CRYSTALLIZATION OF PA 4.34 AND LIPID LIKE MODEL
COMPOUNDS
S. Cabusa, K. Bogaertsa, M. Smetb, B. Godersa
aCatholic
University of Leuven, Chemistry Department, Molecular and Nanomaterials, Celestijnenlaan 200F, 3001
Heverlee, Belgium
bCatholic
University of Leuven, Chemistry Department, Molecular Design and Synthesis, Celestijnenlaan 200F,
3001 Heverlee, Belgium
The similarities between the morphology of fats (triglycerides in particular) and poly(ethylenes) are
striking: in both cases the hierarchical features include a crystalline subcell, a lamellar-type packing
and spherulitic crystal aggregates. Fats usually pass through different (metastable) crystalline phases
before entering the final stable crystal structure [1,2].
Likewise, a transient mesomorphic phase is believed to be formed prior to the conversion of a
poly(ethylene) melt into semicrystalline matter [3,4]. The life time of this mesomorphic phase is very
short and it is believed to be present only as a small interphase at the crystal growth front. As a result,
evidence on its existence is rather circumstantial and its role in the crystallization of poly(ethylene) is
largely hypothetical and a matter of debate.
Knowledge on the mechanisms involved in these liquid-solid and solid-solid transitions is, however,
important in view of controlling the polymer and fat solidification process. In order to increase the life
time of this presumed mesomorphic precursor phase for systematic studies, polyethylene-like aliphatic
poly(amides) have been synthesized in our group and the crystallization behavior is being
investigated. These aliphatic poly(amides) are synthesized by the condensation of 1,4 diamino butane
(NH2-(CH2)4-NH2) with long aliphatic di-acids (HOOC-(CH2)(y-2)-COOH), with y typically larger than 30
(figure 1). More specifically methylene sequences (y) as long as the thickness of typical polyethylene
crystals are aimed for. The amide groups are – because of their ability to form hydrogen bonds at
high temperature and because of their more polar character – supposed to induce a mesomorphic
layer like arrangement of the long aliphatic moieties. The conversion of this poorly ordered material
into well-ordered PE-like crystallites is studied by means of time resolved synchrotron X-ray scattering
methods. Besides PA4.34 also PA4.58 was investigated to some extent together with a set of lipid
like model molecules as illustrated in figure 2. While type B caries amide moieties (just like the
polyamides discussed above), type A resemble fats. Fats are triglycerides with 3 alkyl chains bonded
to their backbone, while the model compound only has 2.
Figure 1
Figure 2
References:
[1] Sato, K., Chemical Engineering Science 56 2255-2265 (2001)
[2] Himawan, C., Starov, V.M., Stapley, A.G.F., Advances in Colloid and Interface Science, 122, 3–33 (2006)
[3] Strobl, G., Progress in polymer science, 2006, 31, 398 – 442
[4] Rabiej S, Goderis B, Janicki J, Mathot VBF, Koch MHJ, Groeninckx G, Reynaers H, Gelan J, Wlochowicz A
Polymer, 2004, 45: 8761 - 8778