Polymer electron beam

A disadvantage of AES is that the intense electron beam easily causes damage to sensitive materials (polymers, insulators, adsorbate layers). Charging of insulating samples also causes serious problems. 

For all three diallyl phthalate isomers, gelation occurs at nearly the same conversion DAP prepolymer contains fewer reactive allyl groups than the other isomeric prepolymers (36). More double bonds are lost by cyclisation in DAP polymerisation, but this does not affect gelation. The heat-distortion temperature of cross-linked DAP polymer is influenced by the initiator chosen and its concentration (37). Heat resistance is increased by electron beam irradiation. 

Advantages of the electron beam processor are its abiUty to penetrate thick and highly pigmented coatings. It is used to cross-link reactive unsaturated polymers, nonreactive thermoplastic polymers, iasulation, and wire-cable covetings (4,9,16) (see Insulation, electric-wire and cable COVERDIGS). 

Computers (uv and electron-beam polymer resist materials)... 

Although these polymers have iaadequate stabiUty and processibiUty for most plastics appHcations, the abiUty to undergo scission back to the gaseous monomers has afforded some utility ia fabrication of electron-beam resists for photoUthography. Polybutene sulfone (251) and polyhexene sulfone (252) have been developed for this small-volume but high value appHcation. 

Overall a customer needs to know under what circumstances it is best to use either the electron-beam techniques of EDS and WDS or the X-ray technique of XRF for an analysis problem. If both are equally available, the choice usually resides in whether high spatial resolution is needed, as would be obtained only with electron-beam techniques. If liquids are to be analyzed, the only viable choice is XRF. If one s choice is to use electron-beam methods, the further decision between EDS and WDS is usually one of operator preference. That is, to commence study on a totally new sample most electron-beam operators will run an EDS spectrum first. If there are no serious peak overlap problems, then EDS may be sufficient. If there is peak overlap or if maximum sensitivity is desired, then WDS is usually preferred. Factored into all of this must be the beam sensitivity of the sample, since for WDS analysis the beam current required is lO-lOOx greater than for EDS. This is of special concern in the analysis of polymer materials. 

Silicone acrylates (Fig. 5) are again lower molecular weight base polymers that contain multiple functional groups. As in epoxy systems, the ratio of PDMS to functional material governs properties of release, anchorage, transfer, cure speed, etc. Radiation induced radical cure can be initiated with either exposure of photo initiators and sensitizers to UV light [22,46,71 ] or by electron beam irradiation of the sample. 

An analogous mechanism should also produce polymers on irradiation of epoxies. Crivello s recent mechanistic suggestions [29] are consistent with the mechanisms given above. One can conclude that radiation-induced polymerization of epoxies can proceed via several mechanisms. However, further work is needed to determine the relative contributions of the different mechanisms, which might vary from one epoxy to another. As part of the Interfacial Properties of Electron Beam Cured Composites CRADA [37], an in-depth study of the curing mechanism for the cationic-initiated epoxy polymerization is being undertaken. 

Electron beam-initiated modification of polymers is a relatively new technique with certain advantages over conventional processes. Absence of catalyst residue, complete control of the temperature, a solvent-free system, and a source of an enormous amount of radicals and ions are some of the reasons why this technique has gained commercial importance in recent years. The modification of polyethylene (PE) for heat-shrinkable products using this technique has been recently reported [30,31]. Such modification is expected to alter the surface properties of PE and lead to improved adhesion and dyeability. 

Unsaturated polyester finishes of this type do not need to be stoved to effect crosslinking, but will cure at room temperature once a suitable peroxide initiator cobalt salt activator are added. The system then has a finite pot life and needs to be applied soon after mixing. Such a system is an example of a two-pack system. That is the finish is supplied in two packages to be mixed shortly before use, with obvious limitations. However, polymerisation can also be induced by ultra violet radiation or electron beam exposure when polymerisation occurs almost instantaneously. These techniques are used widely in packaging, particularly cans, for which many other unsaturated polymers, such as unsaturated acrylic resins have been devised. 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

Chattopadhyay S., Chaki T.K., and Bhowmick A.K., New thermoplastic elastomers from poly(ethyle-neoctene) (engage), poly(ethylene-vinyl acetate) and low-density polyethylene by electron beam technology structural characterization and mechanical properties. Rubber Chem. TechnoL, 74, 815, 2001. Roy Choudhury N. and Dutta N.K., Thermoplastic elastomeric natural rubber-polypropylene blends with reference to interaction between the components. Advances in Polymer Blends and Alloys Technology, Vol. 5 (K. Finlayson, ed.), Technomic Publishers, Pensylvania, 1994, 161. 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

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