Experimental and theoretical approaches for structural and mechanical properties of novel side chain LCP-PP graft coproducts

Authors: SEDAT ÇETİN, BEHİYE ÖZTÜRK ŞEN, UĞUR SOYKAN, ELİF ESRA FIRAT, GÜRCAN YILDIRIM

Abstract: The monomers p-biphenyloxycarbonylphenyl acrylate (BPCPA) and p-biphenyloxycarbonylphenyl methacrylate (BPCPMA) were synthesized by the reaction of p-acryloyloxybenzoyl chloride and p-methacryloyloxybenzoyl chloride with 4-hydroxybiphenyl, respectively, and polymerized by bulk polymerization in vacuum by using dicumyl peroxide. The graft copolymerization of the monomers onto polypropylene were carried out by bulk melt polymerization at 170 $^{\circ}$C with various concentration levels of the monomers and the initiator in reaction mixtures. The content of monomers in their graft coproducts increased with monomer-initiator percentage in the reaction medium. The graft coproducts were characterized by several available experimental techniques including differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and mechanical testing. Moreover, the crucial changes in the mechanical performances pertaining to the polypropylene product were investigated by theoretical computations performed based on the density functional theory (B3LYP) with the standard 6-311++G(d,p) level of theory. According to obtained results, the mechanical properties of the graft coproducts deteriorated significantly with the grafting of the homopolymers due to the damage of the rate-dependent viscoelastic deformation or yielding, leading to enhancement in the surface energy values. At the same time, experimental evidence confirmed that the poly(BPCPA) materials exhibited much weaker secondary Van der Waals bonds than those in the poly(BPCPMA) products.

Keywords: Liquid-crystalline polymers, graft copolymerization, calculations, mechanical properties, glass transition

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