Post-crosslinking

A new class of functional comonomers exemplified by acrylamidobutyraldehyde dialkyl acetals 1 and their Interconvertible cyclic hemlamidal derivatives 2 were prepared and their chemistry was Investigated for use In polymers requiring post-crosslInking capability. These monomers do not possess volatile or extractable aldehyde components and exhibit additional crosslinking modes not found with conventional am1de/forma1dehyde condensates, eg, loss of ROH to form enamides 9 or TO and facile thermodynamically favored reaction with diols to form cyclic acetals. 

Post-crosslinkable and substrate reactive polymers are widely used to Improve water and solvent resistance, strength, substrate adhesion and block resistance In binders, adhesives and coatings. The surprisingly rich chemistry of a new class of functional monomers (eg. 1 and 2) related to standard amide/aldehyde (amlnoplast) condensates, but which eliminate aldehyde emissions, was elucidated by monomeric model and mechanistic studies and discussed In the preceeding paper (1). Results with these monomers In copolymer systems are reported here. 

Fig. 24.3 Peel strength versus contact time of contact at room temperature for EPDM joints made of partially cross-linked networks which are post-crosslinked by an electron beam (peel rate = 5 mm min" ).

Fig. 24.7 Peel strength C versus peel rate R influence of the contact time at 40°C after pre-crosslinking of the sheets separately and before post-crosslinking.

In spite of the negative opinion of many investigators regarding the synthesis of isoporous ion-exchange resins, we assume that the post-crosslinking approach can be considered as an important first step in the desired direction of improving the network structure. 

The band between 1700 and 1705 cm also presents itself in polystyrene networks post-crosslinked with methylal, even in the case when the reaction... 

Spectrum. On the other hand, this band is revealed in the spectrum of the styrene-0.6% DVB copolymer intensively crosslinked with 1 mol of MODE, which contains a comparable amount (1%) of pending chlorine. It is quite possible that industrial MN-200 contains chlorine of a different kind. A part of rather inert chlorine in the form of chloroethyl groups may have originated by the involvement of EDO into the Friedel—Crafts reaction. One may also assume that the initial copolymer of that product incorporates more DVB thus the unreacted pendent double bonds may have interacted with MCDE during the post-crosslinking reaction, leading to the formation of methyl chloropropyl ether fragments [105] ... 

This decisive topological factor largely accounts for the fact that, at equivalent degree of crosslinkings, the swelling abilities of the products of post-crosslinking linear polystyrene in solution or swollen styrene—DVB copolymer are much higher than that of conventional gel-type... 

Figure 7.25 Apparent density of the networks prepared by post-crosslinking with MCDE of styrene copolymers with (1) 0.17, (2) 0.3, (3) 0.6, (4) 1.4, and (5) 2.7% DVB. (Reprinted from [151] with permission of Wiley Sons, Inc.)...

Figure 7.26 Sorption isotherm of nitrogen at 77 K on the hypercrosslinked polymer prepared by post-crosslinking styrene-0.3% DVB copolymer with monochlorodimethyl ether to 100%. Measured by Micromeritics Instrument Corporation.

Figure 7.30 Electron macrographs of the networks prepared by post-crosslinking linear polystyrene (/M = 300,000 Da) with (a, b) p-xylylene dichloride (a) X=100%, (b) X=43% and (c, d) monochlorodimethyl ether (c) X=100%, (d) X=5% (a, b) two-step replicas, transmission electron microscopy, 46,600x (c, d) scanning electron microscopy, (c) 40,000x, (d) 100,000x. (After [198]).

Figure 7.32 Texture of the network prepared by post-crosslinking linear polystyrene of 3,000,000 Da molecular weight with monochlorodimethyl ether to 100% in 6.7% ethylene dichloride solution scanning electron microscopy, 40,000x. (After [198]).

Figure 7.34 Plots of small-angle X-ray scattering (logarithm of intensity vs modulus of scattering vector s = 47rsin ( s/A), normalized on the thickness of a sample and attenuation for (1, 2) the network obtained by post-crosslinking styrene-2% DVB copolymer with monochlorodimethyl ether to 100% and for (3) initial copolymer (1) the sample swollen in n-hexane and (2, 3) dry samples.

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