(US4731388-A)      Prodn. of expandable styrene-based polymer beads by adding a low temp. polymerisation initiator (I) to an aq. medium contg. blowing agent-contg. expandable styrene based polymer small particles (II), adding a blowing agent to the system in amt. 5-15wt.% w.r.t. (II) to inhibit the expansion of (II) while the system is heated for first stage polymerisation, continuously or intermittently adding a styrene-based monomer and a high temp. polymerisation initiator (III), adding further blowing agent to the system and raising the temp. to 100-150 deg.C to effect second stage polymerisation.    (I) has a half-life of 10 hrs. at 50-80 deg.C, and is pref. benzoyl peroxide; and (III) has a half-life of 10 hrs. at 80-120 deg.C, and is pref. tert. butyl peroxybenzoate. (II) pref. contain 2-10wt.% of blowing agent.    USE -   Expandable beads having a narrow particle size range.    (8pp)    (JP93073133-B)      Small grains of foaming styrene polymer contg. the foaming agent which is made grain size even in +- 20% of ave. grain dia. is suspended in a polymerisation container. To this water medium of the polymerisation container, almost all of low temp. type polymerisation initiator (LPI) of which decomposition temp. to obtain 10 hours of period of half decay is 50-80 deg. C, is added. On raising temp. to the first polymerisation temp. (pref. at 40-60 deg. C), the evapd. foaming agent in amt. to inhibit the formation of the small grain of foaming styrene polymer, is supplied to the space of the polymerisation container, with 3-15g (amount of the foaming agent)/1 (volume of the space of the polymerisation container). Then styrene monomer which is added the rest of LPI and high temp. type polymerisation initiator (HPI) of which decomposition temp. to obtain 10 hrs. of period of half decay is 80-120 deg. C, is added to the polymerisation system. Then, the foaming agent of which amt. is enough for formation of the final foaming styrene polymer grain (pref. about 2-10 wt.%) is added to the polymerisation system. First step. polymerisation is carried out at the temp. 10 deg. C lower than the decomposition temp. of LIP-the temp. 20 deg. C higher than the decomposition temp. of LPI. The second step polymerisation is carried out at 100-150 deg. C..    USE/ADVANTAGE -   With the prodn. excellent foaming sytrene polymer grain having desired grain dia. and narrow grain size distribution, can be obtd. industrially. (J62185721-A)