Schwingungsdaempfung

A constrained layer damped structure (see Division B5) adapted for particular conditions of temperature and vibration frequency has a constrained layer which consists of a polyurethane made by reacting an amount W in parts by weight of an aromatic diisocyanate of M.W. up to 300 wherein wherein A is between 4 and 7, B is between 40 and 70, f is a frequency of applied vibration in cycles per second for which the structure is adapted and T is a temperature in DEG C. for which the structure is adapted, with 100 parts by weight of polypropyleneether glycol of number-average M.W. between 750 and 2500 and an amount by weight of a low molecular weight aliphatic polyol, consisting of diol alone or in admixture with a triol, sufficient to react with 70 to 100% of the NCO groups in excess of those required to form a bis-urethane from each molecule of polypropyleneether glycol. Suitable diisocyanates are toluene diisocyanates, ring dichlorinated toluene diisocyanates, methylene bis - (4 - phenylisocyanate), naphthylene diisocyanates and paraphenylene diisocyanate. The preferred diols are 1,3-butane diol, neopentyl glycol and 2-methyl-2-ethyl-1,3-propanediol and the preferred triols are trimethylolpropane and 1,2,6-hexantriol. Either the "one-shot" or "prepolymer" technique may be employed in the preparation of the polyurethane.