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Segmented blockcopolymers with uniform amide segments
Polymer 45 (2004) 4837–4843 www.elsevier.com/locate/polymer
Segmented blockcopolymers with uniform amide segments D. Husken*, J. Krijgsman, R.J. Gaymans Department of Chemical Engineering, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands Received 7 April 2004; received in revised form 4 May 2004; accepted 7 May 2004
Abstract Segmented blockcopolymers based on poly(tetramethylene oxide) (PTMO) soft segments and uniform crystallisable tetra-amide segments (TxTxT) are made via polycondensation. The PTMO soft segments, with a molecular weight of 1000 g/mol, are extended with terephthalic groups to a molecular weight of 6000 g/mol. The crystallisable segment is uniform of length and is based on a tetra-amide with terephthalamide groups. The length of the aliphatic diamine ðxÞ in the tetra-amide segment is varied from x ¼ 2 to 8. The thermal properties of the blockcopolymers were studied with dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Due to the use of uniform TxTxT segments a fast and almost complete crystallization of the hard segments is obtained. The melting temperature of the blockpolymers increases with decreasing diamine length and the well-known odd– even effect is observed. The elastic behavior of the blockcopolymer was studied by compression set. All the blockcopolymers had a low compression set and were highly elastic. q 2004 Elsevier Ltd. All rights reserved. Keywords: Poly(tetramethylene oxide); Tetra-amide; Elastic fibers
1. Introduction In general, segmented blockcopolymers consist of alternating hard and soft segments. The hard segments can crystallize and form physical crosslinks for the amorphous phase. Furthermore, the crystallized segments provide the material dimensional stability, heat stability and solvent resistance [1]. The soft segments have a glass transition temperature ðTg Þ below room temperature, which provide flexibility to the material. The Tg of the amorphous phase depends on the type and length of the soft segments and on the amount of hard segment dissolved in the soft phase. The properties of segmented blockcopolymers are related to the crystallinity of the hard segments [2]. Like all semi-crystalline polymer systems, the modulus above the Tg of the soft phase increases with crystallinity. The effect of crystallinity on the elastic properties of the blockcopolymers is complex. At low hard segment concentration, less than 20 wt%, crystallization is usually slow and the crystallinity low. As a result, the material has a low modulus but good elastic properties. At higher hard segment concentration the copolymers have a higher modulus but the elastic properties deteriorate. For elastic fiber applications it * Corresponding author. Tel.: þ 31-534893890; fax: þ 31-534893823. E-mail address: [email protected] (D. Husken). 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.05.019
is important to have good elastic properties combined with a high modulus. Segmented blockcopolymers comprising uniform crystallisable segments have high crystallization rates and almost complete crystallization [3]. Moreover, the rubbery modulus is relatively high and hardly dependent on the temperature [4]. There is a good balance between the modulus and the elastic properties of these materials [5]. If highly elastic materials are required, like for elastic fiber applications, longer polyether segments are preferred [6]. A disadvantage of using longer segments is that melt phasing might occur. Due to this melt phasing the synthesis of high molecular weight polymers is difficult and the crystallinity of the hard phase is low. With the relative short di-amide and tetra-amide segments and long polyether segments, melt phasing does not occur and high molecular weight polymers can be obtained. The tetra-amide segments (TxTxT) are based on two and a half units of Nylon x; T [7]. The T stands for terephthalicunit and the x represents the number of methylene groups between two amide bonds (spacer length) (Fig. 1). In polyamides the melting temperature of the polymers decreases as x increases and when x is odd [8 – 12]. Generally, the crystallinity does not change much when x is varied but it will be higher for even x compared to the
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Fig. 1. Structure of a tetra-amide segment TxTxT.
uneven x: This odd– even effect is attributed to packing of the methylene units in the crystallites. For the even number of methylene units the packing of the crystals is in planar zig – zag conformation, while for an odd number of methylene units the crystal packing is non-planar. This article describes the effect of the methylene length of the tetra-amide on the crystallinity, modulus and elastic properties. Moreover, it describes whether the odd– even effect has influence on the elasticity.
2. Experimental 2.1. Materials
(105 g, 0.54 mol) and 1,6-hexamethylenediamine (500 g, 4.3 mol) was heated to 80 8C in a 1 l flask equipped with mechanical stirrer, reflux condenser, calcium chloride tube and nitrogen inlet. After 6 h 500 ml toluene was added to the suspension. After 1 h stirring the suspension was filtered with a glass filter. The collected product was washed twice with hot toluene (80 8C). Finally, the product was washed with diethyl ether and dried at room temperature. The purity of the product was about 80%. It contains some 6(T6)n-diamine, with n $ 2; and other impurities. By recrystallization of the product in n-butyl acetate at 110 8C (14 g/l) a purity of . 98% was obtained. The syntheses of the other xTx-diamines were prepared analogous to the synthesis of 6T6-diamine [7]. 2.4. Synthesis of TxTxT-dimethyl
Dimethyl terephthalate (DMT) and N-methyl-2-pyrrolidone (NMP) were obtained from Merck and used as received. Tetra-isopropyl orthotitanate (Ti(i-OC3H7)4) was obtained from Merck and diluted in m-xylene (to 0.05 M) received from Fluka. Irganox 1330 was obtained from CIBA. The diamines used are 1,2-ethanediamine, 1,3propanediamine, 1,4-butanediamine, 1,6-hexanediamine, 1,7-heptanediamine and 1,8-octanediamine, which are provided by Merck. Poly(tetramethylene oxide) (PTMO1000; molecular weight of 1000 g/mol) was provide by DuPont, Arnitel EM400 (segmented copolyether – ester) by DSM and Desmopan KU-8672 (thermoplastic polyurethane) by Bayer.
The synthesis of TxTxT-dimethyl is described according to the example given of T6T6T-dimethyl. A mixture of 6T6diamine (14.5 g, 0.04 mol) and MPT (41 g, 0.16 mol) was dissolved in 600 ml NMP in a 1 l flask equipped with magnetic stirrer, condenser, calcium chloride tube and nitrogen inlet. The mixture was heated to 120 8C and kept at this temperature for 16 h. After cooling to 50 8C the suspension was filtered with a glass filter and washed with successive NMP (50 8C), hot toluene (80 8C) and acetone. The product was dried in a vacuum oven at 50 8C. The syntheses of the other TxTxT-dimethyl segments were prepared analogous to the synthesis of T6T6T-dimethyl [7].
2.2. Synthesis of methyl phenyl terephthalate (MPT)
2.5. Polymerization of (PTMO1000-T)6000 – TxTxT
A mixture of phenol (150 g, 1.6 mol) and triethylamine (61 g, 0.6 mol) was heated to 50 8C in a 1 l flask equipped with mechanical stirrer, reflux condenser, calcium chloride tube and nitrogen inlet. Then MCCB (methyl-(4-chlorocarbonyl)benzoate; obtained from Dalian) (100 g, 0.5 mol), first dissolved in 200 ml NMP, was added dropwise. After 4 h the product was precipitated in 2 l demineralised water. The precipitate was filtered using a glass filter and washed with 1:4 NMP/water (50 8C) and then washed with 1:2 ethanol/water. Finally, the product was dried in a vacuum oven at 50 8C. The purity, determined by 1H NMR, was . 98% and the product had a melting temperature of 114 8C and a melting enthalpy of 135 J/g [7].
The (PTMO1000-T)6000 – TxTxT copolymers were synthesized by a polycondensation reaction in the presence of a solvent (NMP), tetra-isopropyl orthotitanate as the catalyst (0.5 mol%) and Irganox as the antioxidant (1 wt%). The transesterification of PTMO1000, DMT and TxTxT took place under nitrogen atmosphere at 180 8C in a stirred glass reactor (30 ml) for 30 min. The temperature was increased to 250 8C in 1 h. After 2 h at 250 8C the pressure was slowly decreased ðP , 20 mbarÞ to remove all the solvent and than further reduced to allow melt polycondensation ðP , 1 mbarÞ for 1 h. The polymer was slowly cooled to room temperature, while maintaining the low vacuum. 2.6. Injection-molding
2.3. Synthesis of xTx-diamine segments The synthesis of xTx-diamine is described according to the example given for 6T6-diamine. A mixture of DMT
The samples for the dynamic mechanical analysis and compression set experiments were prepared on an Arburg-H manual injection-molding machine. The barrel temperature
D. Husken et al. / Polymer 45 (2004) 4837–4843
was set at approximately 100 8C above the melting temperature of the blockcopolymer, while the mould temperature was kept at room temperature.
thickness of the samples was measured after 60 min. The compression set (CS) was calculated with Eq. (2): Compression set ¼
2.7. Viscometry The inherent viscosity of the polymers was determined at 25 8C using a capillary Ubbelohde type 1B. The polymer solution had a concentration of 0.1 g/dl in a 1/1 (molar ratio) mixture of phenol/1,1,2,2-tetrachloroethane.
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d0 2 d2 £ 100% d0 2 d1
ð2Þ
where d0 is thickness before compression (mm), d1 is thickness during compression (mm) and d2 thickness 60 min after release the compression.
3. Results and discussion 2.8. Dynamic mechanical analysis The torsion behaviour (G0 and G00 versus temperature) was studied using a Myrenne ATM3 torsion pendulum at a frequency of approximately 1 Hz. Before use, the samples of 50 mm length, 9 mm width and 2 mm thickness were dried in a vacuum oven at 70 8C overnight. The samples were cooled to 2 100 8C and than heated up at a rate of 1 8C/min. The glass transition temperature ðTg Þ was defined as the maximum of the loss modulus ðG00 Þ and the flow temperature ðTflow Þ as the temperature where the storage modulus ðG0 Þ reached 1 MPa and is approximately the same as the melting temperature ðTm Þ: The temperature where the rubber plateau starts is denoted as the flex temperature ðTflex Þ and the shear modulus (G0 (25 8C)) of the rubber plateau was defined as the storage modulus at 25 8C. A value for the gradual decrease of the modulus with temperature is quantified by DG0 and was calculated according to Eq. (1). G0 ð60 8CÞ 2 G0 ð140 8CÞ £ 100 DG ¼ G0 ð100 8CÞ 0
½–
ð1Þ
When the rubber plateau is independent of the temperature the DG0 will be very small. 2.9. Differential scanning calorimetry The thermal transitions of the polymer were determined by differential scanning calorimetry using a Perkin & Elmer DSC7 apparatus. The dry polymer sample (5 – 10 mg) was heated in high-pressure pans from 50 to 250 8C at a heating rate of 20 8C/min and kept for 3 min at a temperature of 250 8C. Subsequently a cooling scan from 250 to 50 8C at a cooling rate of 20 8C/min followed by a second heating scan under the same conditions as the first heating were performed. The melting temperature ðTm Þ was determined from the maximum of the endothermic peak in the second heating scan and the crystallization temperature ðTc Þ from the onset of the exothermic peak in the cooling scan. 2.10. Compression set A piece of an injection-moulded bar (, 2.2 mm thickness) was placed between two steel plates and compressed to 1 mm (, 55% compression). After 24 h at 20 or 70 8C the compression was released at room temperature. The
The PTMO1000 segments are extended with terephthalic units to a molecular weight of 6000, denoted as (PTMO1000T)6000. In this way, long soft segments can be prepared with limited crystallization of the polyether segments [13]. A series of copolymers based on (PTMO1000-T)6000 with tetraamide (TxTxT) crystallisable segments were made to investigate the influence of the diamine length ðxÞ in the tetra-amide segment. Crystallisable TxTxT segments were made with x ¼ 2; 3, 4, 6, 7 en 8. The segment with x ¼ 5 is left out because ring-formation of theses segments will most likely occur. Also the properties of two commercial materials, Arnitel (segmented copolyether – ester) and Desmopan (thermoplastic polyurethane), are given. 3.1. TxTxT-Dimethyl segments The uniform crystallisable tetra-amide segments are made of diamide (xTx-diamine) and MPT. In Table 1 the purity, melting temperature and enthalpies of the TxTxTdimethyl segments are given [7]. The purity was calculated on the basis of 1H NMR, by comparing the integrals of the peaks of the aromatic protons of the ester – amide and the amide –amide terephthalic protons. The melting temperature and enthalpies were determined by DSC measurements. The purities of the TxTxT-dimethyl segments were all high. Besides, all the TxTxT-dimethyl segments show a high melting temperature. Because the DSC-apparatus used has a limited temperature maximum of 340 8C, the melting temperature and enthalpies of T2T2T and T4T4T could not be determined since these are expected to be higher than 340 8C. When the number of methylene groups in the Table 1 Properties of different TxTxT-dimethyl segments TxTxT-dimethyl
(CH2)x ðx ¼Þ
Purity (%)
Tm (8C)
DHm (J/g)
T2T2T T3T3T T4T4T T6T6T T7T7T T8T8T
2 3 4 6 7 8
97 97 97 99 96 93
.340a 307 .340a 303 262 268
– 128 – 152 99 163
a
340 8C is the maximum temperature for the DSC apparatus used.
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Table 2 DSC results for blockpolymers made of (PTMO1000-T)6000 –TxTxT, Arnitel and Desmopan
T2T2T T3T3T T4T4T T6T6T T7T7T T8T8T Arnitel EM400 Desmopan KU-8672 a b
TxTxT (wt%)
hinh (dl/g)
Tm (8C)
DHm (J/g)
Cryst.a (%)
Tc (8C)
Tm 2 Tc (8C)
7.00 7.40 7.80 8.57 8.96 9.34 – –
2.5 3.0 2.5 3.1 2.7 3.4 – –
– 182 224 202 172 194 195 166
– 8 11 13 7 14 16 5
– 84 – 98 83 92 – –
– 146 184/224b 136/196b 121 117/173b 99 100
– 36 ,5 6 51 21 96 66
Crystallinity calculated: ðDHm;polymer =DHm;TxTxT £ ðwt%TxTxT=100ÞÞ £ 100%: Two crystallization peaks observed; the second value gives the temperature of the maximum of the second crystallization peak.
diamine increases the melting temperature of the tetraamide segments decreases. The segments with an odd number of methylene groups in the diamine have a lower melting temperature and melting enthalpy than the segments with an even number of methylene units. These ‘odd’ segments have a less good packing of the chains in the crystal structure. This is in agreement with the general trend observed for polyamides, which states that when the diamine unit is more flexible, the melting temperature is lower. 3.2. (PTMO1000-T)6000 – TxTxT The blockcopolymers were transparent during synthesis, which suggest that melt phasing is absent. Even in the solid state the polymers were transparent. This means that the crystallites are too small to scatter light. The inherent viscosity for all the synthesized blockpolymers is high, which indicate high molecular weight polymers (Table 2). The hard segment content in the blockcopolymers slightly increases when the number of methylene groups in the TxTxT segments increases. This increase in hard segment content is due to an increase in the molecular weight of the tetra-amide segment. 3.3. Differential scanning calorimetry With DSC the melting and crystallization temperatures of the PTMO – TxTxT blockcopolymers and two commercial materials, Arnitel and Desmopan, were determined
[14]. The crystallinity was roughly calculated on basis of the melting enthalpy of TxTxT in the copolymer and the TxTxT content (Table 2). The TxTxT content was calculated, assuming that the ester carbonyl does not crystallize and belongs to the amorphous phase [15]. The cooling curve for blockcopolymers with uniform T4T4T, T6T6T and T8T8T segments shows two peaks, which is unusual. The first peak is attributed to the crystallization of the TxTxT segments. The second peak, which has a smaller area, probably attributes to a crystalline transition. This may suggests that the blockcopolymers have a liquid crystalline behavior [16,17]. However, no liquid crystalline behavior of the blockcopolymers is observed with optical microscopy combined with cross-polarizer, which is probably due to a too low content of the hard segments [18]. As expected the melting temperature decreases with increasing number of methylene groups in the diamine and an odd– even effect is observed. When there is an odd number of methylene groups in the diamine the melting temperature is lower. The same is observed for the melting enthalpy, which is lower for the odd numbers. The crystallinity can be determined by using the melting enthalpy of the TxTxT-dimethyl segments (Table 1). Due to the unknown melting enthalpy of T2T2T of T4T4T the crystallinity for the corresponding blockcopolymers could not be calculated. The other blockcopolymers show a high crystallinity of the tetra-amide segments, which indicates that the hard segments crystallize almost completely. The blockcopolymers with an odd number of methylene groups
Table 3 Thermal and mechanical properties measured by DMA of blockpolymers based on (PTMO1000-T)6000 –TxTxT, Arnitel and Desmopan
T2T2T T3T3T T4T4T T6T6T T7T7T T8T8T Arnitel EM400 Desmopan KU-8672
TxTxT (wt%)
hinh (dl/g)
Tg (8C)
G025 8C (MPa)
Tflow (8C)
Tflex (8C)
DG0 (–)
CS55% (20 8C) (%)
CS55% (70 8C) (%)
7.00 7.40 7.80 8.57 8.96 9.34 – –
2.48 3.02 2.54 3.14 2.66 3.40 – –
261 264 262 262 265 264 270 245
6 3 5 6 3 5 18 11
245 173 230 203 164 189 182 150
13 8 11 11 6 10 7 213
,0.1 0.14 ,0.1 ,0.1 0.19 0.12 0.84 1.67
8 6 7 5 8 5 15 13
44 33 24 27 47 33 36 41
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Fig. 2. Shear (a) and loss (b) modulus for blockpolymers based on (PTMO1000-T)6000 –TxTxT: (B) T2T2T, (K) T4T4T, (X) T6T6T, (O) T8T8T, (A) T3T3T, (W) T7T7T.
have a somewhat lower crystallinity compared to the even number of methylene groups, which is probably due to a less good packing of the crystals. The undercooling ðTm – Tc Þ for the PTMO – TxTxT blockcopolymers is relatively low, especially for the T6T6T blockcopolymer. There is no trend visible between the type of TxTxT segments and the values of undercooling. The undercooling values of the PTMO – TxTxT blockcopolymers are lower than the commercial materials Arnitel and Desmopan [14]. This suggests that the PTMO –TxTxT blockcopolymers crystallize faster on cooling although they have a low hard segment content. 3.4. Dynamic mechanical behavior The dynamic mechanical properties of the polymers were measured by DMA. The results are given in Table 3 together with the properties of two commercial materials, Arnitel EM400 en Desmopan KU-8672 [14]. The shear and loss modulus of the PTMO – TxTxT polymers are plotted as function of the temperature in Fig. 2. Despite the extension of PTMO1000 with terephthalic groups the glass transition temperature is close to the Tg of the PTMO homopolymer (2 86 8C) [19]. This means that terephthalic groups do hardly disturb the mobility of the amorphous phase and that there is hardly any TxTxT dissolved in the PTMO phase [13].
The shoulder in the shear modulus after the glass transition temperature in the temperature range of 2 50– 10 8C is the result of a small amount of crystalline PTMO. A material that is flexible at low temperatures requires a low flex temperature, which is the temperature where the rubber plateau starts. For all the blockpolymers the flex temperature is between 7 and 11 8C. The length of the diamine and the number of methylene groups in the diamine, i.e. odd or even, seem to have no effect on the flex temperature. The shear modulus, determined at 25 8C, is around 6 MPa for polymers made with an even number of methylene groups in the diamine. For blockcopolymers with an odd number the shear modulus is somewhat lower, 3 MPa. The modulus of the rubber plateau of the blockcopolymers is mainly determined by the crystallinity. Because of less good chain packing of the odd numbered TxTxT segments, the crystallinity is lower which results in a lower shear modulus of the corresponding blockcopolymers. The rubber plateau is for all the PTMO – TxTxT blockcopolymers temperature independent and the melting temperature is sharp. The slope of the rubber plateau ðDG0 Þ for the PTMO – TxTxT blockpolymers are all low (, 0.19) compared to the commercial materials, Arnitel and Desmopan, respectively 0.84 and 1.67 (Table 3). The low temperature dependence of the modulus is expected to be due to the uniform length of the tetra-amide segments so all
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Fig. 3. Flow temperature of blockpolymers based on (PTMO1000-T)6000 –TxTxT as function of number of methylene groups in the diamine ðxÞ:
the crystals will melt in a narrow temperature range. The commercial materials have a distribution of hard segment lengths and as a result the decrease in modulus with temperature is much stronger. In Fig. 3 the flow temperatures of the blockcopolymers with different TxTxT segments are given as function of the number of methylene groups in the diamine. As expected, the flow temperature decreases with increasing the diamine length x and also a strong odd – even effect is observed. The flow temperature measured by DMA and the melting temperature measured by DSC are nearly the same. In Table 3 are also the results of the elastic properties of materials based on PTMO – TxTxT and the commercial materials Arnitel and Desmopan [14] given. During the compression set (CS) the injection-molded samples were compressed to 55% for 24 h. The compression set values for all the polymers made of PTMO –TxTxT are approximately the same at 20 8C, around 5 –8%. The type and length of x seems to have no effect on the compression set. The distribution of the compression set values at 70 8C is somewhat broader. It seems that T4T4T and T6T6T blockcopolymers have lower compression set values compared to the other blockcopolymers. Arnitel and Desmopan have a higher compression set at 20 8C (, 14%) than the PTMO –TxTxT blockcopolymers (5 – 8%) but the compression set at 70 8C is roughly the same (, 40%). So the elastic properties at room temperature are better for the PTMO – TxTxT materials.
crystallization. Despite the low concentration TxTxT (7 – 9 wt%) the blockcopolymers have a high melting temperature, which depends on the type of diamine ðxÞ: The melting temperature of the blockcopolymers with an even number of methylene units in the diamine decreases with increasing methylene length but the shear modulus is independent on the diamine length. Blockcopolymers with an uneven number of methylene units in the diamine show an odd – even effect on the melting temperature and possess a lower crystallinity. The shear modulus for the blockcopolymers with an odd number of methylene units is lower compared to the even numbered but there is no difference between the uneven numbers (x ¼ 3 and 7). The compression set values of PTMO – TxTxT blockcopolymers at 20 8C were all low (5 – 8%) and no odd –even effect is observed. At 70 8C the compression set values were between 27 and 47% and also at this temperature no odd– even effect is present. The compression set values of PTMO – TxTxT blockcopolymers are comparable with commercial materials (Arnitel and Desmopan). The T4T4T and T6T6T segments are the most efficient segments in the blockcopolymers because they provide the highest modulus and lowest compression set at 70 8C. Compared to commercial materials, like Arnitel and Desmopan, the PTMO – TxTxT blockcopolymers have a more constant rubber plateau and better elastic properties. The undercooling of the blockcopolymers is nearly the same for Desmopan and better than Arnitel, thus the crystallization of the blockcopolymers is faster than Arnitel.
4. Conclusions References Interesting materials for elastic fiber applications possess good elastic properties combined with high moduli. Materials that have this combination of properties are segmented blockcopolymers based on PTMO and uniform crystallisable tetra-amide segments (TxTxT). The uniform TxTxT segments provide a fast and almost complete
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Segmented blockcopolymers with uniform amide segments D. Husken*, J. Krijgsman, R.J. Gaymans Department of Chemical Engineering, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands Received 7 April 2004; received in revised form 4 May 2004; accepted 7 May 2004
Abstract Segmented blockcopolymers based on poly(tetramethylene oxide) (PTMO) soft segments and uniform crystallisable tetra-amide segments (TxTxT) are made via polycondensation. The PTMO soft segments, with a molecular weight of 1000 g/mol, are extended with terephthalic groups to a molecular weight of 6000 g/mol. The crystallisable segment is uniform of length and is based on a tetra-amide with terephthalamide groups. The length of the aliphatic diamine ðxÞ in the tetra-amide segment is varied from x ¼ 2 to 8. The thermal properties of the blockcopolymers were studied with dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Due to the use of uniform TxTxT segments a fast and almost complete crystallization of the hard segments is obtained. The melting temperature of the blockpolymers increases with decreasing diamine length and the well-known odd– even effect is observed. The elastic behavior of the blockcopolymer was studied by compression set. All the blockcopolymers had a low compression set and were highly elastic. q 2004 Elsevier Ltd. All rights reserved. Keywords: Poly(tetramethylene oxide); Tetra-amide; Elastic fibers
1. Introduction In general, segmented blockcopolymers consist of alternating hard and soft segments. The hard segments can crystallize and form physical crosslinks for the amorphous phase. Furthermore, the crystallized segments provide the material dimensional stability, heat stability and solvent resistance [1]. The soft segments have a glass transition temperature ðTg Þ below room temperature, which provide flexibility to the material. The Tg of the amorphous phase depends on the type and length of the soft segments and on the amount of hard segment dissolved in the soft phase. The properties of segmented blockcopolymers are related to the crystallinity of the hard segments [2]. Like all semi-crystalline polymer systems, the modulus above the Tg of the soft phase increases with crystallinity. The effect of crystallinity on the elastic properties of the blockcopolymers is complex. At low hard segment concentration, less than 20 wt%, crystallization is usually slow and the crystallinity low. As a result, the material has a low modulus but good elastic properties. At higher hard segment concentration the copolymers have a higher modulus but the elastic properties deteriorate. For elastic fiber applications it * Corresponding author. Tel.: þ 31-534893890; fax: þ 31-534893823. E-mail address: [email protected] (D. Husken). 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.05.019
is important to have good elastic properties combined with a high modulus. Segmented blockcopolymers comprising uniform crystallisable segments have high crystallization rates and almost complete crystallization [3]. Moreover, the rubbery modulus is relatively high and hardly dependent on the temperature [4]. There is a good balance between the modulus and the elastic properties of these materials [5]. If highly elastic materials are required, like for elastic fiber applications, longer polyether segments are preferred [6]. A disadvantage of using longer segments is that melt phasing might occur. Due to this melt phasing the synthesis of high molecular weight polymers is difficult and the crystallinity of the hard phase is low. With the relative short di-amide and tetra-amide segments and long polyether segments, melt phasing does not occur and high molecular weight polymers can be obtained. The tetra-amide segments (TxTxT) are based on two and a half units of Nylon x; T [7]. The T stands for terephthalicunit and the x represents the number of methylene groups between two amide bonds (spacer length) (Fig. 1). In polyamides the melting temperature of the polymers decreases as x increases and when x is odd [8 – 12]. Generally, the crystallinity does not change much when x is varied but it will be higher for even x compared to the
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Fig. 1. Structure of a tetra-amide segment TxTxT.
uneven x: This odd– even effect is attributed to packing of the methylene units in the crystallites. For the even number of methylene units the packing of the crystals is in planar zig – zag conformation, while for an odd number of methylene units the crystal packing is non-planar. This article describes the effect of the methylene length of the tetra-amide on the crystallinity, modulus and elastic properties. Moreover, it describes whether the odd– even effect has influence on the elasticity.
2. Experimental 2.1. Materials
(105 g, 0.54 mol) and 1,6-hexamethylenediamine (500 g, 4.3 mol) was heated to 80 8C in a 1 l flask equipped with mechanical stirrer, reflux condenser, calcium chloride tube and nitrogen inlet. After 6 h 500 ml toluene was added to the suspension. After 1 h stirring the suspension was filtered with a glass filter. The collected product was washed twice with hot toluene (80 8C). Finally, the product was washed with diethyl ether and dried at room temperature. The purity of the product was about 80%. It contains some 6(T6)n-diamine, with n $ 2; and other impurities. By recrystallization of the product in n-butyl acetate at 110 8C (14 g/l) a purity of . 98% was obtained. The syntheses of the other xTx-diamines were prepared analogous to the synthesis of 6T6-diamine [7]. 2.4. Synthesis of TxTxT-dimethyl
Dimethyl terephthalate (DMT) and N-methyl-2-pyrrolidone (NMP) were obtained from Merck and used as received. Tetra-isopropyl orthotitanate (Ti(i-OC3H7)4) was obtained from Merck and diluted in m-xylene (to 0.05 M) received from Fluka. Irganox 1330 was obtained from CIBA. The diamines used are 1,2-ethanediamine, 1,3propanediamine, 1,4-butanediamine, 1,6-hexanediamine, 1,7-heptanediamine and 1,8-octanediamine, which are provided by Merck. Poly(tetramethylene oxide) (PTMO1000; molecular weight of 1000 g/mol) was provide by DuPont, Arnitel EM400 (segmented copolyether – ester) by DSM and Desmopan KU-8672 (thermoplastic polyurethane) by Bayer.
The synthesis of TxTxT-dimethyl is described according to the example given of T6T6T-dimethyl. A mixture of 6T6diamine (14.5 g, 0.04 mol) and MPT (41 g, 0.16 mol) was dissolved in 600 ml NMP in a 1 l flask equipped with magnetic stirrer, condenser, calcium chloride tube and nitrogen inlet. The mixture was heated to 120 8C and kept at this temperature for 16 h. After cooling to 50 8C the suspension was filtered with a glass filter and washed with successive NMP (50 8C), hot toluene (80 8C) and acetone. The product was dried in a vacuum oven at 50 8C. The syntheses of the other TxTxT-dimethyl segments were prepared analogous to the synthesis of T6T6T-dimethyl [7].
2.2. Synthesis of methyl phenyl terephthalate (MPT)
2.5. Polymerization of (PTMO1000-T)6000 – TxTxT
A mixture of phenol (150 g, 1.6 mol) and triethylamine (61 g, 0.6 mol) was heated to 50 8C in a 1 l flask equipped with mechanical stirrer, reflux condenser, calcium chloride tube and nitrogen inlet. Then MCCB (methyl-(4-chlorocarbonyl)benzoate; obtained from Dalian) (100 g, 0.5 mol), first dissolved in 200 ml NMP, was added dropwise. After 4 h the product was precipitated in 2 l demineralised water. The precipitate was filtered using a glass filter and washed with 1:4 NMP/water (50 8C) and then washed with 1:2 ethanol/water. Finally, the product was dried in a vacuum oven at 50 8C. The purity, determined by 1H NMR, was . 98% and the product had a melting temperature of 114 8C and a melting enthalpy of 135 J/g [7].
The (PTMO1000-T)6000 – TxTxT copolymers were synthesized by a polycondensation reaction in the presence of a solvent (NMP), tetra-isopropyl orthotitanate as the catalyst (0.5 mol%) and Irganox as the antioxidant (1 wt%). The transesterification of PTMO1000, DMT and TxTxT took place under nitrogen atmosphere at 180 8C in a stirred glass reactor (30 ml) for 30 min. The temperature was increased to 250 8C in 1 h. After 2 h at 250 8C the pressure was slowly decreased ðP , 20 mbarÞ to remove all the solvent and than further reduced to allow melt polycondensation ðP , 1 mbarÞ for 1 h. The polymer was slowly cooled to room temperature, while maintaining the low vacuum. 2.6. Injection-molding
2.3. Synthesis of xTx-diamine segments The synthesis of xTx-diamine is described according to the example given for 6T6-diamine. A mixture of DMT
The samples for the dynamic mechanical analysis and compression set experiments were prepared on an Arburg-H manual injection-molding machine. The barrel temperature
D. Husken et al. / Polymer 45 (2004) 4837–4843
was set at approximately 100 8C above the melting temperature of the blockcopolymer, while the mould temperature was kept at room temperature.
thickness of the samples was measured after 60 min. The compression set (CS) was calculated with Eq. (2): Compression set ¼
2.7. Viscometry The inherent viscosity of the polymers was determined at 25 8C using a capillary Ubbelohde type 1B. The polymer solution had a concentration of 0.1 g/dl in a 1/1 (molar ratio) mixture of phenol/1,1,2,2-tetrachloroethane.
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d0 2 d2 £ 100% d0 2 d1
ð2Þ
where d0 is thickness before compression (mm), d1 is thickness during compression (mm) and d2 thickness 60 min after release the compression.
3. Results and discussion 2.8. Dynamic mechanical analysis The torsion behaviour (G0 and G00 versus temperature) was studied using a Myrenne ATM3 torsion pendulum at a frequency of approximately 1 Hz. Before use, the samples of 50 mm length, 9 mm width and 2 mm thickness were dried in a vacuum oven at 70 8C overnight. The samples were cooled to 2 100 8C and than heated up at a rate of 1 8C/min. The glass transition temperature ðTg Þ was defined as the maximum of the loss modulus ðG00 Þ and the flow temperature ðTflow Þ as the temperature where the storage modulus ðG0 Þ reached 1 MPa and is approximately the same as the melting temperature ðTm Þ: The temperature where the rubber plateau starts is denoted as the flex temperature ðTflex Þ and the shear modulus (G0 (25 8C)) of the rubber plateau was defined as the storage modulus at 25 8C. A value for the gradual decrease of the modulus with temperature is quantified by DG0 and was calculated according to Eq. (1). G0 ð60 8CÞ 2 G0 ð140 8CÞ £ 100 DG ¼ G0 ð100 8CÞ 0
½–
ð1Þ
When the rubber plateau is independent of the temperature the DG0 will be very small. 2.9. Differential scanning calorimetry The thermal transitions of the polymer were determined by differential scanning calorimetry using a Perkin & Elmer DSC7 apparatus. The dry polymer sample (5 – 10 mg) was heated in high-pressure pans from 50 to 250 8C at a heating rate of 20 8C/min and kept for 3 min at a temperature of 250 8C. Subsequently a cooling scan from 250 to 50 8C at a cooling rate of 20 8C/min followed by a second heating scan under the same conditions as the first heating were performed. The melting temperature ðTm Þ was determined from the maximum of the endothermic peak in the second heating scan and the crystallization temperature ðTc Þ from the onset of the exothermic peak in the cooling scan. 2.10. Compression set A piece of an injection-moulded bar (, 2.2 mm thickness) was placed between two steel plates and compressed to 1 mm (, 55% compression). After 24 h at 20 or 70 8C the compression was released at room temperature. The
The PTMO1000 segments are extended with terephthalic units to a molecular weight of 6000, denoted as (PTMO1000T)6000. In this way, long soft segments can be prepared with limited crystallization of the polyether segments [13]. A series of copolymers based on (PTMO1000-T)6000 with tetraamide (TxTxT) crystallisable segments were made to investigate the influence of the diamine length ðxÞ in the tetra-amide segment. Crystallisable TxTxT segments were made with x ¼ 2; 3, 4, 6, 7 en 8. The segment with x ¼ 5 is left out because ring-formation of theses segments will most likely occur. Also the properties of two commercial materials, Arnitel (segmented copolyether – ester) and Desmopan (thermoplastic polyurethane), are given. 3.1. TxTxT-Dimethyl segments The uniform crystallisable tetra-amide segments are made of diamide (xTx-diamine) and MPT. In Table 1 the purity, melting temperature and enthalpies of the TxTxTdimethyl segments are given [7]. The purity was calculated on the basis of 1H NMR, by comparing the integrals of the peaks of the aromatic protons of the ester – amide and the amide –amide terephthalic protons. The melting temperature and enthalpies were determined by DSC measurements. The purities of the TxTxT-dimethyl segments were all high. Besides, all the TxTxT-dimethyl segments show a high melting temperature. Because the DSC-apparatus used has a limited temperature maximum of 340 8C, the melting temperature and enthalpies of T2T2T and T4T4T could not be determined since these are expected to be higher than 340 8C. When the number of methylene groups in the Table 1 Properties of different TxTxT-dimethyl segments TxTxT-dimethyl
(CH2)x ðx ¼Þ
Purity (%)
Tm (8C)
DHm (J/g)
T2T2T T3T3T T4T4T T6T6T T7T7T T8T8T
2 3 4 6 7 8
97 97 97 99 96 93
.340a 307 .340a 303 262 268
– 128 – 152 99 163
a
340 8C is the maximum temperature for the DSC apparatus used.
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Table 2 DSC results for blockpolymers made of (PTMO1000-T)6000 –TxTxT, Arnitel and Desmopan
T2T2T T3T3T T4T4T T6T6T T7T7T T8T8T Arnitel EM400 Desmopan KU-8672 a b
TxTxT (wt%)
hinh (dl/g)
Tm (8C)
DHm (J/g)
Cryst.a (%)
Tc (8C)
Tm 2 Tc (8C)
7.00 7.40 7.80 8.57 8.96 9.34 – –
2.5 3.0 2.5 3.1 2.7 3.4 – –
– 182 224 202 172 194 195 166
– 8 11 13 7 14 16 5
– 84 – 98 83 92 – –
– 146 184/224b 136/196b 121 117/173b 99 100
– 36 ,5 6 51 21 96 66
Crystallinity calculated: ðDHm;polymer =DHm;TxTxT £ ðwt%TxTxT=100ÞÞ £ 100%: Two crystallization peaks observed; the second value gives the temperature of the maximum of the second crystallization peak.
diamine increases the melting temperature of the tetraamide segments decreases. The segments with an odd number of methylene groups in the diamine have a lower melting temperature and melting enthalpy than the segments with an even number of methylene units. These ‘odd’ segments have a less good packing of the chains in the crystal structure. This is in agreement with the general trend observed for polyamides, which states that when the diamine unit is more flexible, the melting temperature is lower. 3.2. (PTMO1000-T)6000 – TxTxT The blockcopolymers were transparent during synthesis, which suggest that melt phasing is absent. Even in the solid state the polymers were transparent. This means that the crystallites are too small to scatter light. The inherent viscosity for all the synthesized blockpolymers is high, which indicate high molecular weight polymers (Table 2). The hard segment content in the blockcopolymers slightly increases when the number of methylene groups in the TxTxT segments increases. This increase in hard segment content is due to an increase in the molecular weight of the tetra-amide segment. 3.3. Differential scanning calorimetry With DSC the melting and crystallization temperatures of the PTMO – TxTxT blockcopolymers and two commercial materials, Arnitel and Desmopan, were determined
[14]. The crystallinity was roughly calculated on basis of the melting enthalpy of TxTxT in the copolymer and the TxTxT content (Table 2). The TxTxT content was calculated, assuming that the ester carbonyl does not crystallize and belongs to the amorphous phase [15]. The cooling curve for blockcopolymers with uniform T4T4T, T6T6T and T8T8T segments shows two peaks, which is unusual. The first peak is attributed to the crystallization of the TxTxT segments. The second peak, which has a smaller area, probably attributes to a crystalline transition. This may suggests that the blockcopolymers have a liquid crystalline behavior [16,17]. However, no liquid crystalline behavior of the blockcopolymers is observed with optical microscopy combined with cross-polarizer, which is probably due to a too low content of the hard segments [18]. As expected the melting temperature decreases with increasing number of methylene groups in the diamine and an odd– even effect is observed. When there is an odd number of methylene groups in the diamine the melting temperature is lower. The same is observed for the melting enthalpy, which is lower for the odd numbers. The crystallinity can be determined by using the melting enthalpy of the TxTxT-dimethyl segments (Table 1). Due to the unknown melting enthalpy of T2T2T of T4T4T the crystallinity for the corresponding blockcopolymers could not be calculated. The other blockcopolymers show a high crystallinity of the tetra-amide segments, which indicates that the hard segments crystallize almost completely. The blockcopolymers with an odd number of methylene groups
Table 3 Thermal and mechanical properties measured by DMA of blockpolymers based on (PTMO1000-T)6000 –TxTxT, Arnitel and Desmopan
T2T2T T3T3T T4T4T T6T6T T7T7T T8T8T Arnitel EM400 Desmopan KU-8672
TxTxT (wt%)
hinh (dl/g)
Tg (8C)
G025 8C (MPa)
Tflow (8C)
Tflex (8C)
DG0 (–)
CS55% (20 8C) (%)
CS55% (70 8C) (%)
7.00 7.40 7.80 8.57 8.96 9.34 – –
2.48 3.02 2.54 3.14 2.66 3.40 – –
261 264 262 262 265 264 270 245
6 3 5 6 3 5 18 11
245 173 230 203 164 189 182 150
13 8 11 11 6 10 7 213
,0.1 0.14 ,0.1 ,0.1 0.19 0.12 0.84 1.67
8 6 7 5 8 5 15 13
44 33 24 27 47 33 36 41
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Fig. 2. Shear (a) and loss (b) modulus for blockpolymers based on (PTMO1000-T)6000 –TxTxT: (B) T2T2T, (K) T4T4T, (X) T6T6T, (O) T8T8T, (A) T3T3T, (W) T7T7T.
have a somewhat lower crystallinity compared to the even number of methylene groups, which is probably due to a less good packing of the crystals. The undercooling ðTm – Tc Þ for the PTMO – TxTxT blockcopolymers is relatively low, especially for the T6T6T blockcopolymer. There is no trend visible between the type of TxTxT segments and the values of undercooling. The undercooling values of the PTMO – TxTxT blockcopolymers are lower than the commercial materials Arnitel and Desmopan [14]. This suggests that the PTMO –TxTxT blockcopolymers crystallize faster on cooling although they have a low hard segment content. 3.4. Dynamic mechanical behavior The dynamic mechanical properties of the polymers were measured by DMA. The results are given in Table 3 together with the properties of two commercial materials, Arnitel EM400 en Desmopan KU-8672 [14]. The shear and loss modulus of the PTMO – TxTxT polymers are plotted as function of the temperature in Fig. 2. Despite the extension of PTMO1000 with terephthalic groups the glass transition temperature is close to the Tg of the PTMO homopolymer (2 86 8C) [19]. This means that terephthalic groups do hardly disturb the mobility of the amorphous phase and that there is hardly any TxTxT dissolved in the PTMO phase [13].
The shoulder in the shear modulus after the glass transition temperature in the temperature range of 2 50– 10 8C is the result of a small amount of crystalline PTMO. A material that is flexible at low temperatures requires a low flex temperature, which is the temperature where the rubber plateau starts. For all the blockpolymers the flex temperature is between 7 and 11 8C. The length of the diamine and the number of methylene groups in the diamine, i.e. odd or even, seem to have no effect on the flex temperature. The shear modulus, determined at 25 8C, is around 6 MPa for polymers made with an even number of methylene groups in the diamine. For blockcopolymers with an odd number the shear modulus is somewhat lower, 3 MPa. The modulus of the rubber plateau of the blockcopolymers is mainly determined by the crystallinity. Because of less good chain packing of the odd numbered TxTxT segments, the crystallinity is lower which results in a lower shear modulus of the corresponding blockcopolymers. The rubber plateau is for all the PTMO – TxTxT blockcopolymers temperature independent and the melting temperature is sharp. The slope of the rubber plateau ðDG0 Þ for the PTMO – TxTxT blockpolymers are all low (, 0.19) compared to the commercial materials, Arnitel and Desmopan, respectively 0.84 and 1.67 (Table 3). The low temperature dependence of the modulus is expected to be due to the uniform length of the tetra-amide segments so all
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D. Husken et al. / Polymer 45 (2004) 4837–4843
Fig. 3. Flow temperature of blockpolymers based on (PTMO1000-T)6000 –TxTxT as function of number of methylene groups in the diamine ðxÞ:
the crystals will melt in a narrow temperature range. The commercial materials have a distribution of hard segment lengths and as a result the decrease in modulus with temperature is much stronger. In Fig. 3 the flow temperatures of the blockcopolymers with different TxTxT segments are given as function of the number of methylene groups in the diamine. As expected, the flow temperature decreases with increasing the diamine length x and also a strong odd – even effect is observed. The flow temperature measured by DMA and the melting temperature measured by DSC are nearly the same. In Table 3 are also the results of the elastic properties of materials based on PTMO – TxTxT and the commercial materials Arnitel and Desmopan [14] given. During the compression set (CS) the injection-molded samples were compressed to 55% for 24 h. The compression set values for all the polymers made of PTMO –TxTxT are approximately the same at 20 8C, around 5 –8%. The type and length of x seems to have no effect on the compression set. The distribution of the compression set values at 70 8C is somewhat broader. It seems that T4T4T and T6T6T blockcopolymers have lower compression set values compared to the other blockcopolymers. Arnitel and Desmopan have a higher compression set at 20 8C (, 14%) than the PTMO –TxTxT blockcopolymers (5 – 8%) but the compression set at 70 8C is roughly the same (, 40%). So the elastic properties at room temperature are better for the PTMO – TxTxT materials.
crystallization. Despite the low concentration TxTxT (7 – 9 wt%) the blockcopolymers have a high melting temperature, which depends on the type of diamine ðxÞ: The melting temperature of the blockcopolymers with an even number of methylene units in the diamine decreases with increasing methylene length but the shear modulus is independent on the diamine length. Blockcopolymers with an uneven number of methylene units in the diamine show an odd – even effect on the melting temperature and possess a lower crystallinity. The shear modulus for the blockcopolymers with an odd number of methylene units is lower compared to the even numbered but there is no difference between the uneven numbers (x ¼ 3 and 7). The compression set values of PTMO – TxTxT blockcopolymers at 20 8C were all low (5 – 8%) and no odd –even effect is observed. At 70 8C the compression set values were between 27 and 47% and also at this temperature no odd– even effect is present. The compression set values of PTMO – TxTxT blockcopolymers are comparable with commercial materials (Arnitel and Desmopan). The T4T4T and T6T6T segments are the most efficient segments in the blockcopolymers because they provide the highest modulus and lowest compression set at 70 8C. Compared to commercial materials, like Arnitel and Desmopan, the PTMO – TxTxT blockcopolymers have a more constant rubber plateau and better elastic properties. The undercooling of the blockcopolymers is nearly the same for Desmopan and better than Arnitel, thus the crystallization of the blockcopolymers is faster than Arnitel.
4. Conclusions References Interesting materials for elastic fiber applications possess good elastic properties combined with high moduli. Materials that have this combination of properties are segmented blockcopolymers based on PTMO and uniform crystallisable tetra-amide segments (TxTxT). The uniform TxTxT segments provide a fast and almost complete
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