Polymer chain conformation of copolymers with different monomer size: C-13 NMR spectroscopy and MALS study

Copolymer composition, distribution and molecular size of the comonomer influence the final properties of polymer materials. Such influence can be followed from the effect on the chain conformation in solution determined from the scaling law between radius of gyration and molecular weight. In this work, several copolymers, with similar comonomer content (mol%) and distribution but with different comonomer size, have been studied. Ethylene/propylene (EP), ethylene/1-hexene (EH), ethylene/4-methyl-1-pentene (EMP) and propylene/1-butene (PB) with a comonomer content up to 20 mol% have been analyzed. Characterization was carried out by nuclear magnetic resonance (C-13 NMR spectroscopy) and by gel permeation chromatography with a multi-angle light scattering (GPC-MALS). Obtained copolymers present a relatively homogeneous comonomer sequence distribution along the chain, but C-13 NMR spectroscopy results revealed a more homogeneous comonomer chain distribution for EP copolymers, probably due to the monomer size. MALS data were adequately treated with algorithm for self data reduction. No significant effect of overall composition was found and the MALS results were averaged for each kind of copolymers. Linear dependence of log (R-g) vs. log (n) according to regular scaling law was adequate for EP and PB samples along the whole analyzed range. However, a marked non-linearity was found for EH and EMP samples and, consequently, a unique linear regression of log (R-g) vs. log (n) was not recommended. A new method of regression including two different contributions was developed in this work and different values for the shape parameter (q) was obtained in function of molecular weight range.