Photo‐hardenable and patternable PDMS/SU‐8 hybrid functional material: A smart substrate for flexible systems

The fabrication of flexible electronics and systems, using rigid and brittle materials directly produced on stretchable substrate, leads to some issues and incompatibilities. These include rigidity for processing and modular flexibility for applications, macroscopic flexibility, and local rigidity to shield components from strain, compatibility with technological steps, and at the same time allowing patterning and machining. The development of smart substrate materials which meet such needs is therefore a promising route for flexible systems. Here, we demonstrate that by mixing polydimethylsiloxane (PDMS) and SU‐8 photoresist, we obtain both a photo‐hardenable and patternable stretchable hybrid material. A set of PDMS/SU‐8 and baking process combinations have been tested to determine an effective photo‐sensitive mixture. A standard photolithographic approach has been used on tensile test samples demonstrating a local hardening of millimeter‐sized ultraviolet exposed features and a local strain reduction reaching 35%. In addition, surface topography analysis and wet‐etching techniques have been used to demonstrate a light‐induced molding process and a selective etching of micrometer‐sized ultraviolet exposed patterns. The combined functional properties of the following material, its simplicity of implementation, and the well‐known assets of PDMS and SU‐8 make the PDMS/SU‐8 material very interesting and promising for various applications, especially stretchable systems. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1281–1291     

A fully coupled thermo‐viscoelastic finite element model for self‐folding shape memory polymer sheets

The thermo‐mechanical response of heat activated shape memory polymers (SMPs) has been investigated using a thermo‐viscoelastic finite element analysis that accounts for external and internal heat sources. SMPs can be thermally stimulated by external heat sources, such as temperature and surface heat flux, or from internal viscous heating. Viscous heating can significantly affect the response of SMP sheets by increasing the temperature during pre‐strain, which accelerates stress relaxation. This stress relaxation results in a slower shrinking rate when the SMP is reheated. Viscous heating also causes an increase in temperatures during unconstrained recovery. The predicted results elucidate how the coupled thermo‐mechanical loading conditions affect folding and unfolding of SMP sheets in response to localized heating in a hinged region. A parametric study of sheet thickness, hinge width, degree of pre‐strain, and hinge surface temperature is also conducted. The validated results can provide guidelines for the design of functional, self‐folding structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1207–1219     

Cross‐linking induced thermoresponsive hydrogel with light emitting and self‐healing property

Development of self‐healing hydrogels with thermoresponse is very important for artificial smart materials. In this article, the self‐healing hydrogels with reversible thermoresponses were designed through across‐linking‐induced thermoresponse (CIT) mechanism. The hydrogels were prepared from ketone group containing copolymer bearing tetraphenyl ethylene (TPE) and cross‐linked by naphthalene containing acylhydrazide cross‐linker. The mechanical property, light emission, self‐healing, and thermo‐response of the hydrogels were investigated intensively. With regulation of the copolymer composition, the hydrogels showed thermoresponse with the LCST varied from above to below body temperature. At the same time, the hydrogels showed self‐healing property based on the reversible characteristic of the acylhydrazone bond. The hydrogel also showed temperature‐regulated light emission behavior based on AIE property of the TPE unit. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 869–877     

Synthesis of bisphenol A‐free oligomeric phthalonitrile resins with sulfone and sulfone‐ketone containing backbones

Two new oligomeric sulfone and sulfone‐ketone containing phthalonitrile (PN) resins with excellent processability have been developed. The PN monomers were prepared from the reaction of an excess amount of bisphenol S with 4‐(chlorophenyl)sulfone or 4,4‐dichlorobenzophenone in the presence of a base in a solvent mixture (dimethylsulfoxide/toluene), followed by end‐capping with 4‐nitro‐PN in a two‐step, one‐pot reaction. These PN resins exhibited good viscosities and cure times for molding into various shapes. After being thermally cured to yield crosslinked polymers, these polymers demonstrated superb mechanical properties, thermo‐oxidative stability, and maintained good dielectric properties. Published 2016. 1 J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1639–1646     

Synthesis and characterization of poly(dimethylsiloxane‐urethane) elastomers: Effect of hard segments of polyurethane on morphological and mechanical properties

A series of poly(dimethylsiloxane‐urethane) elastomers based on hexamethylenediisocyanate, toluenediisocyanate, or 4,4′‐methylenediphenyldiisocyanate hard segment and polydimethylsiloxane (PDMS) soft segment were synthesized. In this study, a new type of soft‐segmented PDMS crosslinker was synthesized by hydrosilylation reaction of 2‐allyloxyethanol with polyhydromethylsiloxane, using Karstedt's catalyst. The synthesized soft‐segmented crosslinker was characterized by FT‐IR, ¹H, and ¹³C NMR spectroscopic techniques. The mechanical and thermal properties of elastomers were characterized using tensile testing, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamical mechanical analysis measurements. The molecular structure of poly(dimethylsiloxane‐urethane) membranes was characterized by ATR‐FTIR spectroscopic techniques. Infrared spectra indicated the formation of urethane/urea aggregates and hydrogen bonding between the hard and soft domains. Better mechanical and thermal properties of the elastomers were observed. The restriction of chain mobility has been shown by the formation of hydrogen bonding in the soft and hard segment domains, resulting in the increase in the glass‐transition temperature of soft segments. DSC analysis indicates the phase separation of the hard and soft domains. The storage modulus (E′) of the elastomers was increasing with increase in the number of urethane connections between the hard and soft segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2980–2989, 2006     

Apparent depth‐dependent modulus and hardness of polymers by nanoindentation: Investigation of surface detection error and pressure effects

Nanoindentation is a widely used technique to characterize the mechanical properties of polymeric materials at the nanoscale. Extreme surface stiffening has been reported for soft polymers such as poly(dimethylsiloxane) (PDMS) rubber. Our recent work [J. Polym. Sci. Part B Polym. Phys. 2017 , 55, 30–38] provided a quantitative model which demonstrates such extreme stiffening can be associated with experimental artifacts, for example, error in surface detection. In this work, we have further investigated the effect of surface detection error on the determination of mechanical properties by varying the sample modulus, instrument surface detection criterion, and probe geometry. We have examined materials having Young's moduli from ∼2 MPa (PDMS) to 3 GPa (polystyrene) using two different nanoindentation instruments (G200 and TI 950) which implement different surface detection methods. The results show that surface detection error can lead to apparent large stiffening. The errors are lower for the stiffer materials, but can still be significant if care is not taken to establish the range of the surface detection error in a particular experimental situation. We have also examined the effect of pressure beneath the probe on the nanoindentation‐determined modulus of polystyrene with different probe geometries. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 414–428     

Improving waterproof/breathable performance of electrospun poly(vinylidene fluoride) fibrous membranes by thermo‐pressing

Facing the ever‐increasing demand for waterproof/breathable materials, a rapid and efficient fabrication method of these functional materials with excellent performance as well as robust mechanical properties remains challenging. Herein, a simple and scalable strategy referred to as thermo‐pressing is introduced to improve the waterproof/breathable performance and mechanical properties of electrospun PVDF fibrous membranes. The synergistic effect of temperature and pressure acted on the electrospun PVDF membranes on the fiber morphology and crystal structure was investigated, which can be able to effectively enhance waterproof performance and mechanical properties, endowing the as‐prepared membranes with a modest breathability. The membranes thermo‐pressed at 150 °C with a pressure of 8.27 MPa exhibit robust tensile strength of 40.65 MPa, which is superior to those of the previous reports (below 32.8 MPa). Notably, the optimized membranes enable to show a high hydrostatic pressure of 102 kPa, good WVTR of 10.87 kg m⁻² d⁻¹ and excellent abrasion resistance, which implies that the thermo‐pressing is an efficient and facile way to steer the fiber morphology and crystal structure of electrospun membranes to improve their application performance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 36–45     

Star‐shaped siloxane polymers with various cyclic cores: Synthesis and properties

Six new star‐shaped polydimethylsiloxane (PDMS) with various cyclic siloxane cores were synthesized by the “grafting onto” method. The polymers obtained feature low dispersity and well‐defined structures. Two of them, Q ₈ ‐PDMS and D ₁₂ ‐PDMS , have a three‐dimensional spatial structure traditional for star‐shaped polymers where the arms are arranged in all directions from the branching center. The other four polymers, D ₄ ‐PDMS – D ₈ ‐PDMS , have quite a different spatial geometry (cis‐structure) where all the PDMS‐arms are arranged on one side of the branching center plane. Such star‐shaped structures were not reported before. The structures and purity of the polymers obtained were confirmed using a set of physicochemical methods of analysis. The effect of the macromolecule structure on the properties of the target polymers was identified. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019     

Temperature‐dependent phase‐segregation behavior and antifouling performance of UV‐curable methacrylated PDMS/PEG coatings

Controllable phase segregation adjustment for immiscible polymer blends has always been tough, which hinders the development of amphiphilic antifouling coatings from more accessible blends. Herein, methacrylated poly(dimethylsiloxane) (PDMS‐MA) was synthesized and mixed with poly(ethylene glycol)methylether methacrylate (PEG‐MA). It was interestingly discovered that these PDMS‐MA/PEG‐MA blends displayed upper critical solution temperatures (UCST) due to thermo‐induced conformational change of PEG‐MA and the UCST changed with PDMS‐MA/PEG‐MA mass ratios. Micro‐/nano‐phase segregation, nanophase segregation, or homogenous morphology were therefore achieved. These PDMS‐MA/PEG‐MA blends with different mass ratios were UV‐cured under varying temperatures to fabricate coatings. Their surface morphology and wettability are readily adjusted by phase segregation. For the first time, highly hydrophilic surface was achieved for coatings with microphase segregation because of the exposure of PEG‐rich domains, which exhibited an enhanced protein resistance against bovine serum albumin (BSA). Anti‐bacterial performance (Shewanella loihica) was also observed for these PDMS/PEG coatings. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1612–1623     

Polyisobutylene‐based polyurethanes. VIII. Polyurethanes with ‐O‐S‐PIB‐S‐O‐ soft segments

We describe the synthesis, characterization, and select properties of a novel polyurethane (PU) prepared using a new polyisobutylene diol, HO‐CH₂CH₂‐S‐PIB‐S‐CH₂CH₂‐OH, soft segment and conventional hard segments. The diol is synthesized by terminal functionalization of ally‐telechelic PIB followed by low‐cost thiol‐ene click chemistry. Properties of ‐S‐ containing PU (PIB_S‐PU) containing 72.5% PIB were investigated and compared to similar PUs made with HO‐PIB‐OH (PIB_O‐PU). Hydrolytic resistance was studied by contact with phosphate‐buffered saline, oxidative resistance by immersing in concentrated HNO₃, and metal ion oxidation resistance by exposure to CoCl₂/H₂O₂. Hydrolytic and oxidative resistances of PIB_S‐PU and PIB_O‐PU are similar and superior to a commercial PDMS‐based PU, Elast‐Eon? E2A. According to ¹H NMR spectroscopy the ‐S‐ in PIB_S‐PUs remained unchanged upon treatment with HNO₃, however, oxidized mainly to ‐SO₂‐ by CoCl₂/H₂O_2. Static mechanical properties of PIB_S‐PU and PIB_O‐PU are similar, except creep resistance of PIB_S‐PU is surprisingly superior. The thermal stability of PIB_S‐PUs is ～15 °C higher than that of PIB_O‐PU. FTIR spectroscopy indicates H bonded S atoms (N‐H…S) between soft and hard segments, which noticeably affect properties. DSC and XRD studies suggest random low‐periodicity crystals dispersed within a soft matrix. Energy dispersive X‐ray spectroscopy–scanning electron microscopy indicates homogeneous distribution of S atoms on PIB_S‐PU surfaces. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1119–1131     

Positron annihilation properties of copolyimides and copolyamides with microphase‐separated structures

The positron annihilation lifetime (PAL) of a series of copolyimides and copolyamides with microphase‐separated structures was measured to investigate the effects of different hard‐segment polymers on the PAL properties of soft‐segment domains of poly(dimethyl‐siloxane) (PDMS) and poly(ethylene oxide) (PEO). The lifetime (τ₃) and intensity (I₃) of the long‐lived component are given as a function of the PDMS or PEO content for a series of copolymers, of which the density roughly obeys the additive rule except for the PDMS‐segmented copolyamides. The PDMS‐segmented copolyimides and copolyamides show much smaller I₃ values than those estimated from the additive rule. The lifetime distribution of the long‐lived component for the PDMS‐segmented copolyamides is composed of two components. The longer‐lifetime component is attributed to pure PDMS domains, and the shorter‐lifetime component is attributed to the polyamide domains, intermediate phases, and PDMS domains containing small amounts of short amide blocks. Despite the high PDMS content, the latter component is rather large. Thus, the positronium formation in the PDMS domains of the copolyimides and copolyamides is effectively reduced. This can be explained by the combination of the difference in the electron affinity of the PDMS and polyimide or polyamide segments and the incomplete phase separation. The PEO‐segmented copolyimides show much smaller I₃ values than those predicted from the additive rule. This is likely attributable to the effects of the intermediate phases. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1123–1132, 2000     

On the relevance of the 8‐chain model and the full‐network model for the deformation and failure of networks formed through photopolymerization of multifunctional monomers

Crosslinked networks were synthesized by copolymerization of mono‐functional tert‐butyl acrylate (tBA) with diethyleneglycol dimethacrylate (DEGDMA) or polyethylene glycol dimethacrylates (PEGDMA). By varying the chain length and concentration of the difunctional PEGDMA, we obtained tBA‐PEGDMA copolymer networks while by varying the concentration of difunctional DEGDMA, we obtained tBA‐DEGDMA crosslinked networks. The various materials were submitted to large deformations through uniaxial tension tests. For moderate weight percent of crosslinking agent, up to 20%, the networks showed standard S‐shape stress–strain curves, characteristic of rubber‐like elasticity. Two macromolecular models, the 8‐chain model and the full‐network model, were applied to fit the uniaxial tensile response of the materials. Both models provide good representations of the overall uniaxial stress–strain response of each material. After fitting to stress–strain data, the network models were employed to predict the shear modulus and the elongation at break. Neither the 8‐chain nor the full network model were capable of predicting the failure strain or shear modulus, indicating these models are best used to describe stress–strain relations rather than predict mechanical properties for the network polymers considered here. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1226–1234, 2008     

Photo‐induced thiol‐ene polysulfide‐crosslinked materials with tunable thermal and mechanical properties

Photo‐induced thiol‐ene crosslinked polymeric networks have been extensively explored in constructing a variety of new materials with enhanced mechanical properties for optical, biomedical, and sensing applications. Toward the broad applications, however, tunable mechanical properties are greatly desired. Here, an effective approach utilizing high‐molecular‐weight methacrylate copolymers having pendant thiol and vinyl groups (MCPsh and MCPenes) to modulate thermal and mechanical properties of photo‐induced thiol‐ene crosslinked materials is reported. The MCP copolymers are synthesized by an industrially friendly polymerization method, followed by post‐modification including either a facile coupling reaction or reductive cleavage. Upon UV irradiation, thiol‐ene reactive blends of MCPsh and MCPenes yield highly crosslinked materials through the formation of flexible sulfide linkages. These polysulfide‐crosslinked materials based on rigid MCP backbones exhibit enhanced mechanical properties. Further, their thermal and mechanical properties are tuned by modulating monomer compositions of MCPs as well as varying numbers of pendant SH or vinyl groups (i.e., extent of crosslinking densities). This approach is versatile and effective for development of high performance polymeric materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3060–3068     

Thermo‐/moisture‐responsive shape‐memory effect of poly(2‐ethyl‐2‐oxazoline) networks

In this work, poly(2‐ethyl‐2‐oxazoline) (PEtOx) is crosslinked to realize a moisture‐ and thermo‐responsive shape‐memory polymer. The obtained PEtOx networks exhibit excellent shape‐memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape‐memory cycles. The trigger temperature (T_trig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1053–1061     

Improved thermal and mechanical properties of polybenzoxazines based on alkyl‐substituted aromatic amines

The thermal and mechanical properties of polybenzoxazine thermoset networks containing varying amounts of phenolic Mannich bridges, arylamine Mannich bridges, and methylene bridges have been investigated. In materials based on m‐toluidine and 3,5‐xylidine, the onset of thermal degradation is delayed until around 350 °C with no significant effect on the final char yield. The first of the three weight‐loss events usually seen in aromatic amine‐based polybenzoxazines is absent in these two materials. Materials with additional amounts of arylamine Mannich bridges and methylene bridges show improved mechanical properties, including higher crosslink densities and rubbery plateau moduli. Correlations between the observed mechanical properties and network structures are established. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3289–3301, 2000     

Shape‐memory effect in hyperbranched poly(ethyleneimine)‐modified epoxy thermosets

A series of shape‐memory epoxy thermosets were synthesized by crosslinking diglycidyl ether of bisphenol A with mixtures of commercially available hyperbranched poly(ethyleneimine) and polyetheramine. Thermal, mechanical and shape‐memory properties were studied and the effect on them of the content and structure of the hyperbranched polymer was discussed. Measurements showed that the glass transition temperature can be tailored from 60 °C to 117 °C depending on the hyperbranched polymer content, and all formulations showed an appropriate glassy/rubbery storage modulus ratio. Shape‐memory programming was carried out at TgE′ given the excellent mechanical properties of the materials, with maximum stress and failure strain up to 15 MPa and 60%, respectively. The resulting shape‐memory behavior was excellent, with maximum shape recovery and shape fixity of 98% as well as a fast shape‐recovery rate of 22%/min. The results show that hyperbranched poly(ethyleneimine) as a crosslinking agent can be used to enhance mechanical and shape‐memory properties with different effects depending on the crosslinking density. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 924–933     

Synthesis,self‐assembly,and thermosensitivity of amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymers

In this article, the synthesis and self‐assembly of a novel well‐defined biocompatible amphiphilic POEGMA‐PDMS‐POEGMA triblock copolymer were studied. The copolymer was synthesized by atom transfer radical polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) using α,ω‐dibromo polydimethylsiloxane macroinitiator (Br‐PDMS‐Br). Br‐PDMS‐Br was synthesized through the esterification of α,ω‐hydroxypropyl polydimethylsiloxane and 2‐bromoisobutyryl bromide. The structures of the copolymers were confirmed by proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The copolymers showed reversible aggregation in response to temperature cycles with a lower critical solution temperature (LCST) between 61 and 66 °C, as determined by ultraviolet‐visible spectrophotometry and dynamic light scattering. The LCST values increased in proportion to the length of the hydrophilic block and were lower than that of the POEGMA homopolymer. The self‐assembly behavior of the copolymers in aqueous solution was investigated by fluorescence spectroscopy and transmission electron microscopy. The critical micelle concentration value (1.08–0.26 10^?6 mol L^?1) decreased as the length of the POEGMA chain increased. The POEGMA‐PDMS‐POEGMA copolymers can easily self‐assemble into spherical micelles in aqueous solution. Such biocompatible block copolymers may be attractive candidates as ‘‘smart'' thermo‐responsive drug delivery systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2684‐2691     

Additive‐like amounts of HDPE prevent creep of molten LDPE: Phase‐behavior and thermo‐mechanical properties of a melt‐miscible blend

Low‐density polyethylene (LDPE) is the preferred type of polyolefin for many medical and electrical applications because of its superior purity and cleanliness. However, the inferior thermo‐mechanical properties as compared to, for example, high‐density polyethylene (HDPE), which arise because of the lower melting temperature of LDPE, constitute a significant drawback. Here, we demonstrate that the addition of minute amounts of HDPE to a LDPE resin considerably improves the mechanical integrity above the melting temperature of LDPE. A combination of dynamic mechanical analysis and creep experiments reveals that the addition of as little as 1 to 2 wt% HDPE leads to complete form stability above the melting temperature of LDPE. The investigated LDPE/HDPE blend is found to be miscible in the melt, which facilitates the formation of a solid‐state microstructure that features a fine distribution of HDPE‐rich lamellae. The absence of creep above the melting temperature of LDPE is rationalized with the presence of tie chains and trapped entanglements that connect the few remaining crystallites. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 146–156     

Thiolactone chemistry for the synthesis of functional silicone‐based amphiphilic co‐networks

A series of amphiphilic co‐networks (ACNs) is prepared in a straightforward way via thiolactone chemistry by crosslinking a multivalent thiolactone‐functional poly(dimethylsiloxane) building block with poly(ethylene glycol) diacrylates. Formation of the networks is triggered by the addition of an amine, of which the nucleophilicity and steric bulk control the curing kinetics. Furthermore, some of the crosslinks can be sacrificed to introduce a fluorescent group or dye via a thia‐Michael addition, without affecting the bulk mechanical properties and swelling capabilities. The obtained ACNs exhibit a unique set of properties because of their nanophase separation, resulting in hydrophilic PEG and hydrophobic PDMS phases. Hence, swelling in both water and organic solvents is observed, of which the extent can be tuned by varying the overall PEG content. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 322–333     

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