Luperox® for General Purpose Polystyrene

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

_{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

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.