Molecular weight crosslinked polymers

Carbomers are synthetic, high-molecular-weight, crosslinked polymers of acrylic acid. These poly(acrylic acid) polymers are crosslinked with allyl sucrose or allyl pentaerythritol. The polymerization solvent used most commonly was benzene however, some of the newer commercially available grades of carbomer are manufactured using either ethyl acetate or a cyclohexane-ethyl acetate cosolvent mixture. The Carbopol ETD resins are produced in the cosolvent mixture with a proprietary polymerization aid, and these resins are crosslinked with a polyalkenyl polyether. 

U.S. 5368766 (1994) [71] Dixit (Colgate-Palmolive) High-molecular-weight crosslinked polymer thickener K/Na ratio >1 1 incorporated air bubbles Physical stability low bottle residue low cup leakage improved cleaning... 

The use of phenolic polymers in photocrosslinkable systems usually involves multicomponent systems which incorporate polyfunctional low molecular weight crosslinkers. For example, Feely et al. [9] have used hydroxymethyl melamine in combination with a photoactive diazonaphthoquinone which produces an indene carboxylic acid upon irradiation to crosslink a novolac resin. Similarly, Iwayanagi et al. [10] have used photoactive bisazides in combination with poly(p-hydroxy-sty-rene) to afford a negative-tone resist material which does not swell upon development in aqueous base. 

The search for theoretical relations concerning domain size and shape is ongoing, and several efforts to derive a theoretical formulation have been made. The first attempt was by Donatelll et al, in 1977 [29], who derived an equation especially for seml-IPN s of the first kind (polymer I crosslinked, polymer II linear) and extended to full IPN s by assuming that the molecular weight of polymer II is infinite. Later, this equation was simplified for... 

Influence of melt viscosity and tan 5, measured at a frequency of 10 Hz, on the stability of a LDPE foam (redrawn from (36)). For linear polymers of different molecular weights, crosslinking moves the properties in the... 

As is well known, two main routes can be adopted for obtaining crosslinked derivatives, as schematically depicted in Fig. 159 these include u.se of polyfunctional oligomers or monomers (route a) and reaction of high-molecular-weight linear polymers with crosslinking reagents (route b). 

Precrosslinked" or "intramolecularly crosslinked" particles are micronetworks [1]. They represent structures intermediate between branched and macroscopically crosslinked systems. Their overall dimensions are still comparable with those of high molecular weight linear polymers, the internal structure of micronetworks (p-gels), however, resembles a typical network [2]. Synthesis is performed either in dilute solution or in a restricted reaction volume, e.g., in the micelles of an emulsion. Particle size and particle size distribution can be controlled by reaction conditions. Functional groups can be... 

The formation of crosslinks in a linear polymer causes two polymer chains to join, resulting in an increase in molecular weight. Linear polymers including polystyrene and PVC are most susceptible to crosslinking. Such degradation is detected as increased stiffness, brittleness and a decrease in solubility as the average molecular weight increases. 

As an alternative, side-chain functionalized polymer chains can associate by (c) low molecular weight crosslinkers or (d) mutual heterocomplementary polymer-polymer binding... 

The elastomers from the high molecular weight silicone polymers must be crosslinked to obtain rubber-like properties. One way to accomplish this is through hydrogen abstraction by free radicals that are generated by decomposition of added peroxides. 2,4-Dichlorobenzoyl peroxide is often used for this purpose. It is decomposed between 110-150 C. The reaction can be shown as follows ... 

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