Reactions of low molecular weight highly functionalized maleic anhydride grafted polyethylene with...

Reactions of Low Molecular Weight Highly FunctionalizedMaleic Anhydride Grafted Polyethylene withPolyetherdiamines

Tayyab Hameed,1 David K. Potter,1,2 Elizabeth Takacs1

1Department of Chemical Engineering, McMaster University, Hamilton L8S 4L7, Ontario, Canada2Xerox Centre for Engineering Entrepreneurship & Innovation, School of Engineering Practice, McMaster University,Hamilton L8S 4K1, Ontario, Canada

Received 28 June 2009; accepted 21 October 2009DOI 10.1002/app.31725Published online 14 January 2010 in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: Reaction between low molecular weighthighly functionalized maleic anhydride grafted polyethyl-ene and several diamines were carried out using xylene asa reaction media. The influence of varying the amine tomaleic anhydride (NH2/MAH) molar ratio and chainlength of diamine on reaction was investigated. It wasshown that the reactions of these materials cannot be fol-lowed by FTIR measurements alone. In these examples,colorimetric titrations were used to assess residual acid/anhydride content that was not detected by FTIR. Thereaction between anhydride and amine was observed tobe fast. The degree of reaction and crosslinking in the re-actor was observed to depend on the concentration of the

reaction mixture and the NH2/MAH molar ratio. In somecases, a gelatinous insoluble mass was produced in the re-actor and this material was not easily processed for furthercharacterization. All soluble reaction products obtainedwere observed to be thermoplastic and could be melt proc-essed at elevated temperatures. However, further reactionand crosslinking of these materials occurred during proc-essing to produce thermosets, as demonstrated by rheolog-ical measurements and sintering experiments. VC 2010 WileyPeriodicals, Inc. J Appl Polym Sci 116: 2285–2297, 2010

Key words: maleic anhydride grafted polyolefin; poly-olefin wax; polyether diamines; crosslinked products

INTRODUCTION

Polyolefins (polyethylene and polypropylene) consti-tute the most widely used commodity plasticsbecause they are inexpensive and chemically inertand because they posses adequate physical proper-ties for many applications. Over time, advances incatalyst technology1–3 has resulted in the ability toexert more control over the molecular architecture ofthese polymers so that material engineering for thedesired end use application is possible. Materialswith a wide range of molecular weights (MW) (poly-olefin waxes to ultra high MW high density poly-mers), controlled degree of long and short chainbranching, and varying degree of isotacticity arenow available in the market.3

Polyolefins are very inert and hydrophobic materi-als. Whereas this property is an advantage in manyapplications, these same characteristics limit the useof polyolefins in applications where interaction with

other materials is desirable. Modification of polyole-fins by chemical functionalization is a well estab-lished practice.4–10 In commercial settings it is typi-cal to add this functionalization to the readilyavailable commodity polyolefin polymers. This is of-ten carried out using reactive extrusion processes, inwhich free radical chemistry is used to ‘‘graft’’ smallmolecule functionality to the polyolefin polymermolecule. The most commonly used grafting mate-rial is maleic anhydride (MAH).4–10 This functional-ity renders the polyolefin more hydrophilic andenhances its compatibility with systems containingbasic functionalities. The amount of MAH function-ality that can be added to the polyolefin in a reactiveextrusion process is limited by the residence time inthe extruder and by undesired free radical side reac-tions (crosslinking with polyethylene and degrada-tion with polypropylene), which are associated withprocessing at high temperatures in the presence offree radicals.6,7

Low MW polyolefin waxes are widely used intoner inks,10 as comaptibilizer in wood polymercomposites,11 hot melt adhesive formulations andin personal care products.12 These waxes are usuallygenerated by degradation of high MW polyolefins13

and more recently synthesized using ZieglerNatta and metallocene catalyst technology.14 The

Correspondence to: D. K. Potter ([email protected]).Contract grant sponsors: Ontario Centres of Excellence

(OCE) and Clariant Canada Inc.

Journal ofAppliedPolymerScience,Vol. 116, 2285–2297 (2010)VC 2010 Wiley Periodicals, Inc.

metallocene catalyst technology enables the controlof molecular weight and molecular weight distribu-tion, as well as comonomer placement in the poly-mer molecule. Some commercially available waxesare designed to have low melting temperatures,compared to ‘‘normal’’ polyolefin materials, and asignificantly reduced melt viscosity. These materialscan be functionalized in a batch reactor process,rather than in the conventional extrusion process.The use of a batch process eliminates limitations dueto the residence times associated with a reactiveextrusion process. Lower melting temperatures alsofacilitate processing at temperatures that are consid-erably lower than those used in the extrusion proc-essing of conventional polyolefins. Free radicalchemistry can therefore be used to achieve a muchhigher degree of functionalization with these materi-als in a batch process, compared to the extrusionprocesses.10,12 The relatively high degree of function-ality and low viscosities of these functionalized poly-olefin products enable the potential use of thesematerials in applications that were not previouslyconsidered.

Reaction between MAH and amines in polymericsystems has been extensively studied.14–22 The reac-tion is an important interfacial reaction widely usedin the compatibilization of immiscible polymerblends.15,16,21,22 Song and Baker16 studied the reac-tion between MAH groups and different types ofamines (primary, secondary, tertiary) in polymericsystems. Reactions were conducted between sty-rene/MAH copolymer and diamines in a meltblender at 180�C. Fast reaction between MAH andprimary amine was reported and the generation ofimide reaction product was confirmed by FTIR.

Lu et al.20 investigated the reaction of aminegroups to a PP-g-MAH. Reactions were performedover a range of amine/maleic anhydride (NH2/MAH) molar ratios and were conducted both in amelt blender and an extruder. The mixing data sug-gested that the MAH-amine reaction was completewithin 90 s and this was supported with FTIR analy-sis. The dynamic rheological measurements pre-sented did not show any evidence of crosslinking inthe reaction products at the different NH2/MAHmolar ratios studied. However, the complex viscos-ity and storage moduli were influenced by additionof diamine and ascribed to the increased branchingin the products as a consequence of reaction.

Colbeaux et al.17 explored the generation of aninterfacial coupling agent to compatiblize polyethyl-ene and polypropylene using PE-g-MAH and a dia-mine. The degree of MAH grafting of the PE wasvery low (0.18%). The reactions were carried out in amelt blender at 150�C using two diamines and vari-ous NH2/MAH molar ratios. For reaction betweenPE-g-MAH and 1,12-diaminododecane, the extent of

reaction in the blender was observed to be a strongfunction of the NH2/MAH molar ratio. Based on theFTIR spectra, complete conversion of anhydride wasreported for NH2/MAH molar ratio of 2 and above.Solvent extraction and rheological measurement sug-gested the products to be coupled to varying degrees.Most of the studies conducted to date involving

MAH functionalized polyolefin reactions with poly-amines have utilized traditional polyolefins withhigh molecular weight and low degrees of function-alization. Reactions of these materials with a poly-amine are expected to yield branched reaction prod-ucts that have utility as compatibilizers inimmiscible blends or as modifiers of polymer prop-erties such as melt rheology or mechanical perform-ance. The reaction products are thermoplasticsbecause the extent of reaction is limited by the lowlevel of functionalization of the polyolefin. The workdescribed here is a preliminary study of the reac-tions of highly functionalized low molecular weightpolyolefin with polyamines. It is anticipated that theincreased functionality of the polyolefin shouldallow for the synthesis of crosslinked thermosetmaterials and that the associated processing costsmight be lower than the cost of processing conven-tional thermoplastic polyolefin. Although it is ex-pected that the material cost of these thermosetswould be higher than conventional thermoplasticpolyolefins, it is also anticipated that these materialsmight have utility in markets and applications thatcan support the higher costs. In the current investi-gation reactions between highly functionalized,MAH grafted low MW polyethylene and polyetherdiamines are carried out in solution. The reactionproducts are analyzed to assess the degree of reac-tion using titration and FTIR techniques. Rheologicaland thermal characterizations tools are used toassess the properties of the reaction products.

EXPERIMENTAL

Materials

The MAH grafted (PEMA4351) and ungrafted poly-ethylene wax (PE4201) were commercial gradeLicoceneV

R

PEMA4351 and PE4201 provided by Clar-iant GmBH, Germany. Properties of these materialsare provided in Table I. The molecular weight data(Mw, Mn, and MWD) was obtained by high

TABLE ICharacteristics of Polyolefin Waxes

Mw Mn Mw/Mn

Viscosity3

(mPa s)MAH

content2

PE4201 – – – 60 0.0PEMA4351 3000 1200 2.5 300 5.20

2286 HAMEED, POTTER, AND TAKACS

Journal of Applied Polymer Science DOI 10.1002/app

temperature GPC at 135�C (using PE standards forcalibration) and was kindly provided by the manu-facturer. The MAH content in the grafted productswere measured by colorimetric titration. The colori-metric titration technique was verified using graftedpolyethylenes; PE-g-MA (Sigma Aldrich) and Epo-lene G2608 (Eastman Chemicals, USA), and polypro-pylene; PPMA6252 (Clariant, Germany). DiaminesEDR176, ED600, and D2000 were commercial poly-etherdiamines supplied by Huntsman Chemicals,USA. The diamines had molecular weights of 176,600, and 2000 g/mol, respectively. All diamineswere supplied as liquids and used as received. Anti-oxidant stabilizers Irgafos 168 and Irganox 1010were obtained from Ciba Specialty Chemicals, Basel,Switzerland. Solvents xylene and methanol were rea-gent grade and used as received.

Reactions

All reactions were carried out in a 500 mL glassresin kettle equipped with a thermometer, drop bot-tle, condenser, and an overhead stirrer. The impellerwas a high-speed dispersion blade made of stainlesssteel. A stirrer bearing was used to ensure no sol-vent escaped the reactor during reaction. PEMA4351was vacuum dried overnight at 100�C. Measuredamounts of PEMA4351, and xylene were added tothe clean and dried resin kettle. Approximately0.01% of antioxidant, a 50/50 mixture of Igafos 168and Irganox 1010, was added to protect the poly-mers against possible degradation. The condenser,thermometer, stirrer bearing, and stirrer were thenplaced and the whole assembly was lowered in anoil bath maintained at 200�C or a heating mantle fit-ted with a feedback temperature controller. Stirringwas maintained above 500 rpm for 10 min to ensurecomplete dissolution of polymer. Measured amountsof diamine were then added as a 40% v/v solutionusing the drop bottle in one shot. The rotationalspeed of the stirrer was always �500 rpm before theamine addition. On addition of amine, if the viscos-ity of the reaction mixture increased, the input volt-age to the motor was manipulated to maintain thestirrer speed above 500 rpm if possible. The reactiontime was 10 min unless the reaction mixture turnedinto a gelatinous mass, in which case the reactionhad to be terminated earlier. At the end of each reac-tion, the reactor contents were casted into a rectan-gular mold. These were then dried overnight in afume hood and then vacuum dried overnight at100�C to remove trace amounts of solvent left over.

Titrations

The MAH content of the grafted polyolefins andreaction products was assessed using colorimetric

titrations. Approximately 0.2 g of the sample wasdissolved in 60 mL of xylene under reflux. The hotsolution was then titrated against a standard � 0.01N KOH in methanol. The alcoholic KOH solutionwas standardized against a standard HCl (0.01 N)aqueous solution. Thymol blue in methanol wasused as an indicator. When the blue coloration per-sisted for a minute titration was stopped. Themethod was verified by titrating a standard solutionof succinic acid.

FTIR

FTIR spectra were collected using a Thermo NicoletIR300 spectrometer fitted with a Pike TechnologiesDiffuse IRTM, diffuse reflectance accessory. Theaccessory was purged by a continuous flow of nitro-gen. At least 64 scans were applied and databetween 400 and 4000 cm�1 were recorded. Approxi-mately equal amounts of sample and potassium bro-mide (KBr) were ground using a mortar and pestle.This mixture was then transferred to a small cup.Spectra were then collected at room temperature.For quantitative analysis absorbance at 1460 cm�1

representing the methylene groups in the PEMA4351backbone was used as the internal standard peak.

Rheological measurements

Dynamic viscoelastic measurements were performedin Rheometric Scientific, Advanced RheometricsExpansion System (ARES) controlled strain rheome-ter equipped with a transducer capable of measuringtorque values ranging from 0.2–200 g/cm. In allmeasurements parallel plate geometry with 25 mmplatens was used. Sample disks of 1.5 mm thicknesswere prepared by compression molding in a me-chanical press at 140�C to conduct rheological meas-urements. All measurements were carried out withinthe linear viscoelastic region established by a strainsweep. Dynamic time and frequency sweeps wereperformed at 140�C using a hot air convection oven.Stress relaxation measurements were also performedto verify the presence of a network in the reactionproducts.

DSC measurements

Thermal properties of the compression molded reac-tion products and neat polymer were conductedusing a Q2000 Differential Scanning Calorimeter(DSC), TA Instruments, USA. Approximately 5 mgof sample was encapsulated in aluminum pans fortesting. The first heating cycle from room tempera-ture to 160�C at 10�C/min was used eliminate thethermal history. It was followed by a cooling cycleand the second heating cycle at similar rates.

REACTIONS OF FUNCTIONALIZED POLYETHYLENE 2287


Sintering

Sintering behavior for selected reaction productswere studied to confirm the evidence of flow onheating in the reaction products. The sinteringexperiments were performed on vacuum dried reac-tion products. The apparatus consisted of a heatingchamber and an optical microscope equipped with avideo camera. The camera was connected to a video-recorder and television, which in turn was con-nected to a personal computer with a frame grabberboard, where the images were processed. The heatchamber had glass windows on the top and bottomfor inspection and video recording of the process.The temperature of the oven was controlled by thethermocouple sitting in the wall of the heat chamber.All observations were recorded at 150�C.

RESULTS AND DISCUSSION

Assessment of degree of grafting

For grafted polyolefin products, the assessment ofthe degree of grafting is an important characteriza-tion parameter. Several techniques includingNMR9,23 FTIR5,9,16–20,24–27 and colorimetric titra-tions9,24–26,28 have been reported in the literature toassess the MAH content in functionalized poly-olefins. Titration and FTIR techniques are most pop-ular as they are easy to perform and relatively quick.Several titration procedures, with some variation inthe use of solvent and indicator, are reported in theliterature6,9,24–26,28

Titration results for the four MAH grafted polyole-fins are presented in Table II. These include bothpolyethylene and polypropylene products function-alized to varying degrees. Some studies25 reportedpoor reproducibility of the titration results withstandard deviations as high as 40%. Very goodreproducibility (<0.2%) in the titration results wereobserved in the current investigation. The degree offunctionalization measured for the MAH functional-ized metallocene waxes (PEMA4351 and PPMA6252)is 3–5 times higher than the 1–1.5% that is typicallyobserved with functionalized commodity polymers.

The reported assessment of MAH grafting usingthe titration method assumes that all of the grafted

MAH exists in the anhydride form. As polyolefinshave a tendency to slowly absorb moisture duringstorage, which results in the conversion of anhy-dride into acid groups, not all of the functionalityreported will be in the anhydride form. It is wellknown that the kinetics of reaction between amineand anhydride are quite different from amine andacid reactions.16,20 It is therefore important to under-stand how much of the anhydride is in the hydratedstate.FTIR has been extensively used to characterize the

MAH functionality of grafted products. The FTIRabsorbance spectra of nongrafted PE4201 and MAHgrafted PEMA4351 (vacuum dried at 100�C for 24 h)used in this study are shown in Figure 1. Three dis-tinct absorbance peaks at � 1715, 1780, and 1860cm�1 are present in the PEMA4351 spectrum whilethey are absent in the nongrafted PE4201. The 1780and 1860 cm�1 absorptions are responses from sym-metric and asymmetric stretching of the MAH car-bonyl.5 The absorption at 1715 cm�1 arises from thecarbonyl stretching of a carboxylic acid group.The carboxylic acid absorbance at 1715 cm�1 in

the PEMA4351 spectra is very strong indicating thata significant portion of the MAH functionality ispresent in the hydrated form despite the vacuumdrying process employed. This result is quite differ-ent from some of the work described in the litera-ture where either a relatively weak acid response orno response was observed5,18–20 Vacuum drying ofthe grafted products to convert carboxylic acid func-tionality back to the anhydride form by removal ofwater is commonly practiced5,20,24,27 For example,Schmidt et al. [2003] used FTIR spectra to demon-strate complete conversion of the anhydride intoacid by steam sterilization and back again to anhy-dride by annealing at 120�C for 2 h, in their workwith poly(octadecane-alt-maleic anhydride) thinfilms. On the other hand, Battinni and Agnelli,25

observed little influence of vacuum drying on theconversion of acid groups into anhydride in MAH-g-PP samples vacuum dried at 130�C for 96 h. Our ex-perience here is consistent with the observations ofBattinni and Agnelli.25

More intense processing of the MAH graftedPEMA 4351 in the melt state did not lead to a com-plete conversion of acid functionality to anhydrideeither. The PEMA4351 was melt processed with con-stant stirring in an open cup at 150�C (the peakmelting temperature of PEMA4351 by DSC is 120�C)for different time intervals. The FTIR spectra forthese melt processed samples are shown in Figure 2.The relative intensity of the acid and anhydride ab-sorbances are altered by this treatment and adecrease in the acid absorbance with a concomitantincrease in anhydride response is observed withmelt processing time. For clarity the relative

TABLE IIMaleic Anhydride Assessed Through Colorimetric

Titrations for Various Grafted Polyolefins

Average MAHcontent (wt %)

Standarddeviation (%)

PEMA4351 5.15 0.18PPMA6252 4.32 0.12PE-g-MA 2.15 0.02Epolene G2608 0.92 0.11



absorbance intensities for these functionalities areplotted as a function of melt processing time in Fig-ure 3 using the methylene absorbance at 1460 cm�1

(CAH stretching) as the reference peak. The conver-sion of acid to anhydride appears to be linear withmixing time under these conditions but completedehydration of all of the acid functionality was notachieved.

Following the work of others,5,24 blends were pre-pared by melt mixing 2-dodecen-1-yl succinic anhy-

dride with ungrafted PE4201 to construct a calibra-tion curve for the measurement of functional groupcontent. Measurements of the anhydride content ofthese blends were performed by FTIR and comparedto the known stoichiometry. The FTIR spectra ofthese blends in Figure 4 show strong anhydride ab-sorbance at 1780 cm�1 and significant absorbancedue to anhydride (1860 cm�1) and carboxylic acid(1715 cm�1). The anhydride absorbances (relative tomethylene at 1460 cm�1) are plotted in Figure 5

Figure 2 Overlaid FTIR spectra for PEMA4351 melt processed for different time intervals at 150�C. [Color figure can beviewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 1 FTIR spectra of PEMA4351 and PE4201. [Color figure can be viewed in the online issue, which is available atwww.interscience.wiley.com.]



against the known stoichiometry and a linear trendis observed. The 1780 cm�1 absorbance is more sen-sitive (higher slope) than the 1860 cm�1 absorbancein agreement with earlier reports.16

The calibration plots in Figure 5 provide estimatesof MAH content in PEMA4351 that are lower thanthe MAH content measured by titration (� 70%).This is likely a consequence of the relatively largeamount of anhydride in acid form in the PEMA4351as compared to that in the calibration blend withcomparable anhydride content (4.9%) (Fig. 6). As wewere unable to convert the acid groups into anhy-

dride by vacuum drying or melt treatment, theassessment of anhydride using FTIR to assess thedegree of reaction will not be workable. Earlierreports5,24 where such calibration plots were success-fully generated did not present any FTIR spectra forthe standard blends.

Reaction of MAH functionalized polyolefinwith diamines

Reactions of the highly functionalized MAH graftedlow MW polyethylene (PEMA4351) with diamines ofdifferent molecular were carried out in xylene solu-tion. These experiments are summarized in Table III.In all of these experiments, visual evidence of thereaction between the anhydride and diamine weremanifest as soon the amine was dropped in the solu-tion containing grafted polymer. This was not sur-prising as the MAH-primary amine reactions havebeen reported to be extremely fast.16,20 Lu et al.20

working with high MW PP-g-MAH reported com-plete conversion of MAH into imide within 90 sec-ond in an extruder or a melt blender. Similar evi-dence was reported by other investigators.15,16

Frothing in the reaction mixture and a decrease inthe rotational speed of the stirrer due to viscositybuild up were obvious. The reaction mixture would‘‘climb’’ the agitator shaft as mixing proceeded. Thisis evidence of the formation of sufficient higher mo-lecular weight polymer to develop a Weissenberg

Figure 3 Relative peak height vs. melt processing timesfor PEMA4351.

Figure 4 FTIR spectra of standard blends of dodecenyl succinic anhydride and PE4201 at various compositions. [Colorfigure can be viewed in the online issue, which is available at www.interscience.wiley.com.]



effect. In some cases, the reaction mixture turnedinto a gelatinous mass, which was sometimes torninto small chunks due to shearing by the high-speeddispersion blade. In those experiments where gela-tion was observed, the recovered reaction productcould not be processed into films or disks for furthercharacterization.

The formation of a gelled materials depended onthe concentration of reactants and on the molecularweight of the diamine used. An inspection of thedata in Table III reveals that the concentrations, atwhich gelation occur varies inversely with the mo-lecular weight of the diamine used as coreactant. Allthe reaction products that were soluble at the end ofthe reaction time were casted into rectangular alumi-num molds. The solvent was allowed to evaporatein the fume hood. Samples were then vacuum dried

overnight at 100�C to remove trace amount of sol-vents. The vacuum dried products from these reac-tions were thermoplastic and could be easily formedinto thin films and disks by compression molding atelevated temperatures. These findings suggest thatthe extent of reaction and hence degree of crosslink-ing in the reaction products could be controlled byvarying the concentration of the reaction mixture.FTIR spectra were used to qualitatively follow the

changes in chemistry and assess the extent of reac-tion between amine and MAH. Figure 7 shows theoverlaid FTIR spectra for the recovered reactionproducts of PEMA4351-EDR176 reacted at a concen-tration of 0.25 g polymer/mL of xylene. A consistentdecrease in absorbance at 1860 cm�1 and the disap-pearance of absorbances at 1780 and 1715 cm�1 dueto the consumption of MAH and the development ofnew absorbances at 1700, 1770, 1550, and 1645 cm�1

suggest significant reaction between MAH andamine. New absorbances at 1700 and 1770 cm�1 areascribed to the formation of imide16,18,20,29 Peaksdeveloping at 1645 cm�1 are likely due to amicacid19 or residual amine groups.29 The response at1645 cm�1 grows steadily with the increase in NH2/MA molar ratio in the reaction products (Fig. 8)which suggests it is more likely to be an amineabsorption.Although these spectra qualitatively describe the

change in chemistry as a result of reaction, quantita-tive assessment of the extent of reaction was madedifficult due to two factors. First, as discussed in theprevious section the grafted MAH in PEMA4351was present both in the form of anhydride and acid.

Figure 5 Relative peak heights of 1780 and 1860 cm�1

peaks vs. wt % of dodecenyl succinic anhydride in theblend.

Figure 6 FTIR spectra for PE4201 blend containing 4.9% dodecenyl succinic anhydride and PEMA4351. [Color figure canbe viewed in the online issue, which is available at www.interscience.wiley.com.]



Hence, no unique absorption can be used to trackthe extent of reaction. Secondly, the imide absorp-tions generated as a result of reaction between anhy-dride and amine are observed at 1700 and 1770cm�1 and are very close to the acid (1715 cm�1) andMAH (1780 cm�1) absorptions. In fact the responsesfor MAH and acid around 1780 and 1715 cm�1 aremerged with those of the developing imide responseat 1700 and 1770 cm�1. The generation of imide as aconsequence of the reaction is therefore manifestedas shifting absorbance from 1780 cm�1 to 1770 cm�1,and from 1715 cm�1 to 1700 cm�1 as the imide isgenerated and the acid and anhydride is consumed.These observations are quite different from those

reported by Lu et al.20 Working with a similar sys-tem (PP-g-MAH and diamines) their FTIR spectrashow a very strong imide response around 1700cm�1 but surprisingly no significant imide peak isobserved at 1770 cm�1 as a result of reactionbetween anhydride and amine. Further, a very weakabsorption peak for carboxylic acid in the PP-g-MAH they used, allowed quantification of the extentof reaction in terms of a decreasing MAH absorptionwith NH2/MAH molar ratio. Similar responses wereobserved in the FTIR spectra for the reaction prod-ucts of PEMA4351-D600 and PEMA4351-D2000 reac-tions and these spectra are not reproduced here.Since the extent of reaction could not be quantita-

tively assessed by measuring the residual MAH by

TABLE IIISummary of Composition and Critical ObservationsDuring the Reactions PEMA4351 and Diamines of

Varying Molecular Weights

Diamine

Concentration(g) of polymer/mL

of solventNH2/MAmolar ratio

Observationduringreaction

EDR 176 0.25 0.33 No gelation0.25 0.5 No gelation0.25 0.66 No gelation0.25 1.0 No gelation0.25 1.33 No gelation0.25 1.5 No gelation0.25 2.0 No gelation0.5 0.5 No gelation0.5 1.0 Gelled0.5 1.5 No gelation0.5 2.0 No gelation1.0 0.5 Gelled1.0 1.0 Gelled1.0 1.5 Gelled1.0 2.0 Gelled

D 2000 0.25 1.0 Gelled0.20 1.0 Gelled0.16 1.0 Soft flowing gel0.13 1.0 No gelation0.13 0.75 No gelation0.13 0.5 No gelation0.13 0.25 No gelation

D600 0.16 1.0 No gelation0.16 0.75 No gelation0.16 0.5 No gelation0.16 0.25 No gelation

Figure 7 Overlaid FTIR spectra for PEMA4351 and its reaction products with EDR176. [Color figure can be viewed inthe online issue, which is available at www.interscience.wiley.com.]



FTIR, titration of the reaction products were carriedout to assess the residual MAH groups. The meas-ured MAH content in the reaction products are plot-ted as a function of the NH2/MAH molar ratio inthe Figure 9 for the PEMA4351-EDR176 reactionproducts. The decreasing level of residual MAHwith increasing amine mole ratio that is observed inFigure 9 is generally observed for all of the reactionproducts studied and is consistent with the trendsobserved in the FTIR data for increasing imide con-centration. Significant MAH (>1%) in reaction prod-uct in which the molar ratio of NH2/MAH > 1 areparticularly surprising as no anhydride or acidabsorption could be detected in the FTIR spectra forthese products. The reason for this observed discrep-ancy is not clear yet but may be related to the limitsof sensitivity of the FTIR technique.

Properties of reaction products

All of the reaction products that did not gel in thereactor could be formed into disks for rheologicalevaluation by compression molding at elevated tem-peratures. Although significant reaction did takeplace in the reactor, as evident by FTIR and titrationresults, the material was still thermoplastic.

The thermal behavior of a semi-crystalline poly-mer can sometimes provide an indication of changesin polymer architecture as a consequence of reactionthat leads to branching. For example, short chainbranching hinders the chain folding mechanism inpolymer crystals and hence suppresses the degree ofcrystallinity.30 On the other hand, the presence of

multi-phases is manifested in the characteristic melt-ing peaks for each phase. Figure 10 shows the sec-ond heating DSC scans for PEMA4351 and meltprocessed reaction products of PEMA4351 andEDR176 at different NH2/MA molar ratios. Aunique melting peak is observed for PEMA4351whereas a new developing shoulder is seen in allreaction products. The peak melting temperature forPEMA4351 and the major melting peak in reactionproducts was always around 120�C. However, a sig-nificant drop in the intensity of the major peak wasobserved as the NH2/MA molar ratio increased. The

Figure 8 Development of imide peak (1700 and 1770 cm�1) with NH2/MAH molar ratio. [Color figure can be viewed inthe online issue, which is available at www.interscience.wiley.com.]

Figure 9 MAH content in PEMA4351 and its reactionproducts with EDR176 assessed by colorimetric titrationsas a function of NH2/MA molar ratio.



decrease in peak intensity may be a result of anincreasing number of branches and crosslinks in thereaction products, which hinder chain folding andconsequently lower crystallinity. The developmentof a shoulder around 110�C with increasing NH2/MAmolar ratio might be ascribed to the developmentof a separate crystal population as a consequenceof weaker interactions due to sterically hinderedbranches or crosslinks.

The viscosity of the PEMA4351 starting materialwas too low to be measured using our instrument.Hence, the first evidence of molecular weight buildup as a result of reaction and processing is the factthat unlike the starting material (PEMA4351), thereaction products have viscosities that are highenough to be measured by the equipment. Resultsof a dynamic mechanical time sweep, shown in Fig-ure 11 for the PEMA4351-EDR176 reaction productsreveals that G0 is invariant over the course of timesweep for all of the reaction products. The G0 valuesare always orders of magnitude larger than the G00

values (not shown). These measurements wouldindicate that the material properties are not chang-ing further as a consequence of the conditions ofmeasurement.

Dynamic frequency sweeps followed the timesweep measurements. Data from these frequencysweeps for processed PEMA4351-EDR176 reactionproducts are shown in Figure 12. Almost no depend-ence of G0 on frequency was observed and the G0

curves for all products investigated are flat over thewhole frequency range studied. This behavior is verydifferent from the typical thermoplastic response, inwhich G0 shows a strong dependence on frequency,especially at low frequencies where a typical slope ofabout 2 has been reported (terminal zone behav-ior).31–33 However, this frequency dependence hasbeen reported to decrease with introduction of long

chain branching31,33 and crosslinks,32,33 which intro-duce additional modes of relaxation, absent in the lin-ear polymers of equivalent molecular weight. Theseobservations suggest that the reaction products are ei-ther very high molecular weight branched polymers,or that a crosslink network is present. The observedbehavior is typical of rubbery plateau behavior associ-ated with chain entanglements in high molecularweight polymers, or the molecular weight betweencrosslinks in network polymers. The plateau value ofG0 increases with the increase in the NH2/MAHmolar ratio from 0.33 to 1.0. The viscosity shows typi-cal power law behavior with no zero-shear plateau atlow frequencies. This is different than the zero-shearplateau shown by most thermoplastic materials atlow frequencies and suggests the crosslinking of the

Figure 10 Second DSC heating scan for PEMA4351 andits reaction products with EDR176. [Color figure can beviewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 11 G0 and g* data from dynamic time sweep forPEMA4351-EDR176 reaction products at different NH2/MA molar ratios. (Ttest ¼ 140�C; c� ¼ 0.05; x ¼ 1 rad/sec).

Figure 12 G0 and g* data from dynamic frequency sweepfor PEMA4351-EDR176 reaction products at differentNH2/MA molar ratios. (Ttest ¼ 140�C; c� ¼ 0.05).



reaction products. Dynamic frequency sweeps for thePEMA4351-ED600 are shown in Figure 13 and showvery similar results, with the exception of the reactorproduct having the lowest amine to MAH mole ratio.The low frequency data for this sample appears to betrend toward a zero-shear viscosity limit, whichwould suggest that this sample is not networked tothe same extent.

The nature of the observed plateau zone was fur-ther explored with stress relaxation experiments. Atelevated temperatures, samples capable of significantflow to relieve an applied strain, will exhibit a rapiddecay in the stress relaxation modulus with time.The stress relaxation modulus for network polymerswill decay to a value of modulus that is characteris-tic of the degree of crosslinking of the material.Stress relaxation tests were conducted at 140�C andthe results are shown in Figure 14 for thePEMA4351-EDR176 reaction products. The samplewith 0.33 NH2/MAH molar ratio exhibits thermo-plastic behavior characterized by a rapid decay ofmodulus to zero after imposition of a strain. Theother materials exhibit a plateau zone that is morecharacteristic of a thermoset.

The evidence of plateau behavior that is more con-sistent with a thermoplastic material seemed contra-dictory to the fact that these materials were mold-able at elevated temperature by compressionmolding. The contradiction suggests that the degreeof crosslinking of the material is altered with mold-ing processes or by the measurement processesthemselves. This hypothesis was tested by observingthe ability of the material to flow as a function oftime at elevated temperatures. Specifically, the pro-

pensity of the material to sinter was used as a gaugeof thermoplasticity.In sintering experiments, two small pieces of pow-

dery material are placed in contact at temperaturesabove the melting range of the material. With typicalthermoplastics, surface tension effects will cause thetwo particles to flow into each other to eliminate theboundary between the two particles, resulting in onelarger particle with no remnant of the boundary visi-ble. Figure 15 shows this experiment for thePEMA4351-EDR176 reaction products for NH2/MAratio 1.0. The optical micrograph clearly shows thatflow occurs to eliminate particle boundaries within atime frame of 75 seconds. This is consistent with theobserved moldability of this material.Similar behavior is observed in Figure 15(a) for

PEMA4351-EDR176 reaction product NH2/MAH of1.33 that has been exposed to elevated temperaturefor a period of 1 min before the sintering experi-ment. In fact, this same behavior is repeated for ma-terial that has been maintained at elevated tempera-tures for 2 min and for 3 min (not shown). Whenparticles of this same material are placed side byside in a sintering experiment after being exposed to150�C for 6 min, different behavior is observed [Fig.16(b)]. No sintering is observed at the interface ofthe two pieces over an extended period of time. Thissuggests that the material is in a state, in which itcannot readily flow after a period of 6 min at 150�C.This is the behavior expected of a thermoset materialand these observations reinforce the hypothesis thatthe material converts to a thermoset after extendedperiods of time at elevated temperatures. Thedynamic mechanical frequency sweep data and thestress relaxation data discussed earlier would be

Figure 14 Relaxation modulus as a function of time forPEMA4351-EDR176 reaction products at different NH2/MA molar ratios. (Ttest ¼ 140�C; c� ¼ 0.05).

Figure 13 G0 and g* data from dynamic frequency sweepfor PEMA4351-ED600 reaction products at different NH2/MA molar ratios. (Ttest ¼ 140�C; c� ¼ 0.05).



Figure 16 (a) Sintering of PEMA4351-EDR176 raction products NH2/MA 1.33; left in the melt state at 150�C for 1 min,(b) PEMA4351-EDR176 reaction products NH2/MA 1.33; left in the melt state at 150�C for 6 mins.

Figure 15 Sintering of PEMA4351-EDR176; NH2/MA 1.0 reaction product with time.



characteristic of the material after such a time andtemperature history.

This evidence of a delayed reaction to yield ther-mosetting material is interesting as no residual anhy-dride or acid was detected in the FTIR spectraalthough the titration data clearly shows that thereought to be residual anhydride or acid. The anhy-dride–amine reaction has been observed to proceedat a much faster rate than the acid–amine reaction.Perhaps residual acid in the reaction product is con-verted to anhydride when exposed to elevated tem-peratures for a sufficient time span. The newly avail-able anhydride would react quickly with residualamine to generated new crosslinks, ultimately lead-ing to sufficient crosslinking to produce a thermoset-ting material.

CONCLUSIONS

Thermosetting materials were produced by reactinga highly functionalized MAH grafted low molecularweight polyethylene with diamines in xylene as areaction media. The reaction in solution wasobserved to occur within seconds to minutes, asindicated by visual changes in the rheology of thereaction mixture. The completeness of the reaction insolution was observed to depend on the molar ratioof amine to MAH, the chain length of the diamine,and the concentration of the reactants in solution.Recovered reaction products, for which gelation didnot occur in the reactor, were observed to be ther-moplastic and could be melt processed at elevatedtemperatures. Dynamic mechanical data combinedwith sintering experiments show that these thermo-plastic materials become thermosets when main-tained for sufficient time at elevated temperatures.

Disappearance of the anhydride or acid absorb-ance in the FTIR spectra for the reaction products,for which the NH2/MAH molar ratio was greaterthan one, suggested complete conversion of anhy-dride. However, significant residual anhydride/acidcontent was assessed in the same reaction productsusing colorimetric titrations. Other measurements,such as rheological and thermal analysis, suggest themelt processed products were crosslinked to varyingdegrees depending on the molar ratio of functionalgroups in the reaction mixture. This suggests thatFTIR analysis alone is inadequate in establishing theextent of reaction in such products and should becomplemented by other analytical techniques.

Wewould like to thankHermann Koch, Clariant Canada Inc.and David Alexander, Huntsman Chemicals, TX USA for

providing the LicoceneVR

and polyether diamines. Supportextended by Paul Gatt and undergraduate students (HilaryFleming, Steffi Woo, Nick Childs, Daniel Lu) is highlyappreciated.

References

1. Bubeck, R. A. Mater Sci Eng R: Rep 2002, 39, 28.2. Chum, P. S.; Swogger, K. W. Prog Polym Sci 2008, 33, 797.3. Andrew, J. P. Handbook of Polyethylene: Structures, Proper-

ties, and Applications; Marcel Dekker: New York, 2000.4. Moad, G. Prog Polym Sci 1999, 24, 81.5. De Roover, B.; Sclavons, M.; Carlier, V.; Devaux, J.; Legras, R.;

Momtaz, A. J Polym Sci Part A: Polym Chem 1995, 33, 829.6. Zhang, Y.; Chen, J.; Li, H. Polymer 2006, 47, 4750.7. Al-Malaika, S. Reactive Modifiers for Polymers; Blackie Aca-

demic & Professional: London; New York, 1997.8. Van Duin, M. Macromol Symp 2003, 202, 1.9. Thompson, M. R.; Tzoganakis, C.; Rempel, G. L. 1997, 3, 2981.10. Hohner, G.; Bayer, M. U.S. Pat. 7,005,224 (2006).11. La Mantia, F. P.; Morreale, M. Polym Eng Sci 2006, 46, 1131.12. Hohner, G. U. S. Pat. 5,998,547 (1999).13. Weemes, D. A.; McConell, R. L. U. S. Pat. 3,562,788 (1971).14. Herrmann, H. U. S. Pat. 6,407,189 (2002).15. Orr, C. A.; Cernohous, J. J.; Guegan, P.; Hirao, A.; Jeon, H. K.;

Macosko, C. W. Polymer 2001, 42, 8171.16. Song, Z.; Baker, W. E. J Polym Sci Part A: Polym Chem 1992,

30, 1589.17. Colbeaux, A.; Fenouillot, F.; Gerard, J.; Taha, M.; Wautier, H.

Polym Int 2005, 54, 692.18. Zhang, Y.; Tzoganakis, C. SPE Conference, Boston, Massachu-

setts, 2005, 7, 201.19. Vazquez-Rodriguez, S.; Sanchez-Valdes, S.; Rodriguez-Gonza-

lez, F. J.; Gonzalez-Cantu, M. C. Macromol Mater Eng 2007,292, 1012.

20. Lu, Q.; Macosko, C. W.; Horrion, J. J Polym Sci Part A: PolymChem 2005, 43, 4217.

21. Jeon, H. K.; Zhang, J.; Macosko, C. W. Polymer 2005, 46,12422.

22. Zhang, J.; Cole, P. J.; Nagpal, U.; Macosko, C. W.; Lodge, T. P.J Adhes 2006, 82, 887.

23. Zhang, R.; Zhu, Y.; Zhang, J.; Jiang, W.; Yin, J. J Polym SciPart A: Polym Chem 2005, 43, 5529.

24. Bettini, S. H. P.; Agnelli, J. A. M. Polym Test 2000, 19, 3.25. Sclavons, M.; Carlier, V.; De Roover, B.; Franquinet, P.;

Devaux, J.; Legras, R. J Appl Polym Sci 1996, 62, 1205.26. Sclavons, M.; Franquinet, P.; Carlier, V.; Verfaillie, G.; Fallais,

I.; Legras, R.; Laurent, M.; Thyrion, F. C. Polymer 2000, 41,1989.

27. Schmidt, U.; Zschoche, S.; Werner, C. J Appl Polym Sci 2003,87, 1255.

28. Gaylord, N. G.; Mehta, R.; Mohan, D. R.; Kumar, V. J ApplPolym Sci 1992, 44, 1941.

29. Socrates, G. Infrared and Raman Characteristic Group Fre-quencies: Tables and Charts; Wiley: Chichester; New York,2000.

30. Hussein, I. A.; Hameed, T. J Appl Polym Sci 2005, 97, 2488.31. Wood-Adams, P.; Dealy, J. M.; Degroot, A. W.; Redwine,

O. D. Macromolecules 2000, 33, 7489.32. McCormick, J. A.; Royer, J. R.; Hwang, C. R.; Khan, S. A.

J Polym Sci Part B: Polym Phys 2000, 38, 2468.33. Deleo, C. L.; Velankar, S. S. J Rheol 2008, 52, 1385.



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