Effects of filler–polymer interactions on cold‐crystallization kinetics in crosslinked,silica‐filled polydimethylsiloxane/polydiphenylsiloxane copolymer melts

Crystallization in a series of variable crosslink density poly(dimethyl‐diphenyl)siloxanes random block copolymers reinforced through a mixture of precipitated and fumed silica fillers has been studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), nuclear magnetic resonance (NMR), and X‐ray diffraction (XRD). The silicone composite studied was composed of 94.6 mol % dimethoylsiloxane, 5.1 mol % diphenylsiloxane, and 0.3 mol % methyl‐vinyl siloxane (which formed crosslinking after peroxide cure). The polymer was filled with a mixture of 21.6 wt % fumed silica and 4.0 wt % precipitated silica previously treated with 6.8 wt % ethoxy‐end‐blocked siloxane processing aid. Molecular weight between crosslinks and filler–polymer interaction strength were modified by exposure to γ‐irradiation in either air or in vacuo. Isothermal DMA experiments illustrated that crystallization at ?85 °C occurred over a 1.8 hour period in silica‐filled systems and 2.2–2.6 hours in unfilled systems. The crystallization kinetics for irradiated samples were found to be dependent on crosslink density. Irradiation in vacuo resulted in faster overall crystallization rates compared to air irradiation for the same crosslink density, likely due to a reduction in the interaction between the polymer chains and the silica filler surface for samples irradiated in air. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1898–1906, 2006     

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     

Temperature and aging dependence of strain‐induced crystallization and cavitation in highly crosslinked and filled natural rubber

We have investigated the structural changes occurring in highly crosslinked and carbon‐black filled natural rubber under uniaxial extension by small‐ and wide‐angle X‐ray scattering using synchrotron radiation. The experiments focused on strain‐induced crystallization (SIC) and nanocavitation and were carried out on a model series of materials as a function of temperature and aging conditions. We find that for all materials both SIC and cavitation decrease markedly with temperature and aging. However, the presence of carbon black filler shifts the ceiling temperature where SIC is observed to at least 120°C, presumably by a nucleating effect, maintaining the high strength of the elastomers. Interestingly, although in pure elastomers, the cavitation strength decreases with temperature, we find that in these filled elastomers the critical stress for the onset of cavitation increases significantly with temperature strongly suggesting that cavitation is due to the local confinement between fillers and supporting the idea of a glassy layer near the filler. Aging for 10 days at 110°C in oxygen‐free conditions decreases both SIC and cavitation and reduces the strength of the elastomer at high temperature. This is attributed to the formation of sulfur side chains hindering the crystallization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 780–793     

The effect of heat treatment on water sorption in polylactide and polylactide composites via changes in glass‐transition temperature and crystallization kinetics

Water sorption into polylactide (PLA) and polylactide‐montmorillonite (PLLA‐MONT) composites containing 5 wt % of montmorillonite (MONT) under different heat treatment conditions was studied using the quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) technique. Results showed that water sorption in neat polymer films and composite films increased with heat treatment temperature up to 120 °C. Differential scanning calorimetry was used to measure the glass‐transition temperature and isothermal crystallization kinetics of all samples. The mobility of the amorphous domain in all samples increased with heat treatment temperature, indicated by the decrease in glass‐transition temperature. PLA composites crystallized at a much faster rate than neat PLA did because MONT acted as a nucleating agent. Under the same heat treatment condition, water sorption in PLLA‐MONT composites was always higher than that in neat PLA due to the presence of the hydrophilic hydroxyl groups on the surface of MONT particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Positive‐temperature‐coefficient/negative‐temperature‐coefficient effect of low‐density polyethylene filled with a mixture of carbon black and carbon fiber

Low‐density polyethylene (LDPE) filled with carbon black (CB) and carbon fiber (CF) composites were prepared by a conventional melt‐mixing method. The effects of a mixture of CB and CF on the positive‐temperature‐coefficient (PTC) effect and the negative‐temperature‐coefficient (NTC) effect, as well as the percolation threshold, were examined in detail. A synergy effect between CB and CF occurred, in that continuous conductive pathways formed within the CB/CF‐filled composite. The percolation threshold was moved to a reduced filler content with the addition of CF to an LDPE/CB composite. A model was proposed to explain the difference in the PTC behavior of composites containing CB and CF and composites containing only CB or CF. In addition, the NTC effect was weakened with a mixture of CB and CF, and a relatively small radiation dose was required to eliminate the NTC phenomenon in LDPE/CB/CF composites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3094–3101, 2003     

Polylactide compositions. II. Correlation between morphology and main properties of PLA/calcium sulfate composites

Starting from calcium sulfate (gypsum) as fermentation by‐product of lactic acid production process, high performance composites have been produced by melt‐blending polylactide (PLA, L/D isomer ratio of 96:4) and β‐anhydrite II (AII) filler, that is, calcium sulfate hemihydrate previously dehydrated at 500 °C. Characterized by attractive mechanical and thermal properties due to good filler dispersion throughout the polyester matrix, these composites are interesting for potential use as biodegradable rigid packaging. Physical characterization of selected composites filled with 20 and 40 wt % AII has been performed and compared to processed unfilled PLA with similar amorphous structure. State of dispersion of the filler particles and interphase characteristic features have been investigated using light microscopy (LM) and scanning electron microscopy (SEM). Addition of AII did not decrease PLA thermal stability as revealed by thermogravimetry analyses (TGA) and allowed reaching a slight increase of PLA crystallizability during melt crystallization and upon heating from the glassy, amorphous state (DSC). It was found by thermomechanical measurements (DMTA) that the AII filler increased pronouncedly storage modulus (E′) of the composites in comparison with PLA in a broad temperature range. The X‐ray investigations showed stable/unchanged crystallographic structure of AII during processing with molten PLA and in the composite system. The notable thermal and mechanical properties of PLA–AII composites are accounted for by the good filler dispersion throughout the polyester matrix confirmed by morphological studies, system stability, and favorable interactions between components. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2770–2780, 2007     

Correlation between rheological,electrical, and microstructure characteristics in polyethylene/aluminum nanocomposites

Polyethylene (PE)/aluminum (Al) nanocomposites with various filler contents were prepared by a solution compounding method. We investigated the influence of the surface modification of Al nanoparticles on the microstructure and physical properties of the nanocomposites. The silane coupling agent octyl‐trimethoxysilane was shown to significantly increase interfacial compatibility between the polymer phase and Al nanoparticles. Rheological percolation threshold values were determined by analyzing the improvement in storage modulus at low frequencies depending on the Al loadings. Lower percolation threshold values were obtained for the composites prepared with the original nanoparticles than those prepared with the silane‐modified Al nanoparticles. A strong correlation between the time and concentration dependences of dc conductivity and rheological properties was observed in the different nanocomposite systems. The rheological threshold of the composites is smaller than the percolation threshold of electrical conductivity for both of the nanocomposite systems. The difference in percolation threshold is understood in terms of the smaller particle–particle distance required for electrical conduction when compared with that required to impede polymer mobility. It was directly shown by SEM characterization that the nanoparticle surface modification yielded better filler dispersion, as is consistent with our rheological and electrical analysis. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2143–2154, 2008     

Time dependence of piezoresistance for the conductor‐filled polymer composites

The piezoresistance and its time dependence of conductor‐filled polymer composites have been investigated. To reveal the origin of the time dependence of piezoresistance, the creep of the polymer matrix is also studied. Based on the interparticle separation change under the applied stress, a model has been developed to predict the piezoresistance and its time dependence. By analyzing this model, the influences of applied stress, filler particle diameter, filler volume fraction, matrix compressive modulus, potential barrier height, and the matrix creep behavior on the piezoresistance and its time dependence are interpreted quantitatively. These predicted results are compared with the experimental data obtained on the polymer composites filled with conductor fillers, and good agreements were obtained. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2739–2749, 2000     

Enhanced thermal conductivity of epoxy–matrix composites with hybrid fillers

The results of thermal conductivity study of epoxy–matrix composites filled with different type of powders are reported. Boron nitride and aluminum nitride micro‐powders with different size distribution and surface modification were used. A representative set of samples has been prepared with different contents of the fillers. The microstructure was investigated by SEM observations. Thermal conductivity measurements have been performed at room temperature and for selected samples it was also measured as a function of temperature from 300 K down to liquid helium temperatures. The most spectacular enhancement of the thermal conductivity was obtained for composites filled with hybrid fillers of boron nitride–silica and aluminum nitride–silica. In the case of sample with 31 vol.% of boron nitride–silica hybrid filler it amounts to 114% and for the sample with 45 vol.% of hybrid filler by 65% as compared with the reference composite with silica filler. However, in the case of small aluminum nitride grains application, large interfacial areas were introduced, promoting creation of thermal resistance barriers and causing phonon scattering more effective. As a result, no thermal conductivity improvement was obtained. Different characters of temperature dependencies are observed for hybrid filler composites which allowed identifying the component filler of the dominant contribution to the thermal conductivity in each case. The data show a good agreement with predictions of Agari‐Uno model, indicating the importance of conductive paths forming effect already at low filler contents. Copyright © 2014 John Wiley & Sons, Ltd.     

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     

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     

Investigation of a waterborne epoxy for E‐glass composites

We present a continuing investigation of epoxies based on diglycidyl ether of bisphenol A cured with 2‐ethyl‐4‐methylimidazole in the presence of the nonionic surfactant Triton X‐100. Interest in this epoxy system is due partially to its potential application as a waterborne replacement for solvent‐cast epoxies in E‐glass‐laminated printed circuit boards. The surfactant additive could potentially alter the interfacial properties and durability of composite materials. Previous studies revealed that the viscoelastic behavior of the cured epoxy is altered when it serves as the matrix in a glass‐fiber‐reinforced composite. The additional constraining and coupling of the E‐glass fibers to the segmental motion of the epoxy matrix results in an apparent increased level of viscoelastic cooperativity. Current research has determined that the cooperativity of an epoxy/E‐glass composite is also sensitive to the surface chemistry of the glass fibers. Model epoxy/E‐glass composites were constructed in which the glass was pretreated with either 3‐aminopropyltriethoxysilane or 3‐glycidoxypropyltrimethoxysilane coupling agents. Dynamic mechanical analysis was then used to create master curves of the storage modulus in the frequency domain. The frequency response of the master curves and resulting cooperativity plots clearly varied with the surface pretreatment of the glass fibers. The surfactant had surprisingly little effect in the observed trends in the cooperativity of the composites. However, the changes in cooperativity due to the surface pretreatment of the glass were lessened when the samples were prepared from waterborne emulsions. Moisture‐uptake experiments were also performed on epoxy samples that were filled with spherical glass beads as well as multi‐ply laminated composites. No increases in the diffusion constant could be attributed to the surfactant. However, the surfactant did enhance the final equilibrium moisture‐uptake levels. These equilibrium moisture‐uptake levels were also sensitive to the surface pretreatment of the E‐glass. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2351–2365, 2000     

Structure and mechanical properties of talc‐filled blends of polypropylene and styrenic block copolymers

The structure–property relationships of isotactic polypropylene (iPP)/styrenic block copolymer blends filled with talc were examined by optical and scanning electron microscopy, wide‐angle X‐ray diffraction, and tensile‐ and impact strength measurements. The composites were analyzed as a function of the poly(styrene‐b‐ethylene‐co‐propylene) diblock copolymer (SEP) and the poly(styrene‐b‐butadiene‐b‐styrene) triblock copolymer (SBS) content in the range from 0 to 20 vol % as elastomeric components and with 12 vol % of aminosilane surface‐treated talc as a filler. Talc crystals incorporated in the iPP matrix accommodated mostly plane‐parallel to the surface of the samples and strongly affected the crystallization process of the iPP matrix. The SBS block copolymer disoriented plane‐parallel talc crystals more significantly than the SEP block copolymer. The mechanical properties depended on the final phase morphology of the investigated iPP blends and composites and supermolecular structure of the iPP matrix because of the interactivity between their components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1255–1264, 2004     

Synthesis of imidazolium‐functionalized ionic polyurethane and formation of CdTe quantum dot–polyurethane nanocomposites

A series of positively charged imidazolium‐functionalized ionic polyurethanes (IPUs) were prepared in one‐step polymerization process by polymerization of presynthesized short‐chain imidazolium‐based ionic diol, polyethylene glycols with different molecular weights as long‐chain diols, and toluylene‐2,4‐diisocyanate. The structures of IPUs are confirmed by ¹H NMR analysis, and the thermogravimetric analysis measurement indicates that the IPUs have high degradation temperature. Fluorescent nanocrystal–polymer composites CdTe–IPU can be prepared conveniently, by the electrostatic interaction between positively charged IPUs and the negatively charged aqueous CdTe quantum dots (QDs). UV–vis absorption and photoluminescence spectra indicate the photochemical stability and strong fluorescent emission of CdTe–IPU composites. The quantum yields (QYs) of the composites are high and basically restore the QYs of the pure QDs. In addition, the transmission electron microscopy photographs show that the QDs in composites are uniform (about 3 nm in diameter) and monodisperse. The obtained nanocomposites are powder or elastomers with good film building. The casted CdTe–IPU films are transparent under visible light, and the colors of the composites and their films are vivid under a UV lamp. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of surface‐grafted ionic groups on the performance of cellulose‐fiber‐reinforced thermoplastic composites

The influence of the surface chemistry of the cellulose fiber and polymer matrix on the mechanical and thermal dynamic mechanical properties of cellulose‐fiber‐reinforced polymer composites was investigated. The cellulose fiber was treated either with a coupling agent or with a coupling‐agent treatment followed by the introduction of quaternary ammonium groups onto the fiber surface, whereas the polymer matrix, with opposite polar groups such as polystyrene incorporated with sulfonated polystyrene and poly(ethylene‐co‐methacrylic acid), was compounded with the fiber. The grafting of the fiber surface was investigated with Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy. Experimental results showed that an obvious improvement in the mechanical strength could be achieved for composites with an ionic interface between the fiber and the polymer matrix because of the adhesion enhancement of the fiber and the matrix. The improved adhesion could be ascribed to the grafted ionic groups at the cellulose‐fiber surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2022–2032, 2003     

Surface‐dependent effect of functional silica fillers on photocuring kinetics of hydrogel materials

Two types of silica: precipitated (P, prepared in non‐polar media, a new type, submicrometer sized) and fumed (F, nanosized), both unmodified and surface modified are investigated as functional fillers for potential applications in nanocomposites with poly(2‐hydroxyethyl methacrylate) matrix. Special attention is paid to the kinetics of composite formation in an in situ photopolymerization process. Silica‐containing formulations polymerize faster; this effect is much stronger for silica P having much larger particle size than silica F. Surface treatment leads to further acceleration of the polymerization in case of silica P but to retardation in case of silica F; the effect of modification of the filler surface on properties of composites is different for each of the silicas. The obtained results are discussed in terms of effects of curvature of silica particles, surface properties, solvation cell, interphase region, viscosity changes, and morphology of the resulting composites. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3472–3487     

Synthesis and properties of liquid crystalline urethane methacrylates for dental composite applications

Three novel liquid crystalline methacrylates have been synthesized and characterized to be tested as comonomers in light‐curing dental resin‐based composites. The selected formulations consist of an alkylammonium or cholesteryl urethane methacrylate and 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloyloxypropyl)phenyl]propane (BisGMA) or a BisGMA derivate modified with urethane methacrylate groups, further diluted with triethyleneglycol dimethacrylate (TEGDMA) and reinforced with 70% filler (zirconium silicate nanopowder, silanized filler). This study addresses the relationships between the LC monomer structure, photopolymerization rates (by differential scanning photo calorimetry), and specific properties of the dental resin composites (volumetric shrinkage, water sorption, water solubility, and hydrophobicity). The investigation of LC properties by differential scanning calorimetry and polarizing microscopy indicated that the LC mesophase is stable to room temperature (cationic monomers) or at 40 °C (cholesteryl methacrylate). It was found that the polymerization rate for LC urethane methacrylates used in combination with BisGMA/TEGDMA (0.122–0.136 s^?1) is higher than that of the mesogenic monomers alone (0.085–0.107 s^?1). The structures of the urethane monomers and, consequently, the viscosity of the comonomer mixture influence both the rate and the degree of conversion (44.8–67.5 %) of the photopolymerization process. Polymerization shrinkage measured by pycnometry showed lower values for LC monomers (3.25–3.43 vol %) comparatively with the monomer mixture (5.19–6.65 vol %). Preliminarily, the effect of ammonium groups from two resin composites incorporating alkylammonium structures (4.5 wt %) was tested on Streptococcus mutans, and distinct zone of inhibition was observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Structure and mechanical behavior of nylon‐6 fibers filled with organic and mineral nanoparticles. I. Microstructure of spun and drawn fibers

The crystalline structure and fibrillar texture of nylon‐6 fibers filled with nanosized particles were investigated using wide‐angle and small‐angle X‐ray scattering. As‐spun fibers filled with organic nanoparticles consisting of aromatic polyamide‐like hyperbranched molecules with amine‐terminating groups exhibited strong modification of both the molecular orientation and the crystalline structure compared with that of unfilled spun fibers. Montmorillonite‐filled fibers mainly exhibited orientation improvement. The differences are discussed in terms of the rheological and nucleating effects during spinning. Drawing at 140 °C involves structural changes that resulted in the three kinds of fibers having a similar crystalline form and molecular orientation. In parallel, after significant strain‐induced changes, the microfibrillar texture of the various fibers displayed subtle differences at the ultimate stage of drawing. The changes in the fibril long period and fibril radius as a function of draw ratio are discussed in terms of the two sequential deformation processes of microfibril stretching and microfibril slipping. The occurrence of interfibrillar strain‐induced cavitation is discussed in relation to the nature of the interactions between the filler and the nylon‐6 matrix. And, finally, the mechanical properties are discussed in relation to the filler–matrix interaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3876–3892, 2004     

Properties of a carbon filled cyclic olefin copolymer

This article investigates electrical conductivity and rheological aspects of cyclic olefin copolymer (COC) composites containing both carbon fiber (CF) and carbon black (CB) at various concentrations. The different formulations of carbon filled COC were compression molded in such a manner that the formed circular sheets exhibited preferred in‐plane filler orientation. Through‐plane and in‐plane conductivity were measured by 2‐probe and 4‐probe methods, respectively, while an ARES rheometer in dynamic mode was employed to measure the storage modulus and complex viscosity. It was found that formulations with CF:CB ratios around 3 and where the CB content was close or below its critical percolation concentration resulted in higher electrical conductivity while maintaining the viscosity of the composite at a level acceptable for polymer processing machinery. For those composites containing both fillers, collaborative associations between the CB and CF fillers were found in the established percolating network structure, producing measured conductivities which exceeded the estimated values by the additive rule by up to sixfold. An empirical expression to handle hybrid filler systems is proposed in this work based on the standard percolation model. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1808–1820, 2007     

Combining renewable gum rosin and lignin: Towards hydrophobic polymer composites by controlled polymerization

Rosin polymer–grafted lignin composites were prepared via “grafting from” atom transfer radical polymerization (ATRP) with the aid of 2‐bromoisobutyryl ester‐modified lignin as macroinitiators. Three different monomers derived from dehydroabietic acid (DA) were used for execution of grafting from ATRP, while DA was separately attached onto lignin by a simple esterification reaction. Kinetic studies indicated controlled and “living” characteristics of all monomer polymerizations. Thermal studies indicated that rosin polymer–grafted lignin composites exhibited glass transition temperatures in a broad temperature range from ～20 to 100°C. The grafting of both DA and rosin polymers significantly enhanced hydrophobicity of lignin. Static contact angle measurement of water droplets showed ～90° for all these rosin modified lignin composites. X‐ray photoelectron spectroscopy demonstrated that the surface of rosin–lignin composites was dominated with chemical compositions originating from the hydrocarbon rich rosin moiety. The impartation of hydrophobicity of rosin into lignin provided excellent water resistance of this class of renewable polymers, as all rosin‐modified lignin composites showed water uptake below 1.0 wt %. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011