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Characterization of polymer molecular weight distribution by transient viscoelasticity: Polytetrafluoroethylenes
Author(s) -
Wu Souheng
Publication year - 1988
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760280809
Subject(s) - materials science , molar mass distribution , viscoelasticity , melting point , polymer , quantum entanglement , thermodynamics , relaxation (psychology) , crystal (programming language) , volume fraction , composite material , physics , psychology , social psychology , quantum mechanics , quantum , computer science , programming language
The relationship between the relaxation time spectrum H (τ) in the terminal zone and the volume‐fraction differential molecular‐weight‐distribution function P ( M ) is derived by considering binary chain contacts for stress transmission,where β and λ are constants for a given chemical type. This is used to determine the molecular‐weight‐distribution curves from the stress relaxation modulus spectrum (above the crystal melting point) at 370°C for a number of commercial and experimental poly(tetrafluoroethylenes) (PTFEs). It is found that PTFEs typically have bimodal molecular‐weight distributions. The lower‐molecular‐weight peak conforms essentially to the “most‐probable” distribution, and the higher‐molecular‐weight peak to the binary coupling distribution. The entanglement molecular weight M e is 5490, and the number of main‐chain atoms between entanglement points is 110, consistent with a flexible chain. The zero‐shear melt viscosity at 370°C is η 0 = 1.79 × 10 −13 M w 2.94±0.13 , where η 0 is in Pa.s and M w / M e = 2,000 to 12,000. The monomeric friction coefficient is also determined.