| The effect of the crosslinker chain lengths in the copolymerization reaction with n-BMA and the formation of the resulting latex films was investigated. Three crosslinkers; ethylene glycol dimethacrylate (EGDMA-198 g/mol), Aliphatic Urethane Acrylate (AUA-3728 g/mol) and a novel Macromonomer Crosslinker (Mac-3480 g/mol) were compared. Copolymerization was achieved via a miniemulsion process. The amount of the crosslinkers employed in the copolymers was 0.2 mol%.; When Mac was used as the crosslinker in the latex, high toughness was retained which is comparable to the toughness of the PBMA homopolymer latex films. The P(BMA-co-Mac) films contained 60% gel (crosslinked network) prepared using persulfate (KPS, water-soluble) to >95% gel prepared using azo (AMBN, oil-soluble) initiators. For the P(BMA-co-AUA) copolymer latex films prepared using either of the initiators, no appreciable toughness was recorded at all. For the P(BMA-co-EGDMA) copolymer latex films, a dependence on the type of initiator was obtained. The persulfate initiator gave P(BMA-co-EGDMA) copolymer latex films appreciable toughness while the AMBN initiator gave brittle films. These copolymer latexes have gel contents >95%. In films derived from crosslinked latex particles, the interface or the continuous matrix (continuum) of the film is crucial for the film to be useful mechanically. The toughness in the PBMA homopolymer and P(BMA-co-Mac) copolymer latex films, was due to the long polymer linear chains that can interdiffused and entangled with chains in the adjacent neighboring particles. The network in P(BMA-co-Mac) copolymer latex films, are flexible and are able to deform upon load application such that these films have high extensibility. Lightly crosslinked PBMA polymer chains which are attached to the network chains may exist at the interface of the particles rendering the P(BMA-co-EGDMA) copolymer films the toughness as observed for the persulfate, and not in the AMBN-initiated system. Phase separations were postulated to occur during the synthesis of the copolymers. The phase separation is hypothesized to determine the particle morphology and hence the resulting film morphology and therefore the film properties. |
