The strengthening mechanism of mechanical performance for polyurethanes with micro-content crosslinkers

Chemical crosslinking is one widely used method to endow polyurethane (PU) with desirable properties. However, the introduction of crosslinkers in PU elastomers can often lead to the destruction of phase separation, resulting in weakened mechanical properties. Herein, a series of PUs with micro-content crosslinker were synthesized from poly(oxytetramethylene) glycol (PTMG), diphenylmethane-4,4′-diisocyanate (MDI), and chain extender of butane-1,4-diol (BDO) containing varied amounts of glycerol. The phase separation of PUs decreases with increased glycerol content, while the tensile strength increases. To elucidate this enhancement in mechanical properties, morphology investigation with capability of direct observation of components distribution is employed. An increased thickness of interphase between the domain of hard segment (HS) and soft segment (SS) is observed, which indicates that more HS is moved to the interphase upon the introduction of glycerol. The results of electron energy loss spectroscopy (EELS) further disclosed that glycerol formed aggregations located at the interphase. These aggregations increase the crosslinking density of the interphase, which strengthens HS domains and prevents them from being destroyed under tension, thereby increasing the tensile strength. It is the first time of disclosing distribution feature of micro-content crosslinker of PU as well its strengthening mechanism in tensile strength, which could assist in developing PU with desirable mechanical properties.