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Characterization and crystallization behavior of poly(ethylene-co-trimethylene terephthalate) copolymers.

INTRODUCTION

As well-known, copolymerization is a successful way to obtain polymer materials which could combine the characteristics of each component or show a unique property [1-3]. Aromatic polyesters, including poly (ethylene terephthalate) (PET), poly (trimethylene terephthalate) (PTT), and poly (butylene terephthalate) (PBT), are widely used in many fields, such as textile, electronics, engineering automotive industry, etc [4-6]. Their blends or copolymers have been interested for a long time [7-22].

There are many studies about PET/PBT blends. Shonaike [7] found that the PET/PBT blends showed a single, composition-dependent glass-transition temperature for all compositions, suggesting that PET and PBT were miscible in the amorphous state. Similar results were also observed in PET/PTT blends and PTT/PBT blends by Suparphol et al. [8, 9]. Avramova [10] confirmed those findings and added that, even though each component in PET/PBT blends formed its own crystalline phase upon crystallization, both components could crystallize concurrently at all compositions of the blends, and the presence of one crystalline phase did not deter or enhance the crystallization rates of the other. Yu and Ju [11] observed that even though PET/PBT blends had the same composition and exhibited a similar [T.sub.g], their crystallization behavior could change with prolonged thermal treatment and mixed condition. Some blends exhibited a single crystallization peak and some exhibited multiple crystallization peaks depending upon experimental conditions. The wide angle X-ray diffraction (WAXD) studies of PET/PTT and PTT/PBT blends indicated that the pure components crystallized simultaneously but formed their own crystalline entities [8, 9].

The copolymers of these polyesters have been also studied enthusiastically [15-22]. Lee et al. [19] prepared poly (ethylene-co-trimethylene terephthalate) (PETT) copolymers and investigated their nonisothermal crystallization behavior. It was found that the copolymers containing [less than or equal to]22.2 mol% or [greater than or equal to]46.0 mol% PTT units were crystallizable whereas the other copolymers containing 32.8 mol% or [less than or equal to]39.3 mol% PTT units were amorphous. Wu and Lin [20] studied the isothermal crystallization behavior of PETT copolymers. They explained the presence of multi-melting endotherm which could be attributed to the melting of thinner and imperfect crystallites formed during isothermal crystallization. Poly (ethylene-co-butylene terephthalate) (PEBT) copolymers were also studied by many researchers. Chou et al. [21] discovered that random PEBT copolymers had a lower degree of crystallinity and lower crystallite growth rate than homopolymers. The reduction of the crystallization rate of PEBT copolymers at 25-60[degrees]C undercooling with increasing branch contents in the polymers was also reported [22]. Despite of numerous reports about the crystallization property of these copolymers and blends, some inconsistencies are existed in these references.

In this article, a series of PETT copolymers with various compositions were synthesized by direct esterification and polycondensation. The chemical composition and sequence length of the PETT copolymers were determined by nuclear magnetic resonance (NMR). The nonisothermal crystallization and melting behavior were investigated by means of differential scanning calorimetry (DSC) and the crystallization structure was measured by WAXD.

EXPERIMENTAL PROCEDURES

Materials

The polymerization experiments were carried out in a 20 1 reactor of Yizheng Chemical Fiber. The PETT copolymers used in this work were obtained by the direct esterification of terephthalic acid (PTA) with excess ethylene glycol (EG) and 1,3-propanediol (PDO) (PTA:(EG + PDO) (mol ratio) = 1:1.5) with [K.sub.2]TiO([C.sub.2][O.sub.4])[.sub.2] and Sb(Ac)[.sub.3] (500-700 ppm of the loaded PTA) as the catalyst for copolymerization. Esterification was carried out at a temperature of 240-250[degrees]C in a nitrogen atmosphere. The termination of esterification was estimated according to the quantity of distilled water. The mixture was then subjected to polycondensation directly as the temperature was increased to 260-270[degrees]C. The molecular weight of the copolymers increased when ethylene glycol and 1,3-propane diol were removed from the viscous reaction mass. The intrinsic viscosity of the copolymers was controlled by the power of the stirrer. Trimethyl phosphate as a thermal stabilizer was added to prevent the degradation of the copolymers during the polymerization course. In the same manner, a series of PETT copolymers were prepared by varying the feed ratio of EG and PDO with respect to PTA. PET and PTT homopolymers were purchased from Yizheng Chemical Fiber in order to compare with the synthesized PETT copolymers. The intrinsic viscosity of PET and PTT homopolymers are 0.703 and 0.9, respectively.

Characterization

The intrinsic viscosities ([[eta]]) of the obtained samples were measured in a phenol-tetrachloroethane mixture (1:1, weight ratio) at 20[degrees]C using an Ubbelohde viscometer. The chemical composition was investigated using a NMR spectrometer (Bruker Advance 400 MHz) using D-trifluoroacetic acid as a solvent. The crystallization and melting analysis was carried out using a Modulated DSC 2910 of TA Instrument with temperature calibrated with indium. Each sample was used only once and all DSC measurements were performed under a high-purity nitrogen atmosphere to minimize degradation. To avoid uneven thermal conduction, the samples were maintained at a constant weight of 10 [+ or -] 1 mg. For nonisothermal crystallization studies, all samples were first heated from 25 to 280[degrees]C at a rate of 10[degrees]C/min, and kept at this temperature for 5 min to erase the prior thermal history. Then, they were cooled to 25[degrees]C at the rate of 2.5, 5, 10, and 15[degrees]C/min, respectively. Finally, they were heated again at the rate of 2.5, 5, 10, and 15[degrees]C/min, respectively. WAXD measurements were carried out by means of BRUKER-AXC08 X-ray diffractometer and filtered Cu K radiation ([lambda] = 0.1542 nm; 40 kV; 40 mA). The diffraction patterns of the PETT copolymers were obtained by scanning the samples in an interval of 2[theta] = 1-40[degrees]. All the samples crystallize completely at 120[degrees]C for 6 h.

RESULTS AND DISCUSSION

Copolymer Composition and Sequence Length Analysis

The NMR spectra of the PETT copolymers are illustrated in Fig. 1. There are three possible sequences in the PETT macromolecular chains, as shown in Fig. 1A. The recognizable different protons and carbons are assigned to a, b, c and d, e, f, respectively. Their corresponding peaks in NMR spectra are also labeled in the same letters in Fig. 1B. The copolymer composition is calculated from the relative areas of the [.sup.1.H]-NMR resonance peaks of the methylene group next to carbonyl at 4.89 ppm (peak a in Fig. 1B) [23] for the ethylene terephthalate unit and at 4.63 ppm (peak b in Fig. 1B) [23] for the trimethylene terephthalate unit. In [.sup.13.C]-NMR analysis, the peaks chosen for the determination of the composition are the carbon of the methylene group next to carbonyl at 64.3 ppm (peak d in Fig. 1C) [24] for the ethylene terephthalate unit and that at 64.0 ppm (peak e in Fig. 1C) [24] for the trimethylene terephthalate unit. The feed composition and the actual composition determined by [.sup.1.H]-NMR and [.sup.13.C]-NMR are reported in Table 1. The number after hyphen after PETT indicates the content of PTT in PETT copolymers, for instance, the PETT-15 copolymer is characterized by 85 mol% ethylene terephthalate units and 15 mol% trimethylene terephthalate units of the actual composition.

Both [.sup.13.C]-NMR and [.sup.1.H]-NMR spectra of all copolymers show that the mol ratio of PDO incorporated into the resultant copolymer chains is always larger than the feed ratio in the polymerization, i.e., the content of EG is less than the feed content. It is attributed to that PDO could easily attack the carbonyl carbons of PTA, because of being a relatively strong nucleophile [19]. Moreover, PDO is removed more difficult than EG during the poly-condensation process owing to a relatively higher boiling point of PDO (214[degrees]C) than that of EG (197[degrees]C).

[FIGURE 1 OMITTED]

According to Fig. 1A, there are three possible sequences in PETT, so four kinds of the quaternary aromatic carbons which are clearly assigned to g, h, i, j in Fig. 1A should be recognizable by NMR. In fact, Fig. 1D gives [.sup.13.C]-NMR spectra and their chemical shifts in the three possible triad sequences are presented in Table 2. According to the relative intensity of these four peaks, the number-average sequence lengths ([L.sub.PTT] and [L.sub.PET]) of the copolymers can be calculated in terms of Yamadera's method and the degree of randomness (B) are also obtained after calculation according Yamadera's method [25]. The mol ratio and number-average sequence lengths, as well as the degree of randomness (B) of the PETT copolymers are listed in Table 3.

The B values for all of the samples are less than 1, so the synthesized PETT copolymers are block copolymers. The number-average sequence lengths of PET and PTT units in the copolymers are in proportion to their respective composition, i.e., the higher the content of the component, the longer its sequence length is. Moreover, PDO is more likely to form the alternative copolymer than EG units. When PDO mol ratio increases from 15 to 30%, the [L.sub.PTT] value keeps almost unchanged.

The Crystallization and Melting Behavior of PETT Copolymers

The development for the copolymers to crystallize from the melt during 2.5-15[degrees]C/min cooling rate is investigated by recording the exothermic curves and their melting endothermic peaks are also obtained on the secondary heating. For example, Fig. 2 shows the exothermic peaks (A) and endothermic peaks (B). The crystallization and melting comparison of all samples is given in Fig. 3.

It is obvious that for all the samples, when the cooling rate increases from 2.5 to 15[degrees]C/min, the exothermic peak temperature shifts to the lower temperature (shown in Table 4), i.e. the crystallization from the melt during cooling occurs at the lower temperature, suggesting more under-cooling needed with faster cooling rate. It is inferred that these polymers are in a nucleation-controlled crystallization. Faster cooling means shorter time stayed at every temperature. When the time scale at the fixed temperature is too short for polymer to develop crystallization from the melt, the crystallization will evolve later, i.e. at lower temperature. Moreover, the crystallization exotherms become broader with faster cooling rates indicating that wider temperature range is required to accomplish the crystallization. It can be expected that the crystallites developed during faster cooling may be less perfect with more defects. This is the reason why the melting temperatures of the samples get lower and the melting peaks become wider with faster cooling rate. Furthermore, the change of the crystallization enthalpy [DELTA][H.sub.c] and the enthalpy of fusion [DELTA][H.sub.m] with the cooling rate also explains that the crystallinity developed during cooling from the melt depresses with the increase of cooling rate (shown in Table 4).

In fact, when the cooling rate is high enough, such as 10[degrees]C/min and 15[degrees]C/min, both the neat PTT and PETT copolymers cannot accomplish the crystallization during the cooling procedure. So, the recrystallization occurs again on the second heating, as illustrated in Fig. 2B. It is noticed that for the PETT-30 sample no crystallization takes place during cooling from the melt, therefore only a flat exothermic peak and a small endothermic peak are found on the second heating as shown in Fig. 3. The short neat PET and PTT sequence lengths (in Table 3) can be responsible for this difficulty of PETT-30 crystallization. That is, more time is required for PETT-30 to crystallize after exclusion of heterogeneous chain segments. The study on crystallization behavior of poly(ethylene terephthalate) and its copolymers containing isophthalate units (IPI) shows that slower crystallization enables more effective exclusion of IPI units from the crystal region [26]. It can also be expected that the crystallites formed in PETT-30 are smaller due to shorter crystallizable chain sequences. This is why PETT-30 shows the lowest melting temperature (Fig. 3B). It is reasonable to deduce that the copolymer could not crystallize if the neat sequence length is reduced further to a certain value. As Lee et al. reported, the copolymers containing [less than or equal to]32.8 mol% or [less than or equal to]39.3 mol% PTT units were amorphous [19].

[FIGURE 2 OMITTED]

Nonisothermal Crystallization Kinetics

For nonisothermal crystallization, the relative crystallinity X(t), as a function of crystallization temperature T, can be formulated as [27, 28]:

X(t) = [[[integral].sub.[T.sub.0].sup.[T.sub.c]](d[H.sub.c] dT)dT]/[[[integral].sub.[T.sub.c].sup.[T.sub.[infinity]]] (d[H.sub.c] dT)dT] (1)

where [T.sub.c] is the crystallization temperature, [T.sub.0] and [T.sub.[infinity]] represent the onset and end temperature of crystallization, respectively, and d[H.sub.c] is the enthalpy of crystallization released during an infinitesimal temperature range dT.

[FIGURE 3 OMITTED]

The X(t) can be expressed as a function of crystallization time t, according to a modified Avrami equation.

X(t) = 1 - exp(-[Z.sub.t][t.sup.n]) (2)

log [- ln(1 - ([X.sub.t]))] = log [Z.sub.t] + n log t (3)

where [Z.sub.t] is the growth rate constant and n is the Avrami exponent. Both [Z.sub.t] and n are dependent on the nucleation and crystal growth mechanism.

The crystallization time t can be converted from the cooling rate [alpha] and the crystallization temperature [T.sub.0] and [T.sub.c] as follows:

t = |[T.sub.0] - [T.sub.c]|/[alpha] (4)

In a nonisothermal crystallization process, [Z.sub.t] can be further modified by the cooling rate [alpha], as follows:

log [Z.sub.c] = (log [Z.sub.t])/[alpha] (5)

where [Z.sub.c] is the kinetic parameter of nonisothermal crystallization, which means the crystallization rate constant without the effect of cooling rate [29, 30].

Figures 4 and 5 show the developments of relative crystallinity versus crystallization temperature and crystallization time transformed from crystallization temperature scale by using Eq. 4.

At the same cooling rate, the neat PET initiates crystallization at higher temperature compared to PTT homopolymer. More flexible PTT chains which are not favor to nucleating at high temperature may be attributed to this difference. On the other hand, both PETT-15 and PETT-85 crystallization occur later, i.e., at lower temperature compared to their enriched homopolymers (in Fig. 5). The presence of different blocks in copolymer chains may be a kind of hindrance for macromolecular chains to assemble regularly to crystallize. So more time is needed to exclude the heterogeneous segments before nucleus formation. From the relationship of the relative crystallinity and crystallization time, it is observed that the overall crystallization of PTT is fastest and that of PET is slowest, the two copolymers PETT-85 and PETT-15 are between them. That is PETT-85 with the enriched PTT crystallize a little slower than the neat PTT; PETT-15 with the enriched PET shows a higher crystallization rate than the neat PET. In fact, the crystallizations evolved in PETT-85 and PETT-15 is ascribed to their enriched homopolymer crystallization, which will be discussed in WAXD.

[FIGURE 4 OMITTED]

Figure 6 is obtained by plotting log[-ln(1 - [X.sub.t])] versus log t of the PETT copolymers. It looks like that the experimental data appear to fit extremely well with the modified Avrami equation. From the slopes and the intercepts of the lines, the Avrami parameter n and the crystallization kinetics parameter [Z.sub.t] are obtained, respectively. According Eq. 5, the crystallization rate [Z.sub.t] is corrected to obtained [Z.sub.c]. The values of n and [Z.sub.c] are collected in Table 5. For all samples, the rate constant [Z.sub.c] increases with fast cooling rate, which is also consistent with the experiments. It is obviously that the neat PTT generally shows the greatest rate constant [Z.sub.c] and the neat PET show the smallest [Z.sub.c] value at every cooling rate. It is worth noticing the [Z.sub.c] difference between the copolymer and its enriched homopolymer. For example, the [Z.sub.c] value of PETT-85 is smaller than that of the PTT homopolymer, while PETT-15 exhibits the higher [Z.sub.c] than the PET homopolymer. This means that the introduction of PET unit as a minor component into PTT backbone chains leads to a lower crystallization rate, but the addition of the minor PTT unit into PET backbones results in an enhanced crystallization of PET segments in PETT copolymers. From the other point of view, the more flexible ability of PTT segment which could act as a plasticizer may increase the crystallization rate of the copolymers. Here, the result is contrary to what Lee et al. found when they studied the nonisothermal crystallization characteristic of PETT copolymers [19]. They said the crystallization rate of the PETT copolymers is retarded by incorporating either PDO unit or EG unit into the polymer backbone as a minor component. But when carefully reading the crystallization rate constant and the crystallization half-time, it is difficult to draw this result.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

The Avrami exponent n values vary generally over the range of 3-4 which weakly depends on the composition and the cooling rate. The n values are associated with the nucleation mechanism and the dimensions of growth during crystallization. There are no additives added as nucleating agents with polymerization, so the nucleation mechanism for both the neat polymers and copolymers should be the same as homogenous nucleating. It may be deduced that smaller n values of copolymers are attributed to various dimension of crystallization growth. At the same cooling rate, the macromolecular chains of copolymers are less chemical structure regular, which may somewhat limit the growth of crystals in a particular dimension. Thus, generally the smaller n values for the copolymers are found. It is easy to understand that the n values decrease with increasing cooling rate. The time scale for polymer chains to adjust conformation to form more perfect crystals is reduced, and then the less three-dimensional growth which matches lower n is obtained with increasing cooling rate.

[FIGURE 7 OMITTED]

Wide-Angle X-ray Diffraction Analysis

All samples were annealed at 120[degrees]C for 6 h to investigate the difference of crystalline structures between the homopolymers and copolymers. It is clear from Fig. 7 that the neat PET and PTT show their own well-defined crystalline diffraction peaks. The homopolymer PET shows three strong diffraction peaks at 16.8[degrees], 22.4[degrees], and 25.2[degrees], which correspond to the (010), (1 [bar.1] 0), and (100) diffraction planes, respectively [20, 26]. The diffraction peaks for PTT homopolymer were observed at the scattering angle 2[theta] of 15.3[degrees], 16.8[degrees], 19.4[degrees], 23.6[degrees], and 24.6[degrees] and their corresponding diffraction planes are (010), (0 [bar.1] 2), (012), (102), and (1 [bar.1] 3), respectively [31].

Apparently, apart from those peaks of the PET and PTT homopolymers, no new peaks are observed in the diffraction patterns of the PETT copolymers (as illustrated in Table 6). This implies that the PET units and PTT units do not cocrystallize in the copolymers. Furthermore, the diffraction peaks of the copolymers match the peaks of the homopolymers corresponding to the enriched component, no shift of 2[theta] is observed. This proves that the crystal structure which develops in these copolymers in consistent with the characteristic lattice of the homopolymers. This is in agreement with DSC, i.e., one melting temperature is observed in the PETT copolymers.

The peaks in Fig. 7A are further analyzed to obtain structural information of lamellar crystal dimensions in the direction normal to the individual diffraction plan, i.e., the coherence length. The coherent length of a diffraction plane could be determined by means of the Scherrer's equation [32].

[[beta].sub.0] = ([[beta].sup.2] - [b.sub.0.sup.2])[.sup.1/2] (6)

[L.sub.hkl] = K[lambda]/([[beta].sub.0] x cos [theta]) (7)

where [[beta].sub.0] is the half-width of the reflection corrected for the instrumental broadening according to Eq. 6; [beta] is the half-width of various diffraction peaks; [b.sub.0] is the instrumental broadening factor (0.15[degrees]); [lambda] is the wavelength of radiation used (0.1542 nm); and K is the instrument constant (0.9).

The estimated values of [L.sub.hkl] are plotted together in Fig. 7B as a function of the polymer composition. It is presumed that the [L.sub.hkl] values can be mainly attributed to the lamellar crystal size along the direction normal to the chosen diffraction plane. It appears that the values of [L.sub.010], [L.sub.110], [L.sub.100] in the PETT copolymers are considerably smaller than those of the enriched PET homopolymer and the values of [L.sub.102], [L.sub.012] are also smaller that those of the enriched PTT homopolymer, suggesting smaller lamellar crystals formed in the PETT copolymer than that in the homopolymer. These results are agreeable with inferior melting temperatures of the copolymers to their corresponding enriched homopolymer. As mentioned earlier, there is no cocrystallization of two components in the PETT copolymers. It is the enriched segments that crystallize during the crystallization development. The enriched PET segments or PTT segments in PETT-15, PETT-30, or PETT-85 become shorter, even shorter PET segment in PETT-30 than in PETT-15. So, the crystals composed of the enriched segments become smaller with increasing the minor component.

Another important result obtained from WAXD is the degree of crystallinity ([X.sub.c]). The [X.sub.c] values of the pure PET, PTT, and PETT copolymers after complete annealing are listed in Table 6. The minor component incorporated disturbs the regularity and contributes negatively to the crystal formation. Therefore, the degree of crystallinity of the copolymers decreases with increasing the content of minor component. As shown in Table 6, the PETT-70 copolymer has a smallest crystallinity.

CONCLUSIONS

Poly(ethylene-co-trimethylene terephthalate) (PETT) copolymers were synthesized from PTA, EG, and 1,3-PDO by the direct esterification and polycondensation. They are demonstrated to be block copolymers from [.sup.13.C]-NMR and [.sup.1.H]-NMR. In addition, the content of PTT units incorporated into the copolymers is always larger than that fed in the polymerization. That PDO reacts more favorably with PTA than EG owing to a relatively stronger nucleophile may be responsible for this content difference. The nonisothermal melt crystallization and the subsequent melting behavior at different cooling rate were investigated by means of DSC. The crystallization during cooling from the melt occurs at lower temperature with faster cooling rates for each sample, indicating that the nonisothermal crystallization of these copolymers is controlled by the nucleation. Both PETT-85 and PETT-15 copolymers develop crystallization later than their enriched homopolymers, suggesting more undercooling needed to crystallize from the melt. It is also found that the crystallizations of both homopolymers and copolymers are fitted well by the modified Avrami analysis. The overall crystallization of the PTT homopolymer is fastest and that of PET is slowest, whereas the two copolymers are between them at the same cooling rate. As a whole, the PET units incorporated into PTT polymer chains as a minor component retards the crystallization of the neat PTT, whereas the present PTT segments linked to PET backbone chains seems to accelerate the crystallization rate. The Avrami exponent n varies over the range of 3-4, indicating that the nonisothermal crystallization follows the homogeneous nucleation and two- to three-dimensional growth mechanism. WAXD analysis of the homopolymers and copolymers explains that PET and PTT segments do not cocrystallize and it is the enriched component that crystallizes in the PETT copolymers. The crystal size formed in the copolymers is smaller that that of the homopolymers because of shorter crystallizable segments.

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Hantao Zou, (1,2) Guang Li, (2) Jianming Jiang, (2) Shenglin Yang (2)

(1) College of Textile and Material, WUhan University of Science and Engineering, Wuhan, Hubei 430073, People's Republic of China

(2) State Key Laboratory for Modification of Chemical Fibers and Polymer Mateerials, Donghua University, West Yan'an Road, Shanghai 200051, People's Republic of China

Correspondence to: Guang Li; e-mail: lig@dhu.edu.cn
TABLE 1. Chemical composition of PETT copolymers.

 Feed ratio
 of diols in Composition Composition
 Intrinsic polymerization in polymer in polymer
Samples viscosity (EG/PDO) (a) (EG/PDO) (b) (EG/PDO) (c)

PETT-15 0.70 90/10 84.8/15.2 83.9/16.1
PETT-30 0.72 80/20 70.5/29.5 71.7/28.3
PETT-85 0.70 20/80 14.7/85.3 15.7/84.3

(a) Molar ratio of EG and PDO monomers fed in the polymerization.
(b) Measured by [.sup.13.C] NMR spectroscopy.
(c) Measured by [.sup.1.H] NMR spectroscopy.

TABLE 2. The chemical shift of quaternary aromatic carbon.

The quaternary aromatic carbon Symbol [delta] (ppm)

EG-PTA-EG g 133.95
PDO-PTA-PDO h 134.09
EG-PTA-PDO (EG side) i 133.79
EG-PTA-PDO (PDO side) j 134.24

TABLE 3. The sequence distribution obtained from [.sup.13.C] NMR spectra
of PETT copolymers.

PETT EG/PDO (mol [[phi].sub.PET] [[phi].sub.PTT]
copolymers ratio) (a) (%) (%)

PETT-15 84.8/15.2 67.82 5.04
PETT-30 70.5/29.5 52.05 7.79
PETT-85 14.7/85.3 7.34 68.59

PETT [[phi].sub.PETT]
copolymers (%) B (b) [L.sub.PET] [L.sub.PTT]

PETT-15 27.14 0.670 11.35 1.72
PETT-30 40.16 0.727 6.31 1.76
PETT-85 24.07 0.537 2.18 12.77

(a) Measured by [.sup.13.C] NMR spectra.
(b) B is the degree of randomness; [L.sub.PET] and [L.sub.PTT] denote
the number-average sequence lengths of PET and PTT segments,
respectively.

TABLE 4. The crystallization and melting temperature, the enthalpy of
crystallization, and fusion of PETT copolymers.

 PET
R [T.sub.c] [T.sub.m] [DELTA][H.sub.c]
([degrees]C/min) ([degrees]C) ([degrees]C) (J/g)

15 169 253 32.2
10 173 254 34.2
 5 195 256 44.3
 2.5 205 256 47.7

 PET PETT-15
R [DELTA][H.sub.m] [T.sub.c] [T.sub.m]
([degrees]C/min) (J/g) ([degrees]C) ([degrees]C)

15 36.6 153 226
10 37.7 159 227
 5 39.2 172 228
 2.5 40.2 183 230

 PETT-15 PETT-85
R [DELTA][H.sub.c] [DELTA][H.sub.m] [T.sub.c]
([degrees]C/min) (J/g) (J/g) ([degrees]C)

15 19.4 28.3 139
10 20.3 28.5 142
 5 33.8 30.5 155
 2.5 34.9 31.4 163

 PETT-85
R [T.sub.m] [DELTA][H.sub.c] [DELTA][H.sub.m]
([degrees]C/min) ([degrees]C) (J/g) (J/g)

15 214 33.8 36.7
10 214 42.4 43.8
 5 215 44.3 43.9
 2.5 216 47.0 51.2

 PTT
R [T.sub.c] [T.sub.m] [DELTA][H.sub.c]
([degrees]C/min) ([degrees]C) ([degrees]C) (J/g)

15 166 226 48.6
10 165 227 48.4
 5 171 229 46.9
 2.5 188 230 51.1

 PTT
R [DELTA][H.sub.m]
([degrees]C/min) (J/g)

15 51.7
10 52.2
 5 52.6
 2.5 52.5

TABLE 5. Kinetics parameters from the modified Avrami analysis of
non-isothermal crystallization of PETT copolymers.

Cooling PET PETT-15
rate [degrees]C/min n [Z.sub.c] n [Z.sub.c]

15 3.70 0.80 2.95 0.83
10 3.72 0.53 3.36 0.67
 5 3.84 0.25 3.50 0.25
 2.5 3.90 0.03 3.61 0.03

Cooling PETT-85 PTT
rate [degrees]C/min n [Z.sub.c] n [Z.sub.c]

15 3.1 0.81 2.96 0.88
10 3.2 0.68 3.43 0.79
 5 3.3 0.30 3.46 0.34
 2.5 3.5 0.08 3.58 0.06

TABLE 6. Characteristic X-ray peaks and the crystallinity of PET, PTT,
and PETT copolymers.

Samples Characteristic X-ray peaks (2[theta][degrees])

PET -- -- -- 16.8 -- -- 22.4 -- -- 25.2
PETT-15 -- -- -- 17.1 -- -- 22.5 -- -- 25.5
PETT-30 -- 16.2 -- 17.2 -- 21.2 22.5 -- -- 25.3
PETT-85 15.4 -- 16.5 -- 19.5 -- -- 23.5 -- --
PTT 15.3 -- 16.8 -- 19.4 -- -- 23.6 24.6 --

Samples [X.sub.c] (%)

PET 46
PETT-15 50
PETT-30 45
PETT-85 50
PTT 53
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Author:Zou, Hantao; Li, Guang; Jiang, Jianming; Yang, Shenglin
Publication:Polymer Engineering and Science
Article Type:Author abstract
Geographic Code:1USA
Date:Mar 1, 2008
Words:5218
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