Polymer Dynamics of Well-Defined, Chain-End-Functionalized Polystyrenes by Dielectric Spectroscopy

• Published in: Macromolecules 2009-11, Vol.42 (22), p.8875-8881
• Main Authors: Lund, Reidar, Plaza-García, Sandra, Alegría, Angel, Colmenero, Juan, Janoski, Jonathan, Chowdhury, Sumana Roy, Quirk, Roderic P
• Format: Article
• Language: English
• Subjects: Applied sciences; Electrical, magnetic and optical properties; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma901617u

A novel strategy is described to study polymer dynamics by using a combination of dielectric spectroscopy and functionalized polymers. The first results are presented using various well-defined, chain-end-functionalized polystyrenes (PS) synthesized using a combination of modern anionic polymerization techniques and hydrosilylation chemistry. The end-functionalized polystyrenes investigated contain the cyano (−CN), hydroxyl (−OH), acetyl (−OCOCH3, −Ac), or ethyl ether (−OCH2CH3, −OEt) groups. By applying broadband dielectric spectroscopy (BDS) over an extensive temperature range (approximately 50−413 K), it was possible to fully characterize the polymer dynamics associated with the segmental α-relaxation as well as the local secondary process related to the specific movement of the functional groups themselves. Combining these data with the results from differential scanning calorimetry (DSC), it is shown that for rather large functional groups the overall polymer matrix properties are altered, giving rise to a decrease in the glass transition temperature. The trend can be rationalized in terms of free volume effects caused by the bulky functional groups and points toward matrix plasticization effects. However, for cyano-functionalized PS the inclusion of this group does not significantly affect the matrix properties. By taking advantage of the strong dipole moment of the CN group, a clear dielectric signal can be obtained that can be used to selectively study the specific dynamics where the group is located. In other words, by appropriately attaching cyano groups at different parts of the chains, these can be exploited as in situ dielectric probes that allow determination of specific contributions to dynamical processes in polymers.