Naphthalene Natural” polymers

The absorption and emission of radiation in the near ultraviolet (UV) and visible regions of the electromagnetic spectrum are associated with electronic (and associated vibronic) transitions involving n- and/or n-electron systems of molecules. Synthetic and natural polymers absorb in the UV region and particularly strong absorption spectra are recorded for polymers containing aromatic and heteroaromatic groups (e.g., poly(styrenes), poly(vinyl naphthalenes), poly(vinyl carbazoles)). 

The first attempts to produce a graft copolymer of poly(amino acids) onto the natural polymers, such as cellulose, starch, and their derivatives, were carried out by Zilka and Avny in 1965. Sodium methoxide was known to be an initiator of NCA polymerization. Therefore, they proposed to use alkoxide derivatives of polysaccharides as macroinitiators for the graft copolymerization of NCA s of a-amino acids. All known methods for production of alkoxide derivatives of natural polymers, such as the reaction of polyhydroxy polymers with sodium metal in liquid ammonia, or exchange reactions between lower alkoxides and polyhydroxy polymers, - were unsatisfactory for the subsequent graft copolymerization of NCAs, because any residual base would lead to homopolymerization. In addition, alkoxide derivatives of cellulose acetate and nitrocellulose could not be obtained by these conventional methods due to chemical degradation. Zilka et al., finally found that the reaction of alkali metal naphthalenes [20] with polyhydroxy polymers in either... 

Chem. Des(3ip. High m.w. naphthalene sulfonate polymer, sodium salt, low sulfate Ionic Nature Anionic CAS 9084-06-4... 

The formation ofC—C bonds between aromatic rings is an important step in many organic syntheses and can be accomplished by chemical, photochemical, or electrochemical means. As was noted earlier, fundamental considerations of the parameters for a dielectric which must be dealt with in designing a thermally stable, low-dielectric-constant polymer naturally lead one to consider rigid-rod, nonconjugated aromatic polymers containing no lossy functional groups. A structure such as poly(naphthalene) is a likely candidate. 

The third group ofpolychromophoric compounds to be discussed are homopolymers in which the pendant rings are separated from the backbone by one or more atoms. The polymers of allyl arenes, which lack only the n = 3 ring spacing of aryl vinyl polymers, have been studied very little. The fluorescence spectrum of poly(l-allyl-naphthalene) in dilute dichloromethane solution has been reported 28). Like 1-ethyl-naphthalene, the maximum intensity was seen at 337 nm, but a weak, broad shoulder was also recorded for the polymer at 410 nm. The fluorescence ratio Iu/IM for poly(l-allylnaphthalene) was only 1/100 th the value for P1VN 28). The excimeric nature of the 410 nm emission in the allyl-based polymer has not been confirmed, since neither the lifetime nor the excitation spectrum of this fluorescence band are known. 

Aromatization experiments show some evidence for relatively small aromatic substructures (naphthalene, anthracene, tetracene) and this independently demonstrates the success of the polymer-analogous cyclization process. The occurence of up to 20% non-cyclized vinylic side-groups is an indication of the statistical nature of the ring-closure reaction [58]. 

Nature of the Lower Temperature Transition. The complex nonexponential phosphorescence decays, apparent under the higher time resolution afforded by use of the modified 199 spectrometer are a consequence of interjection by the polymer matrix in the photophysies experienced by the chromophore. Non-exponential decays of triplet naphthalene (and other chromophore) emissions have been observed in PMMA. Horie et al.(18-20) ascribe such effects to dynamic, intermolecular quenching of the excited state by the polymer whereas MacCallum et al(21-23) invoke an energy migrative process within the polymer following quenching of the triplet state of the naphthalene. 

The fluorescence of the phenyl polymer is similar in shape to the fluorescence from the alkyl polymers and the similar shape of the phosphorescence spectrum, as well, suggests that the origins of the electronic spectrum are also much the same. The apparent increased quantum yield for phosphorescence in poly(phenyl methyl silylene) probably reflects a mixing of the ring electronic levels with the levels of the chain. Both the fluorescence and phosphorescence of the naphthyl derivative are substantially altered relative to the phenyl polymer. Fluorescence resembles that of poly(B Vinyl naphthalene) (17,29) which is attributed to excimer emission. Phosphorescence is similar to naphthalene itself. These observations suggest that the replacement of an alkyl with phenyl moiety does not change the basic nature of the electronic state but may incorporate some ir character. Upon a naphthyl substitution both the fluorescence and phosphorescence become primarily tt-tt like. 

Enough groundwork on the generic nature of solubility behavior in SCF solvents has been developed in the previous chapters of this book for the reader to extrapolate from the idealized situation of separating a mixture of naphthalene and chalk dust to other, more practical systems. Other systems may include the extraction of oleoresins from spices where the desired product is the extract, or the extraction of monomers and oligomers from polymers where the desired product is the purified polymer, or the separation of a mixture of chemicals where both streams are valuable products. Many of these examples are enumerated in the following chapters. 

The emission color of PAVs depends crucially on the nature of the arylene unit. Replacement of a phenylene with an oligophenylene unit produces a blue-shift in the emission, e. g. the poly(pentaphenylene vinylene) 58 is a blue emitter (2rnax = 446 nm) [71], while heterocydes induce red-shifts. This is particularly marked in the case of thiophene so that the polymer 59 actually emits in the near-infrared (7m lx = 740 nm) [72]. The picture with fused polycyclic aromatics is more complicated with the 1,4-naphthalene 19 [73] and 9,10-anthracene 60 [74] polymers both being markedly red-shifted in emission compared with PPV (1), while the 2,6-napthalene 18 [75] and 3,6-phenanthrene 61 [58] materials are slightly blue-shifted. 

---