Chromophores intrinsic polymers

Polymers with Impurity Chromophores. Although all the polymers with intrinsic chromophores are inherently sensitive to degradation, at least some are regarded as relatively stable materials, able to resist solar exposure for long... 

Polymers with Impurity Chromophores. Although all the polymers with intrinsic chromophores are inherently sensitive to degradation, at least some are regarded as relatively stable materials, able to resist solar exposure for long periods. In contrast, polymers such as the polyolefins and the hydrocarbon rubbers have remarkably poor lifetimes when exposed to solar light. Unstabilized PP film, for example, has a lifetime of only a few weeks in outdoor exposure. 

Radiation induced changes in the electronic structure of all samples were evident as changes in energy loss spectrum with increased exposure to the electron beam. The spectrum of radiation induced chromophores could thus be studied (1 ). Spectra recorded at the earliest exposure times compared favorably with optical results and are believed to contain primarily intrinsic electronic excitations (1, 2, 4). An analysis of these intrinsic spectra is the subject of the bulk of this paper. The spectra of radiation damaged polymers are described briefly after the intrinsic excitations are discussed. 

Spectroscopic sensing requires that a chromophore must be available and be influenced by the rebinding of the imprinted analyte. This can be accomplished in a variety of ways, the simplest case being when the analyte is itself a chromophore. Sensors based on intrinsic analyte chromophores can benefit from molecular imprinting by both selectivity and sensitivity enhancement. In terms of selectivity, molecules similar to the analyte are likely to have similar spectroscopic parameters that could be the source of interference in a conventional sensing strategy. The inability of an interferent to bind to the imprinted polymer allows discrimination. 

By means of comparison, in related experiments on PI-3 a and PI-3 b, the mean absorbance returned to its initial value within two minutes after removal of the irradiation light. Clearly, the polymer rigidity intrinsic to the donor-embedded samples must affect the rate of isomerization of the cis azobenzene derivative, suggesting that motion of the chromophore and the polymer backbone are somehow coupled. 

Polyamides with azobenzene groups in the backbone are among the earliest in which trans-cis isomerizable chromophores were used to regulate the polymer conformation [13, 14]. The intrinsic viscosity [q] of polyamide (6) in polar AJV-dimethyl-acetamide was found to decrease from 1.22 to 0.5 dl/g upon ultraviolet irradiation... 

This chapter concentrates on the design of efficient dipolar NLO chromophores and the different approaches for their incorporation in non-centrosymmetric materials, including guest-host polymer systems, chromophore-functionalized polymers (side-chain and main-chain), cross-linked chromophore-macromolecule matrices, dendrimers, and intrinsically acentric self-assembled chromophoric superlattices. The different architectures will be compared together with the requirements (e.g., large EO coefficient, low optical absorption, high stability, and processability) for their incorporation into practical EO devices. First, a brief introduction to nonlinear optics is presented. 

Two types of photoinitiation, the so-called Norrish type I and Norrish type II, are known. In the former, two initiating radicals are generated by a-cleavage when the initiator is exposed to UV tight. Benzoin derivatives serve efficiently for this purpose (Scheme 13.1). Such chromophores anchored to the polymer trunk, in chain or side chain, will afford block and graft copolymers, respectively. Here, homopolymer formation is an intrinsic outcome of this kind of initiation that originates from the low molar mass initiator fragment. 

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