Infrared and Raman spectroscopic investigation of crosslinked polystyrenes and radiation‐grafted films

The crosslinking of functionalized polystyrene resins is often of critical importance in determining resin properties and performance in the application of these materials as membranes and supports. In this investigation model systems are developed for quantifying the infrared and Raman spectroscopic properties of copolymers based on poly(styrene‐co‐divinylbenzene). Analytical curves appropriate for the quantification of para‐ and metasubstituted species and pendant double bonds are reported, and corrections to previously reported spectroscopic assignments and analytical methods are made. The usefulness of these two analytical methods in characterizing radiation‐grafted films and commercial copolymers is compared, and typical characterization results are given. The relative concentrations of the species found in the grafted films are quite different from their concentrations in the grafting solution, and empirical relationships between the two are developed. In addition, the graft composition varies as a function of the base polymer film thickness and type and the penetration depth in the grafted film. Radiation‐grafted films are more highly crosslinked in their near surface regions, and thinner films are more extensively crosslinked. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 59–75, 2004     

Chemically stable hybrid polymer electrolyte membranes prepared by radiation grafting,sulfonation, and silane‐crosslinking techniques

To prepare a crosslinked hybrid polymer electrolyte membrane (PEM) with high chemical stability, a silane monomer, namely p‐styryltrimethoxysilane (StSi), was first grafted to poly(ethylene‐co‐tetrafluoroethylene) (ETFE) film by γ‐ray preirradiation. Hydrolysis‐condensation and sulfonation were then performed on the StSi‐grafted ETFE (StSi‐g‐ETFE) films to give them crosslinks and proton conductibility, respectively. Thus, a crosslinked proton‐conducting hybrid PEM was obtained. The crosslinks introduced by the silane‐condensation have an inorganic ? Si? O? Si? structure, which enhance the chemical and thermal stabilities of the PEM. The effect of the timing of the hydrolysis‐condensation (before or after sulfonation) and the sulfonation method (by chlorosulfonic acid or H₂SO₄) on the properties of the resulting hybrid PEMs such as ion‐exchange capacity, proton conductivity, water uptake, chemical stability, and methanol permeability were investigated to confirm their applicability in fuel cells. We conclude that the properties of the new crosslinked hybrid StSi‐grafted PEMs are superior to divinylbenzene (DVB)‐crosslinked styrene‐grafted membranes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5559–5567, 2008     

Mechanical property and biodegradability of solution‐cast films prepared from amphiphilic polylactide‐grafted dextran

Polylactide (PLA)‐grafted dextran was synthesized with a trimethylsilyl protection method to produce novel biodegradable, biomedical materials. PLA‐grafted dextrans with various lengths and numbers of graft chains were synthesized. The properties of solution‐cast films prepared from PLA‐grafted dextrans were investigated with thermal and dynamic mechanical analyses. The graft‐copolymer films exhibited lower glass‐transition temperatures, melting temperatures (T_m's), and crystallinities as well as higher viscosity properties as compared with poly‐L ‐lactide film. The T_m and crystallinity and mechanical properties at 37 °C could be adjusted by controlling the molecular structure such as the lengths and numbers of graft chains. Furthermore, the biodegradability of PLA‐grafted dextran films was investigated through the weight change of film and the molecular weight change of polymer during the in vitro degradation test. PLA‐grafted dextrans exhibited different degradation behavior from poly‐L ‐lactide with the introduction of a polysaccharide segment and branched structure as well as the change of end‐functional group. The degradation rate of PLA‐grafted dextran and the cast film prepared from PLA‐grafted dextran could be adjusted by controlling the sugar content or the length of graft chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2462–2468, 2003     

Monte carlo simulations of polydisperse polymers grafted on spherical surfaces

This article presents effects of polydispersity in polymers grafted on spherical surfaces on grafted polymer chain conformations, grafted layer thickness, and free‐end monomer distribution within the grafted layer. At brush‐like grafting densities, as polydispersity index (PDI) increases, the scaling exponent of radius of gyration of grafted chains approaches that of a single chain grafted on the same nanoparticle, because polydispersity alleviates monomer crowding within the brush. At high PDI, the chains shorter than the number average chain length, N_n, have more compressed conformations, and the chains longer than N_n overall stretch less than in the monodisperse case. As seen in polydisperse flat brushes at high grafting densities, the grafted layer thickness on spherical nanoparticle increases with PDI. Polydispersity eliminates the region near the surface devoid of free‐end monomers seen in monodisperse cases, and it reduces the width of free‐end monomer distribution and shifts the free‐end monomer distribution close to the surface. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Viscoelastic phase diagram of fluorinated and grafted polymer films and proton‐exchange membranes for fuel cell applications

The influence of temperature and moisture activity on the viscoelastic behavior of fluorinated membranes for fuel cell applications was investigated. Uncrosslinked and crosslinked ethylene tetrafluoroethylene (ETFE)‐based proton‐conducting membranes were prepared by radiation grafting and subsequent sulfonation and their behavior was compared with ETFE base film and commercial Nafion^® NR212 membrane. Uniaxial tensile tests and stress relaxation tests at controlled temperature and relative humidity (RH) were carried out at 30 and 50 °C for 10% < RH < 90%. Grafted films were stiffer and exhibited stronger strain hardening when compared with ETFE. Similarly, both uncrosslinked and crosslinked membranes were stiffer and stronger than Nafion^®. Yield stress was found to decrease and moisture sensitivity to increase on sulfonation. The viscoelastic relaxation of the grafted films was found to obey a power‐law behavior with exponent equal to ?0.04 ± 0.01, a factor of almost 2 lower than ETFE, weakly influenced by moisture and temperature. Moreover, the grafted films presented a higher hygrothermal stability when compared with their membranes counterparts. In the case of membranes, a power‐law behavior at RH < 60% was also observed. However, a markedly different behavior was evident at RH > 60%, with an almost single relaxation time exponential. An exponential decrease of relaxation time with RH from 60 s to 10 s was obtained at RH ≥ 70% and 30 °C. The general behavior of grafted films observed at 30 °C was also obtained at 50 °C. However, an anomalous result was noticed for the membranes, with a higher modulus at 50 °C when compared with 30 °C. This behavior was explained by solvation of the sulfonic acid groups by water absorption creating hydrogen bonding within the clusters. A viscoelastic phase diagram was elaborated to map critical conditions (temperature and RH) for transitions in time‐dependent behavior, from power‐law scaling to exponential scaling. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1139–1148     

Monitoring ultrathin film photopolymerization of tetra‐alkylepoxyporphyrin by UV‐Vis spectroscopy

Cationic photopolymerization is a convenient in situ polymerization method for organic thin film preparation. In this work, the polymerization mechanisms is applied for highly viscous cross‐linking monomers, using tetra‐alkylepoxyporphyrin (TAEP) as a case study. By comparing the UV‐Vis spectra of the polymerized sample before and after the unreacted monomers have been dissolved, it is possible to estimate the polymerization yield. An IR spectrum of a reference thick film confirms full polymerization. Scanning fluorescence lifetime microscopy and AFM show the uniformity of the polymer. It was shown that photopolymerization is highly dependent on the substrate nature and requires at best case a 10 min illumination at 90 °C. Thermal polymerization of the same sample requires 10 min heating at 150 °C in dark. It was also shown that TAEP works as a self‐sensitizer for cationic photopolymerization. The proposed method is a mild and versatile technique for in situ preparation of thin polymeric films directly from chromophore monomers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6095–6103, 2009     

Synthesis,physicochemical characteristics,and biocompatibility of self‐assemble polymers bearing guanine,cytosine, uracil,and thymine moieties

We synthesized chemically well‐defined brush (i.e., comb‐like) polymers bearing guanine, cytosine, uracil, or thymine moieties at the bristle ends. The polymers were stable up to 220 °C and were readily solution‐processable, yielding high‐quality films. Interestingly, the brush polymers favorably self‐assembled to form molecular multibilayer structures stabilized by hydrogen bonding interactions among the nucleobase moieties at the bristle ends, which provided nucleobase‐rich surfaces. The multibilayer‐structured polymer films showed high water affinity. They also displayed selective protein adsorption, suppressed bacterial adherence, facilitated cell adhesion, and exhibited good biocompatibility in mice. The brush polymer DNA‐mimicking comb‐like polymers are suitable as biomaterials and in protein separation applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1151–1160     

Polymers from aryl cyclic sulfonium zwitterions—photosensitive materials cast from and developed in water

Upon photolysis or heating, aryl cyclic sulfonium (ACS) zwitterions polymerize by ring‐opening and loss of charge to yield nonionic polymers. These water‐soluble monomers potentially are useful for photolithography because they can be cast from and developed in water. The ACS zwitterion from bisphenol A, 1,1′‐[isopropylidenebis(6‐hydroxy‐3,1‐phenylene)] bis (tetrahydrothiophenium hydroxide) bis(inner salt) (1) is a negative‐tone, photosensitive material that after photolysis yields a crosslinked film. Unexposed regions are removed by water. The cured film has a low dielectric constant, high volume resistivity, a high degree of planarization, low residual stress, thermogravimetric stability, acceptable fracture toughness, and high hardness. These are desirable properties for a dielectric material used in microelectronic applications. However, a shortcoming of the material is its low T_g, at about 140 °C. A second ACS zwitterion, 1,1′‐[fluorenylidenebis(6‐hydroxy‐3,1‐phenylene)] bis(tetrahydrothiophenium hydroxide) bis(inner salt) (2) was prepared that yields a crosslinked polymer with a higher T_g of about 190 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1283–1290, 2000     

Shape memory biomaterials prepared from polyurethane/ureas containing sulfated glucose

Covalently crosslinked polyurethane/urea polymers were synthesized using diamine monomers modified with pendant glucose groups and 2,4‐toluene diisocyanate, poly(ethylene glycol) (PEG), and 1,1,1‐tris(hydroxymethyl)ethane (triol) comonomers. The polymers showed shape memory behavior with a switching temperature dependent on the glass transition temperature. The glass transition temperature is tuned by varying the mole ratio between the glucose‐diamine and PEG used in the polymerization. Increasing PEG content resulted in decreasing glass transition temperature, and a glass transition temperature of 39 °C, close to physiological temperatures, was obtained. The fixed shape showed gradual shape recovery behavior, but a fixity of 70% was achieved when the material was stored at 25 °C. The polymer recovered to the permanent shape when heated to 50 °C. Finally, the surface of a film of the polymer can be sulfated to achieve increased blood‐compatibility without sacrificing the shape memory properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2252–2257     

Diazonium salts for surface‐confined visible light radical photopolymerization

The surface chemistry of aryl diazonium salts has progressed at a remarkable pace in the last two decades, and opened many avenues in materials science. These compounds are excellent coupling agents for polymers to surfaces via several surface‐confined polymerization methods. For the first time, we demonstrate that diazonium salts are efficient for surface initiating radical photopolymerization in the visible light of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) taken as model monomers. To do so, 4‐(dimethylamino)benzenediazonium salt was electroreduced on gold plates or flexible ITO sheets to provide 4‐(dimethylamino)phenyl (DMA) hydrogen donor layers; while excited state camphorquinone acted as the free hydrogen abstractor. In the same way, we co‐polymerized HEMA and MMA with ethylene glycol dimethacrylate in order to obtain crosslinked polymer grafts. We demonstrate by XPS that gold was efficiently screened by the polymer layers and that the wettability of the surfaces accounts for the hydrophilic or hydrophobic characters of the tethered polymers. Homo‐ and crosslinked PMMA grafts were found to resist removal by the paint stripper methyl ethyl ketone. The grafted DMA/camphorquinone system operating in the visible light holds great promises in terms of adhesion of in situ designed continuous or patterned polymer coatings on various substrates. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3506–3515     

Impact of chain architecture (branching) on the thermal and mechanical behavior of polystyrene thin films

The modulus and glass transition temperature (T_g) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) T_g for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in T_g. There are subtle differences between the architectures with reductions in T_g for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ～40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Dual monomer grafting of styrene and maleic anhydride onto model hydrocarbon substrates

Styrene and maleic anhydride (MAn) were successfully grafted, alone and simultaneously, onto various model hydrocarbon substrates at 180 °C with 2,5‐dimethyl‐2,5‐di‐(t‐butyl peroxy)hexane (L101) as a free‐radical initiator. Dodecane, 1‐dodecene, and 2,6,10,14‐tetramethylpentadecane were selected as model compounds to investigate the effects of terminal unsaturation and branching on grafting and crosslinking. These compounds were chosen to mimic the aforementioned microstructural characteristics that are commonly observed in polyethylene. The results demonstrate that terminal unsaturation increases the amount of crosslinked material in the presence of L101. With respect to grafting, for the single monomer systems, MAn prefers to graft as single saturated units, whereas styrene prefers to graft as long chains of polystyrene oligomers. However, when both monomers are grafted simultaneously, graft yields are drastically reduced because of a propensity for the two monomers to form a styrene–maleic anhydride copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2456–2468, 2000     

Crosslinkable polyurethane bearing a methacrylate structure in the side chain

A polyurethane bearing methacrylate groups through urethane linkages was prepared by the addition of 2‐methacryloyloxyethyl isocyanate to the hydroxyl groups in poly(hydroxyurethane) prepared by the polyaddition of a bifunctional cyclic carbonate with 1,12‐diaminododecane. The urethanization proceeded quantitatively in the presence of a catalytic amount of di‐n‐butyltin dilaurate at an ambient temperature, whereas a crosslinked product was obtained from the reaction at 60 °C. The resulting linear polyurethane, bearing a methacrylate structure, was thermally crosslinkable. Its radical copolymerization with vinyl‐type monomers afforded the corresponding crosslinked polymers, whose low glass transition temperatures suggested the flexibility of the polymer chains in the crosslinked product. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3400–3407, 2007     

Photochemical grafting of polysulfobetaine onto polyethylene and polystyrene surfaces and investigation of long‐term stability of the polysulfobetaine layer in seawater

Low‐density polyethylene (LDPE) and polystyrene (PS) films with hydrophilic surface were prepared by photochemical grafting of sulfobetaine‐based copolymer containing photolabile moiety, and long‐term stability of the hydrophilic nature of the surfaces in seawater was proved. The sulfobetaine‐based copolymer was prepared by copolymerization of N,N‐dimethyl‐N‐(3‐(methacryloylamino)propyl)‐N‐(3‐sulfopropyl) ammonium betaine with 2 or 5 mol% of N‐methacryloyl‐4‐azidoaniline, and the resulted polymers were grafted onto the plasma pretreated LDPE and PS films. The contact angle measurements were used to prove the modification as well as to follow the changes in the hydrophilicity during storage at room temperature under air atmosphere as well as in seawater at 32°C. The stability of the polymer layer was confirmed also by FTIR and AFM. Polysulfobetaine‐modified LDPE and PS surfaces exhibited significantly higher long‐term hydrophilicity compared with only plasma treated LDPE and PS surfaces.     

Enhanced mobility and increased gas sorption capacity in thin film and nanoconduit confined polymers

Poly(tert butyl acrylate) (PTBA) is found to exhibit enhanced mobility when spun cast into thin films or impregnated into cylindrical anodic aluminum oxide (AAO) nanoscale pores. In a thin film configuration, the glass transition temperature of 20 nm thick PTBA is found to decrease almost 20 °C compared to the bulk. Consistent with this mobility increase, an increased volume fraction of interphase polymer leads to at least a 2.4 times viscosity reduction when PTBA is impregnated in 100 nm pores versus 200 nm pores. Such increases in mobility result in a 15‐fold increase in CO₂ permeability for an AAO confined geometry compared to a bulk film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 434–441, 2010     

Planar Phase Separation of Weak Polyelectrolyte Brushes in Poor Solvent

Poly(acrylic acid) (PAA) brushes were synthesized on silicon wafer substrates using a silane linker and Z‐group RAFT method, which enables the controlled variation of brush characteristics. Atomic force microscopy (AFM) was used to characterize the brush morphology in the dry state, which ranged from isolated globules to micelles to a continuous film featuring dimples. Surface morphology was primarily determined by total grafted polymer concentration with a critical polymer concentration between 4.5 and 6.5 × 10^?23mol/nm², where the polymer rich regions transition from micellar islands to a continuous film with dimples. However, even at the highest grafting densities and brush strand lengths used in this study, a flat homogenous film was not formed. Morphological consequences of the solvent and thermal history were shown to persist into poorly solvated state after being dried. X‐ray photoelectron spectroscopy (XPS) was used to quantify the degree of remaining salt after drying. It was found that a higher relative amount of salt was retained after drying in the lower grafting density samples. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 370–377     

Synthesis and Properties of Polycarbosilanes Having Lactose‐Derived Structures

A polycarbosilane having lactose‐derived structures was synthesized, and its thermal property, cytotoxicity, chemical crosslinking, and protein adsorption properties were investigated. The polycarbosilane (PSB‐Lac) was prepared by a thiol‐ene reaction between precursor poly(1‐(3‐butenyl)‐1‐methylsilacyclubane) (PSB) and heptaacetyl lactose that carried a thiol group at the anomeric position, and the successive deprotection of the acetyl groups. The lactose introduction efficiency determined by ¹H NMR measurement was 75%. TGA and DSC revealed that the polymer had a 5 wt% decomposition temperature of 260 °C and glass transition temperature (T_g) of 84 °C, which indicated that PSB‐Lac was a thermally stable polymer. PSB‐Lac had no significant cytotoxicity, which was evaluated by human liver cancer cell line HepG2 cultivation on the polystyrene dishes coated with the polymer. Urethane‐crosslinked PSB‐Lac films were prepared by casting solutions of PSB‐Lac and hexamethylene diisocyanate and heating at 120 °C after evaporation of the solvent. The crosslinked PSB‐Lac showed higher adsorption of bovine serum albumin than the similarly crosslinked polycarbosilane that had a glucose structure (PSB‐Glc). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2420–2425     

Synthesis and characterization of grafted/crosslinked proton conducting membranes based on amphiphilic PVDF copolymer

A novel graft copolymer consisting of a poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(glycidyl methacrylate) side chains, that is, P(VDF‐co‐CTFE)‐g‐PGMA, was synthesized through atom transfer radical polymerization (ATRP) using CTFE units as a macroinitiator. Successful synthesis and microphase‐separated structure of the polymer were confirmed by ¹H NMR, FTIR spectroscopy, and TEM. As‐synthesized P(VDF‐co‐CTFE)‐g‐PGMA copolymer was sulfonated by sodium bisulfite, followed by thermal crosslinking with sulfosuccinic acid (SA) via the esterification to produce grafted/crosslinked polymer electrolyte membranes. The IEC values continuously increased with increasing SA content but water uptake increased with SA content up to 10 wt %, above which it decreased again as a result of competitive effect between crosslinking and hydrophilicity of membranes. At 20 wt % of SA content, the proton conductivity reached 0.057 and 0.11 S/cm at 20 and 80 °C, respectively. The grafted/crosslinked P(VDF‐co‐CTFE)‐g‐PGMA/SA membranes exhibited good mechanical properties (>400 MPa of Young's modulus) and high thermal stability (up to 300 °C), as determined by a universal testing machine (UTM) and TGA, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1110–1117, 2010     

Synthesis and characterization of a new acceptor (n‐type) fluorinated and terminal‐functionalized polythiophene

Donor‐ or acceptor‐substituted polythiophenes have many potential applications in optoelectronics. Fluorinated polythiophenes are particularly attractive because of the presence of fluorine, which can withdraw electrons and also improve polymer chemical stability. Because of the promising future of these polymers, there has been much interest in identifying favorable synthetic routes to new fluorinated monomers and polymers. In this study, the monomer had an electron‐withdrawing fluorinated ester and was derived from 3‐thiophene carboxylic acid and 2,2,3,3,4,4,4‐heptafluoro‐1‐butanol. The synthesis of an n‐type fluorinated and terminal‐functionalized polythiophene was accomplished with the Ullmann coupling reaction. A polymer soluble in tetrahydrofuran was obtained with a molecular weight of approximately 15,000 g/mol. In solution, it exhibited a band gap of 2.4 eV, and the photoluminescent excitation and emission maxima were 370 nm and 555 nm, respectively. All peaks were bathochromically shifted when they were measured in the solid state. The glass‐transition and decomposition (in air) temperatures were 129 and 493 °C, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4280–4287, 2005     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. III. The grafting and in vitro degradation of chemically crosslinked poly(1,5‐dioxepan‐2‐one)

Acrylamide was graft polymerized onto the surface of a chemically crosslinked and amorphous biodegradable polyester, poly(1,5‐dioxepan‐2‐one). Electron beam irradiation at a dose of 5 Mrad was used to generate the initiating species in the polyester. The degradation behavior in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated, and acrylamide‐grafted polymer. Differences in weight loss performance were observed between virgin and treated polymers. The acrylamide‐grafted poly(1,5‐dioxepan‐2‐one) was totally degraded after 43 weeks as compared to 48 weeks for the irradiated and 55 weeks for the virgin polymer. On the other hand, the treated polymers showed a higher resistance to degradation in terms of weight loss during the intermediate part of the degradation, i.e., between about 5 and 35 weeks. After this period, the irradiated and particularly the acrylamide grafted poly(1,5‐dioxepan‐2‐one) degraded much more rapidly than the virgin polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1659–1663, 1999