MT copolyamide

As observed in dielectric measurements, the MT copolyamide is the simplest Ar-Al-PA to analyse for it presents only one secondary transition, the j one. 

Fig. 83 Oscillation amplitudes (°) determined for the protonated aromatic carbons ( ), unprotonated aromatic carbons (V) and carbonyl carbons (O) of the MT copolyamide (from [58])...

The lactam-12 units, whose non-conjugated amide groups and methylene carbons undergo motions in a low-temperature range are responsible for the y transition. Furthermore, the intensity of the transition is directly related to the amount of lactam-12 units this transition does not exist in the MT copolyamide. 

Analysis of the ft transition of MT copolyamides (described in [1], Sect. 5) shows that in the mechanical loss ft transition of MT Ii copolyamides, in the low-temperature range part of the involved motions are those of CH2 units. At higher temperatures phenyl ring motions (oscillations then jr-flips), coupled with amide group motions, occur. 

The second group is represented by the following copolyamide, MT, obtained from the condensation of fere-phlhalic acid onto 1,5 diamino-2-methylpentane ... 

Fig. 84 Fraction of phenyl rings undergoing rapid tv-flips in the MT (T), 1 T (A) and 1.8 T (O) copolyamides (from [58])...

Despite experimental evidence, it is very likely that, in both MT and xTyli-y copolyamides, the n-flips of the fere-phthalamide phenyl rings are associated with correlating flips of the adjacent C = O groups. 

The combined investigations of a series of aryl-aliphatic copolyamides (xTyl -y and MT) by dielectric relaxation, solid-state 13C and 2H NMR, and dynamic mechanical experiments demonstrate the existence of three secondary transitions y, ft and co, in order of increasing temperature. 

Table 9 Experimental and calculated values of the transition temperatures (in °C)for xty y copolyamides and experimental values for MT Ii copolyamides... 

Fig.99 Dependence of Kic (left) and Gic (right) at-40°C on the fraction of tere-phthalic units for l.81yli y, lTyli-y and MT Ii copolyamides (From [62])...

The increase of nSSA in the low temperature part to about - 20 °C corresponds to the softening of the medium by the fi transition motions. The leveling observed at higher temperatures is consistent with the fact that, for MT Ii, copolyamides, there are no new motions until the glass-rubber transition temperature is reached, in contrast to the case of xTy -y copolyamides for which there is still an co transition in the range 20-80 °C (Fig. 84b). 

The smaller difference in Gic compared to K c (Tables 10 and 11) reflects only the effect of the higher modulus of the MT Ii-y copolyamides owing to their higher hydrogen bond density. 

Finally, it is important to mention that MT I, copolyamides are characterised by quite a high modulus, E. For copolyamides of this series with high fere-phlhalic unit content (50%) fairly high K c values are obtained, in such a way that, around room temperature, they are only slightly lower than those of BPA-PC. 

Before considering the various mechanical properties, it is important to notice that the transition of these copolyamides, as shown by the dynamic mechanical loss modulus, E", in Figs. 84 and 85 for the xTyli-y and MT, Ii- y series, respectively, occurs at quite low temperatures. Indeed, for the first series the /3 peak maximum occurs at - 60 °C at 1 Hz, and at -110 °C for the second series. From this point of view, these copolyamides look more like BPA-PC (Sect. 4) than PMMA (Sect. 3). 

Fig. 85 Temperature dependence at 1 Hz of a storage modulus and b loss modulus for various MT Ii y copolyamides (From [53])...

It is interesting to notice that in the whole temperature range, ay values of the MT Ii copolyamides are much higher than those of for xT Ii. This results from the higher hydrogen bond density. 

Much larger values are observed for apf of MT ,Ii jy copolyamides than for xT Ii- , copolyamides. 

As regards the onset of CDCs, T233, quite a large temperature shift is observed between the two copolyamide series. Unfortimately, in the MT Ii- ,... 

Looking at the molecular characteristics of the MT Ii copolyamides reported in Table 8, the only consistent explanation for the particular behaviour of MT0.7I0.3 copolyamide deals with the quite large polydispersity of this sample, leading to a much lower value of the ratio Mn/Me and, thus, emphasising the influence of the low MW chains. 

As for the low temperature range, the toughness of MT yIi, copolyamides is much larger than that of ITyli- , copolyamides. 

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