Radical-induced grafting

Modifications of epichlorohydrin elastomers by radical-induced graft polymeri2ation have been reported. Incorporated monomers include styrene and acrylonitrile, styrene, maleic anhydride, vinyl acetate, methyl methacrylate, and vinyHdene chloride (81), acryHc acid (82), and vinyl chloride (81,83,84). When the vinyl chloride-modified epichlorohydrin polymers were used as additives to PVC, impact strength was improved (83,84). 

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

A major issue is the control of the side reactions that accompany grafting. These reactions include radical-induced degradation of the substrate by cross-linking and/or chain scission and homopolymerization of the graflee monomer. 

With a history of more than 25 years, the free radical-induced grafting of MAH onto polyolefin substrates is one of the most studied polyolefin modification processes.29 "29, 302 The process has been carried out in the melt phase, in various forms of extruders and batch mixers, and there are numerous patents covering various aspects of the process. It has also been carried out successfully in solution and in the solid state. The materials have a range of applications including their use as precursors to graft copolymers, either directly, or during the preparation of blends.297... 

Radical grafting, 10 206 Radical-induced decompositions, 14 280 of dialkyl peroxydicarbonates, 14 289 Radical ozone reactions, 17 774 Radical polymerization, 22 40. See also Free-radical polymerization controlling, 14 297 of methacrylic ester polymers, 16 279-290... 

In the present paper, we report on the compatibilization of clay with polyolefins, specifically low and high density poly-ethylenes (LDPE, HDPE), through the radical-induced polymerization of maleic anhydride (MAH) in the presence of the polymer and clay, so that the MAH is grafted on the PE and the anhydride groups concurrently react with the filler surface (l, 2). 

With a few exceptions, most graft copolymers from free radical induced grafting processes usually produce not only the desired graft copolymers, but also homopolymers and other side reactions. Consequently, the exploration and detailed characterization of grafts produced by free radical methods is often cumbersome. 

Vainio et al. (1997, 1996a) have compatibilized PEST/PP blends by graft copolymer formation between acid-terminated polyester and oxazoline-grafted PP. Specifically, 30 parts PBT was mixed with 0-70 parts PP and 0-70 parts PP-g-oxazoline in an internal mixer at 250 °C or TSE at 240 °C. Blends were characterized by SEM, torque rheometry, DMA, and DSC. Oxazoline-functionalized PP was prepared by grafting PP with ricinol oxazoline maleinate in the presence of styrene monomer + RI. The inclusion of styrene monomer suppresses radical-induced decomposition of PP. Some cross-linked copolymer... 

V.K. Thakur, M.K. Thakur, and A.S. Singha, Free radical-induced graft copolymerization onto natural fibers. Int. J. Polym. Anal. Char. 18(6), 430-438 (2013). 

The title of this chapter has also been slightly amended, Reactions on Polymers being preferred to Reactions of Polymers because the former is more specific. Nevertheless, a great diversity of material could still be included under the new title and as before a measure of selectivity has been imposed. Again, photochemistry, crosslinking reactions, and direct radiation or radical-induced grafting reactions have been omitted. 

The present investigation was undertaken in an attempt to correlate the proposed participation of cationic intermediates in the radical-induced homopolymerization of MAH with the use of MAH polymerization conditions in the graft copolymerization onto PE. 

Sundar S, Kundu J, Kundu SC (2010) Biopolymeric nanoparticles. Sd Technol Adv Mater 11 (1) 014104. doi 10.1088/1468-6996/11/1/014104 Thakur VK, Kessler MR (2014a) Free radical induced graft copolymtaization of ethyl acrylate onto SOY for multifunctional materials. Mater Today Commun. doi 10.1016. mteonun.2014. 09.003... 

Chain transfer reactions mostly proceed by abstraction of a monovalent atom such as hydrogen or a halogen. The scission of a bond carbon - oligovalent (e.g., H) atom is of interest for the introduction of endgroups into a polymer produced in a free radical reaction. Radically induced vinyl monomer polymerization with the possibility of chain transfer to a polymer of different chemical structure present in the reaction mixture leads to graft copolymers if bond scission occurs outside the main chain, no matter whether a single atom or a grouping is abstracted. Quite a different result is obtained if a radical attack involves a bond in the main chain of the polymer, if this bond scission occurs at a monovalent atom, which must be at the chain end, there is block copolymer formation. If bond scission occurs inside the polymer backbone, either block or random copolymers are produced [63]. 

Scheme 5 Synthesis of highly pure block copolymers by combination of RAFT polymerization, azide-alkyne click reaction, and de-grafting, in which cleavage of grafted chains from a silica surface can be achieved by either aminolysis or radical-induced addition-fragmentation reactions (RIAFR). Adapted from Zhao et al. [20]...

Stenstad et al. [27] grafted both succinic and maleic anhydride to the surface of microfibrillated wood pulp under water-free conditions. This method introduced negative charge onto the fibril surfaces. Grafting of maleic anhydride to the MFC surface introduced vinyl groups that may serve as starting point for further radical-induced polymerization reactions. Grafting was confirmed qualitatively by FT-IR. The DS was 0.8 and 0.3 for succinic and maleic acid, respectively, as evaluated by XPS. 

---