. Vol.26 No.2 , July - December 2023.

Intrinsic Viscosity-Molecular Weight Relationship for Liquid Natural Rubber

Kraiwut Wisetkhamsai, Weerawat Patthaveekongka, and Wanvimon Arayapranee

Abstract

      In this work, liquid natural rubber (LNR) samples were prepared with the oxidative degradation of natural rubber (NR) by using hydrogen peroxide (H₂O₂), sodium nitrite (NaNO₂), and formic acid (CHOOH) as reagents. The intrinsic viscosity [η] of the LNR samples dissolved in toluene at 30°C was determined using an Ubbelohde viscometer. The average molecular weights (M_n, M_w, and M_z) were measured by using Gel Permeation Chromatography (GPC) in tetrahydrofuran (THF) at 30°C. The relationships between intrinsic viscosity and average molecular weight (M_n, M_w, and M_V) were established for LNR samples using the Mark-Houwink-Sakurada (MHS) Equation. The constants, a and K of the MHS Equation for LNR samples dissolved in toluene at 30°C were determined, and the effect of the polydispersity correction factor (q_MHS) on the relationships was studied for LNR broad MWD (0.9544). This study resulted in the following MHS Equation for broad MWD of LNR as follow:

[η] = 4.8217 ´ 10^-4 M_v^0.7115 = 4.9113 ´ 10^-4 q_HMS M_w^0.7115 = 4.6017 ´ 10^-4 M_w^0.7115

where [η] is the intrinsic viscosity in dL/g. The M_V and M_W are viscosity-average molecular weight and weight-average molecular weight in g/mol, respectively. The value of a (0.7115) indicated that the conformation of LNR in toluene at 30°C was a flexible chain polymer.

Keywords: intrinsic viscosity, Mark-Houwink-Sakurada (MHS) Equation, average molecular weight, liquid natural rubber (LNR), gel permeation chromatography (GPC)

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