Mechanical and rheological properties of styrene/acrylic gradient polymers

Abstract

SYNOPSISA butyl acrylate monomer with a small amount of photosensitizer was diffused into a slightly crosslinked polystyrene matrix. After a certain swelling time, the diffusion gradient was either fixed (by rapid photopolymerization in situ) to form a gradient polymer or changed to form an interpenetrating polymer network (IPN), once thermodynamic equilibrium was achieved. Chemical compositions were determined by FTIR. Mechanical and rheological measurements were performed using a universal testing machine and dynamic rheometer, respectively. Impact properties were evaluated with a Falling Dart Impact Tester. Compared to the IPN materials, the gradient polymers exhibit higher moduli, considerable strain, and similar impact resistance. They are also able to retain plastic properties at higher temperatures. Differences in chemical structure of equivalent layers for gradient and IPN polymers yield such differences in properties. 0 1995 John Wiley & Sons, Inc. INTRODUCTIONIn recent years, the production of about 2 billion pounds of polymer blends per year in the United States was reported.' Furthermore, while the annual growth rate of the plastics industry was 2-496, that of the polymer alloys and blends was 9-11%.2 That production and growth rate has been based mainly on research made over the last two decades on multicomponent polymers. Scientific interest and the technical importance of polymer blends is due to several reasons: First, no new polymers need to be synthesized; in addition, based on thermodynamic studies of phase equilibria in multicomponent polymer systems, blending feasibility has become less o b~c u r e .~-~ Besides, because of their heterogeneous nature, polymer blends lead to systems with two or more phases whose properties depend not only on the individual characteristics of the components, but also on the method of p r e p a r a t i~n .~-~ The long-term * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 58, 2207Vol. 58, -2212Vol. 58, (1995 stability of the properties of such systems can noticeably be affected if the components have the tendency to phase-separate. Blend structure stability and low birefringence can be enhanced if phase separation is restricted to the microscopic level: Furthermore, if the phases are interconnected, the morphology leads to a synergistic performan~e.6,~~~-" For that reason, slightly crosslinked interpenetrated polymer networks offer a good way of making stable products of better performance than that of copoly m e r~.~. " Even, further, if a continuous change in the composition structure of interpenetrated macromolecules is achieved throughout a polymer blend, a continuous change in individual properties would be expected.13 The spatial gradient formed in that way opens up the possibility of making polymer systems with tailor-made properties for different apOne method to prepare such structures is by sequential polymerization. A convenient profile throughout the sample can be reached by diffusing a monomer into a polymer mat...

Synthesis and characterization of styrene‐butyl acrylate polymers, varying feed composition in a semicontinuous emulsion process

“…Such type of behavior is in agreement with results presented with materials synthesized in bulk. 10,11 In fact, VCC50 sample resembles behavior of the VCC70 and VCC85 samples [ Fig. 5(b)], which are lines that allocate closer to the PS curve.…”

“…29,30 However, on the basis of the favorable mechanical behavior shown on systems of variable composition synthesized through sequential bulk polymerizations 7,8,10,11 it can be expected a priori that a synergistic effect could also be obtained when a copolymer is synthesized by means of seeded emulsion copolymerizations, provided that the particles contain copolymer chains with a wide range of compositions. One way to favor that scheme, is to use a semicontinuous process promoting that, in the polymerization locus (e.g., polymer particle), the monomers ratio change throughout the reaction, covering a wide range of ratios.…”

“…7,8 Superior properties of described blends may be obtained maintaining phase separation at microscopic level, increasing in that way the interaction between components; 9 that applies for both homogeneous and gradient composition blends (in the latter ones, homopolymers contribution can be optimized designing the gradient in a specific way). [10][11][12] In bulk polymerization, one way to reach a desired composition gradient is by controlling the diffusion of a second monomer in a host polymer, followed by an ''in situ'' reaction. 13 Pursuing mechanical modification, the second monomer diffusion approach, has been used in amorphous 7,8,10,11,13 and crystalline polymers.…”

“…[10][11][12] In bulk polymerization, one way to reach a desired composition gradient is by controlling the diffusion of a second monomer in a host polymer, followed by an ''in situ'' reaction. 13 Pursuing mechanical modification, the second monomer diffusion approach, has been used in amorphous 7,8,10,11,13 and crystalline polymers. 14 During polymer processing, gradients in morphology have been formed by annealing compression-molded sheets 15 or by slow crystallization in injection molding.…”

Gradient Structure Polymer Obtained from a Homogeneous Mixture: Synthesis and Mechanical Properties

“…[2][3][4][5][6][7][8][9][10][11] Recently, a new method to create gradient materials has been developed. [12,13] Compared to what is usually encountered in the literature, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] the originality of this method relies on the fact that it does not make use of a mixture containing at least one polymer, but it involves a photopolymerization reaction of a homogeneous system, that is to say a system of monomers and oligomers. The principle is based on two steps.…”