# Initial Characterization of PDMAEMA: Styrene Porous Polymer Monolithic Morphologies
## 4 Discussion  
This analysis aims to study DMAEMA in a co-block PPM with styrene for the first time. DMAEMA has been shown to exhibit very strong morphological changes in response to altered pH environments [21; 22; 23]. The amino groups of the monomers are protonated in low pHs which results in repulsion along the polymer chain. This is observed as swelling behavior of the polymer in acidic environments [5]. Conversely, in high pHs, the polymer chain does not have the electrostatic repulsion due to the absence of protons and collapses upon itself [5]. To understand this phenomenon when incorporated into a PPM morphology, three successful fabrications of the co-block PPM (A, B, and C) were tested in extreme acidic and basic environments. SEM images were taken of these with and without exposure to solutions with adjusted pHs. These images showed a consistent behavior that is reliant on environmental pH. These PPMs are reacting in a uniform manner in response to stimuli, which gives them a unique range of potential. Initial efforts to characterize this PPM were performed via SEM. The images collected from the air-dried samples show a distinct and pH-reliant behavior (Figure 3). These were all white, opaque, and flexible solids (SI Figure S1). It can be observed across all three polymers that the polymers exposed to acid appear to relax the solid surface (Figure 3b,e,h). This is especially apparent in polymer B (Figure 3e). A contrasting effect can be seen in the samples exposed to a basic solution, as the polymer appears to constrict and tighten in pockets and veins (Figure 3c,f,i). This illustrates the expected swelling (in acid) and shrinking (in base) behavior of PDMAEMA. However, it is the first time that a PPM fabrication of this copolymer has been reported. Figure 3: Comparative SEM images of polymers (**A**–**C**) that have been air dried (**a,d,g**), exposed to 0.1 M HCl (pH 1.1) solution (**b,e,h**), and exposed to 0.1 M NaOH (pH 12.6) solution (**c,f,i**). IR and UV/Vis readings were taken of HCl and NaOH solutions that had been exposed to the polymers of interest (A, B, C) over the course of seven hours. These measurements were performed to ensure that the exposure of the PPM to the adjusted pH solutions does not alter, or degrade, the PPM. The representative spectra for sample B are shown here (Figures 1 and 2), as this was the sample that appeared to undergo the most change during SEM analysis. Representative spectra for samples A and C can be seen in Supplemental Information Figures S2-S5. PDMAEMA characteristically shows IR stretches at 1180 cm\({}^{-1}\) (C-O), 1650 cm\({}^{-1}\) (N-H) and 1710 cm\({}^{-1}\) (C=O) [24]. These stretches do not appear in Figure 1. This is a clear indication that the polymer is not disintegrating in the acid/base solutions. In a parallel manner, no additional stretches appear in the UV/Vis spectra (Figure 2). This is a clear indication that the polymer is not disintegrating in the acid/base solutions. The time-lapse shows that, although there are small variances present, they do not result in the appearance of the DMAEMA monomer in the solution over time (Figures 1 and 2). Peaks characteristic to the polymers were identified and used for comparison to the time-lapse spectra to check for polymer degradation. When comparing the IR spectra of the polymers themselves (Figures S6-S8) to that of the acid/base solution spectra, polymer-specific peaks at 1180 cm\({}^{-1}\) (C-O), 1650 cm\({}^{-1}\) (N-H) and 1710 cm\({}^{-1}\) (C=O) are not present in the solution spectra [24]. This confirms that the polymer is not degrading into solution in acidic or basic environments, and therefore the PPM remains structurally intact. This leads us to believe that the change observed under SEM is not chemically destructive, but simply a behavior in the morphology of the solids. Various DMAEMA:Styrene co-block polymers were observed in this study. It was shown that the co-block polymer can be formed into a monolithic morphology and retain the stimuli-responsive features of DMAEMA.