Approaches for Novel Polyurethanic Materials of Variable Crystallinity

APPROACHES FOR NOVEL POLYURETHANIC MATERIALS OF VARIABLE CRYSTALLINITY

Cristina Prisacariu, Adrian A. Caraculacu

The Romanian Academy’s Institute of Macromolecular Chemistry “Petru Poni”

Aleaa Grigore Ghica Voda, Nr. 41 A, 6600, Iasi, Romania

Robert H. Olley

J. J. Thomson Physical Laboratory, Whiteknights, Reading RG6 6AF, England.

The structural, mechanical and thermal properties of multiphase polyurethane systems (PU) based on 4,4’-methylene bis (phenyl isocyanate) (MDI), tolylene–2,4 diisocyanate (TDI) and 1,5-naphatalene diisocyanate (NDI) in comparison to novel systems of polyurethane elastomers (PU) derived from diisocyanates with variable geometry, in principal 4,4’-dibenzyl diisocyanate (DBDI), were investigated. The specific –Ø-CH2-CH2-Ø- moiety characteristic to DBDI induces a variable geometry of the hard segments due to the possibility of internal rotation of the two benzene rings around the -CH2-CH2- ethylene bridge [1,2]. This leads to the appearance of both the rotational conformations forms “sin” and “anti”, which coexist in the DBDI based PU macromolecules [3]. As a result, in this later case the PU macromolecules can adopt a more compact packing which enhance significantly the PU tendency to ordinate in crystalline structures, which determines significant changes in this specialty of polyurethanes properties spectrum [2,3]. Novel polyurethane elastomers of variable crystallinity derived from dibenzyl structures were characterized as part of this paper. Experimental techniques employed in this study included the following thermal analyses: differential scanning calorimetry (DSC), thermogravimetry (TGA) and thermal creep (TC) analyses by using a new in house thermal creep testing machine in temperature increasing gradient[2,4]. IR dichroism, wide-angle x-ray, scanning electron microscopy (SEM) as well as tensile and compression testing experimental techniques were also approached for investigation of property–determining morphological state and tendencies in PU with different geometries of the hard segments. {2] The effect of hydrogen bonding on the mechanical behaviour of PU based on hard segments with conformational mobility was undertaken also [2]. The kinetics and postcure reaction mechanism in casting polyurethane elastomers was followed. It was found that the postcure process succeeds especially with the assistance of atmospheric humidity, and the PU polymer network is consolidated mainly by the formation of a new urea group[5].

References

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[2] Prisacariu Cr.-PhD Thesis, Technical University “Gh. Asachi”, Iasi, Romania,

(1998).

[3] Prisacariu Cr, Caraculacu A, 11th International Conference on "Deformation,

Yield and Fracture of Polymers", Cambridge,10-13 April 2000, 458-461.

[4] Prisacariu, Cr.- Polytechnical Inst. "Gh. Asachi", Bull. Iasi - Vol. XLVII,(LI), 1-

2,Section I Mathematics. Theoretical Mechanics.Physics, (2001), 143-156.

[5] Prisacariu Cr, Agherghinei I, J.M.S.– Pure Appl. Chem.m, A37(7), 785- 806 (2000).