![]() Polyols are polymers in their own right and have on average two or more hydroxyl groups per molecule. The choices available for the isocyanates and polyols, in addition to other additives and processing conditions allow polyurethanes to have the very wide range of properties that make them such widely used polymers. One consequence of this is that typical polyurethanes do not soften or melt when they are heated they are thermosetting polymers. In some respects a piece of polyurethane can be regarded as one giant molecule. The crosslinking present in polyurethanes means that the polymer consists of a three-dimensional network and molecular weight is very high. Long chains and low crosslinking give a polymer that is very stretchy, short chains with lots of crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam. High amounts of crosslinking give tough or rigid polymers. ![]() Long, flexible segments, contributed by the polyol, give soft, elastic polymer. ![]() The properties of a polyurethane are greatly influenced by the types of isocyanates and polyols used to make it. ![]()
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