Summary: An improved proton NMR method for the realtime measurement of the hard/soft ratio or the crystallinity, and the mobile-fraction dynamics, in phase-separated or semicrystalline polymers is presented. It avoids some difficulties associated with earlier approaches and can be applied on high-as well as inexpensive low-field instrumentation. A pulsed mixed magic-sandwich echo is shown to provide near-quantitative refocusing of the rigid contribution to the initial part of the free induction decay. This essentially removes the need to account for signal loss during the receiver dead time, and the method should thus be useful for a variety of applications where the magnetization distribution over differently mobile fractions is to be determined. The overall decay of the mobile signal of a semicrystalline polymer was found to exhibit a significant field dependence, such that the apparent transverse relaxation function of the amorphous part is in a real-time experiment best characterized by a subsequent Carr-Purcell-MeiboomGill pulse train. It is demonstrated to be mainly influenced by mobility, while instrumental effects play a minor role. The mobility of the amorphous fraction depends not only on the overall crystallinity, but also on the crystallization conditions, thus on the nanometer-scale morphology.Isothermal crystallization of sPP monitored on a 20 MHz low-field proton NMR spectrometer using the MSE-CPMG experiment.

No abstract

The crystallization of bimodal PDMS molecular‐weight blends consisting of long (115 kda) and short (5.3 kda) chains is investigated using DSC and proton NMR. In agreement with earlier studies, it is found that the pure long‐chain sample crystallizes more rapidly than the short‐chain sample. Furthermore, the rate passes through a maximum for the 60:40 blend. These observations hold true for non‐isothermal cooling at −5 K · min−1 and isothermal crystallization at 203 K (both DSC) as well as at 218 K (NMR). The samples with 40% long chains or less crystallize to about 75–80% under all conditions, and the crystalline fractions derived from DSC and NMR agree very well, thus also confirming the literature value of 61.3 J · g−1 as the perfect heat of fusion for PDMS, and disproving some earlier studies. A relation of the crystallization kinetics with entanglement‐induced segmental orientation correlations in the melt is postulated. The local chain order is characterized by proton multiple‐quantum NMR, and an attempt is made to correlate this observable with a reduced crystallization rate, corrected for effects of chain transport.magnified image

No abstract