Thermoplastic Urethane Molecular Weight-Property Relations

ABSTRACT:The effect of chain extender structure on properties and morphology of ␣,-bis(6-hydroxyethoxypropyl) polydimethylsiloxane (PDMS) and poly(hexamethylene oxide) (PHMO) mixed macrodiol-based aliphatic polyurethane elastomers was investigated using tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA). All polyurethanes were based on 50 wt % of hard segment derived from 4,4Ј-methylenecyclohexyl diisocyanate (H 12 MDI) and a chain extender mixture. 1,4-Butanediol was the primary chain extender, while one of 1,3-bis(4-hydroxybutyl)tetramethyldisiloxane (BHTD), 1,3-bis(3-hydroxypropyl)tetramethyldisiloxane (BPTD), hydroquinonebis(2-hydroxyethyl)ether (HQHE), 1,3-bis(3-hydroxypropyl)tetramethyldisilylethylene (HTDE), or 2,2,3,3,4,4-hexafluoro-1,5-pentanediol (HFPD) each was used as a secondary chain extender. Two series of polyurethanes containing 80 : 20 (Series A) and 60 : 40 (Series B) molar ratios of primary and secondary chain extenders were prepared using one-step bulk polymerization. All polyurethanes were clear and transparent and had number-average molecular weights between 56,000 and 122,100. Incorporation of the secondary chain extender resulted in polyurethanes with low flexural modulus and high elongation. Good ultimate tensile strength was achieved in most cases. DSC and DMTA analyses showed that the incorporation of a secondary chain extender disrupted the hard segment order in all cases. The highest disruption was observed with HFPD, while the silicon-based chain extenders gave less disruption, particularly in Series A. Further, the silicon chain extenders improved the compatibility of the PDMS soft segment phase with the hard segment, whereas with HFPD and HQHE, this was not observed.

Section: Polyurethane Morphologysupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Effect of chain extender structure on the properties and morphology of polyurethanes based on H12MDI and mixed macrodiols (PDMS–PHMO)

Adhikari

Gunatillake

McCarthy

et al. 1999

“…In the solid state, unique elastomeric properties are observed due to microdomain formation. [2][3][4] The so-called hard domains provide both physical crosslink sites and fillerlike reinforcement to the soft-segment matrix. At higher temperatures, the polymer forms a homogeneous viscous melt that can be processed by thermoplastic techniques such as injection molding, extrusion, and blow molding.…”

Section: Introductionmentioning

confidence: 99%

Preparation and properties of segmented thermoplastic polyurethane elastomers with two different soft segments

Kim

Lee

Huh

et al. 1999

Thermoplastic polyurethane elastomers were prepared from 4,4-diphenylmethane diisocyanate (MDI)/1,4-butanediol (BD)/poly(propylene glycol) (PPG) and MDI/BD/poly(oxytetramethylene glycol) (PTMG). The MDI/BD-based hard-segment content of polyurethane prepared in this study was of 39 -65 wt %. These polyurethane elastomers had a constant soft-segment molecular weight (M n , 2000), but a variable hard-segment block length (n, 3.0 -10.1; M n , 1020 -3434). The effects of the hardsegment content on the thermal properties and elastic behavior were investigated. These properties of the PPG-based MPP samples and the PTMG-based MPT samples were compared. The polyurethane prepared in this study had a hard-segment crystalline melting temperature in the range of 185.5-236.5°C. With increasing hard-segment content, the dynamic storage modulus and glass transition temperature increased in both the MPP and MPT samples. The permanent set (%) increased with increasing hard-segment content and successive maximum elongation. The permanent set (%) of the MPP samples was higher than that of MPT samples at the same hard-segment content. The value of K (area of the hydrogen-bonded carbonyl group/area of the free carbonyl group) increased with increasing hard-segment content in both the MPP and MPT samples, and the K value of the MPT samples was higher than that of the MPP samples at the same hard-segment content.

“…Most previous investigations have concentrated on polyurethanes based on hard segments derived from aromatic diisocyanates [1][2][3][4][5][6] with relatively few studies based on aliphatic diisocyanates. [7][8][9][10][11][12][13][14][15][16][17][18] The aliphatic diisocyanate 4,4Ј-dicyclohexyl methane diisocyanate (H 12 MDI) is commercially available and used as a building block for polyurethane elastomers that require light stability and resistance to hydrolysis. This diisocyanate is supplied as a mixture of three geometrical isomers (trans,trans, cis,trans, and cis,cis isomer) and generally has 10 -30% of trans-trans isomer in the mixture.…”

Section: Introductionmentioning

confidence: 99%

The effect of diisocyanate isomer composition on properties and morphology of polyurethanes based on 4,4′-dicyclohexyl methane diisocyanate and mixed macrodiols (PDMS-PHMO)

Adhikari

Gunatillake

Meijs

et al. 1999

Three series of polyurethanes were prepared having 42 wt % hard segments based on 4,4Ј-dicyclohexyl methane diisocyanate (H 12 MDI) with trans,trans isomer contents in the 13 to 95 mol % range and 1,4-butanediol chain extender. The soft segments were based on macrodiols poly(hexamethylene oxide) (PHMO, MW 696), ␣,-bishydroxyethoxypropyl polydimethylsiloxane (PDMS, MW 940), and two mixed macrodiol compositions consisting of 80 and 20% (w/w) PDMS. H 12 MDI with 35, 85, and 95% trans,trans isomer contents were obtained from commercial H 12 MDI (13% trans, trans) by fractional crystallization, and all polyurethanes were prepared by a one-step bulk polymerization procedure. The polyurethanes based on the commercial diisocyanate-produced materials soluble in DMF with molecular weights in the 53,655-75,300 range and generally yielded clear and transparent materials. The polyurethanes based on H 12 MDI with trans,trans contents of 35% or higher yielded materials insoluble in N,N-dimethylformamide (DMF) and were generally opaque. Mechanical properties, such as tensile strength and elongation at break, decreased with increasing trans,trans content, while the Young's modulus and Shore hardness increased. The polyurethanes based on mixed macrodiols yielded higher tensile properties than those of materials based on individual macrodiols. The best mechanical properties were observed for a polyurethane consisting of a soft segment based on PDMS-PHMO (80/20) and a hard segment based on commercial H 12 MDI and BDO. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the polyurethane morphology. DSC results confirmed that the polyurethanes based on H 12 MDI with high trans,trans isomer were very highly phase separated, exhibiting characteristic hard segment melting endotherms as high as 255°C. The other materials were generally phase mixed. FTIR spectroscopy results corroborated DSC results.