Chromophore functionalised maleimide copolymers with high poling stabilities of the nonlinear optical effect at elevated temperature C. Samyn a, * , W. Ballet a , T. Verbiest b , M. Van Beylen a , A. Persoons b a Laboratory of Macromolecular and Physical Organic Chemistry, Katholieke Universiteit Leuven, Celestijnenlaan 200F, B-3001 Heverlee, Leuven, Belgium b Laboratory of Chemical and Biological Dynamics and Center for Research on Molecular Electronics and Photonics, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium Received 8 April 2001; received in revised form 27 May 2001; accepted 27 May 2001 Abstract Nonlinear optical polymers with high glass transition temperatures were prepared by covalent functionalisation of polymaleimide copolymers with hydroxyalkyl chromophores via the Mitsunobu reaction. The polymaleimides were obtained by radical polymerisation of maleimide with 4-phenylstyrene PM1), indene PM2) or 1-adamantylmethacrylate PM3). Glass transition temperatures in the range of 222±2888Cwereobtained.Thinspincoated®lmsofthepolymerswerecorona-poledandanalysedbysecond-harmonicgeneration;second- ordersusceptibilityvaluesd 33 )upto16pm/Vwereobtained.Poledorderstabilitymeasurementsoverperiodsofmorethan200hresultedin 72±90% of remaining NLO-response at 1258C. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Polymaleimide; Nonlinear optics; Stability 1. Introduction Second-order nonlinear optical NLO) polymers are of considerable interest for the development of high-speed modulators and switches. Several important properties are required to be useful in applications for devices, e.g. large optical nonlinearities, low optical loss and stability of the NLO-response in function of time at prolonged elevated temperatures[1].Networkformationorcrosslinkingduring poling is one of the approaches to solve the problem of poled-order stability [2,3]. Another approach is the synthe- sis of high glass transition T g ) polymers, such as poly- imides, that combine high NLO properties with good thermal stability [4±10]. Maleimide based polymers functionalised with chromophores also result in high T g materials which, depending on their composition, give access to the existence of high thermal stability of the NLO-effect [11±13]. So far the latter have been prepared byapolymeranalogousreactionofanaminofunctionalised chromophore and a polymaleic anhydride) precursor copolymer, which gives formation of a polyamic acid) copolymer that by reaction with acetic anhydride/pyridine undersmoothconditionsresultsintherespectivemaleimide copolymer.Asmaleicanhydridecopolymersaresensitiveto moisture, the polymers should be isolated under inert atmosphere and afterwards transformed into the respective chromophore functionalised polymaleimides by a two step reaction with aminoalkyl chromophore, which itself is dif®cult to purify and can give rise to irregularities in the copolymer structure. To avoid this harsh procedure, the aim of our investigation is the synthesis of maleimide copolymers with 4-phenylstyrene, indene and adamantyl methacrylate, respectively. These precursor polymers will then be functionalised with hydroxyalkyl chromophores in the presence of triphenylphosphine and diethylazodicar- boxylate under Mitsunobu conditions [14]. In this way copolymers with a varied concentration of chromophore functionalised maleimide units may be obtained which will result in copolymers with different glass transition temperatures and high second-order nonlinearities. 2. Experimental part 2.1. Materials and instrumentation All reagents were purchased from Aldrich Chemical Co. and Acros Organics. Maleimide and 2,2 0 -azobisisobutyro- nitrilewerepuri®edbycrystallisationfromethylacetateand methanol, respectively. Reagent grade solvents were dried when necessary and puri®ed by distillation. Polymer 42 2001) 8511±8516 0032-3861/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII:S0032-386101)00405-0 www.elsevier.com/locate/polymer * Corresponding author. Tel.: 132-16-327-438; fax: 132-16-327-990. E-mail address: celest.samyn@chem.kuleuven.ac.be C. Samyn).