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HIPS
HIPS consists of:
- a continuous phase of free polystyrene (matrix) and
- a dispersed phase of
- free polybutadiene
- polybutadiene grafted by polystyrene
- occluded polystyrene
The polymerization process is similar to GPPS and typical conditions are:
- 84-90% styrene monomer
- 6% polybutadiene
- 5-10% ethylbenzene (solvent and transfer agent), lubricants, antioxidant, and initiators
- CSTR (2 or 3 in series)
- Temperature profile: Slope form 110°C to 150°C/170°C in 5 hours
- Yield: approx. 50-80%
- Stripping step
- Crosslinking of the rubber phase (post curing) at 180°C
For HIPS production the main requirements are: cost reduction, low levels of dimmers and trimmers, high space-time yield, excellent grafting, small particle size, good mechanical and physical properties.
The initation can be done thermically or by addition of organic peroxides.
Organic peroxides provide better performances and can improve process and product properties by giving:
- A higher conversion rate
- More efficient grafting
Advantages of using organic peroxides can also be demonstarted by:
- A better elastomeric phase distribution
- Better mechanical properties of hips
- Reduced levels of dimmers and trimmers
The initiator of choice for best properties is Luperox® TBICM75.
Kinetic improvement
The table below shows that higher yield could be obtained using organic peroxides but the molecular weight is slightly lower. Mw can be corrected by using lower temperature profiles.
|
% conversion after |
|
| PEROXIDE |
120 min |
180 min |
final Mw (g/mol) |
| Thermal |
15 |
29 |
234.200 |
| Luperox® 531M60 |
30 |
46 |
216.800 |
| Luperox® 331M50 |
26 |
41 |
218.000 |
| Luperox® TBICM75 |
30 |
45 |
215.000 |
Grafting efficiency
The table below shows that compared to thermal process, all organic peroxides enable better grafting.
| PEROXIDE |
Rg (%)
at 18%conversion |
| Thermal |
12,5 |
| Luperox® 531M60 |
21,0 |
| Luperox® 331M50 |
20,5 |
| Luperox® TBICM75 |
52,5 |
Micro pilot experiments: 110°C to 150°C within 5 hours
Rate of Grafting: Rg(%) = 100 x (Styrene grafted PBu - Initial PBu) / Initial PBu
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