Preparation of Polystyrene with Higher Tg Based on Triple Hydrogen Bond Interactions

1.3 Melamine molecule and chemistry

As we known, the physical properties of polymers are significantly altered upon addition of low molecular weight compounds, e.g. the addition of plastizers, which increase chain mobility, and enhance the processability of polymeric materials^[4]. However, a low molecular weight compounds is easy to distribute in polymers and have a strong interaction with polymers in some cases. It's known that the used of secondary interaction(such as hydrogen bond, ion-ion, dipole-dipole or Van Der Waals forces ) is also a well-accepted strategy to enhance miscibility of immiscible polymers, and miscible polymers mixture based on hydrogen bonding^[5]. Most significantly, secondary interaction for the self-assembly of macromolecules has been investigated more recently in detail for liquid crystallinity, rotaxanes, catenanes and amphiphilic structures ^[5]. Recently, Lehn et al. introduced the concept of using well-defined secondary interactions based on hydrogen bonding in the synthesis of liquid crystalline polymer, in which the repeating units are linked by triple-hydrogen bonding instead of by covalent bonding ^[6].

Ronald F.M. Lange et al. have studied the interaction between the alternating copolymer of styrene/maleimide with unsubstituted melamine . They observed that addition of melamine results in a dramatic decrease of T_g up to melamine concentration of 20%(w/w) at which the T_g remains constant at around 215 ^oC ^[5,7].

1.3.1 Structure of Melamine

Melamine is an organic base with the chemical formula C₃ H₆ N₆, with the IUPAC name 1,3,5-triazine-2,4,6-triamine. It is only slightly soluble in water. Melamine is a trimer of cyanamide. Like cyanamide, it is 66% nitrogen (by mass) and provides fire retardant properties to resin formulas by releasing nitrogen when burned or charred.

Fig 1-3 1,3,5-Triazine-2,4,6-triamine

1.3.2 Chemistry of Melamine

It is well-known that melamine forms a 1;1 crystalline complex [5,7,12]with cyanuric acid. The structure of this complex is proposed to be an infinite two dimensional lattice as is showing in the figure 5

Fig 1-4 infinite two dimensional lattices, proposed for the 1:1 complex of melamine and cyanuric acid.

This 1:1 melamine-cyanuric acid lattice has been a source of inspiration in the development of supramolecular chemistry and the theory of secondary interaction ^[7,12].

Various model studies (e.g. complexation of unsubstituted melamine with a low molecular weight imide as well as with various imides containing polymers) have been performed to mimic this triple hydrogen bond formation ^[12].

However, few attempts have been made to mimic this triple hydrogen bond formation using high molecular polymeric materials. In order to mimic this triple hydrogen bond formation only alternating copolymers of SMA have been used in the synthesis of blend between SMA with either melamine or 2.4-diaminotriazine^[12]