Synthesis,Characterization, Curing and Shape Memory Properties of Epoxy‐Polyether System

Epoxy resins were cured by an amine telechelic poly(tetramethylene oxide) (PTMO). The telechelic amine was synthesized from hydroxy telechelic PTMO and was characterized. The kinetics of curing of epoxy monomer by the polyether amine was studied in detail by differential scanning calorimetry (DSC) and rheology to optimize the cure conditions. The cured epoxy system exhibited shape memory properties where PTMO served as the switching segment. Molar ratios of the epoxy monomer and the amine were varied to get polymers with different compositions. The developed polymers were analyzed by DSC, X‐ray diffraction, and Dynamic Mechanical Thermal (DMTA) analyses. Shape memory property was evaluated by bending tests. As the concentration of epoxy resin increased, the transition temperature (T_trans) increased. The tensile strength and % elongation also increased with epoxy resin‐content. The extent of shape recovery increased with PTMO‐content with a minor penalty in recovery time. The polymer with the maximum PTMO‐content exhibited 99% shape recovery with a recovering time of 12 s.     

Synthesis and properties of polycyanoethylmethylsiloxane polyurea urethane elastomers: A study of segmental compatibility

A series of polyurea urethane block polymers based on either aminopropyl-terminated polycyanoethylmethylsiloxane (PCEMS) soft segments or soft segment blends of PCEMS and polytetramethylene oxide (PTMO) were synthesized. The hard segments consisted of 4,4′-methylenediphenylene diisocyanate (MDI) chain-extended with 1,4-butanediol. The hard segment content varied from 11 to 36%, whereas the PTMO weight fraction in the soft segment blends varied from 0.1 to 0.9. The cyanoethyl side group concentration was also varied during the synthesis of the PCEMS oligomer. The morphology and properties of these polymers were studied by differential scanning calorimetry, infrared spectroscopy, dynamic mechanical and tensile testing, and small-angle x-ray scattering. These materials exhibited microphase separation of the hard and soft segments; however, attaching polar cyanoethyl side groups along the apolar siloxane chains promoted phase mixing in comparison with polydimethylsiloxane-based polyurethanes. The increased phase mixing is postulated to lead to improved interfacial adhesion and thus can account for the observed improvement in ultimate tensile properties compared with polydimethylsiloxane-based polyurethanes. Both hard segment content and cyanoethyl concentration are important factors governing the morphological and tensile properties of these polymers.     

Shape memory poly(ester urethane) with improved hydrolytic stability

In two hydrolytic degradation studies the tensile (mechanical) and functional (thermo-mechanical) properties of a hydrolysis-stabilized shape memory poly(ester urethane) and its non-stabilized analog were investigated. Hydrolytic degradation was enforced by specimen immersion in de-ionized water at 80 °C. Significant differences in the fundamental shape memory parameters were monitored as function of aging time for the stabilized and non-stabilized polymer. This included the ability to recover strain (shape recoverability) and stress (stress recoverability) on heating after shape programming. Hydrolysis-related mechanical and functional changes were correlated with morphological ones, detected by differential scanning calorimetry (DSC). The shape memory poly(ester urethane), which was protected by a carbodiimide-based hydrolysis stabilizer, revealed significantly improved resistance towards hydrolysis with respect to various mechanical and shape memory parameters.     

New multiblock poly(ether-ester)s based on poly(trimethylene terephthalate) as rigid segments

A series of novel poly(trimethylene terephthalate)-block-poly(tetramethylene oxide) (PTT--PTMO) segmented block copolymers were synthesised by transesterification in the melt of dimethyl terephthalate, 1,3-propanediol and poly(tetramethylene oxide) glycol (PTMO, 1000 g/mol). A range of multiblock copolymers were synthesized, with flexible PTMO segments contents varying from 20 to 80 wt%. The novel poly(ether-block-ester)s were characterized by using viscometry, hardness measurements, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile properties.     

Blends of a siloxane/urea/urethane-segmented copolymer with an IPDI-based polyetherurethane

A series of copolymer blends have been prepared using a poly(ether urethane) and a poly(siloxane–urea–urethane). The copolymers were prepared by a hardsegment first, two-step polymerization method. The hard segments of the copolymers were derived from isophorone diisocyanate (IP) and 1,4-benzenedimethanol (B), and the soft segments were based on polytetrahydrofuran (PTMO, M_w = 2000), and polydimethylsiloxane (PDMS, M_w =27,000), respectively. The siloxanecontaining copolymer, PDMS27K-IP-B2 (2 moles diol chain extender/mole PDMS27K), was used as the minor component (1.6, 2.5 and 6.0 wt%) in a series of blends. These blends were found to preserve the mechanical properties of the poly(ether–urethane) as well as the surface properties of the poly(siloxane–urea–urethane).     

Studies on thermoplastic polyurethanes based on new diphenylethane-derivative diols. II. Synthesis and characterization of segmented polyurethanes from HDI and MDI

Various new thermoplastic segmented polyurethanes were synthesized by a one-step melt polymerization from aliphatic-aromatic α,ω-diols containing sulfur in the aliphatic chain, including 4,4′-(ethane-1,2-diyl)bis(benzenethioethanol), 4,4′-(ethane-1,2-diyl)bis(benzenethiopropanol) and 4,4′-(ethane-1,2-diyl)bis(benzenethiodecanol) as chain extenders, hexane-1,6-diyl diisocyanate (HDI) or 4,4′-diphenylmethane diisocyanate (MDI) and 20-80 mol% poly(oxytetramethylene)diol (PTMO) with molecular weight of 1000 g/mol as a soft segment. The reaction was conducted at the molar ratio of NCO/OH = 1 and 1.05, and in the case of the HDI-based polyurethanes in the presence of dibutyltin dilaurate as a catalyst. The effect of the diisocyanate used on the structure and some physicochemical, thermal and mechanical properties of the segmented polyurethanes were studied. The structures of these polyurethanes were examined by FTIR and X-ray diffraction analysis. The thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. Shore hardness and tensile properties were also determined. All the synthesized polymers showed partially crystalline structures. The MDI-based polyurethanes were products with lower crystallinity, higher glass-transition temperature (T_g) and better thermal stability in comparison with the HDI-based ones. The MDI series polymers also exhibited higher tensile strength (up to ∼36 MPa vs. ∼23 MPa) and elongation at break (up to ∼3900% vs. ∼900%), but lower hardness than the analogous HDI series polyurethanes. In both series of the polymers an increase in PTMO soft-segment content was associated with decreased crystallinity, T_g, hardness and tensile strength. An increase in PTMO content also involved an increase in elongation at break.     

Shape memory polymers based on cyanate ester-epoxy-poly (tetramethyleneoxide) co-reacted system

Thermoset polymers showing shape memory properties were synthesized by reacting bisphenol A dicyanate (BADC) with diglycidyl ether of bisphenol A (DGEBA) and phenol telechelic poly(tetramethyleneoxide) (PTOH). The cure characteristics of the blend were evaluated by DSC, FTIR and rheometry. Blends with varying proportion of DGEBA/PTOH/BADC were studied for their flexural, dynamic mechanical and thermal properties. The flexural strength and thermal stability increased with increase in cyanate ester concentration, while these properties decreased with increase of PTOH concentration for a given composition. The storage modulus showed a similar trend. The transition temperature (T_trans) of the system increased with increase in cyanate ester content. The polymers showed good shape memory properties wherein the shape recovery increased with increase in PTOH content with a concomitant decrease in the shape recovery time. While the shape recovery increased proportional to the modulus ratio (E_g/E_r), the recovery time showed an inverse relationship with it. The transition temperature could be tuned by the reactant composition and the speed of shape recovery increased with increase in actuation temperature. These epoxy-cyanate ester systems possesses good thermal, mechanical and shape memory characteristics for potential use in smart actuator development.     

Influence of the soft segment length on the properties of water‐cured poly(carbonate‐urethane‐urea)s

Poly(carbonate‐urethane‐urea)s (PCUU) based on oligocarbonate diols (M_n ≈ 2000) with different length of the hydrocarbon chain as soft segments were synthesized and investigated. Carbonate oligomerols were obtained in a two‐step method from dimethyl carbonate (DMC) and linear α,ω‐diols (1,4‐butanediol, 1,5‐pentanediol, 1,6‐hexanediol, 1,9‐nonanediol, 1,10‐dekanediol and 1,12‐dodecanediol). Oligo(trimethylene carbonate) diol was synthesized using ring‐opening polymerization of trimethylence carbonate. PCUUs were obtained by prepolymer method using isophorone diisocyanate (IPDI) and water as a chain extender. Changes in polymers properties with increase of methylene group number between carbonate linkages were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile strength and hardness measurements. The thermal stability was also analyzed by means of thermogravimetric analysis (TGA). Based on FTIR analysis influence of methylene groups number between carbonate linkages on phase separation and concentration of allophanate and biuret groups in the samples were investigated. The obtained poly(carbonate‐urethane‐urea)s exhibited very good mechanical properties. Tensile strength and elongation at break were 40 MPa and 400–600%, respectively, depending on the oligocarbonate used. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhanced thermal and tensile behaviour of MWCNT reinforced palm oil polyol based shape memory polyurethane

Shape memory polyurethane (SMPU) has received tremendous interest because of its low cost, low density, as well as easy processing. However, its inferior mechanical properties compared to shape memory alloys have constrained its application in a broad range of engineering areas. Nanofillers are commonly added to polymers to overcome the problem associated with low mechanical characteristics. This study aims to examine the effect of various loadings of multiwalled carbon nanotubes (MWCNT) on the thermal stability, soft segment crystallinity, tensile and shape memory behaviour of palm oil polyol based SMPU nanocomposites. The SMPU nanocomposites were synthesised using a two-step polymerisation process. Microphase-separated SMPU nanocomposites obtained as the differential scanning calorimetric analysis showed two melting transitions, which belonged to the soft and hard phase domains. Furthermore, it was found that MWCNT had acted as a nucleating agent, which promoted the crystallisation process of SMPU nanocomposites. The thermal stability and tensile properties of SMPU/MWCNT nanocomposites were enhanced significantly as the MWCNT was added to the SMPU matrix. A considerable enhancement in the shape fixity (SF) value was revealed for PU-30 and PU-40 samples with the addition of MWCNT. The shape recovery (SR) time of SMPU was faster for samples reinforced with MWCNT, whereas SF increased while SR decreased upon increasing the shape memory cycle. The SMPU nanocomposites produced demonstrated enhanced thermal and tensile properties, which has the potential as smart material in many industrial applications.     

可生物降解多嵌段聚(酯-氨酯)的合成及其热致形状记忆性质

以端羟基L-丙交酯/乙交酯共聚物(PLLG-diol)和端羟基ε-己内酯/乙交酯共聚物(PCG-diol)为硬段和软段,通过与二异氰酸酯反应制得了软、硬分子量和组成均可调的多嵌段聚(酯-氨酯),表征了它们的形状记忆行为.多嵌段聚(酯-氨酯)具有良好的形状记忆性质,应变固定率达98%~99.5%,应变恢复率达93%~98.5%;通过转变温度的调节,可使多嵌段聚(酯-氨酯)在37℃体温下不发生形状变化,而在稍高于体温的温度(40~50℃)下恢复原始形状,其形状恢复速率可通过温度和升温速率来调节.     

Synthesis and ESCA surface studies of octadecyl chain-extended polyurethanes

Poly(ether urethane)s as biomaterials display certain favorable mechanical and biocompatibility properties. Earlier studies suggest that improved blood compatibility might be attained by introducing hydrocarbon groups at the surface. We synthesized and characterized a series of polyurethanes in which a N-2,3-dihydroxypropyl-N′-octadecyl urea chain extender (ODCE) was incorporated into the poly(tetramethylene glycol) (PTMO)/4,4′-methylenebis(phenylene isocyanate) (MDI) system. Molecular weights of the polymers varied between 40,000 and 250,000. An electron spectroscopy for chemical analysis (ESCA) study of the ODCE polyurethane surface revealed a substantially enhanced hydrocarbon concentration compared to a control PTMO/MDI/ethylene diamine (ED) polyurethane surface. Also, bulk composition analyses and ESCA data of the ODCE polymers indicated that the percentage of carbon was higher in the surface region than in the bulk. Thus, the ODCE polymer showed a marked increase in hard-segment concentration in the surface region compared to the bulk region and to the ED polymer.     

PIB‐based polyurethanes. IV. The morphology of polyurethanes containing soft co‐segments*

Novel polyurethanes consisting of polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) or PIB/poly(hexamethylene carbonate) (PC) soft co‐segments in combination with 4,4′‐methylene‐bis(cyclohexyl isocyanate)/1,6‐hexanediol, 1,4‐butanediol, or 1,6‐hexamethylene diamine hard segments exhibit excellent mechanical properties (upto 31 MPa tensile strength with 700% elongation) together with unprecedented oxidative/hydrolytic stability. A structural model of the morphology of these polyurethanes was developed that reflects this combination of properties. The key new elements of our model are H bridges between the PTMO and PC type soft and urethane hard segments, which compatibilize the soft and hard domains, and the presence of large quantities of chemically resistant PIB soft segments that protect the other oxidatively/hydrolytically vulnerable constituents. A variety of FTIR, DSC, SAXS, AFM, and DMTA experiments strongly support the proposed morphological model. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6180–6190, 2009     

Preparation of modified multi‐walled carbon nanotubes as a reinforcement for epoxy shape‐memory polymer composites

Effectively improving the mechanical properties and thermal resistance of epoxy shape‐memory polymers (ESMPs) without affecting their shape‐memory performance is necessary to expand these polymers in practical applications. In this article, modified multi‐walled carbon nanotubes (MWCNTs) were prepared and used as efficient reinforcement for enhancing the comprehensive properties of ESMPs. Increases of nearly 289% to 444% for impact strength and 112% to 184% for tensile force were obtained by adding only 0.1 to 1 wt% epoxy‐modified MWCNTs. The addition of unmodified and carboxyl‐modified MWCNTs was also investigated but showed less impact on the mechanical properties of the ESMPs than epoxy‐modified MWCNTs. Thermogravimetry analysis (TGA) and dynamic mechanical analyses (DMA) showed that less than 1 wt% modified MWCNTs can enhance the heat resistance of ESMPs greatly. Although the shape recovery time for composite materials increased upon adding the MWCNTs, the entire recovery time was still less than 1 minute, and the shape recovery rate was relatively high, nearly 100%.     

Influence of silica on shape memory effect and mechanical properties of polyurethane-silica hybrids

Polyurethane block copolymer (PU) was synthesized and was followed by a sol-gel reaction with tetraethoxysilane (TEOS) to prepare high performance polyurethane-silica hybrids with shape memory function. Their tensile and shape memory properties were compared as a function of TEOS content and PU hard segment content. A tensile test showed that the mechanical properties were largely influenced by TEOS content, and the maximum elongation-at-break as well as maximum breaking stress and modulus were obtained when TEOS at 10 wt% was used. Shape memory of hybrids was also obtained from a thermomechanical test, and showed good shape retention and shape recovery of more than 80% for all samples. Consequently, by silica hybridization, an improvement in the mechanical properties and shape recovery force of PU could be achieved without any decrease in their shape recovery effect.     

Study on poly(ε‐caprolactone)‐based shape memory copolymer fiber prepared by bulk polymerization and melt spinning

In this paper, a poly(ε‐caprolactone) (PCL)‐based shape memory polyurethane fiber was prepared by melt spinning. The shape memory switching temperature was the melting transition temperature of the soft segment phase mainly composed of PCL at 47°C. The mechanical properties especially shape memory effect were explicitly characterized by thermomechanical cyclic tensile testing. The results suggest that the prepared fiber has shape memory effects. The prepared 40 denier shape memory fiber had a tenacity of about 1.0 cN/dtex, and strain at break 562–660%. The shape fixity ratio reached 84% and the recovery ratio reached 95% under drawing at high temperature and thermal recovery testing.¹ Finally, the fiber thermal/mechanical properties were measured using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Copyright © 2007 John Wiley & Sons, Ltd.     

Preparation and characterization of polyurethan‐block‐poly(trifluoro‐ propylmethyl)siloxane elastomers

A series of polyurethane‐block‐poly(trifluoropropylmethyl)siloxane (PUFS) elastomers were prepared via a two‐step process from toluenediisocyanate (TDI), α ω‐bis(3‐aminopropyldiethoxylsilane) poly(trifluoropropylmethyl)siloxane (APFS), and poly(tetramethylene oxide) (PTMO). The PUFS films were formed through moisture curing and characterized by DSC, DMTA, TGA, mechanical testing, and water contact angle. It was found that the extent of microphase separation of the PUFS system would increase with the increase in APFS content, and result in the decrease in the tensile strength and the thermal stability. On the other hand, the crosslink density of the PUFS system would apparently increase with the increase in the TDI content, which reduced the microphase separation and improved the tensile properties and the thermal stability of the PUFS elastomers. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermo‐responsive shape memory behavior of poly(styrene‐b‐isoprene‐b‐styrene)/ethylene‐1‐octene copolymer thermoplastic elastomer blends

Thermally‐triggered shape memory polymers (SMPs) are smart materials, which are capable of changing their shapes when they are exposed a heat stimulant. Blending semi‐crystalline and elastomeric polymers is an easy and low‐cost way to obtain thermo‐responsive SMPs. In this work, novel poly(ethylene‐co‐1‐octene) (PEO) and poly(styrene‐b‐isoprene‐b‐styrene) (SIS) thermoplastic elastomer blends were prepared via melt blending method. The morphological, mechanical, rheological properties and shape memory behaviours of the blends were investigated in detail. In morphological analysis, co‐continuous morphology was found for 50 wt% PEO/50 wt% SIS and 60 wt% PEO/40 wt% SIS (60PEO/40SIS) blends. The shape memory analysis performing by dynamic mechanical analyzer showed that the 60PEO/40SIS blend also exhibited the optimum shape memory performance with 95.74% shape fixing and 98.98% shape recovery. Qualitatively shape memory analysis in hot‐water pointed out that the amount of semi‐crystalline PEO promotes shape fixing ability of the blends whereas SIS content enhances shape recovery capability. Although the SIS and PEO are immiscible polymers, the blends of them were exhibited good elastomeric properties with regard to tensile strength, toughness, and elongation at break.     

Synthesis and Characterization of Thermoplastic Polyurethaneureas based on Polyisobutylene and Poly(tetramethylene oxide) Segments

New thermoplastic polyurethaneureas (TPUU) based on polyisobutylene (PIB) and poly(tetramethylene oxide) (PTMO) segments have been synthesized possessing tensile properties comparable to conventional PTMO based TPUs. PIB based TPUU containing 35 weight (wt)% hard segment was synthesized by chain extension of H₂N-Allyl-PIB-Allyl-NH₂ with 4,4′ -methylene bis(phenylisocyanate) (MDI) and 1,4-butanediol (BDO) in toluene. The ultimate tensile strength (UTS) = 12 MPa and ultimate elongation = 70% were inferior to PTMO based polyurethane (UTS = 35 MPa, elongation at break = 600%). H₂N-Allyl-PIB-Allyl-NH₂ and HO-PTMO-OH in different proportions were chain extended in presence of MDI and BDO to obtain TPUUs containing 35 wt% hard segment. The polymers exhibited M _ns = 84000–138000 with polydispersity indices (PDIs) = 1.7–3.7. The UTS = 23–32 MPa and elongation at break = 250–675% was comparable to that of PTMO based polyurethane and significantly higher than the PIB based TPUU with the same Shore hardness. The Young's modulus of the polymers was strongly dependent and directly proportional to the PIB wt% in the SS of the TPUUs.     

Synthesis and Properties of Reversible Disulfide Bond-based Self-healing Polyurethane with Triple Shape Memory Properties

A reversible disulfide bond-based self-healing polyurethane with triple shape memory properties was prepared by chain extending of random copolymer poly(lactide-co-caprolactone)(PCLA),hexamethylene diisocyanate (HDI),polytetrahydrofuran(PTMEG),and 4,4'-aminophenyl disulfide.The chemical structures were characterized using~1H nuclear magnetic resonance (~1H-NMR)spectroscopy,Fourier transform infrared spectroscopy (FTIR),and gel permeation chromatography (GPC).The thermal properties,selfhealing properties,triple-shape memory effect,and quantitative shape memory response were evaluated by differential scanning calorimetry (DSC),tensile tests,two-step programming process thermal mechanical experiments,and subsequent progressive thermal recovery.The self-healing mechanism and procedures were investigated using polarizing optical microscopy (POM) and an optical profiler.It was concluded that self-healing properties (up to 60%) and triple-shape memory properties around 35 and 500C (with shape fixation ratios of 94.3%and 98.3%,shape recovery ratios of 76.6%and 85.1%,respectively) were integrated to the shape memory polyurethane.As-prepared polyurethane is expected to have potential applications in multi-shape coatings,films,and step-by-step deploying structures.     

Morphology and Mechanical Properties of Thermoplastic Polyurethanes Containing Polyisobutylene/Poly(tetramethylene oxide) Mixed Segments

We investigated the thermal properties, microphase separated structure and mechanical properties of a series of thermoplastic polyurethanes (TPUs) containing both polyisobutylene (PIB) and poly(tetramethylene oxide) (PTMO) diols in the soft segment (SS). A series of TPUs were prepared with the same weight fraction of the SS but different ratio between PIB and PTMO diols. Molecular weight of the PTMO diol and chemical structure of the hard segment (HS) also varied. Dynamic mechanical analysis (DMA) measurements did not reveal strong microphase separation between PIB and PTMO in the SS. While it has been assumed that incorporating PTMO diol into the SS can enhance the phase mixing between the hard segment (HS) and SS, our results indicated that, in most cases, the degree of microphase separation of TPUs based on mixed diols is slightly higher than that of TPUs based on only PIB diol.