nanocomposites

International Review of Chemical Engineering (I.RE.CH.E.), Vol. 4, N. 2 ISSN 2035-1755 March 2012 Special Section on 3rd CEAM 2011 - Virtual Forum

Functional Copolymer/Organo-MMT Nanoarchitectures. XV. Interlamellar Complex-Radical Alternating Copolymerization of α-Olefins (C6-12) with Maleic Anhydride in the Presence of Reactive and Non-Reactive Organoclays Deniz Demircan Bozdoğan1, Günay Kibarer1, Zakir M. O. Rzayev2 Abstract – This work describes the known conventional methods, especially complex-radical alternating copolymerization of various type of olefin monomers, and complex-radical interlamellar alternating copolymerization of α-olefins with maleic anhydride (MA) in the presence of organoclays. Layered silicate polymer nanocomposites were synthesized by intercalative alternating copolymerization of MA…organo-MMT clay complexes with electron-donor α-olefins (C6-12) such as 1-hexene (HX), 1-octene (OC) and 1-dodecene (DD) in the presence of a radical initiator (AIBN) in dioxane at 65oC under nitrogen atmosphere. Taking into consideration that nature of interaction between functional (co)polymers and the organo-clay is important, and the structure and morphology of the resulting nanocomposites strongly depend on such interactions, we have investigated physical and chemical (amidization) interactions between polar monomer, such as electron-acceptor maleic anhydride (MA) and two types of organo-MMT containing intercalated dimethyldidodecyl ammonium cation and octadecyl amine surfactants (DMDA-MMT and OCDA-MMT, respectively). Chemical and physical structure of poly[MA-alt-α-olefins (C612)]/organoclay nanohybrids were investigated by FTIR and XRD analysis methods, respectively. Thermal behavior and morphology of nanocomposites were studied by DSC-TGA and SEM methods. It was demonstrated that α-olefin units with long alkyl groups in copolymers exhibit internal plasticizing effect and are significantly influenced on the in situ exfoliation process of copolymer chains between silicate layers. The results of XRD and SEM analysis confirmed the formation of nanostructural hybrids with relatively fine distributed nanoparticles. Thermal analysis results indicated that pristine copolymers show amorphous structure while copolymer/organoclay nanohybrids exhibit semi-crystallinity and higher thermal stability. These novel nanocomposites containing long alkyl branches and reactive anhydride groups allow us future utilization in situ processing of thermoplastic polymers, especially polyolefins, as affective nanofiller-compatibilizers using reactive extrusion system. Copyright © 2012 Praise Worthy Prize S.r.l. - All rights reserved. Keywords: Interlamellar Copolymerization, Maleic Anhydride, α-Olefins, Organoclays, Nanocomposites, Nanostructure-Property Relationships

I.

It is known that α-olefins with σ−π-conjugation system belonging to the monomer type with low activity in the radical polymerization, are easily copolymerized with electron-acceptor type monomers, and form alternating copolymers with maleic anhydride and its isostructural analogs [1]-[4]. These copolymers are related to the class of bioengineering functional copolymers, especially as enzyme carriers [5],[6]. Usually, lower olefins react more easily with MA than higher olefins, producing alternating copolymers. For higher olefins, such as 1-hexene and 1-octene, it has been found that copolymerization with MA produces only low-molecular weight copolymers in low yields [7]. It was shown that the potassium salts of these

Introduction

In general, there are three broad approaches for the preparation of functionalized polyolefins such as end functionalization, in chain functionalization and alternating, random and block copolymerization methods. The first method involves chemical reactions of terminally unsaturated polyolefins. The second method relates to predominantly radical grafting reactions of polyolefin chains. The last approach involves the copolymerization of α-olefins with various functional monomers.

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copolymers form hydrophobic microdomains, exhibiting behavior analogue to micelles [8],[9]. Chu and Thomas [8] investigated a potassium salt of a poly(1-octadecenealt-MA) copolymer as a polymeric intermolecular micellar system via steady-state emission, absorption and transient spectroscopy methods. Authors observed that there is a significant effect of the polymer main chain surrounding the polymer micelles on the bimolecular quenching kinetics and exciplex formation of quest molecules. Olea et al. [9] studied the formation and properties of intramolecular micelles from poly[maleic acid-alt-olefin(C6-18)] copolymers by steady-state and time-resolved fluorescence measurements. They observed that all copolymers adopt a compact configuration over the entire pH range while potassium salt of MA-1-hexene copolymer exhibits a pH-induced conformational transition. The hydrophobicity of these microdomains increases with the length of the side alkyl chain. Martinez et al. [10] reported the results obtained in the study of the copolymerization of MA with long-chain α-olefins (C6-16), such as hexene-1, octene-1, decene-1, dodecene-1, tetradecene-1 and hexadecene-1. The thermal behavior and molecular weight of the synthesized copolymers were examined as a function of the olefin length. During thermal degradation, in copolymers of shorter side chains, carboxylic acid products were obtained. The MA–α-olefin copolymers are decomposed by freeing gaseous CO2 close to 200oC. Copolymerization of MA with long-chain α-olefins in the acetone/toluene /benzoyl peroxide system gave copolymers with Mn in the range of 3700–11500 g/mol. These olefins produce copolymers with the highest Mn, in a yield of 15 %. Authors could not observe any Tg in these copolymers. α-Olefins are considered as monomers with lower activity in radical polymerization but their copolymerization occurs easily with MA and preferably form alternating copolymers with equimolar compositions. Samoilov [11] investigated radical emulsion copolymerization of propylene with MA, dimethyl maleate, diethyl fumarate, vinyl acetate and methyl acrylate. Using composition diagrams and Alfrey-Price Q-e scheme, the author determined primarily polarity and to a lesser degree resonance stabilization of the comonomers. It was observed that propylene reacts actively and gives alternating copolymers when comonomer has relatively high electronegativity (e > 1.2) and low resonance stabilization (e.g., maleic anhydride and its derivatives); molecular weight decreases from ∼150.000 to ∼8.000 rapidly with an increase of propylene amount in each type of copolymer. Propylene-vinyl acetate and propylene-methyl acrylate copolymers show glasstransitions which shift to lower temperatures with an increase of propylene content while propylene-maleate and propylene-fumarate copolymers did not exhibit any glass transition in the temperature range from -100oC to +100oC.

Various methods have been suggested for the synthesis of poly[(MA-alt-α-olefin (C2-30)]s [7],[12],[13]. The kinetics and mechanism of radical copolymerization of these systems and the structures of the copolymers were studied extensively. Rzayev et al. [4] have investigated the kinetics and mechanism of complex-radical copolymerization of MA with 2,4,4trimethylpentene-1 (TMP), octene-1 and hexene-1. The constant of CTC (Kc) and copolymerization parameters have been determined. Kc value for for MA…octene-1 complex was found as a 0.16 L/mol at 35 oC in acetoned6. The high value of Kc for MA…TMP complex was explained by the effect of the α-CH3 group which increased the electron-donor properties of the TMP double bond. The monomer reactivity ratios for MATMP and MA-hexane-1 (HX) pairs were determined using various methods and copolymer composition equations such as Fineman-Ross (FR), Kelen-Tüdos (KT), Seiner-Litt (SL) and non-linear regression (NLR). Obtained values of constant copolymerizations are summarized in Table I. TABLE I THE CONSTANTS OF COMPLEX-FORMATION (Kc) AND COPOLYMERIZATION (r1 AND r2) FOR THE MALEIC ANHYDRIDE (MA)– 2,4,4-TRIMETHYL-1-PENTENE (TMP) AND MA–1-HEXENE MONOMER PAIRS. ADOPTED FROM [4]

Some kinetic parameters of the reaction and quantitative contributions of MA…TMP complex to the reactivity ratios of the comonomers have been studied and their contribution to chain growth are estimated as: k12/k21 = 3.51, k1c/k12 = 0.98 and k2c/k21 = 1.03. The copolymerization is found to proceed predominantly by the “mixed” mechanism with equal participation of complex-bound and free monomers in propagation. The higher rate of copolymerization in the MA–TMP– DMF(solvent) system is explained by the effect of the MA-solvent complex increasing the acceptor properties of the MA molecule. Many researchers demonstrated that the initial rate of 1:1 alternating copolymerization is not necessarily maximum at a 1:1 feed composition and that the position of the rate maximum is dependent on the total monomer concentration. Thus the maxima of the copolymerization

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high yield. They observed that the introduction of cyclic and polar substituents into the olefin repeating units increased the glass transition temperature of the obtained copolymers. The free radical copolymerization and terpolymerization of acrylic monomers with olefins in the presence of Lewis acid complexing agent for the acrylic monomer has been investigated by Eisenbach et al. [25]. The course of the polyreaction is in agreement with the features of a radical chain growth reaction, and the polymer properties can be varied by changing the composition of the reaction mixture and the reaction conditions. Authors showed that the alternating copolymers are amorphous materials, and only the alternating ethylene/acrylonitrile copolymer exhibits relatively high crystallinity. Authors also studied the basic features of the polyreaction and the polymer structures as well as some of the physical and material properties of the copolymers. Various water-soluble polymers were used to examine an alternative emulsifier for poly(ethylene-alt-maleic anhydride), used in the preparation of crosslinked polyurea microcapsules [26]. Authors successfully prepared microcapsules by using the water-soluble polymers with large molecular weight alternating copolymers such as poly(olefin-maleic anhydride), poly(olefin-maleic acid), and poly(acrylic acid). These polymeric surfactants are suitable for crosslinked polyurea microcapsules. According to the authors, a polymeric surfactant must have maleic acid or a carboxyl group in order to form a crosslinked polyurea microcapsule membrane. Cincu et al. [27] copolymerized maleic anhydride with various cyclic olefins such as cyclohexene, cyclooctene, cyclo-dodecene, norbornene, indene and thiophene. They showed that the resulting copolymers are alternating and the mechanism of the reaction can be explained by a charge-transfer complex. The influence of the starting cyclic olefin was also studied, and showed that the rate of the reaction largely depends on the nature of the olefin. Various methods of preparation for the alternating copolymers of MA with α-olefins (C2-20) were described [28], [29]. These copolymers and their functionalized derivatives are used as precursors for the enzyme synthesis [30] and as biologically active agents against several transplantable tumors (the half-amide-halfcarboxylate salt of alternating copolymer of MA with ethylene [31]), for the preparation of exchange membrane systems, adhesives and coatings [1], [12]. The oligonucleotide synthesis of MA copolymers covalently bound to silica spherical support and characterization of the obtained conjugates have been described by Chaix [32]. Direct synthesis of oligonucleotides was achieved on the controlled porous glass surface grafted with alternating copolymer of MA including poly(MA-altethylene). The polyelectrolyte behavior of alternating maleic acid copolymer in aqueous solution was presented in many reports. Several characteristic properties have been

rates for the MA–α-olefin monomer systems such as MA-hexene-1 [4],[14],[15], MA–octene-1 and MA– 2,4,4-trimethyl- pentene-1 [4], as well as for the other MA–donor monomer systems such as MA–vinylacetate [16], MA–chlorethyl vinyl ether [17] and MA–isobutyl ether [18] systems shift toward 1:1 feed composition as the total monomer concentrations become larger. The initial rate of radical copolymerization of vinyl ethers and esters, and styrenes with MA is analyzed according to the simplified complex participation model. The copolymerization of MA and its derivatives with some Cl-containing olefin monomers was investigated [19]-[21]. Poly(MA-alt-1,3-dichlorobutene-2) was synthesized by radical bulk copolymerization method and characterized by IR and 1H NMR spectroscopy [21]. Reinhardt et al. [22] studied the viscometric behavior of hydrolyzed poly(MA-alt-1-propene) copolymers with different molecular weights in aqueous solution as a function of polymer concentration, degree of neutralization, concentration of added salt (NaCl) and temperature, respectively. They showed that addition of salt to the solutions restores conformity with the Huggins’ equation; the dependence of the viscosity on the degree of neutralization indicates a maximum at half the degree of neutralization which disappears with decreasing molecular weight. Takada and Matsumoto [23] synthesized an alternating copolymer of N-allylmaleimide (AMI) and isobutene (IB) [poly(AMI-alt-IB)] as a new class of thermosetting polymers by the free radical copolymerization process. They found that the reactivity of the maleimide group of the AMI monomer 103 times higher than that of the N-allyl group based on the results for the ternary copolymerization system composed of Nmethyl maleimide (MMI), N-allylphthalimide, and IB. The maleimide moiety exclusively participated in the propagation during the copolymerization of AMI with IB, resulting in the formation of the soluble poly(AMIalt-IB). The copolymer included an alternating repeating structure consisting of maleimide and IB units in the main chain and the unreacted allyl group in the side chain. The onset temperature of the decomposition for poly(AMI-alt-IB) was over 400°C under a nitrogen stream. The transparent cast film of poly(AMI-alt-IB) was readily cured upon heating without any catalyst. We proposed that this monomer system and its selfcrosslinkable copolymers can also be used to prepare thermosetting transparent nanomaterials through interlamellar alternating copolymerization in the presence of reactive organosilicates. The radical alternating copolymerization of N-methylmaleimide with various olefins was carried out by Omayu and Matsumoto [24] to obtain thermally stable and transparent polymers. According to the authors, cyclic olefins including an exo-methylene group showed high polymerization reactivity during the copolymerization; the introduction of a polar substituent into the olefin monomers results in the formation of copolymers with a

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analogs. However, intercalative copolymerization of αolefins with maleic anhydride/ organoclay complexes and their nanocomposites is not investigated. In the last decade, considerable attention is given to developing various methods for synthesizing polymer nanocomposites, emphasizing layered silicate reinforcement, especially alkyl amine surface modified montmorillonite clay (organo-MMT). Generally, such nanocomposites prepared by intercalative polymerizetion of vinyl and acrylic monomers [46]-[52], and compounding compatibilized thermoplastic blends in melt in the presence of different type of organo-silicate clays as a ‘nano-reactor’[53]-[58]. Taking into consideration that nature of interaction between functional (co)polymers and the organo-clay is important, and the structure and morphology of the resulting nanocomposites strongly depend on such interactions, we have investigated physical and chemical (amidization) interactions between polar monomer, such as electron-acceptor maleic anhydride (MA) and two types of organo-MMT containing intercalated dimetyldidodecyl ammonium cation and octadecyl amine surfactants (DMDA-MMT and OCDA-MMT, respectively). Layered silicate polymer nanocomposites were synthesized by intercalative alternating copolymerization of MA…organoclay complexes with electron-donor α-olefins (C6-12) such as 1-hexene (HX), 1-octene (OC) and 1-dodecene (DD) in the presence of a radical initiator (AIBN) in dioxane at 65oC under nitrogen atmosphere. Synthetic pathway of nanocomposite structure can be represented as follows (Fig. 1).

studied such as the two-step dissociation of carboxylic groups [33] and binding of counterions [34], pH induced conformational transitions [35], a remarkable behavior of viscosity that exhibits a maximum at the halfneutralization point [33], [36]. These results were obtained from potentiometric, viscometric, conductometric, dilatometric, and calorimetric measurements. Complexes of polyelectrolytes with proteins are involved in various chemical and biological processes such as protein separation, enzyme stabilization and polymeric drug delivery systems. Polyelectrolytes containing hydrophobic repeating units are expected to have abilities to bind targeted biopolymers, using affinity precipitation or extraction in aqueous to-phase polymer systems. Acording to Hirvonen [37], linear copolymers of maleic acid with electron-rich vinyl or vinylidene comonomers, or their amphoteric derivatives could be suitable candidates for these purposes as they can be synthesized from easily accessible commercial monomers. Relatively low cost and the possibility to control hydrophobic/hydrophilic character of the copolymers by copolymerization may help to develop new precipitation and extraction methods used in bioseparations. Maleic acid and sodium maleate copolymers are obtained from copolymers of MA, which generally have an alternating chemical structure [3], [12], [38]. The behavior of maleic acid or sodium maleate copolymers in aqueous solutions is governed mainly by electrostatic interactions between the polyions and counterions. It is also influenced by the structural characteristics of the copolymers, such as the presence of two neighboring carboxylic groups in the maleic units and the hydrophilicity/hydrophobicity of the comonomers. These copolymers are known to undergo a two-step dissociation and binding of counterions, and conformational transitions induced by changes in pH [36], [39]-[42]. Synthesis and characterization of stimuli-responsive random copolymers of MA and N-isopropylacrylamide with different compositions (MA-units in copolymers ≤ 20 mol %) and their macromolecular reactions with poly(ethylene oxide) and poly(ethyleneimine) have been reported as a route to obtain new reactive amphiphilic water-soluble polymers potentially useful as carriers for gene delivery [43]-[45]. Copolymers of MA with α-olefins have been extensively investigated, results of which were the subject of a large number patents, periodics and book publications. Most of them are mainly related to the ethylene copolymer [poly(MA-co-E)], which has very useful properties as thickness, stabilizers and suspending agents. Poly(MA-alt-1-hexene) was utilized as enzyme carriers. Thus α-olefins with σ−π-conjugation system belonging to the monomer type with low activity in the radical polymerization, are easily copolymerized with electron-acceptor type monomers, and formed alternating copolymers with maleic anhydride and its isostructural

Fig. 1. Interlamellar copolymerization of α-olefins with MA…O-MMT complex through charge-transfer complex formation

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II. II.1.

cm-1), CH out-of-plane bending (792 cm-1) Si-O-Si streching (1030 cm-1) are the other characteristic peaks for this nanocomposite structure. For poly(MA-alt-1hexene)/Organo-MMT the characteristic absorption bands and their assignments are summarized in Table II.

Results and Discussion Chemical and Physical Structures II.1.1.

FTIR Analysis

The FTIR spectra have been widely used to characterize the polymer-clay nanocomposites. The FTIR spectra of poly(α-olefin-alt-MA) copolymers and their nanocomposite structures are given in Figs. 2-4. The spectra exhibit the presence of characteristic peaks of both copolymers and organo-MMTs. For organo-MMTs, the characteristic absorption bands include CH2 asymmetric stretching (2923 or 2933 cm-1), CH2 symmetric stretching (2851 cm-1), CH2 plane scissoring (1474 cm-1) and CH out-of-plane bending (798 cm-1). In addition, absorption bands related to silicate are also found, such as OH streching of lattice water (3634 cm-1), H-O-H bending (1633 cm-1), Si-O-Si streching (1030 cm1 ).

Figs. 4. FTIR spectrum of (a) poly(MA-alt-1-hexene), (b) Copolymer/ DMDA-MMT and (c) Copolymer/OCDA-MMT clay TABLE II CHARACTERISTIC FTIR ABSORPTION BANDS AND THEIR ASSIGNMENTS FOR Poly(MA-alt-1-hexene)/Organo-MMT HYBRID NANOCOMPOSITE Band assignments Absorpion bands (cm-1) 3700-3550 (w.-m) OH stretching from silicate surface 3050 and 3080 (m) stretching C–N+ bands in alkylammonium 2961 (s) CH stretching in CH3 in n-alkyl or alkylammonium linkage (O-MMT) 2923 and2865 (s) CH2 stretching in alkyl groups of OMMT 1855 (m.-s) antisym. C=O stretching for anhydride unit 1704 (vs) sym. C=O stretching for anhydride unit 1550-1500 (m.-w) –C=O...N+– linkage 1495 (m) C–N stretching in surface alkylammonium ammonium ion from alkylamine 1455(s) and 1470(s) CH2 deformation (scission vibration) 1260 (m.-s) CH3 rocking 1225 (s) C–O–C stretching in cyclic anhydride unit 1190-900 (vs,broad) Si–O silicate bands 1085 (s) out-of-plane Si–O silicate band 1045 (s) in-plane Si–O silicate band 925 (s) C–C stretching 725 (w) and 705 (s) CH2 rocking in alkylamine and n-hexyl

Figs. 2. The FTIR spectra of (a) poly(1-DD-alt-MA), (b) poly(1-DDalt-MA)/DMDA-MMT and (c) poly(1-DD-alt-MA)/ODA-MMT

The existence of these characteristic peaks are ascribed to the exfoliation of MMT layers within the polymer matrix. Analogous FTIR spectra are observed for the other copolymer/organo-MMT systems (Figs. 3 and 4).

Figs. 3. The FTIR spectra of (a) poly(1-OC-alt-MA), (b) poly(1-OC-altMA)/DMDA-MMT and (c) poly(1-OC-alt-MA)/OCDA-MMT

As can be seen from Figure 2(b), for poly(1-DD-altMA)/DMDA-MMT nanocomposite, the broad C=O band of MA unit at 1777 cm-1 appears as a sharp, strong band due to the formation of complexes between MA and clay layers (C=O in -COOH). CH2 streching (olefin) or alkylammonium linkage (organo-MMT) (2971-2823 cm1 ), NH streching and NH3 deformation of C-NH3+ COO- complex or -COO- streching (2500-2300, 1550

II.1.2.

X-ray Diffraction Analysis (XRD)

Polymer-clay nanocomposites are synthesized typically by using organically modified clay with alkylammonium cation and intercalation of a suitable monomer followed by in situ polymerization. The role of alkylammonium cation is to improve penetration of the

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organophilic monomers into the interlayer space and the role of the monomer is to promote dispersion of the clay particles. Fig. 5 shows the XRD patterns of pristine ODA-MMT, DMDA-MMT.

This observation indicated that the large clay tactoids were delaminated and dispersed, as much smaller particles, along with some individual silicate nanoplatelets. Comparative analysis of these nano-systems indicates (1) size of the particles significantly decreases by increasing in length of alkyl groups of side-chain copolymer macromole-cules. Relative higher dispersion degree is observed for the poly(MA-alt-1-dodecene)/OMMT nanocomposites.

Fig. 5. XRD patterns of pristine ODA-MMT and DMDA-MMT clays

Direct evidence of the intercalation is provided by the XRD patterns of the obtained hybrids (Figs. 6-8), where the peaks of DMDA-MMT and ODA-MMT around 2θ = 4° are shifted to lower angles in all the samples. Relatively apparent and strong peaks of the clays were observed for the poly(α-olefin-alt-MA)/O-MMT’s. II.2.

SEM Morphology of Nanocomposites

Scanning electron microscopy (SEM) is a powerful method for the characterization of polymer/clay nanocomposites. SEM observation of the fractured surfaces of poly(MA- alt-1-hexene), poly(MA-alt-1octene), poly(MA-alt-1-dodecene) and their nanocomposites obtained by DMDA-MMT and ODA-MMT organoclays is shown in Figs. 9-11. Intercalation/ exfoliation of the silicate layers is important for polymer/clay nanocomposites as well as homogeneous dispersion. As can be seen from the SEM micrographs, the clay platelets were dispersed in the polymer matrix. The sizes of the dispersed clay particles were in the range of few nanometers to microns.

Figs. 6. XRD patterns of (a) pristine poly(MA-alt-1-hexene) and its nanocomposites prepared with (b) DMDA-MMT and (c) ODA-MMT clays. Effect of organoclay nature

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SEM image parameters also depend on the nature of the used organoclay. In the case of reactive organoclay (ODA-MMT), relative higher dispersed nanoparticles was observed.

Figs. 8. XRD patterns of (a) pristine poly(MA-alt-1-dodecene) and its nanocomposites prepared with (b) DMDA-MMT and (c) ODA-MMT clays. Effect of organoclay nature

Figs. 7. XRD patterns of (a) pristine poly(MA-alt-1-octene) and its nanocomposites prepared with (b) DMDA-MMT and (c) ODA-MMT clays. Effect of organoclay nature

II.3.

Structure–Thermal Behavior Relationships

We investigated both the effects of copolymer nature and two types of organoclays on the thermal properties of three nanosystems, poly(MA-alt-α-olefin)s/reactive and non-reactive organoclays. Obtained results are illustrated in Figs. 12-14 and summarized in Table III. It was shown that the glass transition temperature (Tg) decreases due to the increase in the length of long branch alkyl chains in α-olefins resulting in restricted segmental motion.

Figs. 9. SEM images of (A) pristine poly(MA-alt-1-octene), (B) poly(MA-alt-1-octene) / ODA-MMT clay, (C) and (D) poly(MA-alt-1octene) / DMDA-MMT clay nanocomposites. Scale: (A) x 3.000, 1µm, (B) x 2.000, 10 µm, (C) x 500, 10 µm and (D) x 1.000, 10 µm

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Figs. 10. SEM images of (A) and (B) pristine poly(MA-alt-1-hexene), (C) poly(MA-alt-1-hexene) / DMDA-MMT clay and (d) poly(MA-alt-1 hexene)/ODA-MMT clay nanocomposites. Scale: (A) x100, 100 µm, (B) x 1.000, 10 µm, (C) x 800, 10µm and (D) x 500, 10 µm

Figs. 12. DSC curves of (a) pristine poly(MA-alt-1-hexene) and (b) its nanocomposites: (1) copolymer/DMDA-MMT and (2) Copolymer/ODA-MMT. Heating rate at 10oC/min under a nitrogen atmosphere

Figs. 11. SEM images of (A) pristine poly(MA-alt-1-dodecene) and its nanocomposites: (B) poly(MA-alt-1-dodecene)/ODA-MMT clay, (C) and (D) poly(MA-alt-1-dodecene)/DMDA-MMT clay. Scale: (A) x 10.000, 1µm, (B) x 150, 100 µm, (C) x 1.000, 10 µm and (D) x 2.000, 10 µm

Similar effect is valid for the nanocomposites prepared in the presence of ODA-MMT via covalent interactions since internal plasticizing takes place during the dispersion of the clay in between the polymer layers. However, the same behavior is somewhat less significant in the nanocomposites prepared with DMDA-MMT predominating the effect due to the complex mechanism of nanostructure formation via physical interfacial interactions being weaker than chemical interactions. The thermal decomposition temperatures (Td) were determined by TGA. In Fig. 15, the thermograms for poly(MA-alt-1-dodecene) and its nanocomposites are given. It can be seen that the hybrids exhibit higher thermal stabilities. Evidently, the decomposition rates of the nanocomposites become slower compared to that of pure copolymer, indicating the thermal stability of copolymer.

Figs. 13. DSC curves of (a) pristine poly(MA-alt-1-octene) and (b) its nanocomposites: (1) copolymer/DMDA-MMT and (2) Copolymer/ ODA-MMT. Heating rate at 10oC/min under a nitrogen atmosphere

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TABLE III THERMAL PARAMETERS OF COPOLYMERS AND Poly(MA-alt-α-olefin)/ ORGANOCLAYS Polymers and Tg T(max) T2-outset Tm T1-onset nanocomposites (°C) (°C) (°C) (°C) (°C) poly(MA-alt-1-hexene)

63

73

190

250

503

poly(MA-alt-1-octene)

56

70

186

254

500

poly(MA-alt-1-dodecene)

50

68

225

262

510

52

80

205

395

475

54

74

200

405

505

55

82

262

315

500

55

72

275

305

500

poly(MA-alt-1hexene)/ODA-MMT poly(MA-alt-1octene)/ODA-MMT poly(MA-alt-1dodecene)/ODA-MMT poly(MA-alt-1dodecene)/DMDA-MMT

Figs. 14. DSC curves of (a) pristine poly(MA-alt-1-dodecene) and (b) its nanocomposites: (1) copolymer/DMDA-MMT and (2) Copolymer/ ODA- MMT. Heating rate at 10oC/min under a nitrogen atmosphere

Fig. 16. TGA-DTG thermogram of poly(MA-alt-1-octene)/ODA-MMT nanocomposite

Fig. 15. TGA thermogram of (a) pristine poly(MA-alt-1-dodecene), (b) Copolymer/DMDA-MMT clay and (c) Copolymer/ODA-MMT clay nanocomposites

All copolymers and their nanocomposites were decomposed in two steps of degradation mechanism (Figs. 15-17). The first step is related to decarboxylation of anhydride units. Second step is associated with the main chain degradation reaction. Thermal stabilities of nanocomposites were observed to increase compared to pristine copolymers with regard to the evaluated T1 and Tmax values (Table III). Similarly, as can be seen from Figs. 16 and 17, the decomposition temperatures of poly(MA-alt-1octene)/ODA-MMT and poly(MA-alt-1-hexene)/ODAMMT are higher than those of pristine copolymers. A possible reason is that the inorganic material with high thermal stability and great barrier properties of nanolayers dispersed in the nanocomposites, prevent the heat from being transferred quickly and limit continuous decomposition of nanocomposites.

Fig. 17. TGA-DTG thermogram of poly(MA-alt-1-hexene)/ODA-MMT nanocomposite

III. Conclusion We have successfully prepared the poly (α-olefin-altMA)/organoclay hybrids via in situ interlamellar copolymerization reaction using DMDA-MMT and ODA-MMT organoclays. Good exfoliation and dispersion of the silicate layers were observed in poly(MA-alt-α-olefin)/DMDA-MMT and poly(MA-alt-

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α-olefin)/ODA-MMT, due to the efficient intra-gallery polymerization. The microstructure of prepared nanocomposites were clearly demonstrated by FTIR method. The formation of intercalated complexes and amide linkages, as well as nano-structures in the studied systems were confirmed by FTIR, X-ray powder diffraction (XRD) and SEM morphology analyses. The shape of the the broad C=O band of MA unit at 1777 cm1 appears as a sharp, strong band due to the formation of complexes between MA and clay layers. It was found that exfoliation degree, thermal parameters and morphology of poly(MA-alt-α-olefin)/organoclay nanocomposites strongly depend on the type of organoclay and α-olefin units. Consequently, comparative studies carried out with nanocomposites with ODA-MMT as reactive nanofiller yielded much more improved results rather than those with nonreactive nanofiller. The increasing length of long branch alkyl chain in α-olefins decreases the glass-transition temperature (Tg) values, thus, increasing the exfoliation degree. SEM micrographs represent that the nanocomposites exhibit fine dispersed surface morphology. Moreover, better morphology is displayed in poly(MA-alt-1-dodecene)/organo-clay nanocomposites as compared to other analogs due to the effect of long dodecyl side-chain groups as internal plasticizing agent. XRD, DSC and SEM analyses indicate that pristine poly(MA-alt-α-olefin)s show amorphous structure while their nanocomposites exhibit semi-crystalline structure.This observed phenomena can be explained by internal plasticizing effect in olefin units which in turn facilitates the penetration of copolymer chains in between silicate galleries. This new approach, in the synthesis of polymer nanocomposites may be utilized for a wide range of functional monomers exhibiting tendency towards Hbond formation with various amine compounds. Moreover, these nanocomposites containing long alkyl branches and reactive anhydride groups allow us future utilization in situ processing of thermoplastic polymers, especially polyolefins as effective nanofiller-compatibilizers using reactive extrusion system.

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Acknowledgements

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This study was supported by the Turkish Scientific and Technological Research Council of Turkey (TUBİTAK) via the 2214 - Fellowship Program. We appreciate Prof. Dr. Erol Sancaktar for providing us the facilities in their lab. in Polymer Engineering Department, The University of Akron.

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Authors’ information 1

Department of Chemistry, Faculty of Science, Hacettepe University, Beytepe, 06532 Ankara, Turkey. 2 Institute of Science & Engineering, Division of Nanotechnology and Nanomedicine, Hacettepe University, Beytepe, 06800 Ankara, Turkey.

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Deniz D. Bozdoğan Vitae (Education, degrees): B.Sc. from Chem. Dept., Fac. Sci. at Hacettepe Univ., Ankara, Turkey, 2003. M.S. in Physical Chemistry from Chemistry Deparment at Hacettepe Univ., Ankara, Turkey, 2006. She is a PhD candidate in Phys. Chem. From Dept. of Chem. at Hacettepe Univ., Ankara, Turkey. Research interests: Polymer-inorganic nanocomposites, synthesis and characterization of functional polymers for nano- and bioengineering applications. E-mail: [email protected]

Zakir Rzayev Vitae (Education, degrees): B.Sc. in Organic Chemistry from Fac. Chem., Petrochem. Div., Baku State University., Azerbaijan, 1962. PhD in Polymer Chemistry from Polym. Dpt. Polymer of Inst. Phys. Chem., SU Acad. Sci., Moscow, USSR, 1967, Dr. Sci. in Polymer Science from Moscow State Univ. Fac. Chem. and Inst. Polym. Mater., Azerbaijan Acad. Sci., 1983 and Prof. Dr. from Inst. Polym. Mater., Azerbaijan Acad. Sci., 1984. He is Professor, Chem. Eng. Dept. and Inst. Sci. & Eng., Div. Nanosci. & Nanomed. Hacettepe Univ., Ankara, Turkey, 1999 – to date. He is author more 400 publications (books, reviews, regular articles, patents, proceedings, etc.). Research interests: Polymer Nanoscience & Nanoengineering, smart functional polymers, nanocomposites. He is Member of ACS (American Chemical Society) and Chemical Enginering Society (TR); Frequent Reviewer of SCI Journals of ACS Publications, Wiley, Elsevier, Springer, etc., 2002 – to date. E-mail: [email protected]

Günay Kibarer Vitae (Education, degrees): B.Sc. from Dpt. Chemistry, Fac. Arts & Science, Middle EastTechnical Univ (METU), Ankara, Turkey, 1978. MSc from Dpt. Chem., METU, 1982. PhD from Dpt. Chem., METU, 1989. Prof. Dr. from Dpt. Chem., Hacettepe Univ., Ankara, Turkey, 2002. Research interests: Plasma polymerization, Complex-radical copolymerization, Controlled/living RAFT polymeri-zation, Enzymatic polymerization, Enzymatic degradation, Polymer Nanoscience and Nanomedicine. E-mail: [email protected]

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