Dual-shape polymers

Characterizing the Shape-Memory Effect of Dual-Shape Polymers. 117... 

Cyclic, Thermomechanical Tensile Tests of Dual-Shape Polymers. 118... 

Cyclic, Photomechanical Testing of Light-Induced Dual-Shape Polymers. 129... 

Beilin, L, Kelch, S., and Lendlein, A. (2007) Dual-shape properties of triple-shape polymer networks with crystallizable network segments and grafted side chains. Journal of Materials Chemistry, 17, 2885-2891. 

Shape memory polymers (SMPs) and composites thereof are emerging smart materials in different applications, especially in biomedical, aerospace, and construction engineering helds. SMPs may adopt one (dual-shape), two (triple-shape). 

Mostly, SMPs are dual-shape materials, which are able to change from a first shape (A) into a second shape (B) when exposed to an external stimulus. Shape (A) is a temporary shape while shape (B) is the permanent shape obtained as a result of the initial polymer processing. Besides SMPs with dual-shape capability another class of SMPs, showing a triple-shape capability, have recently been developed to enable complex active movements [10, 24-27]. Triple-shape polymers consist of... 

In this chapter, methods are discussed for the characterization of the chemical structure, the morphology, and the thermal properties of SMPs. Methods for quantification of the macroscopic SME are described in detail for dual-shape and tripleshape polymer systems with thermally-induced SME as well as polymer-systems with photo-induced or magnetically-induced SME. Finally, application-oriented testing of SMPs and also theoretical approaches and computational methods for simulating the SME are described. 

Fig. 1 Four types of SMPs (dual-shape effect) depicted as a function of their dynamic thermomechanical behavior. Plotted is the tensile storage modulus vs temperature as measured using a smtdl oscillatory deformation at 1 Hz for (a) Cat. A-I, chemically crosslinked amorphous polymer network (7, = Tg) (b) Cat. A-II, chemically crosslinked semicrystalline polymer networks (Ttrans = 7m) (c) Cat. B-I, physically crosslinked thermoplastic with r,ra,K = 7g and (d) Cat. B-II, physically crosslinked thermoplastic (Tlrans = Tm). Taken from ref [5], Copyright 2007. Reproduced by permission of the Roytd Society of Chemistry, http //dx.doi.org/10.1039/b615954k...

In a study on an AB polymer network system with triple-shape capability, the influence of the programming and recovery process on the crystalline domains was investigated by means of WAXS and SAXS experiments [24,25]. The triple-shape capability obtained by a one-step triple-shape creation process, similar to a conventional dual-shape programming process, was reported for networks based on PCL and PCHMA. Favorable compositions for obtaining a triple-shape effect contained... 

Triple-shape polymers can change on demand from a first shape (A) to a second shape (B) and from there to a third shape (C), when stimulated by two subsequent temperature increases [10, 26, 27]. Specific cyclic, thermomechanical tensile experiments were developed to characterize the triple-shape effect (Chapter Shape-Memory Polymers and Shape-Changing Polymers [101] and Sect. 2.2) quantitatively. Analogous to the experiments for dual-shape materials, each cycle of these tests consisted of a programming and a recovery module. A cycle started with creating the two temporary shapes (B and A) by a two-step uniaxial deformation, followed by the recovery module, where shape (B) and finally shape (C) were recovered. 

The creation of the triple-shape capability for an AB polymer network system by a simple one-step process similar to a conventional dual-shape progranuning process was shown for networks based on PCL and PCHMA [24] (see Sect. 2.4). In these materials a stress-controlled cyclic, thermomechanical experiment was used to quantify the triple-shape effect. The sample was deformed at 150°C (liigh) to 50% (Ein) and subsequently cooled to —10°C (Tio ). The large temperature interval of around 160 K led to a strong reduction of the strain. When the sample was heated... 

A detailed understanding of the underlying mechanisms for the SME requires a systematic characterization, especially quantification of the shape-memory properties. As typical for a material function, numerous physical parameters are in-fiuencing the SME. Therefore the determination of structure/physical parameter function relationships is challenging. Specific methods are required for dual-shape or triple-shape properties as well as for the different stimuli. The knowledge-based development of SMPs can be supported by modeling approaches for simulating the thermomechanical behavior of such polymers. 

Materials that show a shape-memory effect can be deformed into a temporary shape and afterwards they can recover their original shape on exposnre to an external stimulus [65,66]. Shape-memory polymers (SMPs) are stimuli-responsive smart polymers that have dual shape, which responds to application of an external stimulus. SMP is conventionally processed to receive its permanent shape. Afterward, the polymer is deformed and the intended temporary shape is fixed [67,68]. This process is called programming. These polymers basically consist of two phases, fixed points or frozen... 

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

The discussion directly following Eq (6) provides a simple, physically reasonable explanation for the preceding observations of marked concentration dependence of Deff(C) at relatively low concentrations. Clearly, at some point, the assumption of concentration independence of Dp and in Eq (6) will fail however, for our work with "conditioned" polymers at CO2 pressures below 300 psi, such effects appear to be negligible. Due to the concave shape of the sorption isotherm, even at a CO2 pressure of 10 atm, there will still be less than one CO2 molecule per twenty PET repeat units at 35°C. Stern (26) has described a generalized form of the dual mode transport model that permits handling situations in which non-constancy of Dp and Dh manifest themselves. It is reasonable to assume that the next generation of gas separation membrane polymers will be even more resistant to plasticization than polysulfone, and cellulose acetate, so the assumption of constancy of these transport parameters will be even more firmly justified. 

Figure 26.10 A schematic representation of the meniscus shape and position of the three-phase contact line (solid/liquid/air) during immersion and emersion of a hydrophobic surface (e.g., TMS treated polymers) the dual arrows indicate which direction the beaker is moving, the small arrow on the plate indicates the direction the three-phase contact line is moving.

The structure defined by the matrices B and b (the dual) is also a polymer backbone. From the matrix B, one can now compute the following shape descriptors in analogy with those in the preceding section ... 

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