Studies of methyl methacrylate–glycidyl methacrylate copolymers: Copolymerization to low molecular weights and modification by ring‐opening reaction of epoxy side groups

Abstract

Abstract The copolymerization of methyl methacrylate (MMA) with glycidyl methacrylate (GMA) at 60°C with 2,2′‐azobisisobutyronitrile (AIBN) as radical initiator and in the presence of thiophenol (TP) as chain‐transfer agent has been investigated. Monomer reactivity ratios for MMA and GMA are found to be r 1 (MMA) = 0.80 ± 0.015 and r 2 (GMA) = 0.70 ± 0.015, from which Q and e values are calculated to be 0.68 and −0.36 for GMA. The initial rate of copolymerization R p at 60°C with AIBN (0.02 mole/l.) and TP (0.1, 0.01 mole/l.) were found to increase nonlinearly with increasing GMA concentration in the monomer feed. Homopolymerizations of MMA and GMA monomers were studied in the presence and in the absence of thiophenol. The values of δ (= k t 1/2 / k p ) for MMA and GMA were determined to be 10.25 and 3.00 (mole‐sec/l.) 1/2 , respectively. Using the values r 1 (MMA), r 2 (GMA), δ 1 (MMA), δ 2 (GMA), and R p , the cross‐termination constants ϕ for MMA–GMA monomers were determined (average value ϕ = 0.42). The increase in R p values with increasing GMA content has been attributed to the cross‐termination of MMA–GMA radicals. The transfer constant of TP has also been determined for GMA and found to be 1.00. A MMA–GMA copolymer of low molecular weight, containing 2.01% of oxirane oxygen, was modified by opening of the oxirane ring of GMA by reaction with diethanolamine (DEA). The reaction was carried out at 70 ± 1°C, the copolymer content of epoxy groups and the amine being assumed to be in the molar ratio of 1:4. Addition of a hydrogen‐bond acceptor like nitrobenzene decreases, while addition of a hydrogen‐bond donor like phenol increases the rate of epoxy ring opening with DEA. This indicates that a hydrogen‐bonded intermediate is involved in this reaction and that it weakens the epoxy ring and enhances the rate of its opening with DEA. From the studies of the conversion rates, existence of a “nonspecific” side reaction has been shown which involves the reaction of the terminal epoxy groups of the copolymer and the hydroxyl groups of DEA or formed in the reaction with DEA (involves a chain coupling). DEA can be trifunctional in this reaction. This has been further confirmed from the increase of number‐average molecular weights M̄ n of the copolymers resulting from this coupling and the nitrogen content in the copolymers after modification with DEA.