Polydispersity index PDI

Number-average molecular weights (M ) of the copolymers are often smaller than the theoretical value calculated from the copolymer yield and the total molar amount of initiator. Nevertheless, the polydispersity indexes (PDIs) are small,... 

The ratio Xw/Xn is synonymous with the ratio MwfMn discussed in Sec. 1-4. It is a measure of the polydispersity of a polymer sample. The value of Xw/Xn increases with the extent of reaction and approaches 2 in the limit of large extents of reaction. The ratio XwfX is also referred to as the polydispersity index (PDI). 

A consideration of the preceding equations indicates that high polymer (i.e., large values of X and Xw) will be produced only if p is close to unity. This is certainly what one expects from the previous discussions in Sec. 3-5. The distributions described by Eqs. 2-86, 2-88, and 2-89 have been shown in Figs. 2-9 and 2-10. The breadth of the size distribution Xw/X [also referred to as the polydispersity index (PDI)] has a limiting value of two as p approaches unity. 

It is called polydispersity index (PDI). The value of PDI can range between approx. 1.01 (for anionically prepared polymers) up to more than 30 (high-pressure polyethylene). In general, it is between 2 and 5. 

A pressure glass vessel was charged with a cyclohexane solution of butadiene (60 g) and styrene (15 g) and treated with 11.7 ml of the step 1 product and the mixture polymerized at 50°C for 2.5 hours. The conversion was approximately 100%. Thereafter, 0.5 ml of 5% 2,6-di-f-butyl-p-cresol dissolved in isopropanol was added and the mixture precipitated in an isopropanol solution containing slight amounts of hydrochloric acid and BHT. The mixture was dried and the product isolated having an Mn of 1.74 x 105Da with a polydispersity index (PDI) of 1.02 and MLi+4 (100°C) of 22. 

The Novozym 435-catalyzed ring-opening polymerization of e-caprolactone shown in Figure 6.2 was also performed in the presence of methyl or ethyl gluco-pyranosides. In this way, polyesters with low polydispersity index (PDI) values and initiated by alkyl glucopyranosides (acylated at their primary OH) could be prepared [48]. 

Gel permeation chromatography of polystyrene separated from blend samples indicates that high-molecular-weight polymer is formed. Polystyrene removed from a 43 wt % polystyrene/HDPE specimen exhibited Mw = 628 K with polydispersity index, PDI = 2.7. The corresponding polystyrene formed outside this specimen exhibited Mw = 48 K with PDI = 3.1. 

If the polydispersity index (PDI) has a value of unity, the substance is designated as monodisperse. Monodispersity is considered to be a property of the casca-danes (defect-free dendritic molecules cf. Section 1.4) and almost perfect dendrimers. Since these compounds are synthesised via an iterative approach, monodispersity has so far generally been limited to lower generations. Should it prove possible to repeatedly remove all reactants and by-products of the individual synthetic steps during the construction of a dendrimer, then structurally perfect dendrimers will result. 

A chromatographic technique frequently used in polymer and dendrimer analysis is size exclusion chromatography (SEC) [13], which is often also called gel permeation chromatography (GPC). It is a straightforward method of determining the relative molar mass, the molar mass distribution, and the polydispersity index (PDI) with compatively modest consumption of material and time. 

Application of the two-mode models for a CSTR to the above kinetics results in a set of nonlinear algebraic equations, which when solved gives the MWD and the polydispersity index (PDI). For the case of premixed feed, Fig. 17 shows the variation of the MWD with n, where MWD is defined as... 

Several additional phases are observed experimentally, but are not thermodynamically stable [13]. Moreover, the synthetic nature of the copolymers implies some heterogeneity in the polymer structure and molecular weight distribution. An excellent review has recently been published [97], and the main conclusion is that the polydispersity index (PDI) influences all aspects of the self-assembly. For example, upon an increase of the PDI of one block, the lattice constant of an ordered structure or the size of microphase-separated domains increases, interfacial thickness increases, and phase transitions may be induced. In addition, macrophase-separation may occur as the PDI is increased at certain compositions and segregation strengths. 

The breadth of the molecular weight distribution is described by the ratio of the weight and number average molecular weights or degrees of polymerization, and is referred to as the polydispersity index (PDI) or molecular weight distribution (MWD) [Eq. (8)]. 

To clarify the unique characteristics of the MWD of emulsion polymers, one of the simplest and most common cases [264], where neither chain transfer (Cf=0) nor radical desorption ((5=0) occurs, is considered here. The magnitude of bimolecular termination ( ) is changed with a constant radical entry frequency (c=2xl0 ). Figure 10 shows the calculated number- and weight-average chain lengths and the polydispersity index (PDI= as a func-... 

CdTe quantum dots, resulting in polydisperse nanocrystals. Polydispersity was quantitatively assessed from the polydispersity index (PDI) in gel filtration chromatograms. When the MCR values are above 2.0, the excess polymer leads to better monodispersity and colloidal stability, but a reduced fluorescence quantum yield. Between these two limits is the optimal capping ratio (OCR) of approximately 1.5, yielding small, monodisperse nanocrystals (PDI < 1.5) with bright fluorescence ( 50% quantum yield) and exceptional photostability. 

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