New Heterocyclic Polyurethane-ureas Based on 4,4'-dibenzyl diisocyanate. 2. Influence of Pyridine Units on the Mechanical Properties

Abstract

Heterocyclic polyurethane-ureas containing pyridine units on the main chain have been prepared by a two-step polyadition reaction. First, an urethane prepolymer was prepared in bulk starting from a macrodiol, which was a polyester-diol such as poly(ethylene adipate) (PEA) or a polyether-diol such as poly(tetramethylene glycol) (PTMG), and a diisocyanate such as 4,4'-dibenzyl diisocyanate (DBDI) or 4,4'-methylene-bis(phenyl-isocyanate) (MDI). The resulting urethane prepolymer containing NCO end groups was polymerized afterwards in DMF solution by using 2,6-diamino pyridine (DAPy) as chain extender, leading to polyurethane-ureas containing pyridine units The hard segments contents varied between 1.458–1.967 mol NHCOO/1000 g polymer. The resulting polymers were characterized by IR spectra, elemental and thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, inherent viscosity, water retention measurements and mechanical properties. The study of the relationship between structure and properties reveals the influence of the nature of starting materials, macrodiols, the heterocyclic diamine and diisocyanates on the mechanical properties of the polymers. The large number of hydrogen bondings that formed between urea and urethane groups and the presence of pyridine rings in the polymer chain induced an improved thermal stability and good mechanical properties. The influence of the hard segment length was also studied. A greater length of the hard segments led to higher values of some mechanical tests such as: 100 and 300% moduli, strength stress and elongation at break. The mechanical behavior of these polymers is discussed and compared with that of earlier reported linear polyurethane-ureas based on MDI or with that of related polyurethanes chain-extended with diols.