Poly organic resist materials

In the eady 1920s, experimentation with urea—formaldehyde resins [9011-05-6] in Germany (4) and Austria (5,6) led to the discovery that these resins might be cast into beautiful clear transparent sheets, and it was proposed that this new synthetic material might serve as an organic glass (5,6). In fact, an experimental product called PoUopas was introduced, but lack of sufficient water resistance prevented commercialization. Melamine—formaldehyde resin [9003-08-1] does have better water resistance but the market for synthetic glass was taken over by new thermoplastic materials such as polystyrene and poly(methyl methacrylate) (see Methacrylic polya rs Styrene plastics). 

Plasticizers. Plasticizers are materials that soften and flexibilize inherently rigid, and even britde polymers. Organic esters are widely used as plasticizers in polymers (97,98). These esters include the benzoats, phthalates, terephthalates, and trimeUitates, and aUphatic dibasic acid esters. Eor example, triethylene glycol bis(2-ethylbutyrate) [95-08-9] is a plasticizer for poly(vinyl butyral) [63148-65-2] which is used in laminated safety glass (see Vinyl POLYMERS, poly(vinyl acetals)). Di(2-ethyUiexyl)phthalate [117-81-7] (DOP) is a preeminent plasticizer. Variation of acid and/or alcohol component(s) modifies the efficacy of the resultant ester as a plasticizer. In phthalate plasticizers, molecular sizes of the alcohol moiety can be varied from methyl to tridecyl to control permanence, compatibiUty, and efficiency branched (eg, 2-ethylhexyl, isodecyl) for rapid absorption and fusion linear (C6—Cll) for low temperature flexibiUty and low volatility and aromatic (benzyl) for solvating. Terephthalates are recognized for their migration resistance, and trimeUitates for their low volatility in plasticizer appHcations. 

As may be expected of an amorphous polymer in the middle range of the solubility parameter table, poly(methyl methacrylate) is soluble in a number of solvents with similar solubility parameters. Some examples were given in the previous section. The polymer is attacked by mineral acids but is resistant to alkalis, water and most aqueous inorganic salt solutions. A number of organic materials although not solvents may cause crazing and cracking, e.g. aliphatic alcohols. 

If we consider the LOI values reported in Table 8, it can be clearly seen that the flame resistance of polyphosphazenes is very high and can reach values above 60 when halogenated phenoxy groups (e.g. 4-bromophenoxy) are attached to the polymer chain. However, enhancement of the carbon content in the materials (i.e. by increasing the percentage of organic substituents in the chain) induces a concurrent decrease in the flame resistance of POPs, which can be depressed to 23.4 in the case of poly[bis(4-/sopropylphenoxy)phos-phazene]. 

Photocrosslinking. The second class of photopolymer chemistry that is used in some commercial products is based on the reaction of unsaturated moieties attached to an organic polymer. These photopolymer materials include the [2+2] cycloaddition of the ethylenic groups in poly(vinyl cinnamate) polymers and in the newer styryl pyridinium (10) and thiazolium (77) derivatives of poly(vinyl alcohol). The main advantage of this chemistry is that, unlike free-radical photopolymerization, they are insensitive to the presence of oxygen. This photopolymer mechanism is principally used in applications employing a washout development process (e.g. resists). 

First of all, these materials are ttractive "per se". In particular, poly(styrene-b-caprolac tone) is a semi-crystalline product displaying an amazing resistance to cold-fracture, and also macroscopically biodegradable at least when PCL represents the continuous phase. It can be "organized" into single crystals, wherein lamellae of PSt and PCL alternate with a periodicity of about 80 A. 

As for enviromnental resistance, there exists a design chart that is somewhat useful for this case study, but, more importantly, may be of use in other designs. The compatibility of various materials in six common environments is shown in Figure 8.16. The suitability of a material for each of the six environments improves as you move from the center of the chart outward. In this case, resistance to organic solvents is of primary importance. We see that all ceramics and glasses, all alloys, and some polymers such as poly(tetrafluoroethylene), PTFE, will provide excellent resistance. Composites will provide good resistance, which may be satisfactory for our application. 

Organic-silica hybrid materials have been used for multi-photon microfabrication. These include the acrylate-functionalized oligosiloxanes known as ORMOCERs, which have been polymerized by radical processes using conventional IP radical iniatitors, such as c.2 [221,234]. Commercial poly(dimethylsiloxane)-based resists containing vinyl and Si-H functionalities use two different 2PA-induced processes hydrosilylation catalyzed by the photodecomposition products of Cp PtMes (Cp = ti -methylcyclopentadienyl) and radical initiation by c.4 (Fig. 13) [235]. The former process was complicated by thermally-induced polymerization. 

The other major springboard for the fluorocarbon chemical industry was the "Manhattan Project to develop the atomic bomb. This required the large-scale production of highly corrosive elemental fluorine and uranium(VI) fluoride for the separation of the radioactive 235U isotope. Oils capable of resisting these materials were needed to lubricate pumps and compressors, and polymers were needed to provide seals. Peril uorinated alkanes and polymers such as PTFE and poly(chlorotrifluoroethylene) (PCTFE) proved to have the appropriate properties so practical processes had to be developed for production in the quantities required. In 1947 much of this work was declassified and was published in an extensive series of papers3 which described the fundamental chemistry on which the commercial development of various fluoro-organic products, especially fine chemicals, was subsequently based. 

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