Abstract
Novel segmented thermoplastic polyurethane (TPU) copolymers were synthesized using two-step solventless bulk polymerization. 4,4’-methylenediphenyl diisocyanate (MDI) and 1,4-Butanediol (BDO) were used to form hard segment of TPU and α,ω-dihydroxy-[poly(propyleneoxide)-poly (dimethylsiloxane)-poly(propyleneoxide)] (α,ω-dihydroxy-(PPO-PDMS-PPO)) was used to form soft segment of TPU, where the molar ratio of the –N=C=O/OH was 1.02 and the hard segment weight percentage was 30%. A series of TPUs were characterized by fourier transform infrared spectroscopy (FT-IR). The investigation of triblock oligomer’s PPO molecular weight impact on the derived TPU’s mechanical properties, thermal performance, surface water repellency and morphology performance was carried by Instron material tester, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), water contact angles (WCA), scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX) and wide angle X-ray diffraction (WAXD), respectively. FT-IR confirmed α,ω-dihydroxy-(PPO-PDMS-PPO) well cooperating into urethane structure and analyzed hydrogen bonding between N-H group with hard segment C=O group and N-H group with soft segment C-O-C group. DSC and WAXD results showed α,ω-dihydroxy-(PPO-PDMS-PPO) segments crystallization. SEM-EDX results showed that the presence of a spherulitic morphology, which arose from the crystallization of the PPO segments. The thermal properties measured by TGA and DSC were slightly affected by molecular weight of PPO and microphase separation. The weight loss of TPUs started between 294°C and 300°C, and Tg was in the range of -70°C to -107°C. TPU copolymers’ surface hydrophobicity property was excellent with WCA range of 95° to 112°. TPU-3 with 1000 molecular weight PPO has the optimized mechanical properties with tensile strength 16.4 MPa and the modulus at 100% elongation 6.2 MPa and elongation 398%.
Highlights
PUs have been found in wide applications such as insulation rigid foams, comfort flexible foams, coatings and adhesives, due to their unique properties, and great efforts have been made in the variegation of their chemical and physical properties [1]
The attempts to synthesize PDMS-based TPUs resulted in copolymer with poor mechanical properties, which was attributed to the low molecular weight and to the absence of the intersegment hydrogen bonding between PDMS and the hard segments
The results revealed that the synthesized polyurethanes have good thermal, thermomechanical and surface properties compared to EO-PDMS-EO derived PUs
Summary
PUs have been found in wide applications such as insulation rigid foams, comfort flexible foams, coatings and adhesives, due to their unique properties, and great efforts have been made in the variegation of their chemical and physical properties [1]. The attempts to synthesize PDMS-based TPUs resulted in copolymer with poor mechanical properties, which was attributed to the low molecular weight and to the absence of the intersegment hydrogen bonding between PDMS and the hard segments. High molecular weight siloxane-based urethane and urea copolymers with good thermal and mechanical properties can be prepared by stoichiometric reaction of diisocynates and PDMS prepolymers, without any chain extender or by the conventional prepolymer method through the employment of chain extenders. The synthesis and characterization of these thermoplastic polyurethanes based on soft PCL-PDMS-PCL and hard MDI/BD segments and the influence of reaction conditions on the structure, molecular weight, thermal, and some physical properties of the segmented TPUs with high contents of PCL-PDMS-PCL segments were investigated. The study on PPO molecular weight impacting on TPU copolymers’ mechanical, thermal, hydrophobic, morphology properties is studied in this paper
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