Monofunctional Poly Research Articles

Photothermal Actuation of Thick 3D-Printed Liquid Crystalline Elastomer Nanocomposites.

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials that transduce an input energy into a mechanical response. LCE composites prepared with photothermal agents, such as nanoinclusions, are a means to realize wireless, remote, and local control of deformation with light. Amongst photothermal agents, gold nanorods (AuNRs) are highly efficient converters when the irradiation wavelength matches the longitudinal surface plasmon resonance (LSPR) of the AuNRs. However, AuNR aggregation broadens the LSPR which also reduces photothermal efficiency. Here, the surface chemistry of AuNRs is engineered via a well-controlled two-step ligand exchange with a monofunctional poly(ethylene glycol) (PEG) thiol that greatly improves the dispersion of AuNRs in LCEs. Accordingly, LCE-AuNR nanocomposites with very low PEG-AuNR content (0.01wt%) prepared by 3D printing are shown to be highly efficient photothermal actuators with rapid response (>60%strains-1) upon irradiation with near-infrared (NIR; 808nm) light. Because of the excellent dispersion of PEG-AuNR within the LCE, unabsorbed NIR light transmits through the nanocomposites and can actuate a series of samples. Further, the dispersion also allows for the optical deformation of millimeter-thick 3D printed structures without sacrificing actuation speed. The realization of well-dispersed nanoinclusions to maximize the stimulus-response of LCEs can benefit functional implementation in soft robotics or medical devices.

Mechanoelectrical Transduction of Polymer Electrolyte Membranes: Effect of Branched Networks.

The role of side-chain branching in flexoelectric properties of a flexible, ionic solid polymer electrolyte membrane (PEM) has been investigated subjected to mechanical bending. These PEMs were synthesized via photopolymerization of the bifunctional poly(ethylene glycol) diacrylate (PEGDA) network attached with monofunctional poly(ethylene glycol) methyl ether acrylate (PEGMEA) branches in their ternary mixtures with lithium bis(tri-fluoromethane sulfonyl) imide (LiTFSI) salt. Both the PEGDA polymer precursor and PEGDMA side branches are capable of ionizing the lithium salt, but the dissociated lithium cations can also form the complexation with ether oxygen of PEGDA. With increasing PEGMEA content, not only the glass transition temperature is lowered, but also the ionic conductivity increases with temperature, which may be attributed to plasticization by dangling PEGMEA side chains. The flexoelectric responses of PEMs were investigated under various intermittent and oscillatory cantilever bending modes as a function of PEM composition and frequency. Last but not the least, the mechanoelectrical energy conversion was evaluated for various PEGDA/PEGMEA compositions and discussed its potential applications in energy harvesting from natural resources such as wind and wave motions.

Photopolymerization of enzymatically synthesized methacrylated poly(caprolactone) with poly(ethylene glycol) macromonomer

Polycaprolactone (PCL) based α,ω-methacrylated macromonomer (DMPCL) was synthesized via enzymatic ring-opening polymerization (eROP) by using Novozyme 435 as the enzyme immobilized catalyst. DMPCL was further photopolymerized with monofunctional poly(ethylene glycol) methyl ether methacrylate (PEGMA-950) macromonomer and trimethylolpropane triacrylate (TMPTA) as tri-functionalized crosslinking agent in glass vials when CHCl3 was the solvent and Irgacure 819 was the photoinitiator. Ultraviolet (UV) Light Emitting Diode (LED) bulbs enabled photoinduced reactions at room temperature with low heat generation and high reaction efficiency. The obtained gels were characterized with Fourier Transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). DMPCL participated as an effective crosslinking agent in the photopolymerization of PEGMA-950. Combined usage of DMPCL and PEGMA-950 resulted in significantly more effective polymerization than the separate photopolymerizations of these macromonomers.

Effect of graphene oxide with different exfoliation levels on the mechanical properties of epoxy nanocomposites

The surface of graphene oxide (GO) was covalently modified by two kinds of monofunctional poly(oxypropylene)amines with different molecular chain lengths. Thermogravimetric analysis and other relevant analysis confirmed that both monoamine molecules were successfully grafted onto GO nanosheets. The monoamine molecules with longer molecular chain functionalized GO showed better compatibility and higher degree of exfoliation in the epoxy matrix, achieving better enhancement of both strength and elongation at break. The tensile strength, elongation at break, flexural strength and dielectric constant of the epoxy nanocomposite exhibit 29, 77.9, 28.5 and 6000% (0.1 Hz) increase at 0.05 wt% loading fraction when compared with unmodified counterparts, respectively. Our results demonstrate a great potential for industrial applications.

Comparison of laboratory and field testing performance evaluations of siloxane-polyurethane fouling-release marine coatings

A series of eight novel siloxane-polyurethane fouling-release (FR) coatings were assessed for their FR performance in both the laboratory and in the field. Laboratory analysis included adhesion assessments of bacteria, microalgae, macroalgal spores, adult barnacles and pseudobarnacles using high-throughput screening techniques, while field evaluations were conducted in accordance with standardized testing methods at three different ocean testing sites over the course of six-months exposure. The data collected were subjected to statistical analysis in order to identify potential correlations. In general, there was good agreement between the laboratory screening assays and the field assessments, with both regimes clearly distinguishing the siloxane-polyurethane compositions comprising monofunctional poly(dimethyl siloxane) (PDMS) (m-PDMS) as possessing superior, broad-spectrum FR properties compared to those prepared with difunctional PDMS (d-PDMS). Of the seven laboratory screening techniques, the Cellulophaga lytica biofilm retraction and reattached barnacle (Amphibalanus amphitrite) adhesion assays were shown to be the most predictive of broad-spectrum field performance.

Facile and versatile synthesis of rod-coil poly(3-hexylthiophene)-based block copolymers by nitroxide-mediated radical polymerization

A well-defined and monofunctional poly(3-hexylthiophene)-based (P3HT) macroinitiator has been obtained through a clean, simple, and an efficient multistep synthesis process. The macroinitiator is obtained via intermolecular radical 1,2-addition onto an ω-acrylate-terminated P3HT macromonomer. In a second step, well-defined rod-coil block copolymers were obtained by nitroxide-mediated radical polymerization (NMRP) using the so-called Blocbuilder®. The polymerization was found to be controlled with various monomers such as styrene, isoprene, 4-vinylpyridine, or methyl acrylate. This process constitutes a very promising way to obtain versatile and clean materials for organic electronics. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Water uptake, transport and structure characterization in poly(ethylene glycol) diacrylate hydrogels

Crosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by UV-induced photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) crosslinker in the presence of varying amounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS) when the water content of the prepolymerization mixture was greater than 60 wt%. These phase separated films contain pores that scatter visible light, rendering them translucent or opaque. Visible light absorbance measurements, water uptake, water permeability, and salt kinetic desorption experiments were used to characterize the structure of these phase separated, crosslinked hydrogels. The films with PIPS exhibited a porous morphology in CryoSEM studies. Dead-end filtration experiments using deionized water and 1 g/l bovine serum albumin (BSA) solutions were performed to explore the fundamental transport and fouling properties of these materials. The total flux of pure water through the films after prior exposure to BSA solution was nearly equal to that measured for the as-prepared material, indicating that these PEGDA films resist fouling by BSA under the conditions studied.

Transiently Trapped Entanglements in Model Polymer Networks

The relaxational dynamics of trapped entanglements in model silicone polymer networks is studied through the residual dipolar couplings (RDC) obtained by double quantum nuclear magnetic resonance (DQ NMR). These experiments were performed on model polymer networks containing linear pendant chains. The model networks where synthesized by end-linking a mixture of α,ω-divinyl poly(dimethylsiloxane) (B2) and ω-vinyl poly(dimethylsiloxane) (B1) with trifunctional (A3) or tetra-functional (A4) cross-linkers. At the time scale of the NMR experiments only a small fraction of the linear pendant chains B1 loses the memory of its early configuration. Then, the unrelaxed topological constrains involving pendant material render a nonzero average dipolar coupling that contributes to the solid-like behavior of the NMR response. Irrespective of the functionality of the cross-linkers, upon the presence in the network of pendant chains induced by the insertion of the B1 monofunctional poly(dimethylsiloxane) an important re...

Synthesis of poly(glycidol)‐block‐poly(N‐isopropylacrylamide) copolymers using new hydrophilic poly(glycidol) macroinitiator

AbstractNew, water soluble poly(glycidol) (PGl) macroinitiators for atom transfer radical polymerization (ATRP) were synthesized. This new class of macroinitiators were prepared in a three‐step process. First, series of well‐defined ω‐hydroxyl functional poly(glycidol acetal)s with different molecular weights was synthesized via anionic polymerization followed by quantitative termination of anionically growing active sites. End capping was achieved by treatment of living chain ends with water. The living nature of the system and termination reaction is discussed. In the second stage, monofunctional poly(glycidol acetal)s were functionalized by esterification with 2‐chloropropionyl chloride. Finally, selective deprotection (hydrolysis) of acetal protective groups was performed. As simultaneous partial cleavage of ester bond of attached ATRP moieties was unavoidable, the final functionality of macroinitiator calculated from 1H NMR varied in the range 85–95%. The obtained (2‐chloropropionyl) poly(glycidol) macroinitiator with DP = 55 and 90% functionality was successfully used in ATRP polymerization of N‐isopropylacrylamide (NIPAAm) at room temperature in the DMF/water mixture. Linear block copolymers with relatively narrow molecular weight distribution and controlled composition were obtained and characterized with 1H NMR and SEC‐MALLS measurements. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2488–2499, 2008

Biocompatible and bioadhesive hydrogels based on 2-hydroxyethyl methacrylate, monofunctional poly(alkylene glycol)s and itaconic acid

New types of hydrogels were prepared by the radical copolymerization of 2-hydroxyethyl methacrylate, itaconic acid and four different poly(alkylene glycol) (meth)acrylate components (Bisomers) in a water/ethanol mixture as solvent. The polymers swell in water at 25?C to yield homogeneous transparent hydrogels. All the hydrogels displayed pH sensitive behavior in buffers of the pH range from 2.20 to 7.40, under conditions similar to those of biological fluids. The presence of these two comonomers, which were added to HEMA, increased the swelling degree of the hydrogels and gave gels with better elasticity. The hydrogels were thermally stable in the vicinity of the physiological temperature (37?C). The copolymer containing pure poly(ethylene glycol) acrylate units generally had the best properties. The tests performed on the hydrogels confirmed that they were neither hemolytic nor cytotoxic. The copolymer samples showed better cell viability and less hemolytic activity than the PHEMA sample, confirming the assumption that poly(alkylene glycols) improve the biocompatibility of hydrogels. Due to their swelling and mechanical characteristics, as well as the very good biocompatibility and bioadhesive properties, poly(Bisomer/HEMA/IA) hydrogels are promising for utilization in the field of biomedicals, especially for the controlled release of drugs.

Biocompatible and bioadhesive hydrogels based on 2-hydroxyethyl methacrylate, monofunctional poly(alkylene glycol)s and itaconic acid

Novel poly(Bisomer/HEMA/IA) hydrogels were prepared by radical copolymerization of poly(alkylene glycol) (meth)acrylates, i.e. short chains Bisomers, 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA) in a mixture of water/ethanol as solvent. These hydrogels were characterized in terms of swelling in conditions similar to the biological fluids (pH range 2.20–7.40 buffer solutions), compression-strain measurements, thermal properties and morphology. The influence of the type of Bisomer and of the itaconic acid on swelling and mechanical properties, as well as on morphology and thermal behavior of the resulting hydrogels, were investigated.

The Effect of Cross-Linking on Gas Permeability in Cross-Linked Poly(Ethylene Glycol Diacrylate)

A series of cross-linked polymers, XLPEGDA, was prepared by photopolymerizing poly(ethylene glycol) diacrylate (PEGDA) in the presence of varying amounts of water or monofunctional poly(ethylene glycol) methyl ether acrylate (PEGMEA) to vary cross-link density. All of the polymers had essentially the same chemical composition but displayed a systematic variation in cross-link density as estimated from water swelling experiments, models such as the Flory−Rehner and modified Flory−Rehner theories, and dynamic mechanical testing. Cross-link density decreased with increasing water or PEGMEA content in the prepolymer solutions. Interestingly, gas solubility, diffusivity, and permeability were essentially independent of cross-link density for the series of materials prepared from PEGDA and water. The polymer density, fractional free volume, glass transition temperature, and polymer d spacing were also constant when water was used to vary cross-link density. On the basis of this result, it appears that cross-link density does not necessarily affect gas diffusion and permeation, the polymer glass transition temperature, or the fractional free volume in network polymers, and ascribing changes in these properties to changes in cross-link density alone, as is seen commonly in the literature, should be done with great care.

Telechelic and Star‐Shaped Poly(ε‐caprolactone) Functionalized with Triethoxysilyl Groups – New Biodegradable Coatings and Adhesives

AbstractSummary: Monofunctional poly(εCL) having one CH2OH and one CO2CH3 endgroup was prepared by SnOct2 + MeOH‐initiated polymerizations of εCL at 80 °C. The CH2OH endgroups were reacted with IPTES. In this way, poly(εCL) having one CO2CH3 and one TES endgroup was obtained. Poly(εCL) having two CH2OH endgroups were prepared by means of SnOct2 and Tetra EG or 1,4‐butanediol as coinitiators. The molecular weight distribution significantly broadened when the polymerization temperature increased from 80 to 120 °C. The OH endgroups were quantitatively functionalized by addition of IPTES. Star‐shaped poly(εCL)s having three or four OH endgroups were prepared with 1,1,1‐tris(hydroxymethyl)propane or pentaerythritol as coinitiators. All endgroups were modified with IPTES. The lengths of the poly(εCL) segments were varied via the monomer/coinitiator ratio. All functionalized oligomers were characterized by 1H NMR spectroscopy and MALDI‐TOF mass spectrometry. Preliminary studies of film formation and adhesive properties were performed.MALDI‐TOF mass spectrum of a poly(εCL) initiated with Sn(Oct)2 and 1,4‐butanediol and functionalized with IPTES.magnified imageMALDI‐TOF mass spectrum of a poly(εCL) initiated with Sn(Oct)2 and 1,4‐butanediol and functionalized with IPTES.

Degradation Behavior of Poly(ethylene glycol) Diblock and Multiblock Polymers with Hydrolytically Degradable Ester Linkages

Diblock and multiblock polymers of poly(ethylene glycol) containing degradable ester bonds between the blocks were synthesized and characterized. Monofunctional poly(ethylene glycol) (PEG 2000) was modified by aliphatic dicarboxylic acids (malonic, succinic, glutaric, maleic) to obtain monocarboxylic polymers PEG-COOH containing ester bonds. Diblock polymers (4000) were prepared by polycondensation of a diamine (ethane-1,2-diamine, L-lysine) and the semitelechelic PEG-COOH. The relationship between the structure of the linkage connecting two PEG blocks and the rate of its hydrolytic degradation was studied at pH 5.5, 7.4 and 8.0. The rate of hydrolysis of all polymers was significant already under mild alkaline conditions (pH 7.4 and 8.0) and increased with increasing pH. The ester bonds of polymers with saturated dicarboxylic acid moieties were stable at pH 5.5. However, the presence of double bond in the acid moiety substantially decreased the stability of the polymer not only in alkaline but also in acid medium. The results of this model study can be utilized in the design of biodegradable high-molecular-weight drug carriers and polymers for preparation of "stealth" systems intended for therapeutic application.

Silicone elastomers for reduced protein adsorption

Monofunctional poly(ethylene oxide) polymers of molecular weight (MW) 350, 750, and 2000, respectively, were modified with Si(OEt) 3 groups. These polymers underwent classic condensation cure with hydroxy-terminated silicone polymers and Si(OEt) 4 to give composites with poly(ethylene oxide) (PEO) rich surfaces under aqueous conditions, as shown by contact angle and XPS data. The hydrophobicity of the surfaces was considerably higher in air. The greatest PEO concentration was observed with relatively short chain polymers of MW 350. Silicone polymers bearing short chain PEO chains were also observed to be the most protein rejecting from either buffer (fibrinogen) (90%) or plasma (85%). The silicone/TES-MPEO formulation offers the advantage of a one step/one shot polymerization process that gives materials with a high protein rejection ability than can be cast as films, or molded into complex shapes. Covalently linked PEO films of a variety of chain lengths and total surface coverage can be readily accommodated.

Structure and Dimensions of PAMAM/PEG Dendrimer−Star Polymers

Dendrimer−star polymers are prepared by grafting monofunctional poly(ethylene glycol) (PEG) chains of low polydispersity onto the terminal groups of poly(amidoamine) (PAMAM) dendrimers. A novel gel permeation chromatography technique is used to calculate the average number of PEG branches (“arms”) per star. The maximum number of PEG arms (of Mn = 5000 g mol-1) ranges from about 30 arms for a generation 3 dendrimer−star to about 750 arms for a generation 10 dendrimer−star. Radii of gyration of the stars are measured in dilute solution in a good solvent (methanol-d4) by small-angle neutron scattering (SANS). The stars have measured radii of gyration of about 6−14 nm. Theoretical dimensions of the stars in dilute solution in a good solvent are calculated by treating the stars as a shell of linear chains tethered to a spherical core. The radii of gyration computed from the core−shell model are consistent with the dilute solution values from SANS.

Templating of inorganic nanoparticles by PAMAM/PEG dendrimer–star polymers

Poly(amidoamine) (PAMAM) dendrimers with amine endgroups (PAMAM–NH 2) are converted to starlike copolymers by grafting of monofunctional poly(ethylene glycol) (PEG) ‘arms’ onto the dendrimer endgroups. Generation 4, 7, and 10 dendrimers are converted to 60-arm, 235-arm, and 750-arm PAMAM/PEG stars, respectively. The dendrimer–stars are studied as polymer templates for stabilization of gold and cadmium sulfide nanoparticles of 1–6 nm diameter. PAMAM/PEG star templating reactions are studied by aqueous gel permeation chromatography, ultraviolet–visible absorption spectroscopy, fluorescence spectroscopy, and transmission electron microscopy. PAMAM/PEG stars effectively control nanoparticle size in the same way as PAMAM–NH 2 dendrimers. However, PAMAM/PEG stars are miscible with a wider range of solvents and with selected polymers (e.g. polymethyl methacrylate). Potential applications of dendrimer–inorganic hybrid materials (solution-phase catalysis, additives for polymer blends) could benefit from the versatile solubility of PAMAM/PEG stars.

Block copolymers comprising poly(ethylene oxide) and poly(hydroxyethyl methacrylate) blocks: synthesis and characterization

Monofunctional poly(ethylene oxide) macroinitiators with a molecular weight of 2000, 5000, 10 000, 20 000 and bifunctional poly(ethylene oxide) macroinitiators with a molecular weight of 20 000 were used for the atom transfer radical polymerisation (ATRP) of hydroxyethyl methacrylate (HEMA) in ethylene glycol as a solvent. The polymerisation proceeds in a controlled way up to high conversions. The molecular weight of the obtained copolymers increases linearly with conversion. A high rate of polymerisation was observed for the ATRP of HEMA. The effect of the poly(ethylene oxide) moiety on the course of the reaction is limited to solvating effects. The surface analysis of poly(ethylene oxide)/poly(hydroxyethyl methacrylate) block copolymers by means of atomic force microscopy in tapping mode using phase imaging shows phase separated domains with characteristic features related to the volume fraction of the respective blocks.

Atom Transfer Radical Polymerization of (Meth)acrylates from Poly(dimethylsiloxane) Macroinitiators

The atom transfer radical polymerization (ATRP) of (meth)acrylates from poly(dimethylsiloxane) (PDMS) macroinitiators is described. Hydrosilylation of commercially available difunctional hydrosilyl terminal PDMS (Mw/Mn > 1.3) with allyl- or 3-butenyl 2-bromoisobutyrate resulted in the macroinitiators. Linear semilogarithmic kinetic plots were obtained for the ATRP of acrylates and methacrylates. A nonlinear dependence of molecular weight on conversion was ascribed to a high concentration of low molecular weight chains not readily observed in the size exclusion chromatograph using THF as eluent. Well-defined monofunctional, low-polydispersity PDMS macroinitiators were synthesized by the anionic ring-opening polymerization of hexamethylcyclotrisiloxane. ATRP of acrylates and methacrylates from those compounds showed linear increases in Mn with conversion, demonstrating the effectiveness of ATRP to synthesize a variety of inorganic/organic polymer hybrids. A monofunctional poly(styrene-b-dimethylsiloxane) macroinitiator was used to initiate ATRP of n-butyl acrylate and methyl methacrylate, resulting in ABC organic/inorganic/organic hybrid triblock copolymers.

Tailored synthesis of branched polymers with poly(tetrahydrofuran) having an azetidinium salt end group

Monofunctional poly(tetrahydrofuran), (poly(THF)), having a 1-(diphenylmethyl)azetidinium end group (1) was prepared and subjected to an ion-coupling reaction with various mono- and plurifunctional carboxylates (2a-j). Multiarmed polymers having 2, 3, 4 and 6 arms were obtained in almost pure form by repeating a simple precipitation of a THF solution of 1 into an ice-cooled aqueous solution containing an excess amount of the relevant plurifunctional carboxylates (2c-g) as sodium salts. Another model-branched polymacromonomer was obtained in high yield through the macromolecular ion-coupling reaction of 1 with poly(sodium acrylate) (2h) of DP = 22. Moreover, the ion-coupling reaction of 1 with sodium (L)-tartarate (2i) or sodium 2,2'-dihydroxy-1,1'-binaphthyl-3,3'-dicarboxylate (2j) allowed one to introduce two hydroxyl groups at the center of a linear poly(THF) segment.