Doctoral Dissertations

Date of Award

8-1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Jeffrey D. Kovac

Committee Members

John F. Fellers

Abstract

Gradient polymers are multicomponent polymers whose chemical constitution varies with depth in the sample. Although these polymers may possess unique mechanical, optical, and barrier properties they remain relatively unexplored. This work is a study of the preparation of gradient polymers by sequential exposure of films to a diffusing monomer followed by electron beam irradiation.

Initial experiments involved immersion of poly(vinyl chloride) (PVC) films in styrene or n-butyl methacrylate (BMA) for various time periods followed by irradiation with 1 or 10 megarads of accelerated electrons. A significant amount of poly(n-butyl methacrylate) (PBMA) formed in PVC/BMA systems, but little polystyrene could be found in the PVC/styrene films.

A second set of experiments involved immersion of PVC and polyethylene (PE) films in BMA for 20, 40, 60, and 720 minutes followed by irradiation with 10 megarads of electrons. These films were then characterized using optical microscopy, quantitative transmission Fourier transform infrared spectroscopy (FTIR), and a depth profiling procedure based on quantitative attenuated total reflection (ATR) FTIR.

It was found that the cores of the polyethylene films contained high concentrations of PBMA whereas the surfaces possessed little or none. The PVC/BMA films contained a mixture of residual BMA and PBMA with PBMA concentration increasing with immersion time. BMA monomer appeared to be uniformly distributed within the films. A depth profile of PBMA in the PVC/BMA films could not be determined due to interference by the residual monomer. PBMA concentration within the PVC/BMA films are probably proportional to BMA concentrations at the time of irradiation. BMA concentrations later equilibrated between these films by vapor-phase transfer during storage.

It was concluded that the mechanism of PBMA formation in the polyethylene films was a result of events immediately following irradiation. Atmospheric oxygen diffusing into irradiated films trapped free radicals at the film surfaces. This was followed by storage in an evacuated desiccator where unintentional exposure to BMA vapor took place. This BMA reacted with free radicals that remained within the film cores, polymerizing to PBMA. Additional PBMA may have polymerized near the film surfaces by reaction with peroxides and hydroperoxides there.

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