Synthesis and properties of polyurethane ionomers based on carboxylated polycaprolactone

Abstract

Polycaprolactone containing carboxyl groups (CPCL, M n ϭ 1200) was prepared from caprolactone (CL) and dimethylol propionic acid (DMPA). Based on the CPCL, 4,4Ј-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD), a novel series of polyurethane ionomers could be synthesized with ions in the soft segment. The tensile modulus and ultimate elongation of the ionomer cast films increased, and the glass transition temperature of the CPCL-rich phase moved to a higher temperature after ionization. Moreover, this kind of ionomers showed small amounts of hard segment crystallinity by DSC. WAXD shows an ionic peak at 2 ϭ 8.6°for the ionomer with carboxylate in the hard segment, which is not present in the ionomer with carboxylate in the soft segment.

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“…By comparing Sample D and Sample E, we find that the peak at 1540 cm −1 of Sample D is obviously weaker than that of Sample E. As it is not generally disagreed that the reactivity of NH 2 is much higher than that of OH. Especially at low temperatures, NH 2 reacts with NCO before H 2 O reacts with NCO 42,43 . Therefore, it can be considered that NH 2 in CSGH reacted with NCO and a cross‐linking network was formed.…”

“…As for the viscosity of the emulsion, as the mass of MDEA increased from 7% to 10%, the viscosity gradually increased from 28 to 67 mPa s. In previous studies, it was demonstrated that the increase of the ionic hydrophilic chain extender would increase the viscosity of the polyurethane dispersion and reduce the particle size. This is because the hydrophilic groups of the particles increase, which makes it easier to disperse in water, and the particle size decreases accordingly 42,43 . Moreover, due to the increase of the ion force and the increase of the specific surface area, the interaction between the particles and the water molecules increases, showing an increase in viscosity 44 .…”

“…Especially at low temperatures, NH 2 reacts with NCO before H 2 O reacts with NCO. 42,43 Therefore, it can be considered that NH 2 in CSGH reacted with NCO and a cross-linking network was formed.…”

“…This is because the hydrophilic groups of the particles increase, which makes it easier to disperse in water, and the particle size decreases accordingly. 42,43 Moreover, due to the increase of the ion force and the increase of the specific surface area, the interaction between the particles and the water molecules increases, showing an increase in viscosity. 44 The results of Sample 2, Sample 3, and Sample 4 tie well with previous studies.…”