Polymers relative growth rate

Galvanostatic, potentiostatic as well as potentiodynamic techniques can be used to electropolymerize suitable monomeric species and form the corresponding film on the electrode. Provided that the maximum formation potentials for all three techniques are the same, the resulting porperties of the films will be broadly similar. The potentiodynamic experiment in particular provides useful information on the growth rate of conducting polymers. The increase in current with each cycle of a multisweep CV is a direct measure of the increase in the surface of the redoxactive polymer and, hence, a suitable measure of relative growth rates (Fig. 5). 

The relative growth rate per cycle v is calculated from the peak current of the respective polymer oxidation using Eq. (3) ... 

Finally, we were led to the last stage of research where we treated the crystallization from the melt in multiple chain systems [22-24]. In most cases, we considered relatively short chains made of 100 beads they were designed to be mobile and slightly stiff to accelerate crystallization. We could then observe the steady-state growth of chain-folded lamellae, and we discussed the growth rate vs. crystallization temperature. We also examined the molecular trajectories at the growth front. In addition, we also studied the spontaneous formation of fiber structures from an oriented amorphous state [25]. In this chapter of the book, we review our researches, which have been performed over the last seven years. We want to emphasize the potential power of the molecular simulation in the studies of polymer crystallization. 

It has been reported that the overall rate of crystallization of pure PHB is relatively low compared to that of common synthetic polymers, showing a maximum in the temperature range of 55-60°C [23]. The spherulite growth rate kinetics have been evaluated [59] in terms of the theory by Hoffmann et al. [63], At about 90 °C, the spherulite growth rate displayed a maximum, which is not excessively low compared to that of common synthetic polymers. Therefore it was stated that the low overall crystallization rate of PHB centers on the nuclea-tion process rather than the subsequent crystal growth. Indeed, it has been shown that PHB has an exceptionally low level of heterogeneous nuclei [18]. 

One reaction of popcorn polymers is their very rapid, proliferous growth in appropriate monomers. The rapid growth reaction corresponds to a relatively high content of the growing material on radical chain ends. It is possible to measure the growth rate directly by ob-... 

Excluding loose-fill packaging, which is a relatively more mature sector for starch-based biodegradable polymers, global market tonnage in 2005 is 71,700 tonnes and the compound annual growth rate for the period 2005-2010 is projected to be 20.3%. 

On the other hand, Nomura et al. [14] proposed a different approach for predicting the number of polymer particles produced, where the new concept of radical capture efficiency of a micelle relative to a polymer particle was proposed. The assumptions employed were almost the same as those of Smith and Ewart, except that the volumetric growth rate p of a polymer particle was not considered to be constant. It was also assumed that all of the radicals formed in the aqueous phase enter either micelles or polymer particles with negligible termination in the aqueous phase. In this approach, the following elementary reactions and their respective rates were defined. 

Equation (4Ib) is valid when there are no polymer particles flowing into the reactor with all the particles nucleated within the reactor. It is assumed that density changes can be neglected and that particles follow the streamlines. These are reasonable assumptions in view of the small size of particles and the small density difference between particle and water. When two or more CSTRs are employed in series, however, one must remember that the total residence time of a polymer particle is made up of different times in each reactor in the train. The relative amounts of time spent in each reactor will not matter when the volumetric growth rate of a particle is the same in each. This would require that the temperature, monomer concentration, and average number of radicals per particle he the same for each reactor, an unlikely possibility. This idealization is useful, however, when illustrating the effect of increasing the number of CSTRs in series on the breadth of the particle size distribution. 

Some materials can be produced only in amorphous or polycrystalline phase. For example, SCF precipitation of polymers such as poly(L-lactic acid)(PLLA) and proteins such as lysozyme and insulin have been widely investigated (see, e.g., Chapters 6, 9, and 10 in this book). These molecules form amorphous (proteins) or semicrystalline (PLLA) structures and typically have small values of both Ceq and tn, combined with a relatively large Tg constant (small growth rate). Similarly, organic or inorganic salts usually have very small Cgq and Tn constants. This explains why it is easy to produce very small (often submicrometer), spherical particles of these materials, al-... 

The growth of polymer molecules proceeds by a stepwise intermolec-ular reaction (at a relatively slow rate), normally with the elimination of small molecules as by-products of condensation, such as H2O, HCl, NH3, etc., in each step. The molecule never stops growing during the course of the polymerization. 

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