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GPPS
In a typical continuous mass process, GPPS is polymerized in a series of 2-3 reactors.
The standard recipe/reaction profile is shown below:
- 84-90% styrene monomer
- 5-10% ethylbenzene (solvent/transfer agent), antioxidants, lubricants
- Temperature: 100 to 150/160°C (4 hours)
- CSTR (2 or 3 in series)
- Stripping step
The industry requirements for GPPS polymerization are:
- High molecular weight
- Broad molecular weight distribution
- Low level of dimers and trimers
- High productivity
Most of the requirements can be met with a pure thermal process, but productivity is higher when organic peroxides are used.
The effect of Luperox® 331 of polymerization performances:
Luperox® 331
conc.(ppm) |
Temp. Profile
(°C) |
Conversion
(%) |
Mw
(g/mol) |
| 0 (Thermal) |
120 to160°C (4h) |
82 |
265.000 |
| 361 |
105 to150°C (4h) |
80 |
296.000 |
| 542 |
105 to150°C (4h) |
86 |
289.000 |
Higher molecular weight with the same residence time are readily obtained using Luperox® 331M50 organic peroxide.
- Initial temperature is decreased to use the peroxide at its fullest potential while minimizing the occurrence of thermal polymerization.
- End temperature approaches that of thermal, thus minimizing any problems with high viscosity materials.
- 10% increase in molecular weight is obtained with no loss in productivity.
Difunctional versus Monofunctional peroxides
For polymerization of GPPS, difunctional peroxides are preferred to monofunctional ones. See below for a comparison of the polymerization of styrene using t-butyl perbenzoate (TBPB) to Luperox® 331M50 organic peroxide.
The monofunctional TBPB yields essentially the same conversion as Luperox® 331M50 organic peroxidesbut the difunctional gives exceptional molecular weight.
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click to enlarge
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Polyfunctional Peroxides
Luperox® JWEB50 organic peroxide produces up to 4-branched free radicals. Consequently, this peroxide can generate high molecular weight and long chain branching. This leads to a material with higher shear thinning, melt strength and higher elongational viscosity.
Combination of different peroxides drives higher conversion rates.
Because styrene polymerization occurs over a broad temperature range, peroxide combinations are necessary to optimize output. Luperox® 331M50 organic peroxide works only in the lower temperature range of a styrene polymerization.
To compliment this, Luperox® 101 organic peroxide can supply difunctional radicals for higher temperatures. The graph below shows the number of radicals formed per minute using either Luperox® 331M50 or Luperox® 101 over a common temperature profile.
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| click to enlarge |
Using a combination of Luperox® 101 organic peroxides and Luperox® 331M50 organic peroxides increases rates without losing molecular weight. Using 450 ppm od Luperox® 331M50 and 5% ethylbenzene, a styrene polymerization carried out from 100°C to 150°C requires 5 hours to reach high conversion.
The chart below shows that the same polymerization with just 100 ppm of Luperox® 101 organic peroxides leads to identical results in only 4 hours.
|
without Luperox® 101 |
100 ppm Luperox® 101 |
| Time (hrs) |
Conversion (%) |
Mw (g/mol) |
Conversion (%) |
Mw (g/mol) |
| 4 |
76 |
316.000 |
81 |
311.000 |
| 5 |
84 |
312.000 |
94 |
299.000 |
Cyclic perketals (di-functional initiator) offer higher space-time yield without sacrificing molecular weight, they also provide a broad molecular weight (mono- and di-radicals).
The use of a Luperox® 331 / Luperox® 101 organic peroxides combination offers an efficiency increase over the thermal process of about 50%.
High molecular weight, improved rheology (long-chain branched PS) are achievable using the tetra-functional organic peroxide: Luperox® JWEB50 organic peroxides.
The chart below compares (at same polymerization conditions) performances of various peroxides over thermal process.
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| click to enlarge |
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