Hardness polymer polyols

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

As was the case for graft and PHD polymer polyols, by using PIPA polyols, an increase in hardness, tensile strength and tear strength of the resultant flexible PU foams was observed, as compared to the PU foams made with unfilled polyether polyols. 

Polymer Polyols (BP Chemicals) are dispersions of polystyrene acrylonitrile copolymer particles of 0-5-F5/im in polyether polyols sterically stabilized with non-aqueous dispersants (NAD). Use of these with the conventional urethane polyols enables elastomers of relatively high hardness, high strength and exceptionally high elongation at break to be... 

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. 

Using controlled reaction conditions such as the temperature profile and rate and time of the addition of polyols, more uniform materials can be produced. The correct spacing of the hard segments required to produce the physical properties can be obtained. The controlled conditions will also help prevent the formation of undesirable side products such as allophanate, biuret, and trimers. These reactions will give branching of the polymer chains. 

To study the role of hard segment crystal lizability, two series of polymers were prepared from special reactants as described in the experimental section. In addition some comparative results have been obtained by varying the molecular weight of the polyols used. 

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