Effect on molecular weight

Recently many subtle effects of the ligand structure, concentrations of alkene, and conditions on the polymerisation have been reported to have significant effects on molecular weight, regioselectivity, branching, stereoselectivity or enantioselectivity, incorporation of other monomers, chain transfer, etc. Often these subtle effects can be understood from the mechanism, or they contribute to the understanding of the detailed processes going on. 

Instrumental band broadening or axial dispersion can cause calibration errors when employing polydisperse standards. Correction of the polydisperse standard calibration data for instrumental band broadening will minimize the effect on molecular weight analyses of polymer samples. However, as previously demonstrated in this report, when low dispersion SEC columns are employed instrumental band broadening is minimized and the effect on use of linear calibration methodology is negligible. 

Hausberger, A. G., Kenley, R. A., and DeLuca, P. P. Gamma irradiation effects on molecular weight and in vitro degradation of poly(D,L-lactide-CO-glycolide) microparticles. Pharm. Res. 12(6) 851—856, 1995. 

Our kinetic work (10) showed that the small molecule radical produced by chain transfer with monomer had to be a stable radical. This was confirmed in the present paper by analysis of the isotope effect on the bulk polymerization rates. The isotope effect on molecular weights and rates unequivocally showed that almost 100% of the chain transfer involved the vinyl hydrogen. There is some evidence in the literature to support the idea of a stable vinyl radical. Phenyl acetylene acts as a retarder when copolymerized with styrene or methyl methacrylate (25). Thus the phenyl vinyl radical is very stable compared to the growing styryl or methacrylyl radical. 

The amount of thermal initiation which takes place at 138°C. and its effect on molecular weights and their distributions were also studied. Two batches were polymerized thermally using monomer mixture A. 

TABLE 1. Effect on molecular weight of poly( -caprolactone-co-trimethylene carbonate) end capped with coumarin after a [2 + 2] photo cycloaddition using UV irradiation. 

TABLE 1. Effect on molecular weights and odor using selected thiol derivatives as polymerization regulators. 

Ideally, transfer has no effect on kinetics but has a pronounced effect on molecular weights and polydispersities [11,14,15]. 

Table III. Pressure Effect on Molecular weight of PSBO...

Fig. 1.9. Repartition hypothesis solvent , non-solvent , dilution effects on molecular weight and yield of polybutadiene 96 98 ...

The reaction time 109) seems to be without effect on molecular weight (about 550 for the oligomeric fraction, and 16 500 for the polymeric fraction), but the polydispersity... 

Long reaction times give high sdelds but have little effect on molecular weight. 

Data, given in Table 3, show that small amounts of the dye (up to 2% of mass) do not exert essential effect on molecular weight of polymer. It should be noted that polymer gains bright colour even at dye concentration of 1% of mass. 

Table IV. Common Ion Effect on Molecular Weight and Molecular...

Chain Scissioning and its Effect on Molecular Weight. Table III shows the molecular weight data of the unstabilized HDPE when oxidized at 100° C to different oxygen uptake levels. 

Dose Effects on Molecular Weight. A dose effect is clearly exhibited in Figure 8. As the photolysis time increases the percent of C8 products decreases linearly while the percent of Ci2 products increases linearly. The C8 s extrapolate to 100%v and the Ci2 s extrapolate to 0% at 10 minutes of photolysis time. The data do not guarantee that 10 minutes of photolysis time is significantly different from 0 minutes, but they do indicate that an induction period is present before the dose dependence of the product yields begins. The relative rise of C12 products together with the decrease in C8 products can be explained by Reaction 7 or by Reaction 8. The relationship shown in Figure 8... 

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