Push-pull polymers

In push pull polymer 77, both the absorption and emission maxima are red-shifted relative to 1. The LED performance of these materials appeared to be rather low (the EL efficiency of 0.002cd/A and the maximum luminance of 100cd/m2 was achieved at 30 V), and the turn-on voltage for the push-pull polymer 77 (4 V) was lower than that in more electron-deficient polymers 75 and 76. 

Fig. 9 Time-resolved measurements of the photochemical phase transition of the push-pull polymer azobenzene liquid...

Shi Y, Lin W, Olson DJ, Bechtel JH, Wang W (1999) Microstrip line-slot ground electrode for high-speed optical push-pull polymer modulators. In Organic thin films for photonic applications. Optical Society of America, Washington DC, p 20... 

Osmotic Pressure Controlled Oral Tablets. Alza Corp. has developed a system that is dependent on osmotic pressure developed within a tablet. The core of the tablet is the water-soluble dmg encapsulated in a hydrophobic, semipermeable membrane. Water enters the tablet through the membrane and dissolves the dmg creating a greater osmotic pressure within the tablet. The dmg solution exits at a zero-order rate through a laser drilled hole in the membrane. Should the dmg itself be unable to provide sufficient osmotic pressure to create the necessary pressure gradient, other water-soluble salts or a layer of polymer can be added to the dmg layer. The polymer swells and pushes the dmg solution through the orifice in what is known as a push-pull system (Fig. 3). The exhausted dmg unit then passes out of the body in fecal matter. 

Polymers and supermolecules modified using electron push-pull chro-mophores are also of particular interest for nonlinear optics (NLO) [10-15]. NLO material has attracted much interest over the past 20 years and has been widely applied in various field (telecommunications, optical data storage, information processing, microfabrication, etc.). Chemists have developed ways to introduce NLO chromophores into many type of polymers, such as Hnear polymers, cross-linked polymers, and branched polymers, and have demonstrated their performance in NLO appHcations. 

Delivery systems that use a multicompartment core can theoretically deliver drugs of any solubility [48,49], A basic Push-Pull System consists of two layers the Lrst contains the drug, osmotically active hydrophilic polymer(s), and other pharmaceutical excipients the second layer, often called the push layer, contains a hydrophilic expansion polymer, other osmotically active agents, and the excipients, as shown in Figure 22.6. Poorly water-soluble compounds can be delivered using an ORO Push-Pull tlelivery system by incorporating drug as a micronized form, or as a hot-melt material suspended in a polymer matrix. 

As concerns photochromes in a solid matrix, a question that immediately arises is to what extent the nature of the matrix impedes the photochromic reaction. This problem has been studied in detaih but it is beyond the scope of this review. There is a general rule that states photochromic reactions are sluggish in polymer matrices compared to fluid solutions. This statement is true for some stilbene derivatives, but it is not true for azo derivatives, especially for push-pull azobenzene derivatives like DRl, for which the trans->cis quantum yield equals 0.11 in PMMA at 20°C compared to 0.24 in a liquid hydrocarbon mixture at -110°C. Photochromism of spiropyrans shows an important matrix effect as the quantum yield for the conversion between the spiropyran and the photomerocyanin is equal to 0.8 in ethyl acetate and decreases to 0.102 in PMMA at room temperature. The same decrease is observed for the back photochemical reaction efficiency 0.6 in ethyl acetate, compared with 0.02 in PMMA at room temperature. Conversely, the matrix effect is much less for furylfulgides the quantum yields are almost the same in solutions as in polymer matrices. Although most of photochromic molecules exhibit photochromism in polymers and sol-gels, few of them exhibit this property in the crystalline state, due to topochemical reasons. However, some anils and dithienylethenes are known to be photochromic in the crystalline state. 

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