기능성 PBMA 라텍스와 SAA 사이의 혼화성에 미치는 표면 경화의 영향

윤철현, 신진섭, 김중현

연세대학교 화학공학과 나노입자 공정 연구실

The Effect of Interfacial crosslinking on miscibility behavior between isocyanate-functionalized PBMA latex and Styrene/alpha-methylstyrene/acrylic acid (SAA)

Chul-Hyun Yoon , Jin-Sup Shin, Jung-Hyun Kim

Nanosphere Process & Technology Laboratory, Dept. of Chem. Eng.,

Yonsei Univ., 134 Shinchon-dong, Sudaemoon-ku, Seoul 120-749, Korea

Introduction : The seeded emulsion copolymerization of TMI with the butyl methacrylate has been studied. A butyl methacrylate was used as the seed latex. In order to minimize the risk of hydrolysis of TMI, polymerizations were carried out at 40℃ using redox initiations. The FT-IR spectrum showed that the isocyanate peak increased with increase of the TMI concentration in PBMA. In case of the blends of isocyanated-PBMA and SAA, however, the isocyanate peak disappeared. The miscibility between PBMA and SAA was enhanced due to the isocyanated PBMA grafted with COOH groups from SAA. As the extent of grafting between isocyanated-PBMA and SAA increases, the tensile strength is improved. The results illustrate that the grafting reaction between isocyanate groups and COOH groups SAA enhanced the mechanical properties of the blends of isocyanated-PBMA and SAA.

Dimethyl meta-isopropenyl benzyl isocyanate(TMI) is a novel bifunctional monomer. Immiscible blend film usually accompanies phase separation during film formation. Such phenomena reduces the mechanical properties of films.[1],[2] The synthesis of interfacially crosslinkable latex films under mild curing condition has been of great interest. Isocyanate reacts with a variety of functional groups such as carboxyl and hydroxyl moieties. They also react with water at room temperature. Therefore, if polymer chains were to be functionalized with isocyanate groups, room temperature-curable systems can be developed which can be grafted in the presence of atmospheric moisture. This work describes the miscibility between isocyanated PBMA latex and COOH groups from SAA. This method is to physically absorb ASR onto the PBMA latex particles through emulsion blending.[3] The isocyanated-PBMA reacts with COOH group from SAA, forming ASR-grafted PBMA. Since particle formation and the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PBMA.

Experimental

Preparation of the Blends

The SAA resin was post-added to PBMA latex under moderate magnetic stirring at room temperature. The mixture was kept for saturation prior to use.

Preparation of Latex Films

First the dispersions were degassed at room temperature.  Then they were cast on a nonsticking smooth teflon substrate.  These liquid films were then dried in a convection oven for one day.  The drying temperature was 60℃.

Dynamic Mechanical Analysis (DMA)

This apparatus enabled us to measure the extension storage modulus (E'), the loss modulus (E") and the loss tangent (tan□) over a wide range of temperatures (-50℃∼200℃)

Tensile Strength Measurement

Tensile strength measurements were done in a Universal Testing Machine (UTM, LR10K, Lloyd Instruments Ltd., UK)

FT-IR ATR Spectroscopy

FT-IR spectrophotometer with total internal reflectance or attenuated total reflectance (ATR) accessory was used to obtain the spectra.

Results and Discussion

The blend of PBMA and SAA was found to be immiscible. This film usually accompanies phase separation during film formation. Such phenomena reduces the mechanical properties of films. We made isocyanated-PBMA latex to graft COOH groups from the SAA. From FT-IR data, the isocyanate group appeared apparently in the 2270 cm-1 as the concentration of TMI increased.(Fig. 1) In case of the blends of isocyanated-PBMA and SAA, however, the isocyanate peak disappeared.(Fig. 2)

Figure 3 shows various dynamic mechanical properties, such as damping (tan□), of simple blending film of PBMA latex and SAA solution with respect to variation in the temperature, range from -50 ℃ to 200 ℃. The simple blending film of PBMA and SAA solution shows the two glass transition peaks. The isocyanated-PBMA film had the single and sharp damping curve. This results show that miscibility between PBMA and SAA was improved.(Fig. 4) As the extent of grafting between isocyanated-PBMA and SAA increases, the tensile strength is improved.(Fig. 5) The grafting reaction between isocyanate groups and COOH groups SAA enhanced the mechanical properties of the blends of isocyanated-PBMA and SAA.

References

(1) S. Mohammed et al., Journal of Applied Polymer Sci., 61, 911, 1996

(2) Y.He et al., Journal of Applied Polymer Sci., 64, 1143, 1997

(3) Hee-Young Choi, Doug-Yeon Lee, June-Young Lee, Jung-Hyun Kim, J. Appl. Polym. Sci accepted