Hydrolyzable polymers

Poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (P(3HB-co-3HV)) has been produced commercially under the trade name of Biopol. Due to isodimorphism (Fischera et al, 2004), the mechanical properties of this copolymer are similar to that of PHB. Therefore, copolymers of 3HB and 3-hydroxyhexanoate (3HH) (Doi et al, 1995) have been produced which show high elongation at break, but low tensile strength. To increase the strength, cold-drawing and copolymerization has been proposed (Fischera et al, 2004) and the degradation has been examined (Cao et al, 1999). 

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Table 4. Swelling of hydrogels based on partly hydrolyzed polymers of methyl-2-oxazoline [62]...

The A. irakense strain is clearly able to hydrolyze pectin on solid medium. A clear halo was observed after incubation for seven days and overlayed with HTAB, indicating the degradation of pectin, whereas non-hydrolyzed polymer is precipitated. For the other Azospirilhim species, we were not able to demonstrate pectinolytic activity in this way. 

Poly(starch-g-((l-amidoethylene)-co-(sodium 1-carboxylatoethylene))). Poly(l-amidoethylene) is, however, rarely used as a viscosifier. Instead, the homopolyraer is reacted with base (hydrolyzed with NaOH) to convert some of the amide units of the polymer to carboxylic acid units. The acid units on the hydrolyzed polymer dissociate in water and produce a polyanionic polymer. This polyelectrolyte expands in water because of ion-ion repulsion and, as an enlarged molecule, is a better viscosifier. 

Viscosity of copolymer solutions decreases by, at most, 3 percent when electrolyte concentration changes from 0 to 0.342 M sodium chloride or 2.45 x 10 M calcium chloride. Viscosity of hydrolyzed polymer solutions decreases exponentially with increasing electrolyte concentration in water. 

The interaction of Ca2+ with pectins is discussed. The role of carboxylic acid salt formation and the degree of polymerization are first considered in terms of electrostatic and/or cooperative specific interactions. Then the effect of the degree of esterification and that of the pattern of carboxylic group distribution are discussed pectin esterase forms blocks which behave as fully hydrolyzed polymers and favor aggregation. Finally, the role of the calcium addition on the degree of aggregation was established. All the data show the important role of molecular structure of the pectins on calcium interactions. 

Poly(vinyl acetate), the precursor of poly (vinyl alcohol), hydrolyzed to less than 70%, is claimed to be nonbio degradable under conditions similar to those that biodegrade the fully hydrolyzed polymer (100) (see VINYL POLYMERS POLY (vinyl ACETATE POLYMERS). 

The DOC/enzyme/microbe interaction (DEMI) model divides bacterioplankton into two functional guilds, opportunists and decomposers, and DOC into two pools, labile and recalcitrant. In the context of the model, labile DOC is defined as directly assimilable monomers (saccharides, amino acids, and organic acids) and readily hydrolyzed polymers (polysaccharides, proteins, and nucleic acids). Because these substrates turn over rapidly, thus are unlikely to be transported far, most of the carbon in this pool will be autochthonous lysates and exudates, or allochthonous leachates from storms or seasonal litter fall. Recalcitrant DOC is defined as humic substances created by oxidative reactions among proteins, polysaccharides, hydrocarbons, and phenolic molecules. For inland waters, recalcitrant DOC is largely of allochthonous origin. 

Aliphatic polyesters are an attractive class of polymer that can be used in biomedical and pharmaceutical applications. One reason for the growing interest in this type of degradable polymer is that their physical and chemical properties can be varied over a wide range by, e.g., copolymerization and advanced macro-molecular architecture. The synthesis of novel polymer structures through ringopening polymerization has been studied for a number of years [1-5]. The development of macromolecules with strictly defined structures and properties, aimed at biomedical applications, leads to complex and advanced architecture and a diversification of the hydrolyzable polymers. 

In the early 1970s, the ALZA Corporation began its search for polymers suitable for erodible drug delivery systems. The ideal polymer was identified as one undergoing surface erosion in vivo and degrading to non-toxic, low molecular weight products at a rate that could be manipulated over a broad time span. To meet these criteria, a novel family of hydrolyzable polymers was developed, the poly(orthoesters), POEs [285]. The general structure is schematically shown in... 

Aliphatic polyesters are, together with polycarbonates, polyanhydrides, and poly(amino acids), the most well-known synthetic hydrolyzable polymers. They are often prone to degradation but are at the same time usually not good enough for technical applications. A renewed interest in aliphatic polyesters has resulted in developing new materials important in the biomedical and ecological fields. 

Poly(A-n-hexyl-A-vinylformamide) (0.25 g), 10 ml of 2M hydrochloric acid, and 2 ml of dioxane were stirred under reflux at 80°C under a nitrogen atmosphere for 24 hours. The hydrolyzed polymer was recovered by filtering the suspension and washing 3 times with 50 ml of deionized water. The resulting polymer was dried under reduced pressure at 60°C for 12 hours and then isolated. 

Poly(N-acylethyleneimine)s are also a source for production of totally unsubstituted or partially N-acylated linear poly(ethyleneimine)s. In that case acid hydrolysis is preferred. The physical properties of obtained polymers depend on the degree of hydrolysis. Below 70% of deacylation the polymers are amorphous otherwise they are crystalline. Partially hydrolyzed polymers have applications in paper manufacture, adhesives, coatings, ion-exchange resins, textile manufacture, and water treatment. 

Under conditions of extreme acidity7 or alkalinity, acrylic ester polymers can be made to hydrolyze to poly(acrylic acid) or an acid salt and the corresponding alcohol. However, acrylic polymers and copolymers have a greater resistance to both acidic and alkaline hydrolysis than competitive poly(vinyl acetate) and vinyl acetate copolymers. Even poly(methyl acrylate), the most readily hydrolyzed polymer of the series, is more resistant to alkali than poly(vinyl acetate) (57). Butyl acrylate copolymers are more hydrolytically stable than ethyl acrylate copolymers (58). 

Initiatmn of THF with these silts gives indeed dtains growing in two or three (trimesoyl) inde[ d nt bmnches. This conchiston follows from DP measurements of isolated polymers and, moreover, from a comparison with the DP values of hydrolyzed polymers (Table 5). 

The homopolyester, enriched to 60% in 13C at the carboxyl carbon, was prepared from labelled acctoxy-bcnzoic acid monomer as described by Miihlcbach, et al.. (9) The polymer was characterized by DSC, TMA, and X-ray diffraction. Number-average molecular weight was determined to be >30K from the H - NMR spectrum of hydrolyzed polymer (method of Krichcldorf and Schwarz). (10)... 

The degree of crystallinity in the polymer is only moderately altered, compared to the effect of equivalent weight, when the polymer is hydrolyzed, as demonstrated in Figure 3. Although the crystallinity does decrease somewhat upon hydrolysis, it is clear the hydrolyzed polymer is still partly crystalline. Similar results are obtained for polymer in other cation forms. Thus, any ionic clustering which exists in the polymer does not completely disturb the crystalline portion of the matrix. 

Small Angle X-ray from Hydrolyzed Polymer. When the polymer is hydrolyzed, a new reflection is observed in the SAXS scan, as shown in Figure 8, which corresponds to a Bragg spacing of from 3 to 5 nm. It is this reflection which has been attributed to ionic clustering in "Nation" (1-40. The origin of this reflection is currently the subject of debate and we will defer our discussion of this topic for a subsequent chapter of this text (20). We first will present the results of our SAXS experiments. 

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