Polystyrene activation spectrum

Figure 1 shows the activation spectrum of polystyrene measured by Hirt and co-workers (8). It represents the yellowing, as measured by the increase in absorbance at 4000 A., caused by the various wavelengths of ultraviolet radiation between 2800 and 4000 A. The ultraviolet source used for these measurements was a xenon arc equipped with a borosilicate... 

Figure I. Activation spectrum of polystyrene measured by Hirt et al. (8)...

The authors thank N. Z. Searle for the activation spectrum of polystyrene and M. Maiullo for carrying out part of the experimental work. 

On the other hand, the excimer emission because it is 80% non-correlated with monomer trap emission and because it is effectively quenched in the copolymers even at low temperatures, must largely arise from a mobile precursor. The activation energy for hopping of this precursor is implied to be <10 cm l. This is not unreasonably low(12,17), and indeed, the zero-point energy of the phenyl chromo-phore could in principle allow completely activationless hopping (tunneling) at reasonable rates. Determination of the true situation will require measurements at still lower temperatures, which are now in progress. We note that the polystyrene emission spectrum at 4.2K reported in (Id) indicates a monomer/excitner intensity ratio nearly the same as our 20K spectra. 

Andrady [122] reported an activation spectrum for yellowing of expanded, extruded polystyrene sheets, exposed to filtered xenon-source radiation, using the cut-on filter technique. Yellowness Index as well as the L, a, b color parameters were determined. The activation spectrum for yellowing shown in Fig. 12 shows the most effective radiation band in the source spectrum to be X = 310-345 nm. 

Fig. 12. Activation spectrum for change in yellowness index of extruded, expanded, polystyrene foam on exposure to a filtered xenon source (189 h exposure at 50 Q determin by the cut-on filter technique [122]...

Spectral sensitivity of polystyrene to yellowing on exposure to white light (already referred to in Sect. 2.3) was reported by Allan et al. [20]. While no activation spectrum was reported, they obtained a quantum yield spectrum for yellowing of polystyrene. 

One of the most useful properties of polymerization systems involving styrene or the dienes is the appearance in the solutions of colour associated with the actual active centres. For example, living polystyrene solutions in tetrahydrofuran show a strong red colouration which disappears immediately on the introduction of a trace of oxygen, water or carbon dioxide. The source of this colour is a strong absorption band (e 10 ) in the near-ultraviolet region of the spectrum. The positions of the maximum and intensity of absorption are not very sensitive to changes in solvent or counter-ion (Fig. 1) [Xmax polystyryl anion 328—346 mp, 1.2—1.4 x 10 Xmax polyisoprenyl anion 270—315... 

An optically active polystyrene derivative, 40 ([a]25365 -224° to -283°), was prepared by anionic and radical catalyses.113 The one synthesized through the anionic polymerization of the corresponding styrene derivative using BuLi in toluene seemed to have a high stereoregularity and showed an intense CD spectrum whose pattern was different from those of the monomer and a model compound of monomeric unit 41. In contrast, polymer 42 and a model compound, 43,... 

The IR spectrum of the polymer film prepared under Condition B is shown in Fig. 23. A structure close to polystyrene is revealed as evidenced by peaks at 540, 700, 760, 840, 1070, 1450, 1490 and 1600 cm . Solubility tests with various solvents proved that the polymer was highly cross-linked. The spectrum of the polymer powder is quite different from that of the film. Peaks assignable to acrylic ester and/or epoxy groups (3400, 1720, 1600, 1500, 1200 and 820 cm ) prevail in that spectrum together with that of polystyrene as shown in Fig. 24. Oxidation of the polymer may be the result of reaction with oxygen in the air after the polymer was taken out from the reactor, as pointed out by several authors (8). It suggests that the powder contains many more active sites, e.g. radicals, than the film. The spectrum corresponding to Condition A is shown in Fig. 25, and is seen to have features similar to both of the previous spectra. Thus, it is seen that the structure of the plasma-polymer depends on the polymerization conditions. 

On addition of a stoichiometric amount of anthracene the characteristic spectrum of living polystyrene is replaced by that of the adduct, ( SAn ). The rate of styrene addition, i.e., propagation, becomes very slow and analysis of the kinetic data indicates that the observed reaction arises from the addition to a minute fraction of the active, living polymers, S", which are in equilibrium with the non-active, dormant polymers, SAn". Hence, the rate of propagation decreases inversially proportionally with the increasing concentration of the anthracene excess1 5. 

Grubbs and co-workers have reported the use of polystyrene supported cyclopentadienyl Rh complexes for the hydroformylation of pent-l-ene. Increased selectivity was obtained by increasing the H2 CO ratio or by adding triphenylphosphine where 5% pentane was formed as a by-product. The catalyst did not lose activity on re-use and no change in the i.r. spectrum of the catalysts was observed. 

An important feature of polymer synthesis by the active ester method is that displacement of the polymer-bound activating 0eaving) groups can be readily monitored by IR qiectroscopy of the polymer. Tl% IR spectrum generally shows the disappearance of the phenyl ester carbonyl at about 1760 cm, and the appearance of a new carbonyl absorption at 1620-80 cm (amide) and/or 1720-30 cm (ester), together with other characteristic absorptions due to A and A. In some cases, a relatively weak polystyrene band at ca. 1607 cm is also observed. A typical illustration is provided by Fig. IS, showing the amino-lysis of the activated polymer with 6-tert.-butoxycarbonylaminohexylamine, followed by reaction with dimethylamine (see the first entry in Table 7). 

Diacyl peroxides are used in a broad spectrum of applications, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrylates, and in many non-polymeric addition reactions. The activities of acyloxy radicals in vinyl monomer polymerization (79,80) and imder high-pressure conditions (81,82) have been investigated. 

Table 9.9 Evaporation temperature and activation energies for some of the peaks in the argon Cl spectrum of polystyrene ...

On the other hand, the spectrum of the THF-insol. (spectrum (C) of Figure 3) was quite different from that of the THF-sol. The peaks at 145.6, 45.0, and 41.6 ppm were coincident with those of syndiotactic polystyrene. These findings indicate that the copolymer obtained is a mixture of ES alternating copolymer and syndiotactic polystyrene, suggesting that the active center producing ES alternating copolymer is different from that producing syndiotactic polystyrene. 

The main structural results on these copolymers were obtained for products of low styrene content 41,154) polymerized with Ti-based systems. In all cases the total polymer products can be separated into two parts atactic polystyrene (soluble in ketones) and the true copolymers. These products do not contain isotactic polystyrene 41), which verifies the suggestion that this atactic polystyrene is formed on cationic active sites rather than cm the usual Ziegler-type centers. Copolymers of low styrene content have the styrene units isolated independently from the rit2 value. This was proved by IR and NMR spectra studies. Styrene units absorb at frequencies characteristic for isolated groups at 550-560cm" and at 1075cm" when the styrene content is 5.7-19.1% 41,154), and give rise to a resonance at t 298 in the NMR spectrum (154). 

Solutions of sohds may also be used, and tetrachloromethane, CCI4 is often used as solvent, since it has few IR-active bands, mostly at the low wavenumber end of the spectrum. These must be ignored when the spectrum is interpreted. Thin films of solids such as polymers may be supported directly in the IR beam. Polystyrene is a useful calibration sample to check the performance of an IR spectrometer (see Fig. 1 in Topic Ell). 

Figure 6.1. H NMR spectrum of a polystyrene (with = 1800g-mol ) activated by two different acetai functionai groups.

The hindered piperidines exhibit a complex behaviour when present in combination with other antioxidants and stabilizers. As discussed earlier (see Section 19.4.2.1), these have to be oxidized first to the corresponding nitroxyl radicals before becoming effective. Consequently, both CB-D and PD-C antioxidants which remove alkylperoxyl radicals and hydroperoxides respectively, antagonize the UV stabilizing action of this class of compounds. However, since the hindered piperidines themselves are neither melt nor heat stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. By contrast, the derived nitroxyl radicals are much more effective broad spectrum stabilizers, since not only are they more effective UV stabilizers but they are also highly efficient melt stabilizers and have some thermal antioxidant activity. Hindered piperidines have been reported to synergize with UV absorbers, e.g. the benzotriazole UV stabilizers, in different polymers such as polypropylene, polystyrene and ABS. ... 

More recently, Wang and co-workers reported on a solid-phase total synthesis of 1-p-methylcarbapenem 97 because of interest in its potent broad-spectrum antibiotic activity. In this total synthesis (Scheme 3.19), azetidinone 92, bearing a chiral auxiliary, was loaded onto polystyrene-diethyl-silane resin 91 to give 93, which was condensed with allyl bromoacetate to give supported azetidinone 94. Treatment with TMSCl in the presence of NaN(TMS)2 and diphenyl phosphorochloridate (DPPC) promoted a Dieckmann-type cyclization to give supported vinyl phosphate 95 with concomitant release of the chiral auxiliary. Vinyl phosphate resin 95 was treated with thiophenol to give supported 1-P-methylcarbapenem 96, which was released from the solid support upon treatment with tetra-H-butylammonium fluoride (TBAF). 

---