Acclaim polyols

Example 11. One-Component, Moisture-Cure Polyurethane Sealant. This example is of a low-hardness, high-elongation, moisture-curable polyurethane sealant. The material is based on a low-%NCO prepolymer made from 4,4 -MDI and a low-unsaturation (low-monol-content) Acclaim polyol from Bayer. It is adapted from (a) J. Lear et al., Adhesives Age, February 1999, pp. 18-23 and (b) B. Lawrey, et al., presented at UTECH 2000, The Hague, The Netherlands, March 30, 2000, Crain Communications London, 2000. 

The PU elastomers obtained from polyether diols with DMC catalysts (Acclaim Polyols of Bayer) have a spectacular improvement in the majority of physico-mechanical properties when compared with PU elastomers made from the polyether diols, obtained by anionic catalysis. 

Further improvements in catalyst technology resulted in Lyondell (formerly ARGO Chemical Company) commercialising a new family of PPG with ultra-low monol contents designated Acclaim Polyols. Table 9.2 summarises the unsaturation, functionality, and monol contents of these polyols. Comparing Tables 9.1 and 9.2, one can clearly see the dramatic improvements in functionality. For example, a 4000-MW, ultra-low monol PPG (Acclaim Polyol 4200) has a functionality of 1.98 versus 1.69 for a conventional 4000-MW PPG diol. 

Table 9.2 Monol (unsaturation), functionality and mole % monol of Acclaim polyols (ultra-low monol PPG polyols) ...

Acclaim Polyol Molecular Weight Composition Functionality Hydroxyl Type... 

A review of the elastomer processability and physical property data indicates that there is an optimum hardness range for each polyol MW. Based on the demould time and the percent compression set, the following elastomer Shore hardness ranges are recommended. The lower hardness limits of these ranges can be extended by addition of low levels (less than 10%) of 6000-MW, ultra-low monol triol (Acclaim Polyol 6300). 

Acclaim Polyol 2200 (2000-MW diol) Acclaim Polyol 4200 (4000-MW diol) Acclaim Polyol 8200 (8000-MW diol)... 

The 8000-MW, ultra-low monol PPG is used particularly in the development of soft, plasticiser-free elastomers [16, 17]. The nse of this high MW, low polydispersity polyol allows for the preparation of low viscosity prepolymers with low isocyanate contents. Initial evalnations of these very soft elastomers showed lower than expected physical properties. The lower properties can be attributed to the very low hard-segment content of these polymers. The lack of hard segment (physical crosslinks) can be compensated for by the incorporation of low levels of chemical crosslinks (triol) [18]. This is accomplished by the addition of a 6000-MW, ultra-low monol triol (Acclaim Polyol 6300) into the polymer matrix. Table 9.7 shows the triol effect on prepolymer viscosities, elastomer processability and physical properties. It shonld be noted that very low levels of crosslinking are needed to improve the elastomer properties. 

Table 9.8 Polyurethane elastomers based on Acclaim polyol 3205 ...

The previous studies led to the development of three products, a 2250-MW diol (Acclaim Polyol 2220), 4000-MW diol (Acclaim Polyol 4220) and a 6000-MW triol (Acclaim Polyol 6320). Table 9.4 shows the typical properties of these new higher-reactivity, ultra-low monol PPG polyols. The behaviour of these products in one-shot systems is discussed below. 

MDI/BDO Cured Elastomers Acclaim Polyol 3205 Versus PTMEG-2000... 

For a comparison of PTMEG in MDI/BDO cured elastomers the 3200-MW ultra-low monol PPG diol was chosen which contains about 20 wt% EO (Acclaim Polyol 3205) since it gives the best overall properties in this type of system. A 2000-MW PTMEG was used since it gives the best performance at an 80 Shore A hardness. Elastomers of 80 Shore A hardness were prepared using the prepolymer process. Table 9.14 summarises their prepolymer viscosities, elastomer processing characteristics and physical properties. 

The tensile strengths of ultra-low monol based elastomers are lower than that of PTMEG. However, if one considers the total energy to break as measured by the area under the stress/strain curve, the elastomers based on Acclaim Polyol 3205 are significantly tougher than those based on PTMEG. The tear strengths of the elastomers are comparable. 

Another important feature of these polyols is their narrow MWD. Low polydispersity results in lower viscosities in both the polyol and isocyanate-terminated prepolymers. Polyol MWD has a significant effect on the mechanical and dynamic properties of polyurethane and polyurethane/urea systems. Broad-MWD polyols such as PTMEG or polyester polyols contain significant amounts of hard-segment diol, which limits their softness. Acclaim polyols contain no hard-segment diol and thus have inherent superior properties in soft systems. They can be made to approximate broad-MWD polyols such as PTMEG by incorporation of a low MW glycol. 

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