Conformations of poly(methyl methacrylate) and its degraded forms upon radiation
- Rensselaer Polytechnic Institute, Troy, NY (United States)
The radiation-induced decomposition of syndiotatic (st) and isostatic (it) poly(methyl methacrylate) (PMMA) to yield irradiation products (PMMA(d)) resulting from hydrogen abstraction from alpha-methyl or methylene groups to form main chain (M[double bond]) or side chain (S[double bond]) double bonds is studied by conformational analysis. Relative minimum energy conformations of the st- and it-isomers of PMMA as free molecules are studied. The isomers of PMMA(d) have relative minima in an overall linear (L) chain as well as a global minimum in a bent (B) form. The impact of the change of a tetrahedral C atom to a trigonal C atom upon double bond formation on the conformational energy is fundamental to the understanding of the results. The experimental results are explained by the following theoretical observations. In reactions involving only overall linear conformations, side chain double bond formation is favored because of the resulting large increase in steric repulsion between polymer units in main chain double bond formation. In reactions proceeding to bent conformations, however, the decreased steric interaction yields both main and side chain double bond formation within 6.3 kcal/mol for the st-PMMA(d) isomer and 2.2 kcal/mol for the it-PMMA(d) isomer. Reactions on surfaces are assumed to be constrained to the overall linear conformation of the starting material, PMMA. Prevention of both M[double bond] and S[double bond] degradation products is desired for microlithographic applications. Increased solubility arising from main chain scission (MCS) is desired, and both M[double bond] and S[double bond] for that reason are undesirable with respect to resist sensitivity. It is proposed that the troublesome S[double bond] process can be attenuated or eliminated by replacing alpha-CH[sub 3] with alpha-CF[sub 3], thus enhancing the distribution of products toward MCS.
- OSTI ID:
- 5625486
- Journal Information:
- Macromolecules; (United States), Journal Name: Macromolecules; (United States) Vol. 26:18; ISSN MAMOBX; ISSN 0024-9297
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360605* -- Materials-- Radiation Effects
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CONFORMATIONAL CHANGES
DATA
DECOMPOSITION
ESTERS
EXPERIMENTAL DATA
INFORMATION
ISOMERS
KINETICS
MASKING
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PMMA
POLYACRYLATES
POLYMERS
POLYVINYLS
RADIATION EFFECTS
RADIOLYSIS
REACTION KINETICS
SOLUBILITY
SURFACES