Preparation and Evaluation of Visible Light-Cured Multi-Methacrylates for Dental Composites

Abstract

To explore new VLC oligomers exhibiting low shrinkage, low water sorption, and improved mechanical properties, a family of multi-methacrylates, based on poly(isopropylidenediphenol) resin (BPA), was synthesized, characterized, and evaluated. The BPA resin, having an average of eight phenolic hydroxyl groups per molecule, was treated with ethylene carbonate and the resultant product esterified at four different grafted levels, using methacryloyl chloride. Structures of these EEBPA oligomers, were confirmed by FT-IR and ¹³C NMR. The EEBPA oligomer/TEGDMA (50/50, w/w) blends were combined with 0.5 wt% camphoroquinone(CQ) and 1.0 wt% N,N-dimethylaminoethyl methacrylate (DMAEM). The control was BisGMA/TEGDMA (50/50, w/w) blends having the same levels of CQ/DMAEM. Differential photocalorimetry (DPC) and differential scanning calorimetry (DSC) showed the multi-methacrylate/TEGDMA (neat resin) blends have polymerization characteristics comparable to the BisGMA/TEGDMA control. These multi-functional oligomers have lower polymerization shrinkage and lower uptake of water and other liquids. In addition, two experimental oligomers EEBPA #2 and #3 have higher compressive strength than the BisGMA and comparable diametral tensile strength to the BisGMA control. These results suggest that the new type of multi-functional methacrylate oligomers (EEBPA) have potential application in formulating dental composites with improved properties.     

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.     

NOVEL TRIMETHACRYLATES: SYNTHESIS,CHARACTERIZATION, AND EVALUATION OF NEW MONOMERS FOR IMPROVED DENTAL RESTORATIVES

ABSTRACT

Two novel trimethacrylates, i.e., 1,1,1-tri-[4-(methacryloxyethoxy)-phenyl] ethane (TMPE) and 1,1,1-tri-[4-(2-methyl-2-methacryloxyethoxy)-phenyl]ethane (TMMPE), have been synthesized by reacting methacryloyl chloride with the corresponding hydroxyl intermediates. Both trimethacrylate monomers, having a low viscosity of 11.5 and 13.1 Pa.S, respectively, were blended with TEGDMA at three different weight ratios, i.e., 90/10, 70/30, and 50/50. The mixtures were made visible light-curable (VLC) by the addition of camphorquinone (0.5 wt%) and N,N-dimethyl-aminoethyl methacrylate (1.0 wt%). In addition to evaluation as cured neat resins, VLC formulations with 70% by wt. of silanated microfiller were also prepared and evaluated. The control in both cases was a VLC formulation of BisGMA/TEGDMA (70/30 and 50/50 wt/wt). These new, formulated resins have both improved physical properties and higher double bond conversion than the BisGMA control, as well as decreased linear polymerization shrinkage (LPS). The neat resin having 70/30 (wt/wt) ratio of TMPE/TEGDMA (T7T3, Table 2) exhibited a compressive strength (CS) of 496 (±51) MPa compared to the 70/30 (wt/wt) ratio of BisGMA/-TEGDMA control having 425(±27) MPa. A filled resin having a 90/10 (wt/wt) ratio of TMPE/TEGDMA exhibited a flexural strength (FS) of 122.6(±23) MPa, compared with a similar filled BisGMA/TEGDMA (70/30, wt/wt) resin exhibiting 112.7(±19) MPa. These and other results suggest that these new trimethacrylates have potential application in formulating dental composites with improved performance.     

Syntheses of biodegradable polymer networks based on polycaprolactone and glutamic acid

Biodegradable trifunctional oligomer was synthesized from polycaprolactone and glutamic acid and characterized by Fourier‐transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopies. Injectable and in situ crosslinkable polymer networks were fabricated by the copolymerization of oligomer with triethylene glycol dimethacrylate (TEGDMA) and used to evaluate the initial compressive strengths, viscosities, shrinkages, thermal stabilities, and biodegradabilities in the forms of polymer network neat resin and their composites with β‐tricalcium phosphate. The initial compressive strengths (CS) values of neat resins ranged from 9.54 to 187.6 MPa. Both neat resins and composites had polymerization shrinkage ranging from 0% to 11.7%, which increased with increasing of TEGDMA contents in resin. Moreover, in polymer composite resins, shrinkage values decreased with increasing filler level from 0% to 4.6%, and exothermic evolution values decreased from 33.5°C to 29.7°C as increasing filler level. The composite with the formulation of (polycaprolactone)‐glutamate triacrylate (PCLGTA)/TEGDMA (25/75) and powder/liquid (P/L) ratio of 1.0 exhibited the highest exothermal and lowest shrinkage values. The increase of oligomer in the formulation led to an increase in viscosity.     

METHACRYLOYL DERIVITIZED HYPERBRANCHED POLYESTER. 1. SYNTHESIS,CHARACTERIZATION, AND COPOLYMERIZATION

Three hyperbranched multi-methacrylates (H20-MMA, H30-MMA and H40-MMA) have been synthesized by reacting Boltorn dendritic polyols with methacrylic anhydride and methacryloyl chloride. Their structures were characterized by FT-IR and NMR (¹H and ¹³C) and molecular weights were measured by GPC. These multi-methacrylates (H-MMAs) mixed well with a variety of monomers such as acrylic acid (AA), methacrylic acid (MA), methyl methacrylate (MMA), 2-hydroxy-ethyl methacrylate (HEMA), tri(ethylene glycol) dimethdimethacrylate (TEGDMA), and bisphenol A glycidyl dimethacrylate (BisGMA). The initial studies on thermal polymerization activities of 10% of H-MMAs with AA, MA, and MMA showed that they gave higher polymerization enthalpy than the corresponding homopolymerization. The resulting materials showed one glass transition temperature, indicating a typical single-phase resin. The H-MMAs can effectively copolymerize with AA, MA, and MMA, with essentially no homopolymers produced, as indicated by acetone extraction studies. This indicated that the hyperbranched multi-methacrylates have the potential to be used as crosslinking agents or modifiers with a number of monomers to produce new thermosets.     

Effect of the Poly(Methyl Methacrylate) Molecular Weight on the Mechanical Properties BisGMA/TEGDMA Semi-interpenetrating Polymer Networks

Abstract

The effect of poly(methyl methacrylate) [PMMA], with different molecular weights on the mechanical properties of a polymerized BisGMA/TEGDMA base monomer resin was investigated. With the aid of acetone solvent, PMMA could be readily dissolved in BisGMA/TEGDMA mixtures. The addition of PMMA can significantly improve the compressive strengths and decrease the Knoop hardness values of the BisGMA/TEGDMA/PMMA semi-IPNs. The thermal expansion coefficients rapidly increased before T_g, and decreased after T _g. The observed properties could be attributed to the effect of the molecular weight of the PMMA on the phase structures of the semi-IPNs.     

Properties and Characterization of Organoclay/Dimethacrylate Composites Obtained by In Situ Photopolymerization

Summary: Composites of dimethacrylates/organoclay were obtained by in situ photopolymerization of Bis-GMA (Bisphenol A glycidyl methacrylate) and TEGDMA (tetraethyleneglycol dimethacrylate) in the presence of camphorquinone and DEEMA (2-(diethylamino)ethyl methacrylate). The composites contained up to 10% wt/wt of organoclays. Monomer conversion and polymerization kinetics were determined by real time Fourier-Transform Infrared Spectroscopy – Attenuated Total Reflectance (FTIR-ATR), and showed an increase of conversion with addition of the clay. The storage modulus E' of the composites also had a marked dependence on the composite composition and increased with addition of clay at all temperatures. T_g also increases with clay content. X-Ray Diffraction (XRD) analysis shows that the clay is completely exfoliated for the composites with a lower proportion of clay, whereas for larger clay/polymer proportions peaks corresponding to the interlamellar distance of the clay are still observed. This is probably due to the fact that the amount of monomers in the initial formulation was not sufficient to delaminate the clay. Scanning Electron Microscopy (SEM) images indicate a quite homogenous copolymer, with some clay aggregates that increase in size and number for the higher filler loadings in agreement with the XRD results.     

Synthesis of oligomeric urethane dimethacrylates with carboxylic groups and their testing in dental composites

Carboxyl urethane dimethacrylate oligomers with poly(ethylene oxide) sequences in the structure were synthesized and examined in photopolymerizable resins that could better adhere to various kinds of materials, including tooth substrates. Aspects of the morphogenesis of dental composites formed through a photochemically initiated radical copolymerization of the carboxylic derivatives, in addition to other partners encountered frequently in such materials, were studied comparatively with the corresponding urethane dimethacrylate monomer. The effect of a small quantity of a carboxylic macromer (ca. 10%) on the formation of a network with a non‐carboxyl urethane dimethacrylate oligomer (90%) as a potential substitute for diglycidyl methacrylate of bisphenol A and a filler (1/1 70% Aerosil/glass) was visualized by fluorescence spectroscopy with a pyrene methanol probe. The results showed the following: (1) the degree of conversion in the formulations into which carboxyl urethane dimethacrylate was incorporated decreased with increasing poly(ethylene oxide) chain length, (2) the formation of excimers was inhibited in the derived composites, and (3) an important quenching of the monomer fluorescence emission with the UV–vis irradiation time was observed in the formulation containing a filler (Aerosil+Zr/Sr glass). Preliminary testing of the resin composites suggested that all urethane oligomers containing carboxylic acid could lead to dental materials with reduced polymerization shrinkage and good mechanical properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1956–1967, 2007     

Effects of the structures of polymerizable monomers on the electro‐optical properties of UV cured polymer dispersed liquid crystal films

Polymer dispersed liquid crystal (PDLC) films were prepared by photopolymerization of liquid crystal (LC)/polymerizable monomers/photoinitiator composites. The effects of the structures of the polymerizable monomers on the electro‐optical properties of PDLC films were investigated. It was found that the length of the molecular chain and the rigidity and flexibility of molecules influenced the structure of the polymer network in the PDLC films somewhat, and then affected the electro‐optical properties of the composites accordingly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1369–1375, 2008     

Functionalized acrylic polyhydroxy urethanes as molecular tool box for photocurable thermosets and 3D printing

Liquid urethane (meth)acrylates represent attractive components of photocurable thermosets for applications ranging from coatings and adhesives to 3D printing. Herein we tailor liquid polyfunctional urethane methacrylates (UMA) derived from acrylic polyhydroxy urethanes. Cyclic carbonate methacrylates react with diamines to form dihydroxy-functional urethane dimethacrylates. In an “one-pot” process the hydroxy groups are functionalized either by reaction with 2-isocyanatoethyl methacrylate (IEMA) or by esterification with methacrylic anhydride (MAA) and acetic anhydride (AA). The hydroxy group esterification substantially lowers the resin viscosity (26–156 Pa•s). Hydroxy functionalization with IEMA and MAA affords tetrafunctional methacrylates. The corresponding photo-cured thermosets exhibit higher crosslinking density and improved stiffness as reflected by increasing the Young's modulus from 2900 to 3700 MPa combined with increasing the glass temperature from 135 to 204°C. Hence, this facile molecular UMA design enables to control functionality and thermoset properties over a wide range and meets the demands of 3D printing applications.     

Preparation and electromagnetic interference shielding characteristics of novel carbon‐nanotube/siloxane/poly‐(urea urethane) nanocomposites

Poly(urea urethane) (PUU) with a poly(dimethylsiloxane) soft segment was synthesized. Different types of conductive fillers—carbon nanotube (CNT), silver‐coated carbon nanotube (CNT–Ag), and nickel‐coated carbon nanotube (CNT–Ni)—were blended with PUU to form partially conductive polymer composites. The results showed that highly conductive metals could improve the conductivity of CNTs significantly. When the filler contents were 3, 4, and 5 parts per hundred parts of resin (phr), the PUU/CNT composites possessed electromagnetic interference shielding effectiveness (SE) at 8.5, 28.4, and 26.0 dB as the electromagnetic wave frequencies were 12.3, 16.2, and 15.9 GHz, respectively. SE of the composites that contained CNT–Ni and CNT–Ag increased with the filler loading. At the same modified‐CNT loading, the CNT–Ni‐filled composites had a higher SE than those filled with CNT–Ag. Tensile stresses ranged from 5.7 to 15.6 MPa (a 177.3% increase) when the CNT concentration reached 8 phr. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 345–358, 2005     

Synthesis and curing studies of PPG based telechelic urethane methacrylic macromonomers

A New class of telechelic urethane methacrylic (TUMA) macromonomers were synthesized by a two-step condensation of 1, 6-hexamethylenediisocyanate (HMDI) with polypropylene glycol (PPG) of various molecular weights and capped with hydroxyl ethyl methacrylate (HEMA). A model compound based on diethylene glycol (DEG)—M-1 was synthesized as a low molecular weight analogue. Another model compound—M-2 was also synthesized by direct coupling of two equivalents of HEMA with HMDI. The structure of the telechelic urethanes were confirmed by ¹H, ¹³C NMR and FTIR spectroscopy. Photopolymerization of these telechelic systems was investigated using 2,2-diethoxy acetophenone as the photoinitiator at 5 wt.%. Trihydroxymethylpropane trimethacrylate (30 parts), PPG diacrylates (25 parts), ethylhexyl acrylate (20 parts) were mixed with the various telechelic urethane methacrylates (25 parts) for curing studies. The kinetics of the curing was monitored by following the disappearance of the methacrylic double bonds at 1628 cm⁻¹ using IR spectroscopy. TUMAPPG-425 had the fastest cure rate among the telechelic urethane methacrylates. This could be accounted for by hydrogen bonding pre-association in these systems. The thermal properties of the cured films were studied using TGA measurements. The cured films of the neat resin had a lower 50 wt.% loss temperature compared with that of the same resin in the formulation.     

Structure and dynamics of carbon black‐filled elastomers

The linear and nonlinear melt viscoelastic properties for a series of carbon black‐filled polymer composites were studied. Complementary tapping‐mode atomic force microscopy (AFM) studies were used to examine the dispersion and structural correlations of the filler particles in these composites. The low‐frequency dependence of the linear viscoelastic moduli gradually changes from liquidlike behavior for the unfilled polymer to pseudosolid character for composites with more than 9 vol % carbon black filler. The plateau modulus, inferred from the linear viscoelastic response, exhibits a somewhat discontinuous change at about 9 vol % filler. On the basis of the linear viscoelastic response, we postulate that the carbon black filler forms a continuous percolated network structure beyond 9 vol % filler, considerably lower than that expected from theoretical calculations for overlapping spheres and ellipsoids. We suggest that the lower threshold for percolation is due to the polymer mediation of the filler structure, resulting from the low functionality of the polymer and, consequently, few strong polymer–filler interactions, allowing for long loops and tails that can either bridge filler particles or entangle with one another. Furthermore, the strain amplitude for the transition from linear behavior to nonlinear behavior of the modulus for the composites with greater than 9 vol % filler is independent of frequency, and this critical strain amplitude decreases with increasing filler concentration. Complementary AFM measurements suggest a well‐dispersed carbon black structure with the nearest neighbor distance showing a discontinuous decrease at about 9 vol % filler, again consistent with the formation of a filler network structure beyond 9 vol % carbon black. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 256–275, 2001     

Synthesis of traditional and ionic polymethacrylates by anion catalyzed group transfer polymerization

The hydrophobic ionic liquid 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide was successfully used as solvent in group transfer polymerization of traditional methacrylates (methyl methacrylate, n‐butyl methacrylate, and benzyl methacrylate) and of ionic liquid methacrylates (ILMAs). This demonstrates that this ionic liquid makes reaction conditions, which do not require the use of ultra‐dried solvents. The ILMAs were N‐[2‐(methacryloyloxy)ethyl]‐N,N‐dimethyl‐N‐alkylammonium bis(trifluoromethylsulfonyl)imides bearing methyl, ethyl, propyl, butyl, or hexyl substituents. Increasing size of the alkyl substituent at the cation results in decreasing glass transition temperature in case of both ionic liquid methacrylates and polymers derived of them. Furthermore, the glass transition temperature is significantly higher for these polymers compared with the ionic liquid methacrylates, and the effect of glass transition temperature reduction with increasing size of the alkyl substituent is stronger for the polymers. A mechanism was proposed explaining the catalytic function of the ionic liquid used as solvent for polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2849–2859     

Synthesis and polymerizations of six aminophosphonate‐containing methacrylates

Two different groups of novel aminophosphonate‐containing methacrylates were synthesized. The route to the first group involves reactions of ethyl α‐bromomethacryate (EBBr) and t‐butyl α‐bromomethacryate (TBBr) with diethyl aminomethylphosphonate and diethyl 2‐aminoethylphosphonate. Bulk and solution polymerizations at 60–80 °C with 2,2′‐azobis(isobutyronitrile) (AIBN) gave crosslinked or soluble polymers depending on monomer structure and polymerization conditions. Increasing bulkiness from ethyl to t‐butyl decreases the polymerization rate, correlated well with the chemical shift differences of double bond carbons and consistent with the lower molecular weights of t‐butyl ester polymers (M_n = 1800–7900 vs. 50,000–72,000). The route to the second group involves the Michael addition reaction between diethyl aminomethylphosphonate and diethyl 2‐aminoethylphosphonate with 3‐(acryloyloxy)‐2‐hydroxypropyl methacrylate (AHM) to give secondary amines. The photopolymerization using differential scanning calorimeter showed that these monomers have similar or higher reactivities than AHM, even though AHM has two double bonds. The high rates of polymerization of these monomers were attributed to both hydrogen bonding interactions due to additional NH groups as well as chain transfer reactions. All the homopolymers obtained produced char (17–35%) on combustion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Characterization of dimethacrylate polymeric networks: a study of the crosslinked structure formed by monomers used in dental composites

The resin phase of dental composites is mainly composed of combinations of dimethacrylate comonomers, with final polymeric network structure defined by monomer type/reactivity and degree of conversion. This fundamental study evaluates how increasing concentrations of the flexible triethylene glycol dimethacrylate (TEGDMA) influences void formation in bisphenol A diglycidyl dimethacrylate (BisGMA) co-polymerizations and correlates this aspect of network structure with reaction kinetic parameters and macroscopic volumetric shrinkage. Photopolymerization kinetics was followed in real-time by a near-infrared (NIR) spectroscopic technique, viscosity was assessed with a viscometer, volumetric shrinkage was followed with a linometer, free volume formation was determined by positron annihilation lifetime spectroscopy (PALS) and the sol–gel composition was determined by extraction with dichloromethane followed by ¹H NMR analysis. Results show that, as expected, volumetric shrinkage increases with TEGDMA concentration and monomer conversion. Extraction/¹H NMR studies show increasing participation of the more flexible TEGDMA towards the limiting stages of conversion/crosslinking development. As the conversion progresses, either based on longer irradiation times or greater TEGDMA concentrations, the network becomes more dense, which is evidenced by the decrease in free volume and weight loss after extraction in these situations. For the same composition (BisGMA/TEGDMA 60–40 mol%) light-cured for increasing periods of time (from 10 to 600 s), free volume decreased and volumetric shrinkage increased, in a linear relationship with conversion. However, the correlation between free volume and macroscopic volumetric shrinkage was shown to be rather complex for variable compositions exposed for the same time (600 s). The addition of TEGDMA decreases free-volume up to 40 mol% (due to increased conversion), but above that concentration, in spite of the increase in conversion/crosslinking, free volume pore size increases due to the high concentration of the more flexible monomer. In those cases, the increase in volumetric shrinkage was due to higher functional group concentration, in spite of the greater free volume. Therefore, through the application of the PALS model, this study elucidates the network formation in dimethacrylates commonly used in dental materials.     

Photografting as a versatile,localizable, and single‐step surface functionalization of silica‐based monoliths dedicated to microscale separation techniques

In this work, we developed a surface functionalization way of silica monoliths with a rapid, simple, versatile, and localizable photografting step. The elaboration of a photoreactive layer at the surface of monoliths was first optimized. The functionalization with [γ‐(methacryloyloxy)propyl]trimethoxysilane at 80°C in a hydro‐organic solution containing triethylamine as catalyst allows reachng the highest density of methacrylate photoactive moieties on silica surfaces. These methacrylate reactive surfaces were subsequently photografted within few minutes with acrylate monomers bearing alkyl chains (C₁₂ and C₁₈). The photografting efficiency was determined by monitoring the retentive properties of monoliths in the RP mode. The retention factors are of the same order of magnitude as highly retentive columns obtained by modification of silica surface with long‐alkyl chain silanes or by thermal polymerization of long‐alkyl chain monomers. It was also verified that such grafting neither impaired the efficiency of the monolithic stationary phase (H_min = 6–8 μm in nano‐LC) nor its permeability (about 6 × 10^?14 m²). Further, it was also demonstrated that photografting is localizable in nonmasked defined areas. Results obtained in anion‐exchange chromatography after photopolymerization of [2‐(methacryloyloxy)ethyl]trimethylammonium chloride are presented as well to demonstrate the versatility of the developed approach.     

Organic–inorganic hybrid networks by the sol–gel process and subsequent photopolymerization

Organic–inorganic hybrid materials were prepared by a convenient two‐step curing procedure based on sol–gel condensation and subsequent photopolymerization. Novel bismethacrylate‐based hybrid monomers with pendant, condensable alkoxysilane groups were prepared by Michael addition and possessed number‐average molecular weights between 580 and 1600 g/mol. The formation of inorganic networks by sol–gel condensation of the alkoxysilane groups in the presence of aqueous methacrylic acid was monitored with rheological measurements. The condensation conversion was monitored with solid‐state ²⁹Si cross‐polarization/magic‐angle spinning NMR spectroscopy. Subsequent photopolymerization led to organic–inorganic hybrid networks and low volume shrinkage, ranging from 4.2 to 8.3%, depending on the molecular weight of the hybrid monomer applied. Highly filled composite materials with glass filler fractions greater than 75% showed attractive mechanical properties with Young's moduli of 2700–6200 MPa. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4274–4282, 2001     

Effect of polymer architecture on self‐diffusion of LC polymers

Two LC side‐group poly(methacrylates) were synthesized, and their melt dynamics were compared with each other and a third, main‐chain side‐group combined LC polymer. A new route was developed for the synthesis of the poly(methacrylate) polymers which readily converts relatively inexpensive perdeuteromethyl methacrylate to other methacrylate monomers. Self‐diffusion data was obtained through the use of forward recoil spectrometry, while modulus and viscosity data were measured using rotational rheometers in oscillatory shear. Diffusion coefficients and complex viscosity were compared to previous experiments on liquid crystal polymers of similar architecture to determine the effect of side‐group interdigitation and chain packing on center of mass movement. The decyl terminated LC side‐group polymer possessed an interdigitated smectic phase and a sharp discontinuity in the self‐diffusion behavior at the clearing transition. In contrast, the self‐diffusion behavior of the methyl terminated LC side‐group polymer, which possessed head‐to‐head side‐group packing, was seemingly unaffected by the smectic–nematic and nematic–isotropic phase transitions. The self‐diffusion coefficients of both polymers were relatively insensitive to the apparent glass transition. The presence of moderately fast sub‐T_g chain motion was supported by rheological measurements that provided further evidence of considerable molecular motion below T_g. The complex phase behavior of the combined main‐chain side‐group polymer heavily influenced both the self‐diffusion and rheological behavior. Differences between the self‐diffusion and viscosity data of the main‐chain side‐group polymer could be interpreted in terms of the defect structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 405–414, 1999     

Viscoelastic properties of ionic polymer composites reinforced by soy protein isolate

Both linear and nonlinear viscoelastic properties of ionic polymer composites reinforced by soy protein isolate (SPI) were studied. Viscoelastic properties were related to the aggregate structure of fillers. The aggregate structure of SPI is consisted of submicron size of globule protein particles that form an open aggregate structure. SPI and carbon black (CB) aggregates characterized by scanning electron microscope and particle size analyzer indicate that CB aggregates have a smaller primary particle and aggregate size than SPI aggregates, but the SPI composites have a slightly greater elastic modulus in the linear viscoelastic region than the CB composites. The composite containing 3–40 wt % of SPI has a transition in the shear elastic modulus between 6 and 8 vol % filler, indicating a percolation threshold. CB composites also showed a modulus transition at <6 vol %. The change of fractional free volume with filler concentration as estimated from WLF fit of frequency shift factor also supports the existence of a percolation threshold. Nonlinear viscoelastic properties of filler, matrix, and composites suggested that the filler‐immobilized rubber network generated a G′ maximum in the modulus‐strain curves and the SPI formed a stronger filler network than the CB in these composites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3503–3518, 2005