The Effect Of Compatibilizer Structures On The Morphology Of PMMA/PS Blends

A series of Poly(styrene-r-methyl methacrylate), Poly(styrene-b-methyl methacrylate) block (A-B copolymer), and Poly(styrene-b-(styrene-r-methyl methacrylate)) (A-C copolymer) was synthesized. They were evaluated as compatibilizers for blending PS and PMMA.1-Phenylethyl Phenyldithioacetate (PEPDTA) was used to synthesize random and A-C block copolymer, while 2-Cyanoprop-2-yl Dithiobenzoate (CPDB) was used to synthesize A-B block copolymer. A-C block copolymer was synthesized by two steps. The first step (P(St-r-MMA) block) synthesis involved Reversible Addition-Fragmentation Transfer (RAFT) MMA/St copolymerization in miniemulsion. After the copolymerization was completed, a given amount of deoxygenated St was continuously added via a syringe pump to obtain PS-b-P(St-r-MMA). For synthesizing block copolymer A-B copolymer, the PMMA was synthesized in RAFT miniemulsion polymerization. Then PMMA was precipitated by methanol as Macro-RAFT. Macro-RAFT was dissolved in styrene to synthesize A-B copolymer through miniemulsion polymerization.PS, PMMA, and copolymer were mixed in Brabender at 180℃. The morphology of mixture before and after annealing (200°C, 70min) was observed. It was found that:(1) In the case of PS/PMMA=3/7, a small fraction of A-C block copolymer or random copolymer can reduce the size of dispersed phase whether before and after annealing. However, when a large amount (20wt%) of A-C block copolymer was used, nano-layer structures were formed first and after annealing a co-continuous morphology was seen. In contrast, by adding the equivalent moles (8wt%) of random copolymer, the dispersed phase was elongated. The coalescence of the dispersed proceeds very quickly, even quicker than the blank control system. We drew a conclusion that with the increase of A-C block copolymer dosage, the size of the dispersed phase can be dramatically decreased, in contrast to the classic compartibilizer.(2) In the case of PS/PMMA=7/3, A-C block copolymer, random copolymer andA-B block copolymer all had quite similar performance when the dosage of the compartibilizers was small. TEM images indicated that all of these copolymers can provide better static stability that the blank control. When a large amount (20wt%) of A-C block copolymer was added. We found that the phase domain is extremely smaller than the blends without any copolymer whether before and after annealing. The size of most dispersed phase is smaller than 100nm, and the size distribution are very uniformity. After annealing, the size of dispersed phase is still smaller than 1 micron.(3) The experimental results indicated that since the A-C block copolymer can quickly get to the newly-born interphase created by high shear rate, increasing the amount of A-C block copolymer can extremely minus the size of dispersed phase. It shows a great advantage over the traditional compatibilizer like A-B block copolymer and random copolymer.Also, the compatibilizing effect in thin film was investigated in blending PS/PMMA=3/7. From the TEM images, we saw clearly that random the sea-island structures was obtained by using random copolymer as compatibilizer, whereas A-C copolymers leaded to forming bi-continuous structures. After annealing, the coalescence can not be prevented in the case of random copolymer. By contrast, we found that during the annealing process, the PS phase domain was fragmented in the A-C block copolymers. When increasing the amount of the A-C block copolymer to over 10wt%, the bi-continuous structures were very stable against coalescence.