Shape memory and nanostructure in poly(norbornyl‐POSS) copolymers

Abstract

The microstructure and shape-memory properties of norbornyl±POSS hybrid copolymers having either cyclohexyl corner groups (CyPOSS) or cyclopentyl corner groups (CpPOSS) were investigated by transmission electron microscopy and thermomechanical analysis. Here, POSS refers to the polyhedral oligomeric silsesquioxane macromer. Samples containing 50 wt% of POSS macromer have been mechanically drawn at temperatures above their glass transition temperatures, followed by rapid quenching in LN 2 . Shape-memory properties of such drawn samples were explored by measuring recovered strain while heating above the T g using thermomechanical analysis. Incorporation of POSS comonomers within PN is found to slightly reduce the percentage recovery, while improving thermal stability signi®cantly. Interestingly, the types of corner groups in the POSS macromer affect the shape-memory behaviour, with the CyPOSS copolymer showing lower percentage recovery than the CpPOSS copolymer due to enhanced aggregation of CyPOSS macromers. # 2000 Society of Chemical Industry Keywords: shape-memory polymer; POSS; polynorbornene; nanocomposite. INTRODUCTIONShape memory refers to the ability of certain materials to remember a shape, on demand, even after rather severe deformations. The most common material exhibiting such a property is nitanol, a nickel±titanium alloy the shape-memory effect of which is produced by a solidstate phase transformation.1 In recent years, shapememory polymers have received increasing attention because of their low cost, low density, high shape recoverability and easy processability, compared to conventional shape-memory alloys.2±4 Basic principles of the shape-memory effect in polymeric materials can be well described by their elastic modulus±temperature behaviour. At temperatures above the glass transition temperature (T g ), the polymer achieves a rubbery elastic state where it can be easily deformed without stress relaxation by applying external forces over a time-frame t ( t, where t is a characteristic relaxation time. When the material is cooled below its T g , the deformation is ®xed and the deformed shape remains stable. The predeformation shape can be easily recovered by reheating the material to a temperature higher than the T g . Therefore, admirable shape-memory behaviour requires a sharp transition from glassy state to rubbery state, a long relaxation time, and a high ratio of glassy modulus to rubbery modulus.

Thermal Responsive Shape Memory Polymers for Biomedical Applications

“…According to the polymer classification convention, the first two categories belong to thermosets and the last two belong to thermoplastics, respectively (Gedde, 1995). All four types of SMPs have been realized (Alteheld, 2005;Jeon, 2000;Lendlein, 2001;Ping, 2005). In thermoplastic SMPs, the chain entanglements or local crystalline domains formed by strong chain-chain interactions can serve as the physical crosslinking sites.…”

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.…”

“…Applications for SMPs are diverse and involve deformations like bending, compression and drawing, accordingly there are different testing methods to quantify the SM behavior of a polymer, such as bending tests [174][175][176], fold-deploy tests [135], uniaxial experiments (unconstrained free strain recovery tests, stress recovery tests under full constraint at a fixed strain level [101,177], isothermal uniaxial compression tests [178] and other tests developed for SMP foams [179][180][181][182][183]) and isothermal free strain recovery tests in warm water baths, during which a video camera collects images at a well-defined rate, e.g., at 20 frames-per-second ( Figure 1) [184,185]. In some cases, a dynamic mechanical analyzer has been used to evaluate SM properties [88]. Commonly, functional performance testing is done by using a tensile testing machine equipped with a thermochamber.…”

“…Higher thermal stabilities, e.g., higher activation energies at 10% degradation, were achieved for SMPUs with attached MWCNTs, which seemed to enable a better dispersion of the fillers in the polymer matrix. Looking for SMPs, which combine reasonable shape recoverabilities with good thermal stability, Jeon et al [88] studied the SM properties of two different types of POSS hybrid copolymers, both containing 50 wt% POSS in a polynorbornene matrix (T trans = T g ). Due to the presence of the fillers, T g increased from 57 to 66 °C, when cyclopentyl (Cp) corner groups were chosen, and to 73 °C in case of cyclohexyl (Cy) corner groups.…”

Hybrid thin films derived from UV-curable acrylate-modified waterborne polyurethane and monodispersed colloidal silica

“…Reinforcing of polymer is usually achieved in polymer composites by adding reinforcement such as fibers and particles to the polymer matrix, and some interesting results have been reported using polymer-clay nanocomposites [21], polymer-polyhedral oligomeric silsesquioxane nanocomposites [22], and organic-inorganic hybrids [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Generally, there are two typical kinds of organic-inorganic nanocomposites.…”