The Scissors Effect of the Macromolecular Crosslinker on the Glass Transition of Polystyrene in Its Conetworks with Poly(dimethylsiloxane)

Abstract

The glass transition temperature (T_g) is undoubtedly one of the most important characteristics of polymers, and investigating its dependence on their structure and composition is crucial from both fundamental and application points of view. This study deals with the unexpected relationship between T_g and the average molecular weight between crosslinking points (M_c) in nanophase-separated polystyrene-l-poly(dimethylsiloxane) (PSt-l-PDMS) and polystyrene-l-poly(dimethylsiloxane)/divinylbenzene (PSt-l-PDMS/DVB) polymer conetworks. In order to reveal the correlation between the T_g and M_c, a library of PSt-l-PDMS and PSt-l-PDMS/DVB conetworks was synthesized, and their compositions and T_gs were determined. Instead of the expected increase of T_g with decreasing M_c, a reverse correlation was found. Namely, the T_g decreases with decreasing M_c in these conetworks. Correlation analyses showed that the T_g linearly depends on 1/M_c, similar to the Fox–Flory relationship for homopolymers with their M_n, that is, T_g = T_g,ꝏ −K/M_c for the investigated conetworks, independent of the absence or presence of relatively low amounts of DVB as an additional small molecular weight crosslinker. This means that the PDMS macrocrosslinker acts like scissors by interrupting the mobility of the crosslinked PSt chains in the conetworks, and the T_g of the PSt segments will be close to that of PSt homopolymers with the same M_n as M_c, as found by comparison. Consistent with previous findings with other conetworks, the presence of the scissors effect of the macromolecular crosslinker in the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks indicates that the scissors effect is a general phenomenon for polymer conetworks formed by crosslinking with a macromolecular crosslinker. The observed unusual T_g versus M_c relationship in the conetworks can be utilized in designing such novel materials with predetermined T_gs required for targeted applications.

1. Introduction

Beyond a doubt, the glass transition temperature (T_g) is one of the most important characteristics of polymers. Since the T_g is the temperature at which a polymer undergoes a transition from a glassy state to an elastic (viscoelastic) state, which results in substantial changes in its physical properties, such as elasticity, strength, and stiffness, it is a critical factor for both polymer processing and applications. As a consequence, the effect of structure, topology (i.e., linear, branched, and crosslinked) and the molecular weight of macromolecules on their T_g has been widely investigated since the beginning of polymer science, technology, and production. One of the recently emerging classes of crosslinked polymers belongs to conetworks, which are composed of different polymer chains coupled with chemical bonds to each other (see e.g., Refs. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73] and references therein). In these macromolecular assemblies, two or more polymer chains, which are mostly immiscible, are crosslinked either by covalent, ionic, or supramolecular bonds. Due to the mobility restriction of the crosslinked macromolecules, conetworks with nanophasic morphology are obtained in the cases of immiscible polymer components [13,14,15,16,27,28,51,52,53,61,68,73]. These conetworks usually have a bicontinuous (cocontinuous) structure with a broad composition window [13,14,28,53,61,73]. Due to the unique bicontinuous nanophase separated structure and component-selective swelling behavior of polymer conetworks, these materials offer advanced applications in various fields, such as sensors [5,6,7], self-healing materials [10,11,40,60], membranes [24,25,26], drug delivery [33,34,35,61,62,63], ophthalmic devices [45,46], catalyst supports [47,48,49], etc.

Although the glass transition temperature is a critical property of the amorphous macromolecular materials, not only from fundamental aspects but also from an application point of view, surprisingly, relatively few reports have dealt with the thermal transition behavior of the polymeric components in conetworks, i.e., T_g and/or crystallization and melting temperatures [12,13,50,51,52,53,54,55,56,57,58,59,71,72,73]. Unexpectedly, in two cases, that is, for the poly(N-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) [12] and poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) [13] conetworks, a Fox–Flory-type correlation [74] was found between the T_g of the crosslinked polymers, i.e., PVIm and PMMA, and the average molecular weight between crosslinking points (M_c). This means that the T_g decreases with decreasing M_c, that is, by increasing crosslinking density, according to the Fox–Flory equation for the T_g dependence of homopolymers on the number average molecular weight (M_n) [74]:

$$T_{\mathrm{g}}=T_{\mathrm{g},\mathrm{\infty }}-{\displaystyle \frac{K}{M_{\mathrm{n}}}}$$

(1)

where T_g,ꝏ, represents the glass transition temperature of the polymer with infinite molecular weight, and K is a constant. In the case of the mentioned examples [12,13], this correlation is valid by substituting M_n with M_c. Furthermore, it was found for the PMMA-l-PIB conetworks that the K value fits well with that of the PMMA homopolymers in the same molecular weight region [13]. These findings fully contradict expectations, because it is well known that increasing the crosslinking density leads to increasing the T_g in polymer networks crosslinked with crosslinkers of low molecular weights [75,76,77], on the one hand. On the other hand, the observed decrease in T_g with increasing crosslinking density, i.e., with decreasing M_c, indicates that the macromolecular crosslinkers have a ‘scissors effect’ in polymer conetworks. As a consequence, in relation to their glass transition, the polymer segments between the crosslinking junctions behave like the corresponding homopolymers with molecular weights similar to the M_c in the conetworks [12,13].

Recently, we reported on the synthesis, structural analysis, and selective swelling behavior of nanophase-separated conetworks of polystyrene (PSt) with poly(dimethylsiloxane) (PDMS) as a macrocrosslinker, both in the absence and presence of divinylbenzene (DVB) as an additional low molecular weight crosslinker [73]. In the examined cases, it was found that the T_g of the crosslinked PSt component was lower than expected, while the T_g of the PDMS is nearly the same as that of the PDMS homopolymers, i.e., in the range of −120 °C [78,79,80,81,82,83]. On the other hand, the T_gs of polystyrene homopolymers depend strongly on molecular weight below ~20 kDa [84,85,86,87], then level off above this molecular weight with T_g in the 100–110 °C range, and it follows the Fox–Flory relationship [86,88]. It must also be mentioned that the T_g of the components in PSt-PDMS block copolymers is the same as that of the components, due to the immiscibility of PSt and PDMS [89,90].

Motivated by the unexpected glass transition behavior of the PSt component in the novel polystyrene-l-poly(dimethylsiloxane) (PSt-l-PDMS) and polystyrene-l-poly(dimethylsiloxane)/divinylbenzene (PSt-l-PDMS/DVB) conetworks (-l- stands for linked by), a library of such conetworks with varying compositions and PDMS with different molecular weights has been prepared in order to investigate the effect of crosslinkers on the T_g of the crosslinked PSt. Herein, we report on the results of the systematic studies on the thermal transitions of the PSt and PDMS components in the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks as determined by DSC measurements. Then, a subsequent correlation analysis was performed to determine the existence of the scissors effect by the PDMS crosslinker in these conetworks, and to examine the effect of the DVB, as an additional low molecular weight crosslinker, on the T_g of the crosslinked PSt in the PSt-l-PDMS/DVB conetworks.

2. Materials and Methods

2.1. Materials

Styrene (99%, Sigma-Aldrich, Steinheim, Germany) and divinylbenzene (DVB) (80% m/p-divinylbenzene and 20% ethylstyrene, Honeywell Fluka, Steinheim, Germany) were distilled under vacuum from calcium hydride before use. Methacryloxypropyl-telechelic poly(dimethylsiloxane)s (MA-PDMS-MA, M_n,PDMS = 4700, 9000 and 22,200 Da; Gelest Inc., Morrisville, PA, USA) were purified to remove the inhibitor by precipitation from hexane solution to methanol, then redissolved and extracted with distilled water, dried on anhydrous magnesium sulfate, and finally, the hexane was removed under reduced pressure followed by drying to constant weight under vacuum at room temperature. The initiator, α,α’-azobisisobutyronitrile (AIBN, Sigma-Aldrich, Steinheim, Germany) was crystallized twice in methanol, filtered, and dried under vacuum at room temperature prior to use. Tetrahydrofuran (THF) (VWR International Ltd., Debrecen, Hungary) and toluene (VWR International Ltd., Debrecen, Hungary) for conetwork syntheses were distilled before use. Other solvents, including hexane (Molar Chemicals, Halásztelek, Hungary), 1-nitropropane (Sigma-Aldrich, Steinheim, Germany), and methanol (VWR International Ltd., Debrecen, Hungary) were used as received.

2.2. The Synthesis of PSt-l-PDMS and PSt-l-PDMS/DVB Conetworks, and Polystyrene Homopolymer

The PSt-l-PDMS and PSt-l-PDMS/DVB conetworks were synthesized via free radical copolymerization of MA-PDMS-MA, styrene, and divinylbenzene as previously described [73]. Briefly, the conetworks were synthesized with MA-PDMS-MA contents varying in the 30–80 wt% range. The PSt-l-PDMS/DVB conetworks were prepared with an St/DVB weight ratio of 36:1. The predetermined amounts of the reactants were measured and mixed in a glovebox under nitrogen atmosphere and dissolved in THF or toluene (for conetwork syntheses with PDMS containing M_n,PDMS of 9 or 22.2 kDa) to obtain total reactant concentration of 0.4 g/mL. The [M]/[I]^0.5 ratio was 23.2 in all cases, where [M] and [I] stand for the total concentrations of the monomers and AIBN initiator, respectively. The homogenized reaction mixtures were poured into Teflon molds, sealed, and reacted at 60 °C for 72 h. After the synthesis, the samples were dried and sequentially extracted with hexane and 1-nitropropane to remove unreacted PDMS, and styrene and derivatives, respectively. The PSt homopolymer (M_n,PSt = 44 kDa, D = 3.08) was synthesized under the same conditions as the conetworks.

The conetwork samples are identified with their components (S for styrene, D for divinylbenzene, followed by 36, i.e., the St/DVB weight ratio when DVB was used), the M_n/1000 of the MA-PDMS-MA macrocrosslinker, and the PDMS contents of the conetworks, which were determined by either elemental analysis or the composition of the extracted materials (see Ref. [73] for details).

2.3. Differential Scanning Calorimetry (DSC)

The DSC measurements were carried out on Mettler Toledo DSC821e (Mettler Toledo, Greifensee, Switzerland) equipment in the temperature range of 0 to 200 °C with 10 °C/min heating/cooling rate under 80 mL/min nitrogen flow. The low temperature DSC measurements from −150 °C to zero degree were performed on a Perkin Elmer Diamond DSC (Perkin Elmer, Norwalk, CT, USA) with 10 °C/min heating/cooling rate under 20 mL/min helium flow. Furthermore, TA Instruments 2920 Modulated DSC (New Castle, DE, USA) equipment was also used in this temperature range (−150 to 0 °C). The inflection points of the glass transitions in the second heating runs were determined as the glass transition temperatures (T_g).

3. Results and Discussion

As previously reported, the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks possess bicontinuous nanophase-separated morphology with distinct polystyrene and poly(dimethylsiloxane) nanodomains, as determined by small angle X-ray scattering (SAXS) and atomic force microscopy (AFM) measurements [73]. For the examined cases in this study, DSC curves also indicated the phase separation in these conetworks with two separate glass transition temperatures (T_g) for the PSt and the PDMS components [73]. While these measurements showed the T_g of PDMS within the range of its homopolymer, the observed T_g of PSt in the conetworks fell below that of the expected T_g of the PSt homopolymer. In order to gain insight into the glass transition behavior of PSt in the PDMS-crosslinked conetworks, and in line with previous findings on the scissors effect of macrocrosslinking in other conetworks [12,13], a library of PSt-l-PDMS and PSt-l-PDMS/DVB conetworks was synthesized and analyzed by DSC measurements. Scheme 1 shows the synthesis routes for obtaining such conetworks in the absence or presence of DVB, as an additional low molecular weight crosslinker, which is a widely used crosslinker for preparing PSt networks. As displayed in this scheme, the conetworks were prepared by free radical polymerization in a common solvent for all the components, including the resulting PSt. As shown in

Table 1. The gel fraction, composition (PDMS content), the average molecular weight between crosslinks (M_c), and the glass transition temperature (T_g) of the PSt component of PSt-l-PDMS and PSt-l-PDMS/DVB conetworks.

Sample ID	Gel Fraction (%)	PDMS (wt%)	Mc (Equation (2)) (g/mol)	Mc (Equation (3)) (g/mol)	Tg (°C)
S-4.7-48	55.9	48.4	2510	-	83
S-4.7-59	60.4	59.3	1610	-	69
S-4.7-67	60.2	67.4	1140	-	62
S-4.7-76	63.0	76.4	730	-	n.d.
S-4.7-84	53.2	84.1	440	-	n.d.
S-22.2-51	41.3	51.4	10500	-	96
S-22.2-57	59.6	57.2	8310	-	90
S-22.2-68	54.1	67.9	5250	-	88
S-22.2-79	61.1	78.9	2970	-	81
S-22.2-89	59.6	89.0	1370	-	n.d.
SD36-4.7-33	88.1	33.4	4690	1550	90
SD36-4.7-44	86.3	44.3	2960	1290	79
SD36-4.7-55	86.7	55.4	1890	1030	72
SD36-4.7-65	87.1	65.2	1250	800	59
SD36-4.7-75	86.8	75.4	770	570	n.d.
SD36-9-65	94.6	65.3	2390	1170	70
SD36-22.2-66	91.1	65.6	5820	1660	83

n.d.: not detectable.

, this process with all the applied methacrylate-telechelic PDMS macrocrosslinkers resulted in conetworks with relatively high gel fractions after careful extraction, and their composition was close to that of the feed. The addition of DVB led to higher gel fractions, and it did not prevent the incorporation of the PDMS macrocrosslinkers.

Figure 1 and Figure 2 show the DSC scans in the temperature ranges of −150–0 °C and 0–200 °C for detecting the thermal transitions of the PDMS and PSt components, respectively. These figures clearly indicate that the T_gs of both components can be detected in the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks. Specifically, there is one glass transition near the T_g of the PDMS homopolymers, and another one for the PSt component in the higher temperature region of the DSC measurements. Evidently, the two separate glass transitions mean microphase separation of the PSt and the PDMS domains with significant segregation in these conetworks, which is consistent with previous reported SAXS and AFM results [73]. It must be noted that the glass transition of the PSt component with sufficient certainty cannot be detected in conetworks with low PSt contents (i.e., less than ~25 wt%), as shown in Figure 2A–C. As displayed in Figure 1, the PDMS homopolymers have T_gs, cold crystallization, and melting transitions in the temperature ranges as expected on the basis of literature reports [78,79,80,81,82,83,89,90]. However, signals indicating crystallization of PDMS cannot be detected in both the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks with PDMS macrocrosslinkers having M_n,PDMS of 4.7 and 9 kDa. This means that crystallization of the PDMS component in these conetworks is fully prevented, which is attributed to the nanoconfined constraints of the PDMS nanodomains by the PSt nanophases in the bicontinuous nanophasic morphological structure of these conetworks [73]. Similar findings were recently reported for block copolymers of poly(poly(ethylene glycol) acrylate) (PEGA₇₆) with poly(2-hydroxyethyl acrylate-polyhexanoate), that is, decrease in the crystalline fraction of PEGA76 by decreasing its fraction, but having nearly constant T_g of this component [91]. Weak cold crystallization and melting peaks appear in the DSC scan of the conetwork prepared with the MA-PDMS-MA macrocrosslinker with M_n,PDMS of 22.2 kDa (Figure 1B). This is presumably due to the higher mobility of the longer PDMS chains in this case.

As the data indicate in Figure 2 and Table 1, the T_g of PSt in the conetworks decreases with increasing PDMS macrocrosslinker content, that is, with increasing crosslinking density. This is in sharp contrast to expectations. As evidenced by the experimental data, the glass transition temperature increases with the increasing amount of the crosslinker in cases of polymer networks with low molecular weight crosslinkers [75,76,77]. Inspired by previous similar findings with conetworks, which led to the discovery of the scissors effect [12,13], the M_c, i.e., the average molecular weight between crosslinking points, was determined in order to carry out a correlation analysis between the observed T_g and M_c values of the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks. The M_c for the PSt-l-PDMS conetworks can be obtained by the following relationship:

$$M_{\mathrm{c}}={\displaystyle \frac{W_{\mathrm{S}\mathrm{t}}·M_{\mathrm{n},\mathrm{P}\mathrm{D}\mathrm{M}\mathrm{S}}}{2·W_{\mathrm{P}\mathrm{D}\mathrm{M}\mathrm{S}}}}$$

(2)

where W_St and W_PDMS denote the weight fractions of PSt and PDMS, respectively, and M_n,PDMS stands for the number average molecular weight of the PDMS macrocrosslinker. In the case of the PSt-l-PDMS/DVB conetworks, by taking into account the additional DVB crosslinker as well, the M_c can be obtained by the following formula:

$$M_{\mathrm{c}}={\displaystyle \frac{W_{\mathrm{S}\mathrm{t}}}{2·\left(\frac{W_{\mathrm{P}\mathrm{D}\mathrm{M}\mathrm{S}}}{M_{\mathrm{n},\mathrm{P}\mathrm{D}\mathrm{M}\mathrm{S}}}+\frac{W_{\mathrm{D}\mathrm{V}\mathrm{B}}}{M_{\mathrm{D}\mathrm{V}\mathrm{B}}}\right)}},$$

(3)

where W_DVB and M_DVB denote the weight fraction and molecular weight of DVB, respectively. The M_c data obtained by these two equations fall in the range of 400–10,500 g/mol, that is, covering a more than one order of magnitude range, as presented in Table 1.

The T_g data for the PSt-l-PDMS conetworks prepared with two different MA-PDMS-MA crosslinkers having M_n,PDMS of 4.7 and 22.2 kDa are plotted as a function of 1/M_c in Figure 3. Apparently, the T_g data in this plot can be well fitted with a straight line, resulting in a slope of K = 4.1 × 10⁻⁴ °C·g/mol and an intercept of T_g,ꝏ = 96.8 °C, which agrees well with the T_g of high molecular weight PSt. This linear correlation undisputedly indicates that the T_g of PSt, crosslinked with the PDMS macrocrosslinkers, follows the Fox–Flory relationship when M_c is considered as the variable, according to the following equation:

$$T_{\mathrm{g}}=T_{\mathrm{g},\mathrm{\infty }}-{\displaystyle \frac{K}{M_c}}$$

(4)

This means that the polystyrene segments between two crosslinking points in the PSt-l-PDMS conetworks for their glass transition behave like the corresponding homopolymers with the same average molecular weight. In other words, the MA-PDMS-MA macrocrosslinkers act like scissors from the point of view of glass transition of the crosslinked PSt, as illustrated in Scheme 2. Comparing the K value obtained for the PSt-l-PDMS conetworks with that of PSt homopolymers raises some difficulties. As the literature indicates, three different regions can be distinguished in the T_g dependence of PSt on its number average molecular weight (M_n,PSt) [84,85]. This includes two low molecular weight regions with varying M_n,PSt dependence without sharp boundaries, and a higher molecular weight region with nearly constant T_g. Because the M_c region in the investigated PSt-l-PDMS conetworks lies in the borderline region of the two low molecular weight areas of the PSt homopolymers, only the T_g data of PSt homopolymers from the same molecular weight regions than that of the coneworks’ M_c can be compared. Figure 4 displays the literature T_g of PSt homopolymers [86,87] as a function of 1/M_n,PSt together with the T_g data versus 1/M_c of the PSt crosslinked by MA-PDMS-MA. This plot also includes T_g data reported previously for PSt-l-PDMS conetworks [71]. As can be seen in this figure, the T_g data versus 1/M_n,PSt for the PSt homopolymers and the T_g for the PSt in the conetworks as a function of 1/M_c fit well in the same linear, Fox–Flory-type relationship in this joint plot. This result conclusively verifies the scissors effect of the PDMS macrocrosslinker in the PSt-l-PDMS conetworks.

As displayed in Figure 2B,D, the T_g of PSt in the PSt-l-PDMS/DVB conetworks exhibits a similar trend to that in the PSt-l-PDMS conetworks, that is, the T_g decreases with the increasing PDMS macrocrosslinker content by keeping the DVB/St ratio constant at 1/36 m/m. Figure 5 shows the T_g data as a function of 1/M_c, where M_c is obtained by equation (3). This plot indicates a linear relationship with an intercept of 112.1 °C, which is significantly higher than that of the T_g of polystyrene with high molecular weight. On the other hand, the slope of the fitted straight line is 4.3 × 10⁻⁴ °C·g/mol, which is close to the value of the slope of the T_g versus 1/M_c plot for the PSt-l-PDMS conetworks prepared without DVB, i.e., 4.1 × 10⁻⁴ °C·g/mol. This indicates that the two plots are nearly parallel to each other. This led us to calculate the M_c for the PSt-l-PDMS/DVB conetworks by taking into account only the PDMS macrocrosslinker, i.e., by neglecting the DVB, according to Equation (2), and to plot the T_g data as a function of 1/M_c. The left-hand side plot in Figure 5 includes these data together with that of the PSt-l-PDMS conetworks. As can be seen, the two kinds of data overlap, indicating that the determining component for the T_g of PSt in the conetworks is the amount of the MA-PDMS-MA macrocrosslinker. The DVB, with the applied amount, i.e., DVB/St ratio of 1/36 m/m, does not have a detectable effect on the glass transition behavior in the PSt-l-PDMS/DVB conetworks.

Figure 6 summarizes the observations presented for the Fox–Flory-type correlation between the T_g and 1/M_c for the PSt-l PDMS and the PSt-l-PDMS/DVB conetworks and the T_g and M_n literature data for polystyrene homopolymers [86,87]. As this plot indicates, these data show that both the 1/M_c and 1/M_n,PSt dependence for the conetworks and PSt homopolymers, respectively, exhibits the same trend, validating the scissors effect of the PDMS macrocrosslinker on the glass transition behavior of PSt in the conetworks. These findings indicate that the junction points between the PDMS macrocrosslinker and the crosslinked PSt chains significantly interrupt the mobility of the PSt chains, as illustrated in Scheme 3, by displaying the structure of the junction points in the conetworks. The difference in the chain mobility between the PDMS macrocrosslinker and the crosslinked PSt chains leads to chain segments of PSt with molecular weight of M_c having the same mobility, and thus, glass transition temperature as PSt homopolymers with the same M_n,PSt. As a result, the T_g versus 1/M_c plot shows Fox–Flory-type dependence. This explanation of the scissors effect by the macrocrosslinker is supported by the results of previous solid-state NMR experiments with poly(N,N-dimethylaminoethyl methacrylate)-l-polyisobutylene (PDMAEMA-l-PIB) conetworks prepared with deuterated methacrylate-ended PIB [92]. As found in this study, the more mobile PIB macrocrosslinker with lower T_g significantly influences the mobility of the crosslinking point, and this results in lower T_g of the PDMAEMA component than that of its homopolymer, similar to the investigated PSt-l PDMS and PSt-l-PDMS/DVB conetworks.

4. Conclusions

In order to explore the relationship between the T_g and M_c in PSt-l-PDMS and PSt-l-PDMS/DVB conetworks, a library of these conetworks, consisting of two immiscible, covalently bonded polymers, i.e., PSt and PDMS, was prepared with a wide composition range of 30–80 wt% PDMS content. For the synthesis, MA-PDMS-MA was used as a macrocrosslinker with varying M_n,PDMS of 4.7, 9, and 22.2 kDa. In the presence of DVB, the St/DVB weight ratio was 36:1 when DVB was present as an additional low molecular weight crosslinker. The results of DSC measurements revealed two separate glass transition temperatures, that is, one for the PDMS component in the range of the PDMS homopolymers at around −120 °C, and another for PSt in the range of 60−100 °C. This indicates strong segregation of PSt and PDMS in these conetworks, in agreement with previously published SAXS and AFM results on the nanophase-separated morphology of these conetworks [73]. The DSC thermograms show that the crystallization of the PDMS macrocrosslinkers with M_n,PDMS of 4.7 and 9 kDa is completely suppressed in the conetworks. This is due to the nanoconfinement of the PDMS nanodomains, which prevents nucleation for crystallization in such conetworks. In the case of conetworks with PDMS having higher M_n,PDMS (22.2 kDa), i.e., with longer chains, depleted cold crystallization and melting peaks appear in the DSC scans. Surprisingly, the T_gs of the PSt component in both the PSt-l-PDMS and PSt-l-PDMS/DVB conetworks were found to decrease with decreasing M_c—that is, with increasing the PDMS content. Considering the well-known increase in T_g with decreasing M_c in the cases of conventional polymer networks crosslinked with low molecular weight crosslinkers [75,76,77], correlation analysis was carried out for the unusual M_c dependence of T_g of the crosslinked PSt in the conetworks. It was found that the T_g as a function of M_c follows the Fox–Flory relationship [74], which is obtained for the dependence of T_g on M_n,PSt for homopolymers. This unexpected finding indicates that the MA-PDMS-MA macrocrosslinker behaves like scissors in these conetworks in relation to the glass transition of the crosslinked PSt chains, leading to T_gs which matches that of the PSt homopolymers with the same M_n,PSt as M_c. In other words, the T_g of the PSt component is determined by the scissors effect of the PDMS macrocrosslinkers in these conetworks. On the basis of a literature result, according to which the mobility of the molecular segment of the crosslinking point is similar to that of the macrocrosslinker in the PDMAEMA-l-PIB conetwork [92], it can be concluded that the scissors effect is due to this difference in mobility at and/or most likely in the close vicinity of the crosslinking structural units. Taking into account the findings in this study and similar previous observations with other conetworks [12,13], it can be claimed that the scissors effect can be regarded as a general phenomenon for conetworks prepared by using macromolecular crosslinkers for conetwork formation. The existence of the scissors effect enables designing and applying polymer conetworks with predetermined T_gs for the crosslinked polymer components in such macromolecular assemblies by selecting the proper M_c via either composition or by the M_n of the applied macromolecular crosslinker.