The use of reactive tri-block copolymers of styrene (S), glycidyl methacrylate (GMA), and butyl acrylate (BA) synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization as chain extenders of recycled poly (ethylene terephthalate) (R-PET) by melt processing is reported. Emphasis is placed on the influence of controlled copolymer structures and glycidyl methacrylate content on physical properties, thermal properties and rheological behavior of recycled PET. RAFT-synthesized reactive copolymers turned out to be very effective chain extenders leading to an increase in the molar mass intrinsic viscosity and diminished melt flow, indicating better melt elasticity and processability of R-PET. Tensile and impact analysis showed that functional GMA blocks reacted with PET end groups, causing a dramatic increase in the elongation-at-break and significant improvement of impact and tensile strength. Complex viscosity and rheological moduli of R-PET also increase greatly, indicating that flexibility of modified R-PET is improved. The van Gurp-Palmen plot of chain extended R-PET confirms the increase in melt elasticity.