Elsevier

Thermochimica Acta

Volume 423, Issues 1–2, 1 December 2004, Pages 57-61
Thermochimica Acta

A modulated DSC characterization of morphology of composite latex particles

https://doi.org/10.1016/j.tca.2004.04.025Get rights and content

Abstract

A modulated differential scanning calorimetry (MDSC) method combining transmission electron microscopy (TEM) for characterizing the morphology of composite latex particles has been developed. Sulfonated polystyrene (S-PS)/poly(methyl methacrylate) (PMMA) (50:50 by weight) composite latex particles were prepared as model samples. PS particles were prepared by self-emulsification using lightly S-PS in co-solvents/water. For the preparation of S-PS/PMMA composite latex particles, the guest methyl methacrylate (MMA) monomers first diffused into swollen S-PS particles in S-PS aqueous dispersions, and then the MMA monomers were polymerized. Based on the MDSC method, one can determine quickly whether and what kinds of composite latex particles are prepared. Combing TEM, morphological parameters, such as the radius of core, diffused-phase thickness and thickness of shell of the composite latex particles, can be obtained.

Introduction

Composite latex particles are produced in a wide variety of morphologies for applications in various polymer products [1]. The physical properties are achieved by balancing polymer composition, molecular weight and latex particle morphology. Control of particle morphology in composite latex is important for many latex applications such as adhesives, coatings, graphic arts, and impact modifiers, etc. [2]. Morphology is a subject of intense interest and a great deal of effort is being expended to learn how to control and characterize the final structure of the latex particles [3], [4], because of the importance to their final properties. The ability to predict the final morphology of the latex particles has improved markedly since the introduction of free energy analyses of the phase separated particles [2]. Such analyses have highlighted the importance of the interfacial tensions at the polymer/water and polymer/polymer interfaces. The variation of these interfacial tensions with important parameters such as surfactant level, polymer type, initiator end group, and monomer concentration can be utilized to predict all possible equilibrium of the latex particle morphology. However information on concentration distribution in such latex particles cannot be obtained [2]. Only can such information be obtained, composite latex particles for different purposes can be designed. In this communication, we developed a modulated differential scanning calorimetry (MDSC) method to characterize the morphology of the latex particles.

Section snippets

Materials

Methyl methacrylate (MMA), supplied by Aldrich Chemical, was distilled under vacuum. Polystyrene (Mw=110000), supplied by Yanshan Chemical Ltd., China, was purified by dissolving in tetrahydrofuran and precipitated by using water, and dried under vacuum at 70 °C for 48 h prior to use.

Sulfonated reaction

Sulfonation was carried out in 1,2-dichloro-ethane at 50 °C following the procedure described by Weiss and Sen [5]. Sulfonation agent was acetyl sulfonate, which was prepared by the reaction of concentrated sulfuric

Results and discussion

Fig. 1 shows the TEM result for the S-PS particles, indicating that it has a cavum-structure. This will afford the location for polymerization of guest monomers. Fig. 2 shows the TEM result for the S-PS/PMMA-2 composite latex particles. The cavum-structure disappeared. The S-PS/PMMA-1 and S-PS/PMMA-3 have the same TEM results as S-PS/PMMA-2. From the TEM results, the average particle size can be obtained. The average particle size was found to be 120 and 112 nm for S-PS/PMMA-2 and S-PS/PMMA-3,

Conclusions

A MDSC method for characterizing the morphology of composite latex particles was developed. Based on the MDSC method, one can determine quickly whether and what kinds of composite latex particles are prepared. It is believed that combing TEM and MDSC information of the morphology of polymer composite latex particles can be provided. According to the information, the design and control of the morphology of polymer composite latex particles with different properties and for different purposes

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