Curable compositions for optical articles

Abstract

A curable composition is provided comprising an oligomer having a plurality of pendent and/or terminal ethylenically unsaturated, free-radically polymerizable functional groups, a free-radically polymerizable crosslinking agent, and/or a diluent monomer, and a photoinitiator. The composition, when cured, is non-yellowing, exhibits low shrinkage and low birefringence making it suitable for many optical applications such as optical lenses, optical fibers, prisms, light guides, optical adhesives, and optical films.

1 . A curable composition comprising: 
 a) 50 to 99 parts by weight of a (meth)acryloyl oligomer having a plurality of pendent, free-radically polymerizable functional groups and a T g  of ≧20° C.;    b) 1 to 50 parts by weight of a free-radically polymerizable crosslinking agent and/or a diluent monomer, and    c) 0.001 to 5 parts by weight of a photoinitiator, based on 100 parts by weight of a) and b).    
   
   
       2 . The curable composition of  claim 1  comprising less than 25 parts by weight of said diluent monomer.  
   
   
       3 . The curable composition of  claim 1  comprising less than 1 to 40 parts by weight of said crosslinking agent.  
   
   
       4 . The composition of  claim 1  comprising 1 to 30 parts by weight of said crosslinking agent.  
   
   
       5 . The composition of  claim 1  wherein said oligomer comprises of polymerized monomer units comprising: 
 a) 50 to 99 parts by weight of(meth)acrylate esters monomer units homopolymerizable to a polymer having a glass transition temperature ≧20° C.,    b) 1 to 50 parts by weight of monomer units having a pendent, free-radically polymerizable functional group    c) less than 40 parts by weight of monomer units homopolymerizable to a polymer having a glass transition temperature <20° C., based on 100 parts by weight of a) and b).    
   
   
       6 . The composition of  claim 5  wherein said (meth)acrylate esters are homopolymerizable to a polymer having a glass transition temperature ≧50° C.  
   
   
       7 . The composition of  claim 5  comprising 60 to 97 parts by weight of said (meth)acrylate esters monomer units, and 3 to 40 parts by weight of monomer units having a pendent, free-radically polymerizable functional group.  
   
   
       8 . The composition of  claim 5  wherein said monomer units having a pendent, free-radically polymerizable functional group are prepared by reacting monomer units having a pendent reactive functional group with a mono ethylenically unsaturated compound having a coreactive functional group.  
   
   
       9 . The composition of  claim 8  wherein said pendent reactive functional groups are selected from hydroxyl, secondary amino, oxazolinyl, oxazolonyl, acetyl acetonyl, carboxyl, isocyanato, epoxy, aziridinyl, acyloyl halide, and cyclic anhydride groups.  
   
   
       10 . The composition of  claim 1 , wherein the degree of polymerization of said oligomer is controlled by a chain transfer agent.  
   
   
       11 . The composition of  claim 1  wherein said free-radically polymerizable crosslinking agent has a functionality of at least 2, and is of the formula R-(Z) n , where Z comprises a free-radically polymerizable functional group such as a carbon-carbon double bond, n is greater than 1 and R is an organic radical having a valency of n.  
   
   
       12 . The composition of  claim 1  wherein the sum of said crosslinking agent and said diluent monomer is less than 40 parts by weight.  
   
   
       13 . The composition of  claim 1  exhibiting shrinkage of less than 5% by volume when cured.  
   
   
       14 . The composition of  claim 1  exhibiting a birefringence of less than 1×10 −6  when cured.  
   
   
       15 . The composition of  claim 1  having a T g  of >50° C. when cured.  
   
   
       16 . The composition of  claim 1  having a CIELAB b* value of less than 1.5 when cured.  
   
   
       17 . The composition of  claim 1  having an index of refraction greater than about 1.45 and less than about 1.75 when cured.  
   
   
       18 . The composition of  claim 1  having light transmission greater than about 85% when cured.  
   
   
       19 . The composition of  claim 1  wherein said oligomer is prepared by an adiabatic polymerization process.  
   
   
       20 . The composition of  claim 19 , wherein said process comprises: 
 (a) providing the oligomer composition of the invention in a batch reactor;    (b) deoxygenating the mixture, wherein step (b) can optionally at least partially overlap with step (c);    (c) heating the mixture to a sufficient temperature to generate sufficient initiator free radicals from at least one thermal free radical initiator so as to initiate polymerization;    (d) allowing the mixture to polymerize under essentially adiabatic conditions to yield an at least partially polymerized mixture;    (e) optionally heating the mixture to generate free radicals from some or all of any initiator that has not generated initiator free radicals, followed by allowing the mixture to polymerize under essentially adiabatic conditions to yield a further polymerized mixture;    (f) optionally repeating step (e) one or more times    (g) optionally repeating steps (a) to (e) one or more times with cooling between repeats.    
   
   
       21 . The composition of  claim 20  wherein said oligomer composition further comprises a chain transfer agent to control the molecular weight of the oligomer.  
   
   
       22 . The cured composition of  claim 1 .  
   
   
       23 . A shaped article comprising the cured composition of  claim 1 .  
   
   
       24 . An optical coating comprising the cured composition of  claim 1.