Structural and Viscoelastic Properties of Thermoplastic Polyurethanes Containing Mixed Soft Segments with Potential Application as Pressure Sensitive Adhesives.

Mónica Fuensanta,José Miguel Martín-Martínez

doi:10.3390/polym13183097

Abstract

Thermoplastic polyurethanes (TPUs) were synthetized with blends of poly(propylene glycol) (PPG) and poly(1,4-butylene adipate) (PAd) polyols, diphenylmethane-4,4′-diisocyanate (MDI) and 1,4-butanediol (BD) chain extender; different NCO/OH ratios were used. The structure and viscoelastic properties of the TPUs were assessed by infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, thermal gravimetric analysis and plate-plate rheology, and their pressure sensitive adhesion properties were assessed by probe tack and 180° peel tests. The incompatibility of the PPG and PAd soft segments and the segregation of the hard and soft segments determined the phase separation and the viscoelastic properties of the TPUs. On the other hand, the increase of the NCO/OH ratio improved the miscibility of the PPG and PAd soft segments and decreased the extent of phase separation. The temperatures of the cool crystallization and melting were lower and their enthalpies were higher in the TPU made with NCO/OH ratio of 1.20. The moduli of the TPUs increased by increasing the NCO/OH ratio, and the tack was higher by decreasing the NCO/OH ratio. In general, a good agreement between the predicted and experimental tack and 180° peel strength values was obtained, and the TPUs synthesized with PPG+PAd soft segments had potential application as pressure sensitive adhesives (PSAs).

Highlights

Thermoplastic polyurethanes (TPUs) are versatile polymers commonly used as elastomers, adhesives and coatings in automotive, building and construction, shoe manufacturing and biomedical technology, among others
TPU structure consists of soft (SS) and hard (HS) segments, the SS are due to the interactions between the long polyol chains, and the hard segments (HS) are produced by reacting the diisocyanate with the polyol and the chain extender [1,2]
The TPU pressure sensitive adhesives (PSAs) synthesized with polypropylene glycols (PPGs) polyols with molecular weights of 450 and 2000 g/mol, an NCO/OH ratio of 1.1 and 12.5–38.7% HS content have shown different performance; the increase of the HS content increased the percentage of the hydrogen bonded urethane species and produced a lower degree of micro-phase separation

Summary

Introduction

Thermoplastic polyurethanes (TPUs) are versatile polymers commonly used as elastomers, adhesives and coatings in automotive, building and construction, shoe manufacturing and biomedical technology, among others. The performance of TPU PSAs made with MDI and polyether polyols of different nature and molecular weights has been shown, in which the role of the degree of micro-phase separation on their performance has been demonstrated [37,38] These TPU PSAs showed good tack at 10–37 ◦C and their structures were controlled by the soft domains with minor contribution of the bonded urethane species and an important degree of micro-phase separation [37]. The TPU PSAs synthesized with PPG polyols with molecular weights of 450 and 2000 g/mol, an NCO/OH ratio of 1.1 and 12.5–38.7% HS content have shown different performance; the increase of the HS content increased the percentage of the hydrogen bonded urethane species and produced a lower degree of micro-phase separation. The structure, viscoelastic and adhesion properties of the TPUs and the TPU PSAs synthesized with blends of polyether and polyester polyols have been carried out while paying particular focus to the role of the miscibility of the SS on their viscoelastic and adhesion properties

Materials

Plate-Plate Rheology

Findings

Probe Tack