Morphological differences in semicrystalline polymers: Implications for local dynamics and chain diffusion

Morphological differences in semicrystalline polymers due to different crystallization conditions have implications for the chain motion. The local dynamics in the noncrystalline regions of solution-crystallized linear polyethylene is lower than in a melt-crystallized sample, but the opposite is observed for chain diffusion between noncrystalline and crystalline regions. The activation enthalpy for chain diffusion, however, is the same, indicating that entropic differences in the noncrystalline regions strongly influence the chain diffusion of the same polymer in different morphologies.

Figure 1

(Color) NMR spectra of PE samples at $T=340\mathrm{K}$: (a),(b) ${}^{13}\mathrm{C}$ CPMAS spectra ($6\mathrm{kHz}$ MAS, $2\mathrm{ms}$ CP contact); (c),(d) REREDOR pattern [8] ($25\mathrm{kHz}$ MAS, 3 ${\tau }_{\mathrm{R}}$ recoupling); (e),(f) ${}^{13}\mathrm{C}$ CSA powder line shape (CSA recoupling [9], $3\mathrm{kHz}$ MAS) together with line shape simulations (in gray).

Figure 2

Decay of crystalline NMR signal plotted versus the square root of time $t$ ($6\mathrm{kHz}$ MAS, $T=340\mathrm{K}$, $t=0.1\mathrm{s}$ for normalization).

Figure 3

Arrhenius plots of the chain diffusion coefficients $D$ determined from exchange NMR experiments for the two PE samples.

Figure 4

Arrhenius plots of local and effective jump rates in melt-crystallized PE samples.