Crystalline-structure of Some Alternate Copolymers Between Carbon-monoxide and Styrene Derivatives

The crystal structure of some alternate copolymers of styrene and styrene derivatives with carbon monoxide is presented. We start from the crystal structure previously solved in the case of poly(1-oxo-2-phenyltrimethylene) (STCO), which gave clear evidences of the syndiotactic nature of this copolymer. The very close analogies between the X-ray powder diffraction spectra of copolymers of CO with p-fluorostyrene (pFSTCO), m-methylstyrene (mMSTCO), and p-methylstyrene (pMSTCO) with the spectrum of STCO allow us to postulate an analogous syndiotactic structure and a very similar chain conformation and packing model for them. The structural models have been refined for all four copolymers through the Rietveld method, giving the following results. (a) For STCO: space group P2(1)/c, a = 15.20 angstrom, b = 6.166 angstrom, c = 7.59 angstrom, beta = 102.5-degrees. (b) For pFSTCO: space group P2(1)/c, a = 15.59 angstrom, b = 6.168 angstrom, c = 7.551 angstrom, beta = 98.8-degrees. (c) For mMSTCO: space group P2(1)/c, a = 16.14 angstrom, b = 6.816 angstrom, c = 7.580 angstrom, beta = 100.3-degrees (d) For pMSTCO: space group C2/c, a = 35.54 angstrom, b = 6.262 angstrom, c = 7.536 angstrom, beta = 96.0-degrees. All the studied copolymers crystallize with the chain backbone in a nearly extended conformation, with very similar values of the dihedral angles. Roughly speaking, also the packing models are very similar. In all crystal structures the chains are arranged to form layers parallel to the bc plane piled along a. The packing models for the various copolymers present the most relevant differences in the stacking along a of these bc layers.