Accession Number:

ADA048981

Title:

Study of the Class Transition in Crosslinked Polymers Using Nuclear and Electron Magnetic Resonance.

Descriptive Note:

Final rept. 6 Sep 76-6 Dec 77,

Corporate Author:

MCDONNELL DOUGLAS RESEARCH LABS ST LOUIS MO

Personal Author(s):

• Brown,I. M.
• Lind,A. C.

Report Date:

1977-12-06

Pagination or Media Count:

86.0

Abstract:

Pulsed and cw electron paramagnetic resonance EPR and pulsed proton nuclear magnetic resonance NMR techniques were applied to the study of the main-chain segmental motions associated with the glass transitions in block copolymers and the influence of plasticizers on these motions. In the EPR experiments, both cw and electron spin echo measurements were made of a stable nitroxide radical which was used as an EPR spin probe of its environment in the block copolymer. The proton NMR experiments included conventional spin-lattice and spin-spin relaxation time measurements along with broadline and multiple-pulsed partially-relaxed spectra. Samples of polydimethylsiloxane DMS and bisphenol-A polycarbonate BPAC of varying composition and block length were examined. Above 220 K, the radicals exhibited both broadline and narrowline EPR spectra indicating the coexistence of two phases wherein the radical can undergo either slow motions the slow phase or fast motions the fast phase. The NMR experiments were capable of distinguishing motional activity as a function of proton position along the block. Both the EPR and NMR results indicated that main-chain segmental motion at the center of the DMS blocks exceeded that at the ends and propagated outward along the block as the temperature increased. The temperature dependence of the ratios of a the number of radicals in the fast phase to the number in the slow phase and b the protons in the rubbery phase to those in the rigid phase agreed qualitatively with this model.

Descriptors:

• *NUCLEAR MAGNETIC RESONANCE
• *PHASE TRANSFORMATIONS
• *COPOLYMERS
• *TRANSITION TEMPERATURE
• *ELECTRON PARAMAGNETIC RESONANCE
• *BLOCK POLYMERS
• POLYMERS
• MOTION
• ELECTRON SPIN RESONANCE
• SILOXANES
• CROSSLINKING(CHEMISTRY)
• RELAXATION TIME
• NITROGEN OXIDES
• EPOXY RESINS
• POLYCARBONATES
• CHEMICAL RADICALS
• PLASTICIZERS

Subject Categories:

• Polymer Chemistry
• Atomic and Molecular Physics and Spectroscopy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE