Poly-dispersity index

Pollock et al.(12) have also exploited the fact that poly dispersity index is a function of C2 only in a study utilizing a Monte-Carlo simulation technique to compare error propagation in the method of Balke and Hamielec to a revised method (GPCV2) proposed by Yau et al. (13) which incorporated correction for axial dispersion. 

A round-bottom flask was charged with 15 ml of a toluene and water, 2 1, respectively, phenyltrimethoxysilane (0.02 mol), p-chloromethylphenyltrimethoxysilane (0.02 mol), and methanesulfonic acid (5 mol%) and then stirred at ambient temperature for 12 hours. The organic layer was isolated, concentrated, and then added dropwise to a large quantity of -hexane. The precipitated solid was filtered, dried, and the product isolated in 93 % yield having an Mn of 1300 Da with a poly dispersity index (PDI) of 1.25. 

Abbreviations-. PEO = poly ethylene oxide, PHB = poly hydrobutyrate, and PDI = poly dispersity index. 

The polydispersity of dendritic molecules, expressed in the form of their poly-dispersity index (PDI), is directly related to their structural perfection. The PDI is a measure of molecular weight distribution. 

For crystalline polymers, however, not only the molecular weight and poly-dispersity index are of interest. Besides the degree of crystallinity, there is a specific influence of chain design, i.e., existence, length, and concentration of side chains on the resistance against environmental stress cracking, as will be pointed out in the next section. 

It has been noted (Odian, 1991) that the steady-state approximation cannot be applied in many cationic polymerizations because of the extreme rate of reaction preventing the attainment of a steady-state concentration of the reactive intermediates. This places limitations on the usefulness of the rate expressions but those for the degree of polymerization rely on ratios of reaction rates and should be generally applicable. The molar-mass distribution would be expected to be very narrow and approach that for a living polymerization (with a poly-dispersity index of unity), but this is rarely achieved, due to the chain-transfer and termination reactions discussed above. Values closer to 2 are more likely. 

The theoretical molecular weight distributions for cationic chain polymerizations (see Problem 8.30) are the same as those described in Chapter 6 for radical chain polymerizations terminating by disproportionation, i.e., where each propagating chain yields one dead polymer molecule. The poly-dispersity index (PDI = DP /DPn) has a limit of 2. Many cationic polymerizations proceed with rapid initiation, which narrows the molecular weight distribution (MDI). In the extreme case where termination and transfer reactions are very slow or nonexistent, this would yield a very narrow MDI with PDI close to one (p. 681). 

Fig. 16 Overall conversion versus (a) time and (b) number-average molar mass, M , and poly-dispersity index, A/w/Afn (the line represents the theoretical M ) for the nitroxide-mediated surfactant-free emulsion copolymerizations of methyl methacrylate and styrene in the presence of poly(PEGMA-ct>-MAA-co-styrene)-SGl macroalkoxyamines of different molar masses triangles 9400, and squares 44(X)gmol ) [145]...

The studied triblock copolymer PS-PVP-PEO was purchased from Polymer Source (Dorval, Canada). The number-average molar masses of PS, PVP, and PEO blocks were 2.1 x 10 , 1.2 x 10 , and 3.5 x 10 g mol , respectively, and the poly-dispersity index of the sample was 1.10. The copolymer is insoluble in aqueous media, but the micelles can be prepared indirectly both in acidic and alkaline aqueous solutions by dialysis from 1,4-dioxane-methanol mixtures [88]. The micelles can be transferred from acidic to alkaline alkaline solutions and vice versa, but the addition of a base together with intense stirring promotes aggregation. Two factors contribute to the destabilization of micelles after the pH increase (a) In alkaline media, the PVP blocks become insoluble, collapse and form an upper layer of the core. Since the cores of micelles are kinetically frozen, the association number does not change. The mass of insoluble cores increases, while the length of soluble shellforming chains decreases, which results in a deteriorated thermodynamic stability of micellar solutions, (b) The PVP middle layer shrinks and PEO chains come close to each other, which worsens the solubility due to insufficient solvation of PEO blocks. 

Maa and Hsu (75) reported the formation of nano-particles by the double-emulsion method (W/OAV), using methylene chloride as an organic solvent and poly(vinyl alcohol) (PVA) or human serum albumin (HSA) as a surfactant. Experimental parameters such as the preparation temperature, the solvent-evaporation method, the internal aqueous phase volume, the surfactant concentration, and the polymer molecular weight were investigated for particle size, the zeta potential, the residual surfactant percentage, and the poly-dispersity index. Preparation parameters leading to particles with well-defined characteristics such as an average size around 200 nm and a polydispersity index lower than 0.1 were identified. 

Corresponding number-average molecular weight (Fig. 2.3.6) as well as poly-dispersity index (Fig. 2.3.7) data show asymptotic values with time. What is quite remarkable is that the asymptotic value of the polydispersity index was at 1.7-1.8. 

The initial overshoot in number-average molecular weight (Fig. 2.3.6) and poly-dispersity index (Fig. 2.3.7) at low conversions seems to be consistent with the initial OA line segment of the system trajectory as depicted in Fig. 2.1.11, wherein the system follows a solution polymerization process during the first 10 min (based on Figs. 2.3.5-2.3.7). Subsequently, when the polymer-rich phase was being formed as the system traversed the OB line segment of the reaction trajectory in Fig. 2.2.5, the tendency for this phase was to go into gel effect, as seen from the sharper rise... 

MALDI spectral quality is important, and thus, many authors have collected SEC fractions, recorded their MALDI spectra, and compared them with the spectra of the unfractionated polymer. To the best of our knowledge, there are no reports that quality worsens when using SEC. Vice versa, very often quality increases. For instance, the MALDI spectra of SEC fractions of Poloxamer407 (see above) possess a better spectral quality than the unfractionated sample. Moreover, a poly(bisphenol-A-carbonate) sample [64] with a poly-dispersity index of around 2 was analyzed by SEC and fractions were collected. Figure 45.11 contains the MALDI spectrum of PCF22 corresponding to the SEC... 

In general, number-averaged molecular weight (Mn), and weight-averaged molecular weight (M ) and polys-dispersity index (PDI) can be calculated by apphcation of MS techniques ... 

They then applied these conditions to the preparation of poly-3-alkylthiophene (1). Low molecular weight material was obtained (Mn 3.0kDa, poly-dispersity index (PDI)= 1.1-2.1) with bromo- and iodo-substituted materials, but this was, however, the first example of application to polymeric materials (Chart 19.1). 

The poly(3-hexylthiophene) exhibited a distinct peak at 820 cm due to the out-of-plane vibration of the 2,3,5-trisubstituted thiophene. In the visible spectra, the polymer showed an absorption peak at 505 nm with two shoulders at 550 and 600 nm. The absorption edge was 650 nm. The was 4.5 x [O with a poly-dispersity index of 5.5. The iodine-doped film showed a conductivity of 200 S cm at a stretching ratio of 5. 

Generally, in other identical conditions, the increase of temperature leads to a decrease of nnmber-average molecnlar mass of polystyrene (Fig. 10.12a). Thus, poly-dispersity index increases (Fig. 10.12b). If RAFT-agent initial concentration greatly exceeds AIBN initial concentration, then the temperature practically doesn t influence the molecnlar-mass properties of polystyrene. 

First, well-defined Seesaw-type macromonomer alkyne-(PtBA39-N3)2 was prepared via ATRP and azidation reaction. SEC curve (Fig. 4.16) demonstrates the prepared macromonomer aIkyne-(PtBA39-N3)2 is narrowly distributed with a poly-dispersity index of -1.09. The absolute DP value was calculated to be... 

Moreover, with the increase in the ratio of St/PEG-Cl, the hydrodynamic diameters (i h) of the nanoparticles increased and the poly index decreased both I and poly dispersity index of the nanoparticles prepared tmder microwave irradiation were smaller than those prepared with conventional heating as the concentration of catalyst increased, the Dh of the... 

The material used in this study is a poly (styrene-ethylene-co-butylene-styrene) (SEES) triblock copolymer provided by Kraton Polymers, US EEC. The number-average molecular weight, Mn, as determined by GPC is 107 K gm/mol and the poly-dispersity index, M /Mn, is 1.14 with Mw being the weight-average molecular weight. The weight fraction of PS for this tri-block copolymer is 18-22%. 

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