Synthesis and properties of propene copolymers with ether comonomers

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EUROPEAN POLYMER JOURNAL

European Polymer Journal 44 (2008) 694–703

www.elsevier.com/locate/europolj

Synthesis and properties of propene copolymers with ether comonomers Ulrich Schulze *, Doris Pospiech, Hartmut Komber, Liane Ha¨ussler, Dieter Voigt, Michael Eschner Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, D-01069 Dresden, Germany Received 24 October 2007; accepted 28 November 2007 Available online 28 January 2008

Abstract The direct copolymerization of propene with polar comonomers using metallocene catalysts in solution was investigated. As comonomers, two ether compounds were used in comparison to 10-undecene-1-ol as well-investigated comonomer. The ether comonomers were diethylene glycol mono-10-undecenyl ether (DEGUE) and octaethylene glycol-10undecenyl methyl ether (OEGUME). The influence of the different comonomers on the copolymerization behavior was studied. The copolymers were characterized with respect to their comonomer contents, molar masses, and thermal properties. The incorporation rate of DEGUE and OEGUME into the propene copolymers did not exceed 1.6 mol% for DEGUE and 0.31 mol% for OEGUME and was thus considerably lower than in the reference propene copolymerization with 10-undecene-1-ol. An uncompleted shielding of the oxygen atoms of the ether groups by triisobutyl aluminum (TIBA) to the metallocene catalyst is assumed to be responsible for this behavior. The crystallization kinetics in the copolymers with comparable molar masses is mainly influenced by the side chain density per 1000 propene units, n1000. The incorporation of hydrophilic comonomers into polypropene was expected to alter the surface properties. The slightly lowered water contact angles found on films of copolymers with higher comonomer content indicated the enhanced hydrophilicity of the polypropene copolymer surfaces compared to polypropene (PP). Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Copolymerization; PP; Metallocene catalysts; Polar comonomers; Functionalization

1. Introduction Polypropene (PP) is well-known as polymer with mechanical properties that can be tailored over a wide range. However, one of the major drawbacks of PP is the nonpolar surface which causes weak * Corresponding author. Tel.: +49 351 4658 391; fax: +49 351 4658 565. E-mail address: [email protected] (U. Schulze).

interactions to other compounds. Therefore, the functionalization of PP is an important aim to enhance the polarity of this commodity plastic to provide, e.g., basic materials for varnishable and gluable parts. It is well-known that the introduction of functional groups into the PP chain is possible on different ways, like free radical grafting of polar monomers onto PP, end group modification of PP by hydroboration, copolymerization of propene with diene comonomers and subsequent conversion

0014-3057/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2007.11.029

U. Schulze et al. / European Polymer Journal 44 (2008) 694–703

of the reactive double bonds into polar groups, and different methods of subsequent treatments of the PP surface. A widespread overview to the different methods is given by Mu¨lhaupt et al. [1]. However, all these methods also include several disadvantages. In free radical grafting chain degradation, crosslinking, and averaged side chain length distribution have to be taken into account. By end group modification of PP by hydroboration only a small content of functional groups can be generated. This method and the copolymerization with diene comonomers, too, require an additional step to obtain polar groups. In the last years the direct, metallocene catalyzed copolymerization of olefins with polar comonomers has been described [2–6]. The comonomers reported mostly contained alcohol or carboxylic groups, as for example 10-undecene-1-ol and 10-undecenoic acid, which were also object of our previous investigations [7,8]. The main problem in all these reactions is the deactivation of the catalyst by the polar groups of the comonomer. Deactivation of the metallocene catalyst is due to the competition between olefinic groups and polar groups in their contact to the metallocene cation as the active centre for the polymerization. While the contact to the olefinic bond results in a polymer or copolymer, the interaction with the polar group can generate a stable complex between the comonomer and the electrophilic metallocene cation, which consequently deactivates the catalyst. It is already well-known that two conditions should be met to reduce deactivation: first, the comonomers should possess a long spacer between the polar group and the olefinic group, and secondly, a pre-reaction of the polar comonomers with aluminum alkyls should be carried out before copolymerization [9]. In this paper, we report on the direct copolymerization of propene with new functional comono-

695

mers. The aim of the present work was the synthesis of copolymers with a high content of functional side groups. Thus, we copolymerized propene with ether group containing comonomers of two different lengths and compared the results with reference polymerizations using 10-undecene-1-ol as comonomer (Scheme 1). Furthermore, we investigated the influence of different functional groups and their concentration on the copolymerization behavior, molar mass and the resulting polymer properties like melting and crystallization behavior. The investigations should deliver basic information about the possibilities to enhance the surface polarity of PP by direct copolymerization. 2. Experimental part 2.1. Materials Toluene (Fluka, p.a.) was sodium/potassium dried and distilled prior to use. Propene (2.8 grade) was purchased from Riessner-Gase. It was purified by R3-11 copper oxide catalysts (BASF) followed ˚ molecular sieves. The metalby passing through 3 A locenes, rac-Me2Si[2-Me-4,5-BenzInd]2ZrCl2 (MBI) (Boulder Sci. Comp.) and rac-Et[Ind)]2ZrCl2 (EtInd2) (Crompton GmbH) were used as received. Methylaluminoxane (MAO) solution (10 wt% solution in toluene) and triisobutyl aluminum (TIBA) (both from Crompton GmbH) were used as obtained. 10-Undecene-1-ol (Aldrich) was distilled and stored over molecular sieve before used in copolymerization. 2.2. Synthesis of ether comonomers The ether comonomers diethylene glycol mono10-undecenyl ether (DEGUE) and octaethylene gly-

CH

O CH2CH2 O CH2CH2 OH

(1)

CH

O CH2CH2 O CH2CH2 O CH3

(2)

CH2

CH2

7

CH

OH

(3)

CH2 Scheme 1. Chemical structures of the comonomers diethylene glycol mono-10-undecenyl ether (DEGUE, 1), octaethylene glycol-10undecenyl methyl ether (OEGUME, 2) and 10-undecene-1-ol (3).

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col-10-undecenyl methyl ether (OEGUME) were synthesized as follows: DEGUE: 13.8 g (0.6 mol) Sodium was added stepwise to a solution of diethylene glycol (318 g, 3 mol) in THF under stirring and heating to about 70–80 °C. After complete dissolution 11-bromo-1undecene (76.5 g, 0.5 mol) was added. After stirring for 6 h at 160 °C the solution was cooled to room temperature. DEGUE was obtained by fractionated distillation of the reaction mixture and stored over molecular sieve.

2 CH

4 CH2

CH2 1

CH2 3

pressure and dichloromethane was added to the remaining content, acidified, washed with water and dried over magnesium sulfate. After removing the solvent the raw product was purified by column chromatography using silica. Nonpolar impurities were separated with dichloromethane; the product was eluted with ethyl acetate. Yield: 4.45 g (35%). 1 H NMR (500 MHz, CDCl3): d = 1.26 ppm (10H, H5), 1.36 (m, 2H, H4), 1.53 (m, 2H, H6), 2.02 (q, 2H, H3), 3.36 (s, 3H, H11), 3.43 (t, 2H, H7), 3.53 (t, 2H, H10), 3.56 (t, 2H, H8), 3.63 – 3.61 (24H, H9), 4.91 (d, 1H, H1cis), 4.97 (d, 1H, H1trans), 5.79 (m, 1H, H2). 8 O CH2

6 CH2

2

CH2 1

CH2 3

O

9 CH2

CH2 7

CH2 5 5

4

6

8

CH2

CH2

CH2

CH2

CH2

5

7

OEGUME: Sodium hydride (2.25 g, 75.0 mmol) (80 wt/wt suspension in paraffin) was washed with dry petrol ether under nitrogen atmosphere until free of paraffin and then 20 mL dry THF was added dropwise. After heating to the boiling point the solution was cooled to room temperature and a solution of PEG 350-monomethyl ether (17.5 g, 50.0 mmol) in 50 mL dry THF was added drop by drop. After complete addition the solution was refluxed for 10 min and a solution of 11-bromo-1undecene (14.0 g, 60.0 mmol) in 50 mL dry THF was added dropwise. The solution was refluxed for 16 h, cooled to room temperature and the surplus of sodium hydride was hydrolyzed by addition of ethanol. The THF was distilled off under reduced

10 CH2

O

11 CH3

7

Yield: 52.9 g (41%); b.p.: 140–144 °C (4 mbar). 1 H NMR (500 MHz, CDCl3): d = 1.28 (10H, H5– 9 H ), 1.37 (m, 2H, H4), 1.59 (m, 2H, H10), 2.03 (q, 2H, H3), 2.42 (s broad, 1H, H16), 3.46 (t, 2H, H11), 3.58 (t, 2H, H12), 3.62 (t, 2H, H14), 3.68 (t, 2H, H13), 3.73 (t, 2H, H15), 4.92 (d, 1H, H1cis), 4.99 (d, 1H, H1trans), 5.81 ppm (m, 1H, H2).

CH

9 CH2

2.3. Copolymerizations Before the copolymerization can be started the comonomers have to be pre-reacted with aluminum alkyls. For this, toluene and TIBA were fed into a flask equipped with stirrer. The comonomer was added dropwise with cooling at about 30 °C.

12

10

CH2 CH2 9

CH2

13

14

15

16

O CH2CH2 O CH2CH2 OH

11

The copolymerizations were carried out in 200 mL toluene in a 1 L glass autoclave (Bu¨chi, Switzerland). The propene consumption was monitored by a pressflow-gas controller (Bu¨chi). The temperature, speed of stirrer, pressure, instantaneous gas flow and total gas consumption were monitored and recorded as a function of time. The stirring speed was held constant at 800 rpm. The polymerization temperature was varied from 30 °C to 70 °C, and the total pressure was kept in the range of 1.2–1.5 bar. The reactor was first charged with toluene, cocatalyst (MAO) and the comonomer, pre-reacted with TIBA. The copolymerization was initiated by injecting the catalyst solution into the reactor. The catalysts were either rac-Et[Ind]2ZrCl2

U. Schulze et al. / European Polymer Journal 44 (2008) 694–703

(Et-Ind2) or rac-Me2Si[2-Me-4,5-BenzInd]2ZrCl2 (MBI). For all copolymerizations, the Al/Zr molar ratio was 4000 or 8000 and the catalyst concentration was 1.6  105 mol/L (for polymerizations with Et-Ind2) or 4.5  105 mol/L (for polymerizations with MBI), respectively. Termination of the polymerization, precipitation and purification were carried out as described previously [7,10].

697

copy (XPS) using an Axis Ultra Spectrometer (Kratos Analytical, England; X-ray source: mono-AlKa; with a rated input of the X-ray tube of 300 W by 20 mA, a pass energy of 160 eV at the analyzer, and a low energy electron source for charge compensation) was used. All samples were measured at least on two, mostly five different places of the films. The values were averaged. The O/C ratios were calculated from the overview spectra.

2.4. Polymer characterization 3. Results and discussion 1

H NMR spectra were recorded on a Bruker DRX 500 spectrometer operating at 500.13 MHz. The samples were measured at 120 °C in C2D2Cl4, which was also used as reference and lock. The molar mass of the copolymers was determined by size exclusion chromatography (SEC) performed with a PL-GPC 220 (Polymer Laboratories) connected with refractive index- and light scattering detection (DAWN EOS; Wyatt Technologies, US). The column set contained two PL MIXED-B-LS columns (Polymer Laboratories). The SEC was performed at 150 °C using 1,2,4-trichlorobenzene (stabilized by biphenyl amine) as mobile phase. The concentration of the non-filtrated polymer solutions was 0.025 g/mL and the sample application was 0.60 mg. The calculation of molar mass averages and molar mass distributions was carried out from the light scattering data using ASTRA software (WYATT Technologies, US). The melting temperature and the heat of fusion were measured using a Perkin Elmer DSC 7 calorimeter. Samples were subjected to a cycle of first heating, cooling and second heating with a scan rate of 20 K/min over a temperature range from 60 °C to +180 °C. Since the thermal history can influence the thermal behavior of the sample in the first heating, only the second heating was evaluated. The melting temperature Tm is the temperature at the maximum of the melting peak. The degree of crystallinity a was estimated by integrating the heat flow between 60 °C and 155 °C and using the value for the heat of fusion of 100% crystalline PP, DH0 = 208 J/g [11]. Water contact angles were measured using a goniometer Kru¨ss G40 with the sessile drop method. The contact angles were averaged from at least five measurements. Surfaces are defined as hydrophilic if their advanced contact angles ha has a lower value than 90° [12]. The measurements were carried out on melt-pressed polymer films. The surface composition (O/C ratio) of the melt-pressed polymer films were determined by X-ray photoelectron spectros-

3.1. Synthesis of the copolymers The comonomers were pre-reacted with an aluminum alkyl, preferably triisobutyl aluminum (TIBA), before using in copolymerization. 10-Undecene-1-ol and TIBA react to a triisobutyl aluminum alcoholate dimer [2], in which the polar hydroxyl group is shielded by the bulky triisobutyl group. It is known that the addition of TIBA reduces the poisoning effect of the polar comonomers on the catalyst [13,14]. Using the comonomers described here we observed that this reduction occurred with different efficiency. Higher comonomer contents in the feed are tolerated by the catalyst with 10-undecene-1-ol, while with DEGUE and OEGUME only lower comonomer contents are accepted. The weak secondary valence interaction of the oxygen in the ether groups with the aluminum alkyls and therefore an uncompleted shielding could be the reason for this behavior (Scheme 2). The copolymerization of propene with the ether comonomers used resulted in new functionalized copolymers (Fig. 1). The synthesized copolymers are listed in Tables 1 and 2. Further copolymers were prepared to characterize the copolymerization behavior. The content of the polar comonomers in the copolymers achieved was quite different. Due to the above mentioned different interactions of the species in the pre-reaction, higher comonomer contents in the copolymers with 10-undecene-1-ol were realized than with the ether comonomers. The maximum of comonomer with 10-undecene-1-ol was 9.2 mol%, while the propene copolymers with DEGUE contained a maximum comonomer content of 1.6 mol%. With OEGUME a maximum content of 0.31 mol% was found. The copolymerization of propene with the vinyl comonomers was proven by 1H NMR. The absence of vinyl signals and the presence of the characteristic signals of the ether

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Al

Al Al

O H2CH2C O H2CH2C O

O CH2CH2 O CH2CH2 O Al

Al

weak interaction

Al

strong interaction

weak interaction

Scheme 2. Proposed chemical structure of DEGUE pre-reacted with TIBA.

CH2

CH

CH2

CH

CH3 n

m

X Fig. 1. General formula of synthesized copolymers, X = polar group like alcohol or ether group.

moieties (Fig. 2) indicate that the comonomers were incorporated in the PP backbone. The integral of the ether signals was related to the integral of the PP signals to determine the content of comonomer in the polymer. High ether comonomer conversions were needed to reach the presented comonomer incorporations into these copolymers. The comonomer conversions calculated from the polymer yield and comonomer contents in the copolymer depended on the comonomer content in the feed and on polymerization temperature. As expected, increasing comonomer contents in the feed caused a drop of the comonomer conversions (Tables 1 and 2). The same tendency was described by Aaltonen and Lo¨fgren for the copolymerization of ethene with 10-undecene1-ol [15]. An increased deactivation of the catalyst with rising comonomer concentration in the feed was discussed as a possible reason. The copolymerizations with 10-undecene-1-ol could not be carried out to high comonomer contents since a transparent gel was formed at a propene conversion of higher than about 0.1 mol and the polymerization became diffusion controlled. The gel formation may be explained by a reversible crosslinking via secondary valence interactions of the hydroxyl groups of 10-undecene-1-ol with TIBA

resulting in a dimer. The chemical structure is proposed in Scheme 3. In the copolymerization of propene with both ether comonomers the comonomer incorporation directly depended on the comonomer concentration in the feed, but not on temperature as well as catalyst type used. At monomer concentrations of higher than 3 mol% for DEGUE or 1.2 mol% for OEGUME the metallocene catalyst is completely deactivated (Fig. 3). Consequently no copolymer could be obtained with these concentrations. In opposite, the catalysts tolerated comonomer concentrations up to 48 mol% in the copolymerization with 10-undecene-1-ol caused by the more effective shielding mechanism of TIBA with this monomer. For the propene homopolymerization it is known that the catalyst activity increases with raising polymerization temperature [16]. Ju¨ngling et al. [17] confirmed this behavior in the propene polymerization for the catalyst system MBI/MAO. In contrast, we found a drop of the activity with increasing polymerization temperature for the same catalyst system of our propene copolymerization (Table 1). Obviously in our experiments the polar groups in the comonomers may influence the activity by a faster deactivation of the active catalyst centre at higher polymerization temperatures. The copolymers were characterized with respect to their molar mass. SEC curves of the DEGUE copolymers are shown in Fig. 4. With increasing comonomer content in the copolymers the peak maxima of the SEC curves shifted to higher elution volumes, that is the molar masses of propene copolymers decreased with increasing comonomer contents. Kashiwa et al. [18] suggested that alkyl aluminum acts as a chain-transfer agent at the activated bond between Zr and olefin unit. With increasing comonomer contents in the feed our copolymerization

U. Schulze et al. / European Polymer Journal 44 (2008) 694–703

699

Table 1 Propene copolymerization with the comonomers DEGUE and OEGUME with varied comonomer content in the feed (catalyst: MBI, [Zr] = 4  105 mol/L, ptotal = 1.2 bar, MAO/Zr = 4000–12,000) Sample

Comonomer in feed (mol%)

Tpol (°C)

Comonomer in polymer (mol%)

Comonomer conv. (%)

Activitya (kg Pol/(mol Zr h bar))

Mwb 103 (g/mol)

Mw/Mnb

PP-1

0

n1000

Tm (°C)

aPP (%)

Tc,o (°C)

50

0

–

3538

120

1.6

0

149

44

113

PP-co-DEGUE CP-1 1.52 CP-2 2.25 CP-3 2.31 CP-4 3.05 CP-9 1.52 CP-10 1.52

50 50 50 50 30 70

0.51 0.59 0.91 1.6 0.58 0.49

69 54 33 22 52 92

960 242 106 25 996 207

48 33 28 30 132 15

1.3 1.5 1.4 1.8 1.6 1.5

5 6 9 16 6 5

144 141 139 134 144 135

43 48 44 35 40 44

111 111 110 105 110 107

PP-co-OEGUME CP-5 0.31 CP-6 0.42 CP-7 1.22 CP-8 1.52

50 50 50 50

0.11 0.1 0.31 0

73 50 44 0

640 845 133 0

36 32 27 –

1.6 1.5 1.6 –

1 1 3 –

146 146 143 –

50 50 46 –

115 114 113 –

The calculation of the monomer conversion was performed by the following way: conv: ¼

xcom ðcopÞ  100%: xcom ðfeedÞ

xcom(cop) mol comonomer in copolymer. xcom(feed) mol comonomer in feed. xcom ðcopÞ ¼

xprop ðcopÞ:ccom ðcopÞ  100%: 100  ccom ðcopÞ

xprop(cop) mol propene in copolymer (from propene consumption). ccom(cop) comonomer content in copolymer in mol% (from 1H NMR). cprop(cop) propene content in copolymer = (100  ccom (cop)) in mol%. a Activity is averaged over 2.0 g propene consumed. b Determined by SEC coupled with LS-detection.

Table 2 Propene copolymerization with 10-undecene-1-ol (catalyst: Et-Ind2, [Zr] = 1.6  105 mol/L, ptotal = 1.2–1.5 bar, MAO/Zr = 8000, Tpol = 30 °C) Sample

Comonomer in feed (mol%)

Comonomer in polymer (mol%)

Comonomer conv. (%)

Activitya (kg Pol/(mol Zr h bar))

n1000

Tm (°C)

aPP (%)

Tc,o (°C)

PP-2 CP-11 CP-12 CP-13 CP-14

0 0.72 27.3 35.9 48.4

0 0.15 5.8 6.7 9.2

– 29 15 12 15

4482 3086 2508 1416 936

0 1.5 62 72 101

137 138 98 86 76

45 42 22 10 5

107 n.d. 67 32 n.dt.

n.d. not determined. n.dt. not detectable. a Activity is averaged over 2.0 g propene consumed.

system contained higher TIBA amounts, accelerating the chain-transfer reaction as termination reaction. Consequently, the molar masses of the resulting copolymers decreased. This behavior was already observed in our recent investigation [7].

Table 1 summarizes the molar masses of the copolymers. For OEGUME as comonomer the same tendency was observed. It has to be noted that the molar mass distributions calculated from LS data are mostly undersized compared with results

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a

b all -CH2-O-

O CH2CH2 O CH2CH2 OCH3 7

O CH2CH2 O CH2CH2 OH

all -CH2-O-O-CH3

3.8

3.4

3.0

2.6

2.2

1.8

1.4

3.8

1.0

3.4

3.0

2.6

2.2

ppm

1.8

1.4

1.0

ppm

Fig. 2. 1H NMR spectra of copolymers of propene with: (a) DEGUE (0.9 mol%) or (b) OEGUME (0.31 mol%) using catalyst MBI; Tpol = 50 °C.

Al O

Al

O

O

Al

O Al

Scheme 3. Proposed reversible chemical crosslinking of propene-co-10-undecene-1-olate.

a

b ideal copolymerization

3

activity -1 -1 -1 (kg PP*(mol Zr) *h *bar )

comonomer in copolymer (mol%)

4000

2

1

0

3000

2000

1000

0 0

0.5

1

1.5

2

2.5

comonomer in feed (mol%)

3

3.5

0

0.5

1

1.5

2

2.5

3

comonomer in feed (mol%)

Fig. 3. (a) Copolymerization behavior of the comonomers DEGUE and OEGUME with propene; DEGUE: Tpol = 50 °C, catalysts: MBI (d), and Et-Ind2 (N) or at Tpol = 30 °C, MBI (s), Et-Ind2 (4), OEGUME: Tpol = 50 °C, catalyst: MBI (}), vertical dashed lines are limits of incorporation. (b) Catalyst activity versus concentration of DEGUE (N) or OEGUME (d) in feed with catalyst MBI at Tpol = 50 °C, activity is averaged over 2.0 g propene consumed.

U. Schulze et al. / European Polymer Journal 44 (2008) 694–703

701

0.5

LS, AUX (volts)

0.0

PP-1 CP-1 CP-2 CP-3

-0.5

-1.0

-1.5 10

12

14

16

18

volume (ml) Fig. 4. SEC elution curves of propene copolymers containing DEGUE versus comonomer content: PP-1: 0 mol%, CP-1: 0.51 mol%, CP-2: 0.59 mol%, CP-3: 0.91 mol%; catalyst: MBI, Tpol = 50 °C, overlay of the original chromatograms detected with refractive index.

obtained by relative calibration with a broadly distributed PP standard. Therefore, the obtained values for Mw/Mn are relatively low. The molar masses of 10-undecene-1-ol copolymers were not given since the samples were not soluble after storage. Apparently, interactions by hydrogen bonding between the side chains prevented dissolution. 3.2. Thermal and surface properties of the copolymers The thermal behavior of the copolymers determined by DSC is characterized by the melting tem-

perature Tm, the PP crystallinity aPP and the onset temperature of the crystallization, Tc,o. The crystallinity of PP in the copolymers is nearly constant and did not depend on the comonomer content (DEGUE or OEGUME) as shown in Table 1. The drop of molar mass of DEGUE (Fig. 4) and OEGUME copolymers with higher comonomer contents consequently resulted in a drop of Tm and Tc,o (Table 1 and Fig. 5). A further decrease of Tm and Tc,o with raising n1000 but nearly constant molar mass was observed for CP-2 to CP-4 which may be explained by the disturbance of the supraTc,o

2nd heat

Tm

PP-1

2 W/g

heat flow endo

CP-1 heat flow endo

PP-1 CP-1

CP-3 CP-4

CP-3

2W/g

cooling

CP-4 75

100

125

temperature (˚C)

150

90

100

110

120

temperature (˚C)

Fig. 5. Melting and crystallization behavior dependence on comonomer content in propene copolymers containing DEGUE: PP-1: 0 mol%, CP-1: 0.51 mol%, CP-3: 0.91 mol%, CP-4: 1.6 mol%; Tpol = 50 °C, catalyst: MBI.

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molecular structure of polypropene by the side chains. Both, Tc,o and the rate of crystallization characterized by the reciprocal value of the width of the crystallization peak showed the lowest values for the sample with the highest comonomer content and therefore with the highest number of side chains per 1000 propene units n1000, too. Particularly in the propene copolymers with DEGUE it could be demonstrated imposingly that the comonomer content, and with it especially the side chain density per 1000 propene units, n1000, mainly influenced the crystallization kinetics in copolymers with comparable molar masses (Table 1). The results for the copolymers with 10-undecene-1-ol as comonomer (Table 2) confirmed the correlation of Tm and Tc,o to the comonomer content and n1000 found for copolymers containing DEGUE and OEGUME. The influences of the polymerization temperature on molar mass, grafting degree and the melting and crystallization behavior were also examined for the copolymerization of propene with DEGUE (Table 1). Tm and Tc,o were slightly influenced with increase of the polymerization temperature to 70 °C. The molar masses decreased with raising polymerization temperature. The effect is known from the homopolymerization of propene. The rising temperature accelerates the rate of chain-transfer reactions with respect to propagation as reported by GonzalezRuiz et al. [19]. The surface properties of PP and copolymer films were characterized by water contact angle and XPS

measurements. The contact angle is regarded as measure for the hydrophilicity of the polymer films. The increase of the O/C ratios of the copolymer surfaces with raising comonomer content in the copolymer strikingly confirmed the tendencies of the contact angles ha of the respective copolymers (Fig. 6). Fig. 6a shows that the O/C ratio in the top surface layer of the polymer films found by XPS increased with the comonomer content. As it could be expected, the increase is more pronounced for OEGUME and DEGUE copolymers owing to the higher concentration of oxygen atoms. The contact angles of the undecene-1-ol copolymers varied (which may reflect the influence of crystallinity or sample preparation). The even smaller contents of OEGUME and DEGUE in the copolymers however resulted in decreased contact angles. Fig. 6b illustrates at least a tendency of the influence of polar comonomers and their contents in the copolymers, leading to copolymers with surfaces more hydrophilic than polypropene control samples. The water contact angles decreased with both, increasing polarity of the comonomer and content of polar comonomer in the copolymer. The desired decay of the contact angle is more pronounced with OEGUME as comonomer than with DEGUE due to the longer ether chains of the former, i.e., their higher O/C ratios. Copolymers with 10-undecene-1-ol showed the lowest drop of the contact angle with increasing comonomer content. Unfortunately, with the polymerization conditions used it was not possible to

a

b

110

0.04

PP

10-undecene-1-ol

hydrophobic 100

contact angle (˚)

O/C

0.03 OEGUME DEGUE 0.02

90

0.01

80

0

70

hydrophilic 0

2

4

6

8

comonomer content (mol%)

10

0

2

4

6

8

10

comonomer content (mol%)

Fig. 6. (a) O/C ratio of the copolymer surfaces in dependence on the comonomer content in the copolymer and on the comonomer types used determined by XPS, (b) influence of polar comonomers on the hydrophilicity of the surfaces of PP and of propene copolymers containing DEGUE (N), OEGUME (d), 10-undecene-1-ol (j) measured as water contact angle on melt-pressed polymer films.

U. Schulze et al. / European Polymer Journal 44 (2008) 694–703

synthesize copolymers with ether comonomers containing comparably high comonomer contents as with 10-undecene-1-ol. It is imaginable that such copolymers should have a significantly higher hydrophilicity. 4. Conclusions New propene copolymers with long-chain ether comonomers could be synthesized by metallocene polymerization in toluene. The maximum ether comonomer incorporation in the copolymers was achieved with DEGUE and amounted to 1.6 mol%. The molar masses of propene copolymers containing DEGUE or OEGUME dropped with increasing comonomer contents in the copolymers. It can be assumed that alkyl aluminum acts as a chain-transfer agent. Apparently, with increased TIBA amounts in the copolymerization system the chain-transfer reaction as termination reaction was accelerated and consequently the molar masses of the copolymers decreased. Copolymers with high comonomer contents showed slightly decreased contact angles, which may indicate a higher hydrophilicity of the polypropene copolymer surfaces. Acknowledgements Bundesministerium fu¨r Bildung und Forschung (BMBF, Grant Number 03C0337B) is gratefully acknowledged for financial support. The authors thank D. Pleul for XPS investigations and V. Rose for measurement of the contact angles.

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