A series of mono- and di-functionalized polyisoprenes (PIs) bearing hydroxyl (OH−) end-group(s) with different molar masses ranging from 2 to 30 kg mol–1 were synthesized and studied by a combination of temperature- and pressure-dependent dielectric spectroscopy and rheology. In the di-functionalized PIs, the −OH end-group interactions result in a mixture of linear and cyclic configurations (up to 45% cyclic configurations for the lower molar masses). The formation of cyclic topologies due to increased H-bonding interactions restricted the backbone mobility and increased the glass temperature, Tg, especially for the lower molar masses. Moreover, an additional process (termed α*) was evidenced in the dielectric spectroscopy in the range between the segmental process and the global chain relaxation. It followed a Vogel–Fulcher–Tammann temperature dependence, freezing at a temperature in the vicinity of the liquid-to-glass temperature, being independent of molar mass. Its molecular origin was identified by employing the pressure sensitivity of the characteristic relaxation times and the pressure dependence of Tg. It reflects the relaxation of segments in the vicinity of the H-bonded groups. Overall, this study provided information on the impact of weakly associating polar end-groups (hydroxyl) on the molecular dynamics of type-A polymers. Furthermore, it suggested promising routes for designing polymers with a higher concentration (>50%) of cyclic topologies, for example, by employing (i) short chains with (ii) strongly associating end groups (stronger than the hydroxyl end-groups).
|Original language||English (US)|
|State||Published - Nov 18 2022|
Bibliographical noteKAUST Repository Item: Exported on 2022-11-30
Acknowledgements: This research was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (project number: 183). A.P. was financially supported by the program “PERIFEREIAKI ARISTEIA” (Regional Excellence) cofinanced by the European Union and the Hellenic Republic Ministry of development and investments under NSRF 2014–2020 (Region of Epirus, call 111). K.N. and N.H. would like to acknowledge the support of King Abdullah University of Science and Technology (KAUST).
ASJC Scopus subject areas
- Materials Chemistry
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry