2014 AIChE Annual M eeting
Toughening of Thermosets from Epoxy and Poly(styrene-alt-maleic anhydride)-Polystyrene-Block-Poly(n-butyl acrylate)-Block-Polystyrene Tetrablock Copolymer (SMA-SBAS) Synthesized Via RAFT Mini-Emulsion Polymerization

Abstract

Epoxy resins is one of the main commercial thermosets and widely been applied as the matrices of composites, adhesives, powder coatings and electronic encapsulations. However, epoxy resins are brittle materials due to its highly-crosslink nature. Recently, block copolymers (BCPs) have been shown to be highly effective at improving mechanical properties of thermosets. To form ordered or disordered nanostructures in thermosets, reactive or miscible functionalities
are usually incorporated into BCPs, such as eSBS1, PEO-PEP2, SBM3, 4 and MAM5, 6 etc. These
nanostructured thermosets have improved mechanical properties: they keep high modulus and are super-tough. Meanwhile, reactive block copolymers were considered to be able to minimize reaction-induced phase separation (RIPS) during the curing process using certain hardeners, but are scarcely investigated because of the narrow composition window and restricted monomers via
anionic polymerization7-9.
On the other hand, reversible addition-fragmentation chain transfer radical (RAFT) polymerization have been investigated extensively over the last few years because these methods are compatible with almost all types of vinyl monomers and with emulsion polymerization processes where water is used as polymerization media10. BCPs with large amount of various reactive groups can be prepared by optimizing polymerization process, i.e. RAFT mini-emulsion polymerization.
Based on the method of RAFT mini-emulsion polymerization, the styrene/butyl acrylate block copolymer (SMA-SBAS) was successfully synthesized, mediated by maleic anhydride/styrene alternating copolymer (SMA) as the amphiphilic macroRAFT agent5-7. SMA-SBAS (10%)/ diglycidyl ether of bisphenol A (DGEBA, epoxide equivalent weight
180~190)/MDA blends achieve a nano-micro phase separation. TEM results revealed that due to the compatibility of SMA block with DGEBA matrix and immiscible polystyrene-b-poly-n-butyl acrylate-b-polystyrene chains, they self-assemble to form nano-micro structured spherical micelles. These nano-micro structured thermosets showed 2 folds increase in KIC and 6 folds increase in notched impact strength, while at the same time, brings slight reductions in tensile stiffness, strength and glass transition temperature. This work demonstrated that the RAFT mini emulsion polymerization holds good promise for preparing copolymers with reactive functional blocks, with which high-performance nanocomposites can be achieved.

S

y

z n O OC4H9

O O

O

COOH

NH2

O N H

+ H2O

O

COOH

O O

OH

Two modes of Incorporation of SMA in the Epoxy-Anime System

12.5

10

10% SMA-SBAS

7.5

5

2.5

Neat

Epoxy

10% SBS

0

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