Prepolymerized samples

Figme 9.29 Angular selectivity of prepolymerized TS6 samples 5h (upper open circles), 2 h (full circles), and fresh crystals (lower open circles) [66]. 

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Remember from Sec. 1.3 that graft copolymers have polymeric side chains which differ in the nature of the repeat unit from the backbone. These can be prepared by introducing a prepolymerized sample of the backbone polymer into a reactive mixture—i.e., one containing a source of free radicals—of the side-chain monomer. As an example, consider introducing polybutadiene into a reactive mixture of styrene ... 

The linear relation of electric permittivity parallel to the chain direction vs. polymer content thus established can be used for the control of the polymer content of prepolymerized samples as well as for the derivation of time-conversion curves of individual single crystals in situ. We have used this technique to study the sohd state polymerization of topospecifically and fully deuterated TS. 

Figure 15.7 Calibration space covered by the first calibration set. The x-axis is lab carboxyl ends in meq/kg and the y-axis is DP in repeat units. The samples are labelled by process point 1 - esterifier, 2 - pipeline reactor and 3 - prepolymerizer. Reprinted with permission from Brearley and Hernandez (2000). ...

Afterthe polybutadiene is dissolved,0.3 g fert-dodecylmercaptane (MW-regulator) are added and the reaction mixture heated under stirring (100 rpm) to 80 °C. Now, 0.6 g bisbenzoylperoxide (BPO), dissolved in 1 ml of styrene, are added and the temperature kept at 80 °C. After 2 hours another 0.6 g BPO in 1 ml of styrene are added and the temperature further held at 80 °C until a conversion of 35-40% is reached.This is the case after 2-3 h. In order to control the conversion, samples are taken every 30 min.They are weighed and then heated for 10 min at 220 °C in vacuo in order to remove the styrene monomer. After a solid content of 35-40% is reached, the prepolymerization phase is finished. 

Grmesch and Schneider [30] prepolymerized a distilled sample of vinyl acetate in the presence of as much as 5-8% of larnoyl peroxide. When the extent of the polymerization had been judged to be sufficient, the process was short-stopped by the addition of 2,4-dinitrophenylhydrazine. This step, it seems to us. 

A biaxial shape-changing effect had been realized in SmC elastomers [132]. These LCEs displayed shrinkage (expansion) because of the smectic-isotropic (isotropic-smectic) transformation and shear deformation because of the tilting in the smectic phases. This behavior, which required a macroscopic C2 symmetry of the LC domains, had already been theoretically postulated in the mid 1990s [139]. However, creation of the monodomain samples was an experimental challenge. One approach to obtain monodomain samples having the required symmetry applied a prepolymerization procedure, a first deformation process for the orientation of the... 

The resulting S values range for fresh samples from 0.85 to 0.95 and tend to decrease with increasing prepolymer content. For samples prepolymerized (5-6 hours, 3-4% polymer) we find that S is between 0.65 and 0.80. These values correspond to chain lengths (L) of 0.15 to 0.4 pm or 300 to 800 repeat units [66]. 

Transmission electron microscopy (TEM) was utilized to examine the HNT dispersibility within fibrous networks. Because TEM technique generally deals with bulk film samples, fiber mats were embedded into Araldite epoxy resin to prepare fully cured epoxy composites. A 1 x 1 x 1 cm epoxy resin in volume was initially polymerized for 24 h. Subsequently, fiber mats were macerated in epoxy slurry and placed on prepolymerized solid epoxy before the repolymerization of composites. The composite films were sectioned into 100 nm layers using a diamond knife with a Leica EM UC6 microtome, which were further mounted on carbon grids. A JEOL 2011 transmission electron microscope was used at an accelerating voltage of 200 kV to explore the HNT dispersion level within liber mats reinforced epoxy composites. 

Actually, if ri (the initial polymer/homopolymer - the product of prepolymerization of gel-polymer) is greater than (the product of polymer-analogous transformation/diffusion copolymerization), then decrease of the process duration with the radius of the polymeric/gel-polymeric film/plate from its periphery to center gives a medium with properties of a convex lens and, vice versa, at the increase of the process duration with sample radius from periphery to center, a medium possessing properties of a concave lens may be obtained. 

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