Poly crosslinked network

The term IPN was first used in 1960 to describe the apparently homogeneous product obtained from styrene crosslinked with divinylbenzene. IPNs were prepared from this system by taking a crosslinked poly(styrene) network and allowing it to absorb a controlled amount of styrene and a 50% divinylbenzene-toluene solution containing initiator. Polymerisation of this latter component led to the formation of an IPN, the density of which was... 

NA Peppas, EW Merrill. Poly(vinyl alcohol) hydrogels Reinforcement of radia-tion-crosslinked networks by crystallization. J Polym Sci Polym Chem 14 441-444, 1976. 

Two types of networks were prepared (i) randomly crosslinked polybutadiene, and (ii) model urethane networks, (a) polybutadiene based, and (b) poly(e-caprolactone) based. The randomly crosslinked networks were prepared from polybutadiene (Duragen 1203 obtained from General Tire and Rubber Co.) crosslinked with di-cumyl peroxide. Specifications of the as obtained polybutadiene are given in Table I. Polybutadiene was purified by dissolving in benzene and precipitating in methanol. Precipitated polybutadiene was redissolved in benzene. Seven different weights of dicumyl... 

Figure 2. Structure of diacid molecules that can be functionalized to create crosslinked poly anhydride networks.

The term S represents the strength of the network. The power law exponent m was found to depend on the stochiometric ratio r of crosslinker to sites. When they were in balance, i.e. r = 1, then m - 1/2. From Equations (5.140) and (5.141) this is the only condition where G (co) = G (cd) over all frequencies where the power law equation applies. If the stochiometry was varied the gel point was frequency dependent. This was also found to be the case for poly(urethane) networks. A microstructural origin has been suggested by both Cates and Muthumkumar38 in terms of a fractal cluster with dimension D (Section 6.3.5). The complex viscosity was found to depend as ... 

Kuhn et al. [22] extended their studies to crosslinked networks of poly-(acrylic acid) (PAA) and found that these gels swelled to a high degree in alkaline environment and contracted rapidly when acid was added to the surrounding solution. Dilations and contractions of the order of 300% were observed. They were reversible and could be repeated at will. A contracting and expanding gel... 

A detailed study of the structure of the aggregates of the ionic surfactants in polyelectrolyte networks was presented in Refs. [66,68]. The dynamics of the changes in the microenvironment of the fluorescent probe, pyrene, in slightly crosslinked networks of poly(diallyldimethylammonium bromide) (PDADMAB) during diffusion of sodium dodecyl sulfate (SDS) in the gel phase has been investigated by means of fluorescence spectroscopy. In Ref. [66], an analogous investigation was reported for complexes formal by the sodium salt of PMAA with cetyltrimethylammonium bromide (CTAB). 

Langley, N.R., Ferry, J.D. Dynamic mechanical properties of crosslinked rubbers. VI. Poly(dimethylsiloxane) networks. Macromolecules 1, 353-358 (1968). 

High resolution l3C NMR is also used in the determination of the composition of the dispersed phase in cured rubber modified epoxies in order to analyze the chemical structure of the mobile segments 152). In this case quantitative analysis is possible because the areas under each peak are approximately equal to the number of carbons contributing to the peak, and the intensities of the broad lines from the rigid phase are very low, almost indistinguishable from the baseline noise. The structure of crosslinked networks based on poly(3,4-pyrrolidinediethylene), synthesized by different methods, was determined from gels swollen in water and chloroform 153). 

An example for a synthesis of a poly(siloxane) network is shown in Fig. 37b. In a one-step reaction the mesogenic moieties as well as the crosslinking agent are coupled via an addition reaction to the reactive linear poly(methylhydrogensiloxane) backbone 92). Because of similar reactivity of the crosslinking agent and mesogenic molecules, a statistical, disordered addition to the backbone has to be expected. 

Peppas N, Merrill E. Poly(vinyl alcohol) hydrogels reinforcement of radiation-crosslinked networks by crystallization. Journal of Polymer Science 1976, 14,441 457. 

Figure 2 Pass Ale types ofpolymers based upon catenane architecures A Linear mechanically-linked polymers B mechanically cross-linked polymers C stars with a flexible, potentially switchable, catenane core D combs with catenarw linkages E main chain catenanes with switchable surface properties F highly mechani-cally-crosslinked networks G poly- or [n]catenanes. Only examples of types A and F have thus far been prepared...

Kostereva and coworkers [61] reported solution viscosity, IR and CPMAS measurements of blends of PBI and the poly(amic acid) and poly(im-ide) of Kapton. The presence of PBI in the solution with the poly(amic acid) of Kapton slowed dramatically the decrease in viscosity ascribed to breakage of the amide linkage of the amic-acid. This was seen as evidence of close association of the two polymer chains. CPMAS spectra, reported for samples after heating to high temperature (up to 823 K), showed an increase in the rate of opening of the imide group to form a three-dimensional crosslinked network compared with pure poly(imide). 

The structures listed in Table 1.6 are divided into three categories Short sequences, Long sequences, and Networks. Within the first category a sequence of placement of individual CRU is considered, within the second the placement of long sequences of CRU defines the copolymer type, while to the third belong crosslinked networks, crosslinked polymers, and chemical-type interpenetrating polymer networks. The network is a crosslinked system in which macromolecules of polymer A are crosslinked by macromolecules of polymer B [Sperling, 1992]. The composition can be expressed as, e.g., Woc -co-poly(butadiene/styrene) (75 25 wt%), or gra/i-co-poly[isoprene/ (isoprene acrylonitrile)] (85 15 mole %). 

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