The polyalkylenamides of this invention, which are preferred to produce the polymer coating, may be represented by the following formula: L ORR 11 wherein R is an n-valent organic radical having 4 to 55 carbon atoms, for example, a hydrocarbon radical such as an acyclic alkylene radical or an arylene radical (for example, the 1,3-phenylene radical and the 1,4- phenylene radical), or an aryline rad