MULTIPLE TRANSITIONS IN POLYVINYL ALKYL ETHERS AT LOW TEMPERATURES

A series of polyvinyl alkyl ethers, with the ether side chain ranging in length from methyl to n-decyl, has been studied from ∼60°K to above the glass transition. A linear variable differential transformer was used to measure the linear expansion coefficient, α, complemented by mechanical loss measurements with a freely oscillating torsion pendulum and dielectric loss measurements. In addition to the glass transition, two low-temperature transitions have been observed in these systems. The first below Tg, Tgg(1), follows the same trend as the glass transition, i.e., as the side chain length increases the temperature at which the transition occurs decreases, until n-octyl, where side chain crystallization is manifested. The second transition below Tg, Tgg(2), occurs at ∼100°K irrespective of side chain length. Because of their analagous dependence on side chain length, Tgg(1) is thought to be similar to the glass transition, i.e., due to main chain motion. Δα’ at Tgg(2) is of greater magnitude than Δα’ at Tgg(1) and is thought to be a result of reorientation of the side chain. The value of the Simha-Boyer free volume product, (αl - ±g). Tg, decreases with increasing side chain length, suggesting retention of excess free volume by the flexible pendant group. A generalization of this quantity is considered which takes into account the locations and magnitudes of the g-g transitions and results in a more nearly constant value of a freevolume fraction. © 1969, Taylor & Francis Group, LLC. All rights reserved