the present invention is concerned with core and shell polymeric particles having microvoids in the core and one or more channels connecting the microvoids to the exterior of the particle . these particles , or lcaps are produced by forming a core of polymeric acid , encasing the core in a shell polymer permeable to base , and then neutralizing the core such that the core swells , causing the shell to &# 34 ; explode &# 34 ; in a controlled fashion . this controlled explosion causes channels to form in the shell . these particles can be used as control release devices for target compounds , to impart reinforcing properties to acrylic films , as an opacifying agent in coating compositions , and as a supplement or replacement of part or all of the pigmentary material or extenders that would otherwise be used in such coating compositions .