Using an in situ Diels Alder (DA) "click chemistry" strategy for reactions between anthracene and maleimide functional groups, two prototypes of novel nonlinear optical (NLO) side-chain polymers (PMI-A7 and PMI-B7) containing highly hyperpolarizable but chemically sensitive phenyltetraene-based chromophores were synthesized and their nonlinear optical and thermal properties were characterized. Through rational material design, these NLO side-chain polymers exhibited good processibility, large electro-optic (E-O) coef?cients (r33, of up to 263 and 287 pm/V at 1.31 μ m wavelength respectively), and excellent temporal stability. These combined properties make them promising materials for E-O device applications. Compared to PMI-B7, PMI-A7 exhibited signi?cantly enhanced temporal stability (87% of the initial r33 values was retained after 550 h at 85 °C) and solvent resistance, which was attributed to slight cross-linking from the side reaction between maleimide and phenyltetraenic chromophore moieties. This study showed that it is possible to take advantage of some side reactions to enhance the performance of NLO materials.