Synthesis of Silica-Strengthened
Poly(methylmethacrylate) Using Reversible AdditionFragmentation Chain Transfer Polymerization
Christy Petruczok1 and Dr. Devon Shipp2
In recent years it has become apparent that adding nanoparticles to samples of polymers greatly
increases the samples’ mechanical strength and resistance to heat deformation (3). Given the diverse
applications of polymers—poly(methylmethacrylate), the material used in this particular experiment, is
the key component of Plexiglas windows—it is obvious that these qualities are generally considered
greatly desirable. In this treatment of the topic, Reversible Addition-Fragmentation Chain Transfer
(RAFT) polymerization was used to grow chains of poly(methacrylate) (PMMA) on silica nanoparticles.
The RAFT polymerization technique was chosen for its ability to efficiently generate low polydispersity
polymers with predictable molecular weights (Figure 1). Chains created by this process ideally grow
simultaneously at the same rate—as a result, they have approximately the same length (i.e. low
polydispersity). Such polymers are expected to have homogenous properties, especially when compared
with more polydisperse chains (4).
A conventional RAFT polymerization contains three primary components—a monomer, a radical
initiator, and a chain transfer (RAFT) agent. In summation, the initiator generates radicals, which
propagate into polymeric chains. The RAFT agent “caps” the radicals on the ends of these chains,
temporarily stopping propagation. This capping process is reversible—when the agent is removed from
the chain, growth resumes. Since the total amount of time spent capping and uncapping is miniscule
relative to that spent propagating, all chains essentially grow incrementally at the same rate (5).
The aim of this experiment was to combine the positive attributes of RAFT-synthesized PMMA
with the strengthening effects of silica nanoparticles. The resulting nanocomposite is expected to have
greatly improved mechanical and thermal properties. Additionally, the nanoscopic size of the silica
utilized allows the product to retain its transparency, an essential quality for many Plexiglas applications.
As shown in Scheme 1, benzoic acid and phosphorus pentasulfide were combined with AIBN, the radical
initiator. The mixture was heated in toluene for 1h at 110°C. Cyanoisopropyl dithiobenzoate (CPDB),
the resulting RAFT agent, was combined with silica particles, MMA monomer, and additional AIBN.
Propagating radical polymer chains grew through the propyl methacrylate monomer covalently attached
to the silica. The new chains were capped by the RAFT agent, resulting in low polydispersity polymers
attached to silica nanoparticles. Preliminary results regarding the synthesis of PMMA using both in situgenerated and pre-made RAFT agents are promising—polydispersities of less than 1.25 have been
obtained. Further results regarding synthesis of the nanocomposite will be discussed during the
presentation.
O
OH +
CN
Benzoic Acid
+ P4S10
N N
CN
S
toluene
S
1 hr, 110oC
CN
AIBN
CPDB
O
MMA
O
O
SiO2
O
+ AIBN
S
NC
O
S
O
PMMA
PMMA bound to SiO2
Figure 1: Characteristics of
molecular weight development in
RAFT polymerization
1
Scheme 1: Synthesis of PMMA and silica
nanocomposites using RAFT polymerization
Class of 2008, Department of Chemical Engineering, Clarkson University, Honors Program, Oral Presentation
Project Advisor, Department of Chemistry, Clarkson University
3
Ash, B. J.; Siegel, R. W.; Schadler, L. S. Macromolecules 2004, 37, 1358.
4
Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P.; Mayadunne, R. T. A.; Meijs, G. F.; Moad,
C. L.; Moad, G.; Rizzardo, E.; Thang, S. H. Macromolecules 1998 , 31 , 5559.
5
Shipp, D. A. J. Macromol. Sci., Part C: Polym. Revs. 2005, 45, 171.
2