Polystyrene para-substituted

Figure 34. The Polystyrenes. Polystyrene is a low sensitivity negative resist, poly (a-methylstyrene) is a low sensitivity positive resist and the para-substituted analogs listed are all sensitive negative resists.

Comparison of the UV spectrum of polystyrene in the 2600 A region with that of toluene shows a close relationship in terms of both extinction coefficients and vibronic fine structure. The effect of para substituents is most conveniently characterized by the shift in the band corresponding to the a0-o transition. The comparison of substituent effects on the electronic excited states of thepara substituted polystyrenes parallels those for the corresponding para substituted toluenes. Such a correlation would only be expected if the tr - n transitions were effectively localized within a given pendant group of the polymer system. This conclusion is reinforced by the observation that polystyrene and toluene show similar shake up structure in their ESC A spectra with respect to both band profiles and intensities (when due... 

Fig. 46. Experimentally derived shake up probabilities for components contributing to the low energy stake up satellites in para substituted polystyrenes...

The incorporation of diethyldithiocarbamate groups (Et)2N-C-S-R in a polymer produces active sites which on photolysis can be used for graft or block copolymerization depending on the location of the groups (185). By heating polystyrene with tetraethyl thiuram disulfide, Para substitution occurs... 

The ortho- and mem-substituted polystyrenes do not exhibit a 8 relaxation whereas para-substituted polystyrenes do. These latter materials have a 8 relaxation that is shifted towards higher temperatures as the mass of X is increased and the size of the peak depends on the nature and number of the substituents [16,24]. 

Lutz [120] et al. showed that even -with K3PO4, which is tolerated by many substrates which are labile to hydrolytic conditions, aryl triflates could be arylated. As solid phase the authors used pins [199], which are polypropylene-polystyrene resin bits which, because of their greater mechanical stability than fhat of normal polystyrene resins, can be fixed spatially on arrays of pin-holders or associated directly with Rf transponders. The authors described a method to generate triflates from meta- and para-substituted, but not ortho-substituted phenols. 

Design of Brpnsted Acids. The nucleophilic para-substitution reaction occurs with some nucleophiles. This makes it possible to design Brdnsted acids such as polystyrene resin-bound Br0nsted acid (2), fluorous Brdnsted acid (3), and dibasic acid (4)(eqs4-6). 

Work on substituted polystyrene has concentrated on a- or para-substituted variants these include ct-acetoxy, - a-methyl, flr-trideuterio-/8, -dideuterio 4-methyl, 4-methoxy, 4-isopropyl, 4-t-butyl, 4-chloro, 4-WV-dimethyT amino, - and 4-iVA -diethylaminostyrcnes. All these investigations relate to an inert atmosphere. An especially thorough analysis was carried out on the 4-W-dimethylaminostyrene and 4-A /V-dimethylaminostyrene degradation products. 

Fig. 14. X-ray scattering curves for polystyrene (un) and for meta- and para-substituted t-butyl polystyrene (m and p, respectively). Successive curves have been shifted vertically two divisions for clarity. Intensity scales (per division) un - 200 counts/s m -1,000 counts/s p - 400 counts/s.

FIGURE 1.2. Molecular structure of widely used it-conjugated and other polymers (a) poly(para-phenylene vinylene) (PPV) (b) a (solid line along backbone) and it ( clouds above and below the a line) electron probability densities in PPV (c) poly(2-methoxy-5-(2 -ethyl)-hexoxy-l,4-phenylene vinylene) (MEH-PPV) (d) polyaniline (PANI) (d.l) leucoemeraldine base (LEB), (d.2) emeraldine base (EB), (d.3) pernigraniline base (PNB) (e) poly(3,4-ethylene dioxy-2,4-thiophene)-polystyrene sulfonate (PEDOT-PSS) (f) poly(IV-vinyl carbazole) (PVK) (g) poly(methyl methacrylate) (PMMA) (h) methyl-bridged ladder-type poly(jf-phenylene) (m-LPPP) (i) poly(3-alkyl thiophenes) (P3ATs) (j) polyfluorenes (PFOs) (k) diphenyl-substituted frares -polyacetylenes (f-(CH)x) or poly (diphenyl acetylene) (PDPA). 

Oxidative coupling of phenols was first reported by Hay and coworkers in 1959" and has since been developed to produce commercially useful polymers. In these reactions the parent compound, phenol, has a potential functionality of four, that is the two ortho and the one para position of the aromatic ring and the phenolic group. Not surprisingly, the commercially useful polymers are made from substituted phenols in which the potential functionality is reduced to two. Of these phenols 2,6-dimethylphenol or orf/zo-xylenol has been developed to a commercial polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (54). The General Electric Company sells this as a blend with polystyrene under the trade name Noryl. 

Lithiated polystyrene resins can be obtained either via convenient bromine-lithium exchange reaction using nBuLi starting from 4-bromo-substituted polystyrene 102,111-115 qj. jjy direct lithiation of polystyrene using nBuLi in cyclohexane in the presence of TMEDA 11L116 pjjjj method, however, yields a mixture of para- and meta isomers. The bromination of microporous resins in the presence of the Lewis-acid catalysts was carried out in the dark whereby the degree of functionalisation could conveniently be controlled by the amount of bromine used in the reaction.iii Macroreticular resins were brominated using Br and FeClj or stoichiometric amounts of thallium acetate as Lewis acid catalysts. 2 ... 

Notation. Throughout this chapter the degree of functionalization of polystyrene is reported as DF, the fraction of rings substituted. The % yield of a transformation on a polymer is 1(X) x DF(product)/DF(reactant). The % cross-linking of a polystyrene is reported as wt % divinylbenzene (DVB) in the monom mix at the start of copolymerization. Technical DVB typically contains 55% active DVB meta and para) and 45% ethylvinylbenzenes. Thus a 2% cross-linked polystyrene also contains 1.6% ethylvinylbenzene. Circled P is used for polystyrene, either all para or mixed meta and para isomers. 

Polystyrene/Poly(styrene-co-para-fIuorostyrenc) Systems involving PS and random copolymers of styrene and fluoro-substituted styrenes are among the most... 

The solid support used by Merrifield was a type of polystyrene in which about 5% of the phenyl groups carry a chloromethyl (—CH2CI) group in their para positions (Figure 27.10). These chloromethyl groups, like all benzylic halides, are particularly reactive in nucleophilic substitution reactions. 

Excimer Stability While the adjacent phenyl rings in polystyrene form relatively stable excimers, putting substituent groups on the phenyls may alter the bonding energy. Chakraborty et al. (44) substituted bulky t-butyl groups in the para position. 

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