Important Polymer Properties

Fast high-pressure fractionation of tails in the molar-mass-distribution and/or the chemical-composition-distribution of a (co)polymer [47] during the polymerisation process will indicate eventual drifts in (co)polymer composition. Several important polymer properties depend strongly on such tails in the (co)polymer distribution. On--line fractionation data are strongly needed. 

All of these facts indicate a strong reverse correlation beteen the hydroxyl population on the silica surface and the catalyst activity and termination rate. Possibly these hydroxyls coordinate to the active center and kill or at least retard it. Groeneveld et al. have reported that on barely activated samples, protons from surface hydroxyls later appear in the polymer (5,9). This may be evidence of interference by hydroxyls. Or perhaps the hydroxyls are not directly involved at all, but merely reflect some other important change such as the strain introduced onto the surface by their condensation. Whatever the reason, this relationship is used commercially to control MW and many other important polymer properties. 

Molecular weight is an important polymer property and is regulated by the addition of small amounts of hydrocarbons called modifiers to the reaction medium. Propylene, butylene, or hexane is used for this purpose. These combine with a growing chain through a chain transfer reaction ... 

This limiting sedimentation coefficient is like [77] an important polymer property. The temperature dependence may be approximated by the expression... 

The systems are complex. Many of the important polymer properties depend on interchain interactions and/or on the interaction between polymer chains and nonpolymeric materials. 

Conventional GPC data processing is unable to determine other important polymer properties such as copolymer composition or copolymer molar mass. The reason is that the GPC separation is based on hydro-dynamic volume rather than the molar mass of the polymer and that molar mass calibration data are only valid for polymers of identical molecular structures. 

Most kinetic studies focus on batch emulsion polymerization. These studies enable estimation of important polymer properties. Only recently, the control of particle size and MWD described by population balance models has been achieved. The differences between emulsion polymerization and copolymerization... 

FIGURE 258 The influence of activation hold time can be seen in this experiment in which Cr/silica catalysts (1 wt% Cr) were activated at various temperatures for 15 min and for 20 h. The catalyst activity is plotted, and two important polymer properties— the MW and the relaxation time distribution (CY-a), which represents elasticity. 

Several of the more important polymer properties for sensors are reviewed below. 

A number of important polymer properties depend on the morphology of the polymer. As crystallinity increases ... 

However, there are still a number of important polymer properties that can only be measured by laborious and time-consuming off-line analyses. In this category one can include the MWD (especially in dispersed systems and/or for polyolefins), branching and crosslinking density, the gel content, the PSD, among other properties. (Despite the several examples reported in the scientific literature, at present no commercial equipment can ensure the fast and robust on-hne measurement of the entire size distribution of polymer particles in industrial reactors.)... 

---