§177.1420 Isobutylene polymers
Isobutylene polymers may be safely used as components of articles intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food, in accordance with the following prescribed conditions:
（a） For the purpose of this section, isobutylene polymers are those produced as follows:
（1） Polyisobutylene produced by the homopolymerization of isobutylene such that the finished polymers have a molecular weight of 750,000 （Flory） or higher.
（2） Isobutylene-isoprene copolymers produced by the copolymerization of isobutylene with not more than 3 molar percent of isoprene such that the finished polymers have a molecular weight of 300,000 （Flory） or higher.
（3） Chlorinated isobutylene-isoprene copolymers produced when isobutylene-isoprene copolymers （molecular weight 300,000 （Flory） or higher） are modified by chlorination with not more than 1.3 weight-percent of chlorine.
（b） The polymers identified in paragraph （a） of this section may contain optional adjuvant substances required in the production of the polymers. The optional adjuvant substances required in the production of the polymers may include substances generally recognized as safe in food, substances used in accordance with a prior sanction or approval, and aluminum chloride.
（c） The provisions of this section are not applicable to polyisobutylene used in food-packaging adhesives complying with § 175.105 of this chapter.