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SynopsisA correlation has been established between the dynamic storage modulus ( E ' ) and the mean cross polarization time constants (Tm) for a set of five morphologically diverse polymers, including one a t two temperatures and one at two plasticizer concentrations. The correlation is only possible when the TCH values for all of the motional environments within the polymers are considered. An inversion recovery cross polarization (IRCP) NMR technique is used to obtain motional and morphological information from the main chain carbons of each polymer. After comparing simpiified correlation functions for the two parameters, an experimental relationship between them is established that suggests that TCH and E' are both modulated by a similar distribution of molecular motions. INTRODUCTIONCorrelations between macroscopic physical properties of polymers and solidstate NMR relaxation parameters have been slow to develop despite ongoing efforts. Schaefer and co-workers' were previously successful at making a general correlation between the impact resistance and CP / MAS relaxation constants of several glassy polymers. However, to the best of our knowledge, no one has attempted a correlation based on a simple comparison of the motional models that describe either the macroscopic properties of interest (such as E') or microscopic relaxation constants (such as TCH ).Correlations of this type could potentially be valuable to scientists that are interested in studying polymer structure-property relationships. Here we attempted to establish a correlation between dynamic storage modulus (E') and the average cross polarization constant ( T c H ) with this purpose in mind. BACKGROUND

A relationship between dynamic storage modulus ( E ' ) and the mean cross-polarization time constants ( TcH) for 16 polymer data sets has been established by using a standard linear solid model. This model is used in an attempt to equate the process of cross-polarization with mechanical rigidity by virtue of the implicit dependence of each phenomenon on molecular motion. The apparent validity of the relationship between these parameters indicates that cross-polarization in polymers can be a function of molecular motion in addition to microscopic spin dynamics. The limitations as well as practical applications of this relationship are discussed.

Correlations between the macroscopic bulk polymer properties storage modulus (E′) and loss modulus (E″) and the microscopic property of cross‐polarization as represented by the time constant TCH have been established for a series of polyurethane elastomers. The dependence of E′, E″, and TCH as a function of molecular weight, rigid domain concentration, and temperature are graphically presented as a series of log plots. An experimental relationship is presented that shows that the distribution of motions of the flexible domains appears to be the major factor in the success of these correlations.

13C NMR relaxation parameters have been used to compare the motional characteristics of di-n-hexyl adipate (DHA) in solution and in the solid state of a poly(vinylbutyral-co-vinyl alcohol) (PVB) matrix. The motional behavior of DHA is inherently anisotropic as seen from 13C Ti relaxation measurements in solution. This anisotropy is accentuated in solid PVB/DHA samples where -carbons surrounding the DHA ester groups are found to exhibit less mobility than other DHA carbons. Scalar decoupled relaxation measurements of DHA carbons in the solid PVB/DHA matrix yield 13C 7\ values which are similar to those measured with cross polarization (CP) and high-power decoupling, with the exception of carbons near the ester groups. Inversion-recovery cross polarization (IRCP) data are best fit by a biexponential model for all DHA carbons. However, biexponential behavior is most predominant for carbons near the ester positions. These results indicate that the DHA molecules exist in separate liquid and solid type environments in the PVB/DHA matrix, where the motion of DHA molecules in solid environments is most inhibited near the ester carbon positions, possibly by means of an association between PVB functional groups and DHA ester groups.