Investigation on the Influence of Chain Extenders on the Performance of One-Component Moisture-Curable Polyurethane Adhesives.

Chen Tan,Teija Tirri,Carl-Eric Wilen

doi:10.3390/polym9050184

Abstract

In this work, a number of chain extended moisture-curable urethane prepolymers were synthesized in order to develop isocyanate terminated urethane prepolymer formulations that would simultaneously display both high adhesive strength and low viscosity. Proton nuclear magnetic resonance spectroscopy (1H-NMR), size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and Brookfield viscometry were utilized for characterizing the prepared urethane prepolymers. In addition, the adhesion strength of the cured prepolymers was determined by tensile shear strength test according to the DIN EN (Deutsches Institut für Normung, the German Institute for Standardization) 1465 standard. Especially, the role of different types of linear (butanediol, pentanediol) and branched chain extenders (dipropyleneglycol (di-PPG), tripropyleneglycol (tri-PPG) and the influence of their dosage on the degree of microphase separation between hard segments (HS) and soft segments (SS) in urethane prepolymers were studied. Furthermore, the benefits of utilizing either a one-step versus a two-step polymerization process were investigated. The results revealed that the extent of phase separation of different urethane prepolymers was dependent on the extent of hydrogen bonding interactions which was extensively studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR). The incorporation of branched chain extenders (di-PPG and tri-PPG) did not result in notable phase separation between hard segments and soft segments, while linear chain extenders (pentanediol and butanediol) readily promoted phase separation. The degree of phase separation was particularly pronounced for butanediol, and when the linear chain extender ratio was higher than or equal to 0.74. Compared with a two-stage process, one-stage process produced more randomly distributed polymer chains with highly dispersed hard segments. Thus, urethane prepolymers exhibiting strong adhesive strength with simultaneously low viscosity were successfully developed by systematic adjustment of structural parameters.

Highlights

Isocyanate-terminated urethane prepolymers are curable by ambient moisture, and widely used as one-component adhesives, due to their effective wetting properties, low viscosity, fast curing speed, ease of handling, toughness, and good water and chemical resistance [1,2,3,4,5,6,7,8]
The results revealed that the extent of phase separation of different urethane prepolymers was dependent on the extent of hydrogen bonding interactions which was extensively studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR)
The degree of phase separation was pronounced for butanediol, and when the linear chain extender ratio was higher than or equal to 0.74

Summary

Introduction

Isocyanate-terminated urethane prepolymers are curable by ambient moisture, and widely used as one-component adhesives, due to their effective wetting properties, low viscosity, fast curing speed, ease of handling, toughness, and good water and chemical resistance [1,2,3,4,5,6,7,8]. 1. The segment is made up ofand polyols that and impact. Softness, and isocyanates hard segments derive fromcohesive isocyanates that to inthe turn providematrix cohesive strength to derive from that(HS). In turn provide strength polymer as reinforcement the polymer as reinforcement units [9,10]. The curing strong of urethane prepolymers introduces units [9,10].matrix. The curing of urethane prepolymers introduces urea linkages that can organize strong urea linkages cancan organize bidentate which can further the material.

Methods

Results

Conclusion