Study Of Morphology Evolution And Preparation Of Various Asymmetric Latex Particles By Soap-free Seeded Emulsion Polymerization

In this paper,we demonstrate a brief and generalized approach to prepare anisotropic poly(tert-butyl acrylate)/polystyrene(PtBA/PS)nanoparticles with controllable morphologies by soap-free seeded emulsion polymerization(SSEP).In this approach,non-crosslinked Pt BA seeds with polar functional groups such as ester radical and carbonyl,are presynthesized by emulsion polymerization,subsequently,PtBA/PS composite particles are prepared via SSEP of styrene(St)monomers.We systematically investigate the influence of monomer/seed feed ratio,polymerization time,and polymerization temperature and other factors on the morphology evolution of PtBA/PS composite particles.Phase separation takes place between PS and PtBA because of their thermodynamic immiscibility during polymerization of styrene.And then,a number of intriguing morphologies of PtBA/PS nanoparticles,including hamburger-like,litchi-like,semi-mushroom-like with an open mouth,strawberry-like,full bowl-like and snowman-like etc.are formed.At last,a possible formation mechanism is proposed based on the experimental results.The average particle sizes and distributions of PtBA seeds and composite particles were characterized by Malvin particle size analysis instrument.Fourier transform infrared spectrometer(FT-IR)was used to characterize the chemical compositions and X-ray photoelectron spectroscopy(XPS)was used to analyze the element content of seeds and composite particles surfaces.Scanning electron microscope(SEM),transmission electron microscope(TEM)and ultrathin slices were employed to characterize the apparent and internal microstructure of seeds and composite particle,respectively.The ratio of core/shell components and thermal stability of the composite particles were tested and characterized through thermogravimetric analysis(TGA).And the hydrophilicity of the composite particles was tested by the contact angle tester.The study results show that the PtBA seeds exhibit uniform sphericity,and polar functional groups on the surface of the seeds are evenly distributed.The stability of emulsion mainly relied on polar functional groups on the seeds surface,where the external hydrophilic chain segments tend towards water phase to lower the interfacial tension between water and seeds.After polymerization of St monomers swellen into the seeds,part of PS phases were extruded from the seeds,and phase separation occurred with seeds.Polymerization time,monomer/seed feed ratio,polymetization temperature had a great influence on the morphology of composite particles during polymerization procedure.When the St/Pt BA feed ratio was 3.0 g/1.0 g,composite particles presented hamburger-like structure.When the St/PtBA feed ratio was 4.0 g/1.0 g,raspberry-like particles were obtained.At a high St/Pt BA feed ratio(5.0 g/1.0 g),semi-mushroom-like particles,semi-mushroom-like particles with an open mouth,full bowl-like particles and snowman-like particles were achieved with the extension of polymerization time.At room temperature and a lower St/PtBA feed ratio(2.0 g/1.0 g),litchi-like PtBA/PS composite particles with superhydrophobicity were easily achieved.With prolonging the reaction time,the core/shell ratio of the composite particles gradually decreased,and the thermostability was improved due to the increasing PS.In addition,hydrophilic polar groups on the seeds surface hindered the perfect fusion of PS bulges.