 86 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Using both steady-state and transient fluorescence decay spectroscopy, the formation of intramolecular excimers in dilute solutions of a naphthalene diisocyanate based polyurethane is identified. Investigation of an appropriate model compound leads to the conclusion that hydrogen bonding is a key factor in stabilizing excimers formed from naphthyl carbamates. While the decay kinetics of the model naphthyl carbamate are described by a typical Birks excimer scheme involving a single excited monomer ... |
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| Photophysics of a Naphthalene Diisocyanate Based Polyurethane |
24 SEP 86 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| A naphthalene dissocyanate based polyurethane in dilute solution is found to form intramolecular excimers between chromophores in the polymer backbone. The excimer kinetics is described by a triple exponential decay function. Based on comparison with model compounds, the photophysics of the polymer system is accounted for by the isolated monomer scheme. The relative intensity of the excimer emission depends on the solvent system employed and correlates directly with the intrinsic ... |
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| Photolysis of Aromatic Diisocyanate Based Polyurethanes in Solution |
AUG 86 |
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| Authors:
Charles E. Hoyle; Kyu-Jun Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| Fluorescence analysis has been employed as an analytical technique to elucidate the photolysis mechanism of several aromatic diisocyanate based polyurethanes in solution. Based on a comparison with model arylmonocarbamates and arylbiscarbamates, the photo-Fries rearrangement and cleavage-type products found for the small model arylcarbamates were also identified for the photolyzed polyurethanes in solution. Viscosity and absorbance change results for photolysis of both air and nitrogen saturated polyurethane solutions are consistent with ... |
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| Light Stability of Polyurethane Coatings |
16 JUN 86 |
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| Authors:
Charles E. Hoyle; K. J. Kim; Y. G. No; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| The photodegradation of methylene 4,4'-diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI) based polyurethanes is reported to be dependent on backbone chain flexibility and matrix crystallinity. Both absorbance changes and gel formation decrease as the stiffness and crystalline content of powders and films increase. Stabilizers are only marginally effective in reducing the extent of degradation of the polyurethane films. |
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| Photophysics of Polyurethanes Based on 1,5-Naphthalene Diisocyanate |
16 JUN 86 |
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| Authors:
Charles E. Hoyle; K. J. Kim; UNIVERSITY OF SOUTHERN MISSISSIPPI HATTIESBURG DEPT OF POLYMER SCIENCE
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| In contrast to the vast number of studies on excimers formed between aromatic chromophores pendant to the polymer backbone, relatively few papers have been published on excimers formed from polymers with the interactive species in the backbone. Selected examples can be found in references 2-5. In this paper, we report on the photophysical behavior of polyurethanes based on 1, 5-naphthalene diisocyanate (NDI) which have naphthalene chromophores periodically spaced along the ... |
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