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  Global Journal of Physical Chemistry 2012, 3: 12
  Research Article
The effect of hard segment molecular architecture on the physico-chemical properties in polyurethanes: The example of 4, 4’-diisocyanatodiphenylmethane and toluene diisocyanate
  Pietro Calandra, Antonino Bartolotta  
CNR-IPCF, Consiglio Nazionale delle Ricerche – Istituto per i Processi Chimico-Fisici, sede di Messina Viale Ferdinando Stagno d'Alcontres, n. 37, 98158 Messina, Italy
  Polyurethanes (PUs) elastomers are very interesting materials which can be considered block-copolymers whose main chain is constituted by short inflexible segments interspersed between long and flexible polyester or polyether sequences. In this contribution the influence of the inflexible hard segments molecular architecture on the phase morphology of the whole polyurethane (PU) network has been investigated in two polyurethanes of interest in industrial applications. The studied PUs have hard segments composed of either 4.4'-diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI) both chain extended with 1,4 butanediol (BD), and the same soft-segment chemistry (butylene adipate glycol macrodiol, BAG). The polymers were analyzed by differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA) and the experimental data compared with the structural characteristics known by previous Small angle X-rays scattering (SAXS) measurements. The obtained results may be summarized as follows: i) the molecular architecture of the aromatic urethane units (hard-segments) influence the thermal behaviour and the glass transition regime dynamic of the whole polymeric network, ii) the hard segment architecture influences the hard/soft demixing. In the PU based on MDI the methylene between the two phenyl rings acts as an articulation joint, allowing a better conformational rearrangement in the chain coiling and permitting a better chains packing with a more interlocking homogeneous structure and ultimately a lower microphase segregation.
  Polyurethanes; Differential scanning calorimetry; Dynamic mechanical thermal analysis  

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