Acrylic flexible light pipe of improved photo-thermal stability

A process for preparing a crosslinkable core mixture for a subsequently-cured composite comprising a coextruded cladding polymer and a coextruded crosslinkable core mixture, which mixture contains a thermoplastic core polymer having a weight average molecular weight from about 2,000 to about 250,000 daltons, the process comprising

• a.) preparing an admixture of
• i) from about 80 to about 99.9 weight percent of a bulk monomer mixture selected from a C1-C18 alkyl acrylate or mixtures thereof with up to 50 weight percent of the bulk monomer mixture of a C1-C18 alkyl methacrylate;
• ii) from about 0.1 to about 18.2 weight percent of a functionally reactive monomer, and
• iii) from 0 to about 10 weight of a refractive index increasing monomer selected from styrene, benzyl acrylate, benzyl methacrylate, phenylethyl acrylate or phenylethyl methacrylate;
• b) adding 0.002 to 0.3 weight percent, based on the uncrosslinked copolymer weight, of an azo initiator of polymerization;
• c) prior to, simultaneously, or after the addition of the initiator, adding 0.2 to 2.0 weight percent, based on the uncrosslinked copolymer weight, of a chain transfer agent;
• d) charging the monomer admixture, initiator, and chain transfer agent reaction mixture to a constant-flow stirred reactor heated to 70-120° C., to form a polymerized, non-crosslinked, crosslinkable core mixture
• e) devolatilizing the polymerized, non-crosslinked, crosslinkable core mixture to remove unreacted monomers;
• f) prior to, during, or after the devolatilization and/or co-extrusion, adding from 0.1 to 10 weight percent, based on the crosslinkable core mixture weight, of a reactive additive;
• g) prior to, during, or after the devolatilization adding from 0.01 to 1.0 weight percent, based on the crosslinkable core mixture weight, of a stabilizer/antioxidant combination comprising 20-80 weight percent, based on the combination, of a phosphite which is hydrolytically stable and 80-20 weight percent, based on the combination, of a hindered phenol;
• h) coextruding the crosslinkable core mixture and the cladding polymer to form a curable composite.