Direct evidence for the validity of assessing reaction extent by torque spectrum during reactive processing

In this work, direct evidence for the validity of assessing reaction extent by torque spectrum during reactive processing has been provided by taking PVDF/PLLA/RCC (reactive comb-like compatibilizers) as an example. In RCC, three types of repeat units are found (in a perfectly random fashion) along the backbone, namely MMA units, unreacted GMA units and GMA units reacted with the MMA macromonomer (the latter represent the teeth of the comb). Upon blending, a percentage of PLLA is grafted onto RCC because of the reaction between its terminal carboxyl group and epoxide group in RCC. In the resultant co-continuous structures, extraction and acid hydrolysis have been employed to distinguish reacted and free (un-reacted) PLLA, in which only free PLLA and all (un-reacted and reacted) PLLA can be removed, producing extraction ratio (ER) and acid hydrolysis ratio (AR) respectively. The graft ratio (GR) of PLLA, calculated based on the difference between AR and ER, represents the reaction extent directly. The comparison of GR and torque indicates that they exhibit the same evolution with not only similar increase/equilibrium regimes but also comparable critical transition time. Therefore, our results confirm that torque spectrum can be used to describe the reaction extent as accurately as graft ratio, which is significant for the basic understanding and applications of reactive processing.