Homo‐ and copolymerization of norbornene derivatives with ethene by ansa‐fluorenylamidodimethyltitanium activated with methylaluminoxane

(t‐BuNSiMe₂Flu)TiMe₂ ( 1 ) activated with Me₃Al‐free methylaluminoxane (dried MAO) which conducts vinyl addition polymerization of norbornene (N) with very high activity was applied for homopolymerization of N derivatives (i.e., 5‐vinyl‐2‐norbornene (5V2N), 5‐ethylidene‐2‐norbornene (5E2N), dicyclopentadiene (DCPD)) at 40 °C. The activities for the N derivatives were about two orders of magnitude lower than that for N and decreased in the following order: 5E2N ? 5V2N ? DCPD. Copolymerization of ethene (E) and 5E2N under an atmospheric pressure of E was then conducted by 1 ‐dried MAO. The copolymerization proceeded with better activity than the homopolymerization of 5E2N and gave poly(E‐co‐5E2N) with narrow molecular weight distribution. The content of the ethylidene group in poly(E‐co‐5E2N) was controlled by the feed ratio of 5E2N/E. The T_g value of the copolymer changed from 70 °C to 155 °C according to the 5E2N content from 27 mol % to 68 mol %. The addition of N as a third monomer to the E‐5E2N copolymerization improved the activity and raised the T_g values of the terpolymer above 200 °C. The content of 5E2N was controlled by the 5E2N/N ratio with keeping the high T_g values. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4581–4587, 2007     

Thiol–ene polymerizations using imide‐based monomers

New diene and dithiol monomers, based on aromatic imides such as benzophenone‐3,3′,4,4′‐tetracarboxylic diimide were synthesized and used in thiol‐ene polymerizations which yield poly(imide‐co‐thioether)s. These linear polymers exhibit limited solubility in various organic solvents. The molecular weights of the polymers were found to decrease with increasing imide content. The glass transition temperature (T_g) of these polymers is dependent on imide content, with T_g values ranging from ?55 °C (with no imide) up to 13 °C (with 70% imide). These thermal property improvements are due to the H‐bonding and rigidity of the aromatic imide moieties. Thermal degradation, as studied by thermogravimetric analysis, was not significantly different to the nonimide containing thiol‐ene polymers made using trimethyloylpropane diallyl ether and 3,5‐dioxa‐1,8‐dithiooctane. It is expected that such monomers may lead to increased glass transition temperatures in other thiol‐ene polymer systems as these normally exhibit low glass transition temperatures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4637–4642     

Semicrystalline poly(vinyl ether)s with high and phototunable glass transition temperature: application for thermally stable and reworkable adhesives

The photoinduced solid–liquid phase transition of azobenzene-based polymers is an attractive method to synthesize stimuli-responsive functional materials. As the structure–property relationships of such materials are not fully understood, a new class of polymer backbone, that is, poly(vinyl ether) (PVE), was studied for the development of azobenzene-based polymers with high thermal stability. For this purpose, a series of azobenzene-based PVEs with different monomer structures were synthesized using a Lewis acid catalyst-based cationic polymerization method. Typical PVEs are viscous polymers with low glass-transition temperatures (T_g's). The flexibility of the polymer backbone improves with the use of alkylene spacers, changing the order of alignment of the mesogenic azobenzene moieties attached to the backbone, leading to high T_g's of the azobenzene-based PVEs. One of the synthesized PVEs shows a high glass-transition temperature of 94 °C, which is 14 °C higher compared to that of the corresponding polymethacrylate. Furthermore, the PVE exhibits photoinduced solid–liquid phase transition from the semicrystalline state. This phase transition material, with its high thermal stability, has the potential for broader applications, such as for the phototuning of adhesion. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 568–577     

Highly thermostable and low birefringent norbornene‐styrene copolymers with advanced optical properties: A potential plastic substrate for flexible displays

This article reports the synthesis and characterization of an extremely high thermostable cyclic olefin copolymer with advanced optical properties resulting from the vinyl addition copolymerization of norbornene with styrene catalyzed by a substituted fluorenylamidodimethyltitanium catalyst [Me₂Si(3,6‐tBu₂Flu)(tBuN)]TiMe₂ activated with a [Ph₃C] [B(C₆F₅)₄]/Al(iBu)₃ cocatalyst using o‐dichlorobenzene as solvent. The prepared copolymer possesses a glass transition temperature as high as polyimide (T_g > 300 °C) and a high transmittance which is comparable with that of the conventional optical resins ([T] > 90%). The incorporation of polystyrene, which exhibits a negative birefringence into the vinyl‐added polynorbornene that possesses an intrinsic positive birefringence, effectively reduced the birefringent magnitude of the norbornene‐styrene copolymer due to a mutual compensation between these opposite‐sign birefringences. The absence of any functional and aromatic heterocyclic groups and the presence of highly hydrophobic saturated bicyclic rings in the copolymer main chains effectively prevented the diffusion of water/oxygen and thus enhanced the dimensional and optical stabilities of the material. Preliminary results on the characterization of the thermal stability, mechanical, and optical properties of the vinyl‐added norbornene‐styrene copolymers indicate that they satisfy all the rigorous requirements for a polymer to be applied as a flexible substrate for the manufacturing of the flexible displays. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Thiourethane‐based thiol‐ene high Tg networks: Preparation,thermal, mechanical,and physical properties

Thiourethane‐based thiol‐ene (TUTE) films were prepared from diisocyanates, tetrafunctional thiols and trienes. The incorporation of thiourethane linkages into the thiol‐ene networks results in TUTE films with high glass transition temperatures. Increases of T_g were achieved by aging at room temperature and annealing the UV cured films at 85 °C. The aged/annealed film with thiol prepared from isophorone diisocyanate and cured with a 10,080‐mJ/cm² radiant exposure had the highest DMA‐based glass transition temperature (108 °C) and a tan δ peak with a full width at half maximum (FWHM) of 22 °C, indicating a very uniform matrix structure. All of the initially prepared TUTE films exhibited good physical and mechanical properties based on pencil hardness, pendulum hardness, impact, and bending tests. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5103–5111, 2007     

Statistical copolymers of norbornene and 5‐vinyl‐2‐norbornene by a ditungsten complex mediated ring‐opening metathesis Polymerization: Synthesis,thermal properties,and kinetics of thermal decomposition

Statistical copolymers of norbornene (NBE) with 5‐vinyl‐2‐norbornene (VNBE) were prepared by ring‐opening metathesis polymerization, employing the triply bonded ditungsten complex Na[W₂(μ‐Cl)₃Cl₄(THF)₂].(THF)₃. NMR measurements revealed that the side vinyl groups of the VNBE monomer remain intact during the copolymerization reaction. The reactivity ratios were estimated using the Finemann–Ross (FR), the inverted FR, and the Kelen–Tüdos graphical methods. Structural parameters of the copolymers were obtained by calculating the dyad sequence fractions, which were derived using the monomer reactivity ratios. The glass transition temperatures, T_g, of the copolymers were measured by differential scanning calorimetry measurements and were examined in the frame of several theoretical equations allowing the prediction of these T_g values. The best fit was obtained using methods that take into account the monomer sequence distribution of the copolymers. Finally, the kinetics of the thermal decomposition of the copolymers was studied by thermogravimetric analysis in the frame of the Ozawa–Flynn–Wall and Kissinger methods. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4835–4844     

Synthesis of novel cyclic olefin polymers with excellent transparency and high glass‐transition temperature via gradient copolymerization of bulky cyclic olefin and cis‐cyclooctene

Novel cyclic olefin polymers (COPs) with excellent transparency and high glass‐transition temperature (T_g) synthesized from bulky norbornene derivative, exo‐1,4,4a,9,9a,10‐hexahydro‐9,10(1',2')‐benzeno‐l,4‐methanoanthracene (HBMN), and cis‐cyclooctene (COE) by ring‐opening metathesis copolymerization utilizing the “first‐generation Grubbs” catalyst, RuCl₂(PCy₃)₂(CHPh), and subsequent hydrogenation was reported herein. To get amorphous copolymers, it was of great importance to control the feed ratios and the polymerization time for gradient copolymerization. All these copolymers showed very high T_gs (141.1–201.2 °C), which varied with the content of HBMN. The films of the gradient copolymers with only one T_g were highly transparent. On the contrary, all the block copolymers synthesized through sequential addition showed two thermal transition temperatures, T_g and melt temperature (T_m), and the films of these block copolymers were opaque. The mechanical performances of the COPs were also investigated. It is the first report that transparent COP could be prepared from bulky norbornene derivative and monocyclic olefin. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3240–3249     

Synergism and multiple mechanical relaxations observed in ternary systems based on benzoxazine,epoxy, and phenolic resins

The synergism in the glass‐transition temperature (T_g) of ternary systems based on benzoxazine (B), epoxy (E), and phenolic (P) resins is reported. The systems show the maximum T_g up to about 180 °C in BEP541 (B/E/P = 5/4/1). Adding a small fraction of phenolic resin enhances the crosslink density and, therefore, the T_g in the copolymers of benzoxazine and epoxy resins. To obtain the ultimate T_g in the ternary systems, 6–10 wt % phenolic resin is needed. The molecular rigidity from benzoxazine and the improved crosslink density from epoxy contribute to the synergistic behavior. The mechanical relaxation spectra of the fully cured ternary systems in a temperature range of −140 to 350 °C show four types of relaxation transitions: γ transition at −80 to −60 °C, β transition at 60–80 °C, α₁ transition at 135–190 °C, and α₂ transition at 290–300 °C. The partially cured specimens show an additional loss peak that is frequency‐independent as a result of the further curing process of the materials. The ternary systems have a potential use as electronic packaging molding compounds as well as other highly filled systems. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1687–1698, 2000     

Poly(silarylene–siloxane)polyimides from allyl‐terminated oligoimides and hydride‐functional silarylene–siloxanes via hydrosilylation polymerization

This research was focused on the design and execution of new synthetic routes to low‐temperature‐curable poly(silarylene–siloxane)polyimides. The synthesis of individual oligoimide and silarylene–siloxane blocks was followed by hydrosilylation polymerization to produce crosslinked copolymers. The silarylene–siloxane and polyimide blocks were structurally characterized by IR and ¹H NMR spectroscopy and size exclusion chromatography. The high‐temperature resistance of the copolymers was evaluated through the measurement of heat distortion temperatures (T_HD's) via thermomechanical analysis and by the determination of the weight loss at elevated temperatures via thermogravimetric analysis. Glass‐transition temperatures (T_g's) of the silarylene–siloxane segments were measured by differential scanning calorimetry. Hydrosilylation curing was conducted at 60 °C in the presence of chloroplatinic acid (H₂PtCl₆). The copolymers displayed both high‐temperature resistance and low‐temperature flexibility. We observed T_g of the silarylene–siloxane segment as low as ?77 °C and T_HD of the polyimide segment as high as 323 °C. The influence of various oligoimide molecular weights on the properties of copolymers containing the same silarylene–siloxane was examined. The effect of various silarylene–siloxane molecular weights on the properties of copolymers containing the same oligoimide was also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4922–4932, 2005     

Effects of temperature on cure kinetics and mechanical properties of vinyl–ester resins

The relationships among cure temperature, chemical kinetics, microstructure, and mechanical performance have been investigated for vinyl–ester resins. Fourier transform infrared spectroscopy was used to follow the reactions of vinyl–ester and styrene during isothermal curing of Dow Derakane 411‐C‐50 at 30 and 90°C. Reactivity ratios of vinyl–ester and styrene vinyl groups were evaluated using the copolymer composition equation. The results indicate that the ratio of vinyl–ester to styrene double bonds incorporated into the network is greater for 30 than for 90°C cure. Mechanical properties were obtained for systems subjected to isothermal cures at 30 and 90°C and postcured above ultimate T_g. The results show that the initial cure temperature significantly affects the mechanical behavior of vinyl–ester resin systems. In particular, values of strength and fracture toughness for postcured samples initially cured isothermally at 30°C are significantly higher than those obtained for samples cured isothermally at 90°C. Examination of fracture surfaces using atomic force microscopy revealed the existence of a nodular microstructure possessing characteristic nodule dimensions that are affected by the temperature of cure. Such features suggest the existence of phase separation during cure. A binary interaction model in conjunction with chemical kinetic data and estimated solubility parameters was used to evaluate enthalpic interactions between the growing polymer network and monomers of the vinyl–ester system. The results indicate that the interaction energy becomes increasingly endothermic as cure progresses and that this energy is affected by the temperature of cure through differences in copolymerization behavior. Hence, in addition to entropic factors, the changes in enthalpic contribution to the Gibbs free energy suggest that the probability of phase separation increases with extent of cure and that its onset is potentially affected by cure temperature. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 725–744, 1999     

Cationic cyclopolymerization of divinyl ethers with norbornane‐, norbornene‐, or adamantane‐containing substituents: Synthesis of cyclopoly(divinyl ether)s with bulky rigid side chains leading to high glass transition temperature

Cationic cyclopolymerizations of 2,2‐bis(vinyloxymethyl)bicyclo[2.2.1]heptane ( 1 ), 5,5‐bis(vinyloxymethyl)‐2‐bicyclo[2.2.1]heptene ( 2 ), and 2,2‐bis(vinyloxymethyl)tricyclo[3.3.1.1]^{3, 7}decane ( 3 ), divinyl ethers with a norbornane, norbornene, or adamantane unit, respectively, were investigated with the HCl/ZnCl₂ initiating system in toluene and methylene chloride at ?30 °C. All the reactions proceeded quantitatively to give gel‐free, soluble polymers in organic solvents. The number‐average molecular weight (M_n) of the polymers increased in direct proportion to monomer conversion and further increased on addition of a fresh monomer feed to the almost completely polymerized reaction mixture. The contents of the unreacted vinyl groups in the produced soluble polymers were less than ～10 mol %, and therefore, the degree of cyclization of the polymers was determined to be over ～90%. These facts show that cyclopolymerization of 1 , 2 , and 3 exclusively occurred and the poly(vinyl ether)s with the cyclized repeating units and polycyclic pendants were obtained with their molecular weights being regulated. BF₃OEt₂ initiator also caused cyclopolymerization of 1 , 2 , and 3 to give the corresponding high‐molecular‐weight cyclopolymers quantitatively. Glass transition temperatures (T_g's) of poly( 1 ) and poly( 2 ) were 165–180 °C, and T_g's of poly( 3 ) were 211–231 °C; these values are very high as vinyl ether polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2445–2454     

A–B–A stereoblock copolymers of N‐isopropylacrylamide

A–B–A stereoblock polymers with atactic poly(N‐isopropylacrylamide) (PNIPAM) as a hydrophilic block (either A or B) and a non‐water‐soluble block consisting of isotactic PNIPAM were synthesized using reversible addition fragmentation chain transfer (RAFT) polymerizations. Yttrium trifluoromethanesulfonate was used in the tacticity control, and bifunctional S,S′‐bis(α,α′‐dimethyl‐α″‐acetic acid)‐trithiocarbonate (BDAT) was utilized as a RAFT agent. Chain structures of the A–B–A stereoblock copolymers were determined using ¹H NMR, SEC, and MALDI‐TOF mass spectrometry. BDAT proved to be an efficient RAFT agent in the controlled synthesis of stereoregular PNIPAM, and both atactic and isotactic PNIPAM were successfully used as macro RAFT agents. The glass transition temperatures (T_g) of the resulting polymers were measured by differential scanning calorimetry. We found that the T_g of isotactic PNIPAM is molecular weight dependent and varies in the present case between 115 and 158 °C. Stereoblock copolymers show only one T_g, indicating the miscibility of the blocks. Correspondingly, the T_g may be varied by varying the mutual lengths of the A and B blocks. The phase separation of aqueous solutions upon increasing temperature is strongly affected by the isotactic blocks. At a fixed concentration (5 mg/mL), an increase of the isotacticity of the stereoblock copolymers decreases the demixing temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 38–46, 2008     

Ni(II) and Pd(II) complexes bearing benzocyclohexane–ketoarylimine for copolymerization of norbornene with 5‐norbornene‐2‐carboxylic ester

A serial of late transition metal complexes, which bearing Benzocyclohexane–ketoarylimine ligand and named as Mt(benzocyclohexane–ketoarylimino)₂ {Mt(bchkai)₂: Mt=Ni or Pd; bchkai=C₁₀H₈(O)CN(Ar)CH₃; Ar=naphthyl or fluoryl}, have been synthesized and characterized. The molecular structures of the ligands and nickel complex have been confirmed by X‐ray single‐crystal analyses. The nickel complexes exhibited very high activity up to 2.7 × 10⁵ g_polymer/mol_Ni·h and palladium complexes showed high activity up to 2.3 × 10⁵ g_polymer/mol_Pd·h for norbornene (NB) homo‐polymerization with tris(pentafluorophenyl)borane as cocatalyst. The four complexes were effective for copolymerization of NB and 5‐norbornene‐2‐carboxylic acid methyl ester (NB‐COOCH₃) in relatively high activities (0.1–2.4 × 10⁵ g_polymer/mol_Mt·h) and produced the addition‐type copolymers with relatively high molecular weights (0.5 × 10⁵–1.2 × 10⁵ g/mol) as well as narrow molecular weight distributions (PDI < 2 for all polymers). Influences of the metals and comonomer feed content on the polymerization activity as well as on the incorporation rates (20.9–42.6%) were investigated. The achieved NB/NB‐COOCH₃ copolymers were confirmed to be noncrystalline, exhibited good thermal stability (T_d > 400°C) and showed good solubility in common organic solvents. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Phosphonated homopolymers and copolymers via ring opening metathesis polymerization: Tg tuning,flame resistance,and photolithography

Phosphonated and epoxy‐containing norbornene based monomers were prepared by Diels–Alder reaction. They were then combined with three other commercial cyclic unsaturated monomers to synthesize phosphonated homopolymers and copolymers via ring opening metathesis polymerization (ROMP) using second‐generation Grubbs catalyst. Glass transitions of these polymers were tunable in a broad range from ?14 to 91 °C by varying the flexibility of comonomer. Interestingly, copolymerization with cyclopentene inhibited the crystallization of polycyclopentene, and instead, led to a copolymer with two T_gs. Paradoxically, results from thermogravimetric analysis (TGA) were not consistent with the followed flame‐retarding experiment, implying that the early weight loss from phosphonated moieties did not deleteriously affect the flame‐resistant property which actually depended more on the percentage of char residual after thermal degradation. In application studies, the norbornene derivative phosphonated polymer was tested for the first time as flame retarding material, and showed significant self‐extinguishing ability. In a second study, photolithography was also successfully performed via thiol‐ene “click” chemistry, which allowed the phosphonated polymer a promising negative photoresist. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1396‐1408     

Vitrification/devitrification phenomena during isothermal and nonisothermal crystallization of poly(aryl–ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) blends

We have established time–temperature transformation and continuous-heating transformation diagrams for poly(ether–ether–ketone) (PEEK) and PEEK/poly(ether–imide) (PEI) blends, in order to analyze the effects of relaxation control on crystallization. Similar diagrams are widely used in the field of thermosetting resins. Upon crystallization, the glass transition temperature (T_g) of PEEK and PEEK/PEI blends is found to increase significantly. In the case of PEEK, the shift of the α-relaxation is due to the progressive constraining of amorphous regions by nearby crystals. This phenomenon results in the isothermal vitrification of PEEK during its latest crystallization stages for crystallization temperatures near the initial T_g of PEEK. However, vitrification/devitrification effects are found to be of minor importance for anisothermal crystallization, above 0.1°C/min heating rate. In the case of PEEK/PEI blends, amorphous regions are progressively enriched in PEI upon PEEK crystallization. This promotes a shift of the α-relaxation of these regions to higher temperatures, with a consequent vitrification of the material when crystallized below the T_g of PEI. The data obtained for the blends in anisothermal regimes allow one to detect a region in the (temperature/heating rate) plane where crystallization proceeds in the continuously close proximity of the glass transition (dynamic vitrification). These experimental findings are in agreement with simple simulations based on a modified Avrami model coupled with the Fox equation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 919–930, 1998     

Elevation of the glass transition temperature in flexible‐chain semicrystalline polymers

In the idealized two‐phase model of a semicrystalline polymer, the amorphous intercrystalline layers are considered to have the same properties as the fully‐amorphous polymer. In reality, these thin intercrystalline layers can be substantially influenced by the presence of the crystals, as individual polymer molecules traverse both crystalline and amorphous phases. In polymers with rigid backbone units, such as poly(etheretherketone), PEEK, previous work has shown this coupling to be particularly severe; the glass transition temperature (T_g) can be elevated by tens of degrees celsius, with the magnitude of the elevation correlating directly with the thinness of the amorphous layer. However, this connection has not been explored for flexible‐chain polymers, such as those formed from vinyl‐type monomers. Here, we examine T_g in both isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), crystallized under conditions that produce a range of amorphous layer thicknesses. T_g is indeed shown to be elevated relative to fully‐amorphous iPS and sPS, by an amount that correlates with the thinness of the amorphous layer; the magnitude of the effect is severalfold less than that in PEEK, consistent with the minimum lengths of polymer chain required to make a fold in the different cases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1198–1204, 2007     

Ethylene–propylene copolymerization behavior of ansa‐dimethylsilylene(fluorenyl)(amido)dimethyltitanium complex: Application to ethylene–propylene–diene or ethylene–propylene–norbornene terpolymers

Copolymerization behavior of ethylene (E) and propylene (P) using ansa‐dimethylsilylene(fluorenyl)(amido)dimethyltitanium complex was investigated. P was more reactive than E regardless of the chain‐end monomer unit, which was very unusual in the coordination polymerization system. The terpolymerizations of E, P and norbornene (NB) or 5‐ethylidene‐2‐norbornene (5E2N) were also performed. The each content in the E/P/NB terpolymer was independently controlled by the initial concentration of NB and E/P feed ratio. Glass transition temperature (T_g) of the terpolymer was raised in proportion to the NB content and close to that of the corresponding NB/E random copolymer with the same NB content. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 685–691     

Styrene 4‐vinylbenzocyclobutene copolymer for microelectronic applications

Styrene and 4‐vinylbenzocyclobutene (vinyl‐BCB) random copolymers were prepared by free radical polymerization and studied for suitability as a dielectric material for microelectronic applications. The percentage of vinyl‐BCB in the copolymer was varied from 0 to 26 mol % to optimize the physical and mechanical properties of the cured copolymer as well as the cost. Copolymer in which 22 mol % of vinyl‐BCB was incorporated along with styrene produced a thermoset polymer which, after cure, did not show a T_g before decomposition at about 350 °C. The polymeric material has a very low dielectric constant, dissipation factor, and water uptake. The fracture toughness of the copolymer was improved with the addition of 20 wt % of a star‐shaped polystyrene‐block‐polybutadiene. Blends of the poly(styrene‐co‐vinyl‐BCB) with the thermoplastic elastomer provided material that maintained high T_g of the cured copolymer with only a slight decrease in thermal stability. The crosslinked styrenic polymer and toughened blends possess many properties that are desirable for high frequency‐high speed mobile communication applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2799–2806, 2008     

Structure and property relationships in model diglycidyl ether of bisphenol‐a and diglycidyl ether of tetramethyl bisphenol‐a epoxy systems. I. Mechanical property characterizations

Model epoxy networks, with variations in crosslink density and in epoxy monomer rigidity, were prepared to study how the network structure affects modulus, T_g, and toughness/toughenability of epoxy resins. Diglycidyl ether of bisphenol‐A and diglycidyl ether of tetramethyl‐bisphenol‐A, along with the corresponding chain extenders, were chosen to study how monomer backbone rigidity and crosslink density affect physical and mechanical properties of epoxies. The present study indicates that, as expected, the backbone rigidity of the epoxy network, not the crosslink density alone, will strongly influence modulus and T_g of epoxy resins. Upon rubber toughening, it is found that the rigidity of the epoxy backbone and/or the nature of the crosslinking agent utilized are most critical to the toughenability of the epoxy. That is, the well‐known correlation between toughenability and the average molecular weight between crosslinks (M_c) does not necessarily hold true when the nature of epoxy backbone molecular mobility is altered. The potential significance of the present findings for a better design of toughened thermosets for structural applications is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2137–2149, 1999     

Modular material system for the microfabrication of biocompatible hydrogels based on thiol–ene‐modified poly(vinyl alcohol)

Novel modifications of the synthetic polymer poly(vinyl alcohol) (PVA) were developed for application in the field of biomedical engineering. PVA was modified with allyl succinic anhydride, norbornene anhydride as well as with γ‐thiobutyrolactone to produce macromers with reactive ene and thiol groups, respectively. Cytotoxicity studies have shown that the material exhibits almost no cell‐toxicity, when used in concentrations of 1 and 0.1 wt % for 24 h. The obtained macromers were photocrosslinked via thiol–ene chemistry. Storage stability of the macromer mixtures with different concentrations of pyrogallol as stabilizer were investigated. Photorheometry was employed to optimize mixtures concerning reactivity based on their thiol‐to‐ene ratio, photoinitiator concentration, and macromer content. The crosslinked hydrogels were studied concerning their swellability. To form hydrogels with cellular structure two‐photon‐polymerization (2PP) was employed. Processing windows for 2PP of selected mixtures were determined. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2060–2070