Quantitative analysis of three phases of high-density polyethylene with 2D time-domain proton NMR
✍ Scribed by Changho Choi; Linda Bailey; Alfred Rudin; M. Mik Pintar
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 171 KB
- Volume
- 35
- Category
- Article
- ISSN
- 0887-6266
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✦ Synopsis
With two-dimensional time-domain NMR analysis in the proton spin rotating frame, three phases are identifiable in the solid polyethylene. The major proton magnetization fraction is due to the polymer's crystalline region, where the motion is least isotropic and slowest. A magnetization fraction with intermediate relaxation rate is also intermediate in magnitude. This component is proposed to comprise chain loops on the surfaces of crystallites and effectively entangled chain segments. The most mobile fraction, which is most liquid-like with a T 2 of near 1 ms at 120ЊC, is also the smallest. It is proposed that it is due to polymer chains in the amorphous phase. In the crystalline phase the chain motion is an unexpectedly effective relaxation mechanism at Ç50 KHz. This process, which involves propagation of a twisted region along the crystallite, as has been suggested before, is either not present in the other two phases of the HDPE or is less efficient because of the lower polymer density. The activation energies for the crystalline, intermediate and amorphous phases are estimated to be 34 { 3, 13 { 3, and 8 { 2 Kcal/mol, respectively. The frequencies of the relaxation process at 120ЊC are 43 KHz, 350 KHz, and 1.5 MHz, respectively.