The incorporation of chloroalkyl substituents in well-behaved bulk free radical polymerization systems has significant potential to impact optical fiber and lens applications via its associated refractive index and homogeneous blend forming characteristics. To employ such properties this polymer must be prepared and processed under optically clean conditions. The benchmark optical polymer poly(methyl methacrylate) can be prepared as a monomer-polymerized casting with &gt;99% monomer conversion and with molecular weight control for melt viscosity adjustment in subsequent processing at 230°C. The objective of this work was to analogously prepare and characterize polymers from the monomer series CH2=C(CH3)C(O)OCH2CH3-nCln, n = 1,2,3. An unexpected finding was that each member produces a crosslinked polymer under bulk polymerization conditions. Their crosslink densities correlate with the quantity of added chain transfer agent and with the degree of chlorine substitution in the respective monomer (n=1 &gt; n=2 &gt; n=3). This latter effect is further quantified by chain transfer measurements on the pendant group model compound series CH3C(O)OCH2CH3-nCln, n = 0,1,2,3 in a methyl methacrylate polymerization with a parallel finding for the order of the transfer constants (n=1 &gt; n=2 &gt; n=3 &gt; n=0). An understanding of this result is further probed by chain transfer measurements on three series of chloroalkane compounds as depicted below. Key results are the low chain transfer activity associated with the –CCl3 moiety and the high transfer activity of the t-butyl chloride isomer. The crosslinking during polymerization can be eliminated by using an excessive quantity of mercaptan chain transfer agent or by diluting with an inert solvent (benzene) to a monomer concentration of ≤10% by volume. In the former case the molecular weight is depressed below that useful for melt processing. In the latter the molecular weight distribution becomes quite broad (dispersity &gt;8) which is a significant issue in molecular weight control for melt processing.

Polymerization of mono-, di- and trichloroethyl methacrylates: A study in chain transfer

251st National Meeting (2016)

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