Abstract
Two series of polyurethane films based on hyperbranched polyester of the second pseudogeneration (Boltorn?), 4,4'-methylenediphenyl diisocyanate and two different siloxane prepolymers, ?,?-dihydroxy-(ethylene oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO) and ?,?-dihydroxypropyl-poly(dimethylsiloxane) (HP-PDMS), were prepared by two-step polymerization in solution. The influence of the type and content of soft segment on the morphology, thermomechanical and surface properties of the synthesized polyurethanes was studied by atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA) and water absorption measurements. It was found that these techniques confirmed existence of microphase separated morphology. Synthesized polyurethanes exhibited two glass transition temperatures and one second relaxation process. The results showed that polyurethanes based on HP-PDMS had higher surface roughness, better microphase separation and waterproof performances. Samples synthesized with lower PDMS content had less hydrophobic surface, but higher crosslinking density and better thermomechanical properties. (Projekat Ministarstva nauke Republike Srbije, br. 172062]
Highlights
Polyurethane (PU) networks have different applications, especially in the coatings industry, because of their specific properties such as good mechanical flexibility, toughness, chemical resistance, high gloss and high abrasion resistance [1,2]
The aim of this paper is to examine the effects of the type and content of PDMS on the morphology, surface and thermomechanical properties of the prepared materials using atomic force microscopy (AFM), smallangle X-ray scattering (SAXS), scanning electron microscopy (SEM), water absorption measurement and dynamic mechanical thermal analysis (DMTA)
Two series of polyurethane films were synthesized by two-step polymerization in NMP/THF mixture in order to investigate the effect of the type and content of PDMS soft segment on the morphology and properties of PUs
Summary
Polyurethane (PU) networks have different applications, especially in the coatings industry, because of their specific properties such as good mechanical flexibility, toughness, chemical resistance, high gloss and high abrasion resistance [1,2]. Hyperbranched polyesters (HBPs) have recently attracted considerable attention as crosslinkers for PU networks preparation due to their specific three-dimensional structure, large number of end functional groups and interesting properties such as high solubility in different solvents, low degree of chain entanglements in melt, low viscosity in solution and in melt and good compatibility with other materials [11,12,13,14]. It has been shown that a combination of commercially available hydroxyl-functional HBPs (Boltorn®), PDMS macrodiol and aromatic diisocyanate can be used for the synthesis of PUs with good thermal and mechanical properties [15,16,17,18]. During the synthesis of PU samples, HBP with its numerous end –OH groups provides fast curing and formation of the highly crosslinked material with good mechanical properties and chemical resistance. Baker, dried over lithium aluminum hydride and distilled before use
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