Responsive Polymeric Materials Research Articles

Stimuli-induced instabilities and bifurcations of responsive polymeric materials: a review on analytical and numerical studies

Stimuli-induced instabilities and bifurcations of responsive polymeric materials: a review on analytical and numerical studies

PH Responsive Properties of Methyl Red/PVA Polymers for Smart Food Packaging Applications

Responsive polymers in particular have gained increasing interest during the last decades due to their unique properties. Their Ability to exhibit sharp and reversible changes in response to environmental pH condition have made them suitable for various applications. The pH responsive polymeric materials are being developed by the researcher in the recent year for the improvement of food safety issue in the packaging materials. In this study organic methyl red (MR) dye is used as a pH indicator induced with polyvinyl alcohol (PVA) films prepared by solution casting method. The prepared samples were characterized for microstructural, morphological, mechanical, water absorption and pH responsive properties using various analytical techniques. The XRD analysis has shown better crystallinity property which is in good agreement with the mechanical strength of the material. The morphological studies have shown homogeneous dispersion of MR on PVA matrix and change in the morphology of the MR/PVA polymer composites after acid treatment. The MR/PVA films were treated with rotten papaya fruit and change occurred in the samples were identified using UV-vis spectrometric analysis. The prepared MR/PVA pH-responsive polymers have shown good pH reactivity in the range of pH 4.5 to 6.5. Overall, the prepared samples have good pH responsive properties with additional qualities like good optical, structural, and mechanical characteristics.

Tumor Microenvironment-Responsive Drug Delivery Based on Polymeric Micelles for Precision Cancer Therapy: Strategies and Prospects.

In clinical practice, drug therapy for cancer is still limited by its inefficiency and high toxicity. For precision therapy, various drug delivery systems, including polymeric micelles self-assembled from amphiphilic polymeric materials, have been developed to achieve tumor-targeting drug delivery. Considering the characteristics of the pathophysiological environment at the drug target site, the design, synthesis, or modification of environmentally responsive polymeric materials has become a crucial strategy for drug-targeted delivery. In comparison to the normal physiological environment, tumors possess a unique microenvironment, characterized by a low pH, high reactive oxygen species concentration, hypoxia, and distinct enzyme systems, providing various stimuli for the environmentally responsive design of polymeric micelles. Polymeric micelles with tumor microenvironment (TME)-responsive characteristics have shown significant improvement in precision therapy for cancer treatment. This review mainly outlines the most promising strategies available for exploiting the tumor microenvironment to construct internal stimulus-responsive drug delivery micelles that target tumors and achieve enhanced antitumor efficacy. In addition, the prospects of TME-responsive polymeric micelles for gene therapy and immunotherapy, the most popular current cancer treatments, are also discussed. TME-responsive drug delivery via polymeric micelles will be an efficient and robust approach for developing clinical cancer therapies in the future.

Synthesis and Characterization of Responsive Antimicrobial Materials for Chronic Wound Management

Chronic wound treatment requires the ability to regulate the wound healing process and mitigate the propagation of bacterial infection with constant monitoring, in real-time. The need for multi-functional wound management materials has emerged as a significant research area with promise shown in the incorporation of antimicrobial agents within responsive polymeric materials to elicit signals providing dynamic information about the healing process. Traditional wound dressings provide a barrier between the outside environment and the wound; however, these methods are increasingly becoming less effective. Hydrogels synthesized from natural biopolymers have emerged due to their intrinsic properties such as biodegradability and non-cytotoxicity and enhanced from their well-defined, three-dimensional, non-covalent networks ideal for modification and functionalization to create “micro-reactors.” Previous work focused on the strategic design of an alginate-based hydrogel containing dual functional additives (i.e., amino acids) paired with photochemically prepared Ag- and Cu-TiO2 nanoparticles (Ag/Cu-NPs) to understand the synergistic interactions of the polymer chains, cross-linkers, and additives. The antimicrobial effectiveness of the composite was examined using an epi-fluorescent optical tweezer to measure the rates of bacterial cell death. Results showed that with the incorporation of the NPs there is a decrease in green signal (live cells) within 1 hour of exposure. Furthermore, the healing rates of simulated wounds using human dermal fibroblasts were explored along with changes in the expression of growth factors that promote wound healing, such as collagen and TGF-b. This work focuses on a two-layer responsive material with a wound-healing layer and a conductive layer formed through the secondary functionalization of the composite system through a metal-coordination-assisted photopolymerization of conductive polymers (i.e. aniline). Preliminary results show there is uniform polymeric chain growth seen in enhanced charge transfer through the matrix upon an applied voltage. Studies have also been conducted to measure the impact of saturation of the bandage through simulated wound exudate that revealed once saturation occurs, the passing of electricity between the ions found in wound exudate carried current through the composite, increasing the conductivity, leading to the signaling of an LED prompting replacement. The resulting two-layer nanocomposite system then functions as a responsive, antimicrobial wound healing material capable of eliminating constant monitoring with application in healthcare and home settings.

Tunable Chiral Plasmonic Activities Enabled via Stimuli Responsive Micro-Origami.

Chiral plasmonic nanomaterials with distinctive circularly polarized light-dependent optical responses over a broad range of frequency have great potential for photonic and biomedical applications. However, it still remains challenging to fabricate 3D plasmonic chiral micro-constructs with readily modulated chiroptical properties over the magnitude of ellipticity, mode frequency, and switchable handedness, especially in the vis-NIR range. In this study, polymeric micro-origami-based 3D plasmonic chiral structures are constructed through self-rolling of gold nanospheres (AuNSs)-decorated polymeric micro-sheets. Spherical AuNSs are assembled as highly ordered linear chains on 2D rectangular micro-sheets by polydimethylsiloxane-wrinkle assisted assembly. Upon rolling the micro-sheets to micro-tubules, the AuNS chains transform into 3D helices. The AuNS-assembled helices induce collective plasmonic modes propagating in a helical manner, leading to a strong chiral response over the vis-NIR range. The circular dichroism (CD) is measured to be as high as hundreds of millidegree, and the position and sign of CD peaks are actively modulated by controlling the orientated angle of AuNS chains, enabled by tuning the collective plasmonic modes. This micro-origami-based strategy incorporates the incompatible 2D assembly technique with 3D chiral structures, opening up an intriguing way toward constructing chiral plasmonic structures and modulating chiroptical effects based on responsive polymeric materials.

Coumarin end-capped poly(ε-caprolactone)-poly(ethylene glycol) tri-block copolymer: synthesis, characterization and light-response behavior

Light responsive polymeric materials are of great interest for several applications; in particular, the NIR spectrum is considered an ideal light source for e.g. biomedical applications. Here, we have designed light sensitive poly(ɛ-caprolactone)- poly(ethylene glycol)-poly(ɛ-caprolactone) (PCL-PEG-PCL) triblock copolymer, end-capped with modified coumarin. When dialyzed against water, the coumarin-functionalized triblock copolymers self-assembled into core-shell nanoparticles, characterized by DLS, SEM, and NMR. The hydrophobic Nile Red, used as a model guest molecule, was loaded in the nanoparticles and its release by light irradiation of selected wavelength was demonstrated by fluorescence spectroscopy. When irradiated with UV or NIR light, coumarin end-groups of the copolymer were photolyzed, converting the end groups to carboxylic acids, thus provoking the disruption of the preassembled nanoparticles, and the release of the encapsulated guest molecule.

Stiffness memory nanohybrid scaffolds generated by indirect 3D printing for biologically responsive soft implants

Cell and tissue stiffness is an important biomechanical signalling parameter for dynamic biological processes; responsive polymeric materials conferring responsive functionality are therefore appealing for in vivo implants. We have developed thermoresponsive poly(urea-urethane) nanohybrid scaffolds with ‘stiffness memory’ through a versatile 3D printing-guided thermally induced phase separation (3D-TIPS) technique. 3D-TIPS, a combination of 3D printing with phase separation, allows uniform phase-separation and phase transition of the polymer solution at a large interface of network within the printed sacrificial preform, leading to the creation of full-scale scaffolds with bespoke anatomical complex geometry. A wide range of hyperelastic mechanical properties of the soft elastomer scaffolds with interconnected pores at multi-scale, controlled porosity and crystallinity have been manufactured, not previously achievable via direct printing techniques or phase-separation alone. Semi-crystalline polymeric reverse self-assembly to a ground-stated quasi-random nanophase structure, throughout a hierarchical structure of internal pores, contributes to gradual stiffness relaxation during in vitro cell culture with minimal changes to shape. This ‘stiffness memory’ provides initial mechanical support to surrounding tissues before gradually softening to a better mechanical match, raising hopes for personalized and biologically responsive soft tissue implants which promote human fibroblast cells growth as model and potential scaffold tissue integration. Statement of SignificanceBiological processes are dynamic in nature, however current medical implants are often stronger and stiffer than the surrounding tissue, with little adaptability in response to biological and physical stimuli. This work has contributed to the development of a range of thermoresponsive nanohybrid elastomer scaffolds, with tuneable stiffness and hierarchically interconnected porous structure, manufactured by a versatile indirect 3D printing technique. For the first time, stiffness memory of the scaffold was observed to be driven by phase transition and a reverse self-assembly from a semicrystalline phase to a quasi-random nanostructured rubber phase. Early insight into cell response during the stiffness relaxation of the scaffolds in vitro holds promise for personalized biologically responsive soft implants.

Analytical network-averaging of the tube model: Mechanically induced chemiluminescence in elastomers

Mechanically induced chemiluminescence is a phenomenon where broken chemical bonds send out visible light upon stress application. The intensity of the emitted light is correlated to the underlying evolution of chain scission in the polymer. In this contribution, an anisotropic analytical network-averaging concept is utilized to model mechanically induced chemiluminescence, Mullins effect, hysteresis and induced anisotropy in mechano-chemically responsive polymeric materials. We extend the isotropic analytical network-averaging (Khiêm and Itskov, 2016) by considering anisotropic distribution of polymer subnetworks driven by internal variables. Accordingly, the network damage and recovery alter the distribution of molecules in space and consequently change the mean field deformation measures (mesoscopic stretch and tube contraction). The mechanically induced chemiluminescence is elucidated on the basis of microvoid growth. By this means, its characteristics such as the irreversibility and the anisotropy can be captured. Model predictions demonstrate good agreement to experimental data of dioxetane cross-linked and filled elastomers.

Synthesis, characterization, properties of N-succinyl chitosan-g-poly (methacrylic acid) hydrogels and in vitro release of theophylline

Although there was great interest in the biocompatible and stimuli responsive polymeric materials in oral drug delivery systems in recent years. The stimuli sensitive and swellable hydrogels have got striking attention as promising materials for site specific controlled drug delivery. In the present study, unique biodegradable, biocompatible, swellable, and pH responsive N-succinyl chitosan-g- Poly (methacrylic acid) hydrogels were prepared through free radical mechanism for oral administration of theophylline. In this method, ammonium persulfate (APS) and N, N′-methylenebisacrylamide (MBA) were used as initiator and crosslinking agent, respectively. The physical properties characterization was performed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), differential scanning calorimetry (DSC), field emission scanning electron microscope (FESEM), and rheometer. The results clearly confirmed the successful formation of N-succinyl chitosan-g- Poly (methacrylic acid) gel. In vitro degradation of hydrogels was found dependent on the ratio of monomers to crosslinking concentration. The effect of concentration of monomers, initiator, and crosslinking agent, pH and ionic strength of salts on swelling behavior was investigated. The results revealed the strong influence of these parameters, on swelling properties. Hydrogel prepared with high concentration of initiator and low crosslinking agent showed maximum swelling. The swelling showed good fitting to second order rate equation and the swelling kinetics data demonstrated the swelling behavior followed non-Fickian anomalous transport mechanism. Furthermore, theophylline loading and encapsulation efficiency (EE %) were found to be 14.5–23.5% and 58–94%, respectively. However, the in vitro release profile of theophylline was found dependent on pH, concentration of monomers, initiator, and crosslinking agent. The maximum release was found to be 90% in simulated intestinal fluid (SIF). The drug release data showed good fitting to Ritger-Peppas model. Moreover, the chemical activity of theophylline was also investigated and found that the drug maintained its chemical activity after in vitro release.

CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications.

CO2 is an ideal trigger for switchable or stimuli-responsive materials because it is benign, inexpensive, green, abundant, and does not accumulate in the system. Many different CO2-responsive materials including polymers, latexes, solvents, solutes, gels, surfactants, and catalysts have been prepared. This review focuses on the preparation, self-assembly, and functional applications of CO2-responsive polymers. Detailed discussion is provided on the synthesis of CO2-responsive polymers, in particular using reversible deactivation radical polymerization (RDRP), formerly known as controlled/living radical polymerization (CLRP), a powerful technique for the preparation of well-defined (co)polymers with precise control over molecular weight distribution, chain-end functional groups, and polymer architectural design. Self-assembly in aqueous dispersed media is highlighted as well as emerging potential applications.

Supramolecular Assembly‐Assisted Synthesis of Responsive Polymeric Materials with Controlled Chain Topologies

Tremendous developments, ranging from new synthetic strategies, properties, and novel functional applications, have emerged in the field of stimuli‐responsive polymeric materials. A variety of highly efficient chemical methodologies have been exploited to synthesize stimuli‐responsive polymers, aiming to control their molecular weight, polydispersity, chemical composition, monomer sequence, and chain topologies. Of particular interest is the emerging strategy of supramolecular assembly‐assisted polymer synthesis, which possesses combined advantages such as facile accessibility, design versatility, multifunctional integration, and promising functions. In this trend article, recent advances are elaborated concerning the fabrication of stimuli‐responsive functional polymers assisted by supramolecular self‐assembly. The fabrication of three main types of responsive polymers, namely, linear polymers, non‐linear shaped polymers, and crosslinked nanostructures, aided by templates of supramolecular assemblies will be discussed. image

Environmentally responsive polymeric materials: effect of the topological structure on self-assembly.

A novel amphiphilic homopolymer (PAGC8), containing two hydrophilic head groups and double hydrophobic tails in each repeat unit, has been prepared by solution polymerization and named as "a geminized amphiphilic homopolymer" in this paper, which is capable of self-assembling into various nanoobjects depending on the solution concentration and solvent properties. Characterization of the self-assembly behaviors was carried out by steady-state fluorescence, transmission electron microscopy and nuclear magnetic resonance techniques. Particular emphasis was dedicated to the environmental responsiveness of the assemblies. The morphologies were observed to transform from micelle-type to vesicles on adding a certain amount of ethanol. It is noteworthy that the assemblies were able to trap hydrophilic (rhodamine B) and hydrophobic (Sudan Red) molecules. Subsequently different nanoobjects were found after the encapsulation. To probe the effect of the topological structure on the self-assembly behaviors, the properties of an additional homopolymer with single charge pendant architecture on the backbone were investigated for comparison. Significant differences in structure between the two architectures brought out remarkable variations in aggregates, which were non-responsive to the solvent environment, or encapsulation of molecules. Based on the experimental results, we proposed a possible mechanism of the morphological transitions of the assemblies.

PH responsive polymers with amino acids in the side chains and their potential applications

ABSTRACTDesign and synthesis of pH responsive polymeric materials has become an important subject in academia as well as in industrial field in recent years due to their applications in diverse field including controlled drug delivery, biomedical applications, membrane science, sensors and actuators, oil recovery, colloid stabilization, etc. Efforts have been made to incorporate stimuli‐responsive biomolecules in synthetic polymers to develop pH responsive “smart” non‐biological hybrid macromolecules with high water solubility, enhanced biocompatibility, bio‐mimetic structure and properties. This review is focused on the recent advances in side‐chain amino acid‐based pH responsive polymers synthesis and potential application aspects of these macromolecular architectures in drug and gene delivery, and other fields. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41084.

Engineering responsive polymer building blocks with host-guest molecular recognition for functional applications.

CONSPECTUS: All living organisms and soft matter are intrinsically responsive and adaptive to external stimuli. Inspired by this fact, tremendous effort aiming to emulate subtle responsive features exhibited by nature has spurred the invention of a diverse range of responsive polymeric materials. Conventional stimuli-responsive polymers are constructed via covalent bonds and can undergo reversible or irreversible changes in chemical structures, physicochemical properties, or both in response to a variety of external stimuli. They have been imparted with a variety of emerging applications including drug and gene delivery, optical sensing and imaging, diagnostics and therapies, smart coatings and textiles, and tissue engineering. On the other hand, in comparison with molecular chemistry held by covalent bonds, supramolecular chemistry built on weak and reversible noncovalent interactions has emerged as a powerful and versatile strategy for materials fabrication due to its facile accessibility, extraordinary reversibility and adaptivity, and potent applications in diverse fields. Typically involving more than one type of noncovalent interactions (e.g., hydrogen bonding, metal coordination, hydrophobic association, electrostatic interactions, van der Waals forces, and π-π stacking), host-guest recognition refers to the formation of supramolecular inclusion complexes between two or more entities connected together in a highly controlled and cooperative manner. The inherently reversible and adaptive nature of host-guest molecular recognition chemistry, stemming from multiple noncovalent interactions, has opened up a new platform to construct novel types of stimuli-responsive materials. The introduction of host-guest chemistry not only enriches the realm of responsive materials but also confers them with promising new applications. Most intriguingly, the integration of responsive polymer building blocks with host-guest recognition motifs will endow the former with further broadened responsiveness to external stimuli and accordingly more sophisticated functions. In this Account, we summarize recent progress in the field of responsive polymeric materials containing host-guest recognition motifs with selected examples and highlight their versatile functional applications, whereas small molecule-oriented host-guest supramolecular systems are excluded. We demonstrate how the introduction of host-guest chemistry into conventional polymer systems can modulate their responsive modes to external stimuli. Moreover, the responsive specificity and selectivity of polymeric systems can also be inherited from the host-guest recognition motifs, and these features provide extra advantages in terms of function integration. The following discussions are categorized in terms of design and functions, namely, host-guest chemistry toward the fabrication of responsive polymers and assemblies, optical sensing and imaging, drug and gene delivery, and self-healing materials. A concluding remark on future developments is also presented. We wish this prosperous field would incur more original and evolutionary ideas and benefit fundamental research and our daily life in a more convenient way.

Stimulus-Responsive Au@(MeO2MAx-co-OEGMAy) Nanoparticles Stabilized by Non-DLVO Interactions: Implications of Ionic Strength and Copolymer (x:y) Fraction on Aggregation Kinetics

Functionalized nanoparticles can assist in stabilizing fluid-fluid interfaces; however, developing and applying the appropriate surface modification presents a challenge because successful application of these nanomaterials for biotechnological, food processing, and environmental applications requires their long-term stability in elevated ionic strength media. This work studies stimulus responsive polymeric materials based on random copolymers of di(ethylene glycol) methyl ether methacrylate (x = MeO2MA) and oligo(ethylene glycol) methyl ether methacrylate (y= OEGMA) which, when grafted to gold nanoparticles, show significant, tunable, colloidal stability. The nanoparticles Au@(MeO2MAx-co-OEGMAy) display tunable, reversible aggregation that is highly dependent on the (x:y) ratio and ionic strength. Effects of these parameters on the initial rate constant of aggregation (k11) are studied by time-resolved dynamic light scattering (TR-DLS) experiments. At the same nanoparticle concentration, a strong sensitivity to salt concentration is observed. Over less than 300 mM increase in NaCl concentration, we observed a two-order of magnitude increase in aggregation rate constants, 4.2 × 10(-20) < k11 < 1.8 × 10(-18) m(3)s(-1). Additionally, for the same gold nanoparticles, a higher fraction of OEGMA requires a higher salt concentration to induce aggregation. A linear relationship between the critical NaCl coagulation concentration (CCC) and the copolymer composition is observed. Analysis of the experimental data with an extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory that includes hydration and osmotic forces is used to explain the stability of these systems. We find the hydration pressure, 2.4 < P(h,0) < 7.2 MPa, scales linearly both with the osmotic pressure and the OEGMA monomer concentration (5 < y < 20%). Specific knowledge of P(h,0)(y, C(NaCl)) enables design of both aggregation kinetics and stability as a function of the copolymer ratio and external stimuli.

A comparison of polymer substrates for photolithographic processing of flexible bioelectronics

Flexible bioelectronics encompass a new generation of sensing devices, in which controlled interactions with tissue enhance understanding of biological processes in vivo. However, the fabrication of such thin film electronics with photolithographic processes remains a challenge for many biocompatible polymers. Recently, two shape memory polymer (SMP) systems, based on acrylate and thiol-ene/acrylate networks, were designed as substrates for softening neural interfaces with glass transitions above body temperature (37°C) such that the materials are stiff for insertion into soft tissue and soften through low moisture absorption in physiological conditions. These two substrates, acrylate and thiol-ene/acrylate SMPs, are compared to polyethylene naphthalate, polycarbonate, polyimide, and polydimethylsiloxane, which have been widely used in flexible electronics research and industry. These six substrates are compared via dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and swelling studies. The integrity of gold and chromium/gold thin films on SMP substrates are evaluated with optical profilometry and electrical measurements as a function of processing temperature above, below and through the glass transition temperature. The effects of crosslink density, adhesion and cure stress are shown to play a critical role in the stability of these thin film materials, and a guide for the future design of responsive polymeric materials suitable for neural interfaces is proposed. Finally, neural interfaces fabricated on thiol-ene/acrylate substrates demonstrate long-term fidelity through both in vitro impedance spectroscopy and the recording of driven local field potentials for 8weeks in the auditory cortex of laboratory rats.

Selenium-Containing Polymers: Promising Biomaterials for Controlled Release and Enzyme Mimics

Although researchers have made great progress in the development of responsive polymeric materials for controlled drug release or diagnostics over the last 10 years, therapeutic results still lag behind expectations. The development of special materials that respond to physiological relevant concentrations, typically within the micromolar or nanomolar concentration regime, remains challenging. Therefore, researchers continue to pursue new biomaterials with unique properties and that respond to mild biochemical signals or biomarkers. Selenium is an essential element in human body with potential antioxidant properties. Because of selenium's electronegativity and atomic radius, selenium-containing compounds exhibit unique bond energy (C-Se bond 244 kJ mol⁻¹; Se-Se bond 172 kJ mol⁻¹). These values give the C-Se or Se-Se covalent bonds dynamic character and make them responsive to mild stimuli. Therefore, selenium-containing polymers can disassemble in response to changes under physiological relevant conditions. This property makes them a promising biomaterial for controlled release of drugs or synthetic enzyme mimics. Until recently, few researchers have looked at selenium-containing polymers as novel biomaterials. In this Account, we summarize our recent research on selenium-containing polymers and show their potential application as mild-responsive drug delivery vehicles and artificial enzymes. We begin by reviewing the current state of the art in the synthesis of selenium-containing main chain block copolymers. We highlight the dual redox and gamma-irradiation behaviors of diselenide-containing block copolymers assemblies, discussing the possibility of their use in a combination of chemotherapy and actinotherapy. We also describe the coordination of platinum with monoselenide containing block copolymers. Such structures offer the possibility of fabricating multidrug systems for cooperative chemotherapy. In addition, we summarize the methods for the covalent and noncovalent preparation of selenium-containing polymers with side chains, which highlight the opportunity to reversibly tune the amphiphilicity of selenium-containing polymers. Finally, we present strategies for the design of highly efficient selenium-containing dendritic polymers that can mimic enzymes. This field is still in its infancy period, and further research can only be limited by our imagination.

Self‐Healing Dynamic Polymeric Systems

AbstractThe concept of self‐healing has created a paradigm shift in the development of a new kind of responsive polymeric materials, which have traditionally been used in a passive role. Inspired by nature, the advancements made in this nascent field of research have given materials the ability of not only sensing damage but also responding and mending themselves in an appropriate manner. Self‐healing in polymers can be autonomous, without the need for human intervention, or nonautonomous, requiring some form of external stimulus. The latter type involves the incorporation of dynamic bonds within the polymeric system, giving the ability to heal multiple times. This minireview discusses some of the prominent self‐healing polymeric systems that harness different dynamic bond chemistries, with the aim of highlighting the potential of dynamic bonds to prepare such advanced materials.

On the evolution law for the frozen fraction in linear theories of shape memory polymers

Shape memory properties of thermally responsive polymeric materials are due mainly to a phase transition from the rubbery phase above the transition temperature (glass transition or melting temperature) to the glassy or semicrystalline phase below this temperature. Within constitutive models of shape memory polymers (SMPs), this phase transition is mathematically accounted for by the frozen volume fraction for which a suitable evolution law must be postulated or derived. In this paper, the evolution laws that have been proposed in the literature are examined both from the experimental and from the theoretical point of view. It is found that the predictive capabilities of the phenomenological laws may be improved by admitting involved material constants to depend on parameters such as pre-strain, rate of heating and cooling, and other quantities characterizing thermomechanical cyclic tests. It is next shown that for a wide class of linear constitutive models of SMPs, the evolution law for the frozen volume fraction may be derived in a systematic way from strain and stress profiles experimentally obtained in the standard thermomechanical test.

Development of thermosensitive copolymers of poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate) and their nanogels synthesized by RAFT dispersion polymerization in water

Thermosensitive polymeric materials based on copolymers of oligo(ethylene glycol) methacrylates are attracting significant attention in various materials sectors. The preparation of their thermosensitive microgels/nanogels via the aqueous dispersion polymerization process is, however, limited by low monomer loading and thus low solid content of the final colloids. Moreover, the preparation of nanogels by reversible addition-fragmentation chain transfer (RAFT) mediated dispersion polymerization has been further hampered by the poor RAFT control of the polymerization process. In this article, we report the development of thermosensitive copolymers based on poly(2-methoxyethyl acrylate-co-poly(ethylene glycol) methyl ether acrylate) (P(MEA-co-PEGA)) and their use for nanogel synthesis by RAFT dispersion polymerization in water. The thermosensitive copolymers exhibited sharp thermal transitions upon increasing thee temperature above their lower critical solution temperature. The use of MEA as the majority comonomer and poly(N,N′-dimethylacrylamide) as the RAFT agent and stabilizer for the synthesis of nanogels allowed monomer loadings of up to 20%, which significantly improved the solid content of the dispersion polymerization system. Moreover, the dispersion copolymerization of MEA with PEGA was under excellent RAFT control up to complete monomer conversion. The synthesized nanogels showed an unprecedented linear relationship between nanogel size and temperature, suggesting expanded applications of such responsive polymeric materials.