Studies of the Thermal and Mechanical Properties of Poly(urethane–siloxane)s Cross-Linked by Hyperbranched Polyesters

Abstract

Polyurethane networks based on Boltorn hyperbranched polyesters (HBPs) of different pseudogenerations as cross-linkers, α,ω-dihydroxy(ethylene oxide−poly(dimethylsiloxane)−ethylene oxide) (EO−PDMS−EO) and 4,4′-methylenediphenyl diisocyanate were synthesized using a two-step polymerization reaction in solution. The influence of the pseudogeneration number of Boltorn HBPs on the thermomechanical and thermal properties and morphologies of polyurethane networks was investigated using FTIR, DMTA, TGA, hardness measurements, SEM, and SAXS. Synthesized polyurethanes showed higher cross-linking density and hardness and lower thermal stability with increasing pseudogeneration number of HBP. Samples with lower EO−PDMS−EO content exhibited slightly better thermal stability and higher hardness. All utilized characterization methods yielded consistent results and confirmed the existence of microphase separated morphology with the appearance of certain microphase mixing between segments as the pseudogeneration number of HBP increased. The obtained results revealed that the synthesized polyurethanes have good thermal and thermomechanical properties, which can be tailored by changing the pseudogeneration number of the HBP or the EO−PDMS−EO content.

Surface and thermomechanical characterization of polyurethane networks based on poly(dimethylsiloxane) and hyperbranched polyester

“…The large number of terminal hydroxyl groups present in Boltorn ® HBPs enables fast formation of networks that have good mechanical properties, as well as good resistance to chemicals [11][12][13][14], while the presence of PDMS contributes to the good thermal and surface properties, and to elasticity of the highly crosslinked materials. In our previous studies, we have investigated the influence of the content of !,"-dihydroxyethoxy propyl-poly(dimethylsiloxane) (EO-PDMS) and type of HBPs on the swelling behavior, morphological, thermal and thermomechanical properties of PU networks [15][16][17][18][19][20][21]. These results confirmed that physical and thermal properties are related to the crosslinking density, hydrogen bonding interactions, microphase separation and content of EO-PDMS soft segment.…”

“…Catalyst concentration was kept at 0.02 wt% [25][26][27]. The details for the synthesis of similar PU networks are given in our previously published papers [16][17][18][19][20][21]. Compositions of the synthesized PUs and weights of the reactants used for the synthesis of PUs are presented in Table 1.…”

“…The measurements were carried out using rectangular specimens (15.0 mm&' 7.8 mm&' 1.0 mm±0.2 mm), under torsion mode, using torsion fixture (rectangle) geometry. All details of the calculation of crosslinking density and average molecular weight between two crosslinks using the rubber elasticity theory and calculated from DMTA results, are described in the literature [19][20][21]33]. Some clarification of the calculation of crosslinking density is given.…”

The effect of some disiloxane chain extenders on the thermal and mechanical properties of cross-linked poly(siloxane-urethane)s

“…With the optimal ratio of PSi [6] by using a comacrodiol [11] or different chain extenders [12,13], the segment compatibility and in this way the mechanical and thermal properties could be improved. The cross-linked PSiUs also showed improved physical characteristics [2,14,15]. The thermal degradation of PSiU copolymers and networks was investigated in details in several papers [13,16,17].…”

“…The thermal degradation of PSiUs was studied by using thermogravimetric analysis (TGA) [2,13,14] sometimes coupled with a Fourier transform infrared spectroscopy (TG-FTIR) [16,17], but the isothermal thermogravimetric analysis was usually not favoured [19]. In an earlier work thermal degradation of segmented PSiUs were observed to occur in two steps [13], later in the case of PSiU copolymers two basic steps and further sub-steps were revealed [17]; in some recent papers four steps were distinguished at various PSiU copolymers and networks [14,16]. An improved thermal stability was obtained with poly(siloxane-urethane-imide) copolymers [16,19].…”