# Synthesis and Porous Structure Characteristics of Allyl Methacrylate/Divinylbenzene Polymers
## 3 Results and Discussion
### Porous Structure of AllMeth/DVB Copolymers  
In addition to the amount and type of porogens, crosslinker amount is an important parameter influencing porosity. The same amount of porogen was kept constant, and the changeable parameter was the crosslinking level, which was changed to 50, 40, 30, 20, 15,  
Figure 2: The Raman spectrum of AllMeth/DVB resin.  
and 5 wt% of DVB in this work. Decreasing the amount of the crosslink resulted, of course, in a higher proportion of the relatively polar mers (allyl methacrylate) in the resins. At the same time, the concentration of the allyl groups was getting higher. Measurements of the nitrogen adsorption at low temperatures were conducted to find the parameters of the porous structure of obtained resins.  
As can be seen in Figure 3, by copolymerizations of AllMeth and DVB in the presence of 200 wt% of inert diluents, it was possible to obtain resins having sufficiently high specific surface area, especially when the level of the crosslinker was in the range of 20-50 wt%. Specific surface area is almost constant (the average for resins 1-4 equals 439 m\({}^{2}\)/g, and all values for resins fall into the narrow \(+/-7\)% range). A sharp decrease is seen only when the crosslinker level decreases to 15 and 5 wt% (resins 5 and 6, see Table 1).  
Micropore area has even smaller differences for the first four resins--all values are in the range 110-120 m\({}^{2}\)/g. Micropores are usually responsible for the sorption of organic molecules, and therefore, having a set of resins with almost identical surfaces will give an opportunity to ascribe their sorption properties to the differences in the density of polar carbonyl groups in the future. These densities are as follows: 6, 9, 12, and 14 umol/m\({}^{2}\) of the resins 1, 2, 3, and 4, respectively. Such results are rather surprising because usually, for the majority of polymers described in the literature, specific surface area decreases linearly with the decreasing level of crosslinker. It seems that a reasonable explanation for this would be the involvement of some proportion of the allyl groups in crosslinking the AllMeth/DVB copolymers. It is not possible, however, to describe such involvement in a quantitative manner. It is because during the polymerization with crosslinking, the viscosity of polymer solution, before it reaches the gelation point, is very high, and this causes some portion of vinyl bonds to be unreacted--trapped in the highly crosslinked regions. However, at the same time, the entrapment of the relatively slow-reacting allyl groups can give a chance of the chain transfer to other polymeric fragments and thus increase the level of crosslinking. In such a model, the crosslinking will have two components--the vinyl one and the allyl one.  
Figure 3: Specific surface area as a function of DVB content. Fit with an exponential function (r\({}^{2}>0.95\)).  
As can be seen in Figure 4, the crosslinked polymers with DVB content of 20% and higher display a bimodal contribution of pores to the specific surface area. One set of pores has a diameter between 3 and 5 nm, and the second set of pores contributing to the specific surface area is between 7 and 11 nm, with resin number 1 having the biggest shift to the higher diameter. Monomodal distribution of pores can be seen only for resin 5 with 15% of DVB, for which the decreased specific surface area is observed as well. Finally, resin 6 is non-porous, showing only traces of a specific surface area.