Summary: High Impact Polystyrene (HIPS) was synthesized by radical bulk polymerization at 70 8C using 6% w/w of total rubber and 0.01% w/w of azobisisobutyronitrile (AIBN) as radical initiator, where the total rubber was composed by polybutadiene (PBd) and model graft copolymers PBd-g-PS. Different ratios in weight percent of PBd to PBd-g-PS were used in order to evaluate the effect of the graft copolymers on the morphology development of the rubber particles during the HIPS synthesis reaction. The morphology of the final material was evaluated by Transmission Electron Microscopy (TEM). The model graft copolymers used with controlled architecture and molecular weight were synthesized previously by high vacuum anionic polymerization. Results show that increasing the content and changing the architecture of the graft copolymer significantly affects the phase inversion point.
The properties of HIPS are largely related to the morphology of the disperse rubber particles developed during polymerization. Since the graft copolymer PB‐g‐PS formed in situ has the role of a compatibilizer between the disperse rubber particles and the continuous PS phase, through the control of the molecular characteristics of the grafting species, the rubber particles' morphology and distribution can be controlled. Several HIPS were synthesized by radical polymerization using a mixture of polybutadiene and model graft copolymers, PB‐g‐PS, and the final materials were characterized physicochemically and morphologically. Different ratios of PB/graft copolymer were used in order to study the effects on the molecular characteristics and morphology of the HIPS obtained.
High impact polystyrene (HIPS) is considered a heterogeneous polymeric system and is constituted by a disperse phase of rubber particles within a continuous phase formed by a polystyrene (PS) matrix. During the synthesis of HIPS, PS is formed whereas some PS chains become chemically bonded to polybutadiene (PB) chains, resulting in a PB-g-PS copolymer, which decreases the interfacial tension between both incompatible phases, acting as a compatibilizer. In this study, 2 HIPS systems were evaluated by energy dispersive spectroscopy (EDS). In the first case, a HIPS composite was analyzed by EDS to locate the graft copolymer species containing Si atoms, which were previously synthesized by anionic polymerization using chloro-silane chemistry. The graft copolymer was incorporated to the HIPS synthesis from the beginning of the reaction in order to provide an improvement on the rubber phase stability. The graft copolymer was located at the interphase between the PS occlusions and the PB subdomains of the rubber particles. In the second case, HIPS was synthesized incorporating silver nanoparticles (AgNP´s) during the polymerization reaction, where the system can exhibit different types of morphology of the elastomeric phase (micelles, lamellas and core-shell). These structures overlapped the AgNP´s in the transmission electron microscopy (TEM) images, thus resulting this technique to be inadequate to establish the location of the AgNP´s. In this context EDS was used to evaluate the location and distribution of the AgNP´s by means of the elemental composition analysis. AgNP´s were preferentially detected in the PS phase as bigger clusters.
Styrene oligomers (M n , 2500-3000 g/mol) with low polydispersity index and containing peroxidic groups within their structure were synthesized using a novel trifunctional cyclic radical initiator, diethylketone triperoxide (DEKTP), through nitroxide-mediated radical polymerization (NMRP), using OH-TEMPO. During the synthesis of the polystyrene (PS) oligomers, camphorsulfonic acid (CSA) was used to inhibit the thermal autoinitiation of styrene at the evaluated temperatures (T ¼ 120-130 C). The polymerization rate, which can be related to the slope of the plot of monomer conversion with reaction time, was monitored as a function of OH-TEMPO, DEKTP, and CSA concentrations. The experimental results showed that all the synthesized polymers presented narrow molecular weight distributions, and the monomer conversion and the molecular weight of the polymers increased as a function of reaction time.
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