Molecular weight distribution with

These values are given for polymers of narrow molecular-weight distribution, with number-average molecular weights (M ) of about 20,000 prior to chlorination. Chlorination reactions are carried out under homogeneous conditions in CCl solutions at temperatures between 90 and 110°C with viscosities at about 5 Pa (50 P). 

Using the above model improvements, Figiue 4 shows the variation of the predicted molecular weight distributions with reaction time for an initiator concentration and efficiency of 0.9 wt% and 0.18 respectively. The need for kinetic data to test these predictions again provides motivation for development of experimental techniques to obtain samples at lower reaction time. 

Figure 6.9 Ethoxylation molecular weight distribution with base and Lewis acid catalysts.

In practice, product developers often blend two or more resins together in order to obtain a product that has the required melt flow and solid-state characteristics. Thus, we frequently combine metallocene catalyzed linear low density polyethylene, having a most probable molecular weight distribution, with low density polyethylene, having a broad molecular weight distribution. The linear low density polyethylene provides good impact resistance, while the low density polyethylene improves melt flow characteristics. 

For investigation of the effect of the width, w, of the distribution on the ultimate fibre strength the uniform chain distribution function is chosen. As in experiments often only the molecular weight distribution fw(z)=zfi(z)z l is determined, we used a uniform molecular weight distribution with a width w defined as... 

GPC measurements were used to demonstrate that a monomodal molecular weight distribution with a polydispersity of approximately 2 was obtained. The glass transition temperature was determined on a Perkin-Elmer DSC-2 using a heating rate of 10 C/min and the intrinsic viscosity was determined in NMP at 25°C. These data are summarized in Table I. 

The synthesis of polyoctenamer has been commercialized by Huels.150 In contrast with the transformation of cyclooctene to 1,9-decadiene [Eq. (12.31)], homogeneous catalyst compositions, such as WClg + EtAlCl2, are used to promote ring-opening metathesis polymerization of cyclooctene. A polymer of narrow molecular-weight distribution with high trans content (55-85%) called Vestenamer is produced and used as blend component in different rubbers and thermoplastics. 

COLEMAN and Fox (18) have pointed out that the non Bernoullian sequence distribution observed in some of these systems can be formed without the hypothesis of penultimate effects. All that is required is that two or more types of active species be present which do not rapidly interconvert. Each can add monomer at its own rate and with its own characteristic regulating effect. No penultimate effect is necessary but the sequence distribution will be non-Bernoullian. This type of mechanism is particularly attractive in the explanation of stereoblock polymer formation in the lithium alkyl systems in toluene with small amounts of ether present. The presence of at least two species of active centres has been inferred from an examination of polymer fractions obtained from butyllithium initiated polymerizations (19) in toluene. The change in molecular weight distribution with time suggests the presence of two... 

The point to note is that the polyelectrolytes have a narrow molecular weight distribution with MJMn< 1.2 this enabled an investigation of the molar mass dependence. 

Polymer Fractions I and II were investigated for molecular weight distribution, with the results (showing the range of variations over all the samples so analyzed) given in Table V. (The analyses and interpretations were obtained from ArRo Laboratories, Joliet, 111. Tetrahydro-furan was the solvent used in the column separation.)... 

Description The Hostalen process is a sluny polymerization with two reactors parallel or in series. Switching from a single reaction to a reaction cascade enables producing top quality unimodal and bimodal polyethylene (PE) from narrow to broad molecular weight distribution with the same catalyst. 

In this section we will review some details concerning the chemistry of these systems with a special emphasis on the structure of the active species, kinetics, as well as on the molecular weights and the evolution of molecular weight distributions with conversion. In the last Section VII, we will discuss the mechanistic features of new controlled carbocationic polymerizations. 

To decrease the viscosity at this stage of polymerization requires a continuous or stepped increase in the polymerization temperature [10-15]. The simultaneous addition of small amounts of bifunctional monomers and chain transfer agents ( tr > 2) also results in a more desirable molecular weight distribution with a flat, low A/w side and a sharply decreasing high Mw flank. The procedure of later addition of the chain transfer agent before the gel effect takes off is preferred. 

The development of the molecular weight distribution with increasing conversion as determined by gel permeation chromatography is shown in Fig. 14, During the... 

The absence of termination during a living polymerization leads to a very narrow molecular-weight distribution with polydispersities as low as 1.06. By comparison, polydispersities above 2 and as high as 20 are typical in free radical polymerization. 

For a molecular weight distribution with only two components, the integral in Eq. (3-78) is replaced by a sum ... 

The diversity of initiation termination and transfer reactions and the changes in concentrations of types and activities of catalyst species during polymerization have so far precluded a theoretical treatment of molecular weight distributions. With some of the soluble catalysts, e.g. Zr(CH2Cg-... 

---