Synthesis,characterization and polymerization characteristics of new dimethacrylates,derived from 3,3,5‐trimethylcyclohexan‐1‐one–phenol adducts,as monomers for dental composites

The object of this study was to synthesize, characterize and evaluate several new dimethacrylate monomers, in order to discover new compositions for possible formulation of improved dental restoratives. Dimethacrylates derived from the 3,3,5‐trimethylcyclohexan‐1‐one–phenol reaction products were prepared and characterized by Fourier transform infrared and nuclear magnetic resonance. Thermal‐ and photopolymerization characteristics of these experimental monomers, in blends with triethyleneglycol dimethacrylate (TEGDMA), were evaluated by differential scanning calorimetry and differential photocalorimetry. An additional dimethacrylate derived from the 3,3,5‐trimethylcyclohexanone–phenol adduct, supplied by Bayer AG, was also evaluated during the study. A control for comparison consisted of a 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxy‐propyl) phenyl]propane (BisGMA) blend with TEGDMA. It was found that the polymerization behavior and properties of the visible light‐cured neat resins were dependent on their chemical structures. The experimental resins exhibited comparable curing characteristics, lower water sorption, higher wet glass transition temperature, and other improved properties, compared with the polymerized BisGMA/TEGDMA control. The more rigid and hydrophobic nature of the experimental resins, accomplished by incorporation of the bulky trimethyl‐substituted cyclohexyl moiety in the novel dimethacrylates, was considered to be the major factor contributing to the improved properties. These new dimethacrylates, for formulating thermosets with lower water sorption and higher glass transition temperature, may offer a path to improving composites for a variety of applications, including such things as dental restoratives and bone cements. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis and ring‐opening reactions of tetraphenyl‐substituted bisoxazoline monomers for preparing new thermosets and composites

To develop new monomers for formulating thermosetting composites, three new tetraphenyl‐substituted bisoxazoline monomers were synthesized via the direct reaction of 2‐(diphenylmethyl)oxazoline with bromoalkyls, using tert‐butyllithium. The structures were confirmed by Fourier transform infrared, nuclear magnetic resonance and mass spectrometry. These bisoxazolines have different melting points with varied molecular chain flexibility. They functioned well as crosslinkers when heated with phenolic resins or poly(acrylic acid), providing a path to new thermosetting materials with controlled glass transition temperature. To clarify the crosslinking reaction mechanism, the model reactions of these monomers with phenol and acetic acid were investigated. Copyright © 2000 John Wiley & Sons, Ltd.     

Dynamic mechanical behavior of acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

The dynamic mechanical behavior of uncrosslinked (thermoplastic) and crosslinked (thermosetting) acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) (NBR/EVA) blends was studied with reference to the effect of blend ratio, crosslinking systems, frequency, and temperature. Different crosslinked systems were prepared using peroxide (DCP), sulfur, and mixed crosslink systems. The glass‐transition behavior of the blends was affected by the blend ratio, the nature of crosslinking, and frequency. sThe damping properties of the blends increased with NBR content. The variations in tan δ_max were in accordance with morphology changes in the blends. From tan δ values of peroxide‐cured NBR, EVA, and blends the crosslinking effect of DCP was more predominant in NBR. The morphology of the uncrosslinked blends was examined using scanning electron and optical microscopes. Cocontinuous morphology was observed between 40 and 60 wt % of NBR. The particle size distribution curve of the blends was also drawn. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends, and it decreased with an increase in the NBR content. Various theoretical models were used to predict the modulus of the blends. From wide‐angle X‐ray scattering studies, the degree of crystallinity of the blends decreased with an increasing NBR content. The thermal behavior of the uncrosslinked and crosslinked systems of NBR/EVA blends was analyzed using a differential scanning calorimeter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1556–1570, 2002     

Synthesis and characterization of new segmented polyurethanes with side‐chain,liquid‐crystalline chain extenders

Liquid‐crystalline, segmented polyurethanes with methoxy–biphenyl mesogens pendant on the chain extender were synthesized by the conventional prepolymer technique and esterification reaction. Two, side‐chain, liquid‐crystalline (SCLC) polyurethanes with mesogens having spacers of six and eight methylene units were prepared. The structures of the mesogenic units and SCLC polyurethanes were confirmed by Fourier transform infrared spectroscopy and ¹H NMR. Polymer properties were also examined by solubility tests, water uptakes, and inherent viscosity measurements. Differential scanning calorimetry studies indicated that the transition temperature of the isotropic to the liquid‐crystalline phase decreased with increasing spacer length. Wide‐angle X‐ray diffraction (WAXD) studies revealed the existence of liquid‐crystalline phases for both SCLC polyurethanes. Polarized optical microscopic investigations further confirmed the thermotropic liquid‐crystalline behaviors and nematic mesophases of both samples. Thermogravimetric analysis displayed better thermal stabilities for both SCLC polymers and indicated that the presence of mesogenic side chains may increase the thermal stability of segmented polyurethanes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 290–302, 2004     

Semi‐interpenetrating polymer networks based on crosslinked poly(N‐isopropyl acrylamide) and methylcellulose prepared by frontal polymerization

In this work, semi‐interpenetrating gels of poly(N‐isopropyl acrylamide) and methylcellulose were successfully synthesized by using the Frontal Polymerization (FP) technique. The gels were obtained in the presence of dimethyl sulfoxide and trihexyltetradecylphosphonium persulfate, as polymerization solvent and radical initiator, respectively, hence avoiding the formation of bubbles during polymerization. Then, some of the gels containing dimethyl sulfoxide were thoroughly washed with water, hence obtaining the corresponding hydrogels. The effects of the ratio between poly(N‐isopropyl acrylamide) and methylcellulose, the amount of crosslinker and solvent medium (i.e., dimethyl sulfoxide and water) were thoroughly studied, assessing the influence of temperature and velocity of FP fronts on the glass transition temperature values (dried samples), on the swelling behavior and on the dynamic‐mechanical properties (gels swollen both in water and dimethyl sulfoxide). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 437–443     

Hyperbranched Polyamidoamines Containing β‐Cyclodextrin for Controlled Release of Chlorambucil

This work is focused on the controlled drug release behavior of hyperbranched HPMA in the presence of β‐CD. Hence, three HPMA‐β‐CDs and a pure HPMA were synthesized by Michael addition polymerization. As a model drug, CLB (an anti‐cancer drug) was loaded into them via a solution method for in vitro release studies. The DSC results indicate that the CLB/polymer interactions are at the molecular level. Loading CLB into these polymers results in an evident increase in their glass transition temperatures, and ΔT_g depends on the β‐CD content. The controlled‐release experiments show that the presence of β‐CD can appropriately slow the release of CLB from HPMA‐β‐CDs and adjust the ratio of CLB released in total drug loading.

     

Temperature induced structural evolution of a fluorene‐thiophene copolymer on rubbed surfaces

The thermal alignment of the liquid crystalline fluorene‐thiophene copolymer (F8T2) on rubbed polyimide surfaces is investigated by ex‐situ and in‐situ X‐ray scattering experiments. The ex‐situ characterization allows an assignment of the observed diffraction peaks to distances between polymer backbones (1.6 nm), distances between the flexible side groups of the polymer chains (0.43 nm), and intramolecular distances of adjacent ring units (0.5 nm). The in‐situ characterization allows a temperature dependent observation of the polymer chain alignment. A gradual alignment process of the polymer backbones is observed for temperatures up to 563 K. Decreasing temperature after the polymer chain alignment is accompanied by a glass transition of the side chains at 380 K. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:1599–1604, 2009     

Reversible melting and crystallization of high‐molar‐mass poly(oxyethylene)

The heat capacity of poly(oxyethylene) (POE) with a molar mass of 900,000 Da has been analyzed with differential scanning calorimetry and quasi‐isothermal, temperature‐modulated differential scanning calorimetry. The crystal structure, lattice parameters, and coherently scattering domain sizes have been measured with wide‐angle X‐ray diffraction as a function of temperature. The high‐molar‐mass POE crystals are in a folded‐chain macroconformation and show some locally reversible melting starting already at about 250 K. At 335 K, the thermodynamic heat capacity reaches the level of the melt. The reversible crystallinity depends on the modulation amplitude and has been varied in the melting range from ±0.2 to ±3.0 K. Before melting, there is neither a change in the crystal structure nor a change in the domain size, but the expansivity of the crystals increases at about 320 K. These observations support the interpretation that the monoclinic POE crystals possess a glass transition temperature with a midpoint at about 324 K, whereas the maximum melting temperature is 341 K. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 475–489, 2007     

Glass‐transition temperature behavior of alumina/PMMA nanocomposites

Alumina/poly(methyl methacrylate) (PMMA) nanocomposites were synthesized by an in situ free‐radical polymerization process with 38 and 17 nm diameter γ‐alumina nanoparticles. At extremely low filler weight fractions (<1.0 wt % of 38 nm fillers or < 0.5 wt % of 17 nm fillers) the glass‐transition temperature (T_g) of the nanocomposites drops by 25 °C when compared to the neat polymer. Further additions of filler (up to 10 wt %) do not lead to additional T_g reductions. The thermal behavior is shown to vary with particle size, but this dependence can be normalized with respect to a specific surface area. The nanocomposite T_g phenomenon is hypothesized to be because of nonadhering nanoparticles that serve as templates for a porous system with many internal interfaces that break up the percolating structure of dynamically heterogeneous domains recently suggested by Long, D.; and Lequeux, F. Eur Phys J E 2001, 4, 371 to be responsible for the T_g reductions in polymer ultrathin films. The results also point to a far field effect of the nanoparticle surface on the bulk matrix. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4371–4383, 2004     

Synthesis and characterization of copolyperoxides of indene with styrene, α‐methylstyrene,and α‐phenylstyrene

The oxidative copolymerization of indene with styrene, α‐methylstyrene, and α‐phenylstyrene is investigated. Copolyperoxides of different compositions have been synthesized by the free‐radical‐initiated oxidative copolymerization of indene with vinyl monomers. The compositions of the copolyperoxides obtained from the ¹H and ¹³C NMR spectra have been used to determine the reactivity ratios of the monomers. The reactivity ratios indicate that indene forms an ideal copolyperoxide with styrene and α‐methylstyrene and alternating copolyperoxides with α‐phenylstyrene. Thermal degradation studies via differential scanning calorimetry and electron‐impact mass spectroscopy support the alternating peroxide units in the copolyperoxide chain. The activation energy for thermal degradation suggests that the degradation is dependent on the dissociation of the peroxide (? O? O? ) bonds in the backbone of the copolyperoxide chain. Their flexibility has been examined in terms of the glass‐transition temperature. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2004–2017, 2002     

Oxidative copolymerization of indene with p‐tert‐butylstyrene: Synthesis,characterization, thermal analysis,and reactivity ratios

Copolyperoxides of indene and p‐tert‐butylstyrene of different compositions were synthesized by free‐radical‐initiated oxidative copolymerization. The compositions of the copolyperoxides, obtained from ¹H and ¹³C NMR spectra, were used to calculate the reactivity ratios of the monomers. The reactivity ratios indicated a larger proportion of indene units in random placement in the copolyperoxides. Thermal‐degradation studies by differential scanning calorimetry and electron‐impact mass spectrometry supported alternating peroxide units in the copolymer backbone. The activation energy for thermal degradation suggested that the degradation was dependent on the dissociation of the peroxide (? O? O? ) bonds in the backbone of the copolyperoxide chain. The flexibility of the copolyperoxides was examined in terms of the glass‐transition temperature. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 9–18, 2002     

Diblock copolymers of polystyrene‐b‐poly(1,3‐cyclohexadiene) exhibiting unique three‐phase microdomain morphologies

The synthesis and molecular characterization of a series of conformationally asymmetric polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐b‐PCHD) diblock copolymers (PCHD: ～90% 1,4 and ～10% 1,2), by sequential anionic copolymerization high vacuum techniques, is reported. A wide range of volume fractions (0.27 ≤ ?_PS ≤ 0.91) was studied by transmission electron microscopy and small‐angle X‐ray scattering in order to explore in detail the microphase separation behavior of these flexible/semiflexible diblock copolymers. Unusual morphologies, consisting of PCHD core(PCHD‐1,4)–shell(PCHD‐1,2) cylinders in PS matrix and three‐phase (PS, PCHD‐1,4, PCHD‐1,2) four‐layer lamellae, were observed suggesting that the chain stiffness of the PCHD block and the strong dependence of the interaction parameter χ on the PCHD microstructures are important factors for the formation of this unusual microphase separation behavior in PS‐b‐PCHD diblock copolymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1564–1572     

Properties of well‐defined alternating and random copolymers of methacrylates and styrene prepared by controlled/living radical polymerization

The physical properties of well‐defined alternating copolymers poly(methyl methacrylate‐alt‐styrene) and poly(n‐butyl methacrylate‐alt‐styrene), prepared by reversible addition–fragmentation chain transfer polymerization in the presence of Lewis acids, were investigated with differential scanning calorimetry, wide‐angle X‐ray scattering, and dynamic mechanical measurements. The properties were compared with those of random copolymers of the same overall composition and the corresponding homopolymers. Wide‐angle X‐ray scattering data showed that the alternating copolymers possessed a more regular comonomer sequence than the random copolymers. The thermomechanical properties of alternating copolymers and random copolymers were quite similar and typical for amorphous polymers, but in one of the cases studied the glass‐transition temperature for alternating copolymer was remarkably higher than for the random copolymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3440–3446, 2005     

Noncovalent functionalization of multiwalled and double‐walled carbon nanotubes: Positive effect of the filler functionalization on high glass transition temperature epoxy resins

Double‐walled carbon nanotubes (DWCNTs) and multiwalled carbon nanotubes (MWCNTs) were modified using melamine to attach ? NH₂ to the surface of these fillers, without previous oxidation of their graphene layers. FT‐Raman, elemental (chemical) and thermogravimetric analysis, confirmed the modification, which was more extensive for DWCNTs. The potential of this modification was evaluated by adding the melamin‐modified nanotubes to thermosets based on diglycidyl ether of bisphenol A (resin) and polycyclic amine (hardener). Broadening of the glass transition interval and an increase between 7 and 8 °C of the glass transition temperatures show better filler/matrix interaction for the nanocomposites based on melamine‐modified nanotubes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1860–1868, 2009     

Promoting effect of thiophenols on the ring‐opening polymerization of 1,3‐benzoxazine

Thiophenol and p‐nitrothiophenol were evaluated as promoters for the ring opening polymerization of benzoxazine. The ring‐opening polymerization of p‐cresol type monofunctional N‐phenyl benzoxazine 1a with 10 mol % of thiophenols proceeded at 150 °C, leading to the high conversion of 1a more than 95% within 5 h, whereas the polymerization of 1a without thiophenols did not proceed under the same conditions. The promotion effect of the thiophenols on curing of bisphenol‐A type N‐phenyl benzoxazine 1b was also investigated. In the differential scanning calorimetric (DSC) analysis of the polymerization of 1b at 150 °C without using any promoters, an exothermic peak attributable to the ring‐opening reaction of benzoxazine was observed after 8 h. In contrast, in the DSC analysis of the polymerization of 1b with addition 20 mol % of p‐nitrothiophenol, an exothermic peak was observed within 2 h, to clarify the significant promoting effect of p‐nitrothiophenol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2523–2527     

Synthesis and optical and electrochemical properties of thermotropic,liquid‐crystalline,semirigid copolyesters based on 2,5‐diphenyl‐1,3,4‐thiadiazole units

Novel thermotropic liquid‐crystalline (LC) copolyesters were prepared with three disubstituted (4,4′‐, 3,4′‐, and 3,3′‐) dioxydiundecanol derivatives of terphenyl analogues of 1,3,4‐thiadiazole [2,5‐diphenyl‐1,3,4‐thiadiazole (DPTD)], and their optical and electrochemical properties were examined. Their structures were characterized with Fourier transform infrared, ¹H NMR spectroscopy, and elemental analyses. The thermal and mesomorphic properties of the copolyesters were investigated with differential scanning calorimetry measurements, polarized microscopy observations, and X‐ray analyses; the data suggested that these copolymers formed LC smectic or nematic phases. The mesomorphic tendency decreased in the following order: 4,4′‐DPTD and 3,4′‐DPTD copolyesters > 4,4′‐DPTD and 3,3′‐DPTD copolyesters > 3,4′‐DPTD and 3,3′‐DPTD copolyesters. Solution and solid‐state ultraviolet–visible (UV–vis) and photoluminescence spectra indicated that the copolyesters displayed maximum absorbances and blue emissions according to the DPTD unit; the peak maxima of absorption and emission spectra of the copolyesters shifted to lower wavelengths in the aforementioned order for the LC properties. Cyclic voltammetry measurements indicated that the electrochemical band gaps of the polyesters estimated from the onset of reduction and oxidation processes were almost the same as the optical band gaps determined from the solid‐state UV–vis spectral data. The DPTD unit enhanced the hole‐injection barrier and improved the charge‐injection balance in these polyesters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1511–1525, 2005     

Polymerization of methyl methacrylate by 2‐pyrrolidinone and n‐dodecyl mercaptan

The bulk polymerization of methyl methacrylate initiated with 2‐pyrrolidinone and n‐dodecyl mercaptan (R‐SH) has been explored. This polymerization system showed “living” characteristics; for example, the molecular weight of the resulting polymers increased with reaction time by gel permeation chromatographic analysis. Also, the polymer was characterized by Fourier transform infrared spectroscopy, ¹H NMR, and ¹³C NMR techniques. The polymer end with the iniferter structures was found. By the initial‐rate method, the polymerization rate depended on [2‐pyrrolidinone]^1.0 and [R‐SH]⁰. Combining the structure analysis and the polymerization‐rate expression, a possible mechanism was proposed. n‐Dodecyl mercaptan served dual roles—as a catalyst at low conversion and as a chain‐transfer agent at high conversion. Finally, the thermal properties were studied, and the glass‐transition temperature and thermal‐degradation temperature were, respectively, 25 and 80–100 °C higher than that of the azobisisobutyronitrile system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3692–3702, 2002