Molecular weight, effect copolymers

In comparing observed reactivity ratios between various polymerization systems, it is important to take into account the possible effect of molecular weight on copolymer composition.3475 19 In conventional radical eopolymeri/.ation, the specificity shown in the initiation and termination steps can have a significant effect on the composition of low molecular weight copolymers (usually <10 units). These effects are discussed in Section 7.4.5. In a living polymerization molecular weights are low at low conversion and increase with conversion. In these... 

Blanazs A, Ryan AJ, Armes SP (2012) Predictive phase diagrams for RAFT aqueous dispersion polymerization effect of block copolymer composition, molecular weight, and copolymer concentration. Macromolecules 45 5099-5107... 

Fig. 4 Characterization of an ultra-high molecular weight PAAm-Copolymer by means of porous media flow and degradation effects of strained solutions...

Throughout much of the early growth and evolution of polymer science, the quest for new properties was focused primarily on the two traditional architectures that defined thermoplastic (linear) and thermoset (cross-Unked polymers). Within each of these areas, there was intense activity to evaluate and optimize certain critical parameters. These parameters included various macromolecular chemical compositions, copolymer compositions, molecular weight effects, molecular weight distributions, and cross-link... 

Tanaka et al. used NPLC and RPLC to determine CCD of PMMA- -PS with different compositions and conversions synthesized from the copolymerization of methyl methacrylate and co-p-vinylbenzyl polystyrene macro monomer [ 158]. The good agreement between CCD obtained by both HPLC modes showed that the molecular weight effect on the CCD is negligible. As the macromonomer content increases, the CCD becomes sharper. These results are in accordance with the theoretical predictions. As the conversion increases at the same feed composition, the CCD becomes broader towards the low macromonomer content side, which is in contrast to the CCD of the samples obtained previously from oo-methacryloyl polystyrene macro monomer [159]. They also showed that the CCD is broadened as the graft length increases, in copolymer samples with a similar composition, in accordance with the theoretical prediction [159]. 

Sarzotti et al. [58] investigated the effect of comonomer content on Crystaf profiles using a series of ethylene/l-hexene copolymers with different comonomer contents but approximately the same molecular weight, effectively eliminating any possible misinterpretations that might arise because of molecular weight effects (Fig. 34) [58]. As expected, Crystaf peak temperatures are dramatically influenced by the CC of the copolymer chains. Moreover, the Crystaf profiles become broader with an increase in comonomer content. 

Levels of carboxyl content must be worked out with each thermoplastic structure and molecular weight. With a polyfvinyl acetate) of about 100 000 molecular weight a copolymer of about 99.0% vinyl acetate and 1.0% acrylic acid is quite effective in chemically thickened applications. 

Certain factors would be expected to restrict the segmental motions of polymer chains in the solid state. Obvious among these factors are (a) the presence of crystallinity, (b) stereoregularity, (c) copolymer composition, (d) molecular weight effects, (e) crosslinking, and (f) mechanical stress. We shall give brief examples of these influences. 

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