Poly upon irradiation

Other hand, when an equimolar mixture of 2,5-DSP and l OEt is recrystallized from benzene, yellow crystals, comprising 2,5-DSP and l OEt in a molar ratio of 1 2, deposit. In the DSC curve of this crystal, a single endothermic peak is observed at 166°C, which is different from the melting point of either 2,5-DSP (223°C) or l OEt (156°C). Furthermore, the X-ray powder diffraction pattern of the crystal is quite different from those of the homocrystals 2,5-DSP and l OEt. Upon irradiation the cocrystal 2,5-DSP-l OEt affords a crystalline polymer (77i h = 1.0 dl g in trifluoroacetic acid). The nmr spectrum of the polymer coincides perfectly with that of a 1 2 mixture of poly-2,5-DSP and poly-1 OEt. In the dimer, only 2,5-DSP-dimer and l OEt-dimer are detected by hplc analysis, but the corresponding cross-dimer consisting of 2,5-DSP and l OEt is not detected at all (Hasegawa et al., 1993). These observations by nmr and hplc indicate that the photoproduct obtained from the cocrystal 2,5-DSP-l OEt is not a copolymer but a mixture of poly-2,5-DSP and poly-l OEt in the ratio 1 2. 

Another class of "chain scission" positive resists is the poly(olefin sulfones). These polymers are alternating copolymers of an olefin and sulfur dioxide. The relatively weak C-S bond is readily cleaved upon irradiation and several sensitive resists have been developed based on this chemistry (49,50). One of these materials, poly(butene-l sulfone) (PBS) has been made commercially available for mask making. PBS exhibits an e-beam sensitivity of 1.6 pC cm-2 at 20 kV and 0.25 pm resolution. 

The use of phenolic polymers in photocrosslinkable systems usually involves multicomponent systems which incorporate polyfunctional low molecular weight crosslinkers. For example, Feely et al. [9] have used hydroxymethyl melamine in combination with a photoactive diazonaphthoquinone which produces an indene carboxylic acid upon irradiation to crosslink a novolac resin. Similarly, Iwayanagi et al. [10] have used photoactive bisazides in combination with poly(p-hydroxy-sty-rene) to afford a negative-tone resist material which does not swell upon development in aqueous base. 

This study will show an approach to materials which have many of the desirable features of the poly(phthaladehyde)-onium salt imaging system but do not suffer from the problem of spontaneous gaseous material evolution upon irradiation. The new polyformal-based imaging systems all have a "built-in" thermal activation requirement which allows for image self-development outside of the exposure tool. 

During photolysis, the double bond content of the polysilane(P-l)(15mol% in this experiment) decreased to 10mol%, as measured by 1H-NMR spectroscopy. However, the ratio, quantum yield of scission(Q(S))/quantum yield of crosslinking(Q(X)), was not affected by the reaction of the double bond. West and his coworkers have reported that poly((2-(3-cyclohexenyl)-ethyl)methylsilane-co-methylphenylsilane) crosslinked upon irradiation(55). The difference between our results and West s may lie in the amount of the double bond and inhibitation of the radical closslinking by the phenol moiety. Polysilane with a halogen moiety, P-8, photodecomposed rapidly, compared with P-1 or P-3. The introduction of a chloride moiety was effective for the sensitization of the photodegradation. Similar results has already been reported(55). 

Interest in solution inhibition resist systems is not limited to photoresist technology. Systems that are sensitive to electron-beam irradiation have also been of active interest. While conventional positive photoresists may be used for e-beam applications (31,32), they exhibit poor sensitivity and alternatives are desirable. Bowden, et al, at AT T Bell Laboratories, developed a novel, novolac-poly(2-methyl-l-pentene sulfone) (PMPS) composite resist, NPR (Figure 9) (33,34). PMPS, which acts as a dissolution inhibitor for the novolac resin, undergoes spontaneous depolymerization upon irradiation (35). Subsequent vaporization facilitates aqueous base removal of the exposed regions. Resist systems based on this chemistry have also been reported by other workers (36,37). 

Note 3 A polymer showing a substantial increase in electric conductivity upon irradiation with ultraviolet or visible light is called a photoconductive polymer an example is poly(A-vinylcarbazole) (see [2], p. 302 for photoconductivity). 

Recently Allbritton and Li coated polydimethylsiloxane (PDMS) microfluidic channels with BP [36]. Upon irradiation in the presence of a monomer solution, they were able to graft poly(acrylic acid) and poly(ethylene glycol) monomethoxyl acrylate to the interior walls of the channels. This is a significant achievement since the device did not require disassembly in order to modify the channel walls. The electrophoretic separation of the modified channels was different from the native channels. This technique holds particular promise for the microfluidic separations commimity. 

The decrease in absorbancy of poly U upon irradiation is discussed by Swenson and Setlow.48 Their results are shown in Figure 27. In this figure is also shown the photoinduced dimer splitting. The amount of photorecovery of absorbance for any particular total dose was taken to be a measure of the amount of dimer content at that dose. The amounts of dimer so calculated are shown in Figure 28. The amount of hydrates formed were estimated by measuring the thermal recovery of absorbancy. The results of both thermal and radiation reversal are shown in Figure 29. The total recovery of absorbance for poly U irradiated at 265 nm was 87-90% (after certain corrections, it was estimated that 95% of the absorbance decrease could be accounted for by dimers and hydrates). Of this total reversal of 907o about 67% was effected by the thermal treatment, and presumably this number provides an estimate of the total fraction (0.75) of hydrates in the photoproducts. 

Fig. 35. The effect of temperature upon the template properties of poly C irradiated with UV light (Ono, Wilson, and Grossman021).

Aliphatic polyesters tend to cross-link upon irradiation. Poly(ethylene terephtalate) cross-links with a low efficiency however, it can sustain desirable physical properties up to 0.5 MGy. ... 

Upon irradiation, 1,4 polybutadienes and poly(butadiene-styrene) form free radicals relatively readily, and their concentration has been found to increase linearly proportional to dose up to approximately 100 Mrad (1,000 kGy). ... 

In recent studies, we have observed that the addition of a number of polyhalogenated compounds (see 15-17 for representative examples) greatly increases the rate of bleaching of poly(methylphenyl) silane 2 upon irradiation. This effect is dramatically demonstrated by comparison of Figures 3 and 7. For the example shown in Figure 7, <95% of the incident light (313 nm) is absorbed by the polymer. 

Table II. Various Quantum Yields Upon Irradiation of Poly (styrene-co-vinyl aliphatic ketone)s at 313 nm at 23 C in N2...

Since we had shown earlier18 that the species generated upon (dark) doping were delocalized cations (polarons), one can conclude from the above experiments that in poly(thiophene) irradiation generates both cations and cation radicals in sharp contrast to what is observed in (CH)x-... 

All the reactions may involve attack of a phenylsilyl radical formed upon irradiation on C6o to give the radical intermediate as shown in Scheme 53. There is probably a rapid equilibrium between this radical and the cyclohexadienyl radical. The product ratio depends on the relative rates of recombination with the other silicon radical produced initially. Bulky phenylalkylsilyl radicals react preferentially at the 16-position of the C6o poly cycle in the initially formed radical. In contrast, trimethylsilyl and silylsilyl radicals prefer the cyclohexadienyl ring. 

Similar photosolubility effects have been observed for azo-modified poly(L-omithine) [Scheme 5, VIII (n = 3) 139 and poly(L-a, 3-diaminopropanoic acid) [Scheme 5, VIII (n = 1), 142 monitoring transmittance at 650 nm as a function of irradiation time. The initially turbid samples in HFP/water became dear upon irradiation at 360 nm as a consequence of the trans—>ds isomerization. On new irradiation at 460 nm, the clear solutions became turbid once more as a consequence of the reverse cis/trans isomerization of the azo chromophores. 

Poly(L-lysine) V, containing about 40 mol% of p-phenylazobenzoyl units, was reported to form a stable monolayer at a water/air interface.1791 When the polypeptide monolayer was kept at a constant area, irradiation at 365 nm produced a decrease in the surface pressure, which reversibly reverted to its original value upon irradiation at 450 nm (Figure 17). At constant pressure, alternating irradiation with 365 and 450 nm light produced reversible changes in the surface area of the monolayer. 

In the second approach to self-assembly of polymer-silica nanocomposites, polymerizable surfactants are employed both to direct self-assembly into ordered mesophases and to serve as organic monomers which can be subsequently polymerized. For instance, Brinker et al. developed nonionic surfactants incorporating diacy-telene groups which could be polymerized upon irradiation by UV light.68 69 Similarly, poly(thiophene)70 and poly(pyrrole)71 have been successfully integrated into silica nanostructures in this manner. Importantly, this in situ polymerization produces isolated molecular wires, rather than clustered bundles of conductive polymer.70... 

Silyl radicals have also been observed during /-irradiation of solid polysilanes. Tagawa and coworkers examined the EPR spectrum observed upon irradiation of solid poly-(dimethylsilane) and concluded that the spectrum corresponded to silyl radicals generated by homolysis of the silicon skeleton in the polysilane (equation 5)18. Indeed, the EPR spectrum of the poly(dimethylsilane) radical (13), with hyperfine splitting constants H) and a(y-1 H) of 0.813 and 0.046 mT respectively, corresponded remarkably well to that published for the dimethyl(trimethylsilyl)silyl radical [a( -1H) = 0.821 mT a(/-1H) = 0.047 mT]1. Radical (13) appears to be very stable in solid poly(dimethyl-silane), since the EPR signal was strong and clearly observable at room temperature. 

The Ni and Pt complexes can also be incorporated into polymer films of quaternized poly(vinylpyridine) (PVP) and deposited onto the transparent electrode (84). Photocurrents are enhanced to microamps (pA), an increase that may be attributed to either the effect of immobilization of the complexes near the electrode surface or an increase of the excited-state lifetimes in the polymer matrix. However, the effective concentrations of the complexes in this study were much greater than for the acetonitrile solutions in their earlier work. The polymer films are not stable to continuous photolysis, and voltammograms of the films are quite sensitive to anions used in the supporting electrolyte. The system can be stabilized by using a polymer blend of PVP and a copolymer containing quaternary ammonium ion and including [Fe(CN)6]4- in the electrolyte solution (85). Upon irradiation of the visible MLCT bands of [M(mnt)2]2 (M = Ni, Pt), photocurrents are produced. The mechanism (Scheme 4) is believed to involve photooxidation of the metal bis(dithiolene) triplet state by the Sn02 electrode, followed by [Fe(CN)6]4 reduction of the monoanion, with completion of the ET cycle as ferricyanide, Fe(CN)6 3, diffuses to the other electrode and is reduced. 

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