Dipolar filter

As in the case of CPMAS, the CP-MQMAS transfers are incapable of enhancing the sensitivity, but can provide dipolar filtering of high-resolution spectra of quad-rupolar nuclei and, most importantly, serve as a method for obtaining the HETCOR... 

Dipolar filter techniques (see Section 3) are becoming more common for examining regions of different mobility in polymers.87 In one particular study,88 a dipolar filter is used initially to select 1H spins from mobile regions of coreshell latex systems. Dipolar filters of increasing strength are then applied so as to obtain a characteristic decay curve for each sample. This enabled the mobility of the various components in the system to be compared with the respective pure substances, so that the effect of mixing could be assessed. 

Fig. 10.3.7 Pulse sequence for spin-diffusion imaging with ID spatial resolution [Wei8] and effect of mobility filters, (a) The magnetization source is selected by the dipolar filter which suppresses the magnetization in the sink. During the spin-diffiision time the magnetization dif ses from the source to the sink, (b) The dipolar filter selects magnetization from chain segments which are highly mobile and intermediately mobile. By use of a lineshape filter the signal loss is analysed only for the mobile components. IP(Tc) is the probability for a particular correlation time to arise in the sample. It is essentially the spectral density of motion.

NMR is particularly suited for the measurement of domain sizes in the range of 5 - 20oA (145), which can be probed with a spin diffusion experiment, e.g., Goldman-Shen sequence (146) and dipolar filter pulse sequence (147). The use of multidimensional techniques to study length scales in heterogeneous polymers has been previously reviewed by Spiess (148). 

Summary H solid-state spin diffusion NMR spectroscopy was applied to calculate domain sizes of separated phases in poly(phthalamide)/poly(dimethylsiloxane) block copolymers. To initiate spin diffusion, the dipolar filter technique was used. The correlation between longer PDMS chains in the copolymer and bigger domains of the PDMS phase could be shown. 

For the Ti compensation, measurements with the same mixing time but without the dipolar filter were recorded. The T2 values were obtained by using a Carr-Purcell-Meiboom-Gill (CPMG) sequence. The curves were analyzed by a biexponential decay representing the T2 for the rigid and the mobile component. 

A. Buda, D.E. Demco, M. Bertmer, B. Blumich, B. Reining, H. Keul, H. Hocker, Domain sizes in heterogeneous polymers by spin diffusion using singlequantum and double-quantum dipolar filters. Solid State Nucl. Magn. Reson. 24 (2003) 39-67. 

The possibility to implement a MQ dipolar filter has already been demonstrated. For instance, by use of a DQ dipolar filter working in the initial... 

PnAMAs exhibit a local nanophase separation associated with intriguing chain dynamics PnAMAs were investigated in the melt with a recently-developed solid-state NMR method, NOE with dipolar filter. ... 

Fig. 11 (a, d) Pulse sequences for dipolar filter signal editing, where Tr denotes one... 

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