Characterization and low temperature test of the flexibly crosslinked polyurethane copolymer by poly(dimethylsiloxane)

Abstract

Shape memory polyurethane (SMPU) flexibly crosslinked by a hydrophobic poly(dimethylsiloxane) (PDMS) spacer at its side through allophanate bonding was tested for shape recovery at À30 C and compared to a linear SMPU. The SMPU was composed of 4,4 0 -methylenebis(phenylisocyanate) (MDI), poly(tetramethyleneglycol) (PTMG), 1,4-butanediol (BD), and PDMS that was connected to SMPU chains by a second MDI. The mechanical and shape memory properties of two types of SMPU, differing in PTMG and PDMS content, were compared. In the best case, a 283% increase in maximum stress compared to the linear polymer was attained without any sacrifice of strain. Shape recovery at 45 C increased to 91% and remained at more than 80% after four cyclic tests. Shape recovery at 0 C could be improved by increasing PDMS content, and the critical shape recovery temperature decreased with increasing PDMS content. The PDMScrosslinked SMPU demonstrated instant shape recovery at À30 C in comparison with the linear SMPU that must be warmed to room temperature for complete shape recovery. The extraordinary shape memory results were analyzed and are discussed together with differential scanning calorimetry and infrared data.

Modification of polyurethane by graft polymerization of poly(acrylic acid) for the control of molecular interaction and water compatibility

“…The increase in the maximum stress for the UA and IUA series was due to the physical cross-linking of the grafted PA chains and the light chemical cross-linking of PU chains by MDI-3 (Scheme 1c), whereas the loss of PA chains in the C series was responsible for the low tensile stress. The maximum tensile stresses of the UA and IUA series were comparable to those of PUs with flexible cross-linking: the PEG cross-linked PU exhibited a maximum stress of 56 MPa [35], and the PDMS cross-linked PU showed a maximum stress of 53 MPa [23]. The breaking strain increased slightly for the UA series and remained the same for the IUA series with an increase in the PA content: the breaking strain changed from 1496 % for L to 1686 % for UA-1, 2024 % for UA-3, 1646 % for IUA-1, and 1633 % for IUA-3 (Fig.…”

“…This PU surface grafting method has been reported in the literature [18][19][20][21][22] and was previously demonstrated by our group in developing functionalized PUs; for example, PUs that exhibited flexibility at low temperatures [23], electric attraction in aqueous solutions [24], pH sensitivity [25], and photoluminescence [26] were successfully developed. Specifically, 2-hydroxyethyl methacrylate (HEMA), a vinyl group with a hydroxyl end, was attached to the PU side using MDI as a grafting agent.…”

Graft polymerization of 4‐imidazole acrylic acid onto polyurethane for the improvement of water compatibility and antifungal activity

“…The crosslink densities in the IA and CIA series were compared with the L form using the Flory‐Rehner equation, which utilized the inverse relationship between PU swelling and the degree of crosslinking . The crosslink density of the IA series did not proportionally increase with an increase in IA content but remained constant after the initial increase (Fig.…”

“…The crosslink density was determined using a method explained in our previous investigations . The contact angle of a water drop (2 µL) on the PU surface was measured using a contact shape analyzer (Krűss DSA100, Hamburg, Germany).…”

“…In addition to the antimicrobial activity, other functionalizations of PU have been continuously reported because the target properties could be achieved without significantly changing the intrinsic properties of PU. For example, water‐compatible PU grafted with poly(ethylene glycol) , flexible PU at extremely low temperatures , pH‐sensitive PU responding to the surrounding pH , and electrically conductive PU were introduced. Antifungal PU has potential applications in automobile seats, mattresses, insulation foams, elastic fibers, healthcare products, and protective coatings.…”