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Luperox® for General Purpose and High-Impact Polystyrenes

Productivity (e.g. polymer per hour of reactor time) is higher when using peroxides vs. thermal energy alone.

General Purpose PS

The industry requirements for GPPS polymerization are:

  • high molecular weight
  • broad molecular weight distribution
  • low level of dimers and trimers
  • high reactor productivity


High-Impact PS

For HIPS the industry requirements include:

  • low levels of dimers and trimers
  • high space-time yield
  • excellent grafting
  • small particle size
  • suitable mechanical properties

Luperox® JWEB™ 50

A new initiator for higher MW polystyrene and improved productivity

Luperox® JWEB™ 50 can be used alone or in combination with other initiators to synthesize higher molecular weight resin than using a more traditional di-functional initiator alone.


This table compares the molecular weights of resins produced in batch mode using a linear temperature ramp from 103 to 151°C and a constant, total active oxygen comprising various ratios of Luperox® JWEB™ 50 and Luperox® 331M80.


Luperox® JWEB™ 50 alone increases Mw by 35%. Note that Luperox® JWEB™ 50 is expected to slightly increase the polydispersity index as a result of the high molecular weight fraction produced by the multi-functional initiator fragment.


Luperox® JWEB™50 Luperox® 331M80 Molecular Weight Polydispersity Index
0 100 325,000 2.3
20 80 336,000 2.3
60 40 375,000 2.5
100 0 440,000 2.6

Data shown was produced at internal Arkema R&D by mass polymerization with a continuous stirred tank reactor (CSTR) and pseudo-plug flow reactor (PFR) making polystyrene at 2 lbs/hr.

Peroxide vs. thermal energy polymerization:

Higher molecular weight with the same residence time is readily obtained using Luperox® 331.

  • Initial process temperature is decreased to minimizing thermal polymerization.
  • Ending process temperature similar to thermal process, minimizing viscosity increase.
  • A 10% increase in molecular weight is obtained in the peroxide process.

Luperox® 331 (ppm)


Temp. Profile (°C)


Conversion (%)

Molecular Weight (g/mol)

0 (Thermal)
120 to 160 °C (4h) 82 265.000
361 105 to 150 °C (4h) 80 296.000
542 105 to 150 °C(4h) 80 289.000


Difunctional versus Monofunctional peroxides

For polymerization of GPPS, di-functional peroxides are preferred to monofunctional options. Here is a comparison of a styrene polymerization using Luperox® P (TBPB) to Luperox® 331M50.


The monofunctional Luperox® P yields essentially the same conversion as Luperox® 331M50. The di-functional gives exceptional molecular weight.

Residual Styrene Content using Luperox® 331M50 vs. TBPB

Residual styrene

Polyfunctional Peroxides to Increase Conversion

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 works only in the lower temperature range of a styrene polymerization.

To complement this, Luperox® 101 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.

Thermal gradient: Luperox® 331 and Luperox® 101

Rate of peroxide decomposition

Browse products and solutions

Choose a recommended product and see available formulations or get technical assistance:

Luperox® 26

tert-butyl peroctoate

Luperox® 531

1,1-di-(tert-amylperoxy) cyclohexane

Luperox® 256


Luperox® 270

tert-butyl peroxy isononanoate

Luperox 270

Luperox® JWEB™ 50

polyether poly-tert-butylperoxycarbonate

Luperox® 231


Luperox® 331

1,1-di-(tert-butylperoxy) cyclohexane