Changes in molecular dynamics during the bulk polymerisation of an epoxide/boroxine mixture as studied by dielectric relaxation spectroscopy, revealing direct evidence for a floor temperature for reaction

• Published in: Polymer (Guilford) 2001-04, Vol.42 (8), p.3533-3557
• Main Authors: Williams, G., Smith, I.K., Aldridge, G.A., Holmes, P., Varma, S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemical properties; Dielectric relaxation spectroscopy; Epoxide/boroxine mixture; Exact sciences and technology; Floor temperature; Polymer industry, paints, wood; Properties and testing; Technology of polymers
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(00)00715-1

Real-time dielectric relaxation spectroscopy (DRS), has been used to monitor changes in the dynamics of chain dipoles and of ions during the bulk polymerisation of an epoxide/boroxine system at different reaction temperatures T R in the range 60–120°C. For T R72°C the process moved from high frequencies to settle at audio or higher frequencies, giving a loss peak independent of time that indicated the formation of a chemically stable elastomer. We analysed our results in terms of changes in molecular mobility in the reaction mixture with time and have determined the floor-temperature T F below which a glass is formed and above which an elastomer is formed. The DRS data were also presented as complex impedance Z( ω) which emphasises changes of ionic conductance during reaction. Below T F the peak in the loss impedance Z″ m moved to ultra-low frequencies during reaction in a time-scale far shorter than that for the dielectric loss peak ε″ m. Comparison of the two representations of data made well above T F show that the Z″ data become independent of time before the ε″ data. DRS data presented as dielectric permittivity ε( ω) provides a good indicator of glass-formation below T F and of elastomer-formation above T F. Our data are considered in relation to the TTT-diagram of Gillham and coworkers that describes the onset of gelation, glass-formation and elastomer-formation during cure and we extend this diagram to describe how T g evolves with time for different values of T R.