Shape-memorized crosslinked ester-type polyurethane and its mechanical viscoelastic model

Abstract

A series of shape-memorized crosslinked ester-type polyurethanes (PUs), based on different compositions of 4,4Ј-diphenyl methane diisocyanate (MDI), poly(butylene adipate) glycol (PBAG) with different molecular weight (MW) and trimethylol propane (TMP), were synthesized. The morphology of samples was investigated by using DSC, WAXD, and dynamic mechanical analysis (DMA). It was found that the morphology of the soft segment, which was PBAG with a different MW, was in an amorphous state and no crystalline domain was found. By increasing the crosslinked density (varying the content of TMP) or decreasing the length of the soft segment (MW of PBAG), the glass transition temperature of studied samples increased. But the range of transition broadened and the modulus ratio EЈ (T g Ϫ20°C) /EЈ (T g ϩ20°C) also decreased. The shape-memory behavior was studied by the bending test method adopted from the shape-memory alloy. The sample with high T g showed not only a high recovered temperature (T r ) but also a high recovered rate (V r ) with a high modulus ratio. By introducing the chemical crosslinked structure, the deformed samples completely recovered their original shape and rendered shape-memory behavior under the complex deformation. The shape-memorized crosslinked ester-type PUs can be applied at different operating temperatures. A mechanical viscoelastic model is discussed for the shape-memory behavior of PUs, and the modified Bonart's viscoelastic model properly describes the mechanism of the shape memory of PUs.

Challenges of shape memory polymers: A review of the progress toward overcoming SMP's limitations

“…SMPs can be classified depending on their structures (thermosets vs. thermoplastics) and transformation temperatures (melting or glass transition temperatures) [2][3][4]. In the literature, SMPs based on common chemistries such as polyurethane (PU) [5][6][7][8][9][10][11][12][13][14][15][16][17][18], epoxy [19][20][21][22][23][24][25], polyolefin [26][27][28], as well as more exotic formulations such as partially dehydrochlorinated poly(vinyl chloride) [29], nylon/polyethylene graft copolymers [30], or poly (ether esters) [31][32][33] have been reported to show varying performances. This emphasizes the key role that polymer molecular design plays on tailoring the shape memory (SM) properties.…”

On modeling shape memory polymers as thermoelastic two-phase composite materials

“…The models that have been proposed so far for thermally actuated shape memory polymers, to which this paper is limited, are of two types according to whether rate effects are included or not. In the first type, Tobushi et al [4] developed a four-element variation of a viscoelastic rheological model, the numerical integration of which was detailed by Bhattacharyya and Tobushi [5], and that was extended to nonlinear effects by Tobushi et al [6], whereas Lin and Chen [7] could reproduce experimental results qualitatively with a mere 3-element standard linear solid by relating the dash-pot viscosity to temperature. A less macroscopic approach, using two coexisting substructures in the material, with different mechanical behaviors, was proposed by Kafka [8], while Qi et al [9], Nguyen et al [10], Srivastava et al [11] developed other models by taking advantage of the large amount of knowledge that is available on polymer physics.…”

Review on the Functional Determinants and Durability of Shape Memory Polymers

“…The list of polymers with SM properties is continuously growing; it includes physically [72][73][74][75][76][77][78] and chemically [79][80][81] cross-linked SMPUs, trans-polyisoprene-based SMPU [82,83], poly(ether ester)s like poly(ethylene oxide)/poly(ethylene terephthalate) copolymers [84][85][86], norbornyl/polyhedral oligomeric silsesquioxane (POSS) copolymers [87,88], poly(methylene-1,3-cyclopentane) and its copolymer with polyethylene [89], styrene/butadiene copolymers [90], thiol-ene/acrylate copolymers [91], polynorbornene [90], polymer networks prepared from poly(ε-caprolactone) (PCL) dimethacrylates [92,93], acrylate-based SMPs [94], (meth)acrylate networks [95,96], cross-linked polyethylene [97], epoxy-based polymers [98][99][100][101] and many others. Moreover, various polymer blends like SMPU/phenoxy resin [102], SMPU/polyvinylchloride (PVC) [103] and several others [104][105][106][107][108][109] have received attention.…”