Kirk K. S. Hwang

Segmental orientation studies of polyether polyurethane block copolymers with different hard segment lengths and distributions

The orientation behavior of two series of segmented polyether polyurethanes containing different hard segment length distributions has been studied as a function of the average hard segment length which was varied from one to five methylene bis (p-phenyl isocyanate) (MDI) units. The orientation behavior of the soft segments, isolated hard segments, and of hard segments aggregated in hard domains was determined from the dichroic behavior of representative infrared bands. As the hard segment length increases, a transition in orientation behavior is observed which corresponds to a change in sample morphology.The effects of annealing and hard segment length distribution were also studied and were shown to affect the orientation response through their influence on sample morphology. Orientation hysteresis studies were performed to probe the mechanism of the transverse orientation and orientation inversion which occurred in polyurethanes with the longer, more crystallizable hard segment lengths.

Properties of polyisobutylene polyurethane block copolymers: 3. Hard segments based on 4,4′-dicyclohexylmethane diisocyanate (H12MDI) and butane diol

A series of polyisobutylene (PIB) polyurethanes based on 4,4′-dicyclohexylmethane diisocyanate (H12MDI) have been synthesized and their structure-property relationships have been investigated. The PIB glycol was synthesized by the ‘inifer’ technique. Sample compositions were designed for independent investigation of the effects on physical properties of hard segment content and soft segment molecular weight and for comparison with corresponding 4,4′-diphenylmethane diisocyanate (MDI) based PIB polyurethanes. Increasing hard segment content resulted in improved dynamic and tensile modulus while elongation at break was unaffected. Increasing soft segment molecular weight led to decreased mechanical properties attributed to larger domain sizes as indicated by small angle X-ray scattering (SAXS). Both the soft segment Tg and the extent of interfacial mixing as measured by SAXS were unaffected by hard segment content and soft segment molecular weight suggesting that the materials were highly phase separated. In comparison with corresponding MDI based materials the H12MDI based polyurethanes exhibited less hard segment ordering, slightly less interfacial mixing, smaller domain sizes, and slightly better ultimate tensile properties.

Properties of ultra-violet curable polyurethane acrylates

The relationship between the chemical structure and physical properties of ultra-violet cured isophorone diisocyanate (IPDI) and toluene diisocyanate (TDI) based urethane acrylates were studied. The two systems were prepared with varying soft-segment molecular weight and cross-linker content. Dynamic mechanical test results show one-phase or two-phase materials may be obtained depending on the soft-segment molecular weight. With increasing soft-segment molecular weight, the polyol glass transition shifts to lower temperatures. Increasing the cross-linker content using either N-vinylpyrrolidone (NVP) or polyethyleneglycol diacrylate (PEGDA) causes an increase in Youngs modulus and ultimate tensile strength. Cross-linking with NVP causes an increase in toughness in the two-phase materials and shifts the high-temperature glass transition peak to higher temperatures. In contrast, an increase in PEGDA content does not improve the toughness of the two-phase materials or affect the position of the high-temperature glass transition peak. Comparison of the tensile properties of the TDI- and IPDI-based systems shows no significant differences.

Properties of segmented polyurethane zwitterionomer elastomers

Abstract Four series of polyurethane zwitterionomers based on different soft segment polyols [polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD)] were synthesized, and their properties were investigated using differential scanning calorimetry, dynamic mechanical spectroscopy, infrared dichroism, and stress-strain testing. Two different molar ratios of hard segment [4,4′-diphenylmethane diisocyanate (MDI)] to chain extender [N-methyl diethanol-amine (MDEA)] to soft segment polyol, each with three different levels of ionization, were prepared based on the four different polyols. Zwitterionization was accomplished by quaternizing the tertiary amine of MDEA with γ-propane sultone. For the PBD materials, the un-ionized samples exhibited a high degree of phase separation, and ionization served mainly to improve domain cohesion. Increasing ionic content improved material strength while sacrificing extensibility. For the polyether materials the un-ionized...

Properties of Polyether–polyurethane anionomers

Abstract Two series of polyether-polyurethane anionomers based on 4, 4′-diphenylmethane diisocyanate (MDI), methyl diethanolamine (MDEA), and polytetramethylene oxide glycol (PTMO) were synthesized. The system based on 1000-MW PTMO, which exhibits an interconnected hard domain morphology, showed a substantial decrease in the soft segment Tg upon ionization. The moduli of the corresponding anionomers were found to increase as the cationic charge of the neutralizing species was increased. The series based on 2000-MW PTMO, which exhibits an isolated hard domain morphology, showed little change in thermal or mechanical properties either upon ionization or in varying cationic charge.

Properties of polyurethane anionomers: ionization via bimolecular nucleophilic displacement of the urethane hydrogen

Abstract Two series of polyether polyurethane anionomers based on 4, 4-diphenylmethane diisocyanate (MDI) and polytetra-methylene oxide (PTMO) were synthesized and their properties investigated. Ionization proceeded via a bimolecular nucleophilic displacement reaction with sodium hydride, followed by a ring-opening reaction with γ-propane sultone. The lower hard segment content (20 wt% MDI) control material exhibited an initial one-phase morphology that underwent phase separation upon ionization, with subsequent development of hard segment ordering. These changes in morphology were accompanied by dramatic improvements in mechanical properties. The 38 wt% MDI control material possessed a two-phase morphology and well-developed hard segment ordering. Ionization disrupted the hard segment ordering and at low levels decreased the degree of phase separation. Further ionization led to reattainment of the original degree of phase separation and a marked improvement in mechanical strength. The differences in prop...

Properties of polyurethane oligomeric blends versus high molecular weight block copolymers

Abstract Segmental compatibility has been investigated in both oligomeric polyurethane blends and polyurethane block copolymers. The block copolymers are formed by linking a hard segment, composed of three MDI and two butane diol units on average with various macroglycols. The monodisperse oligomeric hard segment, H 3 , with its chain ends reacted with ethanol is used as the urethane component in blends with macroglycols. The macroglycols used in both the blend and block copolymer systems include polyethylene oxide (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), and polybutadiene (PBD). Blends of H 3 and PEO form a eutectic at a weight ratio of ≈20 80 ( H 3 / PEO ) with a T m,e = 34° C . H 3 and PTMO blends also give rise to a eutectic composition at ≈20 80 ( H 3 / PTMO ) but with a T m,e = 10° C . Both PPO and PBD mix with H 3 to form a crystalline—amorphous blend. The miscibility of H 3 and the soft segments at the melting point of H 3 is in the order of PEO > PTMO > PPO > PBD. In the block copolymer systems, stress—strain and dynamic mechanical testing indicate that the block copolymerization of a hard segment with each soft segment results in a microphase separated elastomer as expected. The extent of phase separation increases in the order of PBD > PTMO > PPO > PEO which is coincident with the trend predicated by the application of Hilderbrands solubility parameter concept. All the soft segments used occur in an amorphous phase in the block copolymers while PEO and PTMO crystallize in a blend with H 3 . The differences between the properties of the blends and block copolymers suggest that the phase separation, segment crystallization and domain coalescence are substantially restricted by the urethane—polyol junction points.

Properties of Polyurethane Ionomers

OLYURETHANE BLOCK COPOLYMERS OF THE (AB), TYPE ARE AN IMPORPtant class of thermoplastic elastomer. These materials consist of rigid, glassy chemical units alternating with soft, flexible units. The hard segment typically consists of a series of aromatic diisocyanates linked by short diol or diamine chain extenders. The soft segment is normally a polyester-, polyether-, or polyalkyl-glycol. During the solidification of these materials from solution or from the melt, the two types of segments undergo phase separation into microdomains. These domains can be either semicrystalline or amorphous. The domains are not chemically pure; some degree of intersegmental mixing occurs. The size, purity, and volume fraction of these domains has a profound effect on the physical properties of these materials. The elastic mechanism in these polymers is due to the hard domains acting