Grafting: a versatile means to modify polymers Techniques, factors and applications

https://www.itqb.unl.pt/~imartins/Fort_etal_2006.pdf

Can ionic liquids dissolve wood? Processing and analysis of lignocellulosic materials with 1-n-butyl-3-methylimidazolium chloride

Biodegradable Polymeric Materials

The amalgamation of polymer and pharmaceutical sciences led to the introduction of polymer in the design and development of drug delivery systems. Polymeric delivery systems are mainly intended to achieve controlled or sustained drug delivery. Polysaccharides fabricated into hydrophilic matrices remain popular biomaterials for controlled-release dosage forms and the most abundant naturally occurring biopolymer is cellulose; so hdroxypropylmethyl cellulose, hydrox- ypropyl cellulose, microcrystalline cellulose and hydroxyethyl cellulose can be used for production of time controlled delivery systems. Additionally microcrystalline cellulose, sodium carboxymethyl cellulose, hydroxypropylmethyl cellu- lose, hydroxyethyl cellulose as well as hydroxypropyl cellulose are used to coat tablets. Cellulose acetate phthalate and hydroxymethyl cellulose phthalate are also used for enteric coating of tablets. Targeting of drugs to the colon following oral administration has also been accomplished by using polysaccharides such as hdroxypropylmethyl cellulose and hydrox- ypropyl cellulose in hydrated form; also they act as binders that swell when hydrated by gastric media and delay absorption. This paper assembles the current knowledge on the structure and chemistry of cellulose, and in the development of innova- tive cellulose esters and ethers for pharmaceuticals.

/pdf/pharmaceutical-significance-of-cellulose-a-review-51cx6newob.pdf

Pharmaceutical significance of cellulose: A review

25.1 Chain Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445 25.2 Chain Entanglement and Tube Diameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 25.3 Critical Molecular Weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446 25.4 Temperature Dependence of Chain Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451

Chain Dimensions and Entanglement Spacings

Cellulose fractions of different molecular weights were subjected to dynamic thermogravimetric analysis in a nitrogen atmosphere. From the experimental data, activation energies and reaction orders were obtained following the Freeman–Carroll and Broido methods. The thermal stabilities of the samples were estimated taking into account the values of Ti, Tmax, and Ea. The results show that thermal stability increases as the molecular weight increases. It was also found that the cellulose pyrolisis process cannot be described as having a single value of Ea over the entire pyrolisis range. The dependence of Ea. The dependence of Ea on molecular weight is also discussed.

Thermogravimetric analysis of cellulose: Effect of the molecular weight on thermal decomposition

In order to graft a vinyl acetate–methyl acrylate mixture onto cellulose, an exploration of the way of addition of the reactants has been made. The influence of several factors on the grafting parameters was studied, i.e., the order of addition of the ceric ion initiator and the monomer mixture, the removal of the ceric ion solution after a cellulose-ceric ion contact time, and the delayed addition along the polymerization period of the more reactive monomer (methyl acrylate) towards the cellulosic radicals. Some grafting parameters were determined: grafting yield, grafting efficiency, cellulose conversion, molecular weight, ceric ion consumption, grafting frequency, number of grafted chains, and synthetic copolymer composition. After a short period (ca. 15 min) for the ceric adsorption on cellulose, a fast formation of cellulosic radicals arises in the initial stages of the polymerization. These initial cellulosic radicals should be trapped by a sufficiently reactive monomer if high grafting yield and high number of grafted chains are to be reached. A portion of the synthetic polymer chains anchored to cellulose that are formed in the first stages of the polymerization, which are generated from cellulosic hemiacetal groups, should constitute block copolymer.

Gonzalo M. Guzmán

Papers

Thermogravimetric analysis of cellulose: Effect of the molecular weight on thermal decomposition

Effect of the way of addition of the reactants in the graft copolymerization of a vinyl acetate–methyl acrylate mixture onto cellulose

Thermal decomposition of poly(ethylene oxide), poly(methyl methacrylate), and their mixtures by thermogravimetric method

Melting point depression in poly (ethylene oxide)-poly (methyl methacrylate) blends

Spherulitic crystallization in blends of poly(ethylene oxide) and poly(methyl methacrylate)