Polyols molecular weight, effect

Effect of varying polyol molecular weight on the glass transition temperature of polyurethanes... 

In a set of parallel studies, a series of polyethylene glycols were tested to confirm the effects of polyol molecular weight. The polymers including a TDI-based prepolymer... 

The principal focus of this paper will be on the effects of polyol molecular weight, polyol oxyethylene group content,... 

The effects of polyol molecular weight and oxyethylene group content on the thermal stability of these polymers have been reported independently by Bonk and Shah ( 7) ... 

Figure 9.5 DMTA curves of 70 Shore A elastomers Effect of polyol molecular weight (6% NCO MDI prepolymers BDO cured)...

Polyol Molecular Weight Distribution Effect on Mechanical and Dynamic Properties of Polyurethanes... 

Silver, J.H., Myers, C.W., Lim, F. et al (1994) Effect of polyol molecular weight on the physical properties and haemocompatibility of polyurethanes containing polyethylene oxide macroglycols. Biomaterials 15(9), 695-704. 

L. Irusta, M. Femandez-Berridi, Aromatic poly(ester-urethanes) effect of the polyol molecular weight on the photochemical behaviour, Polymer 41 (2000) 3297-3302. 

Polyethers produced via the ROP of epoxides have many commercial uses, and are especially important as precursors to polyurethanes (Scheme 20).927-929 Although a wide variety of reagents can effect the cationic or anionic ROP of epoxides, low molecular weight polyols are generally prepared using potassium or sodium hydroxide.930,931... 

It is important to be aware of the chemical effects of isocyanates. The polynre-thanes you will develop will be combinations of polyols and isocyanates. The ratio of the two compounds will in pait dictate both the physical and chemical properties of the product. As a general rule, the isocyanates are hard segments that impart rigidity to the polymer. The polyol is the so-called soft segment. The various molecular weights (more correctly equivalent weights available in the form of polymeric MDIs) provide certain advantages. Table 2.2 lists a few commercially available polyisocyanates and their physical properties. 

Additional tests with ammonium compounds were performed to address the effect of ammonium ion (see Fig. 8). It is clear that the catalyst inhibition was not based only on the presence of ammonium ion. Ammonium carbonate showed the largest inhibition of the glucose hydrogenation reaction, while chloride and hydroxide had lesser effects. Ammonium nitrate caused no apparent inhibition on glucose conversion. A similar lack of effect was shown with potassium nitrate. In the case of ammonium nitrate, the glucose conversion mechanism was affected, so that the sorbitol yield was reduced by about 20%, but numerous byproducts and overreaction products (lower molecular weight polyols) were evident. 

A wide range of materials is included in this class. The common feature is the use of chain extension reactions to provide products with acceptable commercial properties. The chain extension reaction effectively reduces the actual number of chain ends, thereby eliminating the generally poor properties observed when very low-molecular-weight polymers are cross-linked. The chain extension step involves the reaction of a difunctional polymeric polyol with difunctional organic isocyanates to give the polyurethane ... 

Polydextrose (6) is a synthetic polymer of dextrose with the dextrose molecules linked l->6. This link is not common in nature so polydextrose is only one quarter metabolised which gives the psychologically important value of 1 kcal g 1. As laxative effects arise through colligative properties, and because polydextrose has a high molecular weight, the laxative effects experienced are lower than for the low molecular weight polyols. 

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