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

Chapter 2 Experimental

2.1 Materials

Styrene was distilled under vacuum and stored in a freezer until use. Maleimide 2,6-diaminopyridine were used commercially. AIBN (2,2'-azobutironitrile) was recrystallised from methanol before use. DMSO was purified and dried by standard techniques before use. CH₃OH and CH₂Cl₂ were used commercially.

2.2 Instruments

¹H-NMR of copolymer samples were taken in CDCl₃ on a Bruker 600 MHz spectrophotometer with DMSO as a solvent. The glass temperature transition was determined by differential scanning calorimeter (DSC) and was performed on a Perkin Elmer Pyris 1 under nitrogen with a scan rate of 10^o C/min. The glass temperature transition Tg is the midpoint in the heat-capacity change.

2.3 Synthesis of random copolymers of styrene and maleimide

Copolymer of styrene and maleimide were prepared by a free radical copolymerization using AIBN as the radical initiator and DMSO as solvent. The synthesis of random copolymers of styrene and maleimide (Fig. 2-1) which can serve as an example was performed as follow:

Styrene and Maleimide solution was prepared in DMSO. Styrene solution was added with AIBN (80% w/w of the total monomer concentration) in a 3-necked round-bottomed flask equipped with a reflux condenser, mechanical stirrer and nitrogen inlet (septum and a long needle). Maleimide solution was added dropwise with AIBN (20% w/w of the total monomer concentration) shortly and slowly. The polymer solution was precipitated in water and the resulting polymer was dissolve in CH₂Cl₂ and precipitated in CH₃OH, then dried in vacuum at 60^oC.

Fig 2-1 Synthesis Copolymerization of Styrene and Maleimide

2.4 preparation of Blends of Styrene/Maleimide copolymer and melamine or 2,6-diaminopyridine

Co-precipitation method was used to blend melamine or 2,6-diaminopyridine with imides containing copolymers. A series of experiments was done to blend Styrene-Maleimide copolymers with melamine or 2,6-diaminopyridine. Copolymers based on styrene-maleimide were mixed homogenously with various amounts of melamine and carefully dissolved in DMSO for 30 minutes, then co-precipitated in water. The resulting polymer was dissolve in CH₂Cl₂ and precipitated again in CH₃OH then dried in vacuum at 50^oC. After filtration, washing and drying the yield of the blend was determined ^[7].

Fig 2-2 blend of Styrene-Maleimide and Melamine

Fig 2-3 Blend of Styrene-Maleimide and 2,6-diaminopyridine