Here is a halacha snippet from another website. Not that rov poskim argue on this.
Those who believe that one should immerse plastic utensils without a blessing (see Darkei Teshuva 120:14 and Dayan Weiss, Teshuvot Minchat Yitzchak 3:76-78 and 4:114) present the following argument: The Rabbis require glass utensils to be immersed due to their similarity to metal utensils, in that both metal and glass utensils can be repaired if they are broken or shattered. The minority view argues that since plastic utensils can be repaired, they are also required to be immersed due to their similarity to metal utensils. These authorities suggest that the rabbinic enactment recorded in the Talmud should be viewed as a requirement to immerse any utensil that can be repaired if broken.