Methyl methacrylate-starch graft copolymers

The ozonization method has been extended to the most varied polymer/monomer systems, such as polybutadiene-03 with acrylamide, methyl methacrylate or styrene, cellulose-03 with styrene or acrylonitrile (127), starch-03 with styrene (126). In this last case the formation of some homopolystyrene as side-product has been mentionned by the authors. The starch-styrene graft copolymers are claimed to be good emulsifiers for water-oil suspensions. 

Aluminoxanes suppressed side reactions involving hydrogen transfer. They also formed cyclic structures with starch, giving copolymers that were coated with crystalline polyethylene. A catalyst composed of dicyclopentadienylzirconium dichloride and trimethylaluminium permitted polymerization of ethylene on starch in a toluene suspension at 60 °C for 2h.2806 Graft copolymerization of methyl methacrylate onto starch was also performed with an acetylacetone-copper(II) complex in trichloroacetic acid.2807 The grafting yield and efficiency were proportional to the initiator concentration up to 7.0 x 10-3 mole/L. 

Graft copolymers of A and B monomers are named poly(A-g-B) or poly A-grafi-poly B with the backbone polymer -(-A-)/j— mentioned before the branch polymer. Some examples are poly(ethylene-g-styrene) or polyethylene-grq/i-poly styrene and starch-grayi-poly(methyl methacrylate). In the nomenclature of block copolymers, b or block is used in place of g or graft, e.g., poly(A- -B) or poly A-block-po y B, poly(A-b-B-b-A) or poly A-block-po y B-block-po y A, poly(A-b-B-b-C) or poly A-block-poly B-block-poly C, and so on. Thus the triblock polymer (XX) is called poly(styrene- -butadiene-i -styrene) or polystyrene- /cck-polybutadiene-b/ock-polystyrene. For commercial products, such polymers are usually designated by the monomer initials thus, structure (XX) is named SBS block copolymer. 

Copolymers of Vinylidene Chloride. The glass-transition temperatures of these copolymers vary nonlinearly with composition, as is the case for copolymers of methyl methacrylate, but these show a maximum. It is a broad maximum around 105 C at 55-80 wt% acrylonitrile. (The Tg of vinylidene chloride homopolymer is ca -20°C, whereas PAN s is ca 100°C.) Again, sequence distribution explains such behavior (163). These copolymers have good barrier properties and are used for surface Coatings. Acrylonitrile grafting on starch imparts hydrophilic behavior to starch and results in exceptional water absorption capability (164-167). These copolymers can also immobilize enzymes by entrapment or covalent bonding (168). 

---