## 4 Results  
Poly(ethylene-_co_-isosorbide terephthalate) samples with varying isosorbide contents were produced at the pilot scale by Roquette Freres. The isosorbide content is expressed as the molar percentage of ethylene glycol replaced by isosorbide. The characteristics of the studied samples are presented in Table 1.  
The results show that PEIT samples with isosorbide content from 4.9 to 20.8 mol.% were successfully synthetized. Moreover, based on the equation with the polymerization conditions used, the final polymer displayed no coloration. Color parameters were evaluated, and L* was higher than 50, a* was between \(-\)0.6 and 0.2, and b* was between \(-\)1.9 and 2.7. These polymers also displayed reduced viscosities ranging from 0.56 to 0.66 dL/g, indicating that high-mol-mass polyesters were achieved. In this small range of reduced viscosity, it was considered that the molar mass of the polymer had a limited effect on the crystallization kinetics of the polymer. For comparison purposes, a polyester \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Samples Isosorbide**} & \multirow{2}{*}{\
\begin{tabular}{c} **Reduced** \\ **Viscosity** \\ **(dI/g)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Triad** **Molar Fraction** \\ **Viscosity** \\ **(dI/g)** \\ \end{tabular} } & \multicolumn{3}{c}{**Average Sequence**} & \multicolumn{3}{c}{**Degree of**} & \multicolumn{3}{c}{**Coloration**} \\ \cline{3-10}  & & & & & & & **Lengths** & & & & \\ \cline{3-10}  & & & & & & & & & & & \\ \hline PET & 0 & 0.71 & - & - & - & - & - & - & - & - & - \\ PEL\({}_{4}\)gT & 4.9 & 0.65 & 0 & 9.4 & 90.6 & 20.3 & 1.0 & 1.05 & 51.8 & 0.2 & \(-\)1.9 \\ PEL\({}_{6}\)T & 6.5 & 0.59 & - & - & - & - & - & - & 55.8 & 0.1 & 0.6 \\ PEL\({}_{8}\)T & 9.8 & 0.66 & 3.2 & 17.7 & 79.1 & 9.9 & 1.4 & 0.84 & 52.1 & \(-\)0.1 & 1.4 \\ PEL\({}_{10.9}\)T & 10.9 & 0.59 & - & - & - & - & - & - & 57.5 & \(-\)0.2 & 1.3 \\ PEL\({}_{17.1}\)T & 17.1 & 0.61 & 4.2 & 26.7 & 69.0 & 6.2 & 1.3 & 0.92 & 52.8 & \(-\)0.2 & \(-\)0.6 \\ PEL\({}_{19.5}\)T & 19.5 & 0.60 & - & - & - & - & - & - & 56.1 & \(-\)0.6 & 2.7 \\ PEL\({}_{10.8}\)T & 20.8 & 0.56 & 6.3 & 30.2 & 63.6 & 5.2 & 1.4 & 0.90 & 50.0 & \(-\)0.6 & 1.4 \\ PIT & 100 & 0.21 & - & - & - & - & - & - & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of studied samples. PEiT corresponds here to a PEIT containing x% molar of isosorbide. made from isosorbide and terephthalatic acid only was synthetized. The product displayed a reduced viscosity of 0.21 dL/g and a Tg of 140 \({}^{\circ}\)C.  
In order to see the possible influence of the structure of the polymer on crystallization, copolyester triads were further assessed by \({}^{13}\)C-NMR analysis. Identification and quantification of triads were done by analysis of quaternary carbons of terephthalatic acid moieties located in the 132-134 ppm region. Depending on the neighboring diols, these carbons presented variable chemical shifts, as shown in Figure 2.  
Thus, from the integration of these signals, it was possible to evaluate the average sequence length of both ethylene terephthalate (ET) and isosorbide terephthalate (IT) moieties with the following equations [12]:  
\[\text{n}_{\text{ET}}=\frac{\text{I}_{\text{ETE}}+\frac{\text{I}_{\text{TE}+ \text{ETI}}}{2}}{\frac{\text{I}_{\text{ITE}+\text{ETI}}}{2}}, \tag{4}\]  
\[\text{n}_{\text{IT}}=\frac{\text{I}_{\text{ITI}}+\frac{\text{I}_{\text{ITE}+ \text{ETI}}}{2}}{\frac{\text{I}_{\text{ITE}+\text{ETI}}}{2}}. \tag{5}\]  
Figure 2: \({}^{13}\)C-NMR chemical shifts of the different sequences in PEIT. Thus, the degree of randomness R could be evaluated as follows:  
\[\text{R}=\frac{1}{\text{n}_{\text{ET}}}+\frac{1}{\text{n}_{\text{IT}}}. \tag{6}\]  
R takes 2 as a value for an alternating copolymer, 1 for a random structure, \(<\)1 for a sequential block structure, and 0 for a mixture of homopolymers [13].