Shape‐memory polymer networks from oligo(ϵ‐caprolactone)dimethacrylates

Polymer networks showing a thermally induced shape‐memory effect were prepared through the crosslinking of oligo(?‐caprolactone)dimethacrylates under photocuring with or without an initiator. The influence of the molecular weight of the oligo(?‐caprolactone)dimethacrylates and the initiator concentration on the macroscopic properties of the polymer networks was investigated. The isothermal and nonisothermal crystallization behavior of the polymer networks was evaluated as a basic principle of the functionalization process. Shape‐memory properties such as the strain fixity and strain recovery rate were quantified with cyclic thermomechanical tensile experiments for different maximum elongations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1369–1381, 2005     

Impact of poly(ɛ‐caprolactone) architecture on the thermomechanical and shape memory properties

We report the synthesis of linear‐ and brush‐type poly(?‐caprolactone) (PCL) networks and investigate their thermal, mechanical, and shape memory behavior. Brush‐PCLs are prepared by ring‐opening metathesis polymerization (ROMP) of a norbornenyl‐functionalized ?‐caprolactone macromonomer (MM‐PCL) of different molecular weights. The linear analog, diacrylate end‐functionalized PCL (linear‐PCL), having comparable molecular weight of side chain of brush‐PCL is also synthesized. These polymers are thermally cured by a radical initiator in the presence of poly(ethylene glycol) diacrylate crosslinker. Thermal and linear viscoelastic properties as well as shape memory performance of the resulting PCL networks are investigated, and are significantly impacted by the PCL architecture. Therefore, our work highlights that tailoring macromolecular architecture is useful strategy to manipulate thermal, mechanical, and resulting shape memory properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3424–3433     

Reversible plasticity shape memory polymers: Key factors and applications

Reversible plasticity shape memory (RPSM) polymers have been emerging as new smart materials with distinctions compared with conventional SMPs, such as easier shaping programming, stronger recovery stress, and higher recovery strain. For purposeful control of the structure, and therefore the physical and mechanical properties, a full understanding of the deformation habits of such materials under different conditions is essential. This perspective provides the context as to how the deformation temperature and fixing conditions influence the fixity and recovery behavior of RPSM polymers and what are the optimized conditions for RPSM. We hope that this will afford useful information for fabricating RPSM polymers with better memory properties and promote the technical development of new design methods of such materials for advanced applications © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1295–1299     

Chiral oxazoline substituted optically active poly(m‐phenylene)s: Synthesis and coupling polymerizations of (S)‐4‐benzyl‐2‐(3,5‐dihalidephenyl) oxazoline using transition metal catalysts

Optically active poly(m‐phenylene)s substituted with chiral oxazoline derivatives have been synthesized by the nickel‐catalyzed Yamamoto coupling reaction of optically active (S)‐4‐benzyl‐2‐(3,5‐dihalidephenyl)oxazoline derivatives (X = Br or I). The structures and chiroptical properties of the polymers were characterized by spectroscopic methods and thermal gravimetric analyses. The polymers showed higher absolute optical specific rotation values than their corresponding monomer, and showed a Cotton effect at transition region of conjugated main chain. The optical activities of the polymers should be attributed to the higher order structure such as helical conformations. Moreover, the helical conformation could be induced by addition of metal salts into polymer solutions. The polymers showed good thermal stabilities, which was attributable to the oxazoline side chains. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Recent advances in conjugated polymer energy storage

This review covers recent advances in conjugated polymers and their application in energy storage. Conjugated polymers are promising cost-effective, lightweight, and flexible electrode materials. The operating principles of conjugated polymers are presented within the framework of their potential for energy storage. Special focus is given to polyaniline electrodes. Recent advances are reviewed including new methods of synthesis, nanostructuring, and assembly. Also, covered are applications that take full advantage of the mechanical properties of conjugated polymers and future applications of these novel materials. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Biodegradable thermoset shape‐memory polymer developed from poly(β‐amino ester) networks

The purpose of this study was to develop a degradable thermoset shape‐memory polymer from poly(β‐amino ester) (PBAE) networks. PBAE was chosen to be the crosslinker as it is biodegradable and has been projected as a potential material for biomedical applications. The low glass transition temperature of PBAE was increased to a biomedically relevant range using methyl methacrylate and methyl acrylate as the linear chain builders. The thermo‐mechanical properties of the networks were tailored such that they exhibited onset of glass transition temperature in between the room temperature (22 °C) and the body temperature (37 °C). Free‐strain recovery tests under heating and isothermal conditions were performed to quantify shape‐memory behavior. Testing showed that sampled programmed at 10 °C initiated deformation recovery at a lower temperature and a faster rate as compared to programming at 60 °C. Higher thermal conductivity of water enabled the samples to recover faster in water than in air. Samples with higher PBAE crosslinking densities exhibited higher normalized mass loss under regular and accelerated conditions. The amount of water absorption in the networks also increased with the crosslinker concentration independent of the testing conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Hydrogel‐coated polyurethane/urea shape memory polymer foams

Shape memory polymers (SMPs) are a class of responsive polymers that have attracted attention in designing biomedical devices because of their potential to improve minimally invasive surgeries. Use of porous SMPs in vascular grafts has been proposed because porosity aids in transfer of fluids through the graft and growth of vascular tissue. However, porosity also allows blood to leak through grafts so preclotting the materials is necessary. Here hydrogels have been synthesized from acrylic acid and N‐hydroxyethyl acrylamide and coated around a porous SMP produced from lactose functionalized polyurea‐urethanes. The biocompatibility of the polymers used to prepare the cross‐linked shape memory material is demonstrated using an in vitro cell assay. As expected, the hydrogel coating enhanced fluid uptake abilities without hindering the shape memory properties. These results indicate that hydrogels can be used in porous SMP materials without inhibiting the shape recovery of the material. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1389–1395     

Theoretical description of unconstrained thermally induced shape‐memory recovery in crosslinked polyethylenes

A new theoretical approach based on the modified three‐element Eyring‐Halsey model was developed for the derivation of an equation describing the thermally induced recovery of predeformed and crystallized crosslinked polymers. The proposed approach takes into account the influence of crystallizable covalent network and of entangled slipped molecular chains. Modeling of thermally induced shape‐memory (SM) recovery strain and SM recovery rate detected at constant heating rate has been successfully performed for nearly linear and two short‐chain branched polyethylenes, which were crosslinked by peroxide. The values of material constants determined by fitting agree with the estimations existing in literature. Fitting results have shown that increase of degree of branching and crosslink density accompanied with reducing crystallinity results in increasing contribution of the entangled slipped chains to the total stored SM strain. The physical sense of main fitting parameters and their dependences on the material constants such as crystallinity are discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 815–822     

Stress memory polymers

Like shape memory polymers, a novel phenomenon of stress memory was shown in which the stress of a material can respond to an external stimulus. This concept was further enlightened by a switch‐spring‐frame model that would eliminate the limitation of existing models which overlooked the stimulus responsive nature of such polymers. The discovery being reported in this article was stemmed from a real case study into shape memory polymer fibers in compression stocking for varicose veins. The breakthrough of stress memory enabled researchers to develop applications needing stimuli‐responsive forces, which can broaden the horizon of such smart polymers in emerging smart products in many multidisciplinary fields such as sensors, stress garments, and massage devices, electronic skins, and artificial muscles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 893–898     

Recovery stress and work output in hyperbranched poly(ethyleneimine)‐modified shape‐memory epoxy polymers

In this study a series of hyperbranched modified shape‐memory polymers were subjected to constrained shape recoveries in order to determine their potential use as thermomechanical actuators. Materials were synthesized from a diglycidyl ether of bisphenol A as base epoxy and a polyetheramine and a commercial hyperbranched poly(ethyleneimine) as crosslinker agents. Hyperbranched polymers within the structure of the shape‐memory epoxy polymers led to a more heterogeneous network that can substantially modify mechanical properties. Thermomechanical and mechanical properties were analyzed and discussed in terms of the content of hyperbranched polymer. Shape‐memory effect was analyzed under fully and partially constrained conditions. When shape recovery was carried out with fixed strain a recovery stress was obtained whereas when it was carried out with a constraining stress the material performs mechanical work. Tensile tests at Tg^E′ showed excellent values of stress and strain at break (up to 15 MPa and almost 60%, respectively). Constrained recovery performances revealed rapid recovery stress generation and unusually high recovery stresses (up to 7 MPa) and extremely high work densities (up to 750 kJ/m³). The network structure of shape‐memory polymers was found to be a key factor for actuator‐like applications. Results confirm that hyperbranched modified‐epoxy shape memory polymers are good candidates for actuator‐like shape‐memory applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1002–1013     

A novel shape memory poly(ε‐caprolactone) network via UV‐triggered thiol‐ene reaction

A facile method to prepare shape memory polymers crosslinked by SiO₂ is described. A series of biodegradable shape memory networks were obtained through thiol‐ene reaction triggered by UV irradiation between surface‐thiol‐modified SiO₂ nanoparticles and end‐acrylate poly (ε‐caprolactone) (PCL). The highly selective thiol‐ene reaction ensured a uniform distribution of PCL chains between crosslinkers, contributing well‐defined network architecture with enhanced mechanical and shape‐memory properties. Thiol‐functionalized silica nanoparticle was characterized by using FTIR and XPS analysis, and ¹H NMR spectra was used to confirm the successful modification of terminal hydroxyl group of PCL diol. Surface‐modified silica particles were found well dispersible in acrylate‐capped PCL supported by SEM. Thermal and crystalline behaviors of the obtained polymers were analyzed by DSC and XRD, and DMA measurement proved good mechanical property. The shape memory behavior and tensile strength was somewhat tunable by the length of PCL. Acceptably, sample SiO₂‐SMP2k presented 99% recovery ratio and 97% shape fixity, and its relatively high tensile strength showed an attractive potential for biomedical application. Finally, a possible molecular mechanism accounting for the shape memory property was illustrated. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 692–701     

Degradation of poly(β‐amino ester) gels in alcohols through transesterification: Method to conjugate drugs to polymer matrices

Poly(β amino ester) (PβAE) polymers have received growing attention in the literature, owing to their ease of synthesis, versatile co‐monomer selection, and highly tunable degradation kinetics. As such, they have shown extensive potential in many biomedical applications as well. In this work, it is demonstrated for the first time that PβAE polymers containing primary and secondary amine groups can undergo degradation by primary alcohols via transesterification mechanism. While this work emphasizes an important aspect of solvent compatibility of these networks, it also represents an interesting, simple mechanism for post synthesis drug incorporation, with riboflavin conjugation being demonstrated as a model compound. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2019–2026     

In vitro hemocompatibility and cytotoxicity study of poly(2‐methyl‐2‐oxazoline) for biomedical applications

Since poly(2‐methyl‐2‐oxazolines) (PMeOx) attract high attention for the potential use in drug delivery, cytotoxicity, and hemocompatibility of a set of PMeOxs with molar masses in the range from 2 to 20 kDa are systematically investigated under standardized conditions in terms of molar mass, concentration and time dependency. PMeOx polymers are well tolerated in red blood cell aggregation and hemolysis assays without any damaging effects even at high concentrations up to 80 mg/mL. Only in long term cytotoxicity tests PMeOx polymers moderately influence cell viability in a time, concentration, and molar mass dependent manner. Referring to these results it can be concluded that PEtOx could be promising nonionic hydrophilic polymers for many biomedical applications without any cyto‐ and hemotoxic effects at typically used therapeutic doses. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Processing optimization: A way to improve the ionic conductivity and dielectric loss of electroactive polymers

Electro‐active polymers (EAPs) such as P(VDF‐TrFE‐CTFE) are greatly promising in the field of flexible sensors and actuators, but their low dielectric strength driven by ionic conductivity is a main concern for achieving high electrostrictive performance. It is well known that there is a quadratic dependence of the strain response and mechanical energy density on the applied electric field. This dependence highlights the importance of improving the electrical breakdown EAPs while reducing the dielectric losses. This article demonstrates that it is possible to dramatically increase the electrical breakdown and decrease the dielectric losses by controlling processing parameters of the polymer synthesis and fabrication procedure. As a result, an enhancement of around 70% is achieved in both the strain and blocking force. The effects on the dielectric losses of the polymer crystallinity, molecular weight, solvent purity, and crystallization temperature are also investigated. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1164–1173     

Bulky side chain effect of poly(N‐vinylcarbazole)‐based stacked polymer electrets on device performance parameters of transistor memories

Three poly(N‐vinylcarbazole) (PVK)‐based polymer electrets were synthesized through Friedel‐Crafts postfunctionalization for the function of charge storage in nonvolatile organic field effect transistor (OFET) memory devices. The bulky side chain effect of these stacked polymer electrets on the morphology, water contact angles, and memory characteristics were examined with regard to those of precursor PVK. The introduction of steric hindrance groups could interrupt the large length of π‐stacked structures in PVK and block the form of region‐regular structures from region‐random on external electric field. As a result, the memories based on the three modified polymers exhibited approximate memory windows of 32 V increased by 13 V with respect to PVK. Besides, the write‐read‐erase‐read cycles stability of the modified polymers was superior to that of PVK. Furthermore, we found that the holes were mainly located in the region of local π‐stacked structures and bulky π‐conjugated groups also acted as additional electron trapping sites. Molecular engineering of charge trapping site with tunneling polymers will be a promise strategy for the advance of transistor memory. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3554–3564     

Degradable polymer networks and star polymers based on mixtures of two cleavable dimethacrylate crosslinkers: Synthesis,characterization, and degradation

Mixtures of two cleavable dimethacrylate crosslinkers, the hydrolyzable di(methacryloyloxy‐1‐ethoxy)methane (DMOEM) and the thermolyzable 1,1‐ethylenediol dimethacrylate (EDDMA), were used for the preparation of neat crosslinker polymer networks, randomly crosslinked polymer networks of methyl methacrylate (MMA), and star polymers of MMA, using group transfer polymerization in tetrahydrofuran (THF). All star polymers and randomly crosslinked polymer networks containing mixtures of the hydrolyzable DMOEM and the thermolyzable EDDMA crosslinkers gave THF‐soluble final products when subjected to sequential thermolysis and hydrolysis, in this order. When applying sequential hydrolysis and thermolysis, only the star polymers with an EDDMA crosslinker content equal to or higher than 50% gave THF‐soluble final products. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5853–5870, 2009     

Electroactive organic anion‐doped polypyrrole as a low cost and renewable cathode for sodium‐ion batteries

We demonstrate here a remarkable electrochemical activation of polypyrrole chains by doping with redox‐active diphenylamine sulfonate anions. The organic redox dopant can not only serve as anionic counterions to enhance electrochemical activity of the polymer chains, but also contributes their redox capacity to the material. This organic‐polymer composite exhibits a quite high reversible capacity of 115 mA h g^?1, excellent rate capability and cycling stability, capable of serving as a low cost, and renewable cathode for Na‐ion batteries. Since the chemical doping method is simple and easily extendable for a large variety of organic anions and polymer networks, it is possible to adopt this new strategy for creating low cost and electrochemically active polymer materials for widespread electric storage applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Influence of programming strain rates on the shape‐memory performance of semicrystalline multiblock copolymers

Multiblock copolymers named PCL‐PIBMD consisting of crystallizable poly(ε‐caprolactone) segments and crystallizable poly[oligo(3S‐iso‐butylmorpholine‐2,5‐dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape‐memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL‐PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL‐PIBMD. Programming was conducted at 50 °C by elongation to ε_m = 50% with strain rates of 1 or 10 or 50 mm min^?1. The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X‐ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain‐induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape‐memory polymers with designed recovery forces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1935–1943     

Nonlinear rheology of model filled elastomers

Submitted to large sinusoidal strains, filled elastomers not only show a decrease in their storage modulus — the Payne effect, but also a nonlinear behavior — their response is not sinusoidal anymore and involves strain‐stiffening. We show in this study that the two effects can be separated thanks to large amplitude oscillatory shear experiments. The stress signal of filled elastomers consisting of a dispersion of silica particles into a polymeric matrix was decomposed into an elastic and a viscous part and we could observe simultaneously the Payne effect and a strain‐stiffening phenomenon. We showed that the strain‐stiffening was correlated with the Payne effect but came from various intricated effects. It most probably also has its origins in the finite extensibility of the polymer chains confined between solid particles, where the strain is larger. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Synthesis of low polydispersity polybutadiene and polyethylene stars by convergent living anionic polymerization

Star‐shaped polybutadiene stars were synthesized by a convergent coupling of polybutadienyllithium with 4‐(chlorodimethylsilyl)styrene (CDMSS). CDMSS was added slowly and continuously to the living anionic chains until a stoichiometric equivalent was reached. Gel permeation chromatography‐multi‐angle laser light scattering (GPC‐MALLS) was used to determine the molecular weights and molecular weight distribution of the polybutadiene polymers. The number of arms incorporated into the star depended on the molecular weight of the initial chains and the rate of addition of the CDMSS. Low molecular weight polybutadiene arms (M_n = 640 g/mol) resulted in polybutadiene star polymers with an average of 12.6 arms, while higher molecular weight polybutadiene arms (M_n = 16,000 g/mol) resulted in polybutadiene star polymers with an average of 5.3 arms. The polybutadiene star polymers exhibited high 1,4‐polybutadiene microstructure (88.3–93.1%), and narrow molecular weight distributions (M_w/M_n = 1.11–1.20). Polybutadiene stars were subsequently hydrogenated by two methods, heterogeneous catalysis (catalytic hydrogenation using Pd/CaCO₃) or reaction with p‐toluenesulfonhydrazide (TSH), to transform the polybutadiene stars into polyethylene stars. The hydrogenation of the polybutadiene stars was found to be close to quantitative by ¹H NMR and FTIR spectroscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 828–836, 2006