Polymer structure development during flow : monitoring

Solvents can be applied to avoid high processing temperatures or to lower the viscosity. A disadvantage of solution processing is that the solvent has to be removed after processing. A possible solution to this problem is to use reactive solvents (monomers) that are polymerized in situ. This will induce liquid-liquid (L-L) phase separation and, at sufficiently high polymer content, the polymerized solvent will be the dispersed phase—being ‘‘locked up’’ in the system after processing. This new processing technique was applied by Venderbosch et al. (1994) to the intractable polymer poly(2,6 dimethyl-1,4-phenylene ether) (PPE) with epoxy as the reactive solvent. The concept of reactive solvents was also explored for semicrystalline polymers such as poly(ethylene) (PE) with styrene as the reactive solvent (Goossens et al. 1998). Because crystallization can interfere with phase separation in semicrystalline polymers, the morphology development is rather complex. In situ small-angle x-ray scattering (SAXS) studies in combination with wide-angle x-ray scattering (WAXS), DSC and/or Fourier transform infrared spectroscopy (FTIR) were successfully applied in elucidating structure development in several, complex systems (Koberstein and Russell 1986), and studying reactive systems, e.g., by Ryan and co-workers (Ryan et al. 1992 A.J. Ryan, C.W. Macosko and W. Bras, Order-disorder transition in a block copolyurethane, Macromolecules 25 (1992), pp. 6277–6283. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (46)Ryan et al. 1992). Vibrational spectroscopy has proved useful to follow reaction kinetics. The advantage of Raman spectroscopy over FTIR is that Raman spectra can be obtained even from opaque samples—a prerequisite for the systems studied. Since mechanical properties of materials are strongly dependent on their morphology, control over this morphology and understanding of its development are of major importance. For reactive systems, changes in composition and polymerization temperature can significantly change both the reaction kinetics and the concurrent structure development. The combination of SAXS, WAXS, and Raman spectroscopy in one experiment provides a perfect time-correlation between the reaction kinetics and the structure development. Only recently, Bras and co-workers succeeded in constructing a setup for performing simultaneous SAXS and FTIR in a time-resolved mode (Bogg et al. 1995, Bras et al. 1995). This was shortly followed by the development of a SAXS/WAXS/Raman spectroscopy setup by Bryant et al. (1998). This last combination fulfils all the requirements needed for the present purpose