NMR is a useful technique for characterization of the microscopic dynamics and structure of polymeric material, while rheology provides access to the macroscopic mechanical properties of polymer melts. To achieve greater insight into the interplay of these two domains, especially with regard the microscopic effects of nonlinear shear fields, it is desirable to combine these two methods in one setup. To this end, new developments with permanent Halbach magnets were used to shrink NMR magnets to under 20 cm and a few kilograms [1], making it possible to integrate into a commercial high-end strain-controlled rheometer (Rheometrics/TA ARES), together with a convective sample heating system. This unique low-field RheoNMR setup can simultaneously make a full rheological shear characterization (G’, G’’, LAOS, I3/1, FT-Rheology [2]) while monitoring molecular dynamics via 0.7 T 1H TD-NMR up to temperatures of 210 °C [3, 4]. Possible applications for low-field Rheo-NMR include the measurement of quantitative composition in crystallizing polymers [5] and multiphase systems [6] during the application of non-linear mechanic deformations, e.g. shear induced crystallization. It enables to directly correlate changes in rheological moduli with the degree of crystallinity. To display the possibilities of this new technique, the studies on crystallization of isotactic polypropylene and polyethylene variating molecular weight, crystallization temperatures, additives and applied shear are presented. The results are compared to the findings of other groups [7]. Keywords: Rheo-NMR, crystallization, polymer melts References: [1] B. Blümich, F. Casanova, S. Appelt, Chem. Phys. Lett., 2009, 477, 231-240. [2] M. Wilhelm, Macromol. Mater. Eng. 2002, 287, 83-105. [3] V. Räntzsch, M. Wilhelm, G. Guthausen, Magn. Reson. Chem. 2015, DOI 10.1002/mrc.4219. [4] V. Räntzsch, K.-F. Ratzsch, G. Guthausen, S. Schlabach, M. Wilhelm, Soft Mater. 2014, 12, 4-13. [5] A. Maus, C. Hertlein, K. Saalwächter, Macromol. Chem. Phys. 2006, 207, 1150-1158. [6] K. Saalwächter, Prog. Nucl. Magn. Reson. Spectrosc. 2007, 51, 1-35. [7] G. Lamberti, G. W. M. Peters, G. Titomanlio, Int. Polym. Proc. 2007, 22, 303-31.