Abstract: Innovation is the core driver of leading development, and promoting high-quality economic development must elevate the issue of IPR protection to a national strategic level. As a typical combination of IPR protection policies, the pilot policy of model cities for IPR protection makes up for the shortcomings of the IPR protection mechanism, stimulates the innovation vitality of enterprises, and accelerates the transformation of scientific and technological achievements. Observing Chinese A-share listed enterprises from 2007 to 2020, the asymptotic DID model is constructed to examine the impact of IPR protection on enterprise innovation quality in a quasi-natural experiment with IPR demonstration cities, which effectively avoids the interference of other influencing factors on the estimation results. For the measurement of enterprise innovation quality, patent cited data and patent knowledge width are used as proxy variables for enterprise innovation quality, which effectively reduces the error of indirectly measuring innovation quality using patent quantity measurement. The study results show that, on the one hand, the pilot policy of IPR demonstration cities has a significant positive impact on the innovation quality of enterprises, and the estimation results using the OLS model and FE model are non-differential. The event study method results indicate that the impact of the pilot policy of IP demonstration cities on the quality of corporate innovation satisfies the parallel trend hypothesis, and the impact of the pilot policy on the quality of corporate innovation shows an increasing trend from year to year. The main regression results remain significantly positive after a series of robustness tests such as the placebo test, instrumental variables, replacing the explanatory variables, excluding the interference of other policies, and controlling for the time trend term. On the other hand, based on the analysis of institutional change theory and externality theory, it is found that IPR protection has a positive impact on the quality of enterprise innovation mainly through two transmission paths, namely, stimulating enterprises' substantive technological innovation and optimizing resource allocation efficiency. First, the pilot policy of intellectual property protection provides enterprises with an excellent institutional environment and perfect judicial protection, which effectively stimulates enterprises to launch substantive technological innovation and positively impacts the quality of enterprise innovation. Second, the pilot policy of intellectual property protection provides an excellent macro environment for enterprises to introduce high-technology talents and high-technology-rich capital, which helps enterprises adjust the allocation efficiency of innovation factors and positively impacts the quality of innovation. In addition, the heterogeneity analysis finds that the nature of firm ownership and the administrative level of the city have heterogeneous effects on the quality of innovation of firms affected by IPR protection. First, from the perspective of enterprise ownership, the impact effect of IPR protection policy is more beneficial to improve the technological innovation quality of non-state-owned enterprises compared to state-owned enterprises; second, from the perspective of heterogeneity of administrative level and function of cities, the policy only improves the innovation quality of enterprises in cities with high administrative level compared to enterprises in general cities. Based on this, implementing the construction of a robust IP strategy, promoting high-quality development of technological innovation, and forming a high-quality IP governance system need to pay attention not only to the driving role of institutional policies but also to the stimulating effect of incentive policies on the endogenous motivation of enterprises for high-quality development. Finally, there are still points for further research on this topic due to the space limitation. On the one hand, the study on the path mechanism of intellectual property protection inhibiting enterprise innovation has not been empirically tested. On the other hand, there is a lack of examining the impact of IPR protection on enterprise innovation quality based on the perspective of the knowledge spillover effect. Therefore, examining the research on the potential inhibitory paths of IPR protection on enterprise technological innovation and the relationship between IPR protection and enterprise innovation activities based on the technology spillover effect is an important direction to focus on in the future.

Key words: intellectual property protection, quality of innovation, DID, substantive technological innovation, resource allocation efficiency