Thermal conductivity of a polymerizing liquid

Area of Science:

• Materials Science
• Physical Chemistry
• Polymer Science

Background:

• Thermal conductivity (kappa) is a crucial property for understanding heat transfer in materials.
• Polymerization involves the formation of larger molecules, altering material properties over time.
• Real-time measurement of thermal conductivity during polymerization is essential for process control and material characterization.

Purpose of the Study:

• To measure the real-time thermal conductivity of polymerizing liquids at various temperatures.
• To investigate the influence of polymerization time and temperature on thermal conductivity.
• To interpret the observed thermal conductivity behavior using complementary techniques like calorimetry and dielectric spectroscopy.

Main Methods:

• Real-time measurement of thermal conductivity (kappa) for seven polymerizing liquids.
• Calorimetry and dielectric spectroscopy were employed for one liquid to aid interpretation.
• Measurements were conducted at different temperatures to study their effects.

Main Results:

• Thermal conductivity initially increased with polymerization time, correlating with increases in molecular weight, density, and sound velocity.
• A distinct peak in thermal conductivity was observed at a specific polymerization time, followed by a decrease and eventual plateau.
• The peak's position and height were influenced by temperature, measurement pulse time, and polymerization rate.

Conclusions:

• The observed thermal conductivity peak may be an artifact related to the time-dependent heat capacity during measurement, similar to phenomena in glasses and supercooled liquids.
• The peak could also arise from the interplay between the increasing elastic modulus and decreasing equilibrium heat capacity during polymerization.
• The peak's appearance does not definitively distinguish the slowing of Brownian motion during polymerization from that induced by cooling or compression.