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Chain Dynamics of Partially Disentangled UHMWPE around Melting Point Characterized by 1H Low-Field Solid-State NMR
Yan Zhao1, Yuling Liang2, Yingjie Yao1
1Key Laboratory of High-Performance Polymer Materials and Technology of Ministry of Education, Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
Partially disentangled ultrahigh molecular weight polyethylene (UHMWPE) processed via freeze-extraction maintains its less-entangled state during melting. This improved chain mobility offers a promising pathway for enhanced UHMWPE processing.
Area of Science:
- Polymer Science
- Materials Science
- Solid-State Nuclear Magnetic Resonance (NMR)
Background:
- Ultrahigh molecular weight polyethylene (UHMWPE) exhibits significant entanglement, leading to processing challenges.
- Understanding chain mobility in UHMWPE melts is crucial for overcoming processing difficulties.
Purpose of the Study:
- To investigate the effect of reduced entanglement on the chain mobility of UHMWPE during melting.
- To explore methods for improving UHMWPE processability by controlling entanglement.
Main Methods:
- Preparation of partially disentangled UHMWPE using freeze-extraction.
- Utilizing low-field solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, specifically 1H free induction decay (FID) and 1H double quantum (DQ) NMR, to probe chain segmental mobility and residual dipolar interactions.
- Comparative analysis of UHMWPE and high-density polyethylene (HDPE) with varying degrees of entanglement.
Main Results:
- Partially disentangled UHMWPE demonstrated enhanced chain mobility around the melting point.
- Less-entangled UHMWPE retained its disentangled state during melting, unlike less-entangled HDPE.
- No significant difference in residual dipolar interactions was observed in DQ NMR experiments between melts with different entanglement degrees post-melting.
Conclusions:
- Freeze-extraction is an effective method to reduce UHMWPE entanglement and improve chain mobility.
- The ability of less-entangled UHMWPE to maintain its disentangled state near the melting point suggests improved processing potential.
- Further research may be needed to fully understand the role of entanglements in polymer melts using NMR techniques.
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