Molecular weight polydispersity and

TABLE 16.7 Molecular Weight and Polydispersity of Standards for Peak Position Calibration of Superose 6 HR 10/30... 

TABLE 17.4 Molecular Weight and Polydispersity of PVP and PEO for the TSK PWxL Column... 

C. Effect of PEO Calibration Standards and Columns on the Molecular Weight and Polydispersity of Polyvinylpyrrolidone (PVP)... 

Polymerization of Styrene by Zr(benzyl)t ([C]o = O.OS M) in Toluene at SO°C. Dependence of Molecular Weights and Polydispersity on Initial Monomer Concentrations... 

The effect of the nitrone stmcture on the kinetics of the styrene polymerization has been reported. Of all the nitrones tested, those of the C-PBN type (Fig. 2.29, family 4) are the most efficient regarding polymerization rate, control of molecular weight, and polydispersity. Electrophilic substitution of the phenyl group of PBN by either an electrodonor or an electroacceptor group has only a minor effect on the polymerization kinetics. The polymerization rate is not governed by the thermal polymerization of styrene but by the alkoxyamine formed in situ during the pre-reaction step. The initiation efficiency is, however, very low, consistent with a limited conversion of the nitrone into nitroxide or alkoxyamine. 

The important factors in PLA biodegradation are the molecular weight and polydispersity, as well as the crystallinity and morphology of the polymers [36], Others factors that may affect PLA degradation include chemical and configurational structure, fabrication conditions, site of implantation, and degradation conditions. 

Polymer molecular properties such as molecular weight and polydispersivity have a significant effect on the lithographic behavior of the single component negative resists described above. For example, it has been shown for a series of... 

Polymer networks are formed from functional precursors by covalent bond formation [1], As a result, molecular weights and polydispersity increase and the system passes through a critical point, the gel point. At this point, an infinite structure (molecule) is formed for the first time. Beyond the gel point, the fraction of the infinite structure (the gel) increases at the expense of finite (soluble) molecules (the sol). The sol molecules become gradually bound to the gel and eventually all precursor molecules can become a part of the gel - the network. This is not always the case for different reasons sometimes sol is still present after all functional groups have reacted. In passing from the gel point to the final network not only the gel fraction increases, but also the network becomes denser containing increasing amounts of crosslinks and strands between them called elastically active network chains. 

The degree of control over molecular weight and polydispersity. 

Miller et al. [87,88] have described the synthesis of hyperbranched aromatic poly(ether-ketone)s based on monomers containing one phenolic group and two fluorides which were activated towards nucleophilic substitution by neighboring groups. The molecular weight and polydispersity of the formed po-ly(ether-ketone)s could be controlled by reaction conditions such as monomer concentration and temperature. The formed polymers had high solubility in common solvents such as THF. 

Table 14.2 Molecular weights and polydispersity indexes of polycarbosilanes 1 obtained via reactions I and II.

Hence, cation-radical copolymerization leads to the formation of a polymer having a lower molecular weight and polydispersity index than the polymer got by cation-radical polymerization— homocyclobutanation. Nevertheless, copolymerization occnrs nnder very mild conditions and is regio-and stereospecihc (Bauld et al. 1998a). This reaction appears to occnr by a step-growth mechanism, rather than the more efficient cation-radical chain mechanism proposed for poly(cyclobutanation). As the authors concluded, the apparent suppression of the chain mechanism is viewed as an inherent problem with the copolymerization format of cation-radical Diels-Alder polymerization. ... 

Fig. 3-22 Dependence of number-average molecular weight ( ) and polydispersity index (A) on monomer conversion for ATRP polymerization of bulk styrene at 110°C with CuBr, 1-phenylethyl bromide (I), and 4,4-di-5-nonyl-2,2 -bipyridine (L). [M] = 0.087M [CuBr]0 = [L]0/2 = [I] = 0.087 M. After Matyjaszewski et al. [1997] (by permission of American Chemical Society, Washington, DC) an original plot, from which this figure was drawn, was kindly supplied by Dr. K. Matyjaszewski.

Molecular weight and polydispersity determinations were obtained by GPC with THF as elution solvent with styragel columns (60, 100, 500, 10, 10, 10 and 3.10 A). Eluted macromolecule was observed simultaneously by refractive index and by ultraviolet absorption. 

Materials. GMC and PCLS were synthesized by free radical solution polymerization initiated by benzoyl peroxide as described previously (5,6). Nearly mono and polydisperse polystyrenes were obtained from Pressure Chemical Co. and the National Bureau of Standards respectively. Molecular weight and polydispersity were determined by gel permeation chromatography (GPC) using a Water Model 244 GPC, equipped with a set (102-106 A) of —Styragel columns using THF as the elution solvent. The molecular parameters of the above three polymers are listed in Table I. The copolymer, poly(GMA-co-3-CLS), contained 53.5 mole % 3-CLS and 46.5 mole % GMA, as determined by chlorine elemental analysis. The structure of the copolymer is shown in Figure 1. 

Molecular weight and polydispersity were determined by gel permeation chromatography. The values reported are in terms of polystyrene equivalent molecular weights. 

This work examines the effect of long-chain branching on the low-shear concentrated solution viscosity of polybutadienes over a broad range of molecular weights and polydispersity. It will show that the reduction in molecular coil dimension arising from long-chain branching is more sensitively measured in concentrated than in dilute solutions for the polymers examined. 

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