End-group effects

Calculate the value of p at which the reaction should be stopped to obtain this polymer, assuming perfect stoichiometric balance and neglecting end group effects on. ... 

Neglecting end group effects, calculate for each of these polymers from the end group data. Are the trends in molecular weight qualitatively what would be expected in terms of the role of the additive in the reaction mixture Explain briefly. 

RB4 random polymerisations relevant to systems 4 and 5 of Figure 6 and Table II. Apart from possible, small end-group effects m is in general the molar mass of the chain of v bonds. 

J.-I. Lee, G. Klaemer, and R.D. Miller, Oxidative stability and its effect on the photoluminescence of poly(fluorene) derivatives end group effects, Chem. Mater., 11 1083-1088, 1999. 

Collins, S., Peace, S. K. and King, S. M, Transesterification in poly (ethylene terephthalate). Molecular weight and end group effects, Macromolecules, 33, 2981-2988 (2000). 

The free radical polymerization of HPMA in the presence of mercaptans involves two different initiation mechanisms (Scheme 2) [26]. One is the initiation by RS radicals from chain transfer agent the other appears to be the direct initiation by the primary isobutyronitrile (IBN) radicals formed by the decomposition of AIBN [27]. The RS are formed by either the free radical transfer reaction of alkyl mercaptans with the IBN radicals or the chain transfer reaction of an active polymer chain with the mercaptans. The initiation by the RS radicals produces the ST polymers with a functional group at one end of the polymer chain. The initiation by IBN radicals leads to nonfunctional polymer chains with an IBN end group. The presence of the polymers with IBN end groups effects the purity and the functionality of ST polymers. As expected, the production of nonfunctionalized polymer chains is affected by reaction conditions. The polymerization is mainly terminated by chain transfer reaction with the mercaptans, but other termination mechanisms, such as disproportionation and recombination, take place depending on the reaction conditions [26]. 

Equation (33) can be further simplified in the case of homopolymers or copolymers with constant chemical composition. It is well known from the literature that Dtis independent of molar mass [11,21,36,37], and the same holds for (dnldck)p>T>Cl kif M is sufficiently high to neglect end-group effects. Under these preliminaries, the molar mass dependence of ak reduces to the concentration of the respective species ak c0>k. 

The ratio of 6.8 for the two peak areas from stochastic TDFRS is close to the value of 5.9 as expected from the concentration ratio and the refractive index increments of the two PS, which depends on molar mass due to end-group effects. The thermal diffusion coefficient DT= 1.12 x 10 7 cm2 (sK) l is in excellent agreement with the value found previously in our laboratory [36]. 

Monte Carlo Simulations. The epimerization reaction was simulated using the Monte Carlo program we described earlier(17). A 5000 element array was allocated to store information about the configurations of monomer units at various positions in a 5000 unit polymer chain. The positions were indexed in such a way that the polymer could be considered cyclic. This was done to avoid end group effects. The configurations (R or S) at individual sites were indicated by 0 or 1 values. The polymer chain was made isotactic by giving all elements of the array initial values of 0. 

IMR Imre, A. and van Hook, W. A., End group effects on liquid-Uquid demixing of polystyrene/ oligomethylene solutions. Polystyrene/dodecyl acetate solubility. Macromolecules, 33, 5308, 2000. 

Schematic presentation of end group effects of R-PA-PLX-PA-R on sol-gel transition (with permission from American Chemical Society). 

Jalbert, C., Koberstein, J.T., Hariharan, A., Kumar, S.K. End group effects rai surface properties of polymers semiempirical calculations and comparison to experimental surface tensions fora, m-functional poly(dimethylsiloxanes). Macromolecules 30,4481-4490 (1997)... 

Koberstein, J.T., Jalbert, C. Molecular weight dependence and end-group effects on the surface tension of poly(dimethylsiloxane). Macromolecules 26, 3069-3074 (1993)... 

XIA Xia, Y., Burke, N.A.D., and Stoever, H.D.H., End group effect on the thermal response of narrow-disperse poly(V-isopropylaciylanude) prepared by atom transfer radical polymerization, A/acro io/ecM/e5, 39, 2275, 2006. 

The dependence of / on the segment number is not taken into account, because the end group effects are neglected. Using Eq. (10.11), the Gibbs energy of the quasi-binary polymer solution is given by... 

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