Immobilization of polyisobutene in semi-interpenetrating polymer network architecture

The entrapment of linear polyisobutene (PIB) in semi-IPN architecture is shown to be as efficient as it is in cross-linkable telechelic PIB based full IPN architectures as far as the suppression of cold flow is concerned. Indeed, homogeneous linear PIB/cross-linked polycyclohexylmethacrylate (PCHMA) semi-IPNs containing from 20 to 70 wt% PIB and synthesized without solvent show no cold flow and higher mechanical properties than those of linear PIB or 50 wt% PIB containing blend. In addition, the particular barrier properties toward gas and water are preserved. Those properties arise from the phase co-continuity morphology of the semi-IPN materials which moreover compares with that of corresponding IPNs. A systematic study of the synthesis conditions (nature of the initiator, temperature, cross-linking density) showed that the reacting mixture viscosity is an important parameter that controls the phase separation degree in the final material.     

Elaboration and properties of renewable polyurethanes based on natural rubber and biodegradable poly(butylene succinate) soft segments

Natural rubber (NR) is a renewable bio‐based polymer, while poly(butylene succinate) (PBS) belongs to the family of biodegradable renewable polymers. In this article, novel polyurethanes (PUs) were prepared using hydroxyl telechelic natural rubber (HTNR) and hydroxyl telechelic poly(butylene succinate) (HTPBS) as soft segments, and using toluene‐2,4‐diisocyanate (TDI) and 1,4‐butanediol (BDO) as hard segment. HTPBS oligomers of = 2000 and 3500 g mol^?1 were synthesized by bulk polycondensation of succinic acid (SA) with BDO. The polyurethane materials were obtained by casting process after solvent evaporation. The influence of the hard segment content and the molecular weight of HTPBS on the materials’ thermo‐mechanical properties were investigated by means of tensile testing, DSC, TGA, and DMTA. The obtained polyurethanes were amorphous with phase separations between hard and soft segments as well as between HTNR and HTPBS segments, and they exhibited good physical properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42943.     

New perfectly difunctional organolithium initiators for block copolymer synthesis: 2. Difunctional polymers of dienes and of their triblocks copolymers with styrene

New organodilithium initiators were prepared in a hydrocarbon solvent in the absence of any polar additive. Although these initiators are insoluble when they are synthesized, they may be easily purified and reacted with dienes to give perfectly telechelic polydienes having unimodal distributions and low dispersity. A good agreement between experimental and theoretical molecular weights was observed. The polymer microstructures were similar to those of polymers initiated by butyllithium in the same solvent. Triblock thermoplastic elastomers were also prepared, the characteristics of which are given. The mechanical properties of a S.B.S. sample support also the claim of a good initiating ability and difunctionality of these initiators.     

Pressure sensitive adhesives based on interpolymer complexes

Adhesion of noncovalent complexes formed between complementary polymers bearing functional groups capable of hydrogen bonding or ionic interactions is reviewed. The rational design of novel adhesive materials with tailored properties requires a molecular insight into the mechanism of their self-assembly. At the most fundamental molecular level, strong adhesion is the result of a delicate balance between two generally conflicting properties: high energy of intermolecular cohesion and large free volume. These conflicting properties can be achieved in self-assembling interpolymer complexes. The adhesive and mechanical properties of the polymer blends can easily be controlled by blend composition and the type of intermolecular bonding (hydrogen bonding or ionic interactions or combination of both), whereas their solubility and water absorbing capacity are dictated by the hydrophilicity of the parent components. Innovative self-adhering pressure sensitive adhesives are based either on nonstoichiometric interpolymer complexes or on stoichiometric complexes of long-chain polymers with telechelic oligomers. Once the molecular mechanism of self-assembly of adhesive materials has been established, the molecular design of new adhesives with tailored properties becomes feasible. The number of functional polymers suitable to serve as parent components for producing novel adhesives is very large, suggesting that the polymer blending approach, based on molecular design considerations, may revolutionize the adhesive industry in the coming decades.     

Bonding and Debonding on Demand with Temperature and Light Responsive Supramolecular Polymers

Due to their low melt viscosity, competitive adhesive properties, and the stimuli‐responsive nature of supramolecular interactions, various supramolecular polymers have recently been investigated as adhesives with on‐demand (de)bonding capability. The adhesive properties of a series of hydrogen‐bonded supramolecular polymer networks based on a telechelic poly(ethylene‐co‐butylene) (PEB) terminated with isophthalic acid (IPA) groups and a series of bifunctional pyridines (Py) are reported herein. These supramolecular polymers microphase segregate into an IPA‐Py rich hard phase and an amorphous low‐glass‐transition PEB phase, and their properties depend on the nature of the pyridine‐carrying monomer. Rheological measurements show that the polymers disassemble into low‐viscosity melts when heated above the melting or glass transition temperature of the hard phase. Lap joints bonded with the polymers display a shear strength of up to 1.3 MPa, and debonding is possible in less than 10 s upon heating or exposure to UV–light; to enable rapid light‐induced (de)bonding, a light–heat converter is introduced. Cyclic bonding/debonding experiments reveal that the shear strength remains unchanged over five cycles and demonstrate that the process is very robust.     

Telechelic elastomers

Telechelic elastomers, polymers with reactive terminal groups, can be prepared in emulsion and solution systems. Examples of characterization of the polymers and preparation of a mercapto telechelic copolymer in an emulsion system and of mercapto-, hydroxy-, and aziridinyl-telechelic elastomers in solution systems are given. The elastomers were cured in peroxide or sulfur-accelerator formulations. The telechelic polymers exhibited enhanced stress-strain and dynamic properties in comparision to those of the controls. In tread formulations, outstanding properties were obtained for the mercapto-and azieridinyl-telechelic butadiene-styrene copolymers.     

Syntheses and properties of macromolecular fullerenes,a review

The recent progress and prospects of macromolecular fullerenes with respect to their syntheses and properties are compiled and discussed. The variety of macrofullerenes with emphasis on C₆₀ and C₇₀ is presented and synthetic concepts of polymer derivatives of fullerenes are outlined. After a concise consideration of the fundamentals of fullerene reactivity, both major types of fullerene-containing polymers, main-chain and side-chain polymers, together with special types, such as telechelic, macrocyclic, dendrimeric and star-shaped fullerene materials, are covered. Also, the synthesis of fullerene-containing copolymers via radical polyreactions and preparative aspects of surface-attached fullerenes are described. The properties of the macromolecular fullerene derivatives are discussed in view of their structure and application. Finally, the role of macrofullerenes for new materials or their precursors is elucidated. © 1999 Society of Chemical Industry     

Phase behavior of hyperbranched polymer solutions in mixed solvents

Hyperbranched polymers get more and more interesting for several applications due to their tailor-made properties influenced by the architecture and the functional groups of the polymer. The liquid–liquid phase behavior of hyperbranched polymer solutions is an important issue for various applications. Until now, the calculations of these phase equilibria are limited to solutions of hyperbranched polymers in a single solvent using Lattice Cluster theory (LCT). The LCT permits the incorporation of the architecture of the polymer directly in thermodynamic properties, as the Helmholtz energy, without any additional adjustable parameter.This papers aims at the extension of the LCT to ternary systems made from hyperbranched polymer (Boltorn H20), water and propanol. The derived expression for the Helmholtz energy allows for the first time the prediction of miscibility gaps in the ternary system based on experimental data of the binary subsystems.Additionally to the architecture of hyperbranched polymers also the functional groups of hyperbranched polymers play an important role in phase equilibrium. In order to include the association phenomena in the theoretical framework, a modified version of the Wertheim association theory is used. However, during the application of this approach the model lost its predictive power, because ternary data must be used for the parameter estimation procedure. Nevertheless, the combined theory is able to model the experimental phase behavior within the experimental accuracy.     

Polymers with upper critical solution temperature behavior in alcohol/water solvent mixtures

Thermoresponsive polymers are of great importance in numerous nanotechnological and biomedical applications. Compared to polymers that undergo a lower critical solution temperature (LCST) phase transition in aqueous solution, i.e., demixing occurs upon heating, polymers exhibiting the reversed upper critical solution temperature (UCST) behavior in aqueous solution have been much less documented as it is more challenging to achieve this behavior in aqueous solutions. Furthermore, the high sensitivity of UCST behavior to minor variation in polymer structure and solution composition hampered the development of applications based on these polymers [18]. However, polymers with UCST transition in alcohol/water solvent mixtures are more commonly reported and exhibit promising properties for the preparation of ‘smart’ materials. This review will focus on the theory and development of such polymers with UCST behavior in alcohol/water solvent mixtures. By highlighting reported examples of UCST polymers in alcohol/water solvent mixtures, we aim to demonstrate the versatility and potential that such UCST polymers possess as biomedical and ‘smart’ materials.     

Porous ultrathin-shell microcapsules designed by microfluidics for selective permeation and stimuli-triggered release

Microcapsules are versatile delivery vehicles and widely used in various areas. Generally, microcapsules with solid shells lack selective permeation and only exhibit a simple release mode. Here, we use ultrathin-shell water-in-oil-in-water double emulsions as templates and design porous ultrathin-shell microcapsules for selective permeation and multiple stimuli-triggered release. After preparation of double emulsions by microfluidic devices, negatively charged shellac nanoparticles dispersed in the inner water core electrostatically complex with positively charged telechelic α,ω-diamino functionalized polydimethylsiloxane polymers dissolved in the middle oil shell at the water/oil interface, thus forming a porous shell of shellac nanoparticles cross-linked by telechelic polymers. Subsequently, the double emulsions become porous microcapsules upon evaporation of the middle oil phase. The porous ultrathin-shell microcapsules exhibit excellent properties, including tunable size, selective permeation and stimuli-triggered release. Small molecules or particles can diffuse across the shell, while large molecules or particles are encapsulated in the core, and release of the encapsulated cargos can be triggered by osmotic shock or a pH change. Due to their unique performance, porous ultrathin-shell microcapsules present promising platforms for various applications, such as drug delivery.     

Nanofibrous nonwovens based on dendritic‐linear‐dendritic poly(ethylene glycol) hybrids

Dendritic‐linear‐dendritic (DLD) hybrids are highly functional materials combining the properties of linear and dendritic polymers. Attempts to electrospin DLD polymers composed of hyperbranched dendritic blocks of 2,2‐bis(hydroxymethyl) propionic acid on a linear poly(ethylene glycol) core proved unsuccessful. Nevertheless, when these DLD hybrids were blended with an array of different biodegradable polymers as entanglement enhancers, nanofibrous nonwovens were successfully prepared by electrospinning. The pseudogeneration degree of the DLDs, the nature of the co‐electrospun polymer and the solvent systems used for the preparation of the electrospinning solutions exerted a significant effect on the diameter and morphology of the electrospun fibers. It is worth‐noting that aqueous solutions of the DLD polymers and only 1% (w/v) poly(ethylene oxide) resulted in the production of smoother and thinner nanofibers. Such dendritic nanofibrous scaffolds can be promising materials for biomedical applications due to their biocompatibility, biodegradability, multifunctionality, and advanced structural architecture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45949.     

Polymer heterogeneity in waterborne coatings

An overview is presented of the progress in understanding polymer heterogeneity over the last 20 years and how this has contributed to the improvement of coatings. Solvent-based polymers are homogeneous in nature, since all polymeric materials tend to be dissolved in the same solvent mixture. This is different for most waterborne polymers, which tend to be present in a compartmentalized way. Most polymeric materials are present in particles, which are separated by the continuous aqueous phase. This gives excellent opportunities to create particle morphologies that form the basis for the film morphology after drying of the coating. This article gives an overview of the various types of heterogeneity which are accessible in waterborne polymers and will show how heterogeneity in the polymer can contribute to the solution of several persistent problems of the coating industry.     

Zur phasentrennung von polymergemischen in lösung

Usually, mixtures of solutions of two different polymers in the same solvent are incompatible. This incompatibility leads to an intensive turbidity of the mixture and finally, to the formation of two phases. The turbidity disappears on dilution with the same solvent, because the polymers are compatible below a certain polymer concentration c_kr. In principle, the same effects occur also with mixtures of polymers in the solid state (polymer blends), but here the aggregation of the microphases is impossible due to the high viscosity. Up to now, there is little known about the composition of the two phases above c_kr. Therefore, we studied the distribution of two different polymersin solution regarding molecular weight and concentration into both phases. It was varied the polymer ratio, the molecular weight, the overall concentration and the nature of the solvent. Polystyrene and polyvinyl acetate were used as polymers because they can easily be separated from each other which is necessary when analysing the different phases; this analytical separation was carried out for each individual phase. The following results were obtained: Each phase contains both polymers; in addition there occurs a fractionation according to molecular weight during the phase separation for both polymers. The polymer distribution in the two phases regarding molecular weight, amount of polymer, and concentration depends not only upon initial concentration, molecular weight and weight ratio of the two polymers but also upon the different degree of solvation of the macromolecules in different solvents. When mixtures of solvents are used, an additional partially separation of the solvent into both layers takes place.     

Polymer-polymer composites fabricated by the in situ release and coalescence of polymer chains from their inclusion compounds with urea into a carrier polymer phase

Inclusion compounds (ICs) can be formed between small-molecule hosts and guest polymers, where the crystalline host lattice confines the guest polymers to occupy narrow cylindrical channels. The included polymers are highly extended by the narrow channel diameters and are separated from neighboring polymer chains by the walls of the small-molecule host lattice. It is possible to coalesce the polymer chains from their ICs by exposure to a solvent for the small-molecule host which is not a solvent for the included polymer chains. When crystallizable polymers are coalesced from their ICs by solvent treatment, they are observed to crystallize in an extended-chain morphology accompanied by much less chain-folding than occurs when crystallization of the same polymers take place from their disordered melt or solution environments. In this report we outline our initial efforts to create polymer-polymer molecular composites based on the coalescence of polymer chains from their IC crystals with urea, which were previously embedded in a carrier polymer phase. Both film and fiber composites made with chemically identical or distinct IC-included and carrier polymers are described. Water vapor permeation, differential scanning calorimetry (DSC) and microscopic observations are used to probe these composites; and several applications are suggested. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 281–287, 1997     

Morphology and Mechanical Properties of PLLA and PCL Scaffolds

Human tissue engineering, comprising methods and tools to create implants, is a promising although as yet a very underdeveloped field of research into the regeneration of specific damaged or necrotic tissue. Porous scaffolds play an important role in tissue engineering. The porous cell culture scaffolds in this study were produced through thermally induced phase separation (lyophilization). This technique yields considerable variations in scaffold microstructures (pore size and morphology) as a function of the polymer, solvent and thermal processing. PLLA and PCL were used with chloroform, 1,4-dioxane and water as solvent. We observed a decrease in mechanical properties with increasing pore size in the two polymers under study. However, we found that PLLA, which possesses larger pore sizes than PCL, showed superior mechanical properties, which we explain in terms of crystallinity.     

Segmented copolymers of uniform tetra-amide units and poly(phenylene oxide): 3. Influence of tetra-amide content

Copolymers of telechelic poly(2,6-dimethyl-1,4-phenylene ether) (PPE) segments and crystallisable T6T6T units (two-and-a-half repeating unit of nylon-6,T) of uniform length were synthesised. The influence of the T6T6T content (0-20 wt%), the purity of the telechelic PPE and uniformity of the T6T6T segment length on the thermal mechanical (DMA) properties were studied. The polymers are semi-crystalline materials with a high T_g/T_m ratio of above 0.8. Increasing the T6T6T content (0-20 wt%) has little effect on the T_g transition region, but the modulus of the rubbery plateau increases strongly (0-13 MPa) and the flow temperature increases slightly as well (260-275 °C). The materials are transparent when the T6T6T content is below 10 wt%. Surprisingly copolymers based on telechelic PPE of narrow molecular weight distribution had lower crystallinity. The uniformity of the T6T6T segment length seems to have little effect on the properties of the copolymer, as long as at least 70% of the units are of one length.     

Co-extruded multilayer shape memory materials: Comparing layered and blend architectures

Shape memory polymers (SMPs) are a class of materials that exhibit the ability to form multiple temporary shapes, with shape change most often occurring upon exposure to heat. Applications of SMPs can be found in many areas such as sensors, packaging, smart fabrics, and most commonly medicine. Often, thermoplastic SMPs are based on block copolymer or blend morphologies that create two distinct phases, which are on the nano- or micro-scale respectively, to facilitate shape fixing and shape recovery. Forced assembly multilayer co-extrusion of commercially available polyurethane (PU) and polycaprolactone (PCL) polymers was used to create a continuous periodic alternating layer architecture that exhibits shape memory behavior. Similar shape memory properties were observed between PU/PCL layers and blends at 50/50 volume composition; however, offset compositions showed significantly different behavior. The layered structure was maintained across all compositions, as compared with blends that exhibit a composition dependent morphology. The difference in morphology was directly attributed to the difference in shape memory behavior observed between layered and blend films with domain sizes on the micro-scale.     

Structural and mechanical properties of advanced polymer gels with rigid side-chains using coarse-grained molecular dynamics

Computational modeling was utilized to design complex polymer networks and gels which display enhanced and tunable mechanical properties. Our approach focuses on overcoming traditional design limitations often encountered in the formulation of simple, single polymer networks. Here, we use a coarse-grained model to study an end-linked flexible polymer network diluted with branched polymer solvent chains, where the latter chains are composed of rigid side-chains or “spikes” attached to a flexible backbone. In order to reduce the entropy penalty of the flexible polymer chains these rigid “spikes” will aggregate into clusters, but the extent of aggregation was shown to depend on the size and distribution of the rigid side-chains. When the “spikes” are short, we observe a lower degree of aggregation, while long “spikes” will aggregate to form an additional secondary network. As a result, the tensile relaxation modulus of the latter system is considerably greater than the modulus of conventional gels and is approximately constant, forming an equilibrium zone for a broad range of time. In this system, the attached long “spikes” create a continuous phase that contributes to a simultaneous increase in tensile stress, relaxation modulus and fracture resistance. Elastic properties and deformation mechanisms of these branched polymers were also studied under tensile deformation at various strain rates. Through this study we show that the architecture of this branched polymer can be optimized and thus the elastic properties of these advanced polymer networks can be tuned for specific applications.     

Ionomer‐based polyurethanes: a comparative study of properties and applications

Polyurethanes cover a large range of materials exhibiting various physical and mechanical properties making them useful in different applications such as elastomers or biomaterials, for instance. The introduction of ionic groups in the polyurethane backbone opens the way to new applications where the ionic groups can act as physical crosslinkers that greatly modify the final mechanical and thermal properties of the materials. Furthermore, the hydrophilicity of the chains can be enhanced by the presence of the ionic species, and so the materials can be processed as conventional dispersions even in a polar solvent such as water. As a consequence the applications are numerous; the main commercial outlets are focused on coatings and textiles industries where they can be used as waterproof coatings or substitutes for leather. But these materials can also be used in high‐tech industries for shape memory materials, biomedical devices and biocompatible materials. This review summarizes the latest developments of this class of promising materials and provides the reader with the potentialities of these polymers in various areas.     

Synthesis and characterization of multiblock semi-crystalline hydrophobic poly(ether ether ketone)–hydrophilic disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes

Multiblock copolymers based on alternating segments of telechelic phenoxide terminated hydrophilic fully disulfonated poly(arylene ether sulfone) (BPS100) and decafluorobiphenyl (DFBP) terminated hydrophobic poly(arylene ether ketimine) (PEEKt), were synthesized from the hydrophilic and ketimine-protected amorphous hydrophobic telechelic oligomers by nucleophilic coupling reactions. After film formation from DMSO, the copolymer was acidified, which converted the ketimine to semi-crystalline ketone segments and the sulfonate salts to disulfonic acids. A semi-crystalline phase with a T_m of 325 °C was confirmed. The semi-crystalline multiblock copolymer membranes were tough, ductile and solvent resistant. Fundamental properties as proton exchange membranes (PEMs) showed enhanced conductivities under fully hydrated and reduced humidity conditions. These multiblock copolymers exhibited low in-plane anisotropic swelling behavior, in contrast to the random copolymers.