PRIMITIVE MODELS OF CHEMICAL ASSOCIATION .2. POLYMERIZATION INTO FLEXIBLE CHAIN MOLECULES OF PRESCRIBED LENGTH

The structural properties of the totally flexible sticky two-point (S2 P) model for polymerization into chain molecules of fixed length are s tudied. The model is represented by an n-component mixture of hard sph eres of the same size with species 2,...,n-1 bearing two attractive st icky sites A and B, randomly distributed on the surface. The hard sphe res of species 1 and n have only one site per particle, site B for spe cies 1 and site A for species n. Due to the specific choice for the at tractive interaction, which is present only between site B of the part icles of species a and site A of the particles of species a + 1, this version of the S2P model represents an associating fluid that polymeri zes into freely jointed tangent hard-sphere chain molecules. The corre lation functions of this model are studied at all degrees of associati on using a recently obtained general solution of the polymer Percus-Ye vick (PPY) approximation [Yu. Kalyuzhnyi and P. Cummings, J. Chem. Phy s. 103, 3265 (1995)]. Comparison of the results of the present theory in the complete association limit with corresponding computer-simulati on results and results of other theories is presented and discussed. T he complete-association results constitute a quantitatively successful theory of the mean monomer-monomer distribution functions for less th an or equal to 16 but for n = 50 these functions are no longer quantit atively accurate. (C) 1997 American Institute of Physics.