Effect of polydimethylsiloxane macrodiol molecular weight on properties and morphology of polyurethane and polyurethaneurea

Abstract

Two series of polyurethanes and polyurethaneureas were prepared using a two-step bulk-solution polymerization procedure. Each series consisted of three polymers based on three molecular weights of ␣,-bis(6-hydroxyethoxypropyl) polydimethylsiloxane (PDMS): 940, 1913, and 2955. The soft segment in all cases was an 80:20 mixture of PDMS and poly(hexamethylene oxide) (MW 700), and the hard segment was based on 4,4Ј-methylenediphenyl diisocyanate and mixed chain extenders (40 wt %). In the polyurethane (PU) series the chain extender was a 60:40 (mol) mixture of BDO and 1,3-bis(4-hydroxybutyl)1,1,3,3-tetramethyldisiloxane (BHTD), whereas in the polyurethaneurea (PUU) series it was a 60:40 (mol) mixture of BHTD and 1,2-ethylenediamine. The polymerization was carried out by preparing a prepolymer using a bulk polymerization procedure followed by chain extension in a solution of N,Ndimethylacetamide. Polymers were characterized by sizeexclusion chromatography, tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). The number-average molecular weights of the polymers in the PU series were in the range of 114,300 -124,500, whereas they were in the 78,400 -103,300 range for the PUU series. Polymers with good clarity and mechanical properties were obtained with PDMS-940 and PDMS-1913, but those obtained from PDMS-2955, despite having good tensile strength, had a low percentage of elongation, high modulus, and poor clarity. DSC and DMTA results indicated that regardless of the PDMS molecular weight, the siloxane segments existed as a highly phaseseparated state. This poor compatibility was consistent with the low solubility of PDMS compared to that of the hardsegment-forming components. The polymers in the polyurethane series exhibited multiple melting endotherms, attributed to the melting of ordered domains from different hard segments. The combined heats of fusion were similar for the materials in the PU series. In contrast, the polymers in the PUU series showed a hard-segment order that was significantly less defined, with the heat of fusion approximately a third to a half that of the materials in the polyurethane series.

In vitro oxidation of high polydimethylsiloxane content biomedical polyurethanes: Correlation with the microstructure

“…Gunatillake and coworkers17–20 demonstrated the synthesis of a mixed macrodiol PU, in which 80 wt % of the soft segment was PDMS and 20 wt % was polyhexamethylenoxide (PHMO) (now commercially available as Elast‐Eon™). The resulting materials exhibited mechanical properties comparable to those of Pellethane™ 2363‐80A19 and superior biostability,18 as demonstrated by in vivo experiments.…”

Thermally curable polyurethanes containing naphthoxazine groups in the main chain

“…The shape of these curves shows the presence of three values corresponding to the polyurethane, polyol and polynaphthoxazine segments. The high‐temperature side of the tan δ peak is associated with the α‐type relaxation ( T g ) of the polynaphthoxazine segments ( T gPNZ ),44, 45 and the low‐temperature transition is attributed to the glass transition of polyurethane segments ( T gPU ) 46–50. This pattern implies that the prepared samples display a dynamic mechanical behaviour that is characteristic of elastomers.…”

Enhanced Properties of Hyperbranched Polyurethane Elastomers Based on Polydimethylsiloxane/Polyether Mixed Soft Segments

“…It was also found that this material was the most transparent. At low level of HPMS-APE (about 5 wt%) in the composition, PPG may be more associated with the hard segments and probably concentrated more in the interfacial region 16,17 . Figure 4 shows the AFM images of HBPUs.…”

“…At present, some researchers have reported related copolymers, but they mainly concentrate on the studies of linear polyurethanes. For example, Adhikari et al 16,17 have demonstrated that when a relatively small amount of a second macrodiol was incorporated as part of the soft segments along with PDMS in linear polyurethanes, the compatibility of the PDMS soft and urethane hard segments could be significantly improved. Lee and coworkers 15 have reported that the PDMS/polyether mixed soft segments linear urethane membranes had well-phase separated structures.…”