Preparation of Green High Impact Polystyrene Beads via Suspension Polymerization Tatiya Kittiwattanakul,* 1 Pattarapan Prasassarakich, 2 Napida Hinchiranan* 2 Summary: The aim of this research was to investigate the important effects and their interaction on production of Green High Impact Polystyrene (HIPS) synthesized by using natural rubber (NR) as elastomeric phase via suspension polymerization initiated and stabilized by using benzoyl peroxide (BPO) and poly(vinyl alcohol) (PVA), respectively. The effects of reaction parameters: wt ratio of NR/styrene and PVA/NR including agitation rate on HIPS bead size were studied by using 2 k factorial design experiment. The HIPS bead size increased with increasing the NR content (0.01–0.08 w/w of NR/ST) in the mixture of NR/styrene syrup. Whereas, the increase in the PVA content (1.5–2.5 w/w of PVA/NR) and agitation rate (350–450 rpm) decreased HIPS bead size. Thermal gravimetric analysis (TGA) results were showed that HIPS containing the various amounts of NR had more thermal stability than the neat PS. Moreover, the glass transition temperature (T g ) of PS phase in the obtained HIPS bead was shifted from 97.9 to 84.2  C when the wt ratio of NR/ST was increased to 0.08. Keywords: factorial design; natural rubber; polystyrene; suspension polymerization; synthesis Introduction Polystyrene (PS) has been well known that it is brittleness resulting its low impact strength. Many researchers have tried to improve the toughness of PS by incorporating with reinforcing inorganic fillers or blending with elastomers such as butadiene rubber (BR), [1–2] natural rubber (NR), [2–4] SNR, [5–6] and ethylene propylene diene rubber (EPDM). [7] The obtained product produced by adding the rubbers in a styrene (ST) monomer is called as “High Impact Poly- styrene (HIPS)”. HIPS has multiphase struc- ture consisting of rubber granules (1–3 mm) dispersed in the rigid PS matrix. [1] Additionally, the distribution of the rubber particles in the polymer matrix is bimodal leading the enhancement of high impact resistance. [1,3] Normally, HIPS is manufactured by bulk polymerization of ST containing BR (8.2 wt%). This HIPS has high impact strength as 106.7 J/m. [8] However, this process limits the rubber content in PS matrix as 15 wt% due to the difficulty of agitation in the HIPS preparation. [9] More- over, the high viscosity of pre-polymeric syrup causes the problems to handle the process such as temperature control and high energy consumption to agitate. Fur- thermore, the most of polymerization is exothermic process leading the heat accu- mulation. [10] This also includes the problem in the pelletization for doing HIPS resin. To solve these problems, the suspension polymerization has been suggested for synthesis of several polymers since the temperature of the system is easier to be controlled. Additionally, the final product 1 Program in Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bang- kok 10330, Thailand 2 Department of Chemical Technology, Faculty of Science, Chulalongkorn University, Patumwan, Bangkok 10330, Thailand Fax: (þ66) 2255 5831; E-mail: Napida.H@chula.ac.th, Tatiya.Ki@student.chula.ac.th Macromol. Symp. 2015, 354, 69–75 DOI: 10.1002/masy.201400127 | 69 ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com