Preparation of poly(methacrylic acid-block-styrene) particle by using reversible chain transfer catalyzed emulsion polymerization with polymethacrylic acid-iodide as an emulsifying and controlling agent
Abstract:
The objective of this study was to present the effect of preparation of polymethacrylic acidblock-
polystyrene (PMAA-b-PS) particles by reversible chain transfer catalyzed emulsion
polymerization (emulsion RTCP). Moreover, polymethacrylic acid-iodide (PMAA-I) which was
prepared by solution polymerization was used as a macro chain transfer agent and emulsifier.
For the first step, PMAA-I was synthesized by the following reversible chain transfer catalyzed solution polymerization using methacrylic acid (MAA) as a monomer, iodoform (CHI3) as a control agent, germanium iodide as a catalyzed and 4,4'-azobis (4-methoxy-2,4-dimethyl-valero nitrile) as an initiator. The mole ratios of CHI3 and MAA were varied in order to obtain 24, 46 and 53 units of PMAA-I chain length. After that, they were used as a macro chain transfer agent and emulsifier in the emulsion RTCP. For the second step, PMAA-b-PS particles were prepared by emulsion RTCP using 4,4'-azobis (4-cyanopentanoic acid) as an initiator. Apart from this, the types of catalysts (GeI[subscript4], hydroquinone and L-ascorbic acid), the chain length of PMAA-I and the target chain length of polystyrene were also studied in order to obtain good colloidal stability, good livingness and narrow molecular weight distribution (MWD) of PMAA-b-PS praticles.
The result of this study revealed that hydrophilic catalysts which were L-ascorbic acid and hydroquinone represented higher efficiency than GeI[subscript4] in producing PMAA-b-PS particles without coagulation. In addition, L-ascorbic acid presented higher polymerization rate than that of hydroquinone. The reason for this was, during the beginning of polymerization, the particle formation relied highly on the PMAA-I chain length. Long hydrophilic block of PMAA-I (46 and 53 units) needed more time to nucleate the pre-particle because higher repeating units of PS block were required to produce polymer chain with enough hydrophobicity to form the particle by selfassembly short chain. The effect was that the target PS block of 400 units were not able to be prepared using PMAA[subscript46]-I and PMAA[subscript53]-I. In contrast, PMAA[subscript24]-b-PS[subscript400] particles (302 nm) were successfully prepared using PMAA[subscript24]-I.
As a final findings, using hydrophilic catalysts which were L-ascorbic acid and PMAA[subscript24]-I in emulsion RTCP effectively produced PMAA-b-PS particles at the widest PS block with narrow MWD.