Solid-state structure of comb-like polymers having n-octadecyl side chains II. Crystalline-amorphous layered structure

Abstract

Crystalline-amorphous layered structure constructed by comb-like poly[(methyl acrylate)-stat-(n-octadecyl acrylate)]s (PAx), which have crystallizable n-alkyl side chains and amorphous main chain, has been investigated by X-ray diffraction method. Small-angle X-ray scattering profiles of PAx and its blends with n-octadecanoic acid (C18) varies with the change of l/fmain, which is defined as the ratio of the number of the n-alkyl side chain and C18 molecule to that of the main chain -CH2-CH- unit. When 1/fmain is smaller than 0.71, the layer spacing obtained from diffraction angle of a sharp peak at small-angle region gradually decreases with an increase of 1/fmain. In the region of 1/fmain =0.73-0.89, a broad peak coexists with the sharp peak, and locates at smaller angle region than the sharp peak. When 1/fmain is larger than 1.0, i.e., blends of poly(n-octadecyl acrylate) (PA 100) with C18, a newly appeared sharp reflection can be observed at further smaller angle. These complicated variations in layer spacing are interpreted by three packing models, which are named as Interdigitating Form, End-to-end Form, and disordered End-to-end Form, respectively. Differential scanning calorimetry measurements for PA100/C18 blends also suggest the existence of another crystalline form induced by the addition of C18. In the blends of PA100 with n-tetradecanoic acid, the chain length of which is shorter than C18, the structural transformation observed in PA100/C18 system can not be recognized.