Ketone copolymers irradiation

Figure 1. Irradiation of PS-vinyl aliphatic ketone copolymers in N2 at...

Recently it has been shown (36) that electron-beam irradiation of styrene-vinyl ketone copolymers show higher yields of type-I radicals than expected from UV photolysis measurements. It seems clear that some part of the excess energy of high-energy photons and electrons is imparted to the translation kinetic energy... 

Shvinskas, J.A. and Guillet, J.E., y-Radiolysis of ketone polymers. II. y-Irradiation of styrene-methyl vinyl ketone copolymers, /. Polym. Sd. Polym. Chem. Ed., 11, 3057, 1973. 

Photon sensitivities are measured relative to PMMA and were obtained by imaging a 1mm wide slit, illuminated by a 1000 watt Hg lamp focused through quartz condenser optics, onto the substrate for varying times. Exposure times were recorded as the time necessary to allow complete removal of the resist in the irradiated areas, with no thinning in the unexposed areas. The irradiated films were developed in methyl isobutyl ketone (MIBK)/2-propanol (7 3 v/v) for the copolymers and terpoly-mers, and MIBK for PMMA. 

FTIR measurements on the PS-tBVK copolymer showed that after irradiation, a new absorbance in the carbonyl stretching region at 1730 cm-1 appeared in the polymer. This absorbance increased with time of irradiation while that of the original ketone absorbance at 1700 cm-1 decreased, as shown in Table IV. 

Alkyd and polyester resins, epoxy compounds, phenol-formaldehyde resin, urea and/or melamine-aldehyde resin, cyclic urea resin, carbamide acid ester formaldehyde resin, ketone formaldehyde resin, polyurethane, polyvinylester, polyvinyl acetate, polyvinyl chloride and polymer mixtures, polyethylene, polystryrene, styrene mixtures and graft copolymers, polyamide, polycarbonate, polyvinyl ether, polyacrylic and methacrylic acid esters, polyvinyl flouride, polyvinylidene chloride copolymers, UV and/or electron irradiated lacquers. 

If one wishes to prepare a positive photoresist it is important to obtain polymers vdiich undergo efficient chain scission in the solid phase. Recently we reported studies on a series of copolymers of styrene with a variety of ketone functional groups which were introduced by copolymerization with substituted vinyl ketone monomers. The copolymer structures are shown schematically in Table V. Two processes are responsible for the reduction in molecular weight in these polymers when irradiated with either UV light or electron beams. These are shown schematically below. 

The IR spectra of an AES film recorded in the hydroxyl vibration region during the first 38 h of irradiation showed an increase in a broad absorption band centered around 3450 cm-1 attributed to hydroperoxides. The development of a complex band with a maximum at 1713 cm-1 and shoulders around 1690, 1730 and 1770 cm-1 was observed in the carbonyl vibrations region (Figure 30.6). These maxima correspond to carbonylated photoproducts that have been previously identified during photooxidation of EPDM [17] and ethylene-propylene copolymer [18]. The bands at 1713, 1730 and 1770cm-1 correspond, respectively, to the absorption of saturated acids (dimer form) and ketones, esters and lactones or peresters the absorption around 1690 cm-1 is related to the presence of unsaturated carbonyl species. 

More detailed investigations on the photoreactive behaviour of polymeric systems based on the benzoin moiety have been described [103]. Indeed, poly (benzoin acrylate) [poly(AB)] and copolymers of benzoin acrylate with styrene or MMA [poly(AB-co-St) and poly(AB-co-MMA), respectively] have been prepared and characterized. Poly(AB), when irradiated by UV light in the presence of photosensitizers such as benzophenone, /r-beiraxpiinone or methyl phenyl ketone, gives a benzene-insoluble crosslinked polymer. 

Copolymers. The copolsmers were prepared by emulsion polymerization in a "pop bottle" polymerizer at 80° C using sodium aryl alkyl sulphonate (Ultrawet K) as emulsifier and ammonium persulphate as catalyst. The polymerizations were carried to greater than 95% conversion (4-8 hr) and the feed concentrations of the vinyl ketones were taken as their concentrations in the polymer. Copolymers containing 1% and 5% by weight of vinyl ketones were prepared. The cqsolymers were not homogeneous in ketone concentration since the reactivity ratios indicated that the vinyl ketones would be used ip before the end of the polymerizations. Thin films were prepared for irradiation by compression molding in a Carver Press at 150° C at 20,000 psi. The films were usually 0.22 mm thick. 

It is important to point out that the quantum yield for the Norrish II chain scission reaction ( Cs) is highly affected by the mobility of polymer chains. For example, the photolysis CS for a film of the copolymer poly(styrene-co-phenyl vinyl ketone) irradiated at 313 nm in the solid state was shown to be low (0.04—0.09) at temperatures below the copolymer Tg (glass transition temperature) but increased dramatically at,... 

On irradiation with ultraviolet light, the activated ketone groups present can take part in two different types of free radical, bond-breaking reactions. In organic photochemistry, these two reactions are referred to as Norrish I and Norrish II Reactions, and their mechanisms are shown below for the degradation of copolymers of ethylene and carbon monoxide [46, 47] ... 

Weak delayed-emission spectra of vacuum- or air-irradiated copolymer films were similar in intensity and showed a phosphorescence maximum at 432 nm with shoulders ca. 390 nm and 450 nm on excitation at 260 nm in addition to a very weak maximum at 505 nm excited at 380 nm. These spectra are close to those shown in Figure 4 for ketone phosphorescence in photooxidized polystyrene and agree reasonably well with phosphorescence spectra for model napthaleneones (15). Energetically, the quench-... 

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