Temperature effect on polymer mechanochemistry

Abstract

AbstractThe influence of temperature is a fundamental variable for the mechanochemical processes of high polymers. However, it is generally recognized that the effect of temperature in this process is not always direct, as in normal chemical reactions, but is mainly indirect involving change in the properties (principally elastic and viscous), in the physical state of the system, and consequently in the mechanism of rupture. The negative temperature coefficient has been considered a prime criterion of a mechanochemical reaction by many researchers. Recently, it has been suggested that the negative temperature coefficient is really due to the viscous heating during polymer deformation and the low thermal conductivity of polymers.The aim of this paper is to reevaluate the role of temperature on mechanically induced reactions of polymers. In light of evidences published in the last 30 years, the dependence of mechanochemical reaction on temperature must involve the overlapping of the following factors: (1) the usual positive dependence of rate on temperature, as predicted by Arrhenius equation; (2) the true experimental temperature, which depends on viscous heating and on thermostatting efficiency; and (3) the breaking tension at the center of the polymer chain which is inversely dependent on temperature, i.e., greater at the higher viscosity and the slower relaxation at the lower temperatures, this last factor being dominant in determining the characteristic negative temperature coefficient for polymer mechanochemistry.