Acrylic acid crosslinking

Polycarbophils are polymers of acrylic acid crosslinked with divinyl glycol. The molecular weight of these polymers is theoretically estimated to range from 700 000 to 3-4 billion. However, there are no methods currently available to measure the actual molecular weight of a crosslinked (i.e. three-dimensional) polymer of this type. 

Heterogenization of catalytic nanoparticles stabilized by block copolymers can be carried out by their incorporahon into porous membranes based on poly(acrylic acid) crosslinked with a difunctional epoxide [20-22]. Membranes with defined porosities and amounts of palladium were studied in the selective hydrogenahon of propyne to propene as a model reaction. The porosity of the polymer membrane, the content of catalyst, and the residence time of the reaction mixture were found to influence the conversion and selectivity. The main advantage of these membranes compared to other heterogeneous catalysts is simple adjustment to reaction conditions and fadhtated mass transfer. 

Definition Homopolymer of acrylic acid crosslinked with an allyl ether of pentaerythritol or an allyl ether of sucrose Properties Wh. fluffy powd., odorless dens. 1.41 anionic Toxicology LD50 (oral, rat) 4100 mg/kg mod. toxic by ingestion TSCA listed... 

Definition Polymer of acrylic acid crosslinked with allyl ether of pentaerythritol... 

Definition Polymer of acrylic acid crosslinked with allyl ether of sucrose Properties Wii. fluffy powd., si. char, odor when neutralized with alkali hydroxides or with amines, dissolves in water, alcohol, and glycerin m.w. nominally 3,000,000 vise. 30,500-39,400 cps (0.5% aq. disp.) pH 3 (1% disp.) anionic... 

CAS 9003-01-4 (generic) 9007-16-3 (generic) Definition Polymer of acrylic acid crosslinked with allyl ether of sucrose... 

KGM and acrylic acid crosslinked by N,N-methylene bis-(acrylamide) 5-aminosalicylic acid Hydrogel Swelling behavior and degradation process showed that the gel was pH sensitive. Release rate of the model drug 5-ASA was proven to be controlled by swelling and degradation processes. The accumulative release percent of 5-ASA reached 95.19% after 36 h. [103]... 

High molecular weight, aosslinked, acrylic acid-based polymers are known as Carbopol and Noveon . Carbopol homopolymers consists of acrylic acid crosslinked with allyl sucrose or aUylpentaerythritol. There exist also Carbopol copolymers (with C10-C30 alkyl acrylate) and interpolymers (which contain a block copolymer of polyethylene glycol and a long chain alkyl acid ester). Noveon polycarbophil is a polymer of acrylic acid crosslinked with divinyl glycol [19],... 

The same principles that used to form a crosslinking network can be applied to IPN systems. For instance, IPN can be prepared initiating polymerization of a monomer in an existing polymer network. The first hydrogel network was composed of crosslinked poly(oxyethylene). The secondary polymerization was taken place in a mixture of acrylic acid, crosslinker and initiator with the poly(oxyeth-ylene) soaked in it, resulting in interpenetrating pH-sensitive networks of poly(oxyethylene) and PA A [64]. IPN can also be formed simultaneously using two different polymerizations mechanisms such as condensation and free radical polymerizations [65]. If linear polymer penetrate on a molecular scale of cross-linked polymer network, a semi-lPN is formed [66]. 

Mangipudi et al. [63,88] reported some initial measurements of adhesion strength between semicrystalline PE surfaces. These measurements were done using the SFA as a function of contact time. Interestingly, these data (see Fig. 22) show that the normalized pull-off energy, a measure of intrinsic adhesion strength is increased with time of contact. They suggested the amorphous domains in PE could interdiffuse across the interface and thereby increase the adhesion of the interface. Falsafi et al. [37] also used the JKR technique to study the effect of composition on the adhesion of elastomeric acrylic pressure-sensitive adhesives. The model PSA they used was a crosslinked network of random copolymers of acrylates and acrylic acid, with an acrylic acid content between 2 and 10%. 

A significant step towards commercial success came with a discovery in the late 1950s by E. Ulrich at 3M when he found that copolymerization of hydrogen bonding monomers, like acrylic acid with alkyl acrylates resulted in cohesively strong, yet tacky materials [63]. Since then, newer developments in such areas as polymer crosslinking, and the synthesis and copolymerization of new monomers, have led to a rapid penetration of acrylics throughout the PSA industry. 

Fig. 7 shows the effect of an increasing amount of polar monomer on static shear holding tested at room temperature in a non-crosslinked iso-octylacrylate/ acrylic acid copolymer PSA. 

As the amount of acrylic acid in the polymer increases, the degree of hydrogen bonding between polymer chains also increases causing the cohesive strength to improve without the need for crosslinking. Very similar observations can be made for other polar monomers, such as acrylamide. 

Crosslinking the PSA will increase the solvent resistance of the material and it will also have a significant effect on the rubbery plateau modulus of the polymer. Fig. 8 shows the effect of increasing amounts of a multifunctional az.iridine crosslinker, such as CX-100 (available from Avecia, Blackley, Manchester, UK) on the rheology of an acrylic polymer containing 10% acrylic acid. The amounts of crosslinker are based by weight on the dry weight of the PSA polymer. 

Several selective interactions by MIP membrane systems have been reported. For example, an L-phenylalanine imprinted membrane prepared by in-situ crosslinking polymerization showed different fluxes for various amino acids [44]. Yoshikawa et al. [51] have prepared molecular imprinted membranes from a membrane material which bears a tetrapeptide residue (DIDE resin (7)), using the dry phase inversion procedure. It was found that a membrane which contains an oligopeptide residue from an L-amino acid and is imprinted with an L-amino acid derivative, recognizes the L-isomer in preference to the corresponding D-isomer, and vice versa. Exceptional difference in sorption selectivity between theophylline and caffeine was observed for poly(acrylonitrile-co-acrylic acid) blend membranes prepared by the wet phase inversion technique [53]. 

The polymers were prepared using MAA as functional monomer and EDMA as crosslinking monomer if not otherwise noted. VPY= 2- or 4-vinylpyridine TRIM = trimethylolpropane trimethacrylate DPGE = (R)-N,0-dimethacryloylphenylglycinol PYAA = 3-(4-pyridinyl)acrylic acid. 

In distinction to other esters of acrylic acids containing double bonds in the alcohol radical and, therefore exhibiting a tendency to cyclopolymerization43 and formation of crosslinked polymers, 10 reacts with AN in DMF solution41 or in benzene/DMF42 only with the vinyl group of the acid part due to deactivation of the double bond in the 3-chloro-2-butenyl group by the chlorine atom. The copolymer of structure 11 is formed. 

The fact that crosslinking proceeds at considerably high conversions of the monomers (50%) and at copolymerization temperatures > 60 °C is a distinctive feature of this system, as compared with systems containing other unsaturated derivatives of acrylic acids, which is determined by the difunctional nature of 10. 

Manufacture of highly water-absorbent polymers with uniform particle size and good flowability can be carried out by reverse phase suspension polymerization of (meth)acrylic acid monomers in a hydrocarbon solvent containing crosslinker and radical initiator. Phosphoric acid monoester or diester of alka-nole or ethoxylated alkanole is used as surfactant. A polymer with water-absorbent capacity of 78 g/g polymer can be obtained [240]. 

When the five mol percent crosslinked poly(acrylic acid) release curve was compared (Figure 5) to that for a very lightly crosslinked (less than one percent)... 

Figure 5. Release of insulin from lightly crosslinked (Polycarbophil) and 5 mol% crosslinked poly(acrylic acid).

Figure 6. Release of insulin under gastric conditions from crosslinked 1/1 random acrylic acid copolymers with either hydroxyethyl acrylate or methyl acrylate.

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