monomers b 1 is an n valent organic linking group preferably comprising ethylenic unsaturation or b 1 is absent suitable single valent b 1 groups preferably have the formula u2014 cr 8 u2550 cr 9 z wherein r 8 and r 9 are independently selected from hydrogen alkyl groups of 1 to 6 most preferably 1 to 3 carbon atoms and aryl groups and z is selected from hydrogen alkyl groups of 1 to 6 carbon atoms aryl groups u2014 co 2 r 7 wherein r 7 is an alkyl group preferably up to 6 carbon atoms an aryl group an aralkyl group or an alkaryl group most preferably z is u2014 co 2 r 7 wherein r 7 is an alkyl group preferably up to 6 carbon atoms an aryl group an aralkyl group or an alkaryl group suitable divalent b 1 groups include u2014 cr 8 u2550 cr 9 o u2014 z u2032 o 1 wherein r 8 and r 9 are as defined previously o is 1 or 2 and z u2032 is an alkyl group of 1 to 6 carbon atoms an aromatic group or a siloxane group most preferably o is 2 and z u2032 is a siloxane group ar 1 is a polyvalent aromatic or heteroaromatic group and the carbon atoms of the cyclobutane ring are bonded to adjacent carbon atoms on the same aromatic ring of ar 1 preferably ar 1 is a single aromatic ring n is an integer of 1 or more preferably 2 4 more preferably 2 and r 1 is a monovalent group preferably hydrogen lower alkyl of up to 6 carbon atoms the synthesis and properties of these cyclobutarenes as well as terms used.