UV-Curable Biobased Polyacrylates Based on a Multifunctional Monomer Derived from Furfural

The controlled polymerization of
a new biobased monomer, 4-oxocyclopent-2-en-1-yl
acrylate (4CPA), was established via reversible addition–fragmentation
chain transfer (RAFT) (co)­polymerization to yield polymers bearing
pendent cyclopentenone units. 4CPA contains two reactive functionalities,
namely, a vinyl group and an internal double bond, and is an unsymmetrical
monomer. Therefore, competition between the internal double bond and
the vinyl group eventually leads to gel formation. With RAFT polymerization,
when aiming for a degree of polymerization (DP) of 100, maximum 4CPA
conversions of the vinyl group between 19.0 and 45.2% were obtained
without gel formation or extensive broadening of the dispersity. When
the same conditions were applied in the copolymerization of 4CPA with
lauryl acrylate (LA), methyl acrylate (MA), and isobornyl acrylate,
4CPA conversions of the vinyl group between 63 and 95% were reached.
The additional functionality of 4CPA in copolymers was demonstrated
by model studies with 4-oxocyclopent-2-en-1-yl acetate (1), which readily dimerized under UV light via [2 + 2] photocyclodimerization.
First-principles quantum mechanical simulations supported the experimental
observations made in NMR. Based on the calculated energetics and chemical
shifts, a mixture of head-to-head and head-to-tail dimers of (1) were identified. Using the dimerization mechanism, solvent-cast
LA and MA copolymers containing 30 mol % 4CPA were cross-linked under
UV light to obtain thin films. The cross-linked films were characterized
by dynamic scanning calorimetry, dynamic mechanical analysis, IR,
and swelling experiments. This is the first case where 4CPA is described
as a monomer for functional biobased polymers that can undergo additional
UV curing via photodimerization.