Laced polymer

The less simple polymers (like the epoxies, the polyesters and the formaldehyde-based resins) are networks each chain is cross-linked in many places to other chains, so that, if stretched out, the array would look like a piece of Belgian lace, somehow woven in three dimensions. These are the thermosets if heated, the structure softens but it does not melt the cross-links prevent viscous flow. Thermosets are usually a bit stiffer than amorphous thermoplastics because of the cross-links, but they cannot easily be crystallised or oriented, so there is less scope for changing their properties by processing. 

Ziegler, an organic chemist who had little experience with polymers, recognized that this unanticipated result might lead to a method to make linear polyethylene. He knew that there would be a demand for such a material from any number of industrial companies, and he wanted to be the one to hold the first patents. He told his student, Heinz Breil, to test the reaction with ethylene systematically with as many other metals as he could find. In a short time, after trying a number of different metals, Breil ran a reaction laced with zirconium and produced a large quantity of linear polyethylene. 

Figure 18.11. Lacing value vs. time of moisture absorption. [Adapted, by permission, from Hansen H, Polymers, Laminations Coatings Conference, 1995, 653-8.]...

If the solution is cooled slowly (8 C/mln to 1350 C/min), Sol 2 micelles appear. If, however, cooling is too rapid ( b2,000 C/min), a continuous lace-like, noncellular polymer network is apparent in photomicrographs. This lace-like network is the frozen Sol 1 structure which, for kinetic reasons, is unable to assume the Sol 2 configuration before it becomes immobilized. 

C. Either mechanical or pneumatic foam whipping of the oligomer or polymer solution or emulsion contact of the inhibiting vapor phase in the presence of a structural surfactant. The foam is then fixed by lacing the polymer walls. 

MEH-PPV polymer apparently shows very different properties than those of DOO-PPV and PPVDO polymers discussed in Section 22.3.1. Due to its side group the MEH-PPV polymer is able to form an ordered phase when films are cast from bad solvents such as toluene [153,154]. In such films two or more polymer chains are coupled together due to increased interchain interaction, which renders the benzene rings of the polymer backbone to lace each other. Under these conditions the primary excitations and polaron wavefimctions may acquire enhanced 2D delocalization that is in fact spread over two or more chains. Such delocalized photoexdtations were identified in other polymers with improved order such as PFO, mLPPP [54], and regioregular P3HT [72], which will be discussed later. 

From the change of p in presence of polymer the effective hydrodynamic thickness L, is obtained by equation 7 rq>lacing by Li. 

However, notably, none of these models follow the process beginning with the original pellet that then melts and evolves from a pellet to a sheet to a lace and only then to a filament. The models described in the preceding paragraph [144,154,160, 161] are further limited to rather dilute systems. More work is required in modeling of morphology development of polymer blends. 

The science of polymers, natural and artificial, is then a subject of enormous scope, and a book the size of this can do it scant justice. I hope all the same that this brief survey of the field and its often colourful history will convey its allure, and perhaps even stimulate further explorations. The narrative demands no advanced or specialized knowledge, and is meant to be accessible to the layman. Chemistry at a basic level would of course be helpful, and I have laced the text with formulae, mainly of simple compounds, to prod the memories of readers who have forgotten what they may have learned at school. I have provided a list of books and articles for anyone wishing to pursue the subject in greater depth. 

Rosenblum and cowoikers have described a number of routes to lace-to-lace polymetallocenes. Ruthenium- and iron-based materials were synthesized via palladium-catalyzed cross-coupling reaction of 1,8-diiodonaphthalene with metallo-cenylzinc chloride (M=Fe, Ru). The MW of the face-to-lace polyferrocenes with R=H,R = 2-octylwasintherangeof 18,000, while that of200 when R=R =2-octyl, was 139,000. The conductivity of polymer 200 (M=Fe, R=H, R =2-octyl) on doping with I2 was 6.7 X 10 S/cm. The incorporation of nickelocene and cobaltocene units into the fece-to-lace polyferrocenes resulted in materials with magnetic susceptibilities of 3.51 and 5.2 (1 for the Ni Fe and Co Fe ohgomers, respectively. ... 

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