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

3.4 Blends of the copolymer and 2,6-diaminopyridine

In order to evaluate the effect of crosslinking of melamine on the Tg of blend, we prepared a series of blend of Diaminopyridine(DAP) and Styrene/Maleimide copolymer with different styrene/maleimide ratios. DAP is analogue structure to melamine. They both can form a complex with imide through a triple hydrogen bonds in the manner of DAD-ADA arrays, however without crosslinkage is formed in the blends of DAP and Styrene/Maleimide copolymer owing to difference of DAP and melamine in structure, as showed in Fig. 1-7 and Fig.1-8.

DSC curves of the blends of Diaminopyridine and Styrene/Maleimide copolymer are shown in Figure 3-5 and their T_g values are presented in Table3-9.

Table 3-9 Effect of imide/Dap ratio on Tg

Experience	[imide]/[Dap]	[Styr]/ [imide]	Tg/^oC
control	1/0	17.7/1	94.2
S	1/1		95.7
T	1/2		103.9
U	1/3		105.2
V	1/4		113.0
W	1/5		115.2 78.1
X	1/10		117.2 76.5

Figure 3-5 Dependence of Tg on the ratio of DAP to imide in the copolymer

The dependence of Tg on the ratio of DAP to imide showed that Tgs of blends are increasing with addition of DAP, as same as blends of the copolymer with melamine. Single Tg is shown till DAP concentration ratio of 4 times to imide, which correspond to Tg equal 113^oC . Then, two Tg is found although one is still elevated. the behavior is found in blends of the copolymer with melamine.

It is known there is triple-hydrogen bonding between DAP and imide unit. Tg increase of our copolymer in presence of DAP attributes to this kind of triple-hydrogen bonding existing in the blend and restricting the motion of polystyrene segments, making the copolymer look like a copolymer of styrene and complex of maleimide with DAP.

However, the Tg increase of the blends is lower ones of blends of the copolymer with melamine. Contrary to the melamine, DAP molecule can not have crosslinkng with imide unit. So the results confirm there are truly crosslinking formation in blends of the copolymer with melamine.