Cellulose polystyrene graft copolymers

Bonding of hydrophobic plastic materials to wood to create new wood-plastic (polystyrene) materials with improved mechanical and physical properties that incorporate the desirable features of each constituent is difficult to achieve. This is due to poor interfacial adhesion between the wood and polystyrene components because of their inherent incompatibility. New, well-defined, tailored cellulose-polystyrene graft copolymers have recently been prepared using anionic polymerization techniques. Preliminary bonding studies showed that these graft copolymers can function effectively as compatibi-lizers or interfacial agents to bond hydrophobic plastic (polystyrene) material to wood, evolving into a new class of composites. 

Preparation of Cellulose-Polystyrene Graft Copolymers. The polystyr-yl mono- and di-carbanions were prepared in THF at -78 °C by using n-butyl lithium and sodium naphthalene as the initiators, respectively. The carban-ions were reacted with dry carbon dioxide. The products were precipitated in methanol, filtered, washed with water and methanol, and dried. Size exclusion chromatography (SEC) established that the molecular weight of the polystyryl monocarboxylate was 6,200 and that of the polystyryl di-carboxylate 10,2000. The mono- and di-carboxylates were reacted with mesylated cellulose acetate in dimethylformamide at 75 °C for 20 h to give the cellulose-polystyrene graft copolymer (GP 1) and crosslinked cellulose-polystyrene graft copolymer (GP 2), respectively. 

Synthesis of Tailor Made Cellulose-Polystyrene Graft Copolymers... 

Fig. 5. Intrinsic viscosity of a cellulose acetate graft copolymer (44.1% combined polystyrene) and the corresponding homopoly-mers in toluene-acetone mixtures...

Figure 2. Continuous three-dimensional network of plastic (polystyrene) linked to wood via a cellulose-polysytrene graft copolymer.

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

Deters (14) vibromilled a blend of cellulose and cellulose triacetate. The acetic acid content of cellulose acetate decreased with grinding time (40 h) while that of the cellulose increased, suggesting the formation of a block or graft copolymer or of an esterification reaction by acetic acid developed by mechanical reaction. Baramboim (/5) dissolved separately in CO polystyrene, poly(methyl methacrylate), and poly(vinyl acetate). After mixing equal volumes of solutions of equivalent polymer concentration, the solvent was evaporated at 50° C under vacuum and the resultant product ball-milled. The examination of the ball-milled products showed the formation of free radicals which copolymerized. 

The existence of a true graft copolymer was concluded from the weight increase not extractable by polystyrene solvents and by the eventual leveling off of the weight increase while homopolymerization continued. Moreover, the graft of cellulose acetate and styrene after dissolution and precipitation with various solvents and precipitants still showed the infrared absorption of both substituents. In addition to this, the results fitted well with the kinetic theoiy of grafting proved on other systems. 

The properties of cellulosic graft copolymers have been studied to a considerable extent but mainly in the form of grafted fibers or films of ill-defined composition. However, a few properties have been measured on well defined grafts (147). It was found that solutions of cellulose acetate-polystyrene grafts in dimethyl formamide are less tolerant to the addition of polystyrene than cellulose acetate itself. This result was attributed to the greater coil expansion in the case of the graft copolymer. On the other hand, the tolerance of the grafts to each homo-... 

The acetylated true graft copolymer was dissolved in methylene chloride, acetone was added to the solution to obtain a 1 1 methylene chloride-acetone composition of the solvent, concentrated hydrochloric acid was added to obtain a 3N solution, and hydrolysis was carried out for 72 hr at 60 °C. The hydrolysis proceeded not in a homogeneous but in a highly swollen state. The branch was precipitated by pouring the hydrolysis mixture into methanol. A part of the precipitated branch was dissolved in m-cresol and filtered. The other part was treated with 1 2 acetic anhydride-pyridine mixture for 15 hr at 100 °C to acetylate cellulose fragments at the end of polystyrene brandies. 

Similar polymer compatibilization effects were observed by Wellons and co-workers (19) on radiation graft copolymers of cellulose acetate and polystyrene and by Riess and his colleagues (20) on various block copolymers. Hughes and Brown (21) also reported some evidence of compatibilization in a... 

Pendant nitro groups are also effective in chain-transfer grafting reactions. Thus, graft copolymers of polystyrene with cellulose acetate p-nitrobenzoate and with poly(vinyl p-nitrobenzoate) form readily. Nitro groups appear to be more effective in formations of graft copolymers by a radical mechanism than are double bonds located as pendant groups. " ... 

In general, graft copolymers consist of a polymer backbone to which another polymer is chemically attached as side chains. The backbone and side chain polymers may be homopolymer, random copolymers, block copolymers or mixtures of the various types. For example, most graft copolymers of cellulose consist of a homopolymer backbone (cellulose) and another homopolymer (e.g. polystyrene) or a random copolymer (e.g. polystyrene-co-acrylic acid). 

The chemical modification of homopolymers such as polyvinylchloride, polyethylene, poly(chloroalkylene sulfides), polysulfones,poly-chloromethylstyrene, polyisobutylene, polysodium acrylate, polyvinyl alcohol, polyvinyl chloroformate, sulfonated polystyrene block and graft copolymers such as poly(styrene-block-ethylene-co-butylene-block-styrene), poly(1,4-polybutadiene-block ethylene oxide), star chlorine-telechelic polyisobutylene, poly(lsobutylene-co-2,3-dimethy1-1,3-butadiene), poly(styrene-co-N-butylmethacrylate) cellulose, dex-tran and inulin, is described. 

A large variety of polymers has been considered. In the beginning, polystyrene and styrene/ divinylbenzene copolymers (Merrifield resins) were by far the most used.73 Then others were tested such as polyvinyls,47-50,61-64 polyacrylates,72 4,75 and cellulose.76,77 Most commonly, diphenylphos-phane groups were grafted on the polymeric support, either directly or via one CH2 group. 

Keqiang [43] has successfully produced block copolymers, based upon cellulose, while Henglein has been able to produce both graft and block copolymers using polystyrene and polymethyl methacrylate. Price [68] has shovm that the irradiation of mixtures of polystyrene and poly(cis-butadiene) and separately polystyrene and... 

Most synthetic methods for the generation of peptide libraries have been derived from various multiple parallel peptide synthesis techniques developed since 1984.bs-i l Consequently, the sohd supports used for hbrary synthesis are essentially the same as those used for multiple peptide synthesis. Standard divinylbenzene cross-linked polystyrene resins are typically used for hbraries that are cleaved from the resin and screened in solution.P Polyoxyethylene-grafted polystyrene resins,f l or acrylamide-polyoxyethylene copolymers, P on the other hand, are the sohd supports of choice for the synthesis of resin-bound peptide hbraries screened in sohd-phase binding assays.P Such resins are compatible with both organic solvents used for peptide synthesis, as well as aqueous buffers used in the bioassays. Various segmental supports previously employed for multiple peptide syntheses have also been utilized for the synthesis of peptide libraries, including polypropylene pins, PI cotton,t cellulose membrane,and glass shdes.P ... 

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