Molecular weight distribution improvements

Increase in the molecular weight distribution, improving processability and reducing tensile strength of the polychloroprene. 

The polydispersity of the resin is fairly high, although it has been shown that a narrow molecular weight distribution improves lithographic performance. ... 

Tetiafluoioethylene—peifluoiopiopyl vinyl ethei copolymeis [26655-00-5] aie made in aqueous (1,2) oi nonaqueous media (3). In aqueous copolymerizations water-soluble initiators and a perfluorinated emulsifying agent are used. Molecular weight and molecular weight distribution are controlled by a chain-transfer agent. Sometimes a second phase is added to the reaction medium to improve the distribution of the vinyl ether in the poljmier (11) a buffer is also added. 

The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers (see Acrylic ester polymers), olefin polymers and copolymers, and styrene—butadiene copolymers. The degree of VI improvement from these materials is a function of the molecular weight distribution of the polymer. VI improvers are used in engine oils, automatic transmission fluids, multipurpose tractor fluids, hydrautic fluids, and gear lubricants. Their use permits the formulation of products that provide satisfactory lubrication over a much wider temperature range than is possible using mineral oils alone. 

AlCl efficiency (based on g resin/g catalyst) can be markedly improved by polymerizing dry feeds (<10 ppm H2O) with an AlCl /anhydrous HCl system. Proceeding from 250 ppm H2O down to 10 ppm H2O, catalyst efficiency improves from 30.6 to 83.0 (26). Low levels of tertiary hydrocarbyl chlorides have been shown to gready enhance the activity of AlCl, while yielding resins with narrow molecular weight distributions relative to systems employing water or HCl (27). 

Phenolic resin substantially increases open time and peel strength of the formulation (80). For example, higher methylol and methylene ether contents of the resin improves peel strength and elevated temperature resistance. Adhesive properties are also influenced by the molecular weight distribution of the phenoHc low molecular weight reduces adhesion (82). 

When additional lubricants, eg, mineral oil and butyl stearate, are added to PS, easy-flow materials are produced. Improved flow is usually achieved at the cost of lowering the heat-deformation temperature. Stiff-flow PS has a high molecular weight and a low volatile level and is useful for extmsion apphcations. Typical levels of residuals in PS grades are Hsted in Table 2. Differences in molecular weight distribution are illustrated in Figure 4. 

Table 1 shows the carbon chain distributions for several typical commercial alkylates. The carbon chain distributions for linear alkylbenzene (LAB) samples A, C, and E are determined by the distillation cut of n-paraffins used to make the LAB. LAB samples B and D represent blended alkylates made by mixing samples such as A and E in different ratios. This provides to the customer LAB products with a wide variety of molecular weights and improves the utilization of the fl-paraffin feedstocks. 

Mathematical models of the reaction system were developed which enabled prediction of the molecular weight distribution (MWD). Direct and indirect methods were used, but only distributions obtained from moments are described here. Due to the stiffness of the model equations an improved numerical integrator was developed, in order to solve the equations in a reasonable time scale. 

Reactive extrusion is the chemical modification of polymer while it is being transported in an extruder. In this work, polypropylene is intentionally degraded by the addition of a free radical initiator (a peroxide) during extrusion. The product has improved flow properties because of the removal of the high molecular weight tail and the narrowing of the molecular weight distribution. 

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. 

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